Doug Richardson

Doug Richardson

PublishingCompany

CONTENTSIntroduction

Deceiving the Eye

Radar and Radar Cross-Section

Designing a Stealth Aircraft

Early Stealth Aircraft

The World of Black Programmes

Stealth Aircraft

Lockheed U-2S

Lockheed SR-71 Blackbird

Rockwell International B-1B

Eurofighter Typhoon

Dassault-Breguet Rafale C & M

Lockheed F-117A Nighthawk

Northrop B-2 Spirit

Lockheed Martin F-22 A Raptor

Boeing and Lockheed Martin

Joint Strike Fighter (JSF)

Mikoyan 1.42 and 1.44

Sukhoi S-37 Berkut (Golden Eagle)

Boeing Sikorsky RAH-66 Comanche

Aids to Stealth

Stealth in Action

Counters to Stealth

Index

10

14

24

34

58

68

106

108

110

112

114

116

118

120

122

124

126

128

130

146

168

186

INTRODUCTIONFrom the earliest times

when men could recountthe past, the tales which thepoets sang included thosetelling of heroes and mightywarriors. The stories reflecteda simple "world in whichenemies were overthrown bythe manly virtues of strength,courage and force of arms.The poets were less kind tothose who sought to achievetheir end by trickery orstealth; Homer's "wilyOdysseus" is less favourablydepicted than valiant warriorssuch as Hector and Achilles.

In all these stories,deception and stealth are seenas evil or ill-intentioned,an opinion widely held inmany societies. Throughouthistory, armies have nothesitated to execute enemiesfound guilty of wearing falsecolours, while in mediaevalJapan the black-robed ninjawas much feared.

With the arrival in the 1930sand early 1940s of the cinemaswashbuckling heroes,deception suddenly becameinnocent sub-plot, as ErrolFlynn's Robin Hood and hisMerry Men dressed as simplepeasants in order to sneakinto Nottingham. Suchinnocence was not to last.Wartime commandos,saboteurs, special forces andfifth columnists soon restoreddeception to its traditionalrole. In Tolkien's saga of elvesand hobbits, the power ofinvisibility is given not byGandalfs benevolent magicbut by an evil ring of power. Inthe "Star Trek" TV series, it'sthe Klingons who equip theirspace vessels with invisibility-shrouding "cloaking devices".Such trickery is beneath thehonour of the steely-jawedcrew of the StarshipEnterprise. Concealment byshape-changing reached itsdramatic but gory cinematicclimax in John Carpenter's1982 movie "The Thing", aremake of the earlier black-and-white classic directed byHoward Hawks.

Yet in the late 1970s, theconcept of stealth anddeception suddenly becamerespectable. Within theaviation community, rumoursbegan to circulate of a newand highly-secret technologywhich would make aircraft

and missiles near-invisible toradar systems.

The Washington-basedmagazine Aviation Week andSpace Technology was oncedescribed by an ex-astronautas being "... to airplane andspace people what RollingStone is to rock musicians".Around the aerospaceindustry, it is sometimesknown as 'Aviation Leak"because of its long record ofbeing first into print withsensitive items of aviationnews. (In 1947 it published thefirst news of Chuck Yeager'sthen-classified pioneeringsupersonic flight.)

LEAKSFor aerospace professionals,Aviation Week is essentialreading. For anyoneattempting to tell the story ofstealth technology, it is anessential source. Its name willappear again and againthroughout this book.

In the struggle for opinionand support among the keymembers of the defencecommunity, aerospaceindustry executives, Pentagon"top brass", US politicians andthe inevitable consultants andanalysts, the US military oftenturn to the magazine as anideal vehicle for judiciously-timed leaks. In 1980 just suchan operation seemed to beunder way, as stories of stealthappeared in its pages and inseveral US newspapers, liftingthe veil on the newtechnology. Following a series

Above: President Carterinspects a SAC B-52. In 1977he decided to re-equip theseold bombers with air-launched cruise missiles.

of stealth-technology storiesin Aviation Week, PresidentCarter and US DefenseSecretary Harold Brownfinally confirmed that radar-invisible stealth aircraft hadbeen test flown but ordered asecurity clampdown on theentire topic.

It is simple to declare abrand-new technology secretbut -when the secret consistslargely of a blend of existingtechnologies it is moredifficult. Such is the case withstealth. For three yearsfollowing these earlyrevelations, very little usefulinformation on stealth waspublished. Behind the sceneshowever, the new technologywas creeping out of the closet.

Like so many "modern"ideas, stealth technology firstappeared in the world ofnature. The simplest stealthtechnigue is that ofcamouflage. Any child will beable to list examples from theanimal world such as thepolar bear's white fur, thestick insect's ability to mimica twig and the colour-changing capabilities of thechameleon.

Other examples of "lowobservable technology" canbe found in nature. Manylarge marine predators suchas killer whales, spermwhales, dolphins and

10

INTRODUCTION

Below: Until the unveiling ofthe F-117A late in 1988, mostanalysts predicted that theaircraft would rely onrounding, wing/body

blending and extensive use ofRAM. Thanks to tightsecurity, the concept of usingfaceting as a means of RCSreduction remained secret.

Above: When first released,this Testor/Italeri kit of the"F-19" was seen by someobservers as a potentialbreach of security.

Right: Inward canted tailfins, plus 'Venetianblind" exhausts wereseen as likely "F-19"features. In practice, theF-117A tail surfaces weretilted outwards (anequally effective low-RCS shape), but theseengine exhausts are nottoo unlike those actuallyused by Lockheed.

porpoises, search for theirprey by means of a form ofsonar. They emit beams ofsound waves and measurehow long the echo takes toreturn from "targets". To copewith this threat, some fish andcephalopods, such as squidand octopuses, have evolved"stealth" defences. The bodiesof some fish and squid arepoor reflectors of the -whale'ssonar waves, the result oftheir not having an air-filledswim bladder (a good sonartarget) for depth control. Onescientist has even speculatedthat the mucus on their skinmay be a sound absorber, anatural prototype for theradar-absorbing materials(RAMs) carried by stealthaircraft.

CLASSIFICATIONMuch the same concepts laybehind the new and secretstealth technology - avoidradar-reflective structuralfeatures and absorb theincoming energy - but theywere shrouded in secrecy.Since the mid-1970s, all newwork on scattering, shapingand RAMs had been highlyclassified (some observerswould argue excessively so).

Despite this, a substantialamount of informationremained in the publicdomain. Engineers andscientists working in the fieldcould hardly be expected tosurrender their files andpersonal libraries for securityvetting, or to de-programmetheir brains.

Given the amount ofinformation in the publicdomain, it was inevitable thatstealth would begin to creepout of the closet. In 1982,

11

Above: Taken by a ground-based photographer, thisunauthorised picture of theF-117A revealed the trueleading edge angle of theaircraft's highly-swept wing.

Professor Allen E. Funs of theUS Naval Postgraduate Schoolbegan to lecture on thesubject of radar cross-section(RCS) while on a sabbatical toNASA's Ames ResearchCenter. A short course on thesubject was introduced atGeorgia Tech in January ofthe following year.

STEALTH MODELSin a special electronicssupplement published inSeptember 1984 by thejournal International DefenseReview my former Flightcolleague Bill Sweetmanpushed back the bounds ofwhat was in the public domainin a six-page article simplyentitled "Stealth". Hereturned to the subject againin 1985 with a three-pagearticle, "The Vanishing AirForce", in the August issue ofInternational Defense Reviewand again on "Stealth" in thepages of the Novemberedition of Interavia.

By this point, Bill wasrapidly becoming a one-manstealth industry whosedetective work was not alwaysappreciated by those

Right: The B-2 was assembledat Palmdale, so could not bekept under wrapsindefinitely. Even so, guestsat the rollout were allowedonly a frontal view.

attempting to keep stealthtechnology under wraps.Behind the scenes, however,he was preparing themanuscript of an entire bookon the subject.

Before it saw print, twotextbooks on the subjectappeared. Professor Fuhs'sRCS lectures were printed in1985 by the AmericanInstitute of Aeronautics andAstronautics in a volume soondubbed "The No-See-UmBook", while the GeorgiaTech course resulted inEugene F. Rnott, John FShaeffer and Michael T. Tuleypublishing their massivetextbook Radar Cross Section:its prediction, measurementand reduction.

These were both highlytheoretical treatments of thesubject, but 1986 saw theappearance of a popularaccount in the form of BillSweetman's Stealth Aircraft -secrets of future empower.Stealth technology had "comein from the cold".

In July 1986 toy storesaround the USA began to sella plastic construction kitwhich claimed to depict theLockheed "F-19" stealth

fighter. 'Attention all foreignspies", announced the 26 Julyedition of The WashingtonPost, "if you want to knowwhat the Air Force'ssupersecret stealth fighter jetlooks like, try your local toystore". The $9.95 model was aproduct of the TestorCorporation of Rockford,Illinois. Within a few weeks ithad registered orders ofaround 100,000.

Following the release of theTestor model, a Pentagonofficial told Congress that itwas inaccurate and that anyaircraft built to that shapewould crash. Model designerJohn Andrews retaliated byclaiming that the model was"80 per cent accurate" andthat more than 100 copies hadbeen sold by a model shopclose to the Lockheed plantwhere the real aircraft wasbeing built.

FIRST LOOK

Testor national field salesmanager, Steve Kass, deniedthat classified information hadbeen used to design the model."Everything we got, you can getout of any library", he explainedto a Washington Post reporter.The model revealed noinformation which haven'talready been published in tradejournals, he claimed. In practice,the model's rounded shape borelittle resemblance to that of thestill-classified F-117A. Indeedthere has been speculation thatits configuration, and thesimilarly rounded shapes shownin other unofficial artist'simpressions of the US stealthfighter were the result of asuccessful US "disinformation"campaign.

By late 1988, the veil ofsecrecy had to be relaxed. As the

12

INTRODUCTION

first edition of this book wasbeing written, the USDepartment of Defense finallyreleased the first photograph ofthe F-117A stealth fighter, whilethe roll-out of the first NorthropB-2 revealed the shape of theUSAF's second stealthy combataircraft. Here were the firstaircraft designed specifically tooperate in the radar equivalentof Tolkien's "land of darkness,where the shadows fie".

In the years that followed, twoother US stealth aircraft were tobe unveiled - the LockheedHave Blue technologydemonstrator which hadpreceded the F-117A, and theNorthrop Tacit Blue technologydemonstrator for a proposedstealthy radar-surveillanceaircraft. The F-117A was to makeits operational debut overPanama in 1989, and was to go towar in the skies of Iraq in 1991. Inthe previous year, Lockheed and

Northrop had rolled out theirrespective AdvancedTechnology Fighter (ATF)technology demonstrators for acombat aircraft which wouldcombine the manoeuvrability ofthe F-15 with the stealth of theF-117A.

Stealth had now come outfrom under its cloak of secrecy.As the number of books on thesubject increased, aerospacecompanies began to talk aboutthe subject, and at the 1991 ParisAir Show, Lockheed even held apress conference to publicise theF417A.

In the 1920s and 1930s, thenations of Western Europe wereapprehensive about the threatposed by the primitive but near-unstoppable piston-enginedbombers of the day. Within a fewyears, radar was to give thefighter an ascendancy over themedium-and high-altitudebomber.

At first sight it might seemthat stealth technology hassimply restored the status quobut, in practice, the situation ismore complex. Applied tobombers, fighters and evenmissiles, stealth is completelyrewriting the book of air combatoperations and tactics.

In Bram Stoker's gothicclassic Dracula, vampire hunterProfessor Van Helsingdescribes the difficulties whichhis party will experience intheir attempts to locate anddestroy the evil Count. "He can,within limitations, appear atwill, where and when, and inany of the forms which are tohim... he can grow and becomesmall; and at times he canvanish and come unknown.How then are we to begin ourstrife to destroy him?" It is agood description of theproblems faced by would-bevampire hunters but is almost

equally applicable to theproblems faced by future airdefences which must cope witha range of stealthy attackers.

Yet the task is not animpossible one. The sight ofYugoslavian civilians dancingtriumphantly on the wreckageof an F-117A in late March 1999showed that stealth aircraft arenot invulnerable, although theexact circumstances underwhich the aircraft was shotdown remain classified.This book will describethe underlying principles ofstealth technology, give thehistory of the programmeswhich have used it, and looktowards the future to reporton the next generation ofstealthy aircraft. It will alsoexamine the technologieswhich help the stealth aircraftfulfil its mission, and thoseneeded in order to detect andtrack them.

13

DECEIVINGTHE EYEWhen the first military

aircraft were fielded,little thought was given tocolour schemes which mighthelp reduce detection. Thefact that they flew at allseemed more than adequate.Like their civil counterparts,military aircraft had no paintfinish to speak of but were apale yellow, the result ofapplying fabric-tauteningdope and protective varnish tothe linen or cotton covering.

Some work on reducingvisibility had been done priorto the war. This had not beendone by the application ofdeceptive colouring butrather by the even moreobvious approach of trying tomake the aircraft near-invisible by covering itswooden framework not withdoped fabric but with atransparent skin. It maysurprise those working withtoday's highly-classifiedstealth aircraft to learn thatthe first attempts to buildaircraft of this type date backto the era of their great-grandparents.

In 1913 the United StatesWar Department carried outexperiments intended toassess the feasibility ofbuilding an aircraft whichwould be invisible to thenaked eye when flying at analtitude of 1,000ft (300m). Inan attempt to meet what byany standards must be seen asan impossible target, the

Below: US First World Warair ace Eddie Rickentaackerposes alongside his French-built Spad fighter. Althoughmore complex than thecontemporary Britishcamouflage scheme shownabove, the colour finish onthe aircraft was probably nomore effective as anantidetection measure.

wings of an aircraft weremanufactured with what acontemporary newspaperaccount described as "amaterial of a semi-transparentnature, composed partly ofcelluloid". Other trialsinvolved the use of the samematerial in the"understmcture" of airships.A secondary goal of the work

was to give aircrew a betterview of the ground.

In 1914 the magazine Flightreported similar experiments."Only the framework is dimlyvisible, and this and theoutline of the motor and thepilot and passengers presentso small an area for rifle orgun fire, that at the rate ofspeed at which aeroplanes areflown today, accurate aimingat such surfaces becomesnearly impossible."

CAMOUFLAGEBritish troops had adoptedkhaki uniforms as a result ofcasualties to long-range riflefire in the South African wars,so this colour was the logicalchoice for an aircraft finish.When the state-owned RoyalAircraft Factory (forerunner ofthe Royal AerospaceEstablishment) developed apigmented compoundintended to protect the fabriccovering of aircraft from theadverse effects of strongsunlight, the colour chosen forthe resulting ProtectiveCovering (PC) No. 10 was ofthe khaki type. The exactshade used is a matter of somedebate, involving fading

14

HNG THE EYE

Right: RAF Handley PageHampden in typical earlyWWII bomber camouflage.The white ring is omittedfrom the wing roundels.

Below: This replica of the lateWWI Sopwith Snipe has onlynominal camouflage, heavilycompromised by roundelsand white lettering.

Below: The winning side canignore camouflage rules. Thebold insignia on this Bf 109Espoil the effect of the splintergreen finish.

Bottom: For a brief periodprior to the United States'entry into WWII, traditionaltail stripes were retaineddespite the new olive drab.

memories and faded paintsamples, and seems to haveranged from a greenish khakito what can best be describedas chocolate brown.

French aircraft started theFirst World War withoutcamouflage. Early Nieuportfighters carried the company'sstandard silver-grey finish, forexample. A nominally"standard" Frenchcamouflage scheme was lateradopted, a distinctive finishmade up of green and two oreven three shades of brown.This was often retained byFrench built aircraft takeninto Royal Flying Corps or USArmy service. Describing theSpad XIII C.I in a 1960smonograph, C.F. Andrewssummed up the Frenchattitude to camouflage: "Thevariations of Frenchcamouflage patterns during1917 and 1918 have beensomewhat obscure".

The Germans took adifferent approach. Initialexperiments involvedapplying two or three shadesof colour to the aircraft by

means of paints or distempersbut this was soon supersededby a scheme in whichcamouflage colouring wasprinted on the fabric used tocover the aircraft. Thisapproach allowed the use ofcamouflage patterns toocomplex to be cost-effectivelyapplied by hand. The patternchosen was a complicatedone, a dense network ofhexagons in four or fivecolours, and there is noevidence that this "lozengefabric" was any moreeffective than the RFC'ssingle-colour PC No. 10.

NIGHT COLOURSBomber units operating bynight adopted specialisedcolour schemes. Black seemedthe obvious choice for anaircraft intended to operateunder the concealment ofdarkness, but nobody seemsto have realised that to beeffective such a finish must bematt so that reflections fromsearchlight beams beminimised. So disappointing

Early WWII German Colours

1930s American Bomber Scheme

were the results of tests onblack aircraft that few servicemachines were painted in thismanner. The huge HandleyPage 0/400 - a twin-enginedbiplane of 100ft (30.5m)wingspan developed to meetCommodore Murray Sueter'srequirement for a "bloodyparalyzer of an aeroplane" -was finished overall in PC No.10 compound.

A better paint finish fornight operations emerged inearly 1918. Developed by theExperimental Station atOrford Ness, Suffolk, thegrey-green varnish known as"Nivo" was optimised for useon moonlit nights and had asurface sheen intended tomatch that of open water. Itwas too late for large scalewartime use.

With the arrival of peace,camouflage was soonabandoned by most squadronsin favour of brighter colours.The inter-war years were toprove the zenith in the art ofaircraft decoration andnowhere was this more truethan in Britain's Royal AirForce (RAF), successor to theRoyal Flying Corps. Ageneration of pilots serving inwhat they sometimes termed"the best flying club in theworld" flew silver-dopedbiplanes adorned with highly-conspicuous squadronmarkings. In the United States,the Army Air Corps preferredto leave aircraft in theirnatural finish but addedbrightly-coloured tail stripesand squadron insignia.

TONING DOWNBy the mid 1930s, Britain facedthe growing air strength of areborn German Luftwaffewhich would soon re-equipwith modern monoplanefighters and bombers. As thelikelihood of war increased,bright colours gave way todrab low-visibility schemes.

15

Reconnaissance Spitfires

Top: As WWII progressed, theRoyal Air Force developedspecial low-visibilityschemes. This recce Spitfiresports a blue finish.

Camouflage was re-introduced. The basic RAFscheme involved uppersurfaces painted in twocolours - dark green anddark earth, applied in largeareas with curving outlines.

At the same time, the RAF'snight bomber units badefarewell to "Nivo". Tests hadshown that the varnish'ssurface sheen reflected toomuch light if the aircraft wereilluminated by a searchlight.Upper surfaces were finishedin dark green and dark earth,while the undersides receiveda matt black known as RDM2.The low-visibility roundel wasretained, however, and alsoapplied to the wings ofcamouflaged aircraft whichoperated mainly by day.

Other nations similarlytoned down their aircraft. TheUnited States opted for olivedrab upper surfaces and sidesand grey or azure undersides.The US Navy's pale grey oreven bare metal gave way tofinishes based on blue or grey.A typical scheme had uppersurfaces in non-specularblue/grey and under surfacesin non-specular light grey.

For much of the war, theLuftwaffe used a distinctivetwo-tone "splinter" colourscheme for the upper surfacesof its aircraft. This used twoshades of green - dark green(dunkelgrun) and a very darkgreen (schwarzgrun) appliedin large patches with angularoutlines. Undersides werepainted in light blue(helMau).

As the war progressed,camouflage finishes on bothsides were improved and newschemes devised to suit

Above: A pink colour wasalso found to be effective athigh altitude, helping tomatch the aircraft with thesky background.

various specialised roles orgeographical regions. In theUK, the basic "TemperateLand" dark green/dark earthfinish was altered in 1941 withsea grey replacing dark earth.This basic finish wassupplemented by acombination of dark slate greyand extra dark sea grey("Temperate Sea") bettersuited to the over -water role,while aircraft assigned to theNorth African campaign andthe Middle East were finishedin a combination of darkearth and middle stone("Middle East").Undersurfaces were finishedin grey or blue, depending onthe geographical area inwhich the aircraft wasoperating.

RAF night bombers retainedtheir dark green/dark earthupper surfaces but the matt

black area was extendedinitially over the entire lowerhalf of the aircraft then to allbut the upper surfaces in1941. From 1943 onwards,Coastal Command aircraftwere finished in white, exceptfor the upper surfaces whichwere dark slate grey/extradark sea grey.

NEW COLOURSThe most novel colours werethose applied to high-altitudephoto-reconnaissance aircraft.These were finished in asingle colour overall, varyingfrom several shades of blue topink. Night fighters of theRAF and USAAF were alsopainted black overall.

The US Army Air Forceentered the war using its olive

Above: Red outer wings andlarge red stars makenonsense of the white wintercamouflage applied to theseSoviet MiG-3 fighters.

Right: This 1918 photo of theRoyal Navy battleshipRevenge shows thedisruptive "dazzle"camouflage scheme.

16

DECEIVING THE EYE

drab paint scheme, albeitwithout the brightly-colouredunit insignia and tail markingof the pre-war era. Tail stripeshad been deleted fromcamouflaged aircraft in 1940.It was to retain this schemeuntil 1944.

The bright colours appliedto some areas of Luftwaffeaircraft slowly disappearedand new paint schemesattempted to reduce thevisibility of aircraft. For dayoperations the hellblauundersides were frequentlyretained but often mergedgradually into the greenupper surfaces.

Bombers assigned to thenight-time blitz against the UKoften carried hastilyimprovised camouflage. Onthe undersides, black replaced

German Nightf ighter Colours

Above: Painstaking researchresulted in the bizarremottled blue/grey paintscheme used on WWIILuftwaffe night fighters.

Below: As USAAF strengthrose and that of the Luftwaffefaded, US fighters andbombers flew combatmissions in metal finish.

the traditional hellblau andwas often carried up over thefuselage sides. In some cases,the fuselage crosses weretoned down or even paintedout completely.

New camouflage colourswere devised to match theaircraft to their theatre ofoperation. For the NorthAfrican campaign, a sandbrown colour with a distinctlypinkish cast was used onupper surfaces. This workedwell over the desert but, onaircraft operating in areaswhere scrub was common,this basic colour was oftenoverlaid with areas of darkgreen. These varied in sizefrom large sections of theaircraft down to small patches.Given the rightcircumstances, the effect ofthe latter was to make theaircraft near-invisible whenseen from above.

WINTER COATSWinter operations on theRussian front again demandeda custom paint job - in thiscase all-white upper surfacesintended to reduce visibilityover a snow-coveredlandscape. As the spring sawareas of green breakingthrough the snow and ice, it ishardly surprising that manywhite-finished aircraft sportedgreen patches. A non-dryingglyptal paint was developedto aid the application and

removal of such temporarycolour finishes.

For early night fighteroperations, the Luftwaffeadopted an all-black finishsimilar to that used on Alliednight fighters. So obvious didthe virtues of black colouringseem that throughout the warthe RAF and US Army AirForce never fielded asuccessor. Given the growingmagnitude of the RAF's nightbomber campaign againstGerman cities, the Luftwaffecould not be so complacentand had to launch a researchprogramme to test low-visibility paint schemes fornight use.

One suspects that much totheir surprise, they found thatthe ideal finish was very farfrom the traditional black.Tests showed that the nightsky over Western Europe stillcontained sufficient light tosilhouette a black-paintedbomber when seen from theside or below. As the testsproceeded, lighter shadesreplaced black until aircraftwere flying in an odd-lookingscheme or overall pale bluewith mottled grey. This wassoon widely applied tonocturnal hunters such as theJu 88 and He 219.

DAZZLE SCHEMESAt best, these traditionalcamouflage schemes couldonly delay visual detection. Amore subtle approach involvesapplying markings intendedto deceive the eye intowrongly identifying what it isseeing. The first militaryapplication of the concept hadbeen during the First WorldWar when Royal Navywarships sported whatbecame known as "dazzle"camouflage. This took theform of large jagged panels ofbold colouring and wasintended to break up thevessel's visual outline. It couldalso help create a falseperspective. Painted-on bowwaves could complete theillusion, seen though asubmarine periscope, givingthe attacking U-boat a falseidea of the warship's truecourse and speed. The ideawas taken to its extreme inthe Second World War when

17

the Japanese aircraft carrierZuiho had its flight deckpainted to represent a lightcruiser.

With the end of the SecondWorld War, camouflage wasonce more abandoned, withmost air forces flying innatural metal finish. Naviesstayed with camouflage fortheir carrier-based aircraft.Britain's Fleet Air Arm settledfor medium blue uppersurfaces, while the USNadopted light greys.

POSTWAR

In 1955 the USN threwcaution to the wind, adoptingupper surfaces of non-specular light gull grey andlower surfaces finished inglossy insignia white whichformed the background forbrightly-coloured unitmarkings reminiscent of the1920s and 1930s.

With the escalating ColdWar, the UK re-adoptedcamouflage in 1947. Fightersonce more sported grey andgreen upper surfaces. Thenew Canberra light bombersstarted life in 1951 with greyupper surfaces and blackunder sides. Soviet aircraftoperating in North Koreafollowed suit, the result ofAllied air superiority.

For the main part, the USAand Soviet Union stayed withnatural metal for both fightersand bombers. This was aparticularly good choice forsupersonic aircraft since itreduced drag and posed noabrasion problems. In the late1950s, the RAF fielded theLightning in natural metal butthe long-range V-bomberscarried an all-white anti-flashfinish designed to minimise

Above: For almost a decade,USN F-14 Tomcats relied on abasic grey and white finish,and carried brightly-colouredunit insignia.

Below: Like Britain and theSoviet Union, Franceoperated its first-generationMach 2 war planes in naturalmetal finish.

the thermal effects of nuclearexplosions. With the US Navyoperating aircraft from itscarriers in bright paintschemes reminiscent of theinter-war years, the conceptof camouflage seemed to benearly forgotten.

Two factors restored theneed for visual stealth in the1970s. One was the downingof Gary Powers's LockheedU-2 spyplane over Sovietterritory on 1 April 1960 andthe other was the outbreak ofthe Vietnam War.

Early Vietnam Waroperations were flown by

18

DECEIVING THE EYE

Above: The Vietnam Warsaw US re-adopt camouflage,but the schemes used werelittle improved over those oftwo decades earlier.

uncamouflaged aircraft, butthe growing threat posed bythe North Vietnamese fighterforce resulted in the re-introduction of camouflage.Upper surfaces of USAFfighters and fighter-bomberswere given a three-tonetreatment of Forest Green,Medium Green and TanBrown, while the undersideswere finished in the muchlighter Very Pale Grey.

During the war, the USAFgradually reduced the size ofthe national insignia appliedto its aircraft, the final versionbeing only 15in (38cm) high.

Left: As these RAF HarrierGR3s show, the art ofapplying temporary wintercamouflage schemes is stillvery much alive.

Another change applied tosome aircraft later in the war,intended to reduce thedemarcation between theinsignia and the camouflagescheme, was the deletion ofthe blue outline from the"wings" of the insignia.

Other nations followed theUS lead in readoptingcamouflage. Several broadpatterns emerged, setting thestyle for many of today'scolour schemes.

GREY AND GREEN

Camouflage finishes were notalways the result of carefulresearch or study. When theIndian Air Force hastilycamouflaged its fighter forceduring the December 1981war with Pakistan,considerable "artist's licence"seems to have been granted tothose who wielded the paintbrushes. Great variations in

Above: The "air superiorityblue" finish used onprototype and early-production F-15 Eaglesproved unsuccessful.

interpreting the new standardfinish were displayed by themen who worked onindividual aircraft, or even ondifferent parts of the sameaircraft. Some aircraft sportedtwo-tone dark green andgrey/green for example, whileothers displayed a finishreminiscent of the 1940sLuftwaffe "mirror"camouflage.

When the F-15 Eagle firstentered service in the mid-1970s, it was finished all overin air-superiority blue.National insignia were smallin size and had no border. Itwas short lived. The skies maybe blue over Texas but grey iscloser to the normal inWestern Europe. Pale bluegave way to the grey-based"Compass Ghost" finish. Thisuses two different tones ofgrey in an arrangementknown as "counter-shading" inwhich the lighter tone is

19

applied to the parts of theaircraft likely to be in shadow.

The year 1983 saw theintroduction of low-visibilitymarkings for the USN. Overallgrey replaced the long-established gull grey andinsignia white, while nationaland unit insignia shrank insize and were applied in amedium grey only.

In 1979 the RAF tested analternative to its then-currentdark green and grey withlight grey undersides. Thistook the form of an all-greyscheme retaining standard-sized national and squadronmarkings. Radomes remainedblack. This period also sawthe introduction of the palebrown "hemp" finish on largeraircraft such as the Nimrod,Victor and C-130 Hercules.The latest RAF scheme seestactical fighters given an all-green finish. This was firstseen on the Harrier GR5(British version of the AV-8B)and BAe's second Hawk 200prototype single-seater.

Research into multicolouredcamouflage continued. Duringthe JAWS (Joint AttackWeapon System) trials of theA-10 in 1977, the SecondWorld War Luftwaffe conceptof temporary finishes wastaken to its logical extreme.Aircraft were regularlyrepainted to match the

Right: This mottledcamouflage was just one ofthose tested on the A-10during the 1977 Joint AttackWeapon Systems trials.

current terrain and weatherconditions.

In the early 1980s, theUSAF recognised that itsVietnam-era scheme was notideal for NATO low-leveloperations. As an interimmeasure, the pale grey of theundersides was replaced bythe three colours used on theupper surfaces instead,creating a completely "wrap-around" finish.

Eventually the USAF settledon what it termed "EuropeanOne" - a "wrap-around"scheme using medium green,

Below: Dark tones on well-litareas, plus lighter toneselsewhere are a feature ofthe USAF's current "CompassGhost" finish.

dark green and dark grey.This entered service in 1983,gradually replacing the oldercolours as paint stocks for thelatter were used up. At thesame time, Phantoms assignedto air defence were painted inthe pale blue and grey finishused for other interceptors.

Experience showed that theUSAF fighters spent moretime at altitude than at lowlevel. Since the green andgrey scheme had beendesigned for low-level use, itwas thus far from theoptimum. Two permutationssuitable for medium-altitudeuse were tested in themid-1980s. "Hill Gray I"combined medium grey anddark grey upper surfaces withlight grey undersurf aces,while "Hill Gray II" was a"wrap-around" medium greyand dark grey finish. By 1987,USAF aircraft assigned to air-defence and multipleoperations "were beginning toappear in "Hill Gray II".Earlier schemes had involveda separate colour for theaircraft undersides but thisnew finish was applied overthe whole airframe.

FERRIS SCHEMES

Given the number of colourschemes which have beentried, abandoned and, in somecases, retried, it is hard toavoid the conclusion thatcamouflage is at least in part amatter of fashion. As a limitednumber of colours and ideasare regularly changed, littleeffort seems to be going intonovel alternatives. The"dazzle" experiments of theearly 1940s have not reallybeen pursued. One of the fewindividuals to explore theunusual has been US aviationartist Chris Ferris.

Camouflage has been asubject of great interest toFerris. One of his paintings of

20

DECEIVING THE EYE

a pale blue F-15 against a greysky background wasspecifically intended to pointout the folly of that aircraft'sinitial finish. Both the F-14and the F-15 have been testedin a camouflage schemedevised by Ferris with uppersurfaces finished in a mediumblue whose jagged edges arevaguely reminiscent of"dazzle" camouflage.

In the late 1970s, a complex"dazzle" paint scheme wasdevised for Lockheed's HaveBlue stealth demonstratoraircraft. This was intended tomake it hard for a distantobserver to determine theaircraft's shape. It worked sowell that, when the firstphotograph of a Have Blueprototype was released, details

of the aircraft's shape werehard to discern, particularlyaround the rear of the fuselage.

Ferris considers than an all-over grey would have beenbetter in Vietnam than thethree-tone treatment whichwas actually used. Canadaseems to have taken his point;today's CF-18 Hornet fleet iscamouflaged in a dull non-specular grey, while the toneused for the national insigniaand other markings offerslittle contrast. One neat touchof deceptive camouflage is thefalse canopy painted on theunderside, a feature intendedto encourage tactical errorsby the opposition during aircombat manoeuvres.

The importance ofcamouflage was demonstrated

Above: The USN wentvisually stealthy in 1983 withan all-over grey scheme, pluslow-visibility nationalmarkings.

Right: Aviation artist ChrisFerris devised this novelpaint scheme for the F-4Phantom, but it was neveradopted for service.

Below: F-14s test anotherFerris paint scheme. Morerecent experience suggeststhat luminescence is moreimportant that colour.

during the 1991 Gulf War, wherethe use by Iraq of opticallyaimed anti-aircraft guns andshoulder-launched SAMs madeit important that aircraftoperating by day should avoiddetection. During the aircampaign, almost 25 per cent ofUS aircraft casualties were A-10close-support aircraft, 20 ofwhich were hit during the war.None was damaged or shotdown while operating at night.

The aircraft still had the darkgreen paint scheme originallydevised to conceal them fromabove when flying low-leveloperations in northern Europe,and some pilots believed thatthis colouring made the A-10stand out in the desert againstboth sand and sky. At night,the dark paint schemeprobably helped conceal theaircraft, or at the best did notmake it stand out.

Some A-10 units began topaint their aircraft the same lightgrey colour scheme used bymost other USAF aircraft, butwere later ordered by the AirForce Component, CentralCommand (CENTAF) to changethem back to dark green.However, a postwar USAFaircraft-survivability studyconcluded that the concernsover the A-10 paint schemewere "valid" and recommendedthat, in the future, paint schemesshould match the environment

21

in which the aircraft were beingrequired to operate.

SMOKE AND LIGHTSome effort has beenexpended on active opticalcamouflage - the use of lightsand sensors to adjustthe luminance of the airframeto match the background.Work on what werenicknamed "Yehudi lights"started in the USA after theSecond World War. Variousmodels of piston-enginedaircraft including the B-24Liberator and SBD Dauntlessnaval bomber were fitted withan experimental arrangement oflamps built into the wingleading edge. "Yehudi lights" arealso reported to have beentested in the engine inlets ofsome F-4 Phantoms during theVietnam War. Studies haveshown that at longer ranges itis more important to matchthe luminance than the actualshade of colour.

Most modern jet engines arevirtually smokeless, but this wasnot the case 30 or 40 years ago.Early-model B-52 bombers andKC-135 tankers tended to lift offfrom the runway amidst denseclouds of smoke which wouldsend today's environmentalpressure groups scampering fortheir protest banners. Jetfighters of the 1950s and 1960swere almost as bad, and thiscould be a major weakness inair combat. Experience in theskies over North Vietnam soontaught the USAF and USN thatengine smoke could effectivelypinpoint their fighters.

Smoke emission was toremain a bugbear of thePhantom throughout theVietnam War. Smoke outputpeaked sharply when theengine was run at full militaryDower. To avoid this effect

Above: Smoke pours from theengines of an F-4C. Combatexperience in Vietnamshowed that smoke trailscould betray an aircraft.

Below: Good camouflagediscipline is essential whendeploying V/STOL fighterssuch as these Royal Air ForceGR3s off-base.

during combat operations,pilots would sometimes runwith one engine onafterburner and the otherthrottled back. This resultedin the same total thrust as twoengines at full military power,while the close spacing of thePhantom's engine baysminimised the effects of thrustasymmetry.

TRAILSContrails are anotherunwanted phenomenon whichcan betray an aircraft'sposition. More accuratelyknown as "condensationtrails", these are formed ataltitude by the condensationor even freezing of the watervapour created as a by-product when jet fuel isburned.

During trials in 1962 of thefirst Teledyne Ryan Firebeereconnaissance drones (aprogramme which will bedescribed in a later chapter),test interceptions by USAFand USN fighters showed how

Bottom: Lockheed's Burbankplant vanishes underprotective camouflage in theearly 1940s. Fake "trees" helpmaintain the illusion.

easily contrails could guide anattacker, so work was startedin that year on a "no-con"system. This involved twoQC-2C drones equipped witha system which injected achemical agent into theexhaust. It was not verysuccessful; the best method ofeliminating contrails proved tobe giving the drone theceiling performance neededto fly above the altitudes atwhich contrails form.

Details of anti-contrailmeasures are scarce. Like the1962 experiments, most arethought to involve the use ofchemical additives in theexhaust. These alter the size ofthe water droplets created inthe air.

AIRFIELDSSince a combat aircraft spendsmost of its time on the ground,where it is vulnerable tosneak attack, low-visibilityaircraft ideally require low-visibility airbases. Applicationof camouflage to the airfieldfrom which military aircraftoperate was a Second WorldWar development. One of thefirst experiments in heavilycamouflaging military baseswas conducted in the United

Below: Almost two decadesafter the Six Day War,aircraft could still be foundparked in unprotected linesduring major exercises.

22

DECEIVING THE EYE

Right: The Swedes place greatemphasis on off-baseoperations. Their "Base 90"programme emphasised theuse of roads as airstrips.

States. In 1940 BrigadierGeneral Thomas M. Robins,then assistant chief of the USArmy's Corps of Engineers,was responsible for building anew airfield at Windsor Locks,Connecticut. To illustratewhat camouflage could do,Robins worked with LtColonel John Bragdon tobuild the new base to conformto the principles of visualdeception rather than theformal arrangements whichthe conventional militarymind would regard as neatand tidy.

Airfield buildings werepositioned among existingbuildings present at the site.The latter, like the naturalvegetation, were left in placewherever possible. Roadsfollowed normal groundcontours rather than takingdirect routes, fuel tanks wereburied and barracks werebuilt to resemble the tobacco-drying sheds common onnearby farms. To break up theoutlines of the field's threerunways, their surfaces werepainted to match the shapeand colour of nearby fieldsand to create the illusion ofbeing crossed by many pathsor roads.

HIDDEN FACTORIES

Other efforts saw thecamouflage treatment of USaircraft factories on the westcoast. The most famousinstance was Lockheed-Vega's

Burbank works which wasexposed to the full talents ofHollywood's special-effectsmen. The entire site,including buildings andparking lots, disappearedunder a giant camouflageshelter which incorporatedfake houses, gardens, roadsand even parked cars. Tomaintain the illusion, thepositions of the "cars" wereregularly changed, while the"houses" even had fake"washing" hung out to dryonce a week. An idea of thecost and complexity of theillusion can be gleaned fromthe fact that the bill for itsremoval after the war came to$200,000. A similar schemesaw Boeing's vital Seattleplant disappear under a fakecamouflage "town".

Researchers in the USAhave investigated methods ofapplying an up to date versionof such techniques to NATO'shighly-vulnerable air bases inWestern Europe. The aim is tofool not just the human eyebut also infra-red and radarsensors. Some of thetechniques being studied wererevealed in 1985 when theLondon newspaper SundayTimes reported that the USGovernment was fundingsecret trials in the UK ofmethods of reducing thevisibility of airfields. Thereport linked this work withthe development of US stealthaircraft. "If all goes accordingto plan, invisible NATOaircraft could be landing at

invisible airfields all overEurope within a decade",wrote defence correspondentJames Adams.

Some of the techniquesused were a re-run of the1940s work. Trees wereplanted to break up theoutline of buildings andperimeter fences, while allconcrete surfaces, includingthe runways, were treatedwith a chemical solutionintended to give them an IRsignature similar to that of thesurrounding grass.

The article also described howthe Royal Air Force base selectedfor the tests had been equippedwith water sprinklers whichwould be used to douse hangarsand other major facilities withwater if the airfield was about tobe attacked. This would reducethe IR signature of the genuinetargets, while heaters insideinflatable decoy hangars wouldcreate alternative realistic visualand thermal targets.

As radar-invisible stealthaircraft enter service ingrowing numbers, air defenceswill place increasing relianceon alternative sensors. Thesewill include long-range electro-optical television systemsmounted on interceptors andSAM fire-control units inaddition to the more traditional"Mark 1 eyeball". Far fromhaving been made obsolete, thevisual countermeasuresdescribed in this chapter arelikely to grow in importance asthe effectiveness of radar andthermal sensors are degraded.

23

RADAR AND RADARCROSS-SECTIONTo the Latin-speaking

inhabitants of Dark Agesnorthwestern France, the regionwas the end of the known world.Looking out over the often angrysea which stretched to the horizonand beyond, they named it "FinisTerre" - the End of the Land. Inthe centuries that followed, thispeninsula thrusting out into theAtlantic Ocean became a strategicposition which requiredfortification, so the 16th century-French castle builder Vaubanerected a fort to guard the shoreagainst naval threats, particularlythe growing maritime power ofthe British Navy.

In most countries, a fort of thisage would be a tourist attraction,complete with ticket office and tearoom, but this one is guarded bybarbed wire, and off limits totourists. Its ramparts are nowprotected against a threat the likeof which its builder could neverhave dreamed

The upper part of the stonebattlements are now coveredwith blankets of thick rubber-like material. Known to theelectronics industry as RadarAbsorbent Material (usuallyabbreviated to RAM), thecoating is designed to absorbradar energy, ensuring thatthe old fort does not reflectthe radar energy radiated bythe nearby Mengamelectronic-warfare test siterun by electronics giantThomson-CSF.

Inaccessible thoughVauban's battlements may be,they are a good starting offpoint for a study of the mostsecretive of 20th Centurymilitary technologies -"stealth" - the art of makingaircraft, missiles and othermilitary systems invisible toradar. Let us return for amoment to the threat againstwhich Vauban's fortress wasdesigned, the traditionalsailing ship armed withbroadside-firing cannon. Aswill have been seen byanybody who has watched oldmovies, the standard navalcannon (or at least theHollywood version) fired aspherical cannonball about 8inches (20cm) in diameter.

How big would such acannonball have looked to aradar at Vauban's fortress, hadit been so equipped inNapoleonic times. The mostobvious answer is of course the

Above: Most radars operateat microwave frequencies,and must have a direct line ofsight to the target. If over the

area of a circle of 8 inches (20cm)in diameter. To save the readerfrom reaching for a pocketcalculator while muttering theschoolboy formula "Pi times Rsquared", the area in question is1.34 square feet (0.125 sq m).

Substitute a metal plate Win(35.3cm) square, and you'd havethe same physical cross-section,but the radar cross-section couldbe anything from less than atenth of a square metre toseveral hundred square metres,depending on the frequency ofthe radar. For any givenfrequency, that radar cross-section would be at itsmaximum when the plate waspositioned at right angles of theradar beam. Tilt it, and the radarreflectivity will fall dramatically.The position of the edge of the

horizon, the latter will bemasked by terrain, so raisingthe antenna improves long-range coverage.

plate with respect to the radarbeam also influences the plate'sradar cross-section. Welcome tothe strange world of stealth, auniverse where nothing is quitewhat it seems even before theelectronic wizards have begunpractising their super-secretelectronic trickery.

RADAR WAVES

The key to understandingstealth is to understand howradar works and in particularhow radar signals arereflected from aircraftstructures. The following"crash course" on thesesubjects will strike a radar orstealth engineer as grosslyoversimplified but it willattempt to cover in a single

chapter subjects to which astealth technology textbook•would devote 400 pages,while at the same timesteering clear of the sort ofmathematics and numericalanalysis which would satisfyonly the expert.

A radar wave is a form ofelectromagnetic radiation, asare the lower frequenciesused for radio and TV and thehigher frequencies such asinfra-red energy and visiblelight. The basic theory ofsuch waves was first describedin the 19th Century by ClerkMaxwell who predicted theirproperties long before thetechnology needed to provehim right became available.The early pioneers of radiowere starting from a blanksheet of paper; they weretrying to find a method ofcreating and detecting -waveswhose existence had beenforeseen by Maxwell.

An electromagnetic waveconsists of two components -an electric field and amagnetic field - positioned atright angles to one anotherand whose values rapidlyfluctuate in strength, rising toa peak, falling away to zero,then rising to a peak in theopposite direction beforefalling back towards zero. Theentire process then repeatsover and over again. Thewhole electromagnetic -wavetravels (engineers would say"propagates") in a direction atright angles to the electricand magnetic fields. Think ofthe latter as the vanes on adart or arrow; the direction ofpropagation will then bealong the length of the shaft.

FREQUENCY

In any book on radio or radar, letalone stealth technology, theterms "frequency" and"wavelength" are unavoidable.Both describe methods ofmeasuring the rate of this cyclicvariation. "Frequency" is ameasurement of the number oftimes this cycle occurs in everysecond. Until the 1960s, it wasexpressed in cycles, kilocycles(thousand of cycles), megacycles(millions of cycles) or evengigacycles (thousands of millionsof cycles) per second. The self-explanatory term "cycles persecond" was replaced by the

24

RADAR AND RADAR CROSS-SECTION

totally artificial term "Hertz"during the 1960s (after theGerman physicist HeinrichHertz, 1857-94) in theinterests of internationalstandardisation, so in thisbook we refer to megahertz(MHz) and gigahertz (GHz).

"Wavelength" is an olderconcept. The wave propagatesat 90 degrees to its electricand magnetic fields. Thewavelength is the distancebetween two successive peaksin either of these fields. It's auseful measurement, beingdirectly related to the physicalsize of components such asantenna elements - which iswhy it was widely used in theearly days of radio. The twoare directly inter-related.Increase the frequency andthe wavelength is reduced.Decrease the frequency andthe wavelength increases.

RADAR BEAMS

As the reader is probablyaware, radar sets illuminatetheir target with a beam ofhigh-frequency radar energyand detect the resultingreflections. A good analogy isthe Second World Warsearchlight. Lost in the nightsky, a bomber was virtuallyinvisible from the ground.Once caught in the beam of asearchlight, it became visibleand could be engaged by anti-aircraft gunfire.

Only two countermeasureswere available to aid theaircraft, one passive and theother active. For most of thewar, all air arms engaging in

Right: Above the mainantenna of this Thomson-CSFTRS-22XX radar is an upperunit for the interrogation ofaircraft-mounted civil or IFFtransponder systems.

Below: As frequency rises,wavelength falls, as do thedimensions of antenna feedsand waveguides.

Wavelengths

Waveforms

Wavelegth

Right: The wavelength of asignal is the distancebetween successive peaks.The higher the frequency, theshorter the wavelength.

Below: An electromagneticwave has two components atright angles - an electricfield (shown in blue), and amagnetic field (shown in red).

Magnetic and Electric Components of a Wave

Electricfield

Combinedelectromagnetic

field

:

night bombing painted theunderside of their aircraftblack, so as to minimise theamount of light reflectedshould they be caughtmomentarily in a searchlightbeam. If caught and followedby the beam, the aircraft'sonly hope was to manoeuvreviolently in the hope ofslipping out of the narrowbeam of light. If successful,once outside of the beam itwas once more cloaked indarkness.

Both measures werepartially countered by havingseveral searchlightsconcentrate their beams ontoany target detected by one oftheir number. Aircrewdreaded being "coned" by agroup of searchlights. Thecluster of beams interesectingon the coned aircraftilluminated a large volume ofsky in the aircraft's immediatevicinity, while the additionallight from every beam joiningthe cone increased the lightlevel illuminating the aircraft,and thus the amount reflectedback to the ground for theAA gunners to see.

REFLECTIONS

When British scientists startedwork on radar in 1935, theyrealised the importance oftarget reflectivity. If the newmethod of aircraft detection(then known as RadioLocation) was to workeffectively, it was essentialthat the reflection be asstrong as possible. Theilluminating signal would haveto be as powerful as possible,given the state of radartechnology as it existed then,while the frequency usedwould have to be one whichthe aircraft would reflectstrongly.

Use of the word "reflect"simplifies a more complexprocess. The radar energydoes not just bounce the waya squash ball does off thecourt wall. When anelectromagnetic wave meetsan electrical conductor, suchas a wire, it creates withinthat conductor electrical andmagnetic currents at the samefrequency. That is how a radioantenna works - theelectromagnetic wave fromthe distant transmitterinduces a tiny current withinthe antenna which the radioreceiver then amplifies. Atthe transmitter, the processworks in reverse. Thetransmitter feeds an electricalcurrent of the appropriatefrequency into the antenna.This current creates anelectromagnetic wave whichthe radiates outwards fromthe antenna. The process

25

Frequency Wavelength

l00kHZ 3,000m

1MHz 300m

10MHz 30m

100MHz 3m

1GHz 20cm

10GHz 3cm

100GHz 3mm

velocity of light =300 X l06m/s approx

Reflection of Radar Energy

left The scientists andengineers who developed thefirst radars just before theSecond World War found itdifficult if not impossible topredict how a radar wavewould reflect from anaircraft. It seemed to scatterin all directions. No simpletheory could explain what washappening.

works both ways - a currentin a conductor can create anelectromagnetic wave, and anelectromagnetic wave cancreate a current in aconductor.

This is the central principleof the phenomenon whichcauses an aircraft or anyother target to reflect radioenergy. When the radar wavehits the target, it induceselectric and magneticcurrents within that object.By the act of flowing, thesecurrents in turn cause anelectromagnetic wave to becreated. It is this latter wavewhich the radar sees as areflected echo.

From work on antenna(aerial) design, the engineerswho developed Britain's firstradars already knew that awire whose lengthcorresponded to half thewavelength of the radio signalwould re-radiate strongly.Assuming that the wing of ametal aircraft would behave inthe same way as a simple wire,this suggested that theoptimum frequency would bethat which had a wavelengthtwice the length of the wingof a typical bomber of theperiod.

At that time the latestgeneration of Germanbombers was beginning flighttests and the equivalentBritish types -were about to

26

RADAR AND RADAR CROSS-SECTION

Above: The ftrst British"Chain Home" early-warningradar stations were based onshort-wave and televisionbroadcasting technology.

Below left: On 26th February1935, Sir Robert Watson-Wattused this primitive receiverto make the first detection ofan aircraft target.

fly; so a good idea of thedimensions of wingspans oflikely targets was available.

Although a follow-ongeneration of heavierbombers with wingspans ofaround 100ft (30m) or morecould already be envisaged,the radar engineers decidedto regard 80ft (25m) as a goodcompromise value, fixing thefrequency of their equipmentat 6MHz, where thewavelength would be 50m.

CHAIN HOMEUnfortunately, thesefrequencies proved unreliabledue to ionospheric refraction.Wavelengths/frequencies of26m/11.5MHz and eventually13m/23MHz were both tried,before the latter was foundsatisfactory and was adoptedas the basis for the pioneering"Chain Home" radar network.

The use of 23MHz for"Chain Home" had beenunduly conservative from atheoretical viewpoint. Fromthe practical point of view, itwas nearly ideal, since thepower transmitters andsensitive receivers requiredcould be developed using theexperience gained by short-wave radio equipment. Theamateur radio enthusiastswho had steadily reducedoperating wavelengths(increased frequencies) from

Below: Early research intoradar reflectivity showedthat the apparent echoingarea - known as the radarcross-section (RCS) and

80m (3.75MHz) to 40m(7.5MHz) then to 20m(14MHz) during the inter-warera of radio experimentationwere also to provide avaluable pool of trainedmanpower able to help withthe task of keeping thenetwork of "Chain Home"stations operational aroundthe clock during the earlystages of the war.

During the war, engineers inBritain and Germany foundthat further increases inoperating frequency had littleeffect on target detectability.Since increased frequency(shorter wavelength) allowed anarrower beam to be obtainedfrom a given size of antenna,the use of ever higherfrequencies became the key toboth improved accuracy andresolution and of ways ofproducing compact yeteffective sets for airborne and

calculated as an imaginarysphere - varied widely withchanging aspect angle. Asmall change in angle couldaffect the observed RCS.

Variation in RCS with AngleViewing angle Possible RCS

other applications in whichspace and weight were at apremium.

Soon after the war, securityrestrictions on the massiveamount of research anddevelopment which had beeninvested in radar technologywere relaxed, allowing thepublication of severaltextbooks, culminating in theclassic Radiation Laboratoryseries, a collection ofdefinitive textbooks preparedby the Radiation Laboratory ofthe Massachusetts Institute ofTechnology to record thecontemporary state of the art.

CROSS-SECTION

Reading these and other earlyradar textbooks books showshow far the engineers of theearly 1940s had progressed instudying the complexprocesses by which radarenergy is reflected by anaircraft. "It is essential torealise that the cross-sectionof a given target will dependnot only on the wavelength,but also upon the angle fromwhich the target is viewed bythe radar", wrote E.M. Purcellin the 1947 RadiationLaboratory volume on radarsystems engineering. "Thefluctuation of [radar cross-section] with 'target aspect' asit is called, is due to theinterference of reflectedwaves from different parts ofthe target.... Only for certainspecial cases can [radar cross-section] be calculatedrigorously; for most targets [it]has to be inferred from theradar data."

To define the radar cross-section of a target, the radarengineer calculates the sizeof a sphere which wouldreflect the same amount ofradar energy as the aircrafthe has measured. The RCS insquare metres is then the areaof a circle of the samediameter as this imaginarysphere.

A Taylorcraft light aircrafthad an RCS of 170sq ft (16m2),Purcell and collaborator A.J.ESiegert reported, while a B-17bomber had an RCS of SOOsqft (74m2). (Since those earlydays, RCS has by conventionbeen measured in metricterms, so the correspondingimperial/US units will nolonger be given in the textwhich follows.)

"Only a rough estimate ofthe cross-section of suchtargets as aircraft or ships canbe obtained by calculation",they warned. "Even if onecould carry through thecalculation for the actualtarget (usually one has to becontent with considering asimplified model) the

27

comparison of calculated andobserved cross-section wouldbe extremely difficult becauseof the strong dependence ofthe cross-section on aspect."

RCS VARIATIONS

To illustrate this, theyreported on tests made using aB-26 bomber. In many cases,the level of radar energyreflected could vary by asmuch as 15dB when theviewing angle was changedby only a third of a degree.

The decibel (dB) is a unit ofmeasurement much used inelectronics. It is often foundin technical articles onanything from hi-fi toelectronic warfare. The key tounderstanding it is to realisethat it describes a ratiobetween two values and thatit is calculated logarithmicallyand not arithmetically. Anincrease of 3dB amounts to anarithmetic doubling, forexample, while an increase oflOdB represents a tenfoldincrease.

What Purcell and Siegertwere saying in "scientificshorthand" was that a third ofa degree change in viewingangle could affect themeasured RCS of the B-26 bya factor of up to 32. Post-warresearch has shown that inpractice the RCS of real-worldtargets can fluctuate by up to80dB (up to a million).

One factor influencing RCSwas propeller position, theyreported, while the effect ofpropeller rotation bothincreased and modulated theradar return. Tests had shownthat shutting down thestarboard engine of the testB-26 reduced RCS in thesector from 2 to 5 o'clock by amassive amount. Muchresearch in the 1950s and1960s was devoted to studyingthe exact mechanisms bywhich electromagnetic beamswere reflected by objects ofvarious shapes and sizes.

Much of the results remainclassified to this day but thelittle information which hasleaked suggests that, althoughthe individual phenomenawhich caused reflection fromdifferent types of basic shapewere becoming betterunderstood, the problem ofcalculating and predictingRCS remained close tounsolvable.

Two factors resulted in theeventual breakthrough. Onewas the Vietnam War, whereUS military aircraft and theircrews had been exposed toradar-directed air-defences.

The other was thedevelopment of thesupercomputer. These giantand incredibly fast machines

Variation in RCS with Propeller PositionRotating propeller

had been developed for twobasic applications -codebreaking and computersimulation of the intricateprocesses and reactions at theheart of a nuclear or thermo-nuclear explosion. As soon asenough of these costlymachines had been built tosatisfy at least partially theneeds of the codebreakersand nuclear weapondesigners, radar engineersapplied their massivecapability to those thornyproblems of RCS prediction.

To understand the differentways in which an aircraft ormissile reflects radar energy, agood starting point is theprinciple stated earlier in thischapter. "When the radarwave hits the target, it induceselectric and magneticcurrents within that object.By the act of flowing, these

Above: Wartime researcherstrying to understand RCSeven found that stopping andstarting an engine and itsassociated propeller couldmarkedly affect the radarcross-section of a bomber.

Right: In the 1930s, UK radardesigners tried to matchwavelength with thewingspan of typical bombers.

Typical Wingspans of 1930s Bombers

Aircraft

Dornier Do 17

Heinkel Helll

Armstrong Whitworth Whitley

Bristol Blenheim

First flight

1934

1935

1936

1936

Wingspan

59ft (18m)

74ft (22.4m)

84ft (25.6m)

56ft (17.1m)

A&ove:The development ofradar-guided AA weaponssuch as the SA-2 Guidelinecreated new interest inmethods of reducing RCS.

Right: A radar wave whichstrikes a flat metal plate suchas a fin reflects in much thesame way as a light beamreflects from a mirror. Like a

transmitted beam, thisreflected energy formsa main beam, flanked byseveral smaller beams knownas sidelobes.

28

RADAR AND RADAR CROSS-SECTION

currents in turn cause anelectromagnetic wave to becreated. It is this latter wavewhich the radar sees as areflected echo."

This is what radar andstealth engineers call thescattering process, the newlycreated wave being known asthe "scattered field". Stealthtechnology is the art ofcontrolling that scatteringso as to minimise the amountof energy returned to theradar.

The wavelength of a radarwave can have three possiblerelationships with thedimensions of the target - itcan be much bigger, roughlythe same size or muchsmaller. In each case, adifferent type of scatteringwill take place.

SCATTERING

If the wavelength is muchlarger than the dimensionsof the target, all parts of thetarget are illuminated by thesame part of the wave and theresult is what is known asRayleigh scattering. Undersuch conditions, only grosssize and shape of the targetare important and RCS isroughly proportionate totarget size. Since a frequencyof around 100MHz is thelowest normally used forradar, the longest militarysignificant wavelength whicha target will receive is thusaround 3m. In most cases, thiswill be smaller than thetarget, so Rayleigh scatteringis of little importance,although it could besignificant when predictingthe RCS of small details suchas gun muzzles, vents, grillesand protrusions.

In cases where thewavelength is close to thetarget dimensions, resonantscattering is observed. This, it

Reflection

Diffraction

Above: Radar waves grazinga circular structure can creeparound its circumference,while waves striking a

conical point, a sharp edgesuch as a leading edge, or acorner are scattered by aprocess known as diffraction.

may be remembered, is whatthe British tried to achievewith the original choice of"Chain Home" operatingfrequency. Target behaviourunder such resonant andnear-resonant cases (knownas the Mie region) is the mostdifficult to predict. The phaseof the incident wave changesseveral times along the lengthof the target. Overallgeometry of the target isimportant, since every part ofthe target affects every otherpart. Resonance may occurbetween specular reflectedwaves and creeping waves.The resulting Mie-region RCSis very dependent on aspectangle and can fluctuatemassively.

When the wavelength isvery much smaller than thetarget, interactions betweenthe latter's different parts areminimal and the target can betreated as a collection ofindependent scatteringcentres. The incoming waveacts in a manner similar tolight and the laws of optics, sostealth engineers usegeometric optics (GO) to helpthem predict the RCS of atarget.

The smallest target for mostradars will be a jet fighter or acruise missile. A light fighteris normally about 45ft (14m)in length, while a moderncruise missile is often around21ft (6.5m) in length. Theradar signals directed againstthem will have wavelengths ofbetween 0.75in and 10ft (2cmand 3m). In most cases, thetarget will be 10 or morewavelengths long, makinghigh-frequency scattering themost important component ofthe overall RCS.

INTERACTIONS

With high-frequencyscattering, every part of thetarget scatters energyindependently of the rest ofthe structure. This in theorywould make it relatively easyto estimate the effect of eachand, by integration, thescattered field and thus theRCS of the entire target. Inpractice, the interactionbetween all the individualscatterers which make up acomplex shape such as anaircraft is so complex as torequire the use of powerfulcomputers.

Just as a curved surface onan aircraft will exhibit areflection in sunlight, thatsurface will have a similarradar reflection. This istermed specular reflectionand is a strong component ofRCS. When a radar wave isreflected from a flat surface -another form of specular

29

reflection - it behaves ratherlike a beam of light striking amirror, or a squash ballbouncing off the walls of thesquash court. The angle ofincidence equals the angle ofreflection. A simple exampleof this is when a child "skips"a stone across the surface of apond. The stone descendstowards the water at a shallowgrazing angle of 10 or 15degrees (the angle ofincidence) then after strikingthe water begins to rise at thesame 10 to 15 degree angle(the angle of reflection).

The reflected energy doesnot confine itself to a singlebeam or lobe. Diffractionresults in the formation ofsidelobes which send smalleramounts of energy off in anumber of directions slightlydisplaced from the axis of themain lobe.

DIFFRACTION

This simple theory breaksdown completely whendealing with suchdiscontinuities as edges, tipsand corners or changes inslope or curvature. Here there-radiated field is the result ofa process known asdiffraction. It depends on theshape of the feature inquestion, the direction fromwhich it is being illuminated,the position of the observerand the polarisation of theradar wave. To calculate theresult, engineers rely on thegeometric theory ofdiffraction (GTD).

Below: Aircraft fuselages,external stores and even themetal skin of the wing or finscan all provide a habitat fortravelling waves.

Typical Radar Wavelengths

Frequency

150MHz

2GHz

lOGHz

Application

Long-range surveillance

Surveillance

Tracking

Wavelength

6.5ft (2m)

6in (15cm)

1.2in (3cm)

Surface waves of electricand magnetic current flowingalong the structure of anaircraft or missile in responseto the arrival of radar energypose further problems for thestealth designer. Thesesurface waves come in severalforms. Rounded targets suchas cylinders or spheres sufferfrom creeping waves. As itsname suggests, the creepingwave flows around the skin ofa target. Starting from thepoint where the radar wavejust grazes the edge of thecurved surface (known as the"shadow boundary"), thecurrents creep round onto the

Travelling Waves

Above: A combat aircraft islikely to be illuminated bymany different radars, and awide range of wavelengths.

Right: Radar waves grazing along metallic structure suchas this MiG-21 fuselage andits external tanks inducetravelling waves in the skin.

Below: Travelling waves re-radiate radar energy awayfrom the radar. On reachinga discontinuity or the end ofthe structure, they arereflected, and now add thisenergy to the total RCSobserved by the receiver.

side not illuminated by theradar, then back towards theopposite edge. Once at theopposite edge, they then re-radiate energy back towardsthe radar. If the object aroundwhich they are creeping ismore than 10 or 15wavelengths in diameter, theyare of little importance.

TRAVELLING WAVES

Much more troublesome arewhat are known as travellingwaves which affect long slimobjects such as missileairframes, fuel tanks andunderwing stores, or even theentire fuselage of a slenderaircraft such as the F-104 orTR-1. Radar energy strikingsuch a target at low angles ofincidence, that is to say closeto head on, create whatengineers call a surfacetravelling wave. This is anelectric and magnetic currentwhich heads down the lengthof the target object.

As it does so, it will emit itsown electromagnetic field, asignal which heads in thesame general direction as theilluminating radar signal. Theprinciple of "angle ofincidence equals the angle ofreflection" still applies. Sincethis reflected signal is directedaway from the illuminatingradar, it adds nothing to thetarget RCS and is of noimmediate concern to thestealth designer.

The problem comes whenthe travelling wave reachesthe far end of the object alongwhich it is flowing. Havingnowhere to go, it is reflectedback up along the body, stillemitting its own

30

RADAR AND RADAR CROSS-SECTION

electromagnetic field.Unfortunately, this time thereflected energy is directedback towards the illuminatingradar, adding to the target'soverall RCS.

In the case of an aircraftfuselage illuminated from theforward sector, similar surfacewaves will be set up. As thesetravel backwards along thefuselage, they may meetdiscontinuities such as seams,gaps, changes in surfacematerial or sudden changes inshape.

In terms of traditionalaircraft engineering, suchfeatures are common andpose no problems. Forexample, mid-1960s vintageMiG-21s were notorious forlarge gaps between individualfuselage panels. On a stealthaircraft, such surfacediscontinuities must beeliminated. If the surface wavecannot continue along itsroute, it will reflectbackwards along the fuselageas did the travelling wave,adding its own unwantedcontribution to aircraft RCS.All discontinuities such asedges, gaps and corners aregood scatterers of radarenergy.

When an aircraft isilluminated from the rearsector, fuselage travellingwaves can become a majorproblem. Moving forwardalong the fuselage, theyeventually arrive at the nose,where they are reflected backdown the fuselage, adding tothe rearward RCS.

As we have already seen,the largest RCS component isspecular reflection. On atypical aircraft, creeping and

travelling waves will accountfor around 1m2 of the total. AsRCS-reduction measuresreduce specular reflection,these lesser sources becomemore important, so must betreated.

DIHEDRALS

A major headache for thestealth designer is thedihedral, a radar-reflectivearea created whenever twometallic surfaces arepositioned at 90 degrees to

one another. An incomingradar signal entering the rightangle formed by two suchsurfaces will carry out a"double-bounce" manoeuvre,the geometry of whichensures that the signal will bereturned in exactly the samedirection as the incoming. Tosee a simple analogy, drive aball towards the corner of apool table. It will bounce offone edge of the table, then offthe adjacent edge, andemerge heading back towardsthe player.

To continue the analogy, ifyou sawed the corner off thepool table leaving a 12in(30cm) wide gap in place ofthe pocket, then drove theball back towards the corner(but not directly into the gap)it would still carry out asimilar bounce manoeuvrefrom the sides and re-emerge.This illustrates the fact thatthe two surfaces of a cornerreflector need not meet; theyonly need be at 90 degreeswith respect to one another.

Typical Dihedral ReflectorCORNERS

Armed "with this knowledge,the reader should have nodifficulty is identifying radar-reflective corner reflectors ona modern warplane.Horizontal stabilisers areoften at right angles to thevertical fin, underwing pylonsare at right angles to the winglower surface, cruciformwings and fins of missiles andbombs fit the bill nicely, whilecommon features such aswing fences and stiffeningribs add their share of 90degree corners.

Let three surfaces meet at90 degrees and an even moredangerous triple-bouncemanoeuvre is possible,returning a strong radarsignal over a wide range ofaspect angles. This junction ofthree surfaces is called a

Left: Two surfaces at 90degrees can turn a radarsignal through 180 degrees,providing a strong echo.Three surfaces meetingat right angles are evenmore effective at enhancingthe reflection.

31

Incomingradar signal

Reflectiondirectly backtowards radarreceiver

"Double bounce"

corner reflector. In some non-aerospace applications cornerreflectors are deliberatelycreated. For example metalcorner reflectors a few feet(less than a metre) in size areoften fitted to the masts ofsailing beats to helpcoastguard radar detect them.

No aircraft has such anexternal feature but canopiesare transparent to radar wavesand cockpits contain manybox-like objects and 90 degreecorners. Accidental creationof a corner reflector is onlytoo easy.

To see a corner reflector inaction, watch when driving atnight for the reflective "catseyes" often used as roadmarkers. These are designedto catch the light from thecar's headlamps, returning itdirectly to the driver. Themore powerful the headlamps,the brighter the "cat's eyes"will shine. That is how acorner reflector behaveswhen seen by a radar.

CAVITIES

The corner reflector is justone of the features which thestealth designer terms a "re-entrant structure" - an object•which traps and stronglyreflects radar energy.Substitute the word "cavity"for "re-entrant structure", pickup a photo of yourfavourite warplane and you'llbegin to take a jaundiced viewof intakes, jet pipes, suck-indoors, air scoops and othervents, gun muzzles and othercommon features. All areprominent radar targets.

Bear in mind the fact thatradomes, canopies and othertransparencies are also radar-transparent and a new set ofre-entrant structures can befound. The cockpit and anyelectro-optical (EO) fairingsare prime candidates, while

Above: Hidden from sightunder nose radomes, radarantennas are designed tohandle 'friendly' signals, butalso add to RCS.

Below: Count the 90 degreeangles on this Tornadointerceptor and its weapons- each will add its share tothe total radar signature.

32

RADAR AND RADAR CROSS-SECTION

behind the radome lurks anideal reflector in the shape ofthe radar antenna,particularly if the latter is ofthe traditional paraboloid"dish" type. On some aircraft,the radar antenna isdeliberately slewed to anextreme angle when the radaris not being used, so as toreduce its contribution to thehead-on RCS.

RCS CALCULATIONSIn the Middle Ages, studentsof the occult drew up longlists of demons and spirits,solemnly documenting theirrelative positions and powersin a sort of satanic hierarchy.

Stealth engineers have theirown version of the "Hierarchyof Hell", with the three-surface corner reflector castin the role of the majorvillain. Such lists detail all thecommon geometric shapes inorder of descending radarreflectivity. Directly beneaththe three-surface cornerreflector is its two-surfacecousin, followed by the flatplate, cylinder, sphere,straight edge, curved edge,cone, followed by varioustypes of curvature. It mayseem at first sight about aspointless as the listing drawnup by their mediaevalpredecessors, but it is in fact alist of many of the basicshapes into which a larger andmore complex target may bebroken down.

In theory at least, all youhave to do is add up the RCSfrom a dozen or so majorshapes, plus dozens if nothundreds of smaller ones toget the RCS of the completeaircraft. In practice, all theseindividual returns interferewith one another.

Remember how thecomponents of anelectromagnetic wavecontinually swing frompositive to negative and backagain? If all the hundreds ofindividual reflected signalswere all in step with oneanother (engineers would say"in phase" with one another),such simple addition would

Left: This Grumman A-6Intruder has a typicalcollection of exposedcavities, inlets, vents andgrilles - all highly reflective.

work. Unfortunately for thestealth engineer they are not;when one is peaking in thepositive direction, others areapproaching their peak ordying away to zero, while yetmore are doing the samething in the negativedirection. In engineeringparlance, they are "out ofphase" with one another. Tocomplicate matters further,the polarisation of eachindividual return may bechanged by the reflectionprocess, while the reflectivityof each individual scattererwill vary with frequency, eachmember of the hierarchy ofbasic shapes is behaving in adifferent frequency-relatedmanner.

The summation of all theindividual reflections from acomplex target is made evenmore chaotic by the effect ofchanges in viewing angle. Twoindividual reflections whichare in phase to the observer(and thus boosting eachother's strength) will be out ofphase if the observer moves,while further movement willbring them back in phase,then out of phase again, andso on. Signals which are out ofphase with each other willinterfere with one another. Ifthey are of opposite phase,one will tend to cancel outthe other - a process knownas destructive interference.Take into account the factthat literally hundreds ofsignals are involved, then it islittle wonder that the totalfluctuates violently.

Such then are the complexand intractable rules of radarreflection. Given theircompexity, it is little wonder

that as late as 1981, in IEEETransactions on Antennas andPropagation, Edward M.Kennaugh was to describehow "As measurementcapabilities improved,investigation of the variationof RCS with these parameters[target aspect, radarfrequency and wavepolarisation] provided theradar analyst with a plethoraof data, but few insights intothis relation." Despite hispessimism, enough wasunderstood to allow engineersto devise methods of reducingRCS, creating design ruleswhich would make stealthaircraft possible.

The breakthrough had comein the mid-1960s, when PyotrUfmitsev, then the chief scientistat the Moscow Institute forRadio Engineering, made astudy of the equations devisedby Clerk Maxwell andsubsequently refined by theGerman physicist ArnoldJohannes Sommerfield. Fromthese, he devised a workabletheoretical method ofcalculating RCS.

The computer technology ofthe time could not accuratelycompute the RCS of a collectionof curved surfaces, but couldtackle a series of flat surfaces.Since the design of an aircraftrequires the use of curvedsurfaces, Ufmitsev found that theSoviet aircraft designers of thetime were not interested in histheory, which was finallypublished in unclassified formunder the title "Method of EdgeWaves in the Physical Theory ofDiffraction". The key to creatinga stealth aircraft now existed, yetwas to be ignored for almost adecade.

Below: One of the biggestradar-reflective cavities onany aircraft is the cockpitand its cluttered consoles.This is a MiG-29 Fulcrum.

33

DESIGNING ASTEALTH AIRCRAFTC reation of a stealth

aircraft or missile requiresthat the visual, radar, thermaland acoustic signatures bereduced. There are othermore exotic signatures, someof -which have potential as thebasis for anti-stealth sensors,but these are the mostimportant.

To achieve a militarilysignificant reduction in RCS,three techniques may be used:(1) avoid design features whichwill create strong reflections inthe direction of the radar;(2) absorb rather than reflect theincoming radar energy;(3) mask or cancel out anyremaining reflections;

No single approach willprovide enough RCS reduction.The first and second of thesetechniques are already used indifferent degrees by existingstealth aircraft and missiles; thethird could be in use alreadyand will certainly play asignificant role in future aircraftdesigns.

Earlier we used the analogyof comparing a radar systemwith a searchlight. In onerespect, this analogy wasbadly flawed - thesearchlight illuminated itsvictim so that other air-defence weapons could detectthe reflected light. Once thepowerful beam had lit thetarget aircraft, the reflectedlight could be seen by anti-aircraft gunners on theground and even by the crewsof any friendly nightfightersoperating within visual range.

REFLECTIONSIn the case of almost allpresent-day radars, the sensorwhich is looking for thereflected echo uses the sameantenna as was used to sendout the illuminating pulse.Only the reflected energywhich returns directly to theradar is usable. Energy whichis redirected in otherdirections "will do nothing tobetray the target.

Careful control of aircraftshape plays a vital part inreducing RCS at microwavefrequencies by directing thescattered signal away from theradar which is trying toreceive it. On early stealthaircraft, including theLockheed F-117A, it was the

34

DESIGNING A STEALTH AIRCRAFT

main RCS-reduction measure.For shaping to be useful

as an RCS-reducingmeasure, it must be donewhen the aircraft is firstdesigned, and compromisesmust be avoided. For thisreason, little can be done toretrofit stealth onto anexisting aircraft - the bestthe designer can hope toachieve is to delaydetectability. The end resultis not a stealth aircraft.

To avoid directing reflectedenergy back to the hostileradar, the stealth designertries to observe a series ofrules. One of the mostimportant is to avoid the useof large flat vertical surfaces.No attempt was made whendesigning the B-52 to keepRCS to a minimum, so thataircraft's slab sides andrelatively straight lines makeit a prominent radar target. Ifvertical fins or fuselage sidesmust be used, these should becanted inward. Cantedfuselage sides may be seen onthe Boeing AGM-86B ALCMand on Teledyne's Model 324and 350 RPVs, while the samecompany's AQM-91ACompass Arrow RPV shows

left This mid-1980sLockheed AFT "artist'simpression" shows two-dimensional afterburnernozzles.

an example of inward-cantedtail surfaces. Manyearly-1980s artists'impressions of stealth fightersalso incorporated inward-tilted vertical fins.

Two approaches may betaken to eliminate reflectionsfrom the fuselage. The mostobvious is to curve thefuselage surfaces, preferablyin two dimensions - atechnique used on the SR-71and B-l bomber. For bestresults, this curvature shouldbe concave (inward); convex(outward) curvature would bereflective. The designershould avoid discontinuitiessuch as corners and abruptchanges of shape/profile,blending and smoothing allwing/fin and surfacejunctions. This removesgeometric discontinuitieswhich would result in wavescattering.

FLAT CANOPY

There remain limits to whatcan be done with curvature,especially given the fact thatmost practical designsdemand convex curves. Anearly morning walk along afighter flight-line on a sunnyday will show just howeffectively curved surfacessuch as fuselage sides andcockpit canopies can reflectthe sunlight over a range of

aspect angles. Radar waveswould also reflect in a similarmanner.

The first aircraft to try toeliminate this problem in

optical terms was the USArmy's Bell AH-1S Cobra. Onthe earlier AH-1G and AH-1J,the canopy used conventionalrounded transparencies but

Left: Features of the B-52which create high RCSinclude the slab-sidedfuselage, and the engine podsand pylons.

Above: Light glints from thecurved fuselage of a Mirage2000. Radar energy can hereflected in the same manner,increasing RCS.

35

Above: The angular "flat-plate" canopy on this AH-1Suses faceting to reduce opticalglint. A similar technique canalso be employed to reduceRCS.

the version adopted for the -ISwas of flat-panel design,consisting of seven surfaces.Each individual sectionreflected sunlight in onedirection only, making theoverall design less likely tobetray the aircraft's position.

The wing leading edge canbe a strong reflector in theforward sector. Given that thereflected energy from anincoming head-on radar signalwill leave a wing leading edgeat an angle equal to twice thatof the leading-edge sweepangle at the point of "impact",increasing the sweep anglewill increase the amount bywhich the reflected energy isshifted away from the forwardsector, thus reducing thechances that it will bedetected by the receiver ofthe head-on radar. At highangles of sweep, most of the

reflected energy is deflectedat angles away from thecritical forward sector.

FACETING

On most aircraft, the leading andtrailing edges are straight ornear-straight, so the reflectedenergy will be concentratedover a narrow range of angles.This phenomenon was noticedby the Swedish Air Force, "whichrealised that its Saab J35 Drakenwas a difficult radar target whenseen head-on. The two sweepangles of its double-delta wingserved to direct radar energywell away from the forwarddirection.

Since wing and horizontalleading/trailing edges aregood radar reflectors, theangles used on the wing andstabiliser leading and trailingedges must either be keptcommon (scattering the radarenergy in a few carefully-chosen directions) or made asdifferent as possible (so as to"dump" the reflected energyin several pre-plannedsectors).

As wing sweep is increased,the delta wing becomes moreattractive but, by its longchord, will provide anopportunity for travellingwaves to be set up. These canin turn be minimised byrounding the wingtips,minimising the reflectivediscontinuity which thetravelling waves will meetwhen they reach the trailingedge of the -wing.

These are the basic ruleswhich defined theconfiguration of the firststealth aircraft. Both theLockheed (XST/F-117A) andNorthop (B-2) teams came upwith the same solution interms of wing planform -straight leading edges whichwould re-direct the radarenergy well away from thefrontal sector, plus a moderatesweep angle which wouldkeep the chord short enoughto avoid the worst effects ofsurface travelling waves.Lockheed opted for a facetedfuselage - probably the onlypractical configuration givenmid-1970s technology - and

The RCS Effects of Wing Sweep Angle

eliminated horizontal andvertical tail surfaces byadopting a "V" configuration.Faceting would have imposeda significant range penalty ona long-range bomber, soNorthrop backed acombination of curvature andadvanced RAM for its flyingwing design and relied on asophisticated flight controlsystem which would allow theelimination of all verticalsurfaces.

CAVITIES

Creation of a practical stealthaircraft or missile requiresmeticulous attention to detailif RCS is to be minimised.Cavities such as air intakes,known to stealth engineers as"re-entrant structures", have ahigh RCS. Prediction of theRCS of a cavity is difficult anddepends on what is in thecavity. As a first orderapproximation, the stealthengineer can assume that theRCS will be similar to that of aflat plate of equivalent size.

A cavity must either beshielded in some manner so thatthe radar energy cannot enter,or must be treated with radar-absorbent material (RAM). Thetechniques used to createeffective forms of RAM will bedescribed later in this chapter.For the moment it should benoted that devising RAM totreat cavities is not easy, since

Lett: The wing leading edgeof an aircraft can be a strongradar reflector but increasedsweep angles will directradar reflections away fromthe critical head-on sector.Use of a changing sweepangle, such as on the crescentwing of the Handley PageVictor, can scatter thereflected energy over a widerange of angles.

36

DESIGNING A STEALTH AIRCRAFT

the radar frequencies used formilitary purposes cover atbet-ween two and three ordersof magnitude, andelectromagnetic characteristicsof the chosen material (such aspermeability and dielectricconstant) will vary considerablywith frequency, as will theoptimum thickness required.

The powerplant and itsassociated inlets and nozzlesare large cavities, and can be amajor contributor to RCS. Thefront and rear faces of theengine are the primarysignature source, followed bythe inlet edges, and anyvariable-geometry controlsurfaces used for adjustingairflow.

Many stealth configurationshave engine inlets mountedabove the wing or fuselage tokeep them hidden fromground-based radars, but anyaerodynamicist will warn of thepossibility of airflow problemsduring high angle-of-attackmanoeuvres. When radarenergy strikes, the compressoror fan face of a jet engineeffectively acts as a solidsurface, preventing the -wavefrom proceeding further. Themost obvious way of reducingintake RCS would be to coatthe first-stage blades withRAM. This would have the

Faceting on the F-117A

desired effect, but is not apractical solution - theabsorbent material could notcope with the stresses causedby the high rotational speeds.

On a high-flyingreconnaissance aircraft ormaritime patrol aircraft, thethreat may be primarily frombelow, allowing high-RCSfeatures such as inlets andexhausts to be moved ontoupper surfaces where they

Above: The Lockheed F-117ANighthawk stealth fightermakes extensive use offaceting in order to reduceRCS. Its shape remainedsecret until late in 1988.

Below: The huge inlets of theAV-8A (and other members ofthe Harrier family) will giveradars a good view of thefront face of the Pegasusturbofan engine.

will be screened from belowby the -wing. On a low-levelstrike aircraft, the main threatmay well prove to be look-down/shoot-down radars,forcing such reflectivefeatures onto the aircraft'sunderside.

In cases such as an air-superiority fighter whereattack could come from aboveor below, shaping starts to gettricky. In his massive textbookRadar Cross-Section ReductionEugene F. Knott poses thequestion "What rationale canbe taken if all threatdirections are equally likely?"His answer is not comforting- "It is a question that hasnot been satisfactorilyanswered."

Conventional ramp-typeinlets often give a head-onobserver a good view of theengine fan or compressor face,so are near-ideal radarreflectors. A quick look downthe intake of a MiG-29 at the1988 Farnborough air showgave me a good look at thefront face of the powerfulR-33 turbofan and therealisation that a reduced RCSwas far from being asignificant design goal -whenBelyakov and his teamdeveloped this agile andeffective fighter aircraft.

37

Above: The inlets of the B-1Awere designed for Mach 2dash performance, soincorporated variable rampsintended to match the airflowto the engine.

Intakes may be designed touse half-cone centre-bodies ofthe sort used on the Miragefighter. Efficient and light,these would block muchradiation, preventing it fromreaching the engine. Furthermeasures which wouldprevent radars from "seeing"the highly reflective frontface of the jet engines includelong sinuous serpentine oreven zig-zag air trunking inwhich radar energy could betrapped inside the inlet, thenbounced back and forth anddamped by radar-absorbentmaterial (RAM).

In the 1940s, the USNational Advisory Committeefor Aeronautics (NACA)developed flush inlets. Visiblefrom a smaller range of anglesthan a conventional inlet,these could be a viablealternative to conventionaldesigns. Tested in 1950 on thefirst of two experimentalYF-93A prototypes, thesewere replaced on the secondaircraft by conventionallateral intakes. The solecurrent application is on theMcDonnell Douglas Harpoonanti-ship missile.

In the early 1960s, TeledyneRyan reconnaissance droneswere flown with wire-meshscreens over theirprominent "shark's mouth" airinlets. This worked wellagainst long-wavelengththreats such as Soviet

surveillance radars but wouldbe difficult to implementagainst modern centimetricradars. To be effective, themesh must be smaller than asmall fraction of awavelength. A quick look atthe window of a microwaveoven will show just how smalla centimetric mesh must be.

Treatment of engine nozzles isalso very important, and iscomplicated by hightemperatures created by theefflux of a jet engine. Theelectromagnetic designrequirements for radar-absorbentcoatings are not different fromthose used for lower-temperaturecavities such as inlets, butmaintaining structural integrity ismuch more difficult.

The efflux from a jet enginewill also have some level of radarreflectivity, and is dependent onmaximum gas temperature. Whilethe radar return from the efflux ofan engine running in dry(military) power is insignificant,the rise in temperature whichresults from afterburning couldresult in strong radar reflection.

COCKPITSOne of the most troublesomecavities on an aircraft is thecockpit. Virtually as transparentto radar energy as it is to light, thecanopy or windshield allowsradar energy access to thecluttered and radar-reflectivecockpit interior. The pilot's headand helmet, the ejection seat and

all the various controls and dis-plays in the cockpit all contributea major share to the signature ofthe aircraft.

One way of preventing this is touse an external shape for thecanopy -which conforms to goodlow RCS design rules, then tometalise it with a coating whichwill have minimal effect ofvisibility, but will be "seen" by theradar as being an electricallyconductive surface rather than atransparency - virtually anextension of the aircraft's skin.

Such coatings must pass at least85 per cent of the visible energyand reflect virtually all of theradar energy. The techniques fordoing this are well established. Athin layer of gold on the canopytransparency of the EA-6B

38

DESIGNING A STEALTH AIRCRAFT

Above: The B-1B isoptimised for high-subsoniccruise, so the inlets wereredesigned as simpler fixed-geometry units with engine-concealing anti-radarbaffles.

Below: Side-fuselage flushintakes (seen here on theexperimental NorthAmerican YF-93 derivativeof the F-86 Sabre) preventradar from "seeing" theengine inlet.

Right: The antennas,equipment racks and LRUswithin the radome of thisTornado IDS may act as hotspots when illuminated byenemy radar.

Prowler protects the crew from thepowerful signal emitted by theaircraft's jammers. Indium-tin isanother possible canopy coating,and is reported to allow 98 percent transmission of visible light.

For canopy-plating to beeffective, the conductive film onthe transparency must beelectrically continuous with thefuselage. This implies the use ofconductive seals such as theinflatable fabric-reinforcedsilicone rubber seals used on theSaab JAS-39 Gripen. Canopyprofile should also be kept low inorder to minimise scattering atthe fuselage/canopy junction.

Since any form of radio or radarantenna is required to be anefficient receiver or radiator ofelectromagnetic energy, it is adifficult feature to incorporate intoa stealth aircraft. On the F-117A,the radio system uses retractableantennas that can be extendedwhen the pilot wishes to receiveor transmit radio messages, butare kept retracted when theaircraft needs to be stealthy.

Radars are even more of aproblem. Aircraft radomes arecustom designed to match theoperating frequency of the radarthey cover, but are alsotransparent to a much wider bandof frequencies, exposing theantenna to hostile radars.

A radar antenna makes twocontributions to RCS. One is thescattering due to its structure,the other is more subtle, and dueto its function-related shape.Radar energy arriving at aconventional paraboloidal "dish"

antenna will be gathered andfocussed onto the antenna feedin exactly the same way as theecho return signal. Not beingat the frequency for whichthe feed was designed, it willreflect, travelling back alongthe same route and being sentoff on its unwanted way by themain reflector.

Flat planar-array antennasof the type used in morerecent designs are less of aproblem but measures muststill be taken to reduce theirRCS. The design used on theB-1B is deliberately canteddownward to reduce itssignature, relying onelectronic beam steering todirect the radar energy aheadof the aircraft rather than inthe direction the planarantenna is facing.

In the long run, the antennamust be concealed fromhostile radars by mounting itwithin a special radome. Onepossibility for stealth aircraftwould be to devise a "band-pass" radome transparentonly to the relatively narrowband of frequencies used bythe stealth aircraft's ownradar. A more intriguingpossibility is that of anelectrically-switchableradome. This takes the band-pass concept a stage furtherby arranging for suitableelectrical impulses to turn theband-pass characteristic offand on in much the same waythat electrical impulses can beused to darken or extinguish

the characters on the LCDdisplay on a digital watch. Formost frequencies, and foreven the band-pass frequencywhenever the radar was notbeing used, the radome wouldbe opaque.

Panels and doors also add theirreflectivity to the total RCS of theaircraft. In a conventional aircraftthe edges of such features areoften at right angles to thedirection of flight, a locationwhich makes them reflect radarenergy arriving from the forwardsector. The solution is to sweepthe panel edges, aligning thoseedges with other major edges onthe aircraft. On stealth aircraft,door edges are either swept at aconstant angle, or at severalangles that combine to create a"sawtooth" edge.

TRAVELLING WAVES

Travelling waves and othersurface waves flowing on theskin of an aircraft or missilecan give rise to re-radiation ofenergy if they meetdiscontinuities such as seams,gaps between panels, changesin surface material or suddenchanges in shape. In designingand building a stealth aircraft,care must therefore be takento ensure that all gaps andseams are eliminated eitherby closing the gap with anelectrically conductingmaterial (the approach usedon the B-1B) or by working totight tolerances to eliminategaps (as on the B-2).

39

Wing slats and flaps cancreate such gaps, particularlywhen used for manoeuvring.When an aircraft such as theF-14 Tomcat sets its winggeometry to the combatmanoeuvring position, gapsexist between the wing, theslat and the flap. When thewing is illuminated by radarenergy, such gaps will helpreflect a signal. This isparticularly true if the aircraftis illuminated from head-on orthe rear quarter, whensurface waves moving acrossthe wing chord will meet oneof those gaps.

A travelling wave flowingalong a fuselage willeventually meet anunavoidable discontinuity -the point at which thestructure physically ends, forexample, at the tip of aradome or the end of a jetpipeor exhaust. The best way ofdealing with it is to attenuatethe wave before it reaches theend of the structure. This isoften done by applying radar-absorbing material to thesurface.

Stealth designers must alsoeliminate small exposedcavities such as gun muzzles,sensor windows or refuellingreceptacles. Most features ofthis sort should be screenedby small doors but the cannonmuzzle would probablyrequire a small frangible panelof metallised plastic.

Other conventional featureswhich radar sees as scatter-inducing discontinuities aresmall fairings, protrusions,grilles, domes and wingtipfairings. If allowed toprotrude, even rivets and

other fasteners can act asradar reflectors. Conventionalairflow and pressure sensorscan be strongly reflective.These must be designed forminimal radar signature and ifnecessary treated with RAM.

The move towards stealthtechnology in the former SovietUnion must be demanding a re-think by Russian engineers, whoin the past have often resorted toexternal fairings as a means ofaccommodating features such ascontrol surface bell-crankswhich a Western designerwould have buried within theairframe.

Probes and other protrudingfeatures will add to the aircraft'sRCS, and designing low-observability versions is noteasy. The Lockheed Have Bluestealth demonstration aircraft isreported to have usedretractable probes that wereextended for take-off and

Mission Adaptive Wing

Above: The mechanismwithin the US-designedMission Adaptive Wing(MAW) is classified, but thisphoto gives a good view ofthe unit's flexible upper skin.

Below right: Internalweapons carriage reducedthe drag of the Convair F-102Delta Dagger. On stealthaircraft, internal ordnancestorage also reduces RCS.

Below: Unlike conventionalleading edge slats andtrailing edge flaps, theMission Adaptive Wingleaves the upper and lowerskin surface unbroken.Travelling waves flowingwithin the wing skin as theresult of illumination byradar thus never meet gapswhich would cause them tore-radiate energy andincrease the apparent RCS.

landing, but retracted when theaircraft's stealth qualities werebeing measured. While theywere retracted, the aircraftderived speed information fromits inertial navigation system.

F-117A project manager AlanBrown has noted that, "On anunstable, fly-by-wire aircraft, it isextremely important to haveredundant sources ofaerodynamic data. These must

40

DESIGNING A STEALTH AIRCRAFT

Above: As part of theAdvanced Fighter TechnologyIntegration programme, thisF-lll was used to flight test thevariable camber MissionAdaptive Whig.

be very accurate with respect toflow direction, and they mustoperate ice-free at all times.Static and total pressure probeshave been used, but they clearlyrepresent compromises withstealth requirements. Severalquite different techniques are invarious stages of development"

This need to keep theaircraft as clean as possibleeffectively rules out the use

of traditional types ofexternal stores such asmissiles, bombs andequipment pods. External fueltanks are less of a problem -they would be dropped beforecoming into range of a hostileradar just in the way thatKorean War Sabres droppedtanks before tangling withagile MiGs.

All EW and EO systemsmust be carried internallyperhaps on interchangeablepallets, while ordnance mustbe carried in internal weaponbays or in semi-buriedconformal locations. Thelatter might even be covered

with expendable radar-absorbing fairings whichcould be dropped just beforeweapon release.

WEAPONS CARRIAGEIf any other type ofunderwing store is needed, itwould have to be carried in aradar-absorbent container. Aclue to how this may be donecan be seen in surface-shipinstallations of the Harpoonanti-ship missile. This ismounted on the vessel in acylindrical storagecontainer/launcher. As theround leaves the tube at

launch, its wings and finsunfold to their flight position.Delete the solid-fuel tandembooster (which would not beneeded for air launch) andmake the tube slightly greaterin diameter to allow for radar-absorbent material, addstreamlined nose and tail capsand you've got a stealthy air-launched Harpooninstallation.

Missiles and small-sizedbombs could probably becarried in a large underwingcontainer treated with radar-absorbent material and fittedwith "bomb doors" orfrangible panels on the

41

Possible Stealth Weapons Carrier

underside - a stealthyversion of the carrierscurrently used for lightpractice bombs.

To reduce the space whichmissiles take up in a weapon'sbay or the sort of weapon carrierdescribed above, folding orcropped wings and fins arelikely to be used One of theweapons due to arm the USAF'sF-22 Advanced Tactical Fighteris the Raytheon AIM-120AAdvanced Medium Range Air-to-Air Missile (AMRAAM). TheAIM-120C5 version was the firstto introduce cropped surfaceswhich would allow moremissiles to be carried within theaircraft's internal weapons bays.

The exhaust plume from arocket motor contains radar-reflective ionised gases, whichmay limit the degree of RCSreduction possible on a stealthymissile. An air-breathingpowerplant such as a smallturbofan would be more useful.

Moving all the ordnance intoan internal bay, and eliminatingtraditional underwing sensor orEW pods, reduce RCS, but eatinto the space available forinternal fuel. The use of aweapons bay may also reducethe maximum weapon load,while elimination of externalpods prevents the rapidupdating of the aircraft by add-ons.

Imagine how slowly EWmight have developed duringthe Vietnam War if all the vitallyneeded new jamming year hadbeen internally mounted, ratherthan fielded as add-onunderwing pods. The stealthyair force stands to lose this kindof fast-reaction capability. If asudden requirement emerges fora new sensor or item of EW kit,someone is going to have to findspace within an already tightly-packaged warplane.

COMPOSITESThe fact that stealth aircraftare made from composites hasalready taken a deep hold inaviation folklore. After all,composites are not metal anddo not show up on radar.

Such, at least, is the populartheory. What may provesurprising is that the use ofcomposites is not one of themost significant RCS-reduction measures. Thewartime de HavillandMosquito light bomber wasmade of wood but nobodyever suggested that it hadstealth capabilities.

The sad truth is thatbuilding an aircraft frommaterials through which radarenergy may pass simply givesthe radar a good view of theaircraft's "innards" - in thecase of the Mosquito, engines,fuel pumps, electrical wiringand the primitive avionics ofthe time. The Mosquitoundoubtedly did have a lowerRCS than a four enginedLancaster or Halifax but thiswas not militarily significant.The aircraft's survivabilitycame from its highperformance rather than anyreduction in RCS.

On most stealth aircraft, theouter surfaces are coated with ametallic paint, so that the radarcannot penetrate the compositematerials and enter the interior.

The role played bycomposites in reducing RCS isa more subtle one. Carbon is apoor conductor of electricity,being widely used in themanufacture of resistors usedby the electronics industry.Epoxy resin is an insulator. Asa result, the electricalconductivity of compositematerials is low. Radar energyarriving at a composite panelor structure has a hard jobsetting up the electrical andmagnetic currents -which re-radiate the energy and formtroublesome creeping andtravelling waves.

By 1981, Northrop had morethan 30 funded contractsworth close to $50 million todevelop advanced compositestechnology. In the early1980s, the company builtexperimental structureswhich were then subjected toa long-term study toinvestigate the effect ofthermal "spikes", radiation

Above: Many types of missileare already fitted with foldingwings and fins so that they canbe fired from tubularstorage/launch tubes. If thetube and its end caps were to betreated with RAM, stealthaircraft could carry suchweapons as low-RCS externalstores.

Right: The de HavillandMosquito light bomber wasbuilt from wood but this hadsurprisingly little effect on theaircraft's RCS.

Below: Compositemanufacturing techniques usedon the B-2 were the result ofNorthrop R&D efforts in theearly 1980s.

from nuclear explosions andlaser energy.

RAM CONCEPTSIn the struggle to minimiseRCS, a more useful ally will bereinforced carbon-carbon(RCC). This is created bybaking and carbonising amatrix containing carbonfibres. As a material it isstrong and exceptionally heat-resistant. Used in themanufacture of missile re-entry vehicles and the noseand wing leading edges of theUS Space Shuttle, it could be

used to built low-RCS exhaustsystems. To the stealthengineer, the importance ofRCC is that it combines thesephysical virtues with anotheruseful property - the ability toabsorb radar energy.

Once the main reflectionproblems are identified,engineers can modify the designand employ special materials atvulnerable points. Reflectionsmay be reduced by means ofradar-absorbent materials - theradar equivalents of the blackfinish used on the undersides ofSecond World War nightbombers.

42

DESIGNING A STEALTH AIRCRAFT

There are two broad classesof RAM - resonant andbroadband. Resonantabsorbers are designed foruse at a specific frequencybut maintain someeffectiveness over a range offrequencies on either side ofthis nominal operating point.Broadband RAM maintains itseffectiveness over a muchwider range of frequencies.

The simplest type ofresonant RAM is thesandwich-type absorber. Thisoperates on the sameprinciple as the blue- orbrown-tinged antireflectionoptical coatings applied to thelenses of cameras, opticalinstruments and even

spectacles. When the lightstrikes such a lens, a portion isreflected by the coating. Theremainder passes through thecoating and strikes the frontface of the lens. A portion isreflected, while the remainderenters the lens.

RESONANT ABSORBERThere are now tworeflections to consider.Careful choice of coatingmaterial ensures that theamounts reflected by thecoating and the glass aresimilar. The coating isarranged to have a thicknessequal to one quarter of awavelength of visible light. As

Principles of Resonant RAM

a result, the reflection fromthe glass surface has travelledan extra distance totalling halfa wavelength by the time thatit re-emerges from the coatingand meets the reflection fromthe front surface of thecoating. That vital half-wavelength difference makesthe two waves of light out ofphase with one another. Asone wave rises above zero, theother falls below zero by anequal and opposite amount.One is the exact opposite ofthe other and the two canceleach other out, a processknown as destructiveinterference. In theory, all ofthe reflection should vanish,but the cancellation is never

Left: The Salisbury Screen isthe simplest type of resonantRAM. A resistive screen ispositioned in front of theback plate. The resistivity ofthe screen is such that 50per cent of the incomingradar wave (shown in blue)is reflected from the screensurface, while the remainderpasses through to reflectfrom the back plate. If thesetwo surfaces are positionedquarter of a -wavelengthapart, the reflections fromthe screen (mauve) and backplate (red) cancel oneanother.

perfect, so some minimalreflection remains.

The earliest resonant RAMmaterials used the sameprinciple. The SalisburyScreen consisted of a thinsheet of resistive n aterial heldat a quarter wavelengthdistance ahead of a metalbacking plate by a lowdielectric spacer. Dielectricmaterials have the property ofresisting an electric current,•while allowing electrostatic orelectromagnetic forces to passfreely. In the SalisburyScreen, this often takes theform of a specially-designedfoam or honeycomb material.Another type of absorberknown as a Dallenbach Layerconsists of a quarter-wavelength thick slab ofelectrically lossy materialapplied to a metal backingplate. Exposing a radar signalto a slab of lossy material israther like exposing amarathon runner to a strongheadwind. The slab does notconduct electrical currents,but does have the ability todissipate a significant portionof any electric energy towhich it is exposed. A radarwave arriving at the frontsurface of the lossy materialmeets a change in electricalimpedance which gives rise tothe front-surface reflection.

43

Below: Rockwell engineersapplied RAM to key areas ofthe B-1B in the effort tosignificantly reduce RCS. Thewing root area was a source

of reflections and requiredcareful redesign. A thin darkstrip of RAM is visible on thewing of this aircraft inconstruction.

Although widely used formany applications such asdamping the radar returnsfrom buildings at airports orharbours (applications inwhich a single or at most afew frequencies need to becountered at minimal cost),interference absorbers arenarrow-band and physicallybulky, so are not very usefulfor applications such asstealth aircraft.

DIELECTRIC RAMIn more practical types ofresonant (narrow-band)absorber, two effects are usedto soak up the incoming radarenergy - destructiveinterference between thereflections from the surfaceand the backing, andattenuation of the wave bythe dielectric material. This

type of material is known as adielectrically-loaded absorber.

The goal of the RAMdesigner is to create amaterial the front surface ofwhich "will admit a radar waverather than reflect it. Oncewithin the RAM, the radarwave should then beabsorbed, dissipating itsenergy in the form of heat.For decades, componentmanufacturers have fabricatedelectrical resistors fromcarbon, so it is hardlysurprising that the samematerial should form the basisof many types of RAM. Whenradar waves strike such aRAM, its limited conductivitycauses losses, as does theeffort which the moleculesmust make while attemptingto follow the alternatingfields. This is known as "lossydielectric" RAM.

Above: Small dark patcheson the unpainted skin of thisB-1B around the nose-mounted control vaneindicate the presence of RAM.

Had dielectric RAM beenthe sole solution, stealthtechnology might never haveleft the laboratory. Luckily asecond type of RAM has beendeveloped which proved mucheasier to apply to many typesof aircraft structure. Known asmagnetic RAM, this is basedon magnetic material such ascompounds of iron, ferrites(ceramic compounds offerromagnetic materials) orcarbonyl iron. Thesematerials are often embeddedin sheets of natural orsynthetic rubber which caneasily be glued into position.

A resonant absorber basedon magnetic materials works

Right: RAM made frompyramid-shaped elementslines the walls of thisanechoic test chamber at theUniversity of Eindhoven.

in much the same way as itsdielectrically-loadedcounterpart, combiningdestructive interference withattenuation. Here the energyis dissipated as the magneticdipoles within the materialmove in response to theimpinging radar wave. Theamount of lossy material andbinder is selected in order toprovide the optimumelectromagneticcharacteristics for the range offrequencies which thedesigner is trying to counter.

Most readers who own acassette recorder or videorecorder will be familiar withthe brand name TDK. The

44

DESIGNING A STEALTH AIRCRAFT

company is the world's largestmanufacturer of magneticrecording tape. It owes thislead to Doctor Yogoro Kato ofTokyo Industrial University,who passed the patents forthe newly invented ferrite toa venture capitalist in 1932.This co-operation resulted inthe founding of TDK.

FERRITE ABSORBER

In the 1970s, the companyteamed with NEC to studymethods of reducing the metalcontamination of waterdischarged by Japanese steelmills. Having learned how toprecipitate this metal waste as

low-grade ferrite, they tried tofind a commercial applicationfor what was essentially awaste product.

An application whichsuggested itself was thecreation of RAM. By mixingmagnetic material with anepoxy liquid, NEC tried todevelop a paint which couldbe applied to the structure ofmetal bridges to reduce theirreflectivity as seen by radar.A 1979 trial proveddisappointing; the paintcoating applied to the bridgedid absorb a limited amountof radar energy but not over awide enough range offrequencies.

Left and Below: In his bookDragon Lady, author ChrisPocock revealed how U-2aircraft were fitted withpanels of radar-absorbing

Narrow-band absorbers canbe designed to operate at anyfrequency but, for anypractical stealth applications,a broader coverage is needed.One way of accomplishingthis is to make a multilayerabsorber, each layer of whichis designed to resonate at adifferent frequency. Onesimple example is themultilayer Salisbury Screen.The addition of extra resistivesheets and spacers broadensthe range of frequencies oneither side of the nominaldesign frequency. For bestresults, the resistivity of eachsheet is arranged to be lowerthan the one ahead of it, so

Salisbury Screen (fuselagesides below and ahead of thecockpit) and Eccosorb (belowthe inlets) during late-1950sstealth experiments.

that the incoming wave meetssheets of decreasingresistivity. This type of screen,known as a Jaumannabsorber, can have two, three,four or even six layers. Sinceall layers are spaced by thesame amount, the totalthickness of the screen isincreased accordingly. Its bulkmakes it unsuitable for mostairframe applications.

One early practicalapplication of the Jaumannabsorber was a RAMdeveloped during the SecondWorld War by the GermanNavy for the treatment ofsubmarines. It consisted ofseven layers of carbon-impregnated paper, each ofincreasing conductivity,separated by layers of foamplastic dielectric. It waseffective at the 3cm and 10cmfrequency band, but was 2.5in(6.35cm) thick and rigid. As aresult, it was never deployedon operational U-boats.

PYRAMID ABSORBER

Once again, a more practicalsolution can be found basedon dielectrically-loated andmagnetically-loadedmaterials. What the idealRAM should do is to graduallymatch the impedance of theair to that of the metal aircraftskin. If this were achievable,the incoming radar wave•would never meet a change inimpedance sharp enough tocause a reflection.

First attempts at creatinggraded material involveddipping mats of curled animalhair into a conductive mixtureof carbon and neoprene. Themixture clung to the hair but,as the newly-dipped matswere laid out horizontally todry, the mixture tended toflow downwards, creating arough and ready dielectricgradient. The resultingmaterial was largely used inthe laboratory and on thewalls of the first anechoic(reflection-free) radio testchambers developed forindoor antenna testing.

A more practical method ofgrading the dielectric is tomould the material into apyramid the apex of which ispointed in the direction of theradar wave. As the wavemoves forward and thus downthe axis of the pyramid, itexposes itself to more of thedielectric material. Thistechnique is ideal for use inthe construction of anechoicchambers, whose pyramid-studded walls are aconspicuous feature ofmodern photographs showingindoor antenna or RCS tests.The dielectric used here iscarbon-loaded foam.

45

Right'The assembly-line viewof an SR-71 engine nacelle andouter wing clearly shows howtriangular patches of RAMwere built into the wingleading edge, a measureintended to reduce overallRCS.

A pyramidal absorber ofthis classical type isimpractical for aircraft use,except in a two-dimensionalform buried within wing/finleading or trailing edges. Thistype of material "was used inthe wings of the LockheedSR-71 and can be clearly seenin some photographs ofaircraft under construction.

Pyramidal or hair-mat RAMmay be satisfactory forlaboratory use, or for thetreatment of large structures,but is far too bulky for mostaerospace applications. Whencreating more practicaldesigns, the RAM designerachieves the desired dielectricgrading by forming thematerial from layers ofdielectric. If a limited numberof radar bands must becountered, a multilayernarrow-band RAM may haveone of its layers designed tocope with one band and asecond to deal with the other.

RAM PRODUCTSWide-band RAMs arenormally created by adding acarbon-loaded plastic materialto the base such aspolyurethane foam. Thiscreates the required "lossydielectric". The thicker thematerial, the better theabsorption. Maximum valuesof 90 to 99.9 per cent arepossible.

MAGNETIC ABSORBERVery little information hasbeen released on thecharacteristics of ferrite paint- often referred to as "ironball" paint in press reports ofstealth technology. AdvancedAbsorber Products' AAP-021 isa polyurethane-casedsprayable coating, a heavygrey liquid which dries tackfree in 40 minutes andhardens in 12 to 24 hours. ItsRAM properties depend onthe thickness to which it isapplied. A 0.03in (0.76mm)coat will reduce the reflectedenergy by an amountincreasing from 3dB at 6GHzto 13dB at ISGHz.

Being based on iron-likematerial, magnetic RAM isheavy. It also has a tendencyto oxidise, a process whichdegrades its effectiveness.Oxidation is particularlysevere at temperatures ofmore than 900°F (500°C),

46

DESIGNING A STEALTH AIRCRAFT

creating problems whenhypersonic aircraft or ballisticmissile re-entry vehicles arebeing considered for RAMtreatment.

Offsetting thesedisadvantages are the factthat it is thin and that itmaintains its effectivenessdown to sub-gigahertzfrequencies. A SalisburyScreen intended to operate at100MHz would be 29in (75cm)thick; even a dielectricabsorber would be manyinches thick. A magneticRAM able to operate at thesame frequency might be onlya tenth of the thickness of itsdielectric counterpart.Different magnetic materialshave their peak efficiency atvarious frequencies but bylayering them one on top ofanother a broader-bandabsorber will be created.Ferrite paint may also act asan electrical bonding agentbetween panels.

Magnetic RAM is most

Above:The composite wings ofJapan's F-2 fighter makeextensive use of locallydeveloped radar-absorbingmaterial.

Below /eft The radarreflectivity of the ferrite paintused on the Lockheed TR-1 canbe varied by changing itsthickness.

effective at lower frequencies,dielectric types at the highestfrequencies. The logicalapproach is therefore tocombine the two, creatinghybrid RAMs effective overthe highest possible range offrequencies.

A typical advancedmultilayer RAM of the type inservice in the late 1980sapparently consists of threelayers. The outer and innerlayers are partly radarreflective and act rather like aSalisbury Screen. The centrallayer, made from lossydielectric material, is intendedto help contain the energyreflected from the innermostlayer for long enough forcancellation to occur. It alsoacts as a traditional lossydielectric absorber.

CIRCUIT ANALOGUEAnother type of RAM can becreated by replacing theresistive sheet used inSalisbury or Jaumannabsorbers with one on whichconductive material isarranged in geometricpatterns such as thin strips,grids, crosses or morecomplex shapes. The result isknown as a Circuit Analogue(CA) absorber. The materialoffers a higher performancewithin a given volume thansimpler types of absorber butmust be custom-designed foreach application, a tasknormally handled by apowerful computer.

CA absorber technology isprobably the principle behindone new method of producingstealthy canopies. The easiestway of creating a canopy for a

stealth aircraft was mentionedearlier - application of a thinfilm of gold or indium-tin tothe transparent material. Thisconducting film keeps theradar energy out of thecockpit but will tend to reflectit. A more recent techniqueinvolves making the entiretransparency absorb radarenergy. This is done byembedding within it anetwork of thin wires cut todipole (half-wavelength) size.When combined with aninner conductive layer, thistreatment probably turns theentire transparency into a CAabsorber.

Most RAM used in stealthaircraft falls into one of twocategories - sheets or otheroff-the-shelf bulk materialsfor general use and custom-designed components madefrom RAM material. AlthoughRAM solves many RCSproblems, it also creates itsown constraints. Its weightwill reduce aircraftperformance and its bulk mayprove troublesome in volume-restricted applications such asmissiles. Its purchase andmachining and installationcost will make the aircraftmore expensive, while its verypresence may well create newservicing difficulties for

ground crews, increasingdirect operating costs.

By combining RAM withrigid radar-transparentsubstances, it is possible tocreate Radar-AbsorbentStructural (RAS) materials,one of the most classifiedforms of radar absorber. Littleinformation has beenpublished on materials of thistype. RAS can also be created bytaking a non-metallichoneycomb, treating its surfacewith carbon or other lossymaterials, then bonding non-metallic skins to its front andback to create a rigid panel.Honeycomb sections can absorblow-frequency radar if theindividual cells are at least one-tenth of a wavelength of theradar signal.

Early stealth aircraft madeextensive use of RAM and RAS,and paid a penalty in substantialadditional weight.Improvements in analysis anddesign tools have allowed asignificant reduction in theamount of RAM carried by morerecent designs such as the F-22Raptor.

One intriguing but little-discussed possibility forreducing RCS is that ofcancellation of the scatteredsignal by the transmission of asecond signal of equalfrequency and amplitude butof opposite phase. In theory,this could be achievedpassively by creating asuitable reflector (such as anaccurately-machined cavity ofappropriate dimensions)designed to create theappropriate echo. In practicehowever, this technique (oftenreferred to as "impedanceloading") would only work ata single frequency for whichthe reflector had beendesigned, while eachscattering source on theaircraft would require its ownassociated and matchingreflector.

Circuit Analogue Absorbers

Above and above right: Byprinting conductive geometricpatterns on suitable basematerial, engineers can createCircuit Analogue (CA) RAM, a

highly effective radar absorber,but one which must be custom-designed by computer to suiteach new apsorptionapplication.

47

CANCELLATIONThe only realistic method ofcreating the waveform neededfor cancellation would be byactive means. Unfortunately,the technical problems areformidable. Aircraft-mountedsensors would have tomeasure the frequency,waveform, strength anddirection of the signal to becountered. Complex signalprocessing equipment whosesoftware contained detailedinformation on the aircraft'sradar reflectivity at a widerange of angles andfrequencies would have topredict how the incomingwave would reflect, thencreate and transmit a suitablecancellation signal.

Cancellation would notneed to be 100 per cent to bemilitarily useful, -while thetask of matching thecancellation signal to thethreat could be reduced inmagnitude by reducing thethreat sector and frequencyrange to be countered. Active-cancellation systems havebeen discussed in technicalpublicatior.s and it is possiblethat equipment of this type isbeing used on the Dassault-Breguet Rafale and the NorthropB-2 bomber.

Confirmation that France hasdeveloped active-cancellationtechniques came at aconference on guided missilesheld in London in April 1999 bySMi. During a presentation onstealth technology for missiles,Jean-Francois Gondet, seniortechnical adviser at Matra BAeDynamics said that thetechniques which the companyhas developed for minimisingRCS included "active systems",but added that these were toohighly classified to bediscussed at an unclassifiedconference.

Also in the late 1990s camenews of a new and noveltechnique for controlling RCS.Developed in Russia by theKeldysh Research Centre, itbreaks the perceived theoryheld in the West that sinceshape has such a strong effecton RCS, little can be done toreduce the RCS of an existingaircraft. The Western view maybe true when attempts arebeing made to reduce RCS byretrofitting RAM, but theRussian scheme creates anartificially generated plasmaaround the aircraft.

Two phenomena reduce theRCS of an aircraft protected by aplasma cloud, say the Russians.Radar energy tends to passaround a plasma cloud ratherthan penetrate it, and the energythat does penetrate interactswith the plasma-chargedparticles, and is partially

Above and below: The B-2programme made extensive useof computer-aided design andmanufacturing (CAD/CAM)techniques. Computer screens

linked to a 3D databasereplaced drawing boards,allowing the automaticmanufacture of accuratecomponents.

absorbed. Western stealthtechniques degrade thehandling characteristics andagility of the aircraft, theRussians claim, while theirsystem allows the designergreater freedom in terms ofaerodynamic design. Thehardware that must be added tothe aircraft weighs less than2201b (100kg), and consumesbetween 1 and lOkW of electricalpower.

Three generations of plasma-protection system have beendeveloped and tested by theKeldysh Research Centre. Thefirst was a simple RCS-reduction system, while thesecond changed the frequencyof the greatly attenuatedreflected signal, and produced"some false signals" whichhelped to conceal the aircraft'slocation and speed. Progress•with a further-improved third-generation system allowed theRussian government to clear

the first- and second-generationversions for export.

The effectiveness of plasmashielding has beendemonstrated by ground andflight tests, say its developers.These have shown that the radarobservability of an aircraft canbe reduced by a factor of morethan 100. The effectiveness ofsuch a scheme depends on whatthe Russians define as "radarobservability". A reduction inRCS of 100 would reduce theradar cross-section of a MiG-23from around 64.5 sq ft (6 sq m) toaround 0.6sq m. This is less of areduction than that achieved byUS stealth aircraft but, as we willsee later in this chapter, wouldbe enough to sharply degradethe effectiveness of radar-baseddefences.

Given present-day sensortechnology, passive IR offersthe only realistic option toradar for the long-rangedetection of aircraft targets.

With the growing use of IRsensors as a radar substitute,measures must be taken toreduce the thermal signatureof a stealth aircraft.

The main sources of IRenergy are hot metalcomponents of the engineturbine and the exhaustnozzle, components whichhave been heated by the1,800 - 2,300°F (1,000 -1,300°C) efflux from theengine's combustors. Theefflux leaving the tailpipecontributes relatively little -only some ten per cent of thetotal IR emission from aturbojet and even less from aturbofan.

If the engine uses anafterburner, the IR emissionfrom the efflux can beincreased by up to 50 times,causing it to rival or eveneclipse that of the jetpipe. Forthis reason, all the first-generation of stealth aircraft- the XST, F-117A and B-2 -make use of non-afterburningengines.

The hot interior of thetailpipe is visible over aconical sector to the rear ofthe aircraft. From outside ofthis sector, an IR sensor willsee only the outside surface ofthe nozzle, the temperature ofwhich will be lower. The IRsignature can be reduced byusing the aircraft's aftfuselage and/or vertical tailsurfaces to shield the jetpipesfrom view over as large a partof this sector as possible.

IR SCREENING"Venetian blind" horizontallouvres arranged across thenozzle will restrict tailpipevisibility to a narrow range ofvertical angles but would

48

DESIGNING A STEALTH AIRCRAFT

probably require cooling toensure that they did not beginto rival the tailpipe intemperature.

Exhaust masking has beenwidely used by the designers ofhelicopters, but they have theadvantage that much of theenergy in the efflux has beenremoved by the turbine whichdrives the output shaft. On a jet-powered aircraft, the jet providesthe basic propulsive force, somust be masked by aircraftstructure over as wide a range ofangles as possible. On theF-117A, YF-23, and B-2, the hotexhausts could not be seen fromthe lower hemisphere.

In much the same way thatRAM has been developed toreduce radar reflectivity,materials have been devised tocontrol IR reflectivity, but thecritical dimensions such asthicknesses are now expressedin angstroms rather than inmillimetres.

While a low level of IRemissivity may at first sightseem a valuable feature of theinner surface of a jet pipe orefflux duct surface, since it willreduce the emitted energy, itwill also act as a good IRreflector, increasing the reflectedenergy that may be coming froma hotter internal region of theexhaust system. F-117Aprogramme manager AlanBrown has stated that, "a carefuloptimization must be made todetermine the preferredemissivity pattern inside a jetengine exhaust pipe. Thispattern must be played againstthe frequency range available to[IR] detectors, which typicallycovers a band from one to 12microns." In a late-1990stechnical paper, he noted that,"Recently some interestingprogress has been made in

Active Cancellation System

directed energy, particularly formultiple bounce situations", butcoyly added, "...that subject willnot be discussed further here".

Metal layers are currentlyused in such materials, saysBrown, but "the big push atpresent is in moving from metallayers in the films to metaloxides for radar cross-sectioncompatibility. Getting therequired performance as afunction of frequency is not easy,and it is a significant feat to getdown to an emissivity of 0.1,particularly over a sustainedfrequency range. Thus, thebiggest practical ratio ofemissivities is liable to be oneorder of magnitude."

Despite the traditional

Transmitted wavematches and cancelsreflected wave

Above: Another method ofreducing RCS is activecancellation. The incoming(strong blue) radar wave issampled by a receivingantenna. Having predicted theaircraft's reflectivity at thisfrequency and angle, theavionics create and transmit afalse echo (mauve), a signaldesigned to cancel out thegenuine reflection (pale blue)from the aircraft's skin.

Below: In redesigning the B-1Ato create today's B-1B, Rockwellreduced RCS by a factor of ten,taut could do little to reduce theIR output from fourafterburning GE F-101turbofans.

military preference for keepingeverything from soldiers' bootsto warships nicely clean andpolished, the inside of militaryjetpipes is unlikely to satisfy afastidious inspecting officer. Theheat and carbon particles fromjet efflux will soon dull the mostcarefully manufacturedcomponents. Jet fuel is ahydrocarbon, so tends toproduce carbon when burned,though today's combat jets arevirtually smoke-free comparedwith those of the 1950s and1960s. In an engine efflux,carbon particles arecomparatively harmless, addinglittle to the RCS of the exhaustgases, but on the inside of ajetpipe the build-up of carbon -a material with a very high IRemissivity - can create problemsfor the designer of a stealthaircraft, who will demand thatthe powerplant designercontrols carbon output. "For theinfrared coating to be effective, itis not sufficient to have a verylow particulate ratio in theengine exhaust, but to have onethat is essentially zero," saysAlan Brown.

Having denied an enemy IRsensor sight of the hot engine aftsection, the stealth aircraftdesigner must also reduce othersources of IR energy. An obvioustarget for treatment is now theexhaust plume. The effluxleaving the tailpipe contributesrelatively little to the IRsignature - only some ten percent of the total IR emission froma turbojet, and even less from aturbofan.

If the engine uses anafterburner, the efflux emissioncan be increased by up to 50times, causing it to rival or eveneclipse that of the jetpipe. Forthis reason, all the first-generation of stealth aircraft -the Have Blue, F-117A and B-2 -use non-afterburning engines.To minimise the IR signature ofthe efflux, the latter must becooled quickly by mixing theflow of hot gas from the corewith cooler by-pass air. This isalready done in a turbofanengine but it can be taken astage further in a stealth designby using additional air toprovide a cool shroud aroundthe exhaust. Diverting a largeflow of air through the enginebay and around the engine willalso minimise the temperaturerise in the structure of the rearfuselage.

Another way of reducingthe IR signature is to replacethe traditional circularexhaust nozzle with anelliptical or rectangularpattern. This would increasethe perimeter of the plume,creating a wide "beaver-tail" ofhot gases rather than acompact circular jet. It wouldincrease the surface area of

49

Above: The tail surfaces of theFairchild A-10 were designed tomask the engine exhausts fromthe seeker heads of IR-guidedweapons.

the plume, increasing the rateat which the gases cooled,and would also reduce theband of heights from whichan attacking fighter couldobserve a strong IR signature.

A two-dimensionalrectangular nozzle of the typeflight-tested on the F-15 STOLDemonstrator probably has a lowIR and radar signature when theengine is running in dry thrust.

AIRFRAME HEATAs the modern all-aspect IRmissile demonstrates, theairframe is also a source ofdetectable IR energy. Thisheat comes from severalsources - the engine, theavionics and the thermaleffects of friction with theatmosphere at high speed.

As any designer of enginebays will testify, a jet engineruns hot. Nearby structuremust either be built fromtitanium or othertemperature-resistant alloys orbe shielded from engineheat. Stealth aircraft arethrough! to have linings withinthe engine bay to preventengine heat from spreadinginto the structure, warmingthe aft fuselage andincreasing the aircraft's IRsignature.

At present, most aircraftsimply dump the heatgathered by the cockpit andavionics cooling systems but

50

Above and below: Two-dimensional vectored thrustnozzles have a rectangularoutlet and a lower IRsignature than conventional

round nozzles. Thisexperimental nozzle for theFIDO turbofan was developedfor use on the F-15 STOLdemonstrator.

Right: The jet flap/lift concepttested in the early 1960s onthe Hunting 126 researchaircraft probably reduced theIR signature.

DESIGNING A STEALTH AIRCRAFT

stealth aircraft will probablyrely on closed-loop coolingsystems. The heat could bedumped into the fuel, atechnique pioneered in theSR-71 Blackbird, or radiated atfrequencies not welltransmitted by theatmosphere. Anothercomponent of the IR signatureis reflected or re-radiatedsunlight. This can beminimised by the use ofsuitable surface finishes.

ENGINE NOISECurrent stealth aircraft aresubsonic. The levels of airframeheating induced by supersonicflight would make the aircraft an

easy target for IR sensors, whilethe noise of a roaringafterburner would betray acovert reconnaissance or strikeaircraft operating at medium orlow altitude.

Several books discussingstealth technology havesuggested that as a generalrule, supersonic speeds andthe use of afterburning arenot compatible with low-observable operations. Thishad led their authors toquestion the wisdom of thehypersonic fighter orreconnaissance designsproposed by some aircraftcompanies, such as the Mach5 methane-burning monsterwhose proposed configuration

was released by Lockheed inthe early 1980s.

Such a view overlooks oneof the odder aspects of flightat high Mach numbers. Asaircraft speed builds up,increasing ram pressure at theengine inlet reducesefficiency, so effluxtemperature begins to fall. ByMach 3 it can be lower thanthat of the same enginerunning at military (dry)thrust. Move to Mach 3.5 andthe tailpipe emission willcompletely dominate thatfrom the efflux.

One unavoidable factorassociated with highsupersonic speed is airframeheating due to atmosphericfriction. This will be a majorproblem in creating any"Super Blackbird" type ofaircraft. Working on theassumption that the possiblethreats to such aircraft will beSAMs or interceptorsattempting "snap-up" missileattacks, it is possible toenvisage partial solutionsbased on cooling systemswhich extract heat from thelower surface on the aircraft,re-radiating it upwards. Such asystem would confound mostpresent-day and future airdefences but the Super Powerscan afford to orbit space-based IR sensors such as theexperimential US "Teal Ruby".These would find upwardradiation from hypersonicaircraft an easy target.

COMPROMISESWorking with these basicrules for signature reduction,the designer must tackle theproblem of creating apractical stealth aircraft ormissile. The design of anyaircraft it essentially a matter

of compromise betweenconflicting requirements. Thisis even more so when creatinga stealth aircraft, since thedesigner must juggle a newset of rules and constraintsover and above those of thepast. The price paid for lowRCS may be lowerperformance, reduced rangeor a lighter payload. In 1980,Lt Gen Kelly Burke, at thattime USAF Deputy Chief ofStaff for Research andDevelopment, summed up theproblem of developing a lowRCS design: "You don't get anydesirable feature withoutgiving up some otherdesirable feature."

Even within the field ofstealth technology,compromises will be calledfor. One disadvantage ofshaping as an RCS-reductionmeasure is that reducing thereturns in one directioninvolves increasing them inanother. No matter howsurfaces are angled, there willalways be directions fromwhich they are seen at normalincidence and where theirreflectivity is high.

Before the designers canshape the aircraft, the authorsof the operationalrequirement may have toindicate the approach to befollowed. Should RCS be keptmoderately low over a widerange of viewing angles, ordoes the user want the RCSfrom a certain critical sector tobe kept as low as possible atthe expense of "dumping" theenrgy in the form of strongreflections at other lessimportant angles? Techniquessuch as operational analysismay help provide the answerhere by allowing hypotheticalaircraft using bothapproaches to RCS reduction

51

to be "flown" against thepostulated enemy defences.

The powerplant and itsassociated inlets and nozzlescreate their own problems.Many stealth configurationshave engine inlets mountedabove the wing or fuselage tokeep them hidden fromground-based radars but anyaerodynamicist will warn ofthe possibility of airflowproblems during high angle-of-attack manoeuvres. Thesort of ventral air intake flighttested on the North AmericanF-107 was not dropped justbecause it looked ugly.

When radar energy strikesthe compressor or fan face ofa jet engine it effectively actsas a solid surface, preventingthe wave from proceedingfurther. The most obvious wayof reducing intake RCS wouldbe to coat the first-stageblades with RAM. This wouldhave the desired effect but isnot a practical solution - theabsorbent material could notcope with the stresses causedby the high rotational speeds.

Moving all the ordnanceinto an internal bay andeliminating traditionalunderwing sensor or EW podsreduces RCS but eats into thespace available for internalfuel. The use of a weaponsbay may also reduce themaximum weapon load, whileelimination of external podsprevents the rapid updating ofthe aircraft by add-ons.

HOT SPOTSA major part of the designprocess is to identify at anearly stage the main elementswhich contribute to the finalRCS, To make the process ofRCS reduction cost-effective,the stealth designer mustidentify these dominantscatterers, the features on theaircraft which make thegreatest contribution to totalRCS. These are known as "hotspots" or "flare spots". Stealthmeasures applied in these

Above: This Lockheed Mach 5concept would be a good IRtarget. Hypersonic stealthaircraft will have to 'dump' thisunwanted thermal energy insafe directions.

Below: Thomson-CSF hasstudied the likely radar-reflectivity of the fan blades ofM88 turbofan engine whichwere to be used in theproduction Rafale D and M.

critical areas will make thelargest overall difference tototal RCS.

When an aircraft is viewedfrom the front, the largestcontributor to RCS is likely tobe the inlets. Being re-entrantstructures, they tend to actlike corner reflectors,efficiently trapping and re-radiating radar energy. Anycooling ducts or other inletsvisible from the front willprove equally efficient radarreflectors. Another will be anyforward-facing antennasin the nose radome of theaircraft or its missiles. If aradome is not fitted, a near-spherical metal nose may alsoact as an efficient scatterer,while travelling waves movingalong the fuselage may addtheir own contribution. Thecockpit is another cavitywhich may return strongechoes.

Moving away from thecentre line, the wing leadingedges play a major role inscattering. At broadsideangles the fuselage sides,vertical fin, underwing storesand pod-mounted engines

become major sources. Whenradar waves strike wing andfin leading and trailing edgesat near-grazing incidence,travelling waves can be set up,while further towards the rearsector radar returns from thewing and fin trailing edgeswill be observed. From behindthe aircraft, the mostimportant contributors will bethe engine exhausts and anytravelling waves set up alongthe fuselage.

RCS also varies withelevation angle. When anaircraft is viewed from theside and above, the wing/fuselage junction creates aradar-reflective 90 degreefeature, -while the right anglebetween the vertical fin andthe horizontal stabiliser addsits own component. Radarwaves arriving from above orbelow will also find the near-flat areas on the wings andhorizontal control surfaces tobe good radar targets.

Experience will allowdesigners to identify thesefeatures but their effect onoverall RCS must be assessed.In the earliest stages of a

52

DESIGNING A STEALTH AIRCRAFT

Above left: Lockheed'sexperimental Q-Star may lookcrude, but this adaptedsailplane proved the sound-reduction technology used onthe low-noise YO-3A.

hypothetical design, this canonly be done using RCSprediction codes, specialisedcomputer software which makesuse of a company or nation'saccumulated RCS expertise. ALockheed RCS predictionprogramme named Echo 1provided the informationneeded to develop the HaveBlue technology demonstratorand the F-117A.

By a process of analysis, theshape of the complete aircraftis broken down into simple

Above: The North AmericanF-107A (an unsuccessful rivalto Republic's F-105Thunderchief) is the only jetfighter to have flown with adorsal air intake.

parts - the plates, cylinders,edges, spheres and the like•whose individual RCS ispredictable. Then comes thetask which only asupercomputer canrealistically handle -synthesis of these into ahighly-complex total RCS.

There is thus no neat oreasy way to predict RCS andthe magnitude of the taskwhich the designer faces isdependant on the complexityof the shape he is considering.

Non-Stealthy Features of MiG-25 Foxbat

It is thus no accident that oneof the first applications whichThomson-CSF is applying toits RCS-prediction softwaresuite is the design of stealthyre-entry vehicles. The sheercomputer "number-crunching" power needed tocarry out realistic RCSpredictions was not availableuntil the mid to late 1960s.

MEASUREMENTSThe next stage is to carry outmeasurements using anaccurate model of either thewhole aircraft or the areas ofthe aircraft identified as "hotspots". The latter can be testedat full-scale but, when theentire aircraft must be

Gaps and breaksin skin

examined, the normalapproach is to build anaccurate scale model of theproposed design. This musteither be made from metal orbe electroplated or silverpainted after construction sothat its surface becomeselectrically conductive.Unless a low electricalresistance is obtained all overthe skin of the model, surfacewaves will not build up to thecorrect intensity.

In the 1960s and 1970s,most RCS testing was done atoutdoor test ranges. Thesefacilities consisted of amounting able to hold themodel and turn it to anydirection required for the test.The radar transmitters used toilluminate the model and thereceiver which sampled thereturned signal were locatedat a fair distance away, at least100ft (30m), and often 1,000ft(305m) or more. The radarbeam directed at the targetwould at least partiallyilluminate the terrain. Toreduce the effects of this, theground between thetransmitter site and the testposition was carefully treated.One technique involvedcreating a berm, a vee-shapedraised area running from thetransmitter to the test site.

Below: The MiG-25 Foxbat wasoptimised for high-speed dash atMach 2.8 and no attempt wasmade to minimise radar signature.Its huge inlets and abundance ofright angled surfaces all helpreflect radar energy.

Large right-angledtail surfaces

Wing fences andprotrusions

External weaponswith right-angled

surfaces

Protrudingantennae

Sharp tipson wings andtail surfaces

53

Another involved erecting aseries of low lateral fencescoated with RAM.

The problem with outdoorranges is that their size makesthem expensive to build andrun, while the accuracy of thetest results is affected byweather. There is also a riskthat the security of the designof a new aircraft may becompromised. Given aphotograph of a stealthaircraft, a low-observablesexpert can estimate itscharacteristics.

Indoor test ranges allow theradar cross-section of highly-classified stealth warplanesand missiles to be tested incomplete secrecy and alsoeliminate the effects ofweather on the measurementsbeing made.

For the designer of such testfacilities, the problem is todevise a way of creating thesame conditions as an outdoorrange. The most obvioustechnique is to line the wallsof the test chamber withRAM, absorbing the beamonce it has passed the targetand maintaining theelectronic "illusion" that thetarget is out of doors. This isnormally done using thepyramidal type of RAMmaterial described earlier. Aradar signal directed into sucha chamber will almostcompletely disappear when itmeets the wall, with less thana fraction of one per centbeing reflected.

If good results are to beachieved, the wave-front mustbe as flat as could be obtainedfrom an antenna a longdistance away. The mostcommon technigue is to directthe radar energy from theantenna not directly at thetarget but indirectly, via aspecially designed reflector.

54

This collimates the energy,creating an evenly distributedsignal identical to that from anantenna located a longdistance away. An alternativebut less common techniqueinvolves passing the radarbeam through a collimatinglens made of plastic but themanufacture of large enoughlens structures has proveddifficult.

At first, compact rangeswere seen simply asconvenient alternatives tooutdoor ranges, useful largelyfor initial testing only but nosubstitute for definitive trialson a good outdoor range.Improvements in computers,range instrumentation andrange design have now

RCS Measurement Plot

Above: This Lockheedconcept of an ATFproduction line illustratesthe computer-controlledtechnology needed whenbuilding the structure offuture low-RCS fighters.

Right:The complex shape ofthe B-2 inlet follows a preciselycalculated stealthy profile,development of which causedprogramme delays.

Below: The digital computerhas revolutionised the scienceof RCS prediction. As thisThorn EMI polar diagram of anunidentified RPV shows, themeasured RCS (red trace) isclose to the forecast value (bluetrace).

reduced or even eliminatedthis performance gap. With therise of stealth technology, mostof the major US aircraftcompanies own both outdoorand indoor ranges.

RCS TESTING

Whether tested indoors oroutdoors, the proposed designmust be examined at varyingradar freguencies. Wheneverthe wavelength being used isof the same order as the sizeof any feature on the aircraft,a resonance may occur,producing a larger radarecho. As different freguenciesare tested, different-sizedcomponents on the aircraftwill resonate whenilluminated at theappropriate frequency. All thepossible reflectionmechanisms, suchas specular reflections, edgediffraction, plus travelling andcreeping waves arefrequency-dependant,creating a mass of everchanging variables. To keepthe magnitude of the task

DESIGNING A STEALTH AIRCRAFT

Indoor Test Chamber

Above: Indoor RCS test rangesshield stealth designs fromprying eyes, but the radarenergy reaching the target mustbehave as if it had travelled along distance. The most

common scheme involvescollimating the energy by meansof a carefully shaped reflector, sothat it presents a flat wavefront.The chamber is lined with RAMto absorb excess radar energy.

within bounds, engineers willoften confine their tests tothe forward sector or anyother direction in which RCSwill be critical for the aircraftunder investigation.

Many featuresof the proposed designcan be checked with a simpleplot of reflectivity versusrange, repeated atdifferent aspect angles.To get a really detailed radar"look" at a complex targetrequires more sophisticatedtest methods, usuallyinvolving synthetic aperturetechniques.

The most normal use ofsynthetic aperture technologyis in the creation of high-definition sideways-lookingradars (SLRs). These obtaintheir near-photographicresolution by exploitingDoppler shift, the slightmodification in signalfrequencies caused byrelative movement of thesignal source and observer.(The classic example ofDoppler shift is theapparent drop in pitchof the noise from a speedingtrain as it passes an observerstanding on the railwayplatform.)

For RCS testing,instrumentation designers

55

use inverse syntheticaperture radar (ISAR)technology. Instead of movingthe radar, they move thetarget in order to create theDoppler effect. The target wasnormally rotated, so that itsindividual "hot spots" woulddisplay a Doppler shift,dependant on radarfrequency, and any radialmovement caused by theirdistance from the centre ofrotation.

RADAR IMAGESThe end result of an ISAR testis a complex three-dimensional radar imagewhose basic co-ordinates arerange and cross-range andwhere the third dimension(height) indicates reflectivity.This can be compared withthe target and all sources ofreflection swiftly located.

These tests allow thedesigners to identify all thehigh-reflective features of theproposed design - parts of theairframe which make anunduly large contribution tototal RCS and whose physicalsize may have littlerelationship to their apparentradar size. A large airframefeature may contribute littleto RCS while a small one mayprove to be a major scatterer.These "hot spots" must eitherbe eliminated from the designor be treated with RAM toreduce their reflectivity.

INDOOR TESTS

Once a prototype of theaircraft has been completed, itwill undergo RCS testing toverify the results of theearlier tests with scalemodels. Until recently, thiswork had to be done at anoutside test range, but cannow be done in a securemanner thanks to a newgeneration of indoor testfacilities - the designation"compact range" may seemalmost a misnomer for atreated chamber able toswallow an entire fighter!

SECRECY

An advanced indoor rangecommissioned by Boeing in1988 has a test chambermeasuring 225ft x 112ft(68.6m X 34m) under an 80ft(24.4m) roof. This is largeenough to test many types ofaircraft, or half-scale modelsof larger designs. Targetsunder test can either bemounted on a radar-invisiblepylon of ogival cross-sectionor be suspended on a systemof cables which allows the"fly-by" RCS to be measured.High measurement accuracy

is a feature of the facility, as isthe rigorous securitydemanded by "black"programmes. The foundationsof one of the chamber's twotest turntables are isolatedfrom the rest of the basestructure, while the supportstructure of the ceiling-mounted turntable is isolatedfrom the walls by means ofslip joints. In order tomaintain strict "need toknow" rules for models tested,a series of physicallyseparated rooms for modelstorage and preparation areprovided.

Once any remaining "hotspots" identified on the fullscale aircraft or missile havebeen dealt with, the designcan then be cleared for fullproduction. All the test resultsand additional knowledgegathered during thedevelopment effort is thenavailable for study, helping torefine the low-observabletechnologies, materials andtechniques to be incorporatedin the next generation ofstealthy aircraft and missiles.

RCS REDUCTIONAt first sight, the effects ofreducing RCS do not seemparticularly valuable. Byinserting diminishing valuesof RCS into the radar rangeequation - a mathematicalformula which defines thebasic relationship between thevarious parameters of a radarand its range performance - itbecomes obvious that ahalving of RCS does not resultin a halving of targetdetection range. Range varieswith the fourth root of RCS, sohalving the RCS reducesrange by only 15 per cent.

It has been reported that theFolland Gnat lightweightfighter of the late 1950s couldonly be detected by radarwhen closer than the largerHawker Hunter, but thedifference is unlikely to havebeen significant. The smoothlines of the Avro (later HawkerSiddeley) Vulcan are also saidto have made this aircraft adifficult radar target, althoughit probably did not translateinto any great militaryadvantage.

A key factor in determiningthe degradation in range causedby reducing RCS is the figureobtained by dividing thereduced RCS by the originalfigure, lb determine thereduction in radar range, theresult must be raised to thepower 0.25.

reduced radar range =

The B-1A is known to have anRCS one-tenth of that of the B-52,so the range resulting from thisimprovement is reduced to:

A radar tracking a B-1Awould thus have its rangereduced by 44 per cent. If itcould just detect a B-52 at arange of 100 miles orkilometers, it could only tracka B-1A at 56 miles orkilometres. Substitute a B-1B(which has an RCS a tenth thatof the B-1A and one hundredthof that of the B-52), and therange is reduced to:

SEARCH RADAR

Radar range is thus reduced to32 per cent. Reduce RCS by afurther factor of ten bysubstituting an AdvancedTactical Fighter, and the range isreduced to 18 per cent.

In his 1985 book Radar Cross-Section Lectures, Professor AllenB. Fuhs pointed out that thedegradation in real-life militarysituations may be much greater.For a tracking radar, the figuresgiven above do apply, but inorder for a target to be tracked itmust first be acquired.

A ground-based or naval searchradar tasked with locating anincoming target uses a movingradar beam to search a selectedarea in a time defined by theantenna scanning rate.According to Fuhs, thedegradation in range resultingfrom reduced RCS is given by:

A reduction of RCS by afactor of 10 will cut detectionrange to 0.32, whereasreduction by factors of 100 and1,000 will give detectionranges of a mere 0.10 and 0.03of the original range,respectively.

A radar mounted on anaircraft has an even moredifficult task, being required tosearch a volume of airspace ina given time. The formula fordegradation now becomes:

range reduction =

Reducing the RCS is noweven more effective. Reductionfactors of 10,100 and 1,000 nowgive range reductions of 0.18,.03 and .006.

Briefing the press followingthe downing of an F-117A bythe Yugoslavian air defencesin March 1999, USAF Director

RCS

0.1

0.01

0.001

0.0001

Reduced radar range

Tracking

0.56

0.32

0.18

0.1

Area search

0.32

0.1

0.03

0.01

Volume search

0.18

0.03

0.006

0.001

Typical Missile RangesMissile

Crotale

Roland

Rapier

Sea Sparrow

SA-6 Gainful

SA-5 Gammon

R-550 Magic

ATM-7F Sparrow

Max range(km)

8.5

6.3

7

18

35

250

10+

50-100

Min range(km)

0.5

0.5

0.5

1

4

80

0.3

0.6

Min as %of Max

(%)

5.9

79

71

5.6

11.4

32

2

0.6-1.2

56

Assume that an aircraft has anRCS of lOOsq metres - a valueprobably typical for a head-onB-52. Reducing RCS by 50 percent reduces radar range to:

DESIGNING A STEALTH AIRCRAFT

Right: Thanks to stealthtechnology, the RCS of anaircraft is no longerproportional to aircraft size. Inthis diagram, the aircraft aredrawn to a constant scale, butRCS steadily reduces from thatof the B-52 and Blackjack tothat of the B-2 and F-117Astealth aircraft.

of Operational RequirementsMaj. Gen. Bruce Carlsonexplained that, "It's not invisible.It never has been invisible. Weknow radars that can track ourstealthy airplanes. They cansometimes find us. The key isthat that zone ol detectability orlethality is shrunk by orders ofmagnitude, but it's still notinvisible. Our goal is that on thefirst day [of a war], we can,because we've shrunk thosezones of lethality, find our wayinto the target area using good,detailed mission planningwithout being susceptible toenemy radars or their missilesor their airplanes."

RCS reduction will also bluntthe effectiveness of SAMsystems. Look up theperformance of any anti-aircraftmissile in a reference book, oreven the manufacturer'sbrochure, and a maximum rangefigure will inevitably be quoted.Much more difficult to find is themissile's rninimurn range.

Immediately after leaving thelaunch rail, a round is not fullyunder the control of itsguidance system, but must bebrought on to the desiredtrajectory. This is particularlytrue in the case of SAMs, wherethe round will take anappreciable time to reach fullflying speed. On some boost-slide weapons, the control finsare locked until the rocketmotor has burned out, and onlythen does the weapon begin toguide.

For the sake of argument, letus invent a hypothetical "MissileX", a medium-range SAM witha maximum range of 25 miles(40km) and a minimum range ofaround 5 per cent of maximum- 1.25 miles (2km). In designingthe range of the acquisitionradar used to locate targets, thedesigner will have to allowsome performance in hand, soas to ensure that by the timethat the target is within range, itshall have been designated forattack, and the missile launcherwill have slewed on to thecorrect bearing and be preparedfor firing. The longer the rangeof the surveillance radar, thelarger, heavier and costlier itwill be, so the designer is notfree to set any maximum rangespecification he likes. Let usassume that the radar isdesigned to detect a typicaltarget at three times themaximum range of the missile -

Physical Size Compared to RCS

75 miles (120km).If the enemy introduces

stealth technology, and reducesthe RCS of a target by a factor of100 (the sort of improvementwhich the B-1B shows over theB-52), then the maximum rangeof the acquisition radar falls -according to the equationsgiven by Fuhs - to only a tenthof its design value. Instead ofdetecting the target at 75 miles(120km) range, the radarassociated with "Missile X" willnot achieve detection until 75miles (12km).

By the time that the target isfirst detected, it will be well

within the missile's lethalenvelope. Most of the weapon's25 mile (40km) range will havebeen wasted, and the newlydetected target will already beless than six miles (9km) fromthe system's minimum range.

JAMMINGLike ground clutter, the radarnoise created by chaff or radarjamming will also help maskthe low-RCS target. Reducingthe aircraft's RCS also helps inthe EW battle. It can reduce theamount of jamming powerneeded, allowing designers of

jamming equipment to reducevolume, weight and powerconsumption of their systems, oreven to use new jammingtechniques made practicable bythe stealth aircraft's relativeradar invisibility.

The small radar "size" of astealth aircraft also makes iteasier to shelter behind theprotection of a stand-off jammingaircraft. The powerful signal froman aircraft such as the EF-111Awas designed to mask aconventional fighter. It will beeven more effective whenscreening the tiny radar targetpresented by a stealth aircraft.

57

EARLYSTEALTH AIRCRAFTAbout once a decade or so

history throws upmomentous events, the sort ofthing which years later canlead to reminiscences alongthe lines of "I can rememberwhere I was and what I wasdoing when I heard the newsthat...". For many readers ofthis book, these events areprobably the assassination ofPresident Kennedy or theshooting of John Lennon. Forour parents or grandparents, itwas Pearl Harbor, while a newgeneration will probably referto the loss of the SpaceShuttle Challenger.

These events are by definitionmemorable, but few canaccurately date news of adifferent type - the new trendwhich may create majorchanges in some aspect of theworld, but which arrivesunbidden and unannounced."Internet" may have become ahousehold word by the late1990s, for example, but whooutside of a handful of computerenthusiasts could date itsapparent birth?

Much the same applies tothe first news of stealthtechnology. It seems to havecrept into the public domainwith virtually no publicity, aclassic example of how firstnews of a major developmentcan pass almost unnoticed.Legends die hard andaeronautical legends are noexception. An "official version"of the unveiling of stealthseems to have evolved andrequires to be debunkedbefore politically expedientclaims become elevated to thestatus of history.

According to a number of1980 pronouncements by USGovernment officials and evenby President Carter, news ofthe programme had firstleaked in August of that year.A subseguent official releaseof minimal information wasdepicted by the DemocraticParty as a move intended todamp down future press leaks,while the Republican Partysaw it as a blatant attempt bya shaky Administration toboost its image for theforthcoming US Presidentialelection.

Like many legends, it isneat, colourful and bears littlerelationship to reality. Reportsof stealth technology had

been circulating for severalyears before the August 1980incident. Casting my mindback over more than twodecades, I cannot rememberwhen I first heard of stealth. Inmuch the same way as apolice pathologist will give aspread of times of the likelymoment of death for a murdervictim, I can only reply "notbefore 30 June 1977 and notlater than 27 May 1978".

In 1977, Friday was press dayfor the pages which containedregular news features in theBritish aviation magazineFlight International. On 30June 1977, the day was goingmuch like any other. The fullquota of news stories had notyet been completed but theremaining shortages werenothing which a lunchtimevisit to the nearby Rose andCrown public house was nothelping to cure (a processknown to staff reporters as"lubricating the fingertips").Defence Editor Charles Gilsonwas working steadily on alarge news story, while I wason the phone obtaining theregular weekly news reportfrom the magazine's UScorrespondent.

At the end of a lengthyphone call and muchnotetaking, I realised that itwas time to spoil CharlesGilson's entire day. "Carter hasjust cancelled the B-l", Iexplained. Under normal

circumstances, Gilson was theideal boss, radiating a generalair of calm in a professionnoted for stress and frayedtempers. On this occasion, hereacted as if I had kicked himin the seat of the pants. "He'sWHAT?", was his shockedresponse.

STEALTH APPEARS

Rapidly consigning most of

Below: The single-seatconfiguration identifies this "USAir Force" aircraft as a CIAA-12, predecessor of the SR-71Blackbird.

the material we had writtenfor that week's issue tooblivion and warning theproduction department thatour news pages -would beclosing for press late, westarted work on a massivetwo-page news story. Entitled"Rockwell B-l cancelled", thisexplained President Carter'sdecision to abandon theswing-wing manned bomberprogramme in favour ofdeploying the new air-launched cruise missiles.

In the most important of myresearch files on which thisbook is based, a photocopy ofthe B-l cancellation story is

58

EARLY STEALTH AIRCRAFT

Below: When President Cartercancelled the B-1A bomberprogramme in 1977, the firstXST stealth aircraft was alreadybeing built.

the first item. It's not therebecause of what it says butbecause of what it doesn't say.Nowhere in Charles Gilson'sdescription of the reasons forthe B-l cancellation or myaccount of how cruise missileswould take over the Rockwellbomber's intended role doesany mention of stealthtechnology or even the veryidea of low-observablesappear. Obviously neitherCharles Gilson nor I hadheard of it, since it would haveformed a natural part of ourreport. First news thatLockheed was working onnew types of aircraft came in

the Fiscal Year 1977 USdefence budget. The USAFannounced for the first timethat Lockheed was to developand build the TR-1 variant ofthe U-2 family, while theDefense Research ProjectsAgency (DARPA) revealed thatLockheed had received athree-year developmentcontract worth and estimated$90 million to develop and flyan undesignated new aircrafttype. At the time, nobodyseems to have realised thepurpose of these unidentifiedaircraft. The first rumours ofstealth technology were not toleak to the world's aviationpress for sometime.

By the time that I reportedthe first crash of a stealthaircraft in the 27 May 1978issue of Flight International,tales of radar-invisible aircraftwere already in the publicdomain. Although the Flightstory is only the seconddocument in my own stealthfiles, the fact that I did notexplain at great length withinits half-page length exactlywhat a stealth aircraft wasindicates that f was assumingthat the reader was alreadyfamiliar with the concept. Mycontemporary notes have longsince vanished into Flightarchives - I left the magazine18 months later - but I canremember reading other {andalmost certainly earlier)reports of the aircraft'sexistence.

WORLD WAR E STEALTH

The idea of stealth aircraft hadbeen around for some time.During World War II Germanengineers also tried to applyRAM to an aircraft in order toreduce its detectability. TheGotha Go.229 jet-powered flyingwing, ordered into production in

early 1945 following flight trialsof a prototype aircraftdesignated Horten Ho IX, wouldhave been skinned with panelswhich sandwiched a core madeof up charcoal, sawdust and aglue matrix between two sheetsof plywood. None had beendelivered by the time the warended.

In March 1953 the USAF drewup a specification for areconnaissance aircraft able tofly at heights far above thoseobtainable from existing typesand interceptors. It proposed thecreation of a subsonic single-seataircraft with a radius of 1,500miles (2,400km), and the abilityto fly over its target at a height of70,000ft (21,335m) or more whilecarrying a sensor payloadweighing between 100 and7001b (45-315kg). The resultingdesign was expected to combinethe latest in turbojet enginetechnology with an airframewhose light construction andhigh aspect-ratio wings wouldbe more reminiscent ofsailplanes than combat aircraft.

The aircraft would beunarmed, so had to be difficult todetect, and hard to interceptBoth qualities were obtainedlargely by giving the aircraft acruising height well above thatof contemporary interceptors.The formal specificationrecognised that "the enemy willhave limited methods ofdetection and/or interception ofa vehicle of the requiredperformance. The greatestopposition to the operation ofthis aircraft can be expected tobe encountered from guidedmissiles."

Paragraph 2 (g) of thespecification demanded that,"Consideration will be given inthe design of the vehicle torninimising the detectability byenemy radar." The need to avoidemitting signals which an

enemy might detect was alsoappreciated. Navigation was tobe by means of "a non-emanating system" while thesole item of communicationsequipment would be a simpleshort-range UHF radio. "Noemanations from the aircraft willbe permitted over enemyterritory."

Although not invited to bid forthe programme, Lockheed hadlearned of the new requirement.In May 1954, the companyproposed a J73-engined CL-282variant of its F-104 Starfighter.This was rejected in favour ofthe BeH Model 67 and Martin294 designs. In November of thesame year, an evaluation ofupdated Lockheed proposals ledto a contract being placed for asmall batch of aircraft. The BellModel 67 (designated X-16) wascancelled, while the Martindesign was to emerge as thelong-span RB-57D.

The task of building the newspyplane was assigned to theLockheed "Skunk Works". Basedat Burbank, California, theSkunk Works is the stuff ofwhich aeronautical legends aremade - a project office wheresmall, highly motivated designteams worked with a rninimumof organisational constraints andeven less paperwork to createadvanced aircraft.

The Skunk Works is not thesort of establishment whichlooks good in companybrochures. Even in the 1950s,when companies expectedengineers to wear suits and ties,Skunk Works staff tookadvantage of the unit's isolation(it was off-limits to mostLockheed employees) to dresscasually. According to a story inThe Washington Post, when aCongressman visited the site inthe early 1980s, "At Lockheed'sSkunk Works, which resembleda slightly seedy industrial plant,the visitor ate stale doughnuts,drank coffee from a plastic foamcup, and was briefed by anengineer who tapped cigaretteashes into his cupped hand ashe spoke."

Such informality might notimpress visiting VIPs, butattracts talented designengineers the way wasps areattracted to a jar of jam. Focusthat amount of raw talent with abureaucracy-free environment,and advanced technologyaircraft can be created withmaximum speed and irunirnumcost.

The Skunk Works had beencreated in 1943 by Lockheeddesigner Clarence "Kelly"Johnson, by all accounts an

Left: This Lockheed U-2R of theUSAF's 9th StrategicReconnaissance Whig isexternally similar to today'sLockheed U-2S.

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irascible man with a penchantfor "bawling out" or even firingemployees whose workdispleased him. Johnson was abrilliant engineer, famous as thedesigner of the LockheedConstellation piston-enginedairliner, the twin-engined P-38fighter, and the F-80 ShootingStar jet fighter. When thereconnaissaance aircraft projectstarted, Johnson was in his mid-405, and was Lockheed's chiefengineer.

Working in conditions ofunparalleled secrecy, Johnsonand his Skunk Works team builtthe first prototype in only eightmonths, rolling it out at the then-new Groom Lake AFB, Nevada,in mid-July 1955. A brief andunplanned hop during taxi trialson 29 July was followed by afirst flight on 1 August. This firstaircraft was designated U-2, withthe production examples beingU-2A. The "U for utility"designation was intended toconceal the aircraft's true role.

On 4 July 1956, the U-2 madeits first overflight of the SovietUnion, with CIA pilot HarveyStockman at the controls. From abase in West Germany, it flewacross Poland and intoBelorussia, passing over the cityof Minsk before turning north tofly up to Leningrad (now St.Petersburg), then back toGermany. It became obviousthat, despite its high operatingaltitude, it had been tracked bySoviet radars, and MiG fightershad made unsuccessful attemptsto intercept it.

After around half a dozenoverflights of Soviet territory, itwas clear that the Soviet radarnetwork was successfullydetecting and tracking the U-2.Late in 1956 the CIA ordered aproject known as Rainbow tofind ways of reducing theaircraft's vulnerability. KellyJohnson set his engineers towork in attempts to reduce theaircraft's radar signature.

As originally fielded, the U-2flew with an all-black paintscheme designed to minimise itsvisibility at high altitudes. Itssole ally in avoiding radardetection was its small size - notmuch larger than a jet fighter -and its clean lines. At first sight,its long-span wings might seemlike ideal radar reflectors, but inpractice their vast span is sogreat that they resonate in theHF band rather than at radarfrequencies.

The first approach involvedstringing wire along thefuselage to scatter the radarenergy arriving at the aircraft,but the resulting aerodynamicdrag reduced cruising height by3000ft (2,135m). Radar-absorbentmaterial (RAM) in the form of aSalisbury Screen was thenadded to the fuselage, butproved of limited effectiveness.

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Finally, an early form of ferritepaint was applied. This reducedRCS by an order of magnitude

hi July 1957 the first modifiedaircraft - known as a "dirty bird"- made a sortie into Russia inthe Black Sea area. Recordingsshowed that the reduced RCSwas not enough to prevent theaircraft being tracked, butreduced the U-2's operatingaltitude to 58,000ft (17,600m).

Given the limited amount ofextra stealth which could beadded to the aircraft, anelectronic warfare unit knownas the "Granger" was developedto confuse Russian surface-to-airmissiles, and was installed in thetail section of the small U-2 fleet.

U-2 DOWNED

Lockheed and the CIA bothrealised that operations over theSoviet Union could not continueindefinitely. In the winter of1959/60 Skunk Works engineerBill Shroeder studied the likelyeffectiveness of the new SovietS-75 (SA-2 "Guideline") SAMsystem which had begun toenter service. He concluded thatthe aircraft had less than a yearof operating life left. On 1 May1960, a U-2 flown by FrancisGary Powers was shot downnear Sverdlovsk.

From analysis of photos of thewreckage issued by the SovietUnion, Kelly Johnson concludedthat the aircraft had been hitfrom the rear, and it was laterconcluded that shock wavesfrom a near miss had blown offthe aircraft's tail. Johnson alsosuspected that the radar energyemitted by the "Granger"jammer may have helped the

Russians track Powers' U-2.Johnson had already started

work on a supersonic aircraftable to replace the U-2 andoverfly current and futureSoviet defences with impunity.Codenamed "Suntan", the CL-400 was intended to fly at evengreater heights than the U-2,and to have a top speed ofMach 2.5. In appearance, thedesign which took shape onthe Skunk Works drawingboards resembled a giant F-104.Around 300ft (90m) in length, itwould have been powered bytwo wingtip-mounted Pratt &Whitney engines whichburned liquid hydrogen ratherthan kerosene. Thespecification called for a rangeof 3,000 miles (4,800km), butthis proved impossible toachieve, and the project wascancelled.

The earliest useful work onlow-observable technology didnot begin until the end of the1950s. When drawing up plansfrom the spring of 1958 to thelate summer of 1959 for a U-2successor, Kelly Johnson'steam at the Skunk Worksinvestigated measures for RCSreduction. In the winter of1958/59 the CIA concludedthat a supersonic U-2 successorwas feasible, and Lockheedand Convair were asked topropose suitable designs undera project codenamed "Gusto".Once again, Kelly and theSkunk Works engineersturned their talents to the taskof creating a supersonicspyplane, but this time adesign whose engines wouldburn some form ofconventional jet fuel.

Above: On the original photoof this SR-71, triangular RAMpanels are clearly visible on thestarboard wing leading edgeand chine.

A-12/SR-71 DESIGNThe initial design for whatwould eventually become theLockheed SR-71 was the A-l, anaircraft designed to fly at Mach3. However, PresidentEisenhower was not prepared toaccept a solution based purelyon high speed and high altitude- he demanded the lowest

EARLY STEALTH AIRCRAFT

possible radar cross-section. LowRCS had been a desirablequality in the U-2, but for thenew aircraft it was mandatory.

As the A-l design gave way tomore refined offerings, SkunkWorks engineers decided to fitradar-absorbing ferrite andplastic materials to all leadingedges, and to make the verticalsurfaces from radar-absorbingcomposites. The A-l concept wasfollowed by the A-2, then a seriesof further-refined layouts.

By May 1959, design A-ll hadacquired fuselage chines, and anear-flat lower fuselage surface.These measures had reducedRCS by 90 per cent By thesummer of 1959 both teams hadsubmitted designs. TheLockheed proposal was selected,and in August 1959 the companywas given the go-ahead for theconstruction of the firstprototype A-12, an aircraft whichwould incorporate low RCSfeatures such as wing/bodyblending, built-in RAM, andradar-absorbing ferrite paint.

When designing the U-2,Lockheed had been able to takeonly limited RCS-reductionmeasures, but the A-12 took theentire art a massive stepforward. As North Americandesigners working on the XB-70bomber and F-108 Rapier fighterhad discovered, creating anaircraft able to cruise at Mach 3was difficult enough, but increating the A-12 the SkunkWorks tackled the tasks ofcombining this level ofperformance with stealth.

Comparison of the A-12 withthe similar-sized F-108 isinstructive. The fighter had anangular appearance whichbordered on ugliness, with a

Above: In an attempt toimprove the effectiveness of theAGM-28 Hound Dog missile,the USAF ordered an RCS-reduction programme.

Below: Having proved adifficult radar target, TeledyneRPVs became useful recceplatforms for the Vietnam War.

slab-sided forward fuselage, box-shaped rear fuselage, andwedge inlets - features that•were highly radar reflective. TheA-12 had rounded lines whichmade extensive use ofwing/body blending, while itsengines were fed by inletswhose conical centrebodieswould help shield thecompressor face from radarobservation.

The plastic materials used inareas such as the •wing leadingedges, chines and elevens weredeveloped by Lockheed, andtook the form of a radar-absorbent plastic honeycombdesigned to cope withtemperatures of up to 600 deg F(315 deg C). On the A-12, itaccounted for 20 per cent of thetotal wing area. It was not strongenough be used structurally in aMach 3 design, so was added tothe leading and trailing edge inthe form of V-shaped sections.The Skunk Works is alsoreported to have flownexperimental components suchas all-plastic vertical fins.

The dark paint finish used tohelp radiate heat away from theaircraft gave rise to the unofficialdesignation "Blackbird". It wasdesigned with two qualities inmind. It offered high heatemissivity, so helped to radiatefriction-generated heat whenthe aircraft was cruising at Mach3. It also incorporated the radar-absorbing "iron ball" pigment

Above: Soviet radars such asFan Song and its associatedSA-2 Guideline missile forcedthe USAF to study anti-radarmeasures.

used on the U-2 and TR-1.The original A-12 was a single-

seat reconnaissance aircraft builtto meet the CIA requirementWhen the strategicreconnaissance task wastransferred to the USAF in 1960s,the two-seat SR-71 wasdeveloped to handle the task. Athird YF-12A version was testedas a long-range interceptor inthe mid-1960s, but was notadopted for operational service.

In November 1959 Lockheedstarted a long series of RCS testsof a full-scale model of the A-12.Trials were to continue for ayear and a half before the resultswere deemed satisfactory. RCSof the A-12 and the follow-onSR-71 remain classified, but areported figure of only 0.16sq ft(0.015 sq m) for the SR-71 seemshighly optimistic for an early1960s design.

"The SR-71 was an example ofwhere we took theaerodynamic design and thenadded some radar absorbingmaterial to the airplane tomake it slightly stealthy,"explained USAF Director ofOperational Requirements, Maj.Gen. Bruce Carlson, during a1999 press briefing in stealthtechnology. "We focused the lowobservable technology in thefront quarter at certainfrequencies on the radarspectrum, mostly in what we callthe target tracking or X-bandarea. That's the area that SAMsnormally do their target trackingin. There's a slight degradationin the capability of that SAM asthat airplane is coming towardit." From the rear, RCS wasessentially unaltered

Low-observable technologywas also seen as a method ofimproving the survivability of

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unmanned vehicles. In 1960,even before the jet-poweredAGM-28A Hound Dog hadbecome operational with SAC,North American was given acontract to reduce the RCS ofthe follow-on AGM-28B version.

RYAN DRONESEarly in 1960, RyanAeronautical proposed to theUSAF the development of areconnaissance version of theRyan Q-2 Firebee target drone.The company had toyed withthe idea of a reconnaissancedrone in the mid-1950s but itwas not until the growingdeployment of Soviet SAMs inthe late 1950s whichthreatened the future of U-2operations that the USAFshowed serious interest.

On 1 April of that year, aSoviet SA-2 Guideline missiledowned the U-2 being flownby CIA man Francis GaryPowers. On 8 July, Ryan wasgiven a $200,000 USAFcontract to demonstrate theuse of modified target dronesfor reconnaissance known asproject "Rqd Wagon". One ofthe goals of this project wouldbe to assess RCS reductionmeasures which mightimprove survivability withoutan extensive re-design.

A wire screen was fitted tomask the air intake from long-wavelength radars of the sortwhich the Soviet Union usedfor surveillance, blankets ofRAM were fitted to thefuselage sides and the nosesection was treated with whathas been described as "non-conductive paint".

Test results were applied toa new stealthy design knownas the Ryan Model 136. Thisfeatured a high aspect ratiounswept wing, a twin tail withinward canted verticals and adorsal air inlet and engineinstallation. Work had barelystarted on the programmewhen Harold Brown (thendirector of Defense Researchand Engineering) ordered thecancellation of "Red Wagon".

Ryan reworked its proposal,offering in the summer of 1961a design optimised foroperations along and close tothe Warsaw Pact bordersrather than overflight. Knownas "Lucy Lee", this would haveclimbed from 65,000ft(19,800m) to 72,000ft (22,000m)as fuel burned off. Once more,stealth would be a feature,with the RCS being "reducedto a minimum usingdetraction (sic), transmissionand absorption technigues".Once more, Brown declined togive the go-ahead.

Perhaps with the Brown"axe" in mind, the companyhad also submitted a

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minimum-modification reworkof the Q-2C drone as an air-launched platform forreconnaissance missions.Known as the 147A Fire Fly,this was given the go-ahead inearly 1962 funded under theUSAF "Big Safari" specialreconnaissance programme.

The first 147A was a Q-2Cmodified to act as a testbedfor the proposed navigationand guidance system. Theremaining three were Q-2Cswith a fuselage stretch of 35in(89cm) which increased fuelcapacity by 68 US gallons (257

Below: SR-71 technology wastaken a stage further inLockheed's highly-classifiedD-21 reconnaissance RPVprogramme. It provedunsuccessful, and survivingexamples were retired in thelate 1970s.

litres). Several had extended-span wings which the USAFobtained from a US Army Q-2project. Flight trials started inApril 1962 with the firstcamera-equipped sortietaking place on 27 April.

On 17 May, a 147A wasflown from Tyndall AFB,Florida, to test theeffectiveness of the RCS-reduction measures. Thecrews of the five F-106 DeltaDart interceptors sent to huntdown the 147A found itvirtually impossible to obtainradar lock-on, even whenvectored to the drone by GCI.Final interception was carriedout as tail-chase pursuitsfollowing the drone's contrail,while eight Hughes GAR-3A(AIM-4F) Falcon semi-activeradar missiles failed to downthe Ryan aircraft.

Above: Although a good radartarget, the XB-70 cruised atspeeds and heights beyond thereach of present-day SAMs.

CUBADuring a test run over theAtlantic missile range on 5August, Air DefenseCommand had launchedinterceptors to catch thedrone. The result wasembarassment all round. Thefighters failed to locate thedrone but an over-confidentRyan crew ran the tinyaircraft out of fuel, droppingit in the sea 65 miles (105km)off the coast. Another flighton 9 August saw the F-102and F-106 interceptorsobtaining only momentaryradar glimpses of the droneand eventually pursuinga non-existent "target"

EARLY STEALTH AIRCRAFT

across Florida and intoGeorgia.

On 29 August, a U-2 aircraftreturned from a sortie overCuba with photos whichshowed the installation ofSAM sites. Although thepresence of ballistic missileswould not be detected untilmid-October, this was theopening move of what was tobecome the Cuban MissileCrisis. Following the loss of aU-2 over Cuba, two 147Adrones were rushed to TyndallAFB. A drone-equippedaircraft had barely startedengines to begin the firstmission over Cuba when theorder to cancel the flight wasgiven. The 147A was not to seeaction but Ryan haddemonstrated that the tinycraft was ready to go to war.The company was rewardedby a contract for the definitivebig-winged 147B. Flight trialsof this model started in May1963 and missions were flownto test the effectivess of the

craft's RAM blankets. A yearlater, the 147B was rushed tosoutheast Asia to play its rolein the early stages of theVietnam War.

NEW BOMBERS

The year 1964 also saw themuch-delayed first flight ofthe North American XB-70bomber. Nobody watching themaiden flight on 21 Septemberwas under any illusion thatthe six-engined Mach 3monster would ever see SACservice. The decision to makethe programme a purelytechnological demonstrationhad been taken in 1960. In myopinion, it was a bad decisionand one 'which "would be paidin human lives in the skiesover North Vietnam later in1972. Many of the bombercrews who died over NorthVietnam in the Linebacker IIraids would be alive today hadthey been piloting 2,000mph(3,200km/h) B-70s rather than

elderly subsonic B-52sthrough the skies over Hanoiand other heavily-defendedtargets.

In its search for a newbomber during the early1960s, the USAF had carriedout studies of concepts suchas the Advanced MannedPrecision Strike System, theLow Altitude MannedPenetrator, the Strategic LowAltitude Bomber and theExtended Range StrategicAircraft. By 1965, this workhad focused on a conceptknown as the AdvancedManned Strategic Aircraft. Aspecification issued that yearcalled for an aircraft able tofly at high subsonic speed atlow level or at supersonicspeed at high altitude andemphasised the need for RCSreduction. It was to result inthe decision to build theRockwell B-l.

Research into stealthtechnology really got into itssnide in the early to mid-1970s. Itwas aimed at countering thedevelopment by the SovietUnion of jam-resistant high-power monopulse groundradars, and overcoming theperformance of modern look-down/shoot-down that wereradars able to observe targetsflying within ground clutter.

HAVE BLUEIn the 1960s Dr LeoWindecker had designed andbuilt an all-compositefibreglass light aircraft knownas the AC-7 Eagle 1. This wasa four-seat aircraft ofconventional appearance,powered by a 285hp (213kW)piston engine. In 1963 heoffered this to the USAF as apossible low-RCS research

aircraft but the concept fell ondeaf ears. When he re-proposed the idea in 1972, theconcept of low-observableswas coming into vogue.

The prototype Eagle waslent to the USAF for RCS testsand Windecker Aviation wasgiven a USAF contract tobuild the YE-5A, a modifiedEagle with internal changessuch as the addition of RAM.Delivered in 1973, this wastested by the USAF andLockheed, being used instudies of the radarreflectivity of glass-fibreconstructed airframes.

By 1975 the US Air Force'sForeign Technology Divisionhad finally translated andrepublished Pyotr Ufmitsev's"Method of Edge Waves in thePhysical Theory of Diffraction".Ignored in the Soviet Union, itimmediately caught the eye ofUS mathematician DenysOverholser - an employee of theSkunk Works. He decided tobring it to the attention of thechief designer.

Kelly Johnson had retired, andbeen replaced in January 1975 byBen R. Rich. Formerly Johnson'svice-president for advancedprojects, Rich had joined theSkunk Works in 1954 to work onthe U-2, so was a veteran of theCL-400 and A-ll/SR-71programmes. In his 1994 biographySkunk Works, Rich recalled howOverholser had "decided to dropby my office one April afternoon,and presented me with theRosetta Stone breakthrough forstealth technology. The gift hehanded me over a cup of decafinstant coffee would make anattack airplane so difficult todetect that it would beinvulnerable against the mostadvanced radar systems yetinvented, and survivable againsteven the most heavily defendedtargets in the world."

Reading Ufmitsev's paper,Overholser had realised that ifan aircraft could be built whosesurface was made up from flattriangular shapes, its RCS couldbe predicted What can bepredicted can be controlled. Richgave him three months toconvert Ufmitsev's theory into apractical RCS-predictionprogramme. In only five weeks,Overholser, assisted by retiredLockheed mathematician andradar expert named BillShroeder, had created the new"Echo 1" software and, inconjunction with a Skunk Worksdesigner named Dick Scherrer,had used it to devise theoptimum low-observable shapefor an aircraft.

Lett: This P-50 Barlock radar isprobably a US-built replica ofthe Soviet original, a novelresearch tool in the US anti-radar effort.

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The breakthrough had comeat an ideal time. By the summerof 1975 the US DefenseAdvanced Research ProjectsAgency (DARPA) had becomeinterested in the concept ofstealth aircraft. It had awardedfive US aircraft companiesaround $1 million each toconduct proof-of-conceptstudies, and planned to awardthe company which producedthe most promising design acontract to build two flyingtechnology demonstrators.

Unfortunately for Rich,Lockheed was not one of thefive. Its earlier signature-reduction work had beenhighly classified, and thecompany's last successfulfighters had been built duringthe Korean-war era. Althoughthe existing DARPA funding forstealth studies had beenentirely allocated to the existingfive contractors, Lockheed wasallowed the join thecompetition

HOPELESS DIAMONDBy May, Overholser andScherrer had devised a designthey called the "HopelessDiamond". Shaped like anarrowhead, it promised to havean RCS a thousandth of that ofthe D-21 drone. Despiteopposition from Kelly Johnson(\vho still served as a part-timeconsultant to the Skunk Works,and had dismissed the "HopelessDiamond" as "crap"), Rich set upa team to explore the newconfiguration.

KeUy was prepared to wager25 cents that the "HopelessDiamond" would not match thelow RCS of the D-21, but lost hismoney on 14 September when acomparative test conductedusing models of the two designsshowed that the RCS of the"Hopeless Diamond" was exactlyas predicted - a thousandth ofthat of the D-21. These resultswere confirmed by later testsusing a l/10th scale model of theproposed aircraft.

By October, Lockheed andNorthrop had been declared thefinalists in the DARPAcompetition, and in March 1976Lockheed tested a full-scalemodel of their proposed designat the USAF radar test range atWhite Sands, New Mexico. The"Hopeless Diamond" displayedan RCS around the size of a golfball, and proved ten times lessdetectable that the rivalNorthrop design.

In April 1976, Lockheed wasdeclared the winner, and givena $30 million contract to developand manufacture two XST(Experimental Stealth Tactical)demonstrators. The project wascodenamed "Have Blue".Construction of the first aircraftstarted in July 1976.

Early in 1977, PresidentCarter's Defense SecretaryHarold Brown and his advisorscarried out a survey of allcurrent research anddevelopment programmes in thehopes of identifying key areaswhich might yield usefuloperational advantages for theUS military during the newAdministration of PresidentCarter. A similar technologysurvey in the early 1970s hadresulted in the US cruise missileprogrammes, so Browndoubtless hoped that anotherpotential breakthrough could befound. He rapidly identified low-observable technology as alikely candidate. Spending onstealth technology was alreadyrunning at around $10 million ayear, and it was becomingobvious that RCS reductionslarge enough to give realmilitary advantage were withinreach.

Under-Secretary for DefenseWilliam J Perry established anexecutive committee withhimself as chairman. Known asXcom, this included key militaryprocurement officials with theclout needed to drive newtechnologies through thetraditional DoD bureaucracy.From the autumn of 1977onwards, Xcom studied stealthproposals from the services andindustry. Those thoughtpromising received massivefunding; the others wereweeded out. Funding wasincreased tenfold. The mainbeneficiaries were Have Blueand a Lockheed stealthy cruisemissile codenamed Senior Prom.

At the same time, knowledgeof the stealth effort was tightlycontrolled. In DoD parlance,stealth was classified as SAR -Special Access Required. Stealthwas given what Perry wouldlater describe as "extraordinary"security protection "even to thepoint of classifying the everyexistence of the program". Thelong-term effectiveness of suchsecrecy was doubted. "In 19771told the [Defense] Secretary thatwith good luck we wouldconceal programme existencefor two years," Perry would tell aHouse Armed ServicesSubcommittee in 1980.

Two Have Blue aircraft werebuilt at a total cost of $37 million.Neither aircraft was given aUSAF serial number, but werenumbered 1001 and 1002 byLockheed. The first would beused to evaluate the flyingcharacteristics of the facetedairframe, and the second toexplore the effectiveness of theRCS-reduction measures.

Have Blue was similar ingeneral configuration to today'sF-117, but was only 47ft Sin(1158m) long, and 22ft 6in (6.71m)in wing span. Powered by a pairof non-afterburning General

Above: A military pilot whomade an early unauthorisedsighting of the F-117 described itas looking similar to the MartinMarietta X-24.

Electric GE J85-4As turbojets, ithad a maximum take-off weightof 12,0001b (5,400kg). The winghad a leading edge which wasswept back at 72.5 degrees. Itscontrol surfaces consisted of twoinboard trailing edge elevensand four spoilers (two on top ofthe wing and two on thebottom). There were no flaps orspeed brakes. The twin verticaltail surfaces angled inwardabout 30 degrees, andpositioned just ahead of theengine exhausts.

Wherever possible existinghardware was used to save timeand money. The cockpitinstrumentation and ejectorseat were from the NorthropF-5, the fly-by-wire systemneeded to "tame" the airframe'saerodynamic qualities was fromthe F-16, and the undercarriagewas that of the FairchildRepublic A-10. When completed,both aircraft were given acomplex "dazzle" camouflagepaint scheme which made ithard for a distant observer todetermine the aircraft's shape.

The first Have Blue wascompleted in November 1977,then flown by C-5 Galaxy tothe "Ranch" airstrip at theTonopah test range near NeHisAFB. Here it made its first flight

on 1 December 1977. Lockheedtest pilot William M. "Bill" Parkmade the first flights, and waslater joined by Lt. Col. NormanKenneth "Ken" Dyson of theUSAF.

Have Blue 1001 was to have ashort life. The landing speed wasaround 160kt, and when touchingdown after a flight on 4 May, it hitthe ground hard enough todamage the right main landinggear. Worried that the aircraftmight skid off the runway, BillPark increased engine power andclimbed away, retracting theundercarriage. When he began asecond approach, the damagedgear refused to lower. Afterseveral landing attempts, heclimbed to 10,000ft (3,050m) andejected just as the aircraft ran outof fuel. As he ejected, he hit hishead and was knockedunconscious. Unable to control hisparachute, he landed heavilyenough to cause severe injurywhich was to force him to retirefrom flying. The aircraft wasdestroyed in the crash.

Right: While the B-2 was stillunder wraps, several analystsattempted artist's impressions.This concept by Bill Gunstonwas more sensible than manyrival "designs", and boldlypredicted the absence ofvertical surfaces. Thoseventral inlets would havebeen a poor stealth feature ina high-level bomber which isthe B-2's main role.

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EARLY STEALTH AIRCRAFT

In his autumn 1980 testimonyto the House Armed ServicesSubcommittee, Perry was toclaim that, "We have kept its[stealth's] very existence secretfor more than three years" ratherthan the two years he hadpredicted back in 1977 It has tobe assumed that both he and thesubcommittee did not closelyread the newspapers andaviation press. Contrary to hisclaims, the secret had been welland truly "blown" two and a halfyears earlier by the loss of thefirst Have Blue.

At the time, the USAF did itsbest to conceal the loss of such ahighly-classified aircraft.Reporting the loss of anunidentified aircraft operatingfrom Nellis Air Force Base, theUSAF declined to make anystatement beyond the straightadmission that an accident hadoccurred in which a pilot wasslightly injured. A USAFspokesman would add only that,"for security reasons that is allthe information available". Pressreports gave the pilot's name asWilliam Park, noting that heclaimed to work for Lockheed.Admitted to a Los Angeleshospital, and treated for multiplefractures and concussion, he wasdischarged four days later.

At first, the aircraft wasthought to be a Lockheed TR-1,but by late in the month sourceswere confirming that theincident involved a prototypestealth aircraft. This informationled me to write a news story"Stealth Aircraft Lost in Nevada"

in Flight International's 27 Mayissue.

The flight test programmeresumed in June 1978 when LtCol. Ken Dyson made the firstflight of the recently delivered1002. Over the next year and ahalf, Dyson flew 65 test sorties,which assessed the ability of theaircraft to avoid detection byvarious types of radar. Trials arereported to have been madeagainst ground and airborneradars, including thesurveillance radar of the E-3Sentry AWACS aircraft, andcaptured Soviet radar andmissile systems. All of thisdevelopment flying seems tohave been conducted from theGroom Lake test facility at NellisAFB, Nevada, although EielsonAFB in Arkansas was alsolinked to reports of stealthaircraft trials.

On 11 July 1979, Have Blue1002 was lost at Tonopah TestRange during what was to havebeen its second-last scheduledtest flight One of its J85 enginescaught fire, burning through thehydraulic lines and forcingDyson to eject. Unlike Park,Dyson made a safe ejection andwas uninjured, but the aircraftcrashed. The wreckage of bothHave Blues was secretly buriedat Nellis AFB.

Despite the loss of bothaircraft, the programme hadbeen successful, demonstratingthat the faceted fuselage hadreduced RCS just as theory hadpredicted. It has also shown thatmaintaining a low RCS over a

period of operational use wouldnot be easy. Great care had to betaken to seal all joints betweendoors and access panels and theaircraft's fuselage, and to makesure that the aircraft's externalsurfaces were completelysmooth. Flight tests showed thateven a fixing screw not fullytightened to bring its head flushwith the skin was enough tosharply degrade the RCS.Maintaining the stealthcharacteristics of anoperational stealth aircraftwould require painstakingattention to detail, but could beachieved by a skilled groundcrew.

The results of Have Bluetrials gave the US theconfidence to adopt the newtechnology for operationalaircraft and missiles. By theautumn of 1980, several stealth-related programmes had beenlaunched. US spending on thenew technology rose by afurther factor of 10, bringing itto 100 times its early-1977 level.

In the late 1970s and early1980s, DARPA had conducteda series of cruise missilepenetration evaluations.Intended to assess theweapon's ability to cope withSoviet defences, these testedthe weapon's radar and IRsignatures in the presence ofbackground clutter and itsability to use terrain masking.The data gathered were usedto predict the likely capabilityof future Soviet defencesystems against small cruise

Early "Stealth Bomber" Concept

missile targets.Work on the stealthy Senior

Prom cruise missile had beenunder way at Lockheed since1977 under a "black" projectbudgeted at $24 million.Senior Prom was designed tofly at low level, and by 1980 itwas being test-flown from B-52aircraft based at Edwards AFB.Senior Prom was neveradopted for service. It wasfoUowed by DARPA's 1980"Teal Dawn" programme todevelop technology for stealthcruise missiles. At least onecompany - General Dynamics- is known to have flown testhardware as part of thisprogramme.

SABER PENETRATORBy this time the B-l seemedlikely to emulate the XB-70 inbeing reduced to a museumpiece. As recounted earlier,President Carter announcedin June 1977 that he would notapprove production ol the newbomber. Although convincedthat conventional bomberswere too vulnerable tomodern air defences, behindthe scenes he gave the go-ahead for studies of possiblebombers based on low-observable technology. Thesewere carried out under asecret programme code-named"Saber Penetrator".

By 1978 the Lockheed SkunkWorks was beginning to turn itsattention to a possible stealthbomber, and it is likely thatsimilar studies were under wayboth at Northrop and elsewhere.With the help of two seniorbomber pilots on loan fromStrategic Air Command, theSkunk Works drew up proposalsfor a tactical bomber. Able tocarry a 10,0001b (4,500kg)payload, it was in theperformance class of the US AirForce's F-lll. The result was atwo-year study contractcodenamed 'Senior Peg'.

A second contract codenamed"Senior Ice" was awarded toNorthrop, which in 1975 had lostthe competition to select a newlightweight fighter for the USAF,and had to take a back seat toMcDonnell Douglas in theprogramme to convert theunsuccessful YF-17 into thecarrier-capable F/A-18. Havingsubsequently lost thecompetition to build the HaveBlue, and facing the problemthat sales of its long-running F-5series would soon end, thecompany launched a majoreffort to maintain its designcapability by offering a newsingle-engined F-5 derivative onthe fighter market, and anadvanced stealthy bomberdesign to the US Air Force.

In his 1994 memoirs, Ben Richclaimed that Northrop may have

65

received the bomber studycontract because by then the USGovernment wanted tocompensate the company for thedamage done to the salesprospects of the F-20 Tigersharkby a withdrawal of a US licenceto sell the latter aircraft toTaiwan, the most likely customerfor the new fighter. Hisrecollections may not be accurate- the 1978 study contracts wereawarded around the time that theF-20 (then known as the F-5G)was being designed, and wellbefore the Carter Administrationeffectively vetoed its sale toTaiwan.

Management of both "SeniorPeg" and "Senior Ice"programmes was handled by theUSAF's new Low-ObservablesProject Office, which was alsomanaging the Senior Prom cruisemissile project.

In the summer of 1980, agrowing number of Executiveand Congressional officialswere briefed on the stealthbomber concept. At the sametime, the political battlebetween President Carter andCalifornia Governor RonaldReagan for the US Presidencybegan to hot up. Stealth wasabout to become a factor inthe US election.

In its issue of 4 August1980, Aviation Week quotedan unidentifiedAdministration official astalking of "a growingperception that we have madea mistake in cancelling B-l"and reported that the House-

Below: White nose markings onthe B-1B may aid refuelling-boom operators but undersome conditions maycompromise camouflage.

Top: Dense clouds of smokefrom eight Allison J35 turbojetsmade the take-off of Northrop'sYB-49 flying wing far fromstealthy!

Senate AuthorizationConference Committeefavoured the purchase of oneor even two new types ofbomber. Insistent that a newbomber be fielded by 1987, thecommittee suggested thebuilding of 100 modified B-ls,followed by 100 new-technology bombers "using allnew technology, particularlystealth technology to avoidradar detection".

A week later, the magazinecarried an item headed"Bomber Biases". PresidentCarter remained opposed tothe B-l, the magazine

Aftove.'The experience neededto design flying wing bomberswas obtained from the private-venture Northrop N-1M, whichflew in 1940.

reported, and was notconvinced that the USAF wasagreed on the need for a newbomber. Identifying one of theaircraft candidates as "theadvanced stealth bomber", thestory stated that "the WhiteHouse intends to continuestudies" of new bombers,adding that "SomeAdministration officialsbelieve a delay in the studieswill allow more time toperfect stealth technology".

LEAKSIn the September issue ofArmed Forces JournalInternational Benjamin F.Schemmer revealed thathundreds of millions of dollarswere being spent onprogrammes to which only afew dozen US Governmentofficials were privy to fulldetails. "Several differenttypes of aircraft have beenbuilt. Scores of flight testhours have been accumulatedon several prototypes,although only a handful ofpilots have flown the planes."

No one single technicaltrick was responsible forstealth, he explained, correctlyidentifying all the maintechnigues used for signaturereduction - structuralshaping, composites, IRshielding and surfacetreatment with RAM.

AFJI had known about"essential elements of theprogram for several years",claimed Schemmer, "but hasnot revealed them following arequest by a senior Pentagon

official in mid-1978 that AFJInot print, on national securitygrounds, a story...about thefirst stealth test prototypes".

Acting in response to thegrowing number of stories, on22 August Defense SecretaryHarold Brown released somelimited information on theclassified programme. TheUnited States had builtaircraft which could not beintercepted by existing orprojected Soviet air defences,he explained. He denied thatthe existence of stealthtechnology had been a factorin President Carter's decisionto cancel the B-l bomber butsuggested that "any newbomber will use someelements of this technology".

Background informationwas presented by Perry, whoexplained how stealth was a"complex synthesis" of manytechniques which were nowclassified at the "highestsecurity level". In the threeyears since 1977 the USA hadmade "remarkable advances"in the new technology and•was beginning to developpractical applications. Adegree of stealth technologycould be applied to existingaircraft, he explained, butstealth would be mosteffective when applied to anew design. The cost of astealth aircraft would not besubstantially different fromthat of conventional designs.

The Republican Partyclaimed that information ofstealth technology had beenimproperly released by theAdministration in order toboost its image on thesensitive topic of defence -Reagan was attacking theDemocrats as being "soft" ondefence issues. It was evensuggested that the source ofthe leaks might have beennone other than DefenseSecretary Brown.

Two months later, Reaganwon the Presidential election,bringing into power a newAdministration determined toboost America's defencecapability. The most obviousway of doing this was toexploit the new stealthtechnology.

FLYING WINGS

The year 1981 was to prove tobe a key year for stealth.

In the summer of that year,Lockheed was given a secretcontract to develop andmanufacture a productionaircraft based on the XST. Thecompany also received thego-ahead to develop a stealthycruise missile. In early 1981,Congress directed that a newbomber be developed for SACbut did not specify what form

66

EARLY STEALTH AIRCRAFT

this aircraft should take,simply ordering an initialoperating capability (IOC) by1987. A total of $300 million indevelopment money wasadded to the 1981 defencebudget, along with $75million for long-leadprocurement.

The USAF was ordered todecide by 15 March 1981 onthe type of aircraft to beordered. The obviouscandidate was an advancedderivative of the B-l but theUSAF was pushing astretched derivative ol theFB-111A known as the FB-111H, while behind the sceneslurked the possibility of anall-new aircraft based onstealth technology.

Around the time the newAdministration took office inearly 1981, the USAF assignedthe responsibility for stealthaircraft development to GeneralAlt Slay, the head of Air ForceSystems Command. Slay wasnot interested in having an F-lll-sized stealth bomber, andordered that work be re-focusedon a strategic bomber.

A Request for Proposals onwhat was then known as theAdvanced TechnologyBomber (ATB) was issued in1981. To bid for the task ofbuilding the new aircraft,Lockheed linked up withRockwell to create a teamcombining massive expertisein stealth and bombertechnology.

In a little-reportedprogramme in the late 1970s,Northrop invested largeamounts of company money insecretly developing expertisein low-observables technology.By 1981, it was ready tochallenge Lockheed for thetask of building the newbomber. Like Lockheed, thecompany teamed up with anestablished bomber designteam, in this case Boeing.

In addition to its stealthexpertise, Northrop also hadextensive experience withflying wings, a configurationwhich potentially offered lowRCS. The experimental N-1Mhad flown in 1940 and wasfollowed by several examplesof the NM-9 - one-third scaleprototypes for the plannedXB-35 bomber. The latter hada wing span of 172ft (52.4m)and was powered by fourPratt & Whitney Wasp Majorengines drivingcontrarotating propellersmounted at the trailing edgeof the wing. The first flightswere on 25 June 1946 but,even before they had flown,the decision had been takento rebuild both prototypes asjet bombers, redesignatingthem XB-49.

The first modified aircraft

took to the air in October1947, powered by eight 4,0001b(1,815kg) thrust Allison J-35-A-15 engines, and was followedin January 1948 by the secondexample. The latter aircraftcrashed in June 1948following an in-flightstructural failure. Althoughsome pre-production YB-49and YRB-49 aircraft weresubsequently built, the USAFabandoned the flying wingconcept in the early 1950sand none of the Northopbombers saw operationalservice.

Northrop was not the onlycompany to see the potential ofthe flying-wing layout for astealth bomber. In its late 1970sbomber studies, Boeing hadlooked at tailed and tailless deltadesigns. Like Northrop,Boeing wanted to exploit thefact that radar energy tends todiffract off flat horizontalsurfaces, while long-chordwing sections of the type usedin delta or flying wing designsare deep enough to allow theuse of radar-absorbentstructures, and internally-mounted RAM. Rockwell hadalso looked at flying wingsduring the same period,including a 77ft (23.5m) spandesign in the FB-111performance class, but it is notclear whether a similarconfiguration was offered forthe ATB competition.

At the Skunk Works, the team•working under Ben Rich alsoconcluded that the flying-wingwas the best layout for astrategic-range stealth bomber,and his team produced adesign which was so similar tothat on the Northrop drawingboards that a visitor mistook amodel of the Lockheed designdisplayed on Ben Rich's deskfor that of the Northropconcept. The Lockheed designwas smaller than that proposedby Northrop, however.Lockheed decided that the

lower cost of the smallestaircraft able to meet therequirement would be attractiveto the customer, while Northropopted to offer a design optimisedfor maximum range.

Like Have Blue, the newbomber was selected followingcompetitive RCS tests. For HaveBlue, full-scale models had beenused, but the sheer size of therival ATB designs required theuse of quarter-scale models.

ADVANCED BOMBERAttractive though the ATBmight be, there seemed littlechances of its beingdeveloped or fielded by the1987 deadline imposed byCongress. In July 1981 US AirForce Secretary Verne Orrstated that a stealth bombermight take ten to twelve yearsto develop. Any attempts tofield it earlier would involve"tremendous cost". In thedecade or more whichdevelopment of a stealthbomber would take, the SovietUnion might be able todevelop new types of sensorother than radar and IR whichcould be used to detect stealthaircraft, providing a partial oreven total countermeasure.The Air Force would prefer aB-l available in 1986 rather thana stealth bomber in 1992, hesuggested.

Reagan solved the bomberdilemma on 2 October 1981 byannouncing that the B-l wouldbe restored to productionstatus allowing a batch of 100to be built. While these aircraftprovided a low-risk boost toSAC's strength, a newadvanced technology stealthbomber aircraft could bedeveloped in great secrecy forservice in the early 1990s.

Following the RCS modeltests, Lockheed heardunofficially that its design hadoffered a lower RCS than theNorthrop submission, so was

Above: Heavy shadows and adark matt finish hide the longwingspan of the B-2 as the firstprototype rolls out from thehangar.

surprised when it wasinformed in October that theNorthrop design had beenselected. The longer range andheavier payload of their designhad tipped the scales in itsfavour. In his memoirs, BenRich says that the USAF toldLockheed that while theSkunk Works design had beenstealthier than the Northropaircraft, the latter aircraft'sheavier payload would requirefewer sorties to achieve thesame result.

Later that month, theNorthrop public relationsdepartment issued what wasprobably its shortest-ever pressrelease, The entire textconsisted of a mere 75 words:"LOS ANGELES - Oct. 20,1981 - Mr. Thomas V. Jones,Chairman of the board ofNorthrop Corporation,confirmed today that Northrophas been notified by the AirForce of its selection as primecontractor to conduct initialresearch and development onadvanced bomber concepts.This effort will have a materialimpact on Northrop. The keyteam members are Boeing,LTV/Vought and GeneralElectric Aircraft EngineGroup.

All details are classified,and no further comments willbe made".

They meant what they said.In future press briefings forNorthrop products, it wasconsistently made clear thatthis one subject would neverbe covered. With virtually alldetails of the new stealthfighter, stealth bomber andnew cruise missile shroudedin a blanket of secrecy, the eraof the "black" programme hadarrived.

67

THE WORLD OFBLACK PROGRAMMESOne consequence ot the

build-up in US militarystrength during the eight-yearReagan Administration was aconcentration on high-technology programmes suchas the Strategic DefenseInitiative ("Star Wars"). Inparallel with this has been agrowing tendency for much ofthe Pentagon's high-technology budget todisappear under a cloak ofsecrecy in what were dubbed"black" programmes.

"Black", that is to say,virtually invisibleprogrammes are not new. The"Project Manhattan" effort todevelop the atomic bombduring the Second World Warwas probably the first. Similarsecret efforts saw thedevelopment of the U-2spyplane and its A-12successor, while the samecategory of high security hasalways shrouded the USreconnaissance satelliteprogramme.

As their formal title of "SpecialAccess Programs" (SAPs)indicates, "black" programmesuse a rigorous system of securitycontrol, with information beingprovided only to carefullyselected individuals. SAPs fallinto two categories -unacknowledged andacknowledged. Projects oftenstart life in the first category, andmove to the second when theirexistence is finally revealed.

An unacknowledged SAP isone whose existence is classifiedas a "core secret". This is definedin USAF regulations as "anyitem, progress, strategy orelement of information, thecompromise of which wouldresult in unrecoverable failure".

Having decided that outsideknowledge of the existence ofany "black" programme wouldundermine its military value, theUS DoD set the stage for severalforms of deliberate"disinformation" which makesdenials that a specificprogramme exists of little value.For a start, an individualquestioned by an outsider abouta "black" programme maygenuinely have no knowledge ofthat programme, even if thatindividual's position or ranksuggests that he or she should.In 197;; General GeorgeSylvester was commander of theUSAF's Aeronautical Systems

Division and responsible for allUSAF aircraft programmes.Despite this, he was not aware ofthe existence of the Have Blueaircraft

If the questioned individualdoes have knowledge of the"black" programme, that personis by definition required to denythe programme's existence. Thetraditional "no comment" willnot be enough to guard whathas been classified as a "coresecret".

In theory SAPs must report tofour committees of the USCongress - the House NationalSecurity Committee, the SenateArmed Services Committee, andthe defence subcommittees ofthe House and SenateAppropriations Committees.SAP briefings are conducted inclosed, classified sessions, and insome cases are minimal. For themost highly classified SAPs, theneed to conduct even this levelof briefing can be waived by theSecretary of Defense.

Watertight secrecy may begood for security but, as the"black" cloak fell over agreater portion of thePentagon budget, some criticsquestioned whether suchclassified militaryprogrammes were spendingmoney wisely. Denied specialsecurity clearance, mostmembers of Congress cannoteven review the budgets of"black" programmes.

For a nation so committedto openness, democracy and

accountability as the UnitedStates, "black"' programmeshave introduced a new "way ofworking. Secrecy coveringstealth projects has been sotight that the USAF isreported to have filed falseflight plans with civilianagencies when stealth aircraftwere being flown, accordingto Washington Post sources in1987. In the same yearAviation Week reported thatthe DoD had even instructedsome contractors to falsifytheir records in order toconceal the fact that theywere running "black"programmes.

SECRECY

In some cases, excessivesecrecy was hamperingprocurement decisions. In1987, Congress learned thatone US service had recentlyattempted to start a major"black" developmentprogramme, unaware that asimilar programme had beenunder way for several years asa "black" programme byanother service. During thelong-running lawsuit over theA-12 Avenger n programme(described later in this chapter),McDonnell Douglas andGeneral Dynamics claimed thattechnology developed in otherstealth programmes but deniedto the A-12 team could havesolved some of the problems thatled to the project's cancellation.

Above: Given its coat of "IronBall" paint in 1970, this was thelast 100th StrategicReconnaissance Wing U-2 toliterally go "black".

A few recent figures show thescale of current US "black"programmes. In Financial Year2001 (FY01), the USAF plans tospend $4.96 billion on classifiedresearch and developmentprogrammes, a figure whichaccounts for almost 40 per centof its total R&D budget. It willspend a further $7.4 billion onclassified procurementprogrammes.

LOCKHEED F-117

To this day, the best-known"black" programme is theLockheed F-117 stealth fighter. Asecret contract awarded on 1November 1978 covereddevelopment of the aircraft, andmanufacture of a first batch ofproduction examples - initiallyfive, but soon expanded to 25. Inparallel with this work, GE wasgiven a contract to develop anon-afterburning version of theF404 to power the new aircraft.The FY82 defence budget isthought to have contained asmuch as $1 billion in "black"funding for the programme. Theproject was given the codename"Senior Trend". Some reportssuggested that the aircraft'spopular name was "Ghost" or"Specter", but it eventuallyreceived the name "Nighthawk".

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THE WORLD OF BLACK PROGRAMMES

Although the stealth fighterwas often referred to as the F-19during the early 1980s, theUSAF has always insisted thatthe designation F-19 has neverbeen assigned. The ostensiblereason - the risk of confusion•with the MiG-19 - is obviousnonsense; the designation F-21was cheerfully assigned to theKfir fighters leased from Israelfor use in dissimilar combattraining programmes. Therewere suggestions that the truedesignation might be "RF-19", oreven AR-19 (Attack/Reconnaissance 19). LockheedMartin now admits that "thedesignator 'F-19' was brieflyreserved for the aircraft, but itwas never officially applied".

The true designation "F-117A"first emerged in the winter of1987/88. It reflects not the post-1962 system of aircraftdesignations, but the olderUSAF system which producedthe fighter and bomberdesignations from before WorldWar II until the era of the"Century-series" fighters such asthe F-100 and F-104. It seems thatthe USAF applied "old-style"designations to various Sovietfighters which it had acquiredfor evaluation, and that when itneeded a designation for whatshould have been the F-19, ittook the next available "Century-series" number.

The first F-117 was completedin May 1981, and flew on 18 June.It confirmed the basic design ofthe aircraft, which -was 70 percent longer and 97 per centgreater in wingspan than theHave Blue, and had a maximum

Right: This early impression bya Lockheed artist would haverevealed the basic shape andfaceting of the "F-117" that theDoD wanted kept secret.

take-off weight four and a halftimes heavier.

The initial batch of fiveaircraft (780 to 784) was usedfor aerodynamics andpropulsion tests. The onlysignificant change foundnecessary was a stiffening and15 per cent increase in size forthe twin tails. This followed theloss of one tail surface on anaircraft during the initial testprogramme.

Aircraft 785 -was the firstproduction example, but crashedimmediately after take-off on itsfirst flight on 20 April 1982,injuring company test pilot BobRiedenauer. An investigationshowed that the wiring for thepitch and yaw controls had beenreversed. The first aircraft to behanded over to the USAF was786, which was delivered on 23August 1982.

The first USAF squadron tooperate the F-117 A was the4450th Tactical Group. Formedat Tonopah, Nevada, on 15October 1979, it was equippedinitially with 18 A-7D Corsair Hsuntil the first F-117A Arrived.Located at the edge of theNevada test range, Tonopah hadbeen renovated under a $295million programme, and given a12,000ft (3,660m) runway, and 54single-aircraft hangars intendedto keep the aircraft out of sightduring the day.

Next F-117 A unit to form was

P-Unit (which later became the4451st Test Squadron) in June1981. Q-Unit (later the 4452ndTS) began operations on 15October 1982, while Z-Unit(later the 4453rd Test andEvaluation Squadron) wasformed on 1 October 1985. TheGroup was transferred from thedirect control of Tactical AirCommand to Tactical FighterWeapons Center at Nellis AFBin 1985.

The F-117A was a demandingassignment for the hand-pickedaircrew selected to fly the newfighter. Pilots were required tohave a minimum of 1,000 hoursof flying time, mostly on fighters.Normal tour of duty was fouryears, later reduced to three.Families were not allowed onthe base, but lived in or aroundLas Vegas. Personnel spent five-day duty periods at Tonopah,flying to and from the base in

specially chartered Boeing727-200s of Key Airlines.

To maintain security, the newaircraft flew only at night.Hangar doors were not openeduntil half and hour after sunset,and only after the hangar lightshad been extinguished. Groundmovements were lit only byflashlights. There is no two-seattrainer version of the aircraft, sonew aircrew joining the 4450thfaced the daunting prospect ofmaking their first flight in thetype at night from a blacked-outairfield and without the benefitof a check ride. They weretrained by Lockheed instructorsusing what has been describedas (then) the most realistic flightsimulator in USAF service. This

Below: Lockheed Martin couldnot persuade the US Navy toorder the proposed A/F-117Xstrike/attack aircraft.

69

was developed in the mid-1980sby Link-Singer.

Early operating experienceshowed that after flying, pilotshad to be indoors before sunrise.Seeing sunrise disturbed sleeppatterns, and pilots frying tosleep having seen the dawnfound it difficult to do so. BenRich has described the pilots'existence as being like that"at a vampire's convention asdaybreak approached scurryingto their blacked-out rooms beforethey were caught by the sun."

These constraints proved aproblem in the summer months.Flying could not get under wayuntil around 9pm, oftencontinuing until well after Sam,with aircraft sometimes flyingtwo sorties per night - onestarting before midnight,followed by another in the earlymorning hours. Anyone who hasworked shifts will realise thehavoc which changing timecycles can play on the humanconstitution. In this respect,pilots are no different to theirground-based counterparts, andfatigue became a recognisedproblem at Tonopah.

On 10 July 1986 thecommanding officer of onesquadron wrote a report statingthat, "fatigue-induced burnout isgetting worse with time. Ibelieve we are on a collisioncourse with a mishap." Thatnight, Maj. Ross E Mulhare tookoff in F-117A no. 792 to fly atraining mission. At about1.45am, the aircraft crashed on ahillside 15nm (28km) northeast ofBakersfield, California, killing itspilot. A year later, aircraft 815flown by Maj. Michael C.Stewart struck the groundwithin the NeHis Range duringanother training mission. Bothpilots had less than 80 hours ofF-117A flight time, and wereattempting demanding sortieson nights with little or nomoonlight. An official USAFinvestigation concluded thatboth crashes could have resultedfrom pilot fatigue anddisorientation.

Aircraft 804, last of the originalproduction batch, was acceptedon 20 June 1984, but by then afollow-on batch of 39 had starteddown the line, the first beinghanded over in August One ofthese aircraft - 815 - crashed on14 October 1987, almost twoyears after entering service.

Until its unveiling in late 1988,the F-117A didn't officially exist,but no-one was working hard atthe pretence. During a pressconference held on 26September 1986 at MalmstromAir Force Base in Montana, SACcommander General John T.Chain told reporters, "I've visitedthe factory. I've seen theairplane." He pronouncedhimself pleased with theaircraft's technical performance,

Above: Released on 20 April1988, this artist's impression ofthe B-2 gave the world its firstview of a USAF stealth aircraft.Some journalists were sceptical,but the drawing in fact provedreasonably accurate, apart fromthe missing engine exhausts.

citing the development ofstealth aircraft and other newAir Force programmes as beingpartly responsible for the highmorale in his command.

The first artist's impression ofthe B-2 bomber was released inApril 1988, and many observerswondered why the existence ofthe older F-117A had not beenreleased before. Air Force chiefof staff General Larry D. Welchexplained in May 1988 that theAir Force was more concernedabout the Soviets seeingexamples of early stealthtechnology than the B-2. Thelow RCS of the first stealthaircraft (he did not specificallydescribe this as the F-117A)depended almost exclusively onthe aircraft's shape, he claimed,while the B-2 combined avariety of low-observabletechnologies. A goodphotograph the F-117A wouldhave betrayed most of its secrets,thus explaining the extensivemeasures the USAF had takento keep the type away fromprying eyes.

From the mid-1980s onwards,there were rumours that theseveral F-117As had been flownby C-5 Galaxy to bases outsidethe USA. The UK was oftenmentioned as a destination, and

Right:10 November 1988 -Assistant Secretary of Defensefor Public Affairs J. DanielHoward releases the first F-117Aphoto.

the 37th TFW's A-7s are knownto have visited RAFWoodbridge. In a conversationwith the author, the Soviet airattache in London even claimedto have seen the Lockheedaircraft at a UK base. Adiplomatic cocktail party didn'tseem the best time to pursuesuch a delicate subject, butbefore I next had a chance tomeet him, he had joined thelong series of Soviet diplomatsexpelled by Prime MinisterMargaret Thatcher during themid to late 1980s.

Early in 1987, USAF andPentagon seriously consideredreducing the classification of theF-117A, a move which wouldmake sense with the B-2 stealthbomber due to roll out in thefollowing year, followed in theearly 1990s by other stealthydesigns such as the Navy's A-12and the USAF's YF-22 andYF-23. If the Pentagon continuedto try to hide stealth aircraft,"we're going to have to build a

roof over the Air Force", onedefense specialist told TheWashington Post in March of thatyear. Despite the pressure fromCongress, nothing was done.

F-117 "OFFICIAL"

By early October 1988, the timefinally seemed right to unveilthe F-117A. With the B-2 due tobe rolled out in the followingmonth, continued highclassification of an older designseemed illogical, while a courtcase in which some Lockheedemployees were allegingdamage to health from exposureto dangerous chemicals used inF-117A manufacture seemedlikely to uncover moreinformation about the aircraft.

On 4 October, all was readyfor the big event. Press kits(complete with photo) wereprepared, and Senator ChicHecht of Nevada was ready topresent a press briefing thatafternoon. At the last moment

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THE WORLD OF BLACK PROGRAMMES

Above: Clandestine photos ofF-117A operating by day gavethe world its first glimpse of theaircraft's planform.

Below right: How a stealthyadvanced bomber apparentlylooked to a Lockheed SkunkWorks artist working on theconcept of a delta planform.

the plan was scrapped,apparently after intense debateat what one newspaper reportdescribed as the "highest levelsof the Defense Department andon Capitol Hill". One theorybehind the sudden clampdownwas that unveiling of the aircraftduring a presidential electioncould be seen as a political ploy."There was a bipartisan viewthat this was not the mostauspicious time for this," oneDoD source told the AssociatedPress, suggesting that theaircraft might be unveiled afterthe presidential election.

Although the WashingtonTimes had managed to obtain adraft copy of the press release,publishing this on the morningof 4 October, the photo stayedunder wraps until 10 November.Underexposed and heavilyretouched, the picture finallyreleased to the press was almostas unmformative as early-1960sphotos of Soviet space exploits.But it did represent a landmarkin the history of "black"programmes. No aircraft inaviation history had remained"under wraps" for so long.

By April 1989, the F-117A wasoperating by day, allowing thefirst clandestine photographs tobe taken, revealing the aircraft'strue appearance for the firsttime. The 4450th Taclical Group,was reclassified as the 37th TFW,its three squadrons becoming

the 415th TFS "Nightstalkers",416th TFS "Ghostriders", and417th TFS "Bandits". In October1989, the 4450th wasredesignated the 37th TacticalFighter Wing, coming under theoperational command of the 12thAir Force. At the same time, theunit phased out its A-7Ds, andused T-38s for the training role.In April 1990, the DefenseDepartment announced that thetotal cost of developing andbuilding the F-117A had been$6.26 billion, and the unit costwas $106.2 million.

Public debut of the aircraftcame on 21 April 1990, whenseveral aircraft visited Nellis

AFB to be viewed by thefamilies of 37th personnel, andmore than 200 reporters andphotographers. The F-117A gavethe United Statesunprecedented militarycapabilities, pilot Capt RandallPeterson, told onlookers, butadmitted that, "We're notallowed to discuss anycapability. A lot of theinformation is still classified."

"I only wish I could tell youwhat this fighter can really do,"said Ben Rich, who was visitingNellis for the occasion. "Theperformance is awesome and theweapons system is unmatchedanywhere in the world."

By July 1990 Lockheed hadbuilt a total of 64 F-117As - fivepre-series aircraft plus 59production examples. It hadplanned to build 100, but theaircraft's higher than anticipatedcosts had forced a cutback.Seven aircraft were delivered in1982, eight a year from 1983 until1985, seven in 1986, four in 1987and three in 1988. The finalexample was 88-0843, handedover on 12 July 1990.

There is no chance of theF-117A returning to production.The USAF has all theNighthawks it can afford, andthe US Government is reluctantto export stealth technology toany but its closest allies. Britainis reported to have consideredthe F-117 as a possiblereplacement for the HawkerSiddeley Buccaneer lightbomber, but the existence of theTornado made this unlikely."The F-117 production line hasclosed down," F-117programme manager PaulMartin told FlightInternational in September1990,"... any application ofthat airplane to the RAF'sneeds would be somethingthat the [UK] MoD and theUS Air Force would have toagree on."

B-2 BOMBERThe initial development contractfor the larger and moresophisticated stealth bomberwas worth $7,300 million. Basedon the successful Senior Icedesign, it was codenamedSenior CJ. The first five years ofthe programme were atechnology-demonstration

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Above: Every line of thosecurves is dictated by stealth.The dark patches under theleading edge are for conformalradars.

phase, which may have beentimed to end in early 1985 justabout the same time as B-1Bproduction was running down.Had problems emerged with theflying-wing aircraft, a follow-onorder for the B-1B or the proposedB-1C could have been placed.

Work on the technologyneeded for what would becomethe B-2 initially went faster thananticipated, proving moreeffective than planners hadhoped when confronted by thetechnology used in current-generation Soviet radar systemsand new threats still underdevelopment in Sovietlaboratories.

The technology-demonstration phase of theprogramme may haveincluded the airborne testingof a scaled-down prototype.Probably built to 1/2 scale andpowered by four non-afterburning F404s, thiswould provide RCS data,

information on stability andcontrol of such anunconventional shape. Mostsources agree that it flewsometime in 1982.

It is possible that this trialsaircraft was rebuilt in themid-1980s to become morerepresentative of theproposed productionconfiguration. One sourcetold me in the spring of 1988that the sub-scale aircraft hadbeen flying for about 15months, a date in completedisagreement with earlieraccounts and which (if true)could only be explained byeither a rebuilt, or even an all-new second test aircraft.

"From the outset, westressed that the B-2 is on theleading edge of technology,and there were some verysignificant technical risksassociated with the B-2",USAF Chief of Staff GeneralLarry D. Welsh was to tell theBritish magazine Defence inearly 1988. "We had sometwelve risk areas weidentified, and insisted onclosure of each of those riskareas before we embarked on

full-scale development. Sincewe closed out that riskreduction effort, we reallyhaven't had any surprises.Since that time, developmenthas proceeded quitesmoothly".

By 1983, the resultsobtained from early ATBdevelopment work werealready better than had beenanticipated, giving the USAFthe confidence needed topress ahead with the newaircraft at the expence of anyfollow-on B-1B procurement.

PUBLICITYAt the Farnborough Air Showheld every two years inEngland, the world'saerospace companies rentchalets which face therunways and flying displays.Best-positioned of these isChalet Al, a coveted locationhired years ago by theNorthrop Corporation of theUSA, whose booking waspromptly renewed for eachsubsequent show. However,1988 saw a break in this long-running scheme. Not only was

the US company notoccupying its traditional site -it was not exhibiting at theshow at all.

The reason for abandoningthis prime piece ofFarnborough real estate wasnot penny-pinching but thefact that the company was inthe embarrassing position ofbeing unable to discuss itslatest products - all werehighly-secret "black"programmes the end results ofwhich would not be availablefor export in the foreseeablefuture.

Back in the days whenChalet Al was Northropterritory, many aviationjournalists - including theauthor - would rendezvousthere on the first "press-only"day of the show. The object ofthis exercise was to meet thecompany's chief designer LeeBegin. Most companies arenervous about letting theirhead of advanced projects mixwith journalists but Northropallowed Begin to "hold court"with a small audience ofexperienced defencejournalists with whom a

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mutual rapport had beenestablished over the years.

At these sessions, Beginwould talk about hiscompany's projects - some-times on the record andsometimes as unpublishablebackground - with a degreeof freedom which would haveinduced apoplexy in thePublic Relations departmentsof lesser corporations. That•was the way he worked - thejournalists he trusted weregiven extensive briefingsbut they in turn accepted therestrictions which hesometimes imposed as theprice of gaining access to aman "who was helping shapethe future of aviation. I do notknow of any occasion whereanyone let him down.

CONFIGURATIONAt the 1983 Paris Air Show,Begin showed me sketches ofsome of his future concepts forjet fighters - concepts which stillremained "under wraps" (andunreported by me) five yearslater. When I asked if 1 couldhave copies of his sketches, he

laughed, but declined. "Thepublic relations departmentwould lose their lunch if theyeven knew you'd seen them! ButI think you'll find thisinteresting." Reaching into hisbriefcase, he handed me acopy of a recent paper he hadwritten on the history ofNorthrop "Flying Wing"aircraft.

I was puzzled. Lee knew thatmy interest in 1940s and early1950s aviation history wasminimal. Why did he think Iwould find his paper ofinterest? Not until severalweeks later did the long-delayed penny finally drop -the only conceivable reason•why Begin would be spendinghis valuable time dusting offFlying Wing History had to bethat the same configurationwas being used for the thenhighly-secret NorthropAdvanced TechnologyBomber.

When first planned, theNorthrop aircraft was designedto be an approximate matchfor the Soviet Tu-26 Backfire.Specified to cruise at Mach0.8 over ranges of up to5,000nm (9,250km) - adistance equal to the Sovietaircraft's range - the ATBwas to weigh 280,0001b(127,000kg) at take-off andcarry a payload og 10,0001b(4,500kg). During the early1980s, the design was scaledup several times until it was inthe same general range andpayload class as the B-1B. Inearly 1984, the B-2 wasreported to weigh around400,0001b (181,400kg) at take-off and to carry a maximuminternal weapon load ofapproximately 40,0001b(18,100kg).

Work on the B-2 was handledin a former Ford Motor Co. auto-assembly plant in Pico Rivera,California. By 1986, a full-scaleengineering mock-up had beenbuilt at Pico Rivera. This allowedthe basic design to be frozen,with the last significant changesbeing added in 1986. Early in theprogramme, the decision wasmade to build the prototypesusing production tooling. This"was probably done for tworeasons. For a start, transitionfrom prototype to productionaircraft would be made easier.Less obvious is the fact that theuse of production tooling wouldallow engineers to maintainclose tolerances whenassembling the aircraft'sstructure and skin.

At a meeting of Northropshareholders held in May 1988,company chairman ThomasJones described how the tooling"can be adjusted to accuracies ofwithin one thousandth of aninch. The end result is a systemthat allows every major

structural assembly of the B-2,regardless of complexity, to fittogether exactly as designed."What Jones did not tell themeeting was that the reason forthese exacting tolerances wasrelated to the aircraft's stealthcharacteristics. The electricaldiscontinuity created by smallgaps can scatter electro-magneticenergy. On the B-1B, small gaps inthe skin were closed by adhesivetape, but a more sophisticatedsolution was required for the less-observable B-2.

On 19 November 1987, theUSAF awarded Northrop a$2,000 million productioncontract for the B-2, a movewhich was not cleared forpublic release until 26January 1988. On that date,the Air Force confirmed thatproduction funding would begranted to Northrop and tothe main sub-contractors -Boeing, LTV and GeneralElectric - but spokesmanCaptain Jay DeFrank wouldnot identify the roles of thesecompanies, give the numberof bombers which the money"would buy nor even say"whether a firm, fixed-pricecontract or some other typehad been awarded. Nor wouldthe Air Force comment onreports that the date of thefirst flight had slipped.

NEW METHODSFor a long time, the date ofthe aircraft's roll-out and firstflight remained classified.These were widely expectedto take place in late 1987 butthe date came and went.Delivery to Northrop's newfinal-assembly facility atPalmdale airport, California, ofthe first set of B-2 wings didnot take place until August1987 when they were flown inby a Lockheed C-5 Galaxy.

The USAF was not disturbedby the slippage to early 1988,having foreseen thepossibility of delays. GeneralThomas McMullen, then headof the USAF's AeronauticalSystems Division (ASD) hadexplained a year earlier thatthe new bomber had "metchallenges, and there aremore to come, but they arestraightforward engineeringissues. That is not to say thatthere are no risks; there iscertainly a schedule risk, andsome technical risks".

Early in January 1988 theLos Angeles Times quotedtwo unidentified Northropemployees involved in theprogramme and Wall Streetsecurities analysts as sayingthat the bomber's first test-flight had been delayed byfour months and "was notexpected until August of thatyear. Northrop sources had

declined to discuss thereasons for the slippage, thenewspaper said. TheWashington Post suggestedthat the slippage might delayinitial operational capability(IOC) "perhaps more than ayear" due to unspecified"technical and productionproblems".

It seems that one area ofdifficulty lay in the inlets. ByApril 1988, the prototype hadnot yet received its engines.Installation of the powerplant"was reported not to beimminent. Aviation Weeksuggested that a "majorredesign of the inlet andpowerplant mountingstructure" was likely andcould be implemented on thefourth full-scale developmentaircraft.

Some of the difficulties mayhave sprung from theaircraft's massive use ofcomposites, as engineeringstaff learned to adaptconventional tooling andmetal-orientated productionand assembly methods to thenew materials. For this reason,"holes drilled in compositematerials sometimes come outoblong-shaped", AviationWeek reported in early 1988.Despite the use of production-type tooling, installation ofcomponents on the prototypewas largely a matter of labour-intensive hand fitting.

One unfortunate side effectof the high degree ofcompartmentalisationdemanded for securityreasons was that sub-contractors whose equipmenthad to work together werenot able to communicate witheach other. Only afterdelivery did incompatibilityproblems emerge, forcingtime consuming andexpensive modification andredesign work. Technicaldrawings were in many casesbeing reworked rather thanconfirmed.

PROBLEMSProblems were also reportedwith the aircraft's windscreen- part of the load-bearingstructure - and with crackingof the composite leadingedges. The B-2 is the firstlarge and heavy aircraft touse large areas of compositehoneycomb, so such problemswere always a possibility asdesigners and assemblerslearned how to handle andfabricate components made inthe new material.

The short timescale mayalso have resulted in sub-assemblies being shipped tothe Palmdale final-assemblyplant before all testing hadbeen completed, causing

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unplanned trouble-shootingand modification work on theassembled aircraft. "Ship Oneis literally crawling withpeople", an unidentifiedobserver told Aviation Weekin April 1988, "and most ofthem aren't Northrop people,because they can't even geton the airplane".

Below: Shrouded in whiteplastic and rubber mats,production B-2s take shape onthe Northrop line. Blackscreens cover all inlets, plusthe leading edges on the reartwo aircraft.

Despite highly-publicisedpro gramme -managementproblems at Northrop, UnderSecretary of Defense forStrategic and Theater NuclearForces Dr Lawrence Woodrufftold the House ArmedServices Commettee in thespring of 1988 that theprogramme was "progressingwell" but insisted that, inresponse of Congressionalconcerns, the USAF has set up"an initiative for maintainingcost, contractor performanceand management disciplinewithin the B-2 program" andthat Northrop was assessing

"the condition of its ownmanagement system".

News that Boeing was hiringextra staff for the Palmdalefinal assembly plant, -whileNorthrop was apparentlylaying off hundreds of stafffrom its Pico Rivera facility,led to speculation that Boeinghad been secretly given anincreased role in themanagement of theprogramme. This was stronglydenied by Northrop whichissued a USAF-approvedstatement emphasising that nochanges in programmemanagement had been made

or were planned. Boeing'shiring of staff was directly dueto that company's work as asub-contractor to Northrop, thestatement indicated.

B-2 REVEALED

On 20 April 1988, The USAFreleased an artist's impressionof the B-2 and confirmed thatthe prototype would fly in theautumn. "The first flight of theAdvanced TechnologyBomber, or B-2, is currentlyscheduled, for this fall", theservice said. The bomberwould take off from the final

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assembly facility at Air ForcePlant 42 in Palmdale thenland at the Air Force FlightTest Center at Edwards AFB,where flight testing would becarried out. "The initial flightof the B-2 will highlight thereturn of the flying wingdesign to military aviation", itwas stated. No date was givenfor the maiden flight,however, and the servicerefused to give further detailsof the aircraft's size, crewnumber, weapons load,performance or cost.

The drawing whichprovided few details of its

B-2 Advanced Technology Bomber

Above: From above, straightlines dominate the planf orm ofthe B-2. From the side, thecurved line rules supreme.These rules were needed tominimise RCS.

construction aside from itsgeneral shape was not totallyaccurate; the USAF admittedthat several details had eitherbeen omitted or altered. Thescience-fiction shape createdsome scepticism but, duringan interview with Defencemagazine, USAF Chief of StaffGeneral Larry Welch insistedthat the drawing wasgenerally accurate. "There area few details that areobscured for security reasons.You will note that there are noexhausts in the picture."

According to the USAF, theshape of the new bomber hadbeen declassified because theprototype would soon "beoutside doing things andpeople will see it". Some sawthe sudden de-classification asa public-relations ruse, anunexpected move designed todefuse growing Congressionaldemands for greater access toinformation on the growingnumber of major "black"programmes.

Roll-out had been expectedin September 1988, leading toa first flight in October orNovember, but these datescould not be met. On 12thNovember, the long-awaitedroll-out finally took place. Theaudience was given only afrontal view of the newbomber, but a light aircraftwhich overflew the rolloutceremony provided AviationWeek with an unauthorisedview of the hidden rearsection.

For the next eight months,the B-2 became the world'sbest known and mostcriticised "hangar queen"Technical problems delayedthe maiden flight until 17 July1989.

CRUISE MISSILES

The B-2 may have beendeveloped in near-totalsecrecy, but the securityblackout around America'sstealth cruise missile workhas been even tighter.Despite late-1970s claims thatexisting cruise missiles such as

the ALCM and Tomahawkwere virtually unstoppable,by the early 1980s Pentagonplanners feared that growingSoviet EW expertise mightallow them to interfere withthe radar elements of theTERCOM guidance systemand that cruise missiles -particularly the GLCM - werebecoming vulnerable to S-300(SA-10) attack.

During the development ofTomahawk and the ALCM,tests had been carried out tomeasure the weapons' radar,IR and visual signatures. As aresult of this work, RCS, IRoutput and luminosity wereall reduced. It was now clearthat this was not enough. Inthe short term, the USAFhoped to counter the SA-10and interceptor threats bymodifying its cruise missilefleet, adding an on-boardactive ECM system based onwork carried out in anextensive programmecodenamed "Have Rust".

A three-year developmentprogramme was envisaged,allowing deployment in themid-1980s. ALCMs wouldhave to be modified butGLCM rounds would bedelivered complete with theEW sub-system when theseweapons were deployed in theearly 1980s. The status of thecruise missile EW programmeremains highly classified. Onesource told me in 1988 thatthe scheme had not goneahead in the form originallyplanned but confirmed thatsome improvements had beenmade to the weapons.

In July 1982 the USAFcompleted a study of possiblenext-generation cruisemissiles and concluded thatdevelopment of an improvedmodel using the latesttechnologies could counterthe sort of air defence systemwhich the Soviet Union wasexpected to field in the 1990s.Just as the AGM-86 andBGM-109 had exploitedmid-1970s breakthroughs intechnology such as miniatureelectronics and small low-

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consumption turbofanengines, the new weaponwould use the improvedguidance systems and betterengines of the 1980s, couplingthese with stealth technology.

The idea of a low-RCS cruisemissile was not new. Intestimony before the SenateArmed Services Committee in1977 John B. Walsh, DoDDeputy Director of Space andStretegic Systems describedhow studies had been carriedout into ways of reducingmissile RCS.

A formal requirement for anew cruise missile was drawnup that same month and theprogramme was approved byPresident Reagan in August. Arequest for proposals wasissued to industry inSeptember. Technology for anew cruise missile wasalready in hand, thanks toprogrammes such as DARPA'slittle-publicised Teal Dawn.This had explored areas suchas airframe shaping, RAM andadvanced propulsion. Alldesigns to be evaluated woulduse the same engine, theWilliams International F112turbofan which entered full-scale development in July1982. The IOC date for thenew missile was targeted for1986, a goal which some sawas unrealistic even in 1982. Itwas in fact to prove hopelesslyoptimistic.

COMPETITION

Boeing, Lockheed andGeneral Dynamics allcompeted for the task ofbuilding the new missile.Having developed the ALCM-A and -B, Boeing wasobviously in a good positionto win the new programmeand, given the fact that ALCMproduction was being cutback, had the strongestincentive to do so.Unfortunately, Boeing facedsevere competition. Lockheedhad the useful experiencegained from its own stealthcruise missile programme,while General Dynamics hadworked on Teal Dawn and sowas clearly in a good positionto bid for the new weapon.

At the time, GenerafDynamics was somewhatunder a cloud, the results ofquality-control problems withthe Tomahawk. Working in thecompany's favour was thefact that its Teal Dawnexperience would give it thehead start needed to matchthe ambitious timescale of thenew missile. From the first,the company seems to haveset the pace, while its rivalshad to embark on redesigns oftheir submissions.

The initial Boeing

submission was adevelopment of the AGM-86design but the company soonrealised that this could notprovide the performanceneeded to gain the newcontract. By late 1982, thecompany was reported to befrantically working on ahigher-risk concept able totake greater advantage of thelatest stealth developments.

Boeing was "scrambling tocome up with a newaeronautical design", a DoDofficial told Aviation Week inNovember of that year.

Like Boeing, Lockheedredesigned its entry. The firstdesign offered was stealthybut proved aerodynamicallyunstable. It also requiredexternal carriage, a featurenot desirable in a world of

Above: Security breach orpublic relations ploy? A lightaircraft overflew the B-2 rolloutand revealed the novel shape ofthe exhausts.

low-RCS warplanes.Progress was swift enough

to allow the USAF to scaledown its ALCM procurement.The Air Force had planned tobuy 3,418 ALCMs but, in

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Top: In the course ofdevelopment, ALCM-B wasmodified to reduce its RCS, amove dictated by advances inSoviet air defences.

February 1983, announcedthat production of theALCM-B would end after theFY83 buy, bringing the totalnumber of rounds delivered toonly 1,499. The plannedALCM-C would not be built.

AGM-129

On 15 April 1983, GeneralDynamics was announcedwinner of the AdvancedCruise Missile (ACM)competition. It was given afixed-price contract "whichcovered full-scaledevelopment of the AGM-129and contained options on thefirst two production lots. Suchwas the new programme'shigh classification that theAir Force would not releasedetails of the total value of thecontract, the number ofrounds to be procured or theprogramme schedule.Unofficial estimates suggestedthat the unit cost of the newmissile would be about $3million, with the entire ACMprogramme costing about$7,000 million.

The targets set for the ACMwere ambitious. In addition tobeing stealthier than the

Above: As the B-2 lifts off therunway, the huge mainundercarriage doors probablyact as vertical stabilisingsurfaces.

current ALCM, it wasrequired to have betterguidance, a lower terrain-following altitude and alonger range, probably around2,300 miles (3,700km). Afterlaunch, the new missile wasexpected to fly up to 1,000miles (1,600km) farther thancurrent cruise missiles,travelling around, rather thanthrough, Soviet air defences.

As in the case on mannedstealth aircraft, reducing the RCSinvolved careful shaping. TheAGM-129A has a flattened bodyshape with a wedge-shaped nose,forward swept-wings, a foldingvertical fin and folding horizontaltailplane surfaces. The air inlet forthe Williams International F112-WR-100 turbofan engine is underthe missile body just behind thewings, and the exhaust forms partof the missile's flat-wedge tailassembly.

By April 1988, theprogramme was reported tobe at least three years behindschedule and likely to cost anadditional $2,000 million. Areport issued by HouseArmed Services CommitteeChairman Les Aspindescribed the ACMprogramme as a

Below:The pyramid-shapedabsorbers which line the wallsof this test chamber allowaccurate RCS measurements tobe taken of the Matra Apache.

"procurement disaster", citingdeficiencies in guality controland inept supervision by theAir Force and themanufacturer. Aspin blamedthe delays and cost over-runson what he described asmismanagement by GeneralDynamics and the USAF. "Thehighly classified AdvancedCruise Missile is the worstsystem I reviewed", he stated.

The report was vague as tothe exact nature of the ACM'sproblems, noting simply thatthe project was "protected innearly all interesting detailsby high classification".

Problems seem to havearisen in several areas.Quality control problems atGeneral Dynamics had beenresponsible for the initial one-year slippage. In 1987 a total of44 critical components inthe missile were singled outfor quality control checks,while the company acceptedAir Force recommendationsfor ground testing the missileprior to beginning flight tests.In the spring of 1988 GeneralWelch spoke of unspecified"design and manufacturingconcerns" which would requirefurther testing.

DEPLOYMENT

Early flight trials seem to havehigh-lighted other problems.The weapon's low-RCS shapeseems to have had an adverseeffect on its flyingcharacteristics, while otherproblems emerged with themissile's computer software. InJune 1988, SAC commanderGeneral John Chain told anAir Force Associationsymposium that theprogramme "...is not comingalong as quickly or as well as Iwould like". Deputy Chief ofStaff, Plans and Operations,Lt.Gen. Michael Duganexpained that the results ofearly flight trials had beenerratic, having included "acouple of flights that didn't doespecially well". Work wasunder way to identify andcorrect the problems, hestated, but "testing has notbeen completed yet, so how itwill all sort out, I just don'tknow".

The AGM-129A finallybecame operational in 1991. Bythe early 1990s, the USAF

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expected to deploy 1,500 ACMs,which would have made uparound half of the service'scruise missile strength.Although McDonnell Douglaswas awarded a contract in 1987to qualify it as a second sourceproducer of ACM, in 1992procurement was scaled back toonly 460 rounds, and productionended in 1993, The AGM-129Awas designed for use on theB-52H, B-1B, and B-2A, but it isunderstood that only 48 B-52Hwere equipped with theweapon, A scheme to modify asmall batch by replacing the200kT range W80 nuclearwarhead with a conventionalHE payload was proposed in1998, but was not adopted.

Stealth is also an importantfeature of more recent air-to-surface weapons, In the late1990s, the USAF drew up plansfor a l,000nm (1,800km) rangestealthy Long-Range CruiseMissile (LRCM), a concept whichhas attracted interest from theUK, raising the possibility of ajoint development programme,The resulting weapon woulduse stealth to penetrate hostiledefences, but could improve itssurvivability by using very-low-altitude terrain-Mowing flight,or even active countermeasures.It is expected to have a datalinkpermitting in-flight targetupdates, plus some form ofterminal-guidance seeker, and awarhead able to deal with verydeeply buried or hardenedtargets,

Some degree of stealthtechnology is also being built intotactical missiles due to enterservice in the current decade,These include the LockheedMartin AGM-158 Joint Air-to-Surface Stand-off Missile (JASSM),

the Franco-German Matra BAeDynamics Storm Shadow (knownas SCALP EG in French Air Forceservice), and the NorwegianKongsberg Nytt Sjomalsmissile(NSM) anti-ship missile,

Once the Norwegian weaponhas been launched, the lugs on

its upper surface retract, A coverthen closes over them tomaintain the weapon's low radarsignature, The entire nosesection is roll-stabilised withrespect to the missile airframe,As the missile banks to turn, thenose section counter-rotates so

that its stealth-configured noseremains at the optimum anglefor low detectability,

NEW FIGHTERS

By 1976, the USAF was planningto incorporate stealthtechnology in its next-generation fighter, First studiesfor what would become theAdvanced Tactical Fighter (ATF)were begun in 1969-70, and by1975 a tentative plan had beendrawn up to test prototypes in1977-81, Lack of money doomedthese original plans, but by 1976stealth technology waspromising enough to persuadethe USAF to begin the HaveBlue programme, and to add alow-observability requirement tothe specification for its F45replacement.

In 1981 the USAF issued toindustry a request forinformation on possible ATF

Lett; Under the watchful eye ofa chase aircraft, the stealthyLockheed Martin Joint Air-to-Surface Stand-Off Missile(JASSM) flies a test mission.

Right: Wing/body blending,outward-canted tail fins, andInlets under the wing were low-RCS features of this RockwellATF proposal.

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Left: General Dynamics AGM-129 Advanced Cruise Missile(seen here being carried by a B-52 trials aircraft) is stealthy withmore range than ALCM.Following the end of the ColdWar, orders were cut back toonly 460 examples.

Above: A Have Blueprototype. Very small, andwith less faceting than thedefinitive F-117A, it differsmainly in the inward cantedfins and rudders, whichactually increased the infra-red signature.

BeIow:The incredibly highsweep of the Have Blueprototypes is seen here, as is thefact that the under-side isfaceted, unlike the F-117, whichis completely flat. Handling wasextremely difficult, with highsink rates at low speeds.

designs. The proposed fighterhad to be able to handle air-to-air and air-to-ground missions,and was intended to have theperformance needed to evadeSoviet air defences, allowing theaircraft to fly deep insideEastern Europe in order toattack Warsaw Pact fighters andair bases. To achieve this, it wasto combine advanced low-observables technology with theability to supercruise (fly atsupersonic speeds withoutafterburning).

The ATF was required to givepilots a first-look, first-shot, first-kill capability through the use ofreduced observables andadvanced sensors. Its avionicssuite was to be a highly

integrated system that wouldallow the pilot to concentrate onthe mission, rather than onmanaging the sensors, as incurrent fighters. Other demandswere for higher reliability,maintainability, and sortiegeneration rates than wereavailable from the F-15.

In October 1985 the USAFasked contractors to submitproposals for a fighter able toenter service in the mid-1990s asthe eventual replacement for itsF-15 Eagle and F-16 FightingFalcon. Bids were to besubmitted by December of that

year, and would lead to betweentwo and four companies orteams being selected to takepart in a three-year studyintended to balance theperformance and cost of thenew fighter against itsoperational requirements.Choice of a contractor to develop,flight-test and produce ATFwould be made in early 1989,with the plane making its firstflight in late 1991 and enteringservice in the mid-1990s.

By July 1986, the USAFdecided to restructure theprogramme. Instead of flying a

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single selected design in late1991, it would now select tworival concepts to be flown ascompetitive prototypes, anarrangement which the servicelast used in the mid-1970sYF-16/YF-17 Lightweight Fightercompetition. On 31 October 1986it announced that Lockheed andNorthrop had been selected forthis demonstration/validationphase of the programme.

In April 1983 the US Air ForceSystems Command awardedtwo industrial teams contractsworth $691 million covering a50-month developmentprogramme. Each company wasto produce two prototypes and aground-based avionics testbed,A target date of October 1989was set for the first flights of theLockheed YF-22 and theNorthrop YF-23. Lockheedteamed with General Dynamics(Fort Worth) and Boeing MilitaryAirplanes to produce its twoYF-22 prototypes.

One of the first activitiescarried out by both teams was astudy of possible methods of risk

Betow:By 1986 the appearanceof the Lockheed ATP hadchanged greatly. Laterallyraked intakes appeared, muchsmaller canards were nowlocated high and aft of thecockpit, and the fins were muchmore steeply canted.

Bight: An artist's impression ofthe Lockheed ATF contenderreleased in 1985 shows a chinednose similar to that of the SR-71,a fairly orthodox delta wingwith canard foreplanes, andvectoring engine nozzles.

reduction, and alternativetechnologies. This was orderedas part of a larger SystemsRequirement Review carried outby the Air Force. On 11 October1989 the evaluation phase of theprogramme was extended by sixmonths.

Powerplant development wasrunning ahead of that of theairframe, a wise policy in anyaircraft programme. In October1983, General Electric and Pratt& Whitney were given $200million contracts covering thedevelopment and ground testingof rival designs of JointAdvanced Fighter Engine(JAFE). Pratt & WMtney's enginewas the PW5000, designatedXF119 by the US DoD. This ranfor the first time in late 1986.Rival design from GeneralElectric was the GE37.Designated XF120, this variablebypass design began bench testsin mid-1987 In early 1988, bothteams received contracts worthclose to $342 million for thedevelopment of flightworthy"YF" engines. One YF-22 andone YF-23 was to be powered by

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the YF119, the other example ofeach by the YRL20.

The task of producing theATF radar •was given toWestinghouse, teamed withTexas Instruments. In April 1987,the team won this vital contractfor both the YF-22 and theYF-23, a blow to rival radar giantHughes Aircraft, which hadteamed with General Electric tobid for the ATF radar.

YF-22 AND YF-23 DESIGNSLockheed and Northropproduced very different designs.The Lockheed YF-22 had atrapezoidal wing and twin tails,and bore a vague resemblanceto the F-15. The need for stealthdictated the use of a forwardfuselage that was diamond-

Right: Were the Lockheedartist's ATF impressions of 1985and 1986 deliberatedisinformation? The YF-22 seenhere shows no sign of a tail-lesscanard delta; only the thrust-vectoring nozzles remain.

Below: The losing ATFcontender was theNorthrop/McDonnell DouglasYF-23. A more radical designthan the YF-22, its outstandingfeatures were the trapezoidalwing planform and steeplycanted ruddervators.

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shaped in cross-section, andlarge flat fuselage sides. Theinlet ducts were curved inwardsand upwards, shielding the frontfaces of the twin engines fromdirect illumination by hostileradars.

The Northrop/McDonnellDouglas YF-23 was about 7ft(2.1m) longer than the YF-22, andhad a more "science-fiction"appearance. It was more slenderthan the Lockheed aircraft, andhad a diamond-shaped wing,and all-flying twin tail surfacescanted 50 degrees outwards in a"V" configuration. The wingleading edge was swept back at40 degrees, while the trailingedge was swept forward at thesame angle. Every line in the

Above: With its rounded linesand outward-canted V-tail,Northrop's YF-23 looked likesomething out of sciencefiction.

aircraft's planform was parallelto one or the other of the wingleading edges, a measureintended to concentrate theradar returns from the aircraftinto a few well-defineddirections. As on the YF-22, theinlet ducts were curved in twodimensions to shield the frontfaces of the engines. The engineefflux was released into trench-shaped cut-outs in the rearfuselage. This helped cool thehot exhaust gases, reducing theaircraft's IR signature.

Below: On the YF-23, all straightedges were positioned at one ofa handful of predeterminedangles, a measure intended toreduce RCS.

One significant differencebetween the two designs wasthat the YF-22 had two-dimensional engine nozzleswhich could be vectored 20degrees up or down at anypower setting. Northrop opted torely on aerodynamic controlsurfaces, believing that thrust-vectoring would compromisestealth, particularly in therearward sector.

During the flight-testprogramme, Northrop's YF-23achieved its early milestones

Above: This futuristic shapeformed the basis of several "stealthfighter" construction kits, but wasonly an advertising artwork usedby EW manuf actuer Loral.

ahead of Lockheed's YF-22.The first YF-23 was poweredby P&W engines, and wasrolled out at Edwards AFB on22 June 1990. It flew for the firsttime on 27 August 1990, withtest pilot Paul Metz at thecontrols, in a sortie whichlasted for 20 minutes.

The first YF-22 was rolled outon 29 August 1990. Powered byGE YF120 engines, it flew for thefirst time on 29 September 1990,with Lockheed test pilot DaveFerguson at the controls. The

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BefowNot much stealthtechnology Is visible In thisGrumman advanced lighterproposal o! the early 1980s, TheInlets would be good radar targets,

second YF-22 was powered byP&W YF119 engines and flew on30 October 1990, with Lockheedtest pilot Tom MorgenMd at thecontrols, Neither carried anyradar or cannon, but both wereable to carry and launchSidewinder and AMRAAMmissiles, The second YF-23 waspowered by GE engines, andflew on 26 October,

Both aircraft demonstrated"supercmise" capability. The firstYF-23 "supercruised" on its fifthflight, and achieved its highest

recorded supercruise of Mach1,43 on 14 November, The GE-powered YF-22 had an optimumsupercruise speed of Mach 1,58,slightly faster than the Mach 1,43of the P&W-powered example,With afterburning, both YF-22aircraft could exceed Mach 2 at50,000ft (15,250m),

On 15 November, the GE-powered YF-22 demonstratedthrust-vectoring for the firsttime, The concept provedsuccessful; trials showed that theYF-22 could achieve supersonicroll and pitch rates in excess ofthose that can be achieved by aconventional fighter at subsonicspeeds.

The YF-23 demonstrated amaximum speed of Mach 1,8,

manoeuvred at up to 7 g, andreached a maximum angle ofattack of 25 degrees, lake theYF-22, the YF-23 had no radar orcannon, During the flight-testprogramme, it did not firemissiles,

While an intensiveprogramme of competitive flighttests was under way at the AirForce Flight Test Center atEdwards AFB, California, in late1990, in November of that yearthe USAF requested both teamsto submit final engineering andmanufacturing development(EMD) proposals, which they didon 2 January 1991,

YF-22 SELECTEDOn 23 April 1991, the USAFannounced that it had selectedthe F-22 powered by the F119engine, The reasons for thechoice remain classified, but theUSAF seems to have favouredthe manoeuvrability providedby thrust vectoring over theextra stealth offered by the rivaldesign, Perhaps with memoriesof the engine problems it hadsuffered with the FlOO-poweredF-15 and F-16, it had opted for themore conservative enginedesign.

One factor which may havesteered the USAF away from theYF-23 was the design of itsweapon bays, lb maintain a lowRCS, both teams relied oninternal bays to keep non-stealthy ordnance hidden fromhostile radars, However, theNorthrop design would havecarried two Joint Direct AttackMunitions-sized weapons stored

one above the other behind asingle set of weapons-bay doors.If the first weapon could not bereleased for any reason, thesecond could not be used,

An engineering andmanufacturing development(EMD) contract was awarded on2 August 1991 for 11 prototypes(including two tandem-seatF-22Bs) plus one static and onefatigue test airframes, Pratt &Whitney was given an EMDcontract for the engine, Thecombined value of bothcontracts was $10,91 billion ($9,55billion for the airframe and $1,36billion for engines), Subsequentcontract changes, includingthree Congressional budget cutsand subsequent revision of theprogramme schedule haveincreased the contract values toa total of $18,6 billion,

As a result of these changes,the number of prototypes wasreduced to nine, and the two-seat model was eliminated, Allprototypes will be the single-seat F-22A version. Under theEMD contract, the F-22 team willcomplete the design of theaircraft, produce productiontooling, and build and test nineflightworthy aircraft and twoground test articles.

The Critical Design Review(CDR) of the F-22 and the InitialProduction Readiness Review(IPRR) of the F119 engine werecompleted in February 1995,These showed that fabricationand assembly of the EMDaircraft could begin,

The Pratt & Whitney-powerednumber two prototype had notbeen retired at the end of the

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Lett: The primary reason forthe selection of the YF-22 overthe YF-23 was that it hadsuperior high alphaperformance. Here one of theYF-22 prototypes launches itselfvertically skywards.

demonstration and validation(dem/val) phase of theprogramme. It returned toflying status on 30 October 1991.The other prototype wasstripped of its GE engines andused for HMD systems mock-uptests. It is now on display at theUSAF Museum in Dayton,Ohio.

Construction of the firstcomponents for the first EMDaircraft (91-4001) began in thewinter of 1993. The productionconfiguration resembled theYF-22, but had a wing sweep of42 degrees rather than the 48degrees of the YF-22. Thevertical stabilisers werereduced in size byapproximately 20 per cent. Theoriginal YF-22 surfaces hadbeen sized to avoid potentialspin problems. Since nonematerialised, the size wasreduced to reduce drag andweight.

To improve pilot visibility, thecanopy was moved forward 7in(18cm) and the air inlets moved14in (35.5cm) to the rear.Changes to the shape of thewing trailing edges and thehorizontal stabilisers reducedthe aircraft's RCS, improved theaerodynamics, and addedstructural strength.

Aircraft 4001 was rolled outon 9 April 1997 during aceremony at which the nameRaptor was announced for thenew fighter. The planned May1997 first flight date was to slip,apparently due to fuel leaksand other hardware-relatedproblems. The first flight finallytook place on 7 September 1997from Dobbins ARE in Marietta,Georgia, with F-22 Chief TestPilot Paul Metz at the controls.

As more aircraft joined thetest fleet, the scope of testinggradually expanded. Aircraft4002 flew on 29 June 1998 andwas used to expanding theflight-test envelope,demonstrating a 26 degreeangle-of-attack. It was also usedfor testing weapon separationsfrom the internal bay.

First flown on 6 March 2000,aircraft 4003 was the first tohave an internal structure thatis fully representative of theproduction aircraft, and wasused to perform demonstrationsto 100 per cent of the plannedload factors. It also wasearmarked to make the firstAMRAAM launch trials.

Aircraft 4004 was the first tohave a full suite of avionics andsoftware. It started life withBlock 1.1 software (Block 0 had

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been used for initial F-22 flighttests), but was upgraded toBlock 1.2 before its first flight. Itflew for the first time on 15November 2000, and initialreports from the test pilot andinstrumented data indicate thatthe AN/APG-77 radar begantracking multiple targets almostimmediately after the aircraftleft the runway.

Full radar functionalityrequired the use of Block 3.0avionics software, which flewfor the first time on 5 January2001 during the first flight ofaircraft 4005. The Block 3.0software provided functionssuch as radar processing andsensor fusion, electronicwarfare and countermeasures,communication, navigation andidentification, and pilot/vehicleinterface. "Flying Raptor 4005with the Block 3.0 (software)represented the program'scurrent most technicallydemanding challenge," saidF-22 System programmedirector Brig. Gen. Jay Jabour,

Bight: From this angle, featuressuch as the single-piecetransparency to the cockpit,including the sawtooth leadingedge, the chined nose andtrapezpoidal intakes rakedlaterally and vertically, areclearly seen.

"This successful flight, inaddition to our other recentachievements, demonstratesthe program is ready for low-rate production."

Aircraft 4004 through 4009will fulfil a number of functions- testing of theCommunications, Navigation,and Identification (CNI) system,electronic warfare, radarintegration with missiles andthe M61A2 cannon, JDAMreleases, and low-observablestesting. The entire flight-testprogramme is expected to lastfor 4,337 flying hours and 2,409sorties. Less than half will beused for airframe and systemstesting; the greater part is formission avionics testing.

Below: The F-117A is a subsonicattack aircraft, but the F-22 willcombine stealth withsupersonic performance andhigh agility.

Bottom: From some angles,the Lockheed Martin F-22 hasa passing resemblance to theF-15 Eagle which it is due toreplace.

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NAVAL STEALTH

The next US "stealthy" aircraftprogramme - the US Navy'sA-12 Advanced Tactical Aircraft(ATA) - was to have a less happyhistory. First reported in 1985,this was to have been a subsonicall-weather aircraft able to carryout all-weather or night deepinterdiction missions.

Development of the newaircraft was ordered in 1983, withthe intention that InitialOperational Capability (IOC)would be achieved no later than1994. Only two industrial teamsresponded to the Navy's RequestFor Proposals - GeneralDynamics teamed withMcDonnell Douglas, andNorthrop teamed withGrumman and LTV With thecollapse of the T-46 programme,Fairchild was out of the militaryaircraft business, while Boeing,Lockheed and Rockwell seem tohave opted not to bid.

When drawing up its fighterproposals under the ATFprogramme, GD had studiedseveral designs, one of whichwas a flying wing configurationnicknamed "Sneaky Pete",Although rejected by the USAF,the design was to form the basisof GD's ATA submission,

In November 1984, both teamswere awarded concept-formulation contracts, whichwere followed in June 1986 byDemonstration Validation(dem/val) contracts, The twoteams are reported to havefavoured competitiveprototyping, but this provedunaffordable,

Proposals for the full-scaleengineering development andmanufacture of the first eightaircraft were requested in 1987,By late that year it had becomeobvious that the USN could notsupport both the A-12 (at thattime still known simply as theATA) and the new F404-enginedGrumman A-6F Intruder, Workon the A-6F was stopped, Thisdecision has probably increasedthe urgency of the A-12programme, The basic Intruderhas been in service since the1960s, and the planned fieldingof the A-6F in 1989 would havemodernised the Navy's strikepower pending the later arrivalof the A-12,

Grumman might have hopedto recoup its losses on the A-6F(unofficially estimated as at least$150 million) by winning a shareof the ATA work, This was not tohappen, In a surprise move inlate December, theNorthrop/Grumman/LTV team(which was widely tipped to winthe ATA competition) declinedto submit "best and final" bids forthe task of developing the newaircraft,

On 24 December 1987, a mere

four days after Northrop's virtualwithdrawal from thecompetition, the Navypronounced the GeneralDynamics/McDonnell Douglasteam winners of the contract todevelop the new aircraft, Full-Scale Development began inJanuary 1988 under a contractwhich covered eight flight-testaircraft and five ground testairframes, The first flight wasexpected in June 1990,

The A-12 Avenger n was dueto replace the US Navy's A-6Efleet in the mid to late 1990s, anda total buy of around 450seemed likely, The USMChoped to obtain 60 A-12 aircraftas replacements for the A-6EUnder an MoU signed in April1986 between the USAF andUSN, the Air Force wouldconsider the A-12 as a potentialreplacement for the F-lll and, inthe longer term, for the F-15E,Initial A-12 deliveries would beto the USN, with the USAFgetting its first A-12s around1998, The UK was also seen as apossible purchaser, with the A-12a potential replacement for thePanavia Tornado,

Like earlier USN typesadopted by the USAF, the A-12would be modified by the USAFto match Air Forcerequirements, and make it bettersuited to land-based operations.By 1988, discussions betweenthe two services had not thrownup any problems in this area.

The aircraft that took shapewas a delta flying wing with aspan of 70ft 3in (21,41m) - 36ft3,25in (11,06m) with the wingfolded - and a length of 37ft Sin(11,35m). Empty weight was39,0001b (17,700kg), rising to

80,0001b (36,300kg) gross.Powered by two GeneralElectric F412-400 non-afterburning turbofan engines,each developing approximately13,0001b (5,900kg) of thrust, it wasexpected to achieve a speed of580mph (930kmh) at sea level,and a combat radius of 920 miles(1,470km). The ordnance wouldbe carried in internal weaponbays to minimise drag and RCS.

The GE F412 turbofan wasderived from the F404-GE-400used in the F/A-18 Hornet, It hada lower pressure ratio than thefighter engine, plus an improvedtwo-stage low-pressure turbinebased on that of the GE F110engine of the F-15 and F-16, and aredesigned high-pressure turbine.Avionics would include aWestinghouse AN/APQ-183multimode radar, Martin Mariettanavigational FLJR, GeneralElectric Infrared Search and TrackSystem (IRST), and a Honeywelldigital flight-control system.

In December 1989, a MajorAircraft Review (MAR) of fourUS combat aircraft programmesslowed the production rate, cutthe proposed aircraft for theUSMC, and slipped the plannedUSAF purchase by more thanfive years. It was still anticipatedthat the aircraft would fly byearly 1991 and that full-scaledevelopment program would becompleted within plannedbudget.

Unfortunately, the contractorswere faced with structural andcost overrun problems and,despite the Navy asserting thatit was satisfied with the aircraftat the Critical Design Review,the programme was cancelledon 7 January 1991.

Above: When the first editionof Stealth Warplaneswaswritten, the shape of theplanned A-12 Advanced TacticalAircraft (ATA) was stillclassified. Our artist'simpression of the aircraftapproaching a tanker drogue(reproduced here) probablycaused amusement amongmembers of the GeneralDynamics/McDonnell Douglasteam who were building thereal thing, but was intended toshow the reader some of thetechnologies applicable to astealthy strike aircraft.

Right: In reality, the A-12 was apure delta, a planform whichwould have focussed any radarenergy reflected from theaircraft into a small number ofharmless directions.Unexpected growth in weightand cost led to cancellation,leaving the US Navy without adedicated strike aircraft.

In a further attempt to developa new attack aircraft, in 1991 theUSN started the AXprogramme, which called for astrike aircraft to meet a lessambitious specification whichrequired lower range/payloadperformance and less stealth.Described by one observer as"A-12 lite", the programme - laterredesignated AFX - would haveentered service first with theNavy as a replacement forageing carrier-based A-6Es, andlater with the US Air Force as areplacement for F-lll, F-117, andF-15E, While still in its concept-design stage, it was cancelled inSeptember 1993, Since then, theUSN has planned to rely on the

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F/A-18E/F Super Hornet for itsfighter and strike capabilities.

Low-observable technologyis also being built intoconventional aircraft. TheRCS of the F/A-18C/D was

lower than that of the originalF/A-18A/B model, while animprovement ofapproximately the sameorder of magnitude "will beintroduced by the F/A-18E/F.

In the summer of 1995 the USJoint Technical Co-ordinatingGroup on AircraftSurvivability (JTCG/AS)reported in its AircraftSurvivability Newsletter that

this built-in stealth plus theaircraft's advanced EW suite"make the E/F a formidablecombatant that is extremelydifficult for enemy systems toacquire and track."

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TACIT BLUE

During the early and mid-1990s,there were persistent rumours ofa "black" stealth aircraft with alarge fuselage whose bulkyshape earned it the nickname of"Shamu" among the "stealth-watching" community. (The real-life Shamu was a killer whaleexhibited at a US theme park,and the very idea of a whale-shaped stealth aircraft seemedbizarre.) Some artists'impressions showed an aircraftwhich looked a bit like a scaled-down version of the BoeingStratocruiser propeller-drivenairliner of the 1950s.

On 30 April 1996, the USAFfinally lifted a cloak of secrecyfrom Tacit Blue, a technologydemonstrator which was test-flown between 1982 and 1985.Here at last was the aircraft thathad triggered the "Shamu"reports. Developed and built byNorthrop under a $165 million"black" programme -whichstarted in 1978, the single-seatTacit Blue was developed as apotential platform for radarsensors developed under theUSAF's Pave Mover and ArmySOTAS ground-surveillanceprogrammes. It may have hadthe secondary role ofdemonstrating that a stealthaircraft could be built usingcurved surfaces rather thanfaceting.

With a length of 55ft lOin(17.02m), a height of 10ft 7in (3m),and a wingspan of 48ft 2in

(14.68m), Tacit Blue weighed30,0001b (13,600kg). It had anunswept wing, a V-tail, and asingle flush inlet on the top ofthe fuselage to provide air to itstwo Garrett ATF3-6 high-bypassturbofan engines. Its novel shaperequired the use of a quadruplexdigital fly-by-wire flight controlsystem to stabilise the aircraftabout the longitudinal anddirectional axes. Robert E. Wulf,the former Flight Sciencesmanager on stealth projects atNorthrop, has described how"the only requirement was todevelop the best stealthperformance... It was the mostunstable aircraft flown in bothpitch and yaw."

Tacit Blue made its first flighton 5 February 1982, andcompleted 135 flights over athree year period. It often flewthree to four flights a week, andon several occasions flew morethan once a day. It was designedto fly at a speed of 250kt, and atan operating altitude of 25-30,000ft (7620-9,145m). By thetime it flew, the USAF hadcombined the SOTAS and PaveMover projects into a singleprogramme which eventuallybecame Joint STARS, and inMay 1984 the DoD decided thatthe resulting aircraft would usethe Boeing 707 airframe. TacitBlue made its last flight on 14February 1985, and was placedin storage. After being unveiled,it was renovated and placed ondisplay at the US Air ForceMuseum at Wright PattersonAFB.

JSF PROGRAMME

The next stealth fighter to begindevelopment was not launchedas a "black" programme. Fromthe start, the STOVL StrikeFighter project was run as anormal Advanced ResearchProjects Agency (ARPA)programme. The original goal

Above: Some stealthtechnology has beenincorporated into the Boeing(formerly McDonnell Douglas)F/A-18E/F Super Hornet.

was to develop a replacementfor the F/A-18 Hornet and AV-8BHarrier II, but this original USNavy/US Marine Corps projectwas later expanded to cover the

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US Air Force requirement for anew fighter to replace the F-16.The USAF had no need forvertical take-off, so the CALF(Common AffordableLightweight Fighter) schemeenvisaged that, on USAFexamples, the vertical lift systemwould not be fitted, and the freespace would be used to carryadditional fuel to produce

longer-ranged land-based fighter.The CALF project was mergedwith Joint Advanced StrikeTechnology (JAST) programme,and in 1995 was renamed the JointStrike Fighter (JSF).

Three teams competed for thetask of developing the newaircraft. These were headed byBoeing, Lockheed Martin, andMcDonnell Douglas. In

November 1996 Boeing andLockheed Martin were selectedto build concept-demonstrationmodels of their respectiveaircraft. These were given thedesignation X-32 and X-35,respectively. Followingcomparative evaluation of therival designs, a winner will beselected in late 2001. The chosendesign will enter engineering

Above: It may look ugly, butBoeing's X-32 candidate for theUS Joint Strike Fighter (JSF)requirement is intended tocombine stealth and STOVL.

Below: The X-32 made its initialflights in conventional takeoffand landing form, proving thebasic design before STOVL wasattempted.

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and manufacturingdevelopment (EMD), and isexpected to enter service withthe USAF, US Navy/MarineCorps and Britain's Royal Navy.The final JSF will not be asstealthy as the F-22 Raptor, butgreat emphasis is being placedon the need for its low-observable qualities to be easilymaintainable.

FURTHER STEALTH

Although programmes such asthe F-22 and the Joint StrikeFighter are now beingconducted in the public domain,other highly classified "black"programmes are under way.Rumours abound of another USstealth aircraft about to berevealed

The best evidence for theexistence of new "black"programmes is the continuedexpansion of the Area 51classified test facility at GroomLake, a dry lake bed in centralNevada, about 75 miles (120km)north-northwest of Las Vegas.Facilities there have been usedto support development of theLockheed A-12, Have Bluetests, operations with MiGsand other potential-adversaryaircraft, tests of the Tacit Bluestealth technology demon-strator, and undoubtedly otherstealth programmes.

At a time when it apparentlyhas no purpose, Groom Lake hasnever been busier, and never

been in such apparent need ofhigh security. Unless somemassive waste of the UStaxpayers' money is takingplace, one or more secret aircraftare in flight test.

PROJECT AURORAThe best candidate for keepingGroom Lake busy is themysterious Aurora project. Thisfirst came to light in February1985 when a Pentagon budgetdocument accidentally disclosedthat $2.3 billion, had beenearmarked for a USAF projectcode-named Aurora. Reportingthe incident, The WashingtonPost quoted unidentifiedPentagon sources as sayingAurora might have somethingto do with the new stealthbomber or at least with stealthtechnology. Air Force officialsdeclined to discuss Aurora,beyond confirming theaccuracy of the numbers listedin the budget documents. "Thatis a classified program and wecan't talk about it," said Maj.Richard Ziegler, an Air Forcespokesman.

For almost three years, nomore was known about this"black" programme, but inJanuary 1988 the New YorkTimes reported that the USAFwas developing a replacementfor the ageing SR-71 Blackbird.This was described as a long-range reconnaissance jet whichused "special equipment" to

avoid radar detection. Theperformance claimed was amajor step over the SR-71 - acruising speed of more than3,800mph (6,080kmh), plus aceiling of more than 100,000ft(33,000m). This Mach 5 stealthdesign is widely reported to bethe mysterious "Aurora".

The former Soviet Unionseems to have had earlyknowledge of the Auroraprogramme. In 1984 it starteddevelopment of the M1G-31Mand the Vympel R-37 (AA-X-13)missile, systems designed toengage targets cruising atspeeds of up to Mach 6 andaltitudes of up to 130,000ft(40,000m).

Further evidence for theexistence of Aurora emerged inOctober 1990 when AviationWeek & Space Technologyreported sightings of whatseemed to be a high-speed,high-altitude aircraft. Seen atnight, it appeared as a single,bright light, sometimespulsating.

"SKYQUAKE"Since 1990, there have also beenpersistent reports of unusualaircraft noises. One of the first

Right: NASA's Hyper-Xhypersonic UAV will be carriedto height on a B-52, thenbrought to flying speed by apegasus booster.

was published by Aviation Week& Space Technology in 1990, anddescribed how an aircraft takingoff late at night from EdwardsAir Force Base had made a veryloud noise, which somewitnesses said was a pulsingsound with a period of aboutone second. Since 1991, many UScommunities have reportedsounds which appear to besupersonic booms, but of amagnitude which causes themto be confused withearthquakes. Many of these"skyquake" reports come fromcoastal areas. Booms heardbetween June 1991 and June1992 were powerful enough toregister on seismographsoperated by the US GeologicalService, and analysis of thetimes of arrival of the sound atvarious points showed that theculprit seemed to be aircraftsmaller than the Space Shuttle,flying at speeds between Mach3 and 4 and at altitudes of26,000-32,000ft (840,00m). Theestimated flight path headed

Above: Could this be the shapeof the mysterious Project Aurora?The USAF would like areplacement for the SR-71Blackbird, and talks as if no suchaircraft were under development.But, as the F-117A programme hasshown, the very existence of ablack programme can be

officially denied for a decade ormore. One thing is sure, a majorundisclosed stealth programmemust exist to account forLockheed Martin's stealth-related earnings, and forunexplained "Other ProductionCharges" in the US defencebudget.

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northeast over Los Angeles andthe Mojave Desert, and couldhave taken the aircraft to NellisAir Force Base in Nevada or toGroom Lake.

Aviation author BillSweetman has nicknamed theseaircraft the "phantom boomers".Writing in Jane's InternationalDefense Review in January 2000,he noted that, "The phantomboomers appear to avoiddensely populated areas, andthe stories usually go no furtherthan the local paper. Only a fewlocal papers have a searchablewebsite, so it is highly probablethat only a minority of boomevents are reported outside theaffected area."

Present reports of slow-frequency (about IHz, andsometimes 50-60Hz) pulsingsounds, sometimes linked to theappearance of thick, segmentedsmoke trails or contrails, haveled to suggestions that theunknown aircraft may use apulse detonation engine. Theseunusual contrails - oftendescribed as "donuts-on-a-ropecontrails", have been seen notonly in the USA, but also inEurope, which suggests that theaircraft which is producing themis being flown on overseassorties.

However, the evidence for apulse-detonation powerplanthas been questioned by theFederation of AmericanScientists, whose analysis has

suggested that "enginesoperating at the thrust levelsassociated with military aircraftwould operate at between 100and 200 Hertz (pulses persecond)...While doppler shiftingmay reconcile this value withthe reported 50-60 Hertzpulsation, it is more difficult toreconcile this with the reports ofa 1 Hertz pulsation."

The FAS also notes that theapparent 100m spacing of the"donut-on-a-rope" is difficult toreconcile with a 100-200kHzpulse rate. "The association ofthese contrails with a pulsedetonation engine would seemto be predicated on theobservation that each "donut" isa product of a single pulsedetonation... Assuming adetonation pulse rate of 100Hertz, this would imply avelocity of 10 kilometers persecond, or 36,000 kilometers perhour (roughly Mach 36), one-and-one-half times orbitalvelocity." A detonation pulserate of IHz would imply avelocity of only 360kmh, whichwould be far too low.

MACH 8 AND ABOVEThen there is the strange saga ofthe US X-30 National AerospacePlane (NASP) programme todevelop a single-stage-to-orbitlaunch vehicle. The project waslaunched in December 1985, andcontracts were awarded to

Boeing, Lockheed, McDonnellDouglas, General Dynamics, andRockwell International, but inlate 1987 Lockheed and Boeing- the two contractors with thegreatest experience with high-speed aircraft development -were dropped from theprogramme.

Following a gradual process ofsource selection, GeneralDynamics, McDonnell Douglasand Rockwell Internationalteamed to offer a single design,a slender delta-winged liftingbody with two verticalstabilisers, while Pratt &Whitney teamed withRocketdyne on the powerplantThis was to consist of severalhydrogen-powered scramjet(supersonic combustion ramjet)engines, with a single rocketengine being used for the finalapproach to orbit. The air-breathing units were to operateas ramjets at speeds for betweenMach 2 and 6, then as scramjetsfrom Mach 6 up to orbitalvelocity. (Scramjets are similar inconcept to ramjets, but burn thefuel in a supersonic flow ratherthan subsonic as in ramjets andturbojets or turbofans, with thefuel being injected and burnednear the front on the engine.)

Although the US DoD wasfunding 80 per cent of the workon NASP, when George Bushbecame US president in 1989, hisnewly appointed US Secretaryof Defense, Dick Cheney,

cancelled the DoD'sinvolvement in the programme,saying that there was no USAFmission for the vehicle. Theentire project was wound up in1993, having cost several billiondollars.

Given that the US claimed tohave virtually no experience ofair-breathing flight at speeds ofbeyond the Mach 3+ top speedof the SR-71, the idea of creatingan aircraft able to fly at speeds ofup to 18,000mph (29,000kmh)seemed technologicallyaudacious to the point offoolhardiness - the equivalentof trying to jump from theperformance of the 1918 biplaneto the Mach 2 interceptor in asingle design.

Much of the researchconducted under the NASPprogramme was focused on theMach 8+ regime, even thoughthere seemed to be an almostequal lack of information onflight at speeds from Mach 4 toMach 8. Curiously, althoughNASP was not a "black"programme, information on thelow-speed portion of thepropulsion system wasclassified. A similar pattern canbe seen in more recent US high-speed flight programmes suchas the USAF's HyTech projectand NASA's Hyper-X. The focusis on scramjet research andspeeds well above Mach 6. Fourflights of the scramjet-poweredHyper-X UAV are planned -

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one at Mach 5, one at Mach 7and two at Mach 10.

It is hard to avoid theconclusion that NASP was anattempt to research flight atspeeds of Mach 6 and higherwithout the cumbersomeprocedures associated with"black" programmes, and that itsplanners regarded flight atspeeds of Mach 4 - 6 as aproblem which had essentiallybeen solved. This mysteriousMach 4 - 6 experience and thesudden removal of Lockheedand Boeing (perhaps to allowthem to concentrate theirexpertise on a classified aircraftin this speed range) fits neatlywith the dates of the first Aurorareports.

The idea that Lockheed wasbuilding a new spyplane wasboosted by the obvious fact thatwhile Lockheed Burbank hadlarge numbers of employees, ithad no apparent end product InApril 1988, High TechnologyBusiness reported that,"Aeronautical Systems Group,based in Burbank, Calif., willreceive more than $1.1 billion in1988 government funding thatcannot be attributed to anyknown program... Also, there aremore cars in the division'sparking lot than can beaccounted for by employees ofknown programs, indicating thepossible existence of a new andsecret project"

As experience with the B-2had shown, the OtherProduction Charges line item inthe USAF section of the USdefence budget can be used tofund a "black" programme. In1989, the B-2 funding emergedunder its own category; theOther Production Charges fellfrom its 1998 peak of $2,977million to a total of $1,075million, and stabilised atbetween $460 million and $686million in the following fouryears. At this reduced level, itmay still have covered "black"activities.

In its analysis of these figures,the Federation of AmericanScientists concluded that, "Therecent funding level of the OtherProduction Charges line item isstrongly suggestive of acontinuing program to procureadditional stealth aircraft Thisconnection is furtherstrengthened by the similarity inmagnitude between the fundinglevel of Other ProductionCharges, and the cash flowstream and employment atLockheed Aeronautical SystemsGroup."

Interviewed by Defense Newsin 1990, Ben Rich offered hisexplanation of what waskeeping the Shunk Works busy- and that explanation was notAurora. "I have heard and readabout Aurora, and I do not knowwhat Aurora is. And it is not

what we are doing in the SkunkWorks. There are a whole bunchof programs out there, lots ofthem are sensor programs. Andthat is where we are applyingour expertise."

Rich was dismissive of reportsof a new Aurora spyplane. In his1994 memoirs, he said thatAurora had been a codenamefor funding of the late 1970scompetition between Lockheedand Northrop to win thedevelopment contract for whatwould become the B-2.Unfortunately for this theory, theAurora -which sparked rumoursof hypersonic jets did notemerge until the mid-1980s."Although I expect few in themedia to believe me, there is nocode name for the hypersonicplane," he stated, "because itsimply does not exist."

It may seem like anauthoritative denial, but must beconsidered in the light of thepolicy that, when Questioned byan outsider, an individualcleared for access to a "black"programme is reguired to denyall knowledge of theprogramme. In the "wildernessof mirrors" created by "black"programmes, a denial may ormay not be true. There is no way

of telling.A footnote in the US Defense

Airborne Reconnaissance Office(DARO) 1997 report onunmanned aerial vehicle (UAV)development referred to "the U-2and the Air Force SpecialPlatform". According to Jane'sInternational Defense Review,DARO director, Maj. Gen.Kenneth Israel, acknowledgedthat this reference points to "acovert reconnaissance aircraft...in the classified world". This ledthe magazine to conclude theexistence of a "secretreconnaissance aircraft, probablya low-observable counterpart tothe Lockheed Martin U-2".

In September 1998, Lt. Gen.George Muellner, the principaldeputy, Office of the AssistantSecretary of the Air Force forAcquisition, told Jane's DefenceWeekly that the USAF had nooperational "black-world" aircraftin service, but did say that,"There may be other testprogrammes going on right nowin demonstration and things ofthat nature. They are limited innumber and they are notproducing operational platforms.They are just designed tomature the technology."

In its article based on the

Muellner interview, Jane'sDefence Weekly stated that ithad been told by a senior sourcein an internationally recognisedaerospace company that it hassupplied major subsystems fortwo types of "high-flying covertUS military aircraft, both of themmanned", and that one of theseaircraft closely matched populardescriptions of the Aurora. Themagazine concluded: "If theindividual's testimony isaccurate, the timing wouldsuggest that Aurora' is not yet inoperation...but more likely to bein advanced development,possibly progressing as far asflight-test. It could also followthat sightings across the USsouthwest of a high-flying, veryfast aircraft in the late 1980s andearly 1990s were of a hypersonicdemonstrator - or conceivablyseveral demonstrators -designed to 'mature technology',as alluded to by Gen Muellner."

STEALTH TRANSPORTAurora is not the only pro-gramme -whose existence hasbeen deduced by a careful studyof unclassified DoD documents.In 1988 the US DoD announceddetails of a project named

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"Advanced TransportTechnology Mission Analysis".Bidders were being sought forwhat was described as the"second iteration of pre-conceptexploration studies for the nextgeneration theater airlifter".Translated from the official"Pentagonese", this meant "asecond round for studies for anew tactical military transportaircraft".

But what the DoD had in mindwas not going to be an ordinaryC-130-style transport aircraft."Emphasis will be on in-depthexaminations of V vs STOL, lowvs conventional observables, andthe employment of an advancedairlifter in-theater with the C-17,the C-130, and Armyhelicopters."

The appropriate part of thisbid request was an eye-opener!"The bidder must be capable ofconducting programs atclassification levels up throughtop secret, special accessrequired. This requires thebidder to have certifiedor certifiable secure facilities,administrative supportcapabilities and procedures,and personnel with access tohandle, for example, lowobservable and other sensitive

technology and operationalissues."

In plain words, any companybidding for a contract to studythe new transport would haveto be security cleared tohandle a "black" programme.

SENIOR CITIZENThe proposed study may belinked to a "black" projectcodenamed Senior Citizen(Program Element 0401316F).This is thought to be a low-observable, short take-off andlanding (STOL) transport forspecial operations. PaulMcGinnis, an individual "whohas been researching classifiedDoD programmes notes thatseveral advanced STOL aircrafthave been funded. He believesthat Senior Citizen is a low-observable, V/STOL turbofan-powered troop transport, andthat it is probably beingmanufactured by Boeing.

The USAF has studied theMC-X, a new low-observableshort-takeoff and vertical-landing (STOVL) transport forspecial operation forces (SOP). Intheory this could replace theMC-130s currently used for thisrole, but the anticipated quantity

of around 24 is unlikely to besufficient to allow programmestart-up.

OTHER TYPESSeveral other reports of "black"aircraft programmes have beenpublished. However, a degree ofcaution is required whenconsidering these reports.

fn April 2000, Aviation Weekand Space Technology reportedthat unidentified US Air Forceofficials had told the magazinethat an experimental stealthaircraft designated YF-113G hadbeen flown more than 20 yearsearlier at the restricted Nevadatest ranges. The magazinequoted one source as saying thatthe YF-113G was "an airframethat came before Have Blue andthe F-117 We used it in the initialwork to examine the stealthedges problem." Trials hadended by the early 1980s. In acorrection published a weeklater, the magazine explainedthat the designation YF-113Gapplied to the M1G-23, whichhad been flown clandestinely inthe late 1970s by two specialprojects units. Its source hadmistakenly identified the type asa US stealth demonstrator.

Above: Powered by a scramjetpowerplant, the Hyper-X willexplore speeds of more thanMach 6. Aurora may havealready conquered Mach 4-5.

The most likely of these otherrumoured aircraft is a subsonicstealthy reconnaissance aircraft,which eyewitnesses suggest isaround 40ft (12m) long and 60-65ft (18-20m) in wingspan.Reported as operating at lowand high altitudes, and beingseen flying with F-117 stealthfighters, T-38 trainers, andKC-135 tankers, its task is said tobe that of collecting andtransmitting near-real-timedigital photo informationdirectly to F-117 As. Its range hasbeen estimated at more than3,125 miles (5,000km).

The designations "TR-3A' and"Black Manta" are often reportedfor this aircraft, but the formershould be treated with caution."TR-3A" could be a mis-hearingof "Tier 3A", the designation of agiant flying-wingreconnaissance UAV "which wascancelled in the mid-1990s.

Another type of aircraftmentioned in sighting reports isdescribed as having a planformsimilar to that of the XB-70

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Above: The B-2 (seen hereon its sixth test mission)relies on airbornerefuelling to give it globalrange.

bomber. In 1992, Aviation Week &Space Technology publisheddetails of five sightings - twowere near Edwards Air ForceBase, and one occurred near aLockheed-operated radar crosssection test range in the MojaveDesert. Reports describe theaircraft as light-coloured withdark leading and trailing edges.It is said to have a sharp nose, anarrow fuselage with a clear-canopied cockpit, and a deltawing with upward-cantedvertical fins at each outboard tip.Length is believed to be around200ft (60m), wingspan around150ft (45m). Some observersdescribe the aircraft has havinga prominent canard, but othersdo not, causing speculation thatthis may be used only for take-off, landing and slow-speedflight, and may pivot or sweepfor internal stowage duringhigh-speed flight. Someobservers also believe that thisaircraft is a "mother ship"eguipped to launch a smallerhypersonic aircraft.

One of the most reliablesightings of an unidentifiedaircraft was made in August

1989 by Chris Gibson, a drillingtechnologist for a major oil fieldservice company. A member ofBritain's Royal Observer Corpsfor 13 years, and a member ofthe ROC aircraft-recognitionteam for 12 years, he hadproduced an aircraft recognitionmanual for the Corps. Whileworking on the jack-up rig"Galveston Key" in theIndefatigable oil field in theNorth Sea in August 1989, heobserved a four-aircraft formationwhich consisted of a KC-135Stratotanker, two F-lll fighter-bombers, and a triangular-shaped aircraft which he couldnot identify. A trained aircraftobserver, he considered that itmight be a third F-lll flying withits wings fully swept back, butdecided that the planform of theaircraft was too long. Also hecould not see any gaps betweenthe wing and tailplane.

A triangular-shaped aircraftwas reported at Beale Air ForceBase in late February 1992. hithis case the aircraft was flyingat night, and to judge by thespacing of lights on the airframemay have been about one and ahalf times the length of the F-117,and about twice the wingspan.

The possible existence of aprogramme to develop a newstealth fighter to replace boththe F-117 and the F-15E was

suggested in a chart whichformed part of a paper deliveredat a 1997 Air Power Conferencein London, by Col. Richard Davis,commander of the USAFsWright, Laboratory Wright-Patterson AFB, Ohio. Intended toshow the force structure of AirCombat Command over thenext 25 years, this chartsuggested that the new aircraftcould enter service in smallnumbers around 2005, then inlarger numbers after around2015 when retirement of theF-15E is due to begin. Inresponse to inquiries by Jane'sDefence Weekly, Wright-Patterson officials said that thechart was intended to showpossible future USAF systems.

NEW BOMBERThe USAF does not plan todevelop a new bomber in thenear future; a date of 2037 hasbeen mentioned as the likelyoperational date for a follow-onto today's bomber fleet. Theconcept has been dubbed ;B-X',and Boeing, Lockheed, andNorthrop Grumman arereported to be working oncompeting proposals, but havetaken note of suggestions by theUS Congress that a new bomberbe fielded in 2015.

Northrop has the advantage in

that its B-2A is currently inservice. If a 2015 IOC is needed,it proposes a new B-2 variantdesigned to take advantage ofadvanced manufacturingtechniques and moremaintainable stealth coatings.Further cost savings could resultfrom simplifying the structure tocreate an aircraft which wouldoperate only at medium and highaltitudes. More advancedproposals for service on the latertimescale are a subsonic flyingwing, a supersonic design able to"supercruise" in dry thrust, and ahypersonic wave-rider concept.

According to an April 2000report in Aviation Week & SpaceTechnology, Boeing is followingfour lines of investigation. Thesimplest would be to base thenew bomber on a commercialairframe. A 767 derivative with aV-tail, and powered by rear-mounted engines fed by a dorsalinlet system. Treated with RAM,this would achieve stealthperformance. A second designwould be based on a blended-wing body configuration whichthe company hopes to launch asa commercial transport by 2015.The addition of weapons bays inthe aircraft's centre section andthe use of low-observablematerials would create abomber variant.

If the USAF rejects the idea of

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Lett: The OH-58D Kiowa Warriorscout helicopter with its all-weather, day/night, electro-opticalmast-mounted sight (MMS) withvisible and infra-red capability.

obtain a signature which couldidentify what type of helicopterit is.

"Passive" measures able toreduce the acoustic signature ofa helicopter include the use of alarger number of blades on themain rotor. This will reduce thecharacteristic low-frequencysound output, but the reductionin blade chord needed tomaintain the same overall bladearea will make the individualblades more vulnerable tohostile fire. For helicoptersintended for paramilitary orpolice work, this may not beimportant, so it is possible that

some of the "silent" helicopterwork in the USA. may be for theFederal Bureau of Investigation(FBI).

The tail rotor adds its owncomponent to the soundsignature. Possible noise-reduction measures include theuse of offset four-blade tail-rotorsrather than the traditionalcruciform pattern, shroudedanti-torque rotors such as the"fenestron" on the EurocopterGazelle, or even the McDonnellDouglas No Tail Rotor (NOTAR)system.

Active measures could permiteven greater degrees of soundsuppression. An individual bladecontrol technology (IBC) schemedevised by EurocopterDeutschland in association witha number of other Germanaerospace organisations uses a

a commercial-derivative, Boeingcould offer a flying-wing designpowered by two engines andbased on JSF manufacturingtechnology, or a bomber basedon the configuration used by theX-45A unmanned air vehicle.

No information is availableabout the Lockheed proposals,but the company's experiencewith the SR-71 (and perhapswith Aurora) could favour ahypersonic design. RetiredUSAF General Chuck Horner,the air commander during the1991 Gulf War, has predicted thatwork on a stealthy hypersonicaircraft could begin in the USA.within a decade. An aircraft ofthis type could cruise ataltitudes as high as 100,000ft(30,000m).

STEALTH HELOSGiven the presence of a whirlingrotor, the idea of a stealthhelicopter might seem bizarre,but a degree of stealthtechnology has already beenapplied to several types ofhelicopter. The use of measuresto reduce the IR signature ofhelicopters has been commonsince the first use of SA-7 "Grail"IR-homing man-portable SAMsduring the Vietnam War, but thecreation of a stealthy helicopterrequires that similar attention bepaid to the aircraft's radar andacoustic signatures. The mainrotor generates enough radarreturn not only to allow theaircraft to be detected, but willalso allow a Doppler radar to

Above right: On the McDonnellDouglas/Bell LHX design, thearmament is stowed out of sightof enemy radar in a combinedwing/sponson.

Right: This Bell Helicopterartwork of a possible LHXhelicopter configurationfeatures internally-stowedmissile armament.

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Above: The futuristic,composite-constructed LOComanche features internalweapons bays, integrated IRsuppression, and a uniquecanted f antail anti-torquesystem and "T" tail.

moving flap to introduce a veryhigh frequency flutter in theblade at the precise moment thatthe advancing side wouldotherwise produce a loudShockwave. At present, this flapis electro-hydraulically actuated,but a piezoelectric system due tobe tested around 2001 isexpected to be even moreeffective.

In 1981 the US Army startedwork on a Light HelicopterExperimental (LHX) programmein -which it envisaged buying5,000 new helicopters to replacethe UH-1, AH-1, OH-58 andOH-6. By the time a formalrequest for proposals was issuedon 21 June 1988, the requirementhad been scaled back to only2,096 scout/attack helicopters.Two 23-month demonstration/validation contracts were issuedto the Boeing Sikorsky FirstTeam and Bell/McDonnellDouglas Super Team.

Artists' impressions of the rivalLHX designs revealed at the1988 Farnborough air showshowed that both incorporatedsome signature reductiontechnology.

The Army specificationinsisted that the undercarriagebe retractable, and that weaponsbe carried internally. TheBoeing/Sikorsky designmounted ordnance on upward-swinging gull-wing doors in thefuselage sides, while theMcDonnell Douglas/Bell teamfavoured carriage within acombined wing/sponson. Thetwo designs also took differentapproaches to the tail area.Boeing/Sikorsky offer a "V" tailand a Gazelle-style fenestronrotor, while McDonnellDouglas/Bell use a NOTAR (NoTAil Rotor) ducted exhaustsystem.

The Boeing Sikorsky design

Above right: The world's firsttruly low observable (LO)comabt scout, the BoeingSikorsky RAH-66 Comanchewas the winner of the US ArmyLHX competition to replace theCobra and OH-58D.

was selected on 5 April 1991, andthe team was given a contract tobuild four YRAH-66demonstration/validationprototypes, plus a static testarticle (STA) and propulsionsystem testbed (PSTB). The scaleof the programme continued toshrink through the 1990s. Thenumber of prototypes was cutfrom four to two, and in 1999 theproduction quantity wasreduced to only 1,096. Theschedule also suffered, as theprogramme was delayed. A late-1990s restructuring revised andaccelerated the programme,calling for the delivery of 13preproduction aircraft from 2004.The aircraft that finally entersservice will be the first combathelicopter to be given "stealth"features while still on thedrawing board.

Stealth technology forhelicopters is thought to havebeen tested in a number ofclassified technologydemonstration programmes atGroom Lake and other locations,and there are persistent reportsthat the US military hasdeveloped a silent helicopter.

"PRIME CHANCE"When Iranian surface craftbegan attacking commercialshipping in the Persian Gulfduring the late 1980s, BellHelicopter secretly modified anumber of OH-58D Kiowa scouthelicopters for armed missions.As part of an operationcodenamed "Prime Chance", theaircraft were adapted to fireHellfire air-to-surface missiles,

Right: Taken by a US spysatellite, this photograph was"leaked in 1983 to give theworld its first look at theBlackjack bomber (bottom).

Hydra 70 unguided rockets, andStinger air-to-air missiles.Deliveries began in December1987, and the modified aircraftwere operated by A and BTroops of 4th Squadron/17thAviation Regiment until January1991.

In 1999, Jane's Defence Weeklyreported that one of the "PrimeChance" aircraft was modifiedlocally to mount a crew seatfrom a Black Hawk helicopteronto the side. This crudelymodified aircraft was used toattack the oil rigs used by theIranians as bases for their fastattack-craft. Seated in theexternal seat, a sniper with apowerful silenced rifle could

shoot individuals on theplatforms. "They never heard athing," one source told themagazine. "It gave the Iranians abig morale problem, too, becausethey never knew what washitting them."

If this report is correct, the"Prime Chance" aircraft mustalso have had some form ofacoustic stealth measure whichreduced the noise it made to thepoint where the aircraft couldget so close to its target that asniper on what was essentially avibrating platform could score auseful number of hits.

Other helicopters have beenretrofitted with low-observablefeatures. By 1993 the Bell

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Bight: Even before the firstphotos of operationalBlackjacks were available, USintelligence knew much aboutthe aircraft.

OH-58Ds of 147th Cavalry atFort Bragg, North Carolina, hadcoated rotor blades, newwindscreen material and otherchanges intended to reduce thefront-sector RCS. Bell's StealthKiowa Warrior $200,000 stealthkit offers a similar series ofmodifications, plus a reshapednose with radar-absorbentcoatings, engine and gearboxcowlings of radar-absorbentmaterial, and radar-absorbentcoatings on the windows, mast-mounted sight and landing gear.Although 18 aircraft weremodified for Gulf War service,none was deployed.

The Kamov Ka-60 Kasatkavariant of the Ka-62 civilhelicopter is an infantry-squadtransport helicopter whichincorporates IR- and radar-absorbent coatings, a reducedrotor speed, and low-IR-signature exhausts. First flownon 10 December 1998, it isdesigned to carry up to 16soldiers, or six stretchers andthree attendants -when used inthe medevac role. If adopted forservice, it would be fitted with aPastel RWR and an Otklik laserwarning system, while anoptional transverse boom could

Above: Soviet air attache ColVladimir Izmaylov wasexpelled from the USA in 1986,accused of gatheringintelligence on stealth.

carry light armament such as7.62mm or 12.7mm gun pods orB-8V-7 seven-round pods for80mm unguided rockets. TheKa-60 has been evaluated by theRussian Army, and wasdisplayed to potentialinternational customers at theMAKS '99 air show in Moscow.It is reported to have attractedinterest from Iran.

Little is known about a "black"helicopter programmecodenamed "Grassblade". Whenthe first edition of this book waswritten, Grassblade wasbelieved to be a stealthhelicopter under developmentfor the US Army. Since then, thecodename has seen virtually nofurther public exposure, but isstill believed to be an activeprogramme. It may be an aircraftfor use by special forces, a role

which may not necessarilyrequire low RCS.

RUSSIAN STEALTHThe greatest mystery in theworld of low-observables is thestatus of Russian stealthtechnology. Having read a draft ofone of the first magazine articlesever written about stealth aircraft,Nancy Biglin, then circulationmanager of Armed Forces Journal,asked one of the magazine'seditors, "Do the Russians haveone of these airplanes?" Told thatthis was unlikely, she counteredby asking, "But how would weknow, if they can't be seen?" Along silence followed, as theimpact of her comment sunkhome.

hi May 1986, InternationalDefense Review quoted USAFAeronautical Systems Divisioncommander as saying that theUS was "ten to 15 years ahead" ofthe Soviet Union in stealthtechnology, "and we may befurther ahead than that". Duringa 1988 Aerospace EducationFoundation meeting, AssistantUS Air Force secretary foracquisition John J. Welch wasasked if the US held a lead instealth technology over theSoviet Union, and if so whetherthat lead could be maintained.He replied, "The answer has tobe - yes, and hush up." Hishumorous response wasfollowed by the statement thatthe US did have a commandinglead, and that given suitableexploitation and security "it canbe an enduring one".

"When we build a technologyand eventually field it, theRussians tend to do the samething about ten years behind,"said Kent Bankus, a member ofthe Senate Armed ServicesCommittee. "One would hopethat, given the secrecy withwhich we've approached this,

maybe that gap will havewidened." Bankus suggestedthat the US had to assume "thatthe Russians are very activelypursuing [stealth] with all thevigor they possibly can," a viewwhich seems to be shared by theUS defence community. "Bothsides are working very hard oncountermeasures, reduction ofradar cross section andadditional stealthy componentsand tactics," US assistant deputyUnder-Secretary of DefenseJames E O'Bryon told themagazine Aviation Week andSpace Technology in the summerof 1988.

In 1985 the US Navy predictedthat Soviet aircraft and missilesincorporating stealth technologywould enter service by the endof decade. The need to copewith these had been a drivingforce in the decision to fit theGrumman F-14D version ofTomcat with an infra-red searchand track (IRST) system,

The Soviet Union must havebeen aware of the emergence ofstealth technology by the late1970s, by which time it was inthe middle of a massive andcostly programme to replaceobsolescent combat aircraft witha new generation of moreadvanced types such as theMiG-29, Su-24, and Su-27 Likethe US "teen" series of fighters,these were expected to servewell into the 1990s, so the onlychance the Soviets had ofexploiting the new technologywould have been to embark on aproject to create an equivalent tothe F-117A.

Through the late 1970s and1980s, US intelligence wouldhave looked for signs that such aprogramme was under waycarefully monitoring selectedareas of Soviet military researchand development for indicationsthat stealth technologies "werebeing developed, keeping a

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Above: Mikoyan's 1.44technology demonstrator wasto languish on the ground forfive years, awaiting the arrivalof flight-rated engines.

satellite watch on known Sovietaircraft plants and flight testcentres, and gathering infor-mation from agents workingwithin design laboratories andaircraft factories.

Adolf. G. Tolkachev, a Sovietnational whose execution wasannounced by the Soviet Unionin late October 1986, may haveplayed a major role in keepingthe US informed of Sovietstealth developments. Describedin official announcements as "astaff worker of a Moscowresearch institute", he was anaviation engineer, and worked ata Moscow research institute

tasked with developing the mostadvanced forms of militaryaircraft technology. Recruited bythe CIA, he was caught passingsecrets "of a defense nature" toPaul M. Stambaugh, a secondsecretary in the US Moscowembassy.

If the Soviet Union startedwork on an aircraft similar to theF-117; the project must have beenshort-lived. No such aircraft wasreported during the last decadeof the Soviet Union's existence,and has not been reported since.In the early 1980s, the RussianAir Force released preliminaryspecifications for a next-generation proposed MFI(mnogofunktsionalnyy frontovoyistrebitel: multifunctional front-line fighter) and LFI (legkiyfrontovoy istrebitel: lightweightfront-line fighter). Intended to

replace the Su-27 and MiG-29,respectively, both were probablyintended to make some use ofstealth technology, thoughneither the Mikoyan 1.44 designdrawn up around the MFIrequirement, or the Sukhoi S-37technology-demonstrator makeextensive use of low-observabletechnology.

The LFI project to develop alightweight front-line fighterable to replace the MiG-29 andact as a "low" complement to theMFI has yet to result inhardware. The MiG bureaudrew up several proposals,including an F-16-style aircraft,but the requirement wassuspended in 1988. In the 1990s,the designations LFS Qegkiyfrontovoy samolet: lightweightfrontal aircraft), LMFI (legkiymnogofunktsionalnyi frontovoy

istrebitel: lightweightmultifunctional front-linefighter), and Mikoyan 1-2000have all been used to describe aconcept which incorporatessome low-observable features,and bears some resemblance toa scaled-down F-22. As a resultof economic problems, such anaircraft is unlikely to be built inthe foreseeable future. In theshort term, Russia's MiG-29follow-on will be theMiG-29SMT.

In 1995 Col. Gen. Peter S.Deinekin, who was at that timecommander of the Russian AirForce, stated that, the TupolevTu-22 Blinder bomber and theSukhoi Su-24 Fencer would bereplaced by a new "multi-rolestrategic bomber". Tupolev'sgiant Tu-160 Blackjack has littleor no stealth technology, butRussia is thought to bedeveloping a medium-weightstealth bomber for tacticalmissions. The Sukhoi T-60S(sometimes called the S-60) isbelieved to be a variablegeometry design, but a flying-wing design may also be understudy.

Despite Russia's chronicshortage of defence funds, thenew bomber project seems to beproceeding. In early 2000, a

Left: Officially, the Sukhoi S-27Berkut is a technologydemonstrator, but the bureauwould like to develop anoperational version.

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senior Russian Air Force generalconfirmed that the programmewas "a high priority and thatresearch is underway".

JAPAN

Although the US is the onlynation to have fielded stealthaircraft, and no other country isbelieved to be developing"absolute" stealth aircraft, low-observable technology is beingused to some degree in anumber of non-US programmes.

In its search for a suitableaircraft to replace the MitsubishiF-l fighter-bomber during themid-1980s, Japan looked atseveral approaches. The mostobvious was a new indigenouslydeveloped aircraft based onstealth technology. Some workin this area was already underway. In January 1982, the JapanSelf-Defense Agency hadadmitted that it was carrying outresearch into stealth.

lb draw up plans for a newstealthy fighter, an industrialteam known as the FS-X(Fighter, Support, experimental)Joint Study Team was set up.Headed by Mitsubishi HeavyIndustries, this includedKawasaki, Fuji Heavy Industries,engine maker Ishisawajima-Harima, and Mitsubishi Electric.

Working at Mitsubishi HeavyIndustries' Nagoya Works underchief engineer Itsuro Masuda, a

team of 31 engineers took astheir starting point a 1983experimental conversion of aMitsubishi T-2 trainer. Thedesign which took shape ontheir drawing boards wasintended to have a low-altitudecombat radius of up to 450nm(833km) at Mach 0.9 whilecarrying a payload of four Type80 ASM-1 anti-ship missiles.

As the new design took shape,the various companies involvedbegan to explore some of thekey technologies needed for thenew aircraft. Mitsubishi joinedforces with its partners toresearch the stealth technologyneeded for the FS-X. New typesof RAM were developed, andtested in the anechoic chamberat Mitsubishi's Komaki Southfactory, while softwareengineers tackled the task ofcreated computer programmesfor the design of RAM and theprediction of aircraft RCS.

By 1987 the team wasconvinced that its FS-X wouldhave a higher performance andlower cost than rival designs, allof which were being offered byforeign companies. Four aircraftwere seen as alternatives to theindigenous design: developedversions of one of the existingWestern fighters - the F-16Fighting Falcon, F-18 Hornet,F-15 Eagle and the PanaviaTornado. Early in October 1987,Japan announced that the FS-X

would be a derivative of anexisting US aircraft, the choice ofthe basic airframe being eitherthe F-16 or the F-15. DefenceMinister Yuko Kuriharaannounced that the chosenairframe would be fitted withselected items of Japanesetechnology such as a phased-array radar and a new fire-control system, and would alsoincorporate stealth technology.

By the autumn of 1987,however, discussions hadfocused on a design whosereported designation was SX-3(perhaps a mis-spelling of"FX-3"). A stage beyond the "big-winged" Agile Falcon beingproposed to Western Europe,SX-3 was intended to incorporateadvanced technology compositematerials in the forward and aftfuselage sections, and in theincreased-span wings. It wouldalso incorporate the stealthmeasures planned for theindigenous design.

This F-16 derivative wasselected by the Japanese Self-Defense Agency a decisionwhich received the formalendorsement of the JapaneseNational Security Council inOctober 1987. In 1988 the twogovernments signed an MoUwhich would give Japaneseindustry access to manyadvanced US technologies. Itspecified that an Japaneserefinements to existing

technologies must be madeavailable to the US free ofcharge, while technologydeveloped entirely by Japanhad be to requested (and paidfor) by the USA.

Development of the resultingaircraft was slow. The firstprototype did not fly until 7October 1995, and the firstsguadron to be equipped withwhat by now had beendesignated the F-2 was formedin 2000 and was expected tobecome operational in thefollowing year.

The experience gained withthe F-2 has given the Japaneseaerospace industry theconfidence to embark on anambitious project to develop anindigenous FI-X next-generation fighter to replacethe F-15J. This was expected tobe around 44ft (13.4m) long and30ft (9.1m) in wingspan, with afuselage made from compositesand incorporating radar-absorbent materials. Anambitious avionics suite wasplanned, including a conformalradar and an electro-opticalsensor, plus digital fly-by-fightand digital engine-controlsystems.

Below: Outwardly, theMitsubishi F-2 closelyresembles the GeneralDynamics F-16 from which itwas derived.

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Development of a suitablell,2401b (5,100kg) class turbofanwas started in the mid-1990s,and the first XF-7 engine wasdelivered for ground testing inJune 1998. Construction ofprototype aircraft was due tostart around 2000, but theprogramme has been stretchedin timescale. Flight tests of theXF-7 engine have been delayeduntil 2007, and no date has beengiven for prototypeconstruction.

CHINA

China is also working on stealthtechnology. On 26 January 1987,Hangzhou radio reported that"practicable stealth technologiesand theories" had beenmastered and claimed that a"considerable quantity" ofexperimental data had beencollected by Chinese scientistsand engineers. "It will not belong before our country canmake our own stealth aircraft,"listeners were told.

The claim seems to have been

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Above; The dazzling flightperformance of Rafale A hasnot blinded France to the needfor RCS reduction.

premature. No Chinese stealthfighter has appeared, but trials oflow-observable technologies areknown to be under way. In early1999, trials of a ShenyangAircraft Corporation J-8("Finback") with some parts of itsstructure covered in Xrkai SF18radar-absorbent material werereported, along with proposals tofit the same material to the XianAircraft Company JH-7 heavyfighter-bomber.

INDIA

India sees China as asignificant potential threat, so itis hardly surprising that the useof some low-observabletechnologies such as radar-absorbent materials is plannedfor India's next-generationMedium Combat Aircraft(MCA). Intended to replaceIndian Air Force Jaguars and

Mirage 2000s, the MCA isexpected to be a twin-enginedaircraft with a maximum take-off weight in the 40,0001b(18,000kg) class.

EUROPE

Europe has been pursuing itsown stealth studies, and asignificant amount of work hasbeen done in the UK, which hasbeen able to share stealthtechnology with the US. RAM-treated aircraft were tested atFarnborough in the 1950s, whilea pair of Canberra light bombersbelonging to 51 Sqn weretreated with RAM during thelate 1950s and early 1960s, andtested at Wyton, home of theRoyal Air Force's small elint fleet.

In the 1990s, the UK spentaround £100 million on stealthtechnology, building a newresearch and developmentfacility, including a securehangar, at the Warton plant ofwhat was then BAe (now BAESystems). In the late 1990s thecompany was promoting theconcept of a national stealthdemonstrator to be known asExperimental AircraftProgramme II. (The originalExperimental AircraftProgramme had been the 1980stechnology demonstrator whichproved the basic concept lateradopted for the Eurofighter 2000.)

Similar stealth technologydemonstration efforts areprobably under way at Dassault,and the UK and France haveproposed the construction of acollaborative manneddemonstrator. The earliestapplication of the results of thisstealth work could be the airplatform selected to meet theRoyal Air Force Future OffensiveAir System requirement for asystem to replace the TornadoGR.4 after 2015. The latest

generation of European militaryaircraft - Eurofighter and Rafale- incorporate some degree ofRCS reduction, but probably notenough to be militarilysignificant. In this respect, theyare inferior to the US F-22.

Germany and Italy are knownto be working on stealthtechnology, both individuallyand in collaboration, In 1986 theUK magazine Flight Internationalpublished a drawing of theDornier LA-2000, a proposedsubsonic ground-attack aircraft.The original drawing on whichthe magazine's sketch was basedhad not been released by thecompany, but seems to have"leaked" from the Germandefence ministry. The drawingshowed a small delta-wingedaircraft, whose pure triangularshape was marred only by araised section on the centreline.This incorporated a smallcanopy close to the apex of thedelta. The aircraft's two engineswere located in a propulsion baymounted under the wing. Theinlet was between a quarter anda third of the way back from thenose, and the two low-bypass-ratio turbofans - each with athrust of 5,6001b (2,550kg) - feeda single two-dimensionalvectoring nozzle at the trailingedge of the wing. Two largeelevens were mounted oneither side of the wing trailingedge, and would presumablyshare the task of controlling theaircraft. An internal weaponsbay of about 200 cubic feet (6cubic metres) capacity containsa retractable weapons platform.

This design was probablydeveloped under the GermanMoD's plan to build a stealth

Below: The curved inletsshown on the EFA mockupwere a modification whichreduced the aircraft's RCS.

THE WORLD OF BLACK PROGRAMMES

demonstrator. The Lampyridae(Firefly) programme was begunin 1981. Lampyridae (also knownas the Medium Range MissileFighter) was a faceted design,but used fewer facets than theF-117A. As a result, it •would havebeen a supersonic aircraft.Although a three-quarters scalemodel was test-flown in a wind-tunnel, the project was cancelledin 1987, apparently due to lack ofmoney.

In 1989 DASA and Aermacchilaunched a programme todevelop a light aircraft whichcould be used as an advancedtrainer or a light combataircraft. Aermacchi withdrewfrom the project in 1994, butDASA kept the programme

alive, collaborating with theSouth African company Denelon avionics, and Hyundai inSouth Korea who planned tobuild some non-compositeelements of the structure. Thedesign is modular, so should beeasy to modify for the differentroles. It incorporates a chinedforward section, wing/forebodyblending, and air intakesdesigned for minimal RCS.These measures are expectedto give an RCS of around10.76sqft(lsqm).

Below: The Raytheon AMRAAMmedium-range missiles whicharm RAF Eurofighters willeventually be replaced by ramjet-powered weapons.

A full-scale mockup of whatwas now named the Mako(Shark) was displayed at the1999 Paris Air Show, butdevelopment will begin onlywhen DASA (now part ofEADS) can find risk-sharingpartners. Given a prompt go-ahead, EADS says it could flyprototypes in 2003 and deliverproduction aircraft towards theend of the decade.

STEALTHY RPVsFor the moment, most Europeanstealth efforts seem to befocused in the field ofunmanned air vehicles (UAVs).As already described earlier inthis chapter, some the

Above: As this BritishAerospace artwork shows, theRoyal Air Force's eventualTornado replacement could bea stealthy UAV.

pioneering US efforts in low-observables were aimed atimproving the combatsurvivabiiity of remotely pilotedvehicles. This trend -was tocontinue through the 1970s, 1980and 1990s.

Soon after the combat debutof the Ryan Model 147B RPVover Vietnam in the autumn of1964, drones were returning tobase with photos of fightersflying between 5,000-10,000ft(l,500-3,000m) below them.Although SAM sites could do

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nothing against these tinytargets, manned fighters weresoon scoring kills. The firstdrone to be shot down was 147BNo. B-19, -which was lost oversouthern China on 15 November.Later reports suggest that it wasattacked by 15 to 20 fighterswhich made a large number ofpasses before scoring the kill.Similar mass attack tactics wereadopted by the NorthVietnamese Air Force, leadingto further drone losses.

The 147H model fielded in thelate 1960s had a cruise altitudeof 65,000-70,000ft (19,800-21,300m), and incorporated somemeasures intended to reducevulnerability to interception. ARAM installation known asHIDE (High-absorbencyIntegrated Defense) was fitted tothe inlet to reduce RCS, whilethe HEMP (H model EvasiveManeuver Program) system

Below: Lockheed's YMQM-105Aquila started life as a simpleRPV which would offer manyadvantages over mid-1970spiston-engined designs, whilehaving a lower RCS. As therequirement grew moreambitious, high-technologysystems were added and thetotal cost of the systemskyrocketted.

Bight: The Northrop GrummanPegasus UAV is intended toexplore the concept of usingunmanned combat air vehiclesfrom US Navy carriers.

used an RWR tuned toVietnamese fighter radarfrec[uencies to initiateprogrammed turns if a MiGclosed in for a firing pass. A laterHAT-RAC (High Altitude ThreatRecognition andCountermeasures) system tookthe concept a stage further,responding to SAM and fighterradars by initiating flightmanoeuvres.

Contrails were to remain theFirebee's weak link. The 1962test interceptions had shownhow trails could betray a drone,and work on a "no-con" systemhad started in that year. Thisinvolved two QC-2Cs equippedwith a system which injected achemical agent into the exhaust.It was not very successful. SomeH models carried an anti-contrail system known as CRL.Developed by CambridgeResearch Laboratories, it wasintended to suppress the contrailat specific altitudes. A history ofthe drone programme describesthis as "quite successful".

Successor to the 147H was the147T. This had a more powerful

Continental J100-CA-100 engineoffering 45 per cent more thrust,boosting cruise height tobetween 66,300 and 75,000ft(20,200-22,850m). The 147Tretained the HIDE system. OtherRCS-reduction measuresincluded greater use of built-inRAM in areas such as the nose,wings, dorsal spine and tailsurfaces. A wing-root filletwhich blended the wing into thefuselage also helped reduce

Below: In developing theModel 147T long-wing versionof the Firebee reconnaissancedrone, Teledyne engineersapplied RAM to the nose,wings, dorsal spine and tail,and added a degree of wing-body blending. By 1969 it was

RCS. Operations with the 147Tstarted in 1969, and this basicdesign led to the follow-on elintmodel used in the early-1970s"Combat Dawn" programme, theTE and the improved TF.

The limited degree of stealthtechnology built into the Firebeewas extended in the laterTeledyne Ryan AQM-91A Model154. Development of this largeRPV was ordered in 1966, underthe USAF's "Compass Arrow"

ready for service, flying into theface of Chinese and NorthVietnamese air defences.Despite all the aid which theSoviet Union could give, theynever fully mastered the art ofdowning these tricky radartargets.

Right: The use of RAM andshaping on the Model 147Tgave Teledyne the confidenceto tackle the custom-designedModel 154 stealth RPV The flatunderside reduced radarreflectivity from below, whilethe sloped fuselage sides andtail surfaces cut RCS at higheraspect angles. The Model 154(also known as the AQM-91ACompass Arrow) flew at highaltitudes, so the dorsal enginebay screened the engine inletand exhaust from upward-looking radars.

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THE WORLD OF BLACK PROGRAMMES

programme. In the summer of1969, the emergency descent ofone example onto a road at theLos Alamos ScientificLaboratory gave a first glimpseof the first custom-designedstealth aircraft to enter service.Almost half as long again as theFirebee, and weighing up to5,2451b (2,379kg), the 154 hadmany features first proposed inthe unbuilt 1960-vintage Model136 "Red Wagon" RPV Theseincluded a dorsal engineinstallation and inward cantedtwin fins. The 48ft (14.6m) spanwing was swept, and was low-mounted on the flat-bottomedfuselage, a configurationintended to reduce RCS whenseen from below.

A much lower level oftechnology was used in theLockheed YMQM-105 Aquila.Intended for target acquisition,this 3301b (150kg) piston-enginedflying wing first flew as aprototype air vehicle in 1975.Results seemed promisingenough to allow full-scaledevelopment to be ordered in1979. As the requirements grewmore ambitious, costs soared.The programme came underrepeated attack, and the Fiscal1988 defence budget submittedto Congress in November 1987finally killed the Aquilaprogramme, with no fundingbeing authorised. Aquila usedmuch less body-wing blendingthan the B-2, and relied for itslow RCS on a combination ofsmall size, careful shaping, andthe large-scale use ofcomposites.

TIER HAND TIER fflLike the F-117A, the first stealthUAV may have been a Lockheeddesign. Designated Tier HI (thealternative designation of "Q"has also been reported), this isunderstood to have been a 150ft(45m) span flying wing. Little isknown about the UAV, which

may have been built in smaUnumbers before the project wascancelled. The specification mayhave been too demanding,making the resulting designunaffordable. A unit cost ofanything from $150 million to$400 million has been reported.

Two less ambitiousspecifications were drawn up forcomplementary patterns of long-endurance UAVs. lb developthese Tier H Plus and Tier IEMinus designs, the US DoD usedthe Advanced ConceptTechnology Demonstration(ACTD) concept. ACTDs areintended to allow a very earlyoperational assessment of a newsystem concept without theneed to invest the large amountsof money required by traditionaldevelopment projects.

Under the first-ever ACTD,the US DoD ordered theLockheed Martin/BoeingDarkStar (also known as Tier fllMinus), a stealthy UAV designedto penetrate heavy air defences.Powered by a single l,9001b(860kg) thrust Williams F129turbofan engine, it was intendedto operate at ranges greater thanSOOnm (926km), loitering formore than eight hours ataltitudes greater than 45,000ft(13,700m).

The contract for a moreconventional UAV to meet theTier n Plus requirement wasawarded to Teledyne/Ryan.Describing the contract award,Lieutenant Colonel Blackwelder,Lead Co-ordinator for UAV andDecoy ACTDs, stated thatTeledyne-Ryan's Global Hawkwas intended to be "more of aworkhorse for the wide areacoverage. It will be a moderatelysurvivable system with threatwarning and electronic

Right: The Northrop GrummanGlobal Hawk outperformedDarkStar, but being unstealthycould prove vulnerable toattack by SAMs or fighters.

countermeasures that will havemuch greater range, payload,and endurance capabilities,giving it the ability to cover40,000 square nautical miles aday with one system. It will havethe endurance to fly about 40hours, so you can trade off thatendurance for range and timeover target. The objective was toproduce a system that wouldhave 3,000 nautical mile range,be able to stay there for 24 hours,and come back home again, anddata link that imagery back tothe warfighter so he can have itimmediately."

Stealth aircraft tend to be ofnovel shape, and DarkStar wasno exception. It had a short, disk-shaped body and long wings of69ft (21m) span, but no verticalsurfaces or tail. The wings wereslightly swept forward,positioning the elevens close tothe center of pressure - aconfiguration which givesreduced stability. With its wingsdetached for shipping, thevehicle could be carried by aC-130. Construction was mainlyfrom graphite composites, butthe wing has an aluminium

Above: Boeing's stealthDarkStar reconnaissance UAVwas rejected by the USAF, butsome observers think thedecision was a mistake.

fuselage carry-through spar. Theairframe was treated with RAMto minimise radar reflectivity. Tomaximise stealth, DarkStar's airintake and F-117-style exhaustwere invisible from below. Thedesign was intended to bestealthy in both the 8-12 GHzand 140-180 MHz (UHF) bands,with its radar reflections beingfocussed in two sideways facing"spikes".

Boeing built the wings andrelated subsystems, whileLockheed Martin provided thefuselage, and carried out finalassembly at its Skunk Worksfacility. In the best Skunk Workstradition, the project moved fast,with the first example beingproduced just under a year fromcontract signature. Rolled out inJune 1995, DarkStar was due tofly in October of that year, butthe first flight was delayed untilin March 1996, largely due tosoftware problems. Following

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the first flight, changes weremade to the flight-controlsoftware and to the take-offtechnique. Immediately afterliftoff for what would have beenits second flight, DarkStarpitched up and crashed justnorth of the runway.

The second DarkStar made itsfirst flight in early 1998, flying formore than two-and-a-half hours,and reaching an altitude of25,000ft (7,600m). The flight wasfully automated from take-off tolanding, with the UAVnavigating via differentialGlobal Positioning System (GPS)guidance, and demonstrating itsability to update its preplannedmission during flight. The testcleared the way for further teststo evaluate its flightcharacteristics and systemperformance, and to evaluatethe performance of its high-resolution synthetic apertureradar and electro-optic payloads.DarkStar was designed to carryeither a Ream/Optical electro-optical camera or aWestinghouse SyntheticAperture Radar (SAR). Bothwere intended to transmit real-time still images via satellite.

Early in 1999, the USAF, USDoD, and Advanced ConceptTechnology Demonstrationofficials unanimously agreed tocancel the LockheedMartin/Boeing DarkStar infavour of the Global Hawk,which had outperformed thestealth UAV in recent flight tests.Now a Northrop programme,following that company'spurchase of Teledyne Ryan,Global Hawk will be the futureUS long-duration UAV GlobalHawk has no low-observablefeatures and will rely on its highoperational altitude and

Below: Boeing's X-45A isintended to test the concept of astealthy unmanned combat airvehicle (UCAV) which could flyhigh-risk missions.

Right: This photo of theNASA/Boeing X-36 shows thegeneral configuration of theUAV, but hides the classifiedthrust-vectoring system.

defensive EW suite forsurvivability.

The NASA/Boeing X-36 UAVis a canard design intended toassess whether stealth and highin-flight agility could besuccessfully combined in asingle configuration. The X-36was developed in 28 months bya team from NASA AmesResearch Center and "what wasthen the McDonnell DouglasPhantom Works. It uses ablended wing-body design witha chined fuselage, sharp leading-edges, and no vertical tail. Thesegive a low RCS, but poor lift andagility. Yaw control is partly viasplit ailerons that can be used asdrag rudders, and partly via anengine thrust vectoring system,hi January 2000, Jane'sInternational Defense Reviewreported that the X-36 used "astill-classified thrust vectoringsystem with an externally fixednozzle".

STEALTH UCAVs

More recently, the US hasbecome interested in theconcept of stealth UAVs able tofly combat missions and deliverweapons. Known as UCAVs(Umanned Combat AirVehicles), these could helpreduce casualties during airstrikes.

As this book was beingcompleted, Boeing waspreparing to flight test the firstof two X-45A UCAVs. Beingdeveloped under a $131 millioncost-share agreement with the

Below right: An unmannedstealth aircraft, the X-45 hasstraight edges arranged tobe parallel whereverpossible.

US Defense Advanced ResearchProjects Agency (DARPA), theX-45A has an aluminium sub-structure and graphite-epoxycomposite skin. This choice wasmade to minimise cost, but anyproduction version would have acomposite sub-structure. TheUCAV is powered by a singlenon-afterburning HoneywellF124 engine fitted with arectangular yaw-vectoringexhaust nozzle that minimisescontrol surface deflections.

The X-45A is around 26.5ft(8.08m) long and has a wingspan of 33.8ft (10.30m). Emptyweight is around 8,0001b(3,630kg), rising to the region of15,0001b (6,800kg) at maximumtakeoff gross weight It can carrya payload of approximately3,0001b (1,360kg) in two weaponsbays, one on each side of thefuselage centreline. For trialspurposes, the right-hand bay

will be used to carry avionics.The bays have been sized tocarry up to six 2501b (113kg)bombs or a single l,0001b (453kg)Joint Direct Attack Munition(JDAM) guided bomb. Themaximum range is believed tobe around 300-400nm, but anoperational version would havethe ability to loiter for up to 30minutes over a target around650nm from the launch point.

Tests are expected to concludein 2002 with a mission in whichthe UCAV will detect and attacka simulated hostile emitter. Thenext stage could be theconstruction of a third example,which would take advantage ofthe experience gained with thefirst two, and be closer to theconfiguration of a prototypeoperational version. Engineeringand manufacturing development(EMD) of an operational UCAVcould begin in 2005.

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THE WORLD OF BLACK PROGRAMMES

EUROPE'S UAVs

Given that stealthy UAVs areless expensive than stealthaircraft, it was hardly surprisingthat the unmanned concept wasto be explored in Europe, hi2000, three types of stealthyUAV were announced byFrance, Germany, and Sweden,respectively.

On 18 July 2000, DassaultAviation began flight tests of ascale model of a low-observableUAV design. Developed under arapid prototyping scheme, theAeronef de ValidationExperimentale (AVE) is intendedto meet a French militaryrequirement for a low-observable target which can beused to train airborne andground-based radar operators,but it is also intended todemonstrate to the FrenchMinistry of Defence that thecompany has mastered stealthtechnology.

Dassault Aviation also hopesthat the AVE will be the firststage in the development of afull-scale UAV demonstratorwhich could lead to anoperational design able to carryout reconnaissance, or air-to-airand air-to-ground combatmissions, perhaps under thecontrol of a Rafale fighter. Likethe X-45A, any combat versionwould have internal -weaponsbays. The version now flying is7.87ft (2.4m) in length andwingspan. Powered by twinAMT engines, it has an emptyweight of 77\b (35kg) and amaximum take-off weight of1321b (60kg). Maximum speed isMach 0.5, and the UAV has amaximum range ofapproximately 93 miles (150km).

Germany has begun theFuture Airborne WeaponSystem (FAWS) programme tostudy possible replacements forthe Tornado fighter-bomber. Likethe UK, Germany is not sure thatthe solution is another mannedaircraft. Cruise missiles or UAVsmay be a partial solution,perhaps supplemented by asmaller number of new aircraft.In September 2000, EADSannounced that it was studyinga stealthy UAV configurationunder the FAWS effort.

Sweden has been studyingstealthy UAVs since the late1990s. The project is beingconducted under Sweden'sNationellt FlygteknisktForsknings-Program (NationalAeronautics Research Program),and involves Saab's Avionics andDynamics divisions, Ericssonand the Aeronautical Research

Bight: Dassault Aviation hopesthat the AVE will demonstrateto the French Ministry ofDefence that the company hasmastered stealth technology.

Institute of Sweden (PEA). Nineconfigurations were studiedbetween April and June 1998,and a low-speed model of theresulting Swedish HighlyAdvanced ResearchConfiguration (SFIARC) waswind-tunnel tested starting inMarch 1999. The initial testschecked weapon deploymenttest from the UAV's internal bay,and later tests in the T1500 windtunnel at FFA explored thevehicle's flight envelope.

SHARC is 32ft (10m) long, hasa wing span of 26ft (8m), and isexpected to have a take-offweight of around ll,0001b(5,000kg). It is intended tocomplement existing mannedaircraft, providing a lower-costmethod of attacking targets.However, there is currently nospecific Swedish Air Forcerequirement for such a UAV.SHARC's a low signature isintended to prevent detectionand counter-attack from anti-aircraft units and fighter aircraft.Unlike non-stealthy mannedaircraft, it will need no ESMsensors, or the ability to fly evasivemanoeuvres with steep turnsinvolving heavy "g" loads. Thiswill help keep costs down. SinceSHARC -would be armed withexisting non-stealthy weapons, itwill carry these in an internalweapons bay to screen them fromenemy sensors.

ISRAELI UAVsIsrael hopes to develop it ownmodels of stealthy UAVs. Thesewould be long-endurancedesigned intended to trackdown and destroy enemyballistic-missile launch vehicles.In 1994, IAJ, Rafael, and Walesteamed to design the HA-10stealthy UAV a platformintended to use two or threeMoab (Python-derivative) air-to-air missiles to attack Scud-typeballistic missiles in the first 65-80seconds of powered flight.Funded by the US BallisticMissile Defense Office (BMDO),the study concluded that themanufacture of such a weaponsystem would be very expensive.

With the emerging threat ofnew Iraqi or Iranian long-range

ballistic missiles, the idea of astealthy counter-weapon isagain finding favour, but nowthe objective -would be to attackenemy ballistic missiletransporters, erectors andlaunchers (TELs) before thesecan launch their missiles. Theproposed UAVs would have anendurance of up to 60 hours.One version -would carry thesensors needed to detect TELtargets, while the other wouldconduct the attack.

The required airframes andpropulsion systems wouldprobably have to be imported.Although Israel has developedconventional long-enduranceUAVs, Israeli stealth technologyis still at an early stage canprovide only reduced ratherthan low RCS. For example, the

Top: Dassault Aviation's Aeronefde Validation Experimentale(AVE) is intended to meet aFrench military requirement fora low-observable target drone.

Above: The AVE's diamond-shaped wing and V-tailcombine to form a similarconfiguration to that devisedfor the Northrop YF-23.

proposed HA-10 would have hadan RCS only one order ofmagnitude below that of thenon-stealthy Global HawkAccording to a September 2000report in Aviation Week & SpaceTechnology, Israeli researcherswould have to achieve a further10-15dB reduction in radarreflectivity to create anindigenous stealthy UAV.

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LOCKHEED U-2S

Role: high-altitudereconnaissanceLength: 63ft Oin (19.20m)Height: 16ft Oin (4.88m)Wingspan: 103ft Oin (31.39m)Max takeoff weight: 40r0001b(18,140kg)Max. speed: 475+ miles per hour(Mach 0.58)Ceiling: 90,000ft (27400m)Range: more than 6,090nm(11,280km)Armament: nonePower plant: one GeneralElectric F-118-101 turbofan of17,0001b (7,710kg) dry thrust

First flown on 1 August 1955,the U-2 was developed tomeet a US requirement for ahighly specialisedreconnaissance aircraft able tofly over Soviet targets ataltitudes of 70,000ft (21,000m) ormore. The aircraft would relyprimarily on height forsurvrvability, but the need forstealth was also appreciated.Low RCS was a design goal, butin practice little could be done toreduce the radar signature.Optimised as it was for ultimatehigh-altituue performance, thebasic design of the U-2 was sospecialised that it left the designteam with little leeway for large-scale modifications.

Reconnaissance operationsover the Soviet Union began on4 July 1956. When it becameobvious that Soviet radars wereable to track the U-2, Lockheedinvestigated several methods ofreducing the aircraft's RCS, butmost proved impractical. Theonly technique to be adoptedwas the use of a new paintscheme containing radar-absorbing "iron-ball" ferritepigment.

Overflights of the SovietUnion continued until 1 May1960, but fewer than 30 had beencompleted when a U-2 flown byFrancis Gary Powers was shotdown near Sverdlovsk. The "U-2Incident" caused the collapse ofthe 1960 US-Soviet summitmeeting between PresidentEisenhower and Soviet PremierNikita Khrushchev. Eisenhowerordered an end to theoverflights. They had generatedabout 1,200,000ft of photographicfilm covering more than amillion square miles of Sovietterritory, giving US intelligenceexperts an unprecedented viewof Soviet aircraft, missile and

nuclear deployments.Surveillance of the Soviet

Union continued, but the aircraftwas now used to fly missionsalong the Soviet border, usingsideways-looking sensors to lookdeep into Soviet territory. Asmall batch of U-2s supplied toTaiwan carried out overflights ofChina between 1959 and 1974.Four were shot down. In 1974,CIA involvement in the U-2programme ended, and the 20surviving aircraft were handedover to the USAF

The initial production runsaw around 55 aircraft built. Atleast seven U-2As werereworked as U-2Bs, receivingstructural strengthening and themore powerful Pratt & WhitneyJ75-P-13 turbojet. The follow-onU-2C (a mixture of reworked andnew-build aircraft) introduced aslightly extended nose, a longdorsal equipment fairing,increased fuel capacity, enlargedintakes, and the J75-P-13Bengine.

The U-2D had a modified Qbay able to house specialisedsensors or a second crewmember, while the U-2E was a

CIA version with advancedECM systems. At least fourU-2As were modified into U-2Fsby addition of a USAF-stylerefuelling receptacle.

The aircraft returned toproduction in 1968 in its U-2Rform, a variant which had firstflown in prototype form on 28August 1867. Powered by thesame F75-P-13B engine as theearlier aircraft, this was intendedto overcome the airframe-imposed performance limitationsof the older -13B-powered aircraft,improve handling characteristics,increase the range and payload,and provide a less crampedcockpit.

The result may haveresembled the earlier U-2models, but was essentially anall-new design. Wingspan wasincreased by 23ft (7m), theoutboard 5.9ft (1.8m) of eachwing folding inwards for storage.Maximum altitude is reported tohave been 75,000ft (22,860m),slightly below that of the earliermodels. Most obvious newfeature of the U-2R was theunderwing equipment pods,which supplemented the

volume of the fuselage bays. In1978 these would be replaced bystill larger underwing fairingspod known as "superpods".

A total of 25 serial numberswas assigned to the initial batchof U-2Rs but the numberactually built in this initialproduction run was at least 14,probably 17 Aircraft wereinitially assigned to both theUSAF and the CIA, rapidlysupplanting the older models,but the surviving CIA exampleswere passed to the USAF in 1974.

Final version of the U-2family was the TR-1A.Structurally identical to theU-2R, it was ordered in 1979 toact as a source of "day or night,high-altitude, all weather stand-off surveillance of a battle areain direct support of US andallied ground and air forces".The first example flew on 1August 1981 and was deliveredto the USAF in the Mowingmonth. Operational TR-lAs wereused by the 17th ReconnaissanceWing, Royal Air Force StationAlconbury, England, starting inFebruary 1983. The lastproduction aircraft were

Above: The main anti-radarfeature of the U-2R is its skin of"Iron Ball" paint. As itsnickname suggests, thismaterial consists of tinyparticles of magnetic material(known as ferrite) suspended ina non-magnetic binder. When aradar wave strikes the aircraft,some of its energy is absorbedby this paint. The inidividualferrite particles are magnetisedthen remagnetised in theopposite polarity billions oftimes each second by the cyclesin the wave's magnetic field.

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STEALTH AIRCRAFT

delivered in October 1989. In1992 the USAF decided to dropthe designation TR-1, and toclassify all operational aircraft asU-2R.

In May 1988 the USAF gaveLockheed a contract todemonstrate and flight test aGeneral Electric F118-GE-101turbofan engine) in the U-2R. Avariant of the F101-GE-F29, thenew engine was lighter,produced more thrust, andburned less fuel than the olderJ75-P-13B turbojet. The first re-

engined aircraft flew for the firsttime on 23 May 1989. Theupgrade proved successful, andwas applied to the entire fleet.Other upgrades improved theaircraft's sensors and added aGlobal Positioning System (GPS)satellite-navigation system thatwould record geographical co-ordinates directly on thecollected images. The re-engined single-seat aircraft aredesigned U-2S, while the traineris the U-2ST

The first production example

flew on 12 August 1994, and thefirst operational single-seatersand trainers were delivered tothe 9 KW, Beale AFB, California,on 28 October 1994. The aircraftserves with four operationaldetachments located throughoutthe world, and the firstoperational U-2S mission wasflown from Osan AB, SouthKorea, on 20 October 1995.It is capable of collecting multi-sensor photo, electro-optic,infrared and radar imagery aswell as performing other types

of reconnaissance, but requires askilled pilot An official USAFdescription of the U-2 notes thatit "...can be a difficult aircraft tofly due to its unusual landingcharacteristics."

The aircraft that the Sovietsonce dubbed "the black lady ofespionage" has outlived itssupersonic SR-71 replacement.On 11 August 1994, U-2R number0338 became the first U-2 toachieve 20,000 flying hours, andthe type is expected to remain inservice for many years.

Bight: Originally built for theCIA as a U-2A, 66701 was laterassigned to the USAE Rebuilt asa U-2B, then as a U-2C, it waspainted for the first time in 1970.

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LOCKHEED SR-71 BLACKBIRD

R61e: strategic reconnaissanceLength: 107ft Sin (32.74m)Wingspan: 55ft 7in (16.94m)Height: 18ft 6in (5.64m)Max takeoff weight: 170,0001b(77,000kg)Max speed: Mach 3+Service ceiling: approx. 86,000 ft(26,000m)Range: 2,600nm (4,800km)Armament: nonePowerplant: two Pratt &Whitney J58 each of 32,5001b(14,700kg) thrust withafterburner

Despite their age, the smallfleet of SR-71 Blackbird

aircraft represented a uniqueintelligence-gathering assetright up to their moment of finalretirement in 1998. More than 35years after the type's first flight,this sinister-looking aircraftcould still operate with impunityin the face of most defencesystems. The Soviet Union wasprobably the only nation able todefend itself against Blackbirds.Others have tried - firing off SA-2 Guidelines against SR-71s hasbecome a regular event for theNorth Korean air defences, butto date the exercise has provedfruitless. In 1986 Blackbirdsoperated in the face of the threatposed by Libyan SA-5 Gammonlong-range/high-altitude missilebatteries in order to record theresults of US air strikes againsttargets in Tripoli and Benghazi.

Like the XB-70 bomber

programme, the A-12 projectrequired a long series oftechnological developments tomake Mach 3 flight possible.Materials, lubricants,powerplants, fuels andsubsystems all had to be custom-developed. When the aircraftcruised for prolonged periods atMach 3, the external skintemperature rose to at least 450degrees Centigrade, and to morethan 1,000 degrees in areaswhere the thermal effects wereseverest. To cope with this levelof thermal stress, most of theairframe was made from Beta B-120 titanium alloy.

When designing the U-2,Lockheed had been able to takeonly limited RCS-reductionmeasures, but the A-12 took theentire art a massive stepforward. As North Americandesigners working on the XB-70bomber and F-108 Rapier fighterhad discovered, creating anaircraft able to cruise at Mach 3was difficult enough, but increating the A-12, the SkunkWorks tackled the tasks ofcombining this level ofperformance with stealth.

Comparison of the A-12 withthe similar-sized F-108 isinstructive. The fighter had anangular appearance whichbordered on ugliness, with aslab-sided forward fuselage, box-shaped rear fuselage, andwedge inlets - features whichwere highly radar reflective. The

A-12 had rounded lines whichmade extensive use ofwing/body blending, while itsengines were fed by inletswhose conical centrebodieswould help shield thecompressor face from radarobservation. The twin fins werecanted inwards to reduce theirradar reflectivity, while the longchines on the forward fuselagepresented highly inclinedsurfaces to incoming radarenergy.

Invisible to the untrained eye"was another breakthrough instealth technology - the use ofplastic materials in areas such asthe wing leading edges, chinesand elevons. Developed byLockheed, this took the form of aradar-absorbent plastichoneycomb designed to copewith temperatures of up to600deg F (315deg C). On theA-12, it accounted for 20 per centof the total wing area. It was notstrong enough to be usedstructurally in a Mach 3 design,so was added to the leading andtrailing edge in the form of V--shaped sections. The SkunkWorks is also reported to haveflown experimental componentssuch as all-plastic vertical fins.

The dark paint finish used tohelp radiate heat away from theaircraft gave rise to the unofficialdesignation "Blackbird". It wasdesigned with two qualities inmind. It offered high heatemissivity, so helped to radiate

friction-generated heat whenthe aircraft was cruising at Mach3. It also incorporated the radar-absorbing "iron ball" pigmentused on the U-2 and TR-1.

The first A-12 prototype wascompleted in the winter of1961/62, and made its maidenflight (with interim J75 turbojetengines) on 26 April 1962, anddeliveries to the CIA startedtowards the end of the year. Bythis time a second variantexisted - the YF-12A interceptor.The first of three prototypefighters flew in August 1963 and,although extensively tested, thetype was never adopted forservice. Fifteen A-12s were built,all but one of -which were single-seaters.

Existence of the aircraft wasrevealed by President Johnsonon 29 February 1964, althoughhe gave the designationincorrectly as "A-ll". Fourmonths later, he revealed that adefinitive operational versionwas under development, butonce more gave a wrongdesignation, referring to the newaircraft as the SR-71. It was tohave been designated RS-71(Reconnaissance-Strike) ratherthan SR (Strategicreconnaissance). A dedicatedR-12 nuclear strike derivative ofthe A-12 is known to have beenproposed.

The SR-71 had been orderedat the end of 1962. Like the U-2,the A-12 had been a single-seat

Left: The SR-71 gave the worldits first example of wing-bodyblending, a significant methodof reducing RCS taken toextreme in the B-2.

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Above: Most of the SR-71'ssensor payload was packed intoequipment bays within the longchines. Built from metal, these

incorporated RAM and werecarefully blended with thefuselage, measures aimed atreducing overall RCS.

aircraft (although several two-seat trainer versions of the latterwere completed). The SR-71 hada two-seat cockpit, aconfiguration first tested on theYF-12A. It was also slightlylarger and heavier than the A-12.The chines were made frommetal, and used to house theaircraft's sensors.

First flight of the SR-71 tookplace on 22 December 1964, theaircraft being one of an initialbatch of six. Productiondeliveries started in January1966 with the delivery to theUSAF of the first SR-71B two-seater. The first SR-71A wasdelivered in May of the sameyear. A total of 32 SR-71s wasbuilt, all but two of which weretwo-seaters.

Just how well the aircraft'sRCS-reduction measures workedremains debatable, but classified.Not all of the components flight-tested in plastic found their wayinto the production aircraft. Inhis book Stealth Aircraft, BUISweetman recalls withamusement how when theUSAF flew an SR-71 to the 1974Farnborough Air Show, PlesseyRadar announced that its AR-5Dcivil air-surveillance radar haddetected the plane at a range of

more than 200 miles (320km).By the late 1980s, the USAF

was operating only nine SR-71s,and decided that he cost ofoperating such a small fleet ofspecial-purpose aircraft was notviable. Defense Secretary DickCheney retired the SR-71 fleet in1990. Most of its aircraft weresent to or made available tomuseums, but at the instructionsof the US Congress, five SR-71Asand one trainer were set asidefor possible future use.

By 1994, Congress hadrealized that there was acontinuing shortfall in USreconnaissance capability, soordered that three SR-71As bereactivated. The USAFreactivated two, making themfully operational, but did not usethem for any significantmissions.

In 1996, the SR-71 wastemporarily grounded becausethe USAF said that funds fortheir operation were notauthorized. Congress authorizedthe funds, but in October 1997,President Clinton used his line-item veto powers to delete the$39 million budgeted for theSR-71, and on 30 October 1998the SR-71 was officially retired,after a 32-year military career.

Above: Despite being the firstWestern aircraft to incorporatesignificant RCS-reductionfeatures, the SR-71 also offeredMach 3 performance and anundeniable beauty. This aircraftmade extensive use of RAM inall the sharp horizontal edgeswhich might be seen by anenemy radar - the chines, wingleading edges, and elevens.

Further RCS reduction wasprovided by the use of "IronBall" paint. So sophisticated wasthe aircraft, that it is hard toremember that the firstproduction delivery was in1966. Over thirty years later, thehigh cost of keeping the aircraftoperational led to the finaleight or so examples beingretired.

109

ROCKWELL INTERNATIONAL B-1B

Role: strategic bomberLength: 147ft Oin (44.81m)Height: 34ft Oin (10.36m)Wingspan: 78ft 2in (23.84m)swept, 136ft Sin (41.67m)unsweptMax. takeoff weight: 477,0001b(216,360kg)Max. speed: Mach 1.25Range: c.6,475nm (12,000km)Armament: up to 75,0001b(34,000kg) of ordnance in threeinternal weapons baysPowerplant: four GeneralElectric F101-GE-102 turbofans ofc.30,0001b (13,600kg) withafterburning

When President Reaganentered office in 1981, he

was determined to improveAmerica's defences. PresidentCarter had ordereddevelopment of the B-2, but thiswas still in the earliest stages ofdevelopment, and not due to flyuntil the late 1980s. Reaganordered a batch of 100 improvedB-1B production models, givingthe USAF and RockweU theproblem of getting it intoproduction, then into serviceearly enough to make a usefulcontribution to SAC's strengthbefore the B-2 arrived. Thattimescale called for a five-yearprogramme rather than theseven to ten years normallyneeded to field a major weaponssystem.

The B-1A had already beendesigned to have a much lowerRCS than the B-52 it wouldreplace. By the early 1980s,Soviet development of improveddefence systems intended tocope with ALCM and

Tomahawk cruise missiles -weapons such as the SA-10 andSA-N-6 - made the Rockwellbomber seem increasinglyvulnerable, so steps were takento lower its RCS. The inlets wereredesigned, eliminating thevariable ramps needed for Mach2 flight. The revised design hasinlet sides and splitter platesswept slightly backwards fromthe vertical, and incorporatecurved ducts and streamwiseradar-absorbent baffles. RAMwas also added as a liningmaterial.

A major move towardreducing the aircraft's RCS wasthe removal of the fuselagedorsal spine. This had originallybeen fitted to house electricalcabling associated with theaircraft's Westinghouse ALQ-153tail-warning system. When theUSAF opted to integrate the tail-warning task directly into theALQ-161, the spine could beremoved.

New absorbent seals for theB-1B wing were developed bythe British company WoodvillePolymers. These replaced anearlier less-absorbent design inpart of an exercise which sawthe entire inboard wingstructure redesigned.

Among the measures takenunder later 1985 contracts forRCS-reduction were a series of

modifications to the noseradome cavity and to cavities inthe fuselage side fairings. Aspecial adhesive tape was alsoapplied to all seams in the skinonce system testing had beencompleted, and prior to painting.This tape was probablyelectrically conductive, and thuslinked all the skin panelstogether into a common con-ducting surface, thus eliminatingsurface discontinuities whichwould re-radiate energy.

B-lB's RCS is one hundredththat of the B-52, and a sevenththat of the FB-111. In May 1986,International Defense Reviewquoted USAF AeronauticalSystems Division commander assaying that when the B-l flewinto the 1985 Paris Air show, theFrench were surprised by itssmall radar cross-section. "Theydidn't believe we could do it."The aircraft has also proved anelusive target for fighters duringRed Flag exercises. "In order forthe monitoring radar to get ourposition, we either have to climbor put our transponders on," thecommander of SAC's 337th

Bombardment Squadron toldAviation Week in 1987.

In October 1986, weU aheadof the Congressional 1987deadline, the first B-1B squadronwas declared operational atDyess AFB, Texas. The base had15 aircraft, 12 of which hadenough defensive avionics toallow them to be declaredoperational. With delivery of the100th and final B-1B due in April1988, and no prospect of a follow-on order, Rockwell began to layoff staff, with more than 10,000leaving the B-l operation in thefirst half of 1987 alone. In thespring of 1988, Rockwellannounced that its long-established North AmericanAircraft division at Columbus,Ohio, would cease operationsover the next 15 months. Thefinal example was delivered on 2May 1988, and the type nowequips three squadrons of AirCombat Command, and two ofthe Air National Guard. It is nowsupported by Boeing.

The B-1B was designed to

Left: Careful engineering hasgiven the B-1B a head-on RCS ofaround Isq. m, making it a moredifficult radar target than asmall fighter.

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Below:The rounded shape ofthe B-1A fuselage had played asignificant part in getting theRCS an order of magnitudebetter than that of the B-52.Reducing the B-1B RCS by as

much again involvedpainstaking attention todetail, with RAM beingapplied to key areas of thefuselage and wings to dampout radar hot spots.

fly low-level, high-speedmissions which impose greaterstrain on the airframe than thehigh-altitude missions of theB-52. The aircraft is expected tohave a 10,000 hour service life,which should allow it to remainin service until around 2020.Like the B-2, it is expected toretire long before the mucholder B-52. Designed toconservative engineeringstandards at a time when littlewas known about aircraft lifeexpectancy, the B-52 is expectedto have an operating life of morethan 30,000 hours, and couldremain in service until around2040.

Above: The engine nacelles(seen below in cross section)had to be redesigned on theB-1B to add anti-radar bafflesand a curved duct. These moveshad a drastic effect on topspeed, making the aircraftsubsonic under most flightconditions, but the price wasworth paying. Radar signalscould no longer enter the inlet

and pass down to reflect fromthe front face of the engine.This reduces RCS, and alsoprevents advanced radar signal-processing algorithms beingused to observe the modulationeffects of the rotating fan stages,a phenomenon which canallow radars to identify the typeof aircraft being tracked.

The B-lB's ability to deliverconventional "weapons is beingimproved under a multi-stageConventional Mission UpgradeProgram (CMUP). CMUP BlockC, fielded in August 199̂ gaveB-lBs the capability to dropcluster bombs, while the Block Dchanges due to be completed in2003 allow the aircraft to carryup to 24 JDAM guided bombs(eight in each of its threeweapon bays), fit an IntegratedDefensive ElectronicCounterMeasures (IDECM)towed decoy intended toenhance the survivability of theaircraft, and add a newcommunication/navigationsystem. A planned Block Emodification will allow the B-1Bto carry wind-compensatedmunitions, the Joint StandoffWeapon (JSOW), and the JointAir To Surface Standoff Missile(JASSM), while Block F willmake further improvements tothe bomber's defensive system.

Other upgrades beingprojected for the B-1B includethe addition of a satcomsterminal and a Link 16 datalink,a cockpit upgrade, andmodifications to the aircraft'sradar which would allow it totake synthetic aperture radar(SAR) images of the target,improving the aircraft's ability totarget GPS-guided bombs.Studies have also looked at EWimprovements such as anupgraded version of theAN/ALR-56M radar warningreceiver, and advancedcountermeasure flares.

Ill

EUROFIGHTER TYPHOON

Role: multirole fighterLength: 52ft 4.25in (15.96m)Wingspan: 35ft Inn (10.95m)Max. takeoff weight: 46,3001b(21,000kg)Max. speed: Mach 2.0Tactical radius: typically 750nm(1,390km)Armament: 27mm Mausercannon (omitted from UKaircraft) plus up to 14,3301b(6,500kg) of external storesPowerplant: two Eurojet EJ200turbofans each of 13,4901b(6,120kg) dry and 20,2501b(9,185kg) thrust with A/B

Under a memorandum ofunderstanding signed in

May 1988, development of thistwin-engined canard-delta wasbegun by what were thenBritish Aerospace (UK), MSB(Germany), Aeritalia (Italy) andCASA (Spain). Initial prototypeswere powered by two Turbo-Union RB.199-122 turbofans, butlater prototypes had theproduction engine. Known asthe EJ200, this twin-shaftturbofan was developed by theEurojet consortium, acollaborative venture set up bywhat were then Rolls-Royce(UK), MTU (Germany), Fiat (Italy)and Sener (Spain).

In its basic single-seatversion, the aircraft is optimisedfor the air-to-air role, but has a

secondary attack capability. Atwo-seater is available fortraining.

Much of the technologyneeded for Typhoon was provenusing the BAe EAP(Experimental Aircraft Pro-gramme) technology demon-strator. The first prototype ofwhat was originally known asthe European Fighter Aircraft(EFA), then Eurofighter 2000, wasoriginally expected to fly atManching in Western Germanylate in 1991. In practice, the firsttwo aircraft (developmentaircraft 1 and 2) were notcompleted until late in 1992, butwere not to fly for some 18months, while exhaustive checkswere made of the flight-controlsystem (PCS). DAI finally flew on27 March 1994.

The flight-test programmeremained slow, and PCSsoftware was often a delayingfactor. This led to speculation inthe mid to late 1990s that thesystem was experiencing

technical difficulties, reportswhich were encouraged by thedevelopment team's regular butbland pronouncements that thesubject could not be discussed,but that all was well.

In practice, two factors hadcaused the team to be ultra-conservative when developingthe PCS. One was the FCS-related accidents which hadbeen experienced by the YF-22(25 May 1992) and JAS 39 Gripen(2 February 1989 and 8 August1993); the other was the fact thatthe Typhoon was designed tohave a very high level of agilityat supersonic speeds. Sincestability increases at supersonicspeeds, the aircraft had an evenhigher level of agility atsubsonic speeds which posedformidable challenges to thePCS development team.

DAS, the third aircraft to fly,and the first Italian-assembledexample, was the first to bepowered by Eurojet EJ200engines. The UK-assembled

DA4 was the first two-seater andfirst with full avionics. Theremainder of the developmentfleet consists of three moredevelopment aircraft (DA4 - 7)and five instrumentedproduction aircraft (IPA1 -5). Droptrials of air-to-surface weaponsstarted in 1999 using DAS, and in1997 DA7 made the first launchon an air-to-air missile.

When the programme wasset up, the UK and WestGermany intended to order 250.Italy was to buy around 170, withSpain taking 100. Inevitablythese figures -were to decrease.By 2000 they had dropped toGermany 180, Italy 121 plus nineoptions, Spain 87 plus 16 options,and the UK 232 plus 65 options.Deliveries to the user air forcesare due to begin in June 2002.First units to eguip will be anOperational Evaluation Unit atBAE Warton, then anOperational Conversion Unit atRAF Coningsby, JG 73 at Laage,Germany, and 4 Stormo at

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Below: While the aircraft is notintended to be stealthy,measures were taken tominimise its RCS. The mostobvious is the "smiling" airintake. The original designfeatured a rectangular intakesimilar to that on the EAPtechnology demonstrator, buttests showed that a curvedconfiguration would have alower RCS. The aircraft willenter service with RaytheonAMRAAM missiles, but thesewill be replaced by theramjet-powered Matra

BAe Dynamics Meteor. Thesame company's AdvancedShort-Range Air-to-Air Missile(ASRAAM) will be fitted toRAF aircraft, while other usersmay select theinternationallydevelopedIRIS-T.

Grosseto, Italy. First exportcustomer was Greece, which in1999 announced its intention topurchase 60 aircraft, withoptions for 30 more.

Flyaway unit cost wasoriginally seen as being around£10 to 12 million ($17 to 20million). By 1992 this had risen toan estimated £25 to 26.5 million,and by 1996 to £38 million.There was no officialrequirement for the Typhoon tohave a high order of stealthiness.It is not a stealth aircraft, but wasdesigned for reduced RCS, amore modest goal which does

Left: Given the risksassociated with test flying,building only a single EAPprototype was a gamble, butone which paid off.

not require the specialised andcostly technology used in theF-117A and B-2. Much can beaccomplished even by simplemeasures such as keeping sizeand weight to a minimum, andusing rounded shapes andprofiles.

Several factors helpminimise RCS. It is a smallaircraft, and much of its profileis rounded. The main straightareas, such as the wing and finleading edges, are highly swept,so will reflect radar energy inmain lobes well away from thefrontal sector. Extensive use isalso made of carbon-fibrecomposites. RCS is also reducedby careful attention to detail. Atthe 1987 Paris Air Show, arevised full-scale mock-upshowed some of the

refinements made to the designin the final stages of projectdefinition work. The mostobvious was a redesignedventral intake. On EAP and theoriginal EFA design, this hadbeen of rectangular shape, butthe final configuration is aslightly curved ''smiling" design.This has less drag, and less radarcross section. The RAF hasstated that Typhoon meets therequired level of low-observability. No official figurehas been released, but theaircraft is understood to have anRCS of just under one squaremetre.

Some F-22-type capabilitiesmight be added to Typhoon aspart of its mid-life updatingprogramme, a possibilityforeseen by the RAF and

Luftwaffe before the programmewas launched. These couldinclude three-dimensionalthrust-vectoring through anglesof up to 10 degrees, and off-taoresight weapon aiming bydecoupling the fuselage bymeans of CCV flying surfacesand vectored thrust. Technologyfor such an update could bedrawn from the results of flighttesting of the Rockwell/MSBX-31A.

The engine manufacturingconsortium has drawn up plansfor uprated EJ200 variants withthrust levels of 23,1551b (10,503kg)and 26,3001b (11,930kg). A thrust-vectoring nozzle has beenstudied in Spain by FTP andSener, and 20 hours of benchtests had been completed bySeptember 1998.

113

DASSAULT-BREGUET RAFALE C & M

R61e: multi-role fighterLength: 50ft 1.25in (15.27m)Height: 17ft 6.25in (5.34m)Wingspan: 35ft 5.25in (10.80m)Max. takeoff weight: 49,6001b(22,500kg)Max. speed: Mach 1.8Tactical radius: 570-950nm(l,055-l,760km)Service ceiling: 55,000ft(16r760m)Armament: up to 21,0001b(9,500kg) of ordnance, plusinternal cannonPowerplant: two SNECMAM88-2 turbofans each of 16,4001b(7440kg) thrust with A/B

At the 1983 Paris Air Show,Dassault showed a mock-up

of a technology demonstrator fora next-generation fighter. Twofeatures of this ACX (AdvancedCombat experimental) designproved striking - the hugevertical fin, and the novel inlets.The size of the fin had beendictated by the need fordirectional stability, but the

inlets, -which incorporated themoveable conical centrebodiesfound all Mirages since the IDC,were mounted under theleading-edge root extensions ofa carefully sculpted forwardfuselage.

The author assumed thatthis configuration had beenadopted to ensure a goodairflow at high angles of attack,but Northrop's Lee Begin had analternative theory. "Take anotherlook," he urged me, "they'reshaped that way because ofstealth." As the design wasrefined to create today's Rafale,the tail fin shrank in size, thelower fuselage assumed a V--

shaped cross-section, and theinlets were changed for asimpler pattern withoutcentrebodies or other movingparts. There was no loss ofstealth, however. The revisedinlets remained tucked underthe fuselage and largelyscreened from the attention oflook-down radars.

Like the Eurofighterconsortium members, Franceapparently concluded that thecost of developing a trulystealthy fighter was politicallyand economically unacceptable.Like EFA, the Dassault-BreguetRafale is a reduced-RCS design.

In France, the task of

developing RCS-predictionsoftware was tackled byThomson-CSE To allow a start tobe made on the task ofeliminating "hot spots" from thedesign, Thomson-CSF adaptedexisting software, and used thisto study the radar cross-sectionof the aircraft. Three areas wereguickly identified as majorcontributors to RCS - the radarand EW antennas, the inlets andengine, and the cockpit. Aparallel effort involveddeveloping software for the CrayXMP 18 supercomputer whichwill allow the design of largemetallic structures of up to 10sguare metres in area. This

Above: Although not a trueDassault stealth fighter, Rafalewill have a lower radar crosssection than today's Mirage Flor Mirage 2000.

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Below: Rafale's rounded inletsmay appear very conspicuous,yet they're one of the aircraft'sstealthier features. Today's aircombat is at low level, andmajor threats include AEWradar and interceptorsequipped with look-downradars. From most observationangles above the aircraft, theinlets - a prime radar target inany aircraft - are concealed bythe forward fuselage. They're

barely visible in the photo atthe bottom of the oppositepage, for example. The aircraftshown here is on aninterception mission, andcarries two Matra R530F radar-guided missiles, plus twowingtip-mounted Magics. Iftasked with an air-superioritymission into unfriendly skies, itwould probably carry the newMatra BAe Dynamics MICA.

would initially be used to carryout studies of aircraft inlets.

The Rafale A prototype flewfor the first time on 4 July 1986,just ahead of the rival BAe EARLike the British aircraft, it was atechnology demonstrator ratherthan a true fighter prototype.About l,0001b (450kg) heavierthan the planned Rafale Dproduction version, it waspowered by two GE F404turbofans. First flight with asingle SNECMA M88 replacingone GE F404 was on 27February 1990.

A series of test flights weremade in the winter of 1987/88 tomeasure the RCS and the IRsignature of the Rafale A. Aseries of 13 missions was flown,allowing the radar signature tobe assessed with differentexternal loads and under severalcombat conditions. These

included an air-combat sortiewith the aircraft carrying twoMatra Magic 2 heat-seekingmissiles, and a low-level flightwith two 530 gallon (2,000 litre)external tanks.

Like the UK, France hadhoped that a flyingdemonstrator might act as thecatalyst for an internationalprogramme, but the path to anyagreement was made difficult byconflicting views over aircraftweight. Given the closerelationship between aircraftweight and cost, and the need toattack large-scale export ordersto make programmescommercially viable, Dassaulthas always favoured lightweightdesigns. French determinationthat the cost (and thus theweight) of a next-generationfighter had to reflect the needfor maximum export potential,

and French demands to begiven design leadership of anyinternational fighter programmewhich might emerge frominternational discussions, endedany prospect of a viableprogramme.

The UK, West Germany, Italyand Spain chose to go their ownway with the EPA, leavingFrance to continue with Rafaleas a national venture. Theprogrammes to develop thedefinitive aircraft and its M88-2powerplant were launched inDecember 1992, and the firstproduction aircraft were orderedin March 1993.

Four versions have beenplanned. Rafale B started out asa two-seat, dual-control versionfor the French Air Force, but hasnow evolved into an operationalversion suitable for single ortwo-seat (pilot + weapon systemofficer) use. The version for theFrench Air Force was originallyto have been Rafale D, but thishas now become a genericdesignation for French Air Forceversions. Rafale C is the single-seat combat version for FrenchAir Force, while Rafale M is thenaval single-seat version for useon aircraft carriers.

The designation Rafale R hasbeen applied to a possiblereconnaissance version whichwould carry a pod-mountedsensor suite, and replace FrenchAir Force F-1CR and FrenchNavy Super Etendardreconnaissance aircraft

The Rafale programme did

not go smoothly. When the firstedition of this book was -writtenin 1988, there were alreadysuggestions that the projectcould prove an "abyss forbillions". In the mid-1990s theFrench Government hadproblems with its defencebudget, and demanded costreductions for Rafale. InNovember 1995 the programmewas suspended Work onproduction aircraft wastemporarily halted in April ofthe following year, but inJanuary 1997 Dassault andFrench defence ministry agreedon a 10 per cent cost reductionand the procurement of 48aircraft between 1997 and 2002.The arrangement had to beabandoned following a changeof government, and a new dealagreed in January 1999 coveredonly 28 (plus 20 options) fordelivery between 2002 and 2007.

The first production aircraftwas a Rafale B, which made itsfirst flight on 24 November 1998.It was followed on 7 July 1999 bythe first production Rafale M.The first Rafale C is due to bedelivered mid-2002.

First version into service willbe the Rafale M, and the firstnaval squadron is due to beequipped by June 2002.Deliveries to the French AirForce should begin in late 2002,with the first squadron beingequipped in 2005. The deliveryrate will be slow, with the 294thand final aircraft for the Frenchforces being delivered in 2023.

115

LOCKHEED F-117A NIGHTHAWK

Role: strike fighterLength: 65ft llin (20.08m)Wingspan: 43ft 4in (13.20m)Max. takeoff weight: 52,5001b(23,800kg)Max. speed: Mach 0.9Armament: c.4,0001b (1,800kg) ofstores carried internallyPowerplant: two non-afterburning General ElectricF404-GE-F1D2 turbofans each ofc.lO,8001b thrust

Asa result of the successfulflight testing of the XST

technology demonstratorsstarting in 197̂ President Carterwas able to authorise thedevelopment of a productionstealth fighter in the followingyear. The project wascodenamed "Senior Trend".

The aircraft that project headBen Rich and his Skunk Worksteam created was of verydifferent shape to the widely-projected "F-19" seen in mid-1980s books and magazines. Tokeep RCS to a minimum,extensive use was made offaceting. Straight lines ratherthan curves dominate theaircraft's configuration. Itsangular lines make one half-seriously wonder whether BenRich had impounded every setof French curves owned bySkunk Works personnel.

The faceted panels aremounted on skeletal sub-frame,and coated with radar-absorbentmaterials. The wing is of two-spar construction, and has afaceted aerofoil. The originaloutward-canted ruddervatorshave been replaced by amodified design made fromthermoplastic graphitecomposites, which give theadditional strength needed toavoid nutter problems that hadplaced a speed restriction on theaircraft. The cockpit canopy andmost access panels havesawtooth edges to suppressradar reflection.

The engines are fed by airintakes which incorporate screenswith rectangular 1.0 x 0.625in (2.5 x1.5cm) openings. These preventradar energy from entering theintake. Part of the incoming airbypasses the engine and is mixedwith the engine efflux to lower itstemperature. The mixture isejected through narrow-slotexhausts in the rear fuselage.These are 5ft Sin (1.65m) but only4in (10cm) and have 11 verticalguide vanes.

All ordnance is carried in aninternal weapon bay 15ft 3in(4.7m) long and 5ft 9in (1.75m)wide and covered by two largedoors hinged on the centreline.When lowered, these greatlyincrease RCS, so changes havebeen made to rninimise thelength of time for which they areopened for weapon-release.

The faceted airframe playshavoc with the aircraft's inherenthandling qualities. To make theaircraft flyable, it has a GECAstronics quadruples fly-by-wirecontrol system. A TexasInstruments Forward-LookingInfra-Red (FLIR) sensor with dualfields of view is mounted in acavity just below the front of thecanopy, while a Downward-Looking Infra-Red (DLIR) andlaser designator also made by TIis mounted in another cavitybeneath the forward fuselage tostarboard of the nose-wheel bay.Both cavities are covered by finemesh screen to prevent theentry of radar energy.

The designation "stealth

Below: The side view of theF-117A reveals what must surelybe the strangest shape to fly sincethe 1930s. The steeply-slopedfuselage sides and the highlyswept wing leading and trailingedges ensure that radar energy isdefected harmlessly, rather than

being reflected back to theenemy radar. RCS is greatlyreduced, but a penalty must bepaid in terms of airframe dragand internal volume. Since mostUSAF bombs and missiles areunstealthy, they are carried ininternal weapons bays.

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fighter" is partly a misnomer; theaircraft is essentially a strikeaircraft designed to fly close to atarget at subsonic speed, launcha guided missile or "smart"bomb, then turn away. In termsof speed or agility it is no matchfor a traditional fighter. It wouldbe a vulnerable target if caughtby an enemy fighter, lb avoidthis, it normally operates atnight, conditions under which itis virtually undetectable. Interms of radar penetration, theF-117A has met its specifications,but at a price of restricted speedand manoeuvrability. Its

successors such as the F-22 andJoint Strike Fighter will combinestealth with improved speed,altitude and manoeuvrability.

Although several developedversions have been proposed,none resulted in an order.F-117A+ was a development ofthe basic F-117A which wouldhave taken advantage of morerecent technologies to producean aircraft with improvedsurvivability in the face of high-threat environments, while theA/F-117X (originally known asthe F-117N Seahawk) was aproposed long-range naval

strike/attack aircraft based onthe F-117A. If the A/F417X hadbecome a firm programme, theSkunk Works planned to offer aland-based F-117B which wouldhave used the redesigned wingand horizontal tail surfaces ofthe naval variant, and been fittedwith GE F414 afterburningturbofan engines, and all-weather sensors.

Three upgrade schemeshave kept the F-117A combat-effective. The Weapon SystemComputational Subsystem(WSCS) programme replacedthe aircraft's Delco M362F

computers by IBM AP-102 units.The first aircraft to be modifiedflew in October 1986 and theentire fleet had been updated by1 January 1992.

By this time, the OffensiveCapability ImprovementProgram (OCIP) was alreadyunder way, with the firstupgraded aircraft beingdelivered in November 1990,Completed in March 1995, theOCIP programme added animproved flight-managementsystem, a digital moving map,and digital situation displays,new cockpit instrumentationwith Honeywell colour multi-firction displays, a digital autothrottle and pilot-activatedrecovery system.

The most recentmodification scheme replacesthe FLIR and DLJR sensors witha new Texas Instruments turret-mounted Infra-Red Acquisitionand Designation Sensor (IRADS),while the Ring Laser GyroNavigation ImprovementProgram (RNIP) adds aHoneywell ring laser gyroinertial navigation system and aCollins Global PositioningSystem (GPS) satellitenavigation receiver.

Lett: So important was facetingto the stealth qualities of theF-117A, that the USAF kept theaircraft's appearance classifieduntil November 1988. The"butterfly tail' has not beenused on a military aircraft sincethe days of the Fouga Maglstertrainer. It eliminates one of thethree traditional tail surfacesand avoids a radar reflectivevertical fin, but controlauthority is limited at highspeed. A quadruples fly-by-wire system tames the aircraft'sstrange aerodynamics.

117

NORTHROP B-2 SPIRIT

R61e: strategic bomberLength: 69ft (21.0m)Height: 17ft (5.18m)Wingspan: 172ft (52.43m)Weights - empty: 153,700 lb(69,717kg)

normal T-O: 336,5001b(152,600kg)

maxT-O:376,0001b(170,550kg)Max. speed: high subsonic(Mach 0.85?)Ceiling: 50,000ft (15,000m)Range (typical hi-hi-hi):6,300nm (11,667km)Armament: 40,0001b (18,000kg)of ordnance in internal baysPowerplant: four GeneralElectric F118-GE-100 turbofanseach of 17,3001b (7,850kg)

Like the Lockheed F-117Astealth fighter, the B-2

bomber has the simplestpossible front profile - twostraight moderately sweptleading edges which meet at thenose. This layout ensures thatthe main RCS sidelobes in theforward sector are well awayfrom the direction of flight Themassive sawtooth trailing edgeis made up from 14 straightedges, aligned at one of twofixed angles, a layout which willdirect radar energy reflectedfrom the trailing edges into twodirections well away from theimmediate rear of the aircraft.Each wing side has a dragrudder and elevon on theoutboard trailing edge, plus twomore elevens on the next-inboard section. The central"beaver tail" forms anothermoving surface. The aircraft hasno vertical stabiliser, a featurethat helps reduce RCS. There isa quadruplex digital flightcontrol system developed byGeneral Electric, whichincorporates fly-by-wire controls,plus a sophisticated stability-augmentation system.

Segmented inlets on theupper wing feed air to theengines buried within thefuselage. A secondary inletmounted just ahead of the maininlet, and offset slightlyoutboard, also draws in air,perhaps for engine bay andefflux cooling. The inlets make asignificant contribution to totalRCS. A redesign was needed toget these right, and to solvemanufacturing problemsassociated with their complexshape. The engine efflux isdischarged via recessed cut-outsin the wing upper surface. Linedwith heat-resistant carbon-carbon material, these open-topped ducts are probablyintended to spread the exhaustlaterally to reduce its IRsignature. Two doors on theupper surface of each nacelleare opened when the aircraft istaxying and flying at low speed.These are auxiliary inlets usedto supply extra air to the

engines.The aircraft was originally

intended to be a high-altitudebomber, but in 1984 theprogramme was restructured toallow a redesign of the wingcarry-through structure. Thiscost around $1,000 million, anddelayed the programme by eightmonths, but achieved two majorgoals. The increased structuralefficiency of the revised designgave greater strength for lessweight, curing an identifiedweight-growth problem, andproviding enough strength forterrain-following flight at lowaltitude. It also reduced RCS.Design goal was probably anRCS at least an order ofmagnitude below that of theB-1B. The latter aircraft hadalready taken bomber RCS toless than 1 square metre,suggesting that the likely figurefor the Northrop aircraft was atleast below O.lsq m, perhaps aslittle as 0.05.

Since all B-2s were built onproduction tooling, use of theterm "prototype" is almostmisleading. Air Vehicle 1 (82-1066) was rolled out on 22November 1988, and made itsfirst flight on 17 July 1989. A total

of six aircraft were assigned todevelopment testing. The firstaircraft was placed in storage in1993 at the end of a trialsprogramme of 81 sorties, but theothers -were reassigned asoperational aircraft.

Although the USAForiginally planned to procure 133B-2s (the first of which wouldnever be used as an operationalaircraft), the planned force wasgradually reduced, and inOctober 1991 was set at only 16by the US Congress. The USAFmanaged to fund one more inFiscal Year 1992 and four morein the following year. Sixteenaircraft were delivered to theBlock 1 standard. Armed -withB83 or Mk 84 weapons, theycould operate in small numbersfrom Whiteman AFB.

Nos. 17 to 19 were Block 2aircraft, and five (Nos 12-16) wereretrofitted to the same standard.This equipped the aircraft withpartial terrain-followingcapability, the GATS (GPS-AidedTargeting System), and allowed

Above: The complex shape ofthe B-2 intakes and centrefuselage must be amanufacturing nightmare, butthe shape and smoothness mustbe accurately controlled tominimise RCS.

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it to operate from forward bases.Block 20 aircraft could deliver 16Joint Direct Attack Munitions(only four per target), and had alimited capability to handle thenew AGM-137. Aircraft 20 and 21were built to the Block 30standard, to which the other 19will be upgraded. Block 30 hasfull low-observabilityperformance, full JDAM launchcapability, and can carry up to80 Mk 82,36 Mil? or 80 Mk 62bombs.

As production ended in themid-1990s, the tooling •wasplaced in storage, but attemptsby the US Congress to order afollow-on batch of 20 aircraftwere overruled by the Clintonadrninistration. However it wasdecided to remove the firstaircraft from storage, and rebuildit as an operational aircraft.

The 509th Bomb Wing wasformed 1 April 1993 to operatethe new bomber. It was locatedat Whiteman AFB, Missouri,where the first operating unit -the 393rd Bomb Squadron - wasformed on 27 August 1993 andreceived its first aircraft inDecember of that year. The B-2

was granted limited operationalstatus on 1 January 1997, andInitial Operational Capabilityfollowed on 1 April 1997.

The B-2 was designed for aservice life of 40,000 hours, so intheory could out-last the B-52(with a service life of more than30,000 hours) or the B-1B (10,000hours). In practice, the retirementdate of the B-2 will probably bedetermined by attrition of thesmall number built.

When the aircraft firstentered service, caulk andpressure-sensitive tape wereused to shield the gaps aroundpanels and doors, In flight, thetape tended to peel away fromthe skin, allowing the exposedgaps to reflect radar energy.During regular depotmaintenance, the B-2 is beinggiven an improved anti-radarcoating based on magneticradar-absorbing materials(MagRAM), and high-access

areas of the airframe are beingretrofitted with 119 easilyremovable panels. MagRAM isan iron-filled elastomer whichstores radar energy rather thanconducting it. The radarreflection from the gaps arounda MagRAM-coated panel will beabsorbed before it can escape,removing the need to caulk andtape the gap. Thesemodifications will increase theaircraft's weight by 3,6661b(1,660kg), but should reduce the

time needed for low-observablemaintenance from 20.8maintenance hours per flyinghour to less than ten.

The B-2 was intended tohave a contrail-suppressingsystem. Located in two baysimmediately outboard of themain wheel wells, this wouldhave sprayed highly corrosivechemicals into the exhaust. Thisscheme was abandoned infavour of using a rearward-facing laser radar to detectcontrails, allowing the pilot tomove to an altitude where thecontrails cease. The vacantspaces earmarked for thecontrail-suppressing systemcould be used in a proposedupgrade to house small missileswith decoy or jammingpayloads.

Left: Despite its novel lines andstealthy characteristics, the B-2is a fuel-efficient aircraft. "Theaerodynamic design of the ATB[B-2] is markedly more efficientthan its predecessors,"explained USAF General LarryWelch in the late 1980s. "Itrequires far fewer tankers, forexample, to do its job than docurrent bombers because of theaerodynamic efficiency. Itcarries a very healthy bombload and has very good rangeand would be a superb bombereven if it weren't stealthy."

119

LOCKHEED MARTIN F-22A RAPTOR

R61e: air-superiority fighterLength: 62ft tin (18.92m)Wing span: 44ft Gin (13.56m)Weights - empty: 31,6701b(14,365kg)

maxT-O:c.60,0001b.(c.27,200kg)Max. speed: Mach 2+Ceiling: over 50,000ft (15,250m)Range: l,735nm (3220km)Armament: see belowPowerplant: two Pratt &Whitney F119-PW-100 turbofanseach of 35,0001b (15,900kg) class

The F-22 is intended to allowUSAF pilots to establish

absolute control of the skiesthrough the conduct of counter-air operations, defeating threatsthat the F-15 will no longer beable to counter. It will use stealthand advanced sensors to givethe pilot a first-look, first-shot,first-kill capability.

Lockheed MartinAeronautical Systems isresponsible for overall weaponsystem integration. It developedand now manufactures theforward fuselage (including thecockpit and inlets); the verticalfins and stabilators; wing andempennage leading edges;ailerons, flaperons; and landinggear.

Lockheed Martin TacticalAircraft Systems is responsiblefor the mid-fuselage; armament;electronic warfare system; theintegrated communications,navigation, and identification(CM) system; storesmanagement and inertialnavigation systems; anddevelopment of the supportsystem.

Boeing is responsible for thewings and aft fuselage, plusstructures in the aircraft forinstallation of the engines andnozzles. Boeing also handlesradar system development andtesting, and operates theground-based AvionicsIntegration Laboratory (ATT.), andthe Boeing 757 Avionics FlyingLaboratory.

Although the shape ofaircraft is fairly conventional,many of its features weredictated by the need to reduceRCS. The fuselage and canopyhave sloping sides, the verticaltails surfaces are canted, and theleading and trailing edges of thewing and tail have identicalsweep angles. Known asplanform alignment, this choiceof a relatively small number ofangles helps direct any reflectedradar energy into a smallnumber of directions. The edgesof the canopy, weapon bay doorsand other opening surfaces aresawtoothed, a stealth featurefirst seen on the F-117A.

A serpentine inlet ductconceals the front face of theengines from radar, while theavionics antennas are mostlylocated in the leading- or

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trailing-edges of the wings andfins, or are flush with surfaces, inorder to minimise RCS. ByMarch 1994, the companies andthe USAF had identified someshortfaUs in the aircraft's radarcross-section (RCS). Detected bya new computer modellingtechnique, these were rectifiedby reducing the number of drainholes on the bottom of theaircraft and combining accesspanels.

Final assembly of the F-22will take place at LockheedMartin Aeronautical Systems inMarietta, Georgia. To test the"stealthiness" of each F-22 whenit comes off the assembly line,the company has built a 50,000sguare foot radar cross-section(RCS) verification building. A 45-foot-diameter turntable mountedwithin a 150 x 210 feet testchamber will position the fighterduring RCS tests. Another 60 x210 foot chamber will be usedfor aircraft antenna testing.The avionics suite of the F-22 ishighly integrated, aUowing thepilot to concentrate on themission, rather than onmanaging the sensors as incurrent fighters. The AN/APG-77 radar, EW suite andcommunications/identificationare managed by single systemthat presents relevant data onlyto the pilot, and controls thelevel of electromagneticemission (such as radar andradio transmissions) according tothe tactical situation.

The basic concept wasderived from the 1980s PavePillar programme in the 1980s,and locates all the signal anddata processing resources in acentral collection of modularprocessors, linked to the sensors,subsystems and pilot by high-speed data busses. The avionicssuite is based on two CommonIntegrated Processor (CIP) unitslinked by a 400 Mbits/s fibreoptic network, but there arespace, power, and coolingprovisions within the aircraft fora third CIP, when this becomesnecessary. The CIP itself will beimproved by a plannedtechnology-insertionprogramme which will exploitnew developments in computertechnology. The avionics has thecomputing power of two Craysupercomputers, and produces alarge amount of heat, so iscooled by a mixture of air andliquid cooling.

The aircraft is controlled by atriplex, digital, fly-by-wiresystem. Thrust vectoring viatwo-dimensionalconvergent/divergent engineexhaust nozzles (able to move 20degrees upwards anddownwards in the vertical plane)is used to augment aerodynamicpitch control, particularly at lowspeeds and high angles of attack.

The aircraft will carry

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Belo w: The F-22 has aperformance which eclipsesthat of any other fighter presentor planned. Yet some criticsquestion the need for the USA

to spend large sums of moneyon an expensive new fighter ata time when the Russian AirForce is a mere shadow of itsformer sell.

Below:The aircraft's air-to-airmissiles are carried in internalbays. This 1990 test firing usedan AIM-9 Sidewinder.

existing and planned mediumand short range air-to-airmissiles, plus a 20mm M61A2internal cannon. AIM-9Sidewinder missiles will becarried in bays in the sides ofintake ducts, while the otherweapons are carried in theventral weapons bay. Fourunderwing stores stations caneach carry 5,0001b (2,268kg) ofadditional ordnance or stores,but this will make the aircraftnon-stealthy.

Internal carriage of themissiles reduces RCS, butrequires weapons -whichoccupy the mmrrnum of spacewithin the bay. The maximumspan of the tail surfaces of thenew AIM-9X short-range

missile is only 17.3in (44cm), lessthan the 25.2in (64cm) of earlierversions, while the AIM-120C5AMRAAM medium-rangemissile has the clipped wingsand fins needed for internalcarriage requirements on theF-22 Raptor and the Joint StrikeFighter. It incorporates a rocketmotor which is Sin (12.7cm)longer than the previous motor,but a shortened control sectionfor the moving tail surfaceskeeps the overall missile lengthunchanged in order to maintainaircraft compatibility.

The air-to-air missiles arecarried on and launched fromlaunch adapt units (LAUs). Thetrapeze launcher for theSidewinder is the LAU-141/A,while the AMRAAM VerticalEject Launcher (AVEL) is theLAU-142/A.

The aircraft has a groundattack capability, so can carryand direct precision groundattack weapons such as theGBU-32 Joint Direct AttackMunition (JDAM). This is carriedand released from a BRU-47/Abomb release unit in the mainweapons bay.

The USAF plans to procure339 production F-22s, andproduction is scheduled to rununtil 2013, but this could beextended by export orders. Testand training F-22s will beassigned to the Air Force FlightTest Center at Edwards AFB,California, the Air ForceFighter Weapons School atNellis AFB, Nevada, and the325th Fighter Wing at TyndallAFB, Florida, but theoperational locations for theF-22 force have not yet beenannounced.

121

BOEING & LOCKHEED MARTIN JOINT STRIKE FIGHTER (JSF)

Boeing X-32

Length overall: 45ft (13.7m)Wingspan (CTOL): 36ft (11.0m)

(STOVL): 30ft (9.1m)

Lockheed Martin X-35

Length overall: 50ft 9in (15.47m)Wingspan (STOVL): 33ft Oin(10.05m (33 ft 0 in)

The US Joint Strike Fighter(JSF) is the largest military

aircraft programme everplanned in the West; it is alsoone of the most ambitious. Likethe controversial Tactical FighterExperimental (TF-X) programmeof the early 1960s (whichproduced the General DynamicsF-lll), it attempts to create a

high-performance design able tomeet the requirements of landand naval operations but, tomake life more difficult, it alsoplans to incorporate short-take-off/vertical landing (STOVL)capability, affordable and easy-to-maintain stealth, and anaffordable price-tag.

The prize which Boeing andLockheed Martin are competingfor is a possible production runof around 3000 aircraft - around2,000 for the US Air Force, 600for the US Marine Corps, 300 forthe US Navy, and 90 for Britain'sRoyal Navy. This represents amassive series of orders, buteach customer has a differentrequirement.

While the USAF needs anattack aircraft to replace the F-16,

the USN wants a stealthy long-range strike aircraft. Both wouldbe conventional take-off andlanding (CTOL) aircraft, but theUSMC and the Royal Navy arelooking for a STOVL aircraftable to replace the AV-8B andSea Harrier, respectively. Bothteams competing for the job ofbuilding the JSF also envisagelarge export orders from nationsneeding to replace aircraft suchas the F-16 and early-model F-18.

The JSF requirement isspecifying what is essentially aCTOL strike aircraft with atactical radius of more than600nm, and a STOVL variantwith a tactical radius of 450-SOOnm. Both should have amaximum speed of Mach 1.5,and a manoeuvrabilitycomparable with that of theaircraft they will replace.

The two aircraft that Boeingmanufactured were to a designwhich the company callsConfiguration 372. This has amodified delta planform andtwin fins. Both are powered by asingle Pratt & Whitney JSF119-614 turbofan engine, a modifiedand refanned derivative of theF119 engine used in the F-22Raptor. While these were takingshape, the company continuedto refine its design, producingConfiguration 373 with asmaller, swept wing, and withnew horizontal tail surfaces in

left: Lockheed's X-32 will winno prizes for visual appearance,but the design is intended tocombine stealth andaffordability.

addition to two outward-cantedfins. This was further refined inConfigurations 374 and 375, thefirst of which introduced a newbackward-swept straighttrailing-edge for the wring, whilethe second incorporated weight-saving measures needed tomake sure that the STOVLvariant could land whilecarrying a 4,0001b (1,800kg)payload.

The CTOL version of theaircraft would have a full-spanwing with cambered leadingedges and leading-edge flaps onthe outer wing sections, but tosave weight the STOVL versionwould have a wing of reducedspan. Neither versionincorporates wing folding.Production CTOL aircraft wouldbe powered by the -614C versionof the engine, while the STOVLwould have the -614S versionwhich incorporates a Rolls-Roycelift module and spool duct.There is no auxiliary lift systemin the STOVL version of theaircraft; most of the engineexhaust is ducted forward to tworetractable nozzles. The enginereceives air via a chin inlet witha short duct. This does notprovide the line-of-sightblockage needed to screen thefront face of the engine fromhostile radars, but the fact thatphotographs of the JSF radarcross-section model have beencensored to obscure the inletduct suggests that Boeing mayhave developed some novelmethod of screening theengines.

The Boeing design uses side-

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Left: Full-scale mock-up of theX-35 Joint Strike Fighterproposal on the LockheedMartin Tactical AircraftSystems flight line.

Right: The version of theBoeing JSF designed for USAFuse will not have the auxiliarylift system planned for theSTOVL version.

mounted weapon bays. Thesewill give ground crews eye-levelaccess for maintenance andweapons loading. They will alsoallow the pilot to open the bayon the side of the aircraft awayfrom enemy radar and drop aweapon without compromisingthe JSFs low observability. Thebay design was tested inJanuary 2001 when USAF testpilot Lt. Col. Edward Cabreraopened and cycled the X-32A'sweapons bay doors as part ofvibration and acoustic testingduring the aircraft's 61st flightFor these tests, the aircraftcarried an instrumented ADvl-120 AMRAAM and a JointDirect Attack Munition (JDAM).

Lockheed Martin's X-35design is more conventional inappearance, and bears someresemblance to the F-22. TheX-35A demonstrator was used totest Configuration 230A, whichis intended to meet the USAFrequirement, and was thenupgraded to the X-35B standardto test Configuration 230B, theSTOVL configuration beingproposed for the USMC and theRoyal Navy. The RN versionwould be similar to the USMCversion, but would have foldingwings. The second aircraft wasbuilt as an X-35C to testConfiguration 230C for the USNavy.

All three variants useversions of the Pratt & WhitneyJSF119-PW-611 derivative)turbofan. The -611C versionplanned for USAF and USNaircraft has an axisymmetric(thrust-vectoring) exhaustnozzle, while the STOVLvariants would use the -611Sversion. This has a Rolls-Royce-developed three-bearing swivel-duct nozzle "which can deflectthe thrust downwards, while aRolls-Royce lifting fan locatedbehind the cockpit and drivenby a shaft from the main engineincreases the bypass ratio andthrust of the engine in the hovermode, balancing the aircraft viaa rear vectoring nozzle. A bleed-air reaction control valve in eachwingroot provides stability atlow speeds.

On CTOL aircraft, extra fuelwould be carried in the spacetaken up by the lift fan and shafton the STOVL versions.Changes to the USN versioninclude a wing, fin and elevatorwhose areas have beenincreased by extending the

chord The wing would fold, andhave ailerons as well asQaperons, the control surfaceswould be enlarged, and thelanding gear strengthened Allversions would carry ordnancein internal weapons bays.

Both JSF candidates havebeen designed to be stealthy.The required RCS is about thatof a golf-ball-sized metal sphere.While aircraft such as the F-117Aand B-2 require large amounts ofcareful maintenance in order tomaintain low RCS, the JSF isintended to be easy to maintain.This will involve the use of low-observables which are durableand easy to repair if damaged.

Given the degree to whichthe US tightly controls access ofstealth technology, the JSFprogramme faces problems onthe export market. One possible

solution is that the selectedaircraft may be built in stealthyand semi-stealthy versions, andperhaps even in a non-stealthyversion.

Both designs flew for thefirst time during 2000. Boeing'sCTOL X-32A made its first flighton 28 September, but the STOVLX-32B had yet to fly in early 2001.The Lockheed Martin X-35Aflew on 24 October 2000, andwas due to complete a series offlight tests before beinggrounded and converted to theSTOVL X-35B standard. InSpring 2001 both companieswere test-flying ConceptDemonstration Aircraft (CDA).

The UK committed $200million in funding to theconcept demonstration phaseof the JSF programme, andunder the terms of a US/UK

Memorandum ofUnderstanding (MoU) signedin January 2001, the UK willparticipate in the formalevaluation process of the rivaldesigns. British industry is alsoexpected to receive about 10per cent of the work in theEMD programme.

The winning design will notbe selected until both teamshave clocked up 20 flight hourson their STOVL designs, and inOctober 2000 Pentagonprocurement chief Dr. JacquesGansler expressed concern thatthe programme could bedelayed if either contractor hadproblems with STOVLtechnology. In earlier comments,he had indicated that if eitherteam failed to achieve STOVLflight, that design could "self-eliminate''.

123

MIKOYAN 1.42 AND 1.44

R61e: multi-role fighter (1.42);technology demonstrator (1.44)Length: 74ft 10.75in (22.83m)Wingspan: 55ft 10.5in (17.03m)Height overall: 18ft 9.25in(5.72m)Max. takeoff weight: 77,2001b(35,000kg)Max. speed (high-altitude:clean): Mach 2.6Service ceiling: 65,600ft(20,000m)Range: 2,429nm (4,500km)Powerplant: Two Saturn/LyulkaAL-41P turbofans each ofc39,3501b (17,850kg) withafterburning

Tn 1983 the Russian Air Forceireleased its requirement for anMFI (mnogofunktsionalnyyfrontovoy istrebitel:multifunctional front-linefighter). The USAF had issued itsown request for information onwhat would become theAdvanced Tactical Fighter twoyears earlier, and awardedconcept-definition studycontracts in September 1983, sothe two programmes werestarted on similar timescales.

Having completedpreliminary design studies in1985, Mikoyan were given finalperformance requirements in1988 and started work on the1.42 in 1989. The resulting designis a large, twin-engined, canarddelta with widely spacedoutward-canted twin tailfins.Like other agile canard deltas,the Russian aircraft requires afly-by-wire system. This is aKSU-142 quadruplex digitalsystem which may be derivedfrom the BTsK-29 system flownon MiG-29E testbed.

Work on a suitablepowerplant started in 1985. Thiswould offer performance betterthan that of any fighter engine ofthe time, and have the lowest-possible number of parts toimprove reliability. The resultingSaturn/Lyulka two-shaftvariable-bypass turbofan wasrunning on the bench by theearly 1990s.

To prove the basic design, atechnology-demonstratordesignated 1.44 was devised.This would test theaerodynamics, performance, andintegrated flight/power plantcontrol system of the planned1.44 so would carry no weaponsor mission systems. The 1.44does not have the double-deltawing featured on MiG artist'simpressions of future fightersand expected to be used on theMFI. According to Russianofficials the definitive 1.42 designwould have better aerodynamiccharacteristics than theLockheed Martin F-22, and beable to fly faster, reachingspeeds of up to Mach 2.6, andcruising at Mach 1.6 -1.8 withoutafterburner.

Stealth was obviously a

requirement for the new fighter.In 1995 Jane's InternationalDefense Review quoted MiGbureau general designerRostislav Belyakov as saying that"any aircraft delivered aroundthe end of the century that doesnot fully incorporate stealth doesnot have a chance of success".But this should not result inperformance penalties, heinsisted. A future fighter "shouldnot lose any of its flightperformance for the benefit ofstealth".

The structure of the 1.44makes extensive use of radar-absorbent coatings, and it hasbeen conjectured thatproduction examples of thedefinitive 1.42 could be fittedwith the Keldysh ResearchCentre's "plasma cloud" stealthsystem Some observers believethat a plasma system has beeninstalled on the 1.44, but theprobes -which they see as beingplasma sources are more likelyto be associated with flight-testinstrumentation, or with theaircraft's fly-by-wire flight-controlsystem.

Four side-by-side shallowtroughs below the fuselage ofthe 1.44 are believed to be semi-conformal missile carriagestations, but the 1.42 is expectedto have one or more internalweapons bays which wouldallow the carriage of air-to-airmissiles.

Progress with the 1.44 wasslow. Although completed in1991, the first prototype had towait for engines to becomeavailable, and was not deliveredto the flight test facility atZhukovsky until mid-1994. Somefast taxi trials were undertakenlate that year, and some reports

suggest these included anaborted take-off. The aircraft wasthen placed in storage. Variousreports attributed its fate to non-availability of flight-ratedSaturn/Lyulka AL-41F engines,problems with the flight controlactuators, or simple lack ofmoney. Work on the aircraft andits powerplant had beeneffectively halted when fundingdried up.

By this time, such a heavyand potentially expensiveaircraft had little attraction forthe cash-strapped Russian AirForce, which in 1996 had beenable to purchase only a singlenew combat aircraft. In March1997, the ITAR-Tass news agencyquoted unidentified Russiangovernment officials as sayingthat cash constraints hadprecluded further developmentwork.

The aircraft was shown toVIPs on 24 August 1997, and inFebruary of the following yearMikoyan officials claimed thatthe Russian Air Force wasprepared to fund flight tests, andthat the aircraft would fly inAugust. Both hopes proved vain.

In the autumn of 1998development funding for theAL-41F turbofan finally becameavailable, allowing enginedevelopment to proceed. Firstphotographs of the 1.44 werereleased in December 1998, anda month later it was displayed to

the press at Zhukovsky. It finallyflew on 29 February 2000. It isstill possible that the 1.44 or theplanned 1.42 version could beadopted by the Russian AirForce, though the reportedprice-tag of around US$70million could limit anyproduction run.

At the press demonstrationin January 1999, MikhailKorzhuyev, general director ofwhat was now the AviatsionnyiNauchno-PromyshlennyiKomplex (ANPK) MiG, said thatthe 1.44 was not a commercialprogramme, but would form thebasis of "a new fighter that willbe smaller and cheaper, but notworse, than the MFI".

This new design could resultfrom studied of the proposed1-2000 LFS (legkiy frontovoysamolyot) lightweight fighter,•which is expected to be jointlydeveloped by Mikoyan, Sukhoiand Yakovlev. The LFS is

Left: H the 1.44 is developed intoan operational fighter, itsflattened nose would be used tohouse a next-generation phasedarray radar.

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Below: On paper, the 1.42/44looks like an effective counterto the US Air Force's F-22, butthe chronic shortage of defencefunds in Russia makes itunlikely that such a heavy andcostly fighter will be adoptedfor service. A new lighter-weight design will probably beflown within the next fiveyears.

expected to meet any of theperformance goals originally setfor the MFI, but with a smalleraircraft offering lower operatingcosts. It is expected to combineradar and infrared stealth withhigh manoeuvrability and shorttake-off and landingcharacteristics.

For the moment, the bestfighter that Russia can offer isthe MiG-29SMT-2. Flown for thefirst time in April 2000, this isfitted with a Phazotron Zhuk-Mfire-control radar, RamenskoyeMFI-9 multifunction liquidcrystal displays, and a 2,000-litreconformal fuel tank installedover the fuselage spine. Newradar-dissipating coatingsreduce RCS to around 1 squaremetre. A similar MiG-29SMTupgrade uses avionics from theRusskaya Avionika company.

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SUKHOIS-37 BERKUT (GOLDEN EAGLE)

Length overall: 74ft (22.6m)Wingspan: 55ft (16.7m)Height 21ft (6.4m)Max. take-off weight: 74,9601b(34,000kg)Max. speed: Mach 2.1Service ceiling: 59,000ft(18,000m)Powerplant: two AviadvigatelD-30F6 turbofans each of20,9301b (9,490kg) dry and34,3921b (15,600kg) withafterburning

In the late 1980s, the Sukhoidesign bureau started work on

a technology demonstrationaircraft with a forward-sweptwing (FSW). This was a private-venture project funded bypayments received from exportsales of the Su-27.

Russian interest in FSWtechnology probably started inthe late 1970s. According toValery Sukhanov, deputy headof the Russian Central Aero-Hydrodynamics Institute(TsAGI), during the 1980s workon FSW designs in the formerSoviet Union and the USA hadbeen going on "practically inparallel".

By 1982 an earlier (FSW)demonstrator is reported to havebeen tested at Saki test airfield,and may have been evaluatedby the Russian Navy for possiblecarrier-borne use. It seems tohave been rejected, as was arival aircraft based on theMiG-23. The first carrier-basedfighter other than the semi-experimental Yak-38 was to bethe Su-33 derivative of the Su-27

The S-37 Berkut which tookshape in the mid-1990s wasintended to explore post-stallmanoeuvrability and"supermanoeuvrability" whichcould be applied to futurefighters. It combines forward-swept ring wings, a short-spantailplane, and broad chordbroad-chord foreplanes. Thehorizontal tail surfaces are of thetraditional all-moving pattern,but the canard foreplanes mayoperate differentially or inunison. The configuration hasbeen described as an "integratedtriplane".

Wherever possible theaircraft uses major sub-assembles from the Su-27 series,such as tailfins, canopy, andlanding gear. A forward-sweptwing needs high stiffness, so theS-37 wing is made almostentirely from composites. Theflight-control system is probablybased on the quadruplex digitalFEW system used on the Su-35and Su-37

The aircraft is powered bytwo Aviadvigatel D-30F6 two-shaft turbofans. This engine wasoriginally developed in the 1970sto power the MiG-31. Theversion used on the S-37 isprobably identical to that for theMiG interceptor, which has

completed several hundredthousand flight hours.

According to TsAGI, thecombination of FSW and thrust-vectoring gives better control athigh angles of attack, and super-manoeuvrability at subsonicspeeds. However, the currentengines do not have vectoringnozzles. At some stage in theflight-test programme theD-30F6 engines could bereplaced with the Soyuz R-79Mturbofans (a developed versionof the R-79-300 which poweredthe Yak-141 supersonic V/STOLfighter), Saturn/Lyulka AL-37FUturbofans with two-dimensionalvectoring nozzles (developed forthe Su-35 technologydemonstrator), or by theSaturn/Lyulka AL-41F AL-41Fengine from the MiG 1.44/42.

The aircraft may havestarted life as the Su-32, but hadbeen renumbered when theoriginal S-37 concept wascancelled in 1994 when it failedto attract Russian or exportbacking. (This was to have beena stealthy long-range multiroleaircraft similar in configurationto the Rafale, but single-engined.)

Although the S-37 wasintended to be technologydemonstrator, the designersmade provision for the futureinstallation of the mission

equipment and systems whichwould be needed to turn theaircraft into a prototype heavytwin-engined fighter. Forexample, it has forward- and aft-facing radomes, a vented gunbay with cannon port, a dummyIRST installation ahead ofwindscreen, and dielectricpanels in the leading edges ofthe foreplanes, LERX, and tailsurfaces which could be used tohouse EW antennas. The aircraftis reported to be fitted forconformal weapons carriage,

which would reduce RCS.The design also incorporates

other low-RCS features whichwould not be required in a puretechnology demonstrator. Thestructure incorporates radar-absorbent materials, the twintailfins are canted outwards toreduce front-sector RCS, the air

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intakes are shaped to reduceradar reflectivity, and connect tothe twin Aviadvigatel D-30F6turbofans via S-shaped internalducting which would screen thefront faces of engine fromforward-sector radar threats.Redesigned engine nozzles maybe configured to help cool theengine efflux, reducing theaircraft's ER signature.

Compared with the Su-27family of fighters, the S37 has "alower radar signature from thefront hemisphere", according toan ITAR-TASS publication

released at the 1997 Dubai airshow. This also stated that theaircraft incorporated "a coatingof radar absorbent materials".The first example flew for thefirst time at the Zhukovsky testcentre on 25 September 1997, butafter only eight flights wasgrounded in late November 1997for modifications. The tailplanewas increased in span and area,the engine installation wasrefined, and the avionicsupdated. Following thesechanges, flight testing wasresumed, and the aircraft was

publicly displayed at the August1999 Aviation Day at Tushino.

Although Sukhoi promotedthe aircraft as an alternative tothe Mikoyan 1.44/42, it seems tohave attracted little interest fromthe Russian Air Force, thoughthere have been suggestionsthat the S-37 and the 1.44 couldundergo a competitive fly-off.Even if the aircraft is notadopted for service, it has testedspin-off technologies whichcould be used to improve orupgrade the existing Su-27series and its derivatives.

Below:The Sukhoi bureaumakes no secret of its wish tosee the S-37 Berkut adopted asan operational fighter, and theprototype has been designedfor rapid conversion to acombat role. To date, theRussian Air Force has shownlittle enthusiasm for theconcept.

Below:The complex planformadopted for the S-37 has led tothe aircraft being described asan "integrated triplane".

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BOEING SIKORSKY RAH-66 COMANCHE

Role: reconnaissance/attack andair combat helicopterLength (fuselage): 43ft 3.75in(13.20m)Main rotor diameter: 40ft Oin(12.19m)Empty weight: 8,9511b (4,060kg)Take-off weight (primarymission): ll,6321b (5,276kg)Max speed: 172kt (319km/h)Tactical radius (internal fuel):ISOixm (278km)Armament: three HeMre or sixStinger missiles or otherweapons in each of twoweapons bays; four moreHellfires or eight Stingers onoptional stub-wings; GeneralDynamics XM-301 three-barrel20mm cannon in an undernoseturretPowerplant: two LHTEC T800-LHT-801 turboshafts each ofl,563shp (1,165k W)

•"Hhe first combat helicopterJ. designed to incorporate

stealth technology, the RAH-66Comanche is similar in size tothe AH-64 Apache which it willreplace. It will handle the USArmy's scout/attack mission, butwill also be able to engage in air-to-air combat.

Construction of theprototype began in November1993, with Sikorsky building theforward fuselage at Stratford,and Boeing building the aftfuselage in Philadelphia. Thetwo sections were mated atStratford in January 1995,allowing the completedhelicopter to be rolled out on 25May 1995. The first flight wasmade from Sikorsky'sDevelopment Flight Test Centerin West Palm Beach, Florida, on4 January 1996. The secondprototype flew in March 1999.

The airframe has a facetedconfiguration, and all armamentis carried internally, featuresintended to reduce RCS.According to official statements,the frontal RCS is 360 timessmaller than that of the AH-64,

250 times smaller than that ofthe OH-58D, and 32 timessmaller than OH-58D with mast-mounted sight. RCS of the entirehelicopter is lower than that ofthe AGM-114 Hellfire missile itfires. If necessary, detachablestub wings can be fitted to carryadditional weapons or auxiliaryfuel tanks, but this will degradeRCS.

like all modern attackhelicopters, the RAH-66 hasfeatures intended to blunt theeffectiveness of infrared-guidedmissiles. The efflux from theaircraft's twin T800 engines isducted through long, thin slots,then ejected beneath the chinethat runs either side of the tail.Total level of IR emission isaround a quarter that of theAH-64D, allowing the aircraft toenter service without a built-inIR jammer. (Provision has beenmade for the Advanced ThreatInfrared Countermeasuressystem to be fitted as anupgrade.)

Measures have also beentaken to reduce the acousticsignature. The five-blade all-composite main rotor system hasnoise-reducing anhedral tips (afeature first seen on the HMDaircraft), while the eight-bladetail rotor is of shrouded "fan-in-fin" type. Head-on, Comanche issix times quieter than theApache.

The planned level of radar,infra-red, acoustic and visualsignature are intended to defeatthe future threat systemspostulated by the US Army. Thelikely level of RCS wasmeasured during 2001 using a

full-scale model of the aircraftwhich incorporated all thedesign changes that had beenadded since an earlier series ofmodel tests.

As with the earlier AH-64Apache, great attention hasbeen given to survivability. Thecockpit is fitted with sidearmour, and an optional armourkit is available for the cockpitfloor, while the crew seats aredesigned to cope with thestresses of a 38ft/sec (11.6m/sec)vertical crash landing.

The nav/attack system willconsist of a nose-mounted sightwith IR and TV channels, plus alaser range-finder/designator.All aircraft will be fitted out tocarry a miniaturised and further-developed version of theLongbow millirnetric-wave radarcarried by the AH-64DLongbow Apache, but only athird of the fleet will beequipped with this sensor.Defensive aids will include radarand laser warning receivers,

plus an RF jammer.There has been some weight

growth during development; by1992 the original target of 7,5001b(3,402kg) for empty weight hadbeen relaxed to 77651b (3,522kg)to accommodate additionalsubsystems demanded by thecustomer. The new anhedral-tipped main rotor blades devisedto reduce the aircraft's acousticsignature are 12in (305mm)greater in diameter than theoriginal pattern, allowing theaircraft to maintain its specifiedvertical rate of climb without theneed for an expensive and time-consuming weight reductionprogramme. The original bladeshad a 15in (380mm) chord, butthis was increased to provideadditional survivability, and toallow the use of materials for

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signature control which werenot practical with the narrowerchord.

Tail buffeting problemsuncovered during flight-tests ofthe first prototype were found tobe a result of the airflow fromthe main rotor mast impingingmore strongly on the vertical tailthan had been expected. Aredesign slightly reduced theheight of the vertical tail, andadded vertical endplates to thehorizontal stabilizer tocompensate for any reduction indirectional stability. Flight-testedin the winter of 2000/01, itproduced no significant weightpenalty, and did not degradationthe aircraft's low-observablecharacteristics.

The upper part of the tailfolds down for air transportation.Once the main rotor has beenremoved, eight Comanches canbe loaded into a Lockheed C-5Galaxy. On arrival, the mainrotor is re-fitted and the tailunfolded, and the helicopter canbe ready for flight only 20minutes after being unloaded.

Engineering andmanufacturing development(HMD) started in 2000 and is dueto end in December 2006. Thisphase of the programme isexpected to require 13 furtheraircraft - five for flight-testingand eight to be used in initialoperational tests andevaluations.

The US Army plans to buy1,096 Comanches. Beforeproduction is begun, theprogramme will undergo severalreviews to assess aircraft weight,in-flight vibration levels, andprogress with integrating theaircraft's radar and other missionequipment. Initial operationalcapability is expected inDecember 2006.

Above: This drawing shows theRAH-66 with the definitivetailplane devised to curebuffeting problems. Theaircraft's sloped fuselage sidesand shrouded tail rotor all helpkeep RCS to a tiny fraction ofthat of the AH-64 Apache. Thebuilt-in stealth capability isintended to defeat all knownand predicted threats.

Right: These stealthy hunterswill be formidable anti-armourweapons, but cost will limit thenumbers purchased.

129

AIDS TOSTEALTH"Tmagine a man with a

Lpowerful flashlight tryingto find another man on a darknight", says Tom Amlie, formertechnical director of the ChinaLake Naval Weapons Center."He might find him at 100-200feet (30-60m). The other mancan see the flashlight at arange of at least one-half mile(0.8km). To pursue the analogya bit farther, if the second manhas an automatic rifle andhomicidal tendencies, thefellow with the flashlightcould be in deep trouble."

It is a neat little story andone which formed part ofAmlie's outspoken attack onthe US over-dependence onradar, a central theme of a1987 interview with TheWashington Post. It is also agood analogy of the problemfacing operators of stealthaircraft. The use of stealthtechnology to reduce thedetectable signature offighters and strike aircraftdoes much to reduce theirvulnerability but, on its own,signature-reduction is notenough. The stealth aircraft'son-board systems must also bedifficult to detect.

Ideally, a stealth fighter orbomber should emit no radar,radio, IR or EO energy whichmight betray its position.Many of the traditionalavionics systems carriedaboard military aircraft, suchas high-powered radars,Doppler navaids, IFFtransponders andconventional communicationsequipment, must beeliminated as far as possibleand be replaced with stealthyequivalents. In practice, thiswill be hard to achieve. Ifpassive replacements cannotbe devised, the traditionalequipment must be redesignedto keep the amplitude of itsemissions as low as possible,preferably in areas of thespectrum less intensivelymonitored than the radio andradar bands.

RADARS

Most obvious candidate forredesign is the aircraft's radar.Conventional systems mustgive way to new LowProbability of Intercept (LPI)designs. Exact details of LPI

Above: Warplanes such as theF-15 Eagle rely on theirpowerful radars for targetdetection, but such easily-detectable emissions wouldbetray a stealth fighter.

Radar Waveforms

Below & Right: A stealthy lowprobability of intercept (LPI)radar will use long pulses oflow amplitude rather thanthe more detectable tauttraditional short high-

amplitude pulses. Its antennawill also be designed to havea narrower beam and smallersidelobes, so will offer lessstray radiation to hostile ESMreceivers.

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radar technology remainclassified but many can bededuced.

For a start, the signaltransmitted must be of a typewhich will be hard to detectby ESM. This involves using awide-band waveform with ahigh duty cycle, ideally onewhich has noise-likecharacteristics. Aconventional pulse radar has alow duty cycle and transmitspowerful but narrow pulses ofenergy. A high duty cycleradar will transmit muchlonger pulses, but at a lowerpower level, and will spreadthis radiated energy over a

Radar Beam Shapes

LPI narrow main lobe

wide range of frequencies inthe hope that it will becomeinconspicuous to an enemyESM system effectively"buried" among the normalbackground of civil andmilitary radar signals andcommunications links whichclutter the microwave region.

The technique is not assimple as it sounds. Oneadvantage of a low duty cycleis that the radar's receiver canlisten for the returned echo attimes when the transmitter issilent and can thus share thesame antenna. The LPI radarwill have to transmit andreceive at the same time, so

must either use two antennasor rely on sophisticated signalprocessing.

To further reduce thechances of the signal beingintercepted by an ESMsystem, it must be confined tothe narrowest beam whichwill meet the tacticalrequirements for which theradar is designed. The use ofa high frequency will give thenarrowest possible beam froman antenna of fixeddimensions, while carefulantenna design will minimisethe size of the sidelobes(unwanted minor beams atdifferent angles).

Smallside lobes

Conventional wide main lobe

Above: By means of theJTIDS data link, E-3 Sentryaircraft will be able to passtarget information to NATOfighters, allowing the latterto avoid using radar.

In the long run, it will beimpossible to disguise a LPIradar's powerful (albeit muchnarrowed) main beam butdenying the enemy anychance to exploit sideloberadiation will be a major stepforward. The chances of main-beam detection will bereduced largely bytransmitting only in shortoccasional bursts, retainingthe radar "snapshot" betweentransmissions, and updatingtarget tracks by deadreckoning.

In an air battle involvingstealth fighters, it is likely thatat any one time only a fewaircraft - AEW platforms andsome long-range interceptors- would rely on active radar.Using LPI communications,these aircraft would passtarget data to the others. It ispossible to imagine tactics inwhich each stealth fighter inturn might use its own radarfor a few seconds, then jinkonto a new course whiletransmitting targetinformation to the rest of theformation. Next generationradars such as those proposedfor EFA and Rafale have a

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Largersidelobes

large number of operatingmodes. Switching rapidly fromone to another may helpcomplicate the task faced byan enemy ESM system.

B-2 SYSTEMSThe F-117A relies entirely onelectro-optics for target locationand weapon-aiming, but for theB-2, Raytheon ElectronicSystems developed the J-bandAN/APQ-181. This lowprobability of intercept radar has21 operating modes for terrain-following and terrain-avoidance;navigation system updates;target search, location,identification and acquisition;and weapon delivery.

Each B-2A carries two 2,1001b(953kg) radars, each made up often line-replaceable units (LRUs)including two electronicallyscanned antennas. The LRUs aremounted in the walls of thenose-wheel well, while theantennas are behind largeradomes close to the aircraftcentreline and just below theleading edge. To ensure missionreliability, all LRUs apart fromthe antennas are able to functionas part of either or both radars.

F-22 RADAR

For the Lockheed Martin F-22,Northrop Grumman isdeveloping the AN/APG-77multimode radar. This uses anactive electronically-scannedantenna made up of around2,000 individual transmit/receivemodules, and makes extensiveuse of Monolithic MicrowaveIntegrated Circuit (MMIC) andVery High-Speed IntegratedCircuit (VHSIC) technologies.Operating modes are reported toallow long-range detection of airtargets (including stealthaircraft) in all weathers, targetrecognition, multi-missile multi-target engagement, anddogfight engagements. Theradar is designed to cope withheavy clutter environments, andoffers advanced air-to-surfaceoperating modes.

With the F-22, the boundariesbetween radar and EW begin toblur. The AN/APG-77 isreported to have a high-gain,passive listening mode whichcovers a bandwidth or around 2GHz in the forward sector. At arange of around 120 miles(190km), the AN/APG-77 isreported to have an 86 per centprobability of detecting a targetwith an RCS of Isq m with onlya single radar "paint" whichwould give the target aircraft'sradar-warning receiver aminimal signal to detect. AnUltra High-Resolution (UHR)mode used for targetrecognition is said to have aresolution of 12in (30cm) at arange of around 100 miles

(160km), more than enough fornon-co-operative targetrecognition.

The F-22 will not be the firstfighter to offer passiveidentification of non co-operating targets. Under theMSIP (Multi-StagedImprovement Program)upgrades applied to the F-14Tomcat and F-15 Eagle, bothaircraft are being given a degreeof passive target identification.This area is highly-classified butis largely a matter of signalprocessing. There is a relationshipbetween target shape and thecharacteristics of the reflectedwave, so inverse scattering isone of the few clues -which willallow a radar to identify abeyond-visual-range target.

Aircraft approaching head-

on may be identified byanalysis of the radar returnsfrom the engine inlets, sincethe signal will have beenmodulated by the spinningblades of the first-stage of theengine fan/compressor. Suchmodulation effects have beenknown for some time. Thehuge contra-rotatingpropellers on the Kuznetsovengines fitted to the Tu-95and -142 Bear aircraft madethem easily-recognisableradar targets on analogueradar displays, while earlytests of the APG-63 radarused in the F-15 Eagle showedthat the modulated radarreturn from the enginecompressors could beinterpreted by the radar as amultiple target.

Above: During this Dorniertrial, an experimental laserradar produces recognisableimages of a group ofvehicles.

Above right: In-flightrefuelling extends the rangeof the B-2, giving thenumerically small force aglobal reach.

Below: The massive contra-rotating propellers on theTupolev Bear create adistinctive and recognisableecho on western radars.

Below right: This Thomson-CSF photo is an example ofthe high-resolution imageryavailable from a radar whichuses SAR techniques.

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LASER RADAR

Many of the problems associatedwith microwave radar can beeliminated by using a laserradar. The very narrow beambeam would be difficult todetect, and would have nosidelobes through which energycould leak. Performance wouldbe dependent on weather, andlaser radars would be of shortrange. Air-to-ground seems amore likely role than air-to-air.By scanning the terrain ahead ofthe aircraft, the laser radarwould be able to build up animage of FLIR-like quality, alsoobtaining range and velocityinformation which could beused for targeting and terrainfollowing.

One of the first equipments ofthis type was developed byHughes in conjunction withGeneral Dynamics. Althoughintended for use in cruise missileguidance systems, it clearlycould be used in place of aconventional terrain-followingradar. Trials have shown that alaser radar has a betterresolution than that availablefrom millimetre-wave seekers oreven thermal imagers, saysHughes. Tests have shown that itcan detect trees and electricitypylons.

EO SYSTEMS

In the past, some aircraft haveused, infra-red or other types ofelectro-optical sensor for targetrecognition and fire-controlpurposes. Examples include theAAA-4 IR sensor on early-modelPhantoms, the ASX-1 Tiseo(Target Identification SystemElectro-Optical) in the wingleading edge of some F-4Es, andthe EO systems in the nose ofthe MiG-29 and Su-27.

On a conventional fighter, theEO system is a secondarysensor, but the passive nature of

EO systems make them idealfor use of stealth fighters. Forthe F-117A, Texas Instrumentsdeveloped a forward-lookinginfra-red (FLIR) sensor, and adownward-looking infra-red(DLIR) sensor and a laserdesignator. Mounted in acavity in the upper nose, theFLIR had two fields of view,and was shielded from enemyradar by a fine mesh screen.The DLIR and laser designatorwere located beneath theforward fuselage to starboardof the nosewheel bay. FLIR andDLIR imagery was viewed on alarge cockpit-mounted head-down display located betweenthe aircraft's two multifunctionCRT displays. Targets wereinitially detected by the FLIR,then at closer range were

"handed over" to the DLIR,with the laser being used forranging and target-illumination.

In the mid-1990s, the existingTI sensors -were replaced by ainvolved new turret-mountedInfra-Red Acquisition andDesignation Sensor (IRADS).

DIGITAL MAPS

Radar is also widely used as anavaid and as a method ofsteering the aircraft in terrainfollowing flight. FLIR systemsare one passive alternative toradar but the pilot tasked -withmanually flying a longmission at very low levelusing only the small field ofview presented by FLIR-derived HUD imagery has an

unenviable task. Thedevelopment of powerfulairborne computers has madepossible a stealthyreplacement for theconventional terrain-followingradar. Known as terrain-reference navigation (TRN),this relies on carefulmeasurement of the profile ofthe terrain passing beneaththe aircraft and its comparisonwith digitally-storedgeographic data.

Measurement of the terrainis done using a radaraltimeter. At first sight thismight seem a weak point ofthe system, particularly iffitted to a stealth aircraft. Inpractice, radar altimeters havea narrow beam-width and lowpower output, directing theirenergy downwards ratherthan forwards, so are thus apoor target for enemy ESMsystems.

DATABASES

A conventional terrain-following radar (TFR) can only"see" the terrain ahead of theaircraft and within radarrange. It has no informationon terrain concealed by ridgelines. This is not shown untilthe aircraft has reached aposition \vhere the radarbeam can illuminate theconcealed terrain. Thanks toits database, a TRN system"knows" the terrain overwhich it is flying and canpredict the profile of theground well ahead of theaircraft's current position,even if this region is

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concealed by a ridge or peak.By using this information, theTRN system can initiate pull-up and descent manoeuvres atthe optimum time, minimisingsudden unwanted gains inheight (or "ballooning") of theaircraft flight path.

TRN obviously requiresterrain irregularities in orderto "fingerprint" and identify itscurrent location. Deprived ofthese irregularities whenflying over water or flat ground,the system must rely on INSdata. The use of Kalmanfiltering (powerful software forcombining multiple inputs)allows gyro drift to beestimated, maintaining systemaccuracy until TRN-suitableground is once moreoverflown. The accuracy of agood TRN system is a few tensof metres in the horizontalplane, and about 10 to 20ft (3 to6m) vertically.

NAVAIDS

For routine navigation of long-range stealth aircraft such asthe B-2, other passive navaidsare required. Over a longmission, an inertial navigationsystem slowly drifts, building upand ever-increasing error. Twodecades ago this could only beremoved by obtaining anaccurate positional fix, butmodern navigation systemsteam INS with an integratedsatellite-navigation receiver.The accuracy of the encryptedP-code signal from the USGlobal Positioning System(GPS) satellites is higher thanthat from the C/A-code signalused by civilian receivers, soaircraft fly using satnav dataand rely on the INS only if thesatellite signals are lost due tojamming or sharp aircraftmanoeuvres.

Until the late 1980s, fewindividuals outside the highly

classified world of "black"programmes realised thatLockheed-Sanders had becomea major player in the new fieldof automatic mission planning.The concept had been born ayear after the F-117A enteredservice, when a group ofLockheed engineers developeda system in only 120 days. Basedon two computers loaded withgeographic, intelligence, aircraftand weapon data, the systemcan plan sorties, routing theF-117A around the mostdangerous threats, and bringingit over the target at thespecified time. To maximise theeffectiveness of the aircraft'slow-observable features, thesystem generates a flight paththat carefully orientates theaircraft to maximise itsstealthiness in the direction ofthe most dangerous radar orSAM systems.

Automatic mission planningis also important for the B-2A.First introduced as part of theblock 30 upgrade to the B-2A,the AFMSS provides the crewwith the most effective routingthat will accomplish the missionwhile providing the highestsurvivability. The system wasinitially unsatisfactory, but anupgrade which included a newcomputer with faster speedsand new software was intendedto correct most of thedeficiencies identified duringinitial operational testing.A March 1999 B-2A foUow-ontest and evaluation reportshowed that a softwarecomponent known as thecommon low observable auto-router (CLOAR) still haddeficiencies. While theupgraded AFMSS was capable

Right: Originally used byhelicopter aircrew, night visiongoggles (NVG) are a stealthyalternative to terrain-warningradar.

Above: Hughes APG-65 radarfor the F-18 uses target-recognition software whosealgorithms are kept secret bythe US Government.

of planning most B-2 A missionswithin the eight-houroperational requirement, theCLOAR shortcomings wouldextend the time taken to plansome missions to ten hours.Although new CLOAR softwarewas developed for delivery tothe operational B-2A wing byearly 2000, the USAF acceptedthat even with the CLOARimprovements there would besome small percentage ofmissions that could take longerthan 8 hours to plan because ofthe complexity of thesemissions and their plans.

Above: Electro-optics in action:this F-4 Phantom is fitted with awing-mounted TISEO TVsensor, and carries a GBU-15"smart" bomb.

ESM SYSTEMS

Since stealth aircraft operatepassively for most of the time,they will make extensive use ofa sophisticated ESM system towarn the crew of nearby threats.A next-generation ESM systemmust be able to cope with radar,millimetre-wave, IR and laserthreats. It must be able todetermine the location andnature of all threat systems,warning aircrew if they arebeing tracked, have beentargeted or are being engaged.

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In the long run, it should bepossible for stealth aircraft suchas the F-22 to detect enemyfighters via ESM, then launchfire-and-forget missiles. Not untilthe missiles' active seekers wereenergised "would the enemypilot realise that he was underattack.

ESM plays a vital role inkeeping the crew of a stealthaircraft aware of the location andidentity of potential threats,allowing them to makeadjustments to the mission planto ensure survivability. On theF-117A, the pilot is warned ofthreats to the aircraft, andaccording to one report the ESMsystem is linked to themechanism which opens theweapon bay doors. Sinceopening these adds a reflectivesurface (the door) and a cavity(the bay) to the lower surface ofthe aircraft, it temporarily stripsthe aircraft of its stealth qualities.If a dangerous threat isilluminating the aircraft, theESM system reportedly preventsthe door from opening.

The USAF spent over $740million to develop the defensiveavionics for the B-2, only to findthat this did not provide theplanned capability.Developmental and initialoperational testing showed the

system either incorrectlyidentified threats or did notprovide an accurate location ofthreats, significantly reducingthe situational awareness to thecrew. The USAF concluded thatthese deficiencies would be toocostly to correct, and decided tomodify the defensive avionicssystem to provide a usefulcapability, but less capabilitythan had originally beenconsidered necessary. Acombination of effective tactics,mission planning, and lowobservability features would stillprovide adequate survivability, itbelieved. The failure of thedefensive avionics to provide thecrew with all of the intendedsituational awareness infor-mation did not prevent use ofthe B-2A in combat operations.

ESM needs to be backed upby a reliable missile-warningsystem able to detect passivelyguided rounds, or those whoseradar parameters are unknown.First attempts to develop asystem of this type involvedspecialised radar-warningreceivers designed to detect

Below: More than 300 USNF-14A Tomcats are fitted with aNorthrop Television CameraSet (TCS) target identificationsystem.

Above: The spherical housingahead of the windshield of theMiG-29 houses stabilised opticsshared by an IR sensor andlaster rangefinder.

Below: This infra-red air-to-ground image of oil tanksshows the level of liquid ineach. Such information can beuseful during an attack.

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changes in radar threat signalswhich intelligence-gatheringhad identified as beingindicative of SAM missilelaunch. Equipments of this typewere designed to be effectiveagainst only one or two types ofSAM. Creation of a moregeneral-purpose missile warnerinitially relied on detecting theIR energy for the missile's rocketmotor. Early equipments of thistype were not very successful,and had a high false-alarm rate.

An obvious alternative was touse a low-powered aft-facingradar. One successful example isthe Sanders ALQ-156, a tinypulse Doppler radar whichprovides 360 degree coveragefor US Army CH-47 Chinookhelicopters. In the UK, Plesseydeveloped the Missile ApproachWarner (MAW) for use on theRAF's Harrier GR.5 (AV-8B)fighters. MAW is a low-poweredpulse-Doppler radar, and hasbeen designed to trigger therelease of flares or other decoysat the optimum moment.

Active warners have two greatoperational advantages. Theycan detect empoweredprojectiles such as anti-aircraftartillery rounds, and canmeasure range. Their Achillesheel is that they emit radarenergy that might be detectedby enemy ESM systems.Designers of radar warners tryto keep the level of poweremitted to an absoluteminimum, but cannot eliminatethis tell-tale energy.

hi the long run, the future maybelong to improved IR warners.The Honeywell Electro-OpticsAAR-47 is fitted to some US P-3Orions, helicopters and fixed-wing transports, and is alsoplanned for the V-22 Osprey tilt-rotor. Honeywell is now "workingwith General Dynamics todevelop a version for use on the

F-16 Fighting Falcon.Data from both the ESM and

missile-warner need to beintegrated into a single displayable to inform aircrew if theyhave been detected, tracked orengaged. Given a degree ofartificial intelligence, suchequipment might also be able tosuggest the bestcountermeasure or mix ofcountermeasures.

Hughes Aircraft (now part of

Raytheon) has devised a totallypassive technique for locatinghostile radar emitters. This isbased on terrain reflections, sodoes not require direct line ofsight to the emitter; all that isrequired is that there existterrain areas that are mutuallyvisible to both the hostileemitter and to the aircraft-mounted receiver. Tests using abrassboard system suggest thatan operation version could

Terrain Following System

TFR beam givesadvance warningto enemy ESM

Terrain Reference System

Above:lt's not necessary toown a spy satellite to createdigital maps like these. TRNsystems will work with Landsator Spot data.

locate non-co-operatingemitters to within a CEP of lessthan 1,640ft (500m)independent of range andazimuth. Since no line of sightis required, the sensor wouldallow the pilot to locate radar

Left and below: A terrain-referenced navigation (TRN)system compares radaraltimeter readings with pre-stored geographic data, so canpinpoint its location. Anaircraft relying on terrainfollowing radar will tend togain height by "ballooning"over obstacles (top left), butthe TRN-equipped aircraft(bottom left) can predict theterrain ahead, so can fly closerto the ground.

TRN Grid

TRN signals giveno advance warning

TRN compares groundwith stored database

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Burn-Through RangeTarget hiddenin jamming

Above: Even when hidden by ajamming strobe, a target willeventually become visible onceits echo is strong enough toburn through the jamming(left). Reduce target RCS andyou reduce the echo strength.The target must come muchcloser (right) before the newburn-through range is reached.

threats before being exposedto them, giving him the chanceto use terrain masking andavoid detection. Such acapability would reduce thetactical advantages normallyobtained by deploying mobileair-defence systems whoseposition cannot be predictedby the attacker.

Reducing aircraft RCSprovides advantages whendesigning self-protectionjammers. Since most EWtechniques rely on swampingthe echo from the target withnoise, or seducing the hostileradar away from the truetarget by providing it with anacceptable but false substitute,any reduction in the size ofthe genuine echo must be ofbenefit.

EW engineers use the term"J.S. ratio" to describe theratio between the strength ofthe normal radar return froman aircraft and the signalwhich the hostile radarreceives from the jammer. Asthe distance between theradar and the target isreduced, this ratio degrades,with the true echo becomingstronger and stronger until itis detectable through thejamming.

JAMMINGThe term "burn-throughrange" is used by engineers todescribe this vital distance at•which the EW system gives nofurther protection. Its valuedepends on the power of theradar transmitter, thesensitivity of the receiver, thepower of the jammer and theRCS of the target. The need tokeep burn-through range aslarge as possible led Sovietdesigners to install a massive

Right: The Visually CoupledAirborne System Simulateprogramme was expected toprovide technology for thecockpit of the YF-22/23 ATF.

600kW transmitter in the FoxFire radar carried by theMiG-25 Foxbat.

If the RCS of an aircraft isreduced, the amount ofjamming power needed toachieve the same burn-through range falls by thesame amount. Since highlevels of jamming powerinvolve large, bulky andpower-hungry transmitters,stealth is obviously good newsfor the designer of EWsystems. If the aircraft plans torely on the use of chaff ratherthan jamming, the reductionsin the amount of chaff neededare similar to those forjamming power.

Over the life of the B-52,some $2,600 million has beenspent on EW upgrades. Thecurrent system weighs about5,5001b (2r500kg) and consistsof 238 LRUs (line-replaceableunits). Given that the B-1B hasa radar echo only 1 per cent ofthat of the older bomber, itwould at first sight seemreasonable to assume that thelower levels of jammingpower needed would result ina lighter EW suite. In practice,the Rockwell aircraft carriesabout 5,0001b (2,250kg) of EWequipment, virtually noweight saving.

The likely reasons are nothard to guess. If RCS isreduced by a factor of fourwhile keeping the amount ofjamming power constant, theburn-through range will behalved. Reduce it by a factor often and the burn-throughrange will fall to less than athird; while an RCS of one

Right: On the B-S2, high levelsof jamming power wererequired to swamp thebomber's huge radar echo. Lesspower is needed to mask theB-lB's reflection, so thedesigners of this EW suite wereable to allocate more weight tosophisticated signal processing.

B-1B Defensive Avionics

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Stealth targetburn-throughmuch closer

Burn-throughrange

Above: Every four-vehiclebattery of these SA-6 SAMsrelies on a single Straight Flushradar, so is vulnerable tostealth.

hundredth of the originalvalue will reduce burn-through range to a tenth of itsoriginal value.

Rather than accept all of thepotential weight saving whicha lower level of transmitterpower would allow, the USAFwill have opted to have extrapower in hand in order toincrease burn-through rangewell beyond that available tothe B-52. The ALQ-161 systemon the B-1B is also likely todevote more of its weight tosignal-processing circuitry,allowing the use of the mostadvanced decption jammingtechniques.

EW SYSTEMSEW systems must be updatedto adapt to the latest threattechnologies. Even today nosingle EW technique can cope

Right: Flares remain aneffective counter to IR-guidedmissiles, and are cheaper todevelop and deploy than IRjammers.

with all types of radar-guidedweapon. Next-generationECM suites will have toincorporate the normal radarbands, plus millimetre wavesand IR wavelengths. They willalso be tightly co-ordinatedboth with the aircraft's ESMand missile-warning systemand with the systems whichrelease towed or expendabledecoys.

Some indication of futuretrends in EW was provided inthe spring of 1988 whenFrench electronics giantThomson-CSF revealed thedirection which its ownelectronic-warfare effortswere taking. Stealthtechnology and low-leveloperations may reduce thevulnerability of future combataircraft, explained Thomson-CSF Technical Director PierreBaratault, but the importance

of electronic countermeasuresis undiminished.

Low-peak radars, such aspulse Doppler radars andmissiles fitted with solid-stateactive seekers, force anincrease in EW receiversensitivity, while newjamming techniques designedto counter techniques such asmonopulse radars demandhigher levels of transmitterpower. "Detailed analysis ofpotential threats indicates thatall of the most significanttechnical characteristics (ofEW systems) will have to beincreased by one or twoorders of magnitude." Tocomplicate the problem, thesefuture high-powertransmitters and sensitivereceivers will be required tooperate simultaneously.

Radar, IR and laser warningsystems, jammers and decoysmust be integrated into acoherent defensive system,which in turn must be fullyintegrated into the aircraftwhich carries it.

TOWED DECOYSOne relatively new type ofEW system is the toweddecoy. Widely used bywarships since the early 1940sas a method of counteringacoustic homing torpedoes,towed decoys were notseriously promoted for aircraftuse until the late 1980s. Thesedevices take the form of a smallradar jammer towed behind theaircraft it is protecting. Beingvulnerable to destruction oraccidental loss, this is kept assimple as possible, with most ofthe signal processing beingcarried out by avionics mountedwithin the aircraft and linked tothe decoy via the towing cable.

The current US towed decoyis the E-Systems ALE-50, whichwas selected for use on theFA-18E/F, B-1B, and F-16. Theaircraft-mounted hardwareincludes the onboard techniquesgenerator, a sub-system thatcombines a receiver and a

Lett: This Luftwaffe Tornadohas a BOZ chaff pod andCerberus jammer. Stealthaircraft will also require EWsystems.

Right: Matra developed theSycomor chaff-dispensing podfor use on fighters such as theMirage Fl, but it could also beused to protect Rafale.

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processor. The jammingmodulations devised by thetechniques generator areconverted from electrical signalsinto pulses of light, which passdown a fibre optic towing cable,and control a travelling-wave-tube (TWT) transmitter in thedecoy. The fuselage-mountedreceiver win monitor the signalsfrom the threat being jammed,and can use the resultinginformation to refine thejamming signals being sent tobe decoy.

Similar decoys are beingdeveloped in Europe. GECMarconi (now part of BAESystems) started developmentwork on towed decoys in themid-1980s and the resultingAriel decoy entered service onthe British Aerospace Ninrrod in1990. The company has alreadytested towed decoys atsupersonic speeds usingTornado trials aircraft, and isresponsible for the wingtip-mounted towed decoy whichforms part of the defensive aidssub-system (DASS) of theEurofighter 2000.

The Swedish companyCelsiusTech has developed theBO2D towed decoy to provide

protection against radar-guidedmissiles which use Dopplersignal-processing. After release,it acts as a wide-band repeaterjammer which can be turned onor off and switched from onemode to another by signals sentdown the tow line by theaircraft. BO2D operates in H, Iand J bands, and can counterseveral Doppler-based threatssimultaneously.

Although Daimler-BenzAerospace is developing atowed decoy, this does not formpart of the currentKampfwertanpassung/Kampfwerterhaltung (KWA/KWE) mid-life improvement programme forLuftwaffe Tornado IDS, but islikely to be fitted as a futureupgrade. Suitable for use onfighters or transports, and forinstallation in existing EW pods,it uses a monopulse anglejamming technique.

For a long time the primarythreat to aircraft was seen asbeing radar-guided weapons,so the bulk of Western EWfunding was applied to thecreation of RWRs and radarjammers. This was the resultof the large-scale use of SA-2,SA-3 and SA-6 missiles in theconflicts of the 1960s and1970s. A recent USDepartment of Defense studyof combat losses in the decadefrom 1975 to 1985 revealed that90 per cent of the tacticalaircraft downed fell to IR-guided air-to-air missiles orIR-guided SAMs.

CHAFF AND FLARES

In the past, such IR threatswere detected visually andcountered by manoeuvringand/or the release of flares.This worked well againstthreats such as the AA-2 Atollor SA-7 Grail. These oldermissiles were essentially "tail-chase" threats but the latestmodels of missile have betterseekers, offering all-aspectattack capability and goodresistance tocountermeasures.

Flares will have some effectagainst such weapons,particularly the newer typesbeing developed in the late1980s. Current dispensers areused to release chaff, IRcartridges or expendable

Above: Even zero RCS woulddo nothing to protect an aircraftfrom this Stinger SAM. IRsignature must also be kept to aminimum.

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Below: ALQ-159 IR jammer onthe tail of a Chinook. Manycurrent units of this type weredeveloped for helicopterapplications.

Above: The hunter and thehunted - the F-117 can deliverlaser-guided ordnance on high-priority targets such as thishardened shelter.

active decoys. Future trendsare likely to be the use of"smart" dispensers, able torelease decoy payloads only inthe direction of the threat, andalso by the development ofmulti-spectral expendablecartridges.

IR JAMMERSCountering the moresophisticated IR threats willrequire the use of IR jammersbut to date such systems haveonly been installed aboardhelicopters and transports. Thetechnology needed to createIR jammers for fighter use wasnot available; the existingmodels of IR jammers werelarge, power-hungry andunable to mimic the highnozzle and effluxtemperatures of after-burningengines. In the case of astealth aircraft, the low IRsignature would in theorymake current IRCMtechnology usable but, inpractice, new types of IRjammer will probably becreated for deployment onstealthy and non-stealthyfighters alike.

The earliest IR jammers usedelectrically-powered or fuel-heated hot elements as theirsource of IR energy, but by theearly 1980s, IR tubes werebeing used. All these patternsof IR jammer radiate theirlimited jamming energy over awide volume so may be tooweak to jam advanced seekers.

For a fighter-based IR jammer,

Above: Most RWR systemsincorporate a small CRT screenwhich shows the bearing andnature of detected threats.

Left:Five antennas, twoelectronics units, a control unitand a display are all that isneeded to locate radar threatsto a helicopter.

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Above: AGM-88 HARM, seenhere on a German Tornado, isthe most effective anti-radiationmissile. The EW pod isGermany's Cerberus.

Below left: The EF-111 Ravenwas an effective jammingaircraft, but the decision tophase out the F-lll doomed it toearly retirement.

Below: AGM-88 HARM anti-radiation missiles, (wings andfins not yet installed), arewheeled toward a FLIR-equipped A-7 Corsair.

a more likely power sourcewould be an IR laser, whosenarrow beam would generatethe high levels of power neededto defeat the latest types ofimaging IR seeker. The onlypractical solution is a directionaljammer that uses some form ofsensor to track the incomingmissile, then aims a highly

directional beam of modulatedfR energy at it. Since thejamming energy is concentratedin the direction of the threat, thejammer-to-signal ratio seen bythe seeker is maximised.

The two main directional IRsystems currently underdevelopment are the NorthropGrumman Nemesis DirectionalInfra-Red Countermeasures(DfRCM) system and theSanders ALQ-212 AdvancedThreat Infra-RedCountermeasures (ATIRCM).Nemesis uses a modified versionof the Westinghouse AAR-54 (V)ultra-violet missile warningreceiver to detect and tracktargets and to steer its jammer,while ATIRCM relies on theAAR-57 Common MissileWarning System. At presentboth systems use an arc lamp asa source of jamming energy. Inthe longer term Nemesis couldbe fitted with a laser tosupplement the arc lamp, while

the ALQ-212 will switch to amulti-band laser. Both areintended for use on transportsand helicopters, but work isunder way to miniaturise thistechnology to the point -where itcan be used on fast jets.

EW FOR FIGHTERSIntegrated EW installations areplanned for all next-generationfighters. The Sanders AN/ALR-94 electronic warfare EW systemfor the F-22 is part of a highlyintegrated avionics suite whicheffectively combines the radar,ESM, communications andidentification functions into asingle system while presentingthe pilot with the relevant data,and controlling the level ofemissions from the aircraft tomatch the tactical situation. It ismade up of apertures,electronics, and processors thatdetect and locate threat signalsand control the release ofexpendable countermeasuressuch as chaff and flares viaAN/ALE-52 dispensers. It alsoprovides a missile launchdetection capability.

Similar systems are beingdeveloped in Western Europe.The BAE Systems towed decoymentioned earlier as part of theDASS on Eurofighter 2000 formspart of an integrated suite whichalso includes an RWR, LWR,MAW, and chaff/flaredispensers.

In 1989 Dassault Electroniqueteamed with Thomson-CSF to•work on the electro-magneticdetection and jamming systemfor Rafale. It is responsible forthe warning and ESM parts ofthe resulting Spectra system,plus the jamming techniquesgenerators, while Thomson-CSFhas teamed with Elettronica toproduce the system's solid-statejamming transmitters. Full-scale

development of Spectra beganin 1990, and eight prototypeshave been built. These havebeen tested on a Mystere 20 andon a Mirage 2000 prototypedevoted to Spectra developmentand integration.

JAMMERS

Just like conventional fightersand bombers, stealth aircraftneed the support of stand-offjamming aircraft. In the late1980s, the USAF relied on theEF-111A Raven stand-offjamming aircraft, F-111A fighter-bombers which had be rebuilt inthe early 1980s as EW assets.These had been expected toremain in service until around2010, but when the collapse ofthe Soviet Union and theWarsaw Pact allowed the USAFto retire its F-lll fleet, theeconomics of retaining theEF-111A proved unviable, so theEW variant was retired in thesummer of 1998, leaving theUSAF dependent on the USNavy's force of EA-6B Prowlerjamming aircraft.

This in turn required the USNto increase the number ofProwler squadrons from 14 to 20,expanding the 80-strong force tomore than 100 by returningstored aircraft to operationalservice. The limitations of such asmall force were demonstratedin 1999 when the US found itselfinvolved in two simultaneous aircampaigns in the skies over Iraqand Yugoslavia.

Before the start of OperationAllied Force againstYugoslavian forces operating inKosovo, the DoD had to dispatchan additional eight EA-6B to theregion, where the Yugoslavianair defences were assessed asbeing far more dangerous thanthose in Iraq. Most combatmissions flown over Yugoslavia

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during Allied Force weresupported by EA-6Bs.

During that conflict, the USAFstudied the possibility ofmodifying a B-52H bomber forthe EW mission. The resultingEB-52 would have carried ALQ-99 jamming pods under itswings. Although not put intopractice, it generated longer-term interest in the possibility ofcreating a dedicated EW variantof the B-52, B-1B or even the B-2.If the plan goes ahead, the endresult could be an EB-52 fittedwith the Improved Capability-3(ICAP-3) jamming system beingdeveloped for the EA-6B. Theaircraft would be able to stay onstation about 12 hours, standingoff at ranges of more than 150miles (240km). A similar upgradeof the B-1B could create an EB-1able to escort strike forces intoenemy airspace. Operatingmuch closer to the radars it isjamming, an EB-1 would need amuch lower level of jammingpower than an EB-52.

SUPPORT AIRCRAFTStand-off jammers mounted inaircraft such as the EA-6B andEF-111 are best used againstearly warning and GC1 radars,where their high power canprevent the enemy predictingthe direction from whichstrike aircraft or fighters maybe coming. Deprived of thistactical information, targetacguisition and trackingradars must carry out theirown search for the incomingformations.

Since the high-poweredjammers on an EA-6B -would bea good target for a SAMlaunched in home-on-jam mode,a group of several jammingaircraft can protect themselvesby sharing target data via a datalink, and taking turns to be thejammer. Faced with a target thatseems to be jumping around thesky, the missile will expend itspropulsive power in a vainattempt to chase the source ofjamming energy.

The EA-6B is currentlyexpected to serve until around2015, and various potentialreplacements are under study.These include a "Command &Control Warfare" (C2W) variantof the two-seat F/A-18F (a designtentatively designated F/A-18GGrowler), a SEAD version of theJoint Strike Fighter, a jammer-equipped version of the F-22,and a jammer-equipped UAVOne feature of stealth aircraftwhich makes them attractive asjamming platforms is that theycarry their armament inweapons bays, internal spaces"which could easily be adaptedto house EW hardware.

There have also been reportsthat the USAF is developing -presumably as a "black"

Top: The F-4G Wild Weasel hasbeen retired; advances indigital electronics allowed theanti-radar mission to beassigned to HARM-equippedF-16 aircraft.

Above: HARM ignites its rocketmotor after a trials release froma German Tornado. Furtherexport orders for this defencesuppression missile areanticipated.

Left: During a 1980 flight test atChina Lake in the USA, anunarmed HARM round gougedthis hole through the targetantenna.

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programme - a stand-offjamming pod which could becarried by a fighter such as theF-15.

There is a limit to what eventhe best EW techniques cando. Defence suppression isalso needed to ensure that anaircraft will survive in hostileairspace. This is largely a jobfor anti-radiation missiles(ARMs). Weapons of this typefirst saw service during theVietnam War on dedicatedanti-radar aircraft known as"Wild Weasels". A moregeneral term would be SEADaircraft.

Although the USAFpioneered the "Wild Weasel"concept, and used the F-4G togood effect during the 1991 GulfWar, the aircraft has since beenretired. The USAF no longeroperates dedicated anti-radaraircraft, but relies on Block 50/52F-16CJ aircraft fitted withHARM ARMs and the HARMTargeting System (HTS) pod.Developed under a "black"programme, the HTS detectsand identifies radar threats, andprovides target locationinformation to the pilot.

US air operations over Iraq

Right: Decked out in a high-visibility paint scheme,Northrop's Tacit Rainbow anti-radar drone flies over a US testrange.

following the 1998 Desert Fox airstrikes has built up usefuloperating experience for theF-16CJ/HARM combination. In1999 the journal ElectronicDefense reported that pilots haddiscovered "both somelimitations and somecapabilities" of the system.In August 1986 the US Navybegan to fit HARM to its EA-6BProwler EW aircraft. The EA-6Bhas proved an effective HARMcarrier. The effectiveness of anyadd-on ARM installation can beenhanced by linking the missileseeker to the aircraft's ESMsystem, so that high-prioritythreats which it detects may beautomatically assigned to theARMs. Prowler's on-board ESMsystem is well-suited to this task.

The unique mixture of hard andsoft-kill capability offered by theaircraft was summed up by onepilot following the April 1986 USattack on targets in Libya. "Assoon as they come on, you squirt'em, with electrons or withmissiles," he told a US reporter.

Outside of the USA, Germanyis the only NATO ally to haveordered SEAD (Suppression ofEnemy Air Defences) aircraft -the Tornado ECR. Based on thestandard Tornado IDS, the ECRcarries two AGM-88A HARMmissiles, two AIM-9LSidewinders for self-defence, ajamming pod, a chaff/flaredispenser pod, plus two externalfuel tanks. It lacks the twin27mm Mauser cannon of thestrike version. These were

deleted to make room for theinternally mounted EW avionics.

A developing trend is theinstallation of ARMs on manytypes of strike aircraft. HARMmay be carried on any aircraftwhich has digital avionics andsufficient computer capacity.The US Navy was ahead of theUSAF in this respect, since itsmain HARM carriers becamestandard F/A-18 Hornets and A-7Corsair Hs, the types which gavethe weapon its combat debutduring operations against Libyain April 1986.

MISSILE GUIDANCEIn parallel with this work toinstall HARM on a wider rangeof platforms, improvements arebeing made the to missile'sguidance system. A newreprogrammable memoryallowed the seeker to bemodified in the field in order tomatch new threats or changes intactics by means of softwarechanges. One effect of these is togive the missile a degree ofawareness of its geographicalposition by using informationfrom its mechanical gyroscopesto create a crude form of inertialnavigation. This limitedcapability can probably be usedto restrict the weapon's attackcapability to an area of terrainwhen enemy emitters can beexpected

Under a more advancedInternational Harm UpgradeProgram (fHUP) beingconducted by the US, Germanyand Italy, the missile will begiven an inertial measurementunit and a GPS receiver. Thesewill provide a precisionnavigation capability, and mayallow the missile to attack radarswhich have shut down followingthe HARM launch.

Technology for a longer-termHARM replacement is beingexplored by the Advanced Anti-Radiation Guided Missile(AARGM) programme. Beingdeveloped by Science AppliedTechnology, the proposedmissile would have a dual-modeseeker which combines passiveantiradiation homing with active

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millimetre-wave terminalguidance. AARGM willnormally rely on passiveguidance, but if the threat radarshuts down, it will switch toactive millimetre-wave guidanceand continue to home. AARGMis an advanced technologydemonstration programme, andis expected to conclude withseveral guided launches late in2001.

At least two other projects todevelop dual-mode ARMs areunder way. Under a privateventure, Raytheon isinvestigating dual-modeseekers which would combinepassive anti-radiation homingwith imaging infrared seekers,laser-radar or millimetre-waveguidance, while the Germancompany BGT is studying theArmiger, a high-speed ARMwhich would use acombination of passive RF andimaging infra-red guidance.Armiger would be ramjetpowered, and a similarpowerplant is beingconsidered for AARGM. Bothmissiles would probably have atop speed of around Mach 3.

Below: Like a hungry mosquitoin a darkened bedroom, an anti-radar drone can loiter waitingfor an opportunity to attack. Ifno emitters are present, or if theintended victim shuts down, thedrone climbs back to cruiseheight to await a fresh signal onwhich it may home. Anendurance measured in hourskeeps radars silent.

Anti-Radar Drone

Lightweight self-protectionARMs are a relatively recentdevelopment. Weapons of thistype can be carried in additionto a strike aircraft's normalarmament The only example tohave entered service is theBritish Aerospace ALARM, aweapon whose parachute-bornetarget search and near-verticalattack profile remain unique.Problems with the originaldesign of the rocket motordelayed flight trials to the end of1986. A new powerplant wasdeveloped by the Germancompany Bayern Chemie, andthe missile was rushed intoservice to arm UK Tornadostrike aircraft during OperationDesert Storm in 1991.

DECOY RPVsDespite years of stop-godevelopment work, progress withanti-radiation and decoy RPVs hasbeen slow. Israel used decoy RPVsto good effect during its battlesagainst Syrian-manned airdefences in the Bekaa valleyduring the 1982 invasion ofLebanon, and has since fieldedHarpy, a piston-engined dronewhich carried a passive anti-radiation seeker and a smallwarhead. Harpy can loiter overthe battlefield, then dive onto anyhostile emitter which it detects.Cheap enough to be launched insignificant numbers, this type ofanti-radar UAV can force theenemy to keep his radars off forlong periods of time.

The US used ground-launched

£e#:The small size and non-metallic structure of RPVssuch as the Israel AircraftIndustries Scout keep RCS to aminimum.

Right: The weapons bay of anFB-111 bomber opens to revealthe ultimate defence-suppression weapon - thenuclear-tipped SRAM.

Below: Britain's Royal AirForce adopted the lightweightAlarm anti-radar missile, butthe only other user is SaudiArabia.

drones as decoys to confuse theIraqi air defences during theopening stages of Desert Storm. Inthe mid-1990s Teledyne Ryan wasasked to develop a miniature air-launched decoy (MALD) whichwould be powered by a 501b(22.7kg) thrust Sundstrand TJ-50turbojet, and carry an EWrepeater payload able to mimicthe VHP, UHF and microwaveradar returns from a full-sizedcombat aircraft. MALD was testedfrom the F-16 during the late 1990s,but the B-52H was seen as a likelyfirst operational application.Mimicking a B-52 would involveincreasing the strength of theapparent radar return (probablyby an amount which varies withfrequency band), and a similar butsmaller increase would be neededto mimic a conventional fighter.

If the energy emitted by the

repeater payload were to be onlyslightly boosted, and perhapsmade erratic by turning therepeater on and off at frequent butransom intervals, MALD or asimilar type of free-flying decoymight be able to imitate the tinyand fleeting radar returns from astealth aircraft. Enemy pilots andSAM operators would have noway of telling whether the targetthey were struggling to locate wasa $60 million stealth aircraft or a$30,000 decoy.

Targetidentified

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ACTIVE SKINS

As counters to stealth technologybecome available, stealthdesigners will be able to looktoward the avionics industry fornew aids to stealth. In its futuristicforward-looking study "Forecast2", the USAF predicted that one ofthe key technologies fortomorrow's aircraft and avionicswould be the use of "outer skins

containing embedded phasedarrays to permit aircraft to senseand communicate in optical andother frequency bands, and in anydirection from any aircraftattitude". The concept was rapidlydubbed "smart skin". Thesephased arrays would consist ofarrays of microscopically tinyactive transmitting elementsburied within the aircraft skin.Given suitable signal processing,these would work together like

the active elements of a phasedarray antenna.

The most obvious use of smartskins will be for communications.Radar applications would beexpected to follow, but theserequire increasing levels of power.In March 1997 the F/A-18 SystemsResearch Aircraft (SRA) based atthe Dryden Flight ResearchCenter was used to test anexperimental Smart SkinAntenna. Developed jointly by

Northrop Grumman and TRW'sAvionics Systems Division, thenew antenna was embedded in aspecially built tip mounted ontothe aircraft's right verticalstabiliser. Connected to theairframe electrically as well asphysically, it made both its ownstructure and the aircraft skinoperate as an antenna.

Addressing an Air ForceAssociation symposium in June1986, Brigadier General Eric B.Nelson, AFSC deputy chief of stafffor plans and programmess,revealed another potentialapplication of smart skins. FutureUS warplanes might try to matchtheir apparent radar signature withthat of ground clutter. An antennaarray on the underside of a low-flying aircraft could be used tosample the ground clutter from theterrain being overflown. "If you canmake the topside of the aircraft looklike the clutter in a frequency andpower sense, then you have donesomething nearly ideal - you havemade an [electronic] chameleon outof your airplane."

A February 1996 report by themagazine Aviation Week & SpaceTechnology suggests even morebizarre qualities for future aircraftskins. According to the magazine,the skin coating on a newclassified stealth aircraft beingtested at Groom Lake uses a 24Velectrical charge to trigger anactive method of reducing radarcross section. It also claimed thatthe colour of the skin could bechanged to blend the aircraft intothe sky background if viewedfrom below, or the terrain if seenfrom above.

It may read like science fiction,but science fiction has a habit ofbecoming science fact. It is possiblethat smart skins may helptomorrow's stealth aircraft vanishamidst the ground clutter.

Below: Long obsolete, the tinyQuail decoy equipped SAC'sB-52 fleet in the 1960s and 1970s.Able to fly as fast as a bomber,this jet-powered drone carriedequipment which boosted itsRCS to B-52 proportions,allowing it to mimic thebomber which had released it.

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The F-117A Nighthawk hadbeen developed as a "magic

bullet" which could help eventhe odds between the US andthe former Soviet Union in theevent of a conflict between thetwo superpowers. However,once the aircraft was in service,the US Government began toconsider it a possible tool for usein military strikes against othernations when such operationswere required by US policy. Thequestion that had to beanswered at the highest politicaland DoD levels was - what sortof crisis would warrant using theNighthawk in combat, strippingaway part of the veil of secrecythat protected the aircraft?

By 1983 three squadrons ofF-117A were operational atIbnopah, and in October of thatyear two operations wereapparently contemplated. Thefirst would have involved theaircraft in Operation UrgentFury, the October 1983 USinvasion of Grenada, while asecond would have targetedPalestine Liberation Army (PLO)sites in the Lebanon. Support forthe Grenada operation couldhave been given by F-117Asbased on US territory, but theLebanese strike would have

involved deploying a smallnumber of aircraft to a Europeanbase, reportedly Rota in Spain.

In April 1986, preparationswere made to use the F-177A inOperation El Dorado Canyon,the planned air strike againstthe Tripoli-based headquartersof Libyan leader MuammarGaddafi. A batch of between 8and 12 aircraft would deployfrom their Tonopah base to anairfield on the US east coast.From there, they would flyacross the Atlantic and into theMediterranean, supported byrefuelling aircraft. Afterattacking their targets at aroundSam in the morning, they wouldreturn to the USA.

Hours before the planneddeparture from Tonopah on 15April, the plan was scrubbed.The attack on Gaddafi would bemounted by carrier-based USNavy aircraft instead, supportedby UK-based F-llls, allowing theF-117A to remain secret.

The crisis that would see thefirst operational use of theF-117A developed much closerto the USA. In 1988 two USFederal grand juries in Floridaindicted General ManuelAntonio Noriega, the leader ofPanama's military forces on

charges of drug smuggling andracketeering in the USA.When Panamanian PresidentEric Arturo Delvalle dismissedNoriega from his command, hesuffered in indignity of beingforced out of office byNoriega's supporters, andseeing the general becomePanama's new leader. Afurious US Governmentimposed economic sanctionsagainst Panama.

In the following year

Guilleremo Endara opposedNoriega in a presidentialelection, and apparently "won,only to have the Noriegagovernment declare theelection invalid. When the USprovided some assistance to anattempt by a group within thePanamanian military whoattempted unsuccessfully totopple Noriega, the stage wasset for a confrontation betweenthe US and Panama. The sightof General Noriega declaring

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left: The F-117A's combat debutcame in 1988, in support of USground forces in Operation JustCause, Panama.

Below left: As captured on FURtape, an AC-130 pounds thePanama Defense ForcesComandancia headquarterswith 105mm cannon rounds.

Above: When US Rangerscaptured Torrijos Airport it hadthe support of USAF specialoperations aircraft as well asF-117 fighter-bombers.

war on the United Statesseemed closer to farce thaninternational politics, but thekilling of a US Marineprovided the impetus for theUS Government to act.President George Bushordered US forces to invadePanama and bring Noriega tothe USA to stand trial.

Just before lam on the nightof 20 December 1989, a massiveblast shook the PanamanianDefense Forces base at RioHato, 80 miles (130km)southwest of Panama City. Thestrike, delivered by an unseenF-117 A, was part of a co-ordinated US attack. The basewas about to be attacked bythe US Army's 82nd AirborneDivision, and a pair of F-117 Asdropped two 2,0001b (900kg)high-explosive bombs close toa barracks that housed some ofNoriega's best soldiers. Thetwo stealth fighters flew the

mission directly from the USA,refuelling in flight four or fivetimes.

This combat debut for theF-117 A was soon to be thesubject of controversy. The USDoD claimed that thePanamanian forces defendingthe compound at Rio Hatowere quickly subdued, thanksto the distraction caused by thestealth fighters, but USparatroopers who captured thebase were reported as sayingthat they landed into anintense firefight. Several dayslater, US newspaper reportsquoted unidentifiedgovernment sources asclaiming that someF-117 As had been tasked withattacking Noriega. On 26December the US DoDconfirmed that US militarycommanders had consideredbut rejected other missions forthe aircraft during the attack.Pentagon spokesman PeteWilliams refused to say howmany aircraft took part, whattype of ordnance had beendropped or what othermissions had been consideredfor the aircraft.

He repeated earlier DoDclaims that the objective of theF-117 A strike had been "not tohit the barracks, but rather, infact, the mission was to missthe barracks and hit the field -and by nature of the explosion,disorient and stun and confuseand frighten" the Panamaniandefenders. "The mission was

successful," he said.Williams explained how

Defense Secretary Richard B.Cheney had been told severaldays earlier that the bombs fromthe F-117 As had "precisely hittheir targets . . . I'm told that theF-117 hit it very precisely andthat it was the precision of theF-117's bombing capability thatwas the reason it was used." Healso conformed that the attackon Rio Hato had been the solemission assigned to the stealthfighters. "Others wereconsidered but they werediscarded."

Given that Panama had noeffective air force or air defences,the use of the F-117 A seemedstrange but, following afactfinding trip to Panama inearly January, Senate Armed

Services Committee ChairmanSam Nunn stated that Army Lt.Gen. Carl W. Stiner,commanding general of theJoint Task Force South thatimplemented the invasionplan, had asked for the F-117Anot because of its radar-evading capability, but toexploit its advancednav/attack systems. "They hitexactly where they weremeant to," he told reporters,adding that the strike wasintended not to kill largenumbers of Noriega's troops, butto stun them by dropping bombs

Below: Following the USinvasion of Panama, US agentsarrest General Noriega andprepare to return him to theUSA to stand trial.

147

outside their barracks.The entire affair of the bombs

that missed came to a head inApril, when the New York Timesand the industry newsletterAerospace Daily revealed thatone of the F-117As had missed itsintended target by more than300 yards (275m). A few dayslater a spokesman for Cheneyexplained to news reporters thatthe USAF had not told his bossthat the two F-117As haddropped a bomb "way off target",until a few days before. As aresult, Cheney had for monthsbeen praising the aircraft'saccurate weapon delivery,unaware of the facts. "The pilotswere told to drop their bombs nocloser than 50 meters" from twoseparate PDF barracks buildings,explained Pete Williams. Due toa last-minute misunderstandingbetween the pilots, the secondF-117A dropped its bomb on ahillside some distance away,Williams said. "The first bombhit 55 meters from one of thebarracks, but the second bombwas way off target."

In July 1990, Lockheeddelivered the 59th and finalF-117A stealth fighter to the USAir Force. The aircraft wasdelivered under budget and twomonths ahead of the schedulefirst drawn up in 1978. A monthlater, the Lockheed fighter was

Below: A line-up of F-117Astealth fighters beforedeployment to the Gulf.Beneath the open weaponsbays are cargo pods for spares.

on its way to a war that wouldmore than vindicate itsreputation.

THE GULF WARAt 2am on 2 August, units of theIraqi Army rolled over theborder with Kuwait, rapidlyoverwhelming the Kuwaitiarmed forces and occupying thecountry. Ostensibly this actionhad been taken at the request ofa newly establishedrevolutionary government thathad toppled the government ofthe Emir of Kuwait, Sheikh JaberAhmed al-Sabah. In practice itwas Iraq's response to abreakdown in talks between thetwo countries held in Jeddahthe day before.

With an army of around100,000 men poised on thefrontier, Iraq had demanded thatKuwait pay reparations for theoil Kuwait had "stolen" from Iraqvia the border oilfields, write offloans made to Iraq during theIraq/Iran war in the 1980s, andaccept Iraq's territorial claims toBubiyan and Warba, Kuwaitiislands that controlled thewaters through which Iraqmaintained in access to the Gulf.Kuwait rejected these demands,and walked out of the talks.With Kuwait firmly occupied,the pretence of a "revolutionarygovernment" was soonabandoned. On 8 August Iraqformally annexed Kuwait as its"19th province".

On 6 August, a UN resolutioncalled for mandatory sanctions

against Iraq. With Iraqi troopsnow along the border betweenKuwait and Saudi Arabia, thelatter nation feared for its ownsecurity, and requested that UStroops be sent.

On 7 August, US PresidentGeorge Bush ordered the start ofOperation Desert Shield, whichwould protect Saudi Arabia andother Gulf States from the threatposed by Iraq. The first US unitssent to the area were an initialforce of fighter aircraft plus 4,000troops. Responding to furtherUN resolutions, other Arab and

Above: General Norman H.Schwarzkopf ("Stormin1

Norman"), Commander of USand Allied forces in the Gulf, ina typically forceful pose at apress conference.

Western nations joined therapidly growing Allied Coalition,while the UN passed furtherresolutions calling for a navalblockade, then for UN membersto use "all necessary means" torestore international peace andsecurity in the area.

The Coalition was directed by

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Headquarters US CentralCommand, under the commandof US Army Gen. H. NormanSchwarzkopf. USAF Lt. Gen.Charles A. Homer was made theCoalition's supreme aircommander, and within dayshad established theHeadquarters CentralCommand Air Forces (Forward)in Saudi Arabia. From thisheadquarters, he wouldcommand the subsequent aircampaign.

Within five days, five fightersquadrons, a contingent ofAWACS, and part of the 82ndAirborne Division had movedinto the area. A total of 25 USAFfighter squadrons flew non-stopto the theatre, and within 35days the USAF fighter force inthe region matched the numbersof Iraq's fighter strength. Soonafter the buildup of militarystrength had started in August, itbecame clear that the US wasdispatching forces which wouldgive the Allies an offensivecapability. Besides Marineamphibious forces, units sent tothe Gulf included a squadron ofF-U7As, triggering pressspeculation that they might beused to attack Iraqi supplydepots or oil installations.

Col. Anthony Tolin, untilrecently commander of the 37thTactical Fighter Wing at Nells,and by now assistant deputychief of staff of the Tactical AirCommand at Langley, was bluntabout the aircraft's capability. "I

guess it would be tough toclassify the F-117A as a purelydefensive weapon. Its defensivenature is its ability to penetrateenemy radar without detection,"he told reporters who visited thebase on 19 August to see thesquadron's arrival en route toSaudi Arabia. "They give us anability, should we need it, to getin with the least amount ofcasualties and attack thoseimportant targets if necessary."

A total of 22 F-117AS 415th TFS"Nightstalkers" had arrived atLangley, but only 20 set offacross the Atlantic on thefollowing day. The two otheraircraft had been spares, broughtto Langley to make sure that 20could be despatched overseas.Flight time to Saudi Arabia wasapproximately 15 hours, theaircraft refuelling in flight fromKC-10 Fjctenders. Like most fly-by-wire aircraft, the F-117A ismore stable during therefuelling operation than oldertypes, but its faceted upperfuselage and flat-plate canopylimited upward visibility as itspilot approached the refuellingboom. The pilot of one of theKC-135Q tankers used to fuel theF-117As during the flight fromTonopah to Langley told anAviation Week & SpaceTechnology reporter that he wasaware of this poor visibility, andwas ready to rapidly break awayif the boom operator thought thesituation was becomingdangerous. In all other respects,

refuelling is normal, with theboom mating with a receptaclejust aft of the "peak" on top ofthe F-117A fuselage.

The F417s were deployed toKing Khalid Air Base nearKhamis Mushait in thesouthwestern corner of SaudiArabia. This was more than 1,000miles (1,600km) from Baghdad,which meant a round-tripoperational mission wouldaverage more than five hoursand require multiple refuellings.It is likely that the air base atKhamis Mushayt was one of thefew in the area with sufficienthangars to house the F-117 forceand protect its sensitive radar-absorptive coating from theelements. It was out of range ofIraqi Scud missiles and, giventhat the F-117 was designed fornight attacks, the aircraft wasnot able to exploit a moreforward base in the way thataircraft flying several sorties byday could.

On arrival at King Khalid AirBase, the pilots of the 20 F-117Asstarted a programme of training.Initial sorties intended tofamiliarise them with the localterrain were carried out by day,but the emphasis was soonswitched to night flying. Thelocal area was similar inenvironment and altitude toTonopah. An exotic aircraft builtin small numbers might beexpected to have reliabilityproblems. In practice,serviceability of the F-117 As sent

Above: An F-117A refuels froma USAF tanker during the longflight from the USA to a newoperation location in SaudiArabia.

to Saudi Arabia remained high,with mission readiness ratesequalling those of conventionalfighters.

Soon after arriving in SaudiArabia, the F-117A was againattracting publicity. On 13September, the Frenchmagazine L'Express claimed thata Thomson-CSF military radarin service with the Saudi Armyhad on several occasionssuccessfully detected F-117 As ata range of up to 10.5 miles (17km).The story, which was based onsources "close to the SaudiArmy", claimed that, followingthe incidents, US commandershad moved the Lockheedaircraft away from the frontlines, relocating them at a basehi southwest Saudi Arabia,close to the Yemen, hi anotherincident, Saudi troops arereported to have been puzzledby the failure of a US-builtradar to detect the angular-looking black jets flying from anearby airfield.

In November, DefenseSecretary Cheney announcedthat a second squadron ofF-117 As was being sent to SaudiArabia. This was the 416th TFS"Ghostriders". By the lime thathostilities broke out early in thefollowing year, they had been

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joined by the 417th TFS"Bandits". More than 40 of the 56available aircraft were to takepart in Desert Shield

COALITION BUILD-UPBy mid-January 1991, a massivemilitary force from 30 nationswas In place ready to enforcethe UN resolutions. In particular,the scale of the US airdeployment was huge. Withintwo months of Desert Shieldbeginning, it had reached theequivalent of five tactical fighterwings, and included - besidesthe F-117As - F-15C/Es, F-16Cs,F-4Gs, RF-4Cs and A-lOAs drawnfrom more than 20 different USand Europe-based wings. F-lllstrike aircraft and B-52 bombershad been redeployed to Turkeyand the Indian Ocean,respectively. Carrier-based airunits had added at least 100more combat aircraft, with theUSMC providing another 150aircraft.

By the time the Coalition'sland, sea and air build-up wascomplete, Saddam Hussein wasthought to have stationed590,000 troops and 4,200 tanks inKuwait and southeastern Iraq.Total air strength of the Iraqi airforce was around 500 aircraftand 250 combat helicopters.

The F-117A was the onlystealth aircraft taking part in thewar, but several of theconventional aircraft weremodified to make them less easy

Below: Part of the array ofRussian-built air defencesystems the Coalitionforces faced in the GulfWar. Below left, the SA-13SAM system, which hasfour missile launchers,although only one can befired at a time.

to detect. Royal Air ForceTornado F.3 fighters - theinterceptor version of the aircraftused for strike missions - hadbeen fitted with a spray-on RAMalong the leading edges of thewing, tailplane, and vertical fin,plus the nose and leading edgesof its underwing stores such asthe Phimat chaff/flare pods.RAM tiles were also added tothe inlets to dampen their radarresponse. This feature initiallygave trouble, with several tilescoming loose in flight and beingingested by the engine. TheRB.199s kept running in everycase, but were changed as aprecaution after the aircraft hadlanded. Better adhesive hadcured the problem by December1990. The effectiveness of thisimprovised signature-reductionprogramme was never tested inaction. No Iraqi warplane wouldever challenge a Tornadointerceptor.

A few weeks before theinvasion of Kuwait, the US Navyhad installed NVG systems,blue-green NVG-compatiblecockpit lighting, andwindscreens with better IRtransparency on some of its A-6EIntruders. These gave visibilityout to around seven miles (llkm)under good conditions, whichallowed the crew turn off theaircraft's radar, denying Iraqielint units any signal that mightwarn of an incoming attack. As abonus, it also overcame some ofthe radar's limitations. Crews

Below:The SA-6 is morecompact than the SA-4(below right). It provedeffective in the 1973Middle East Conflict, butthe US and its allies haddevised suitablecountermeasures longbefore the 1991 Gulf War.

Right: Armed with Skyflashand Sidewinder air-to-airmissDes and carrying long-range fuel tanks, this RAF"Desert Eagle" Tornado F.3 fliesa combat air patrol (CAP) alongthe Saudi/Iraq border.

could now fly as low as 200ft(60m) on a clear night ratherthan the 500-600ft (150480m)allowed by radar, banking theaircraft more aggressively tomake best use of terrain features.(The radai allowed bank anglesof no more than 45 degrees.)Radar was better than NVGsduring the actual attack, so wasturned at the last moment.

US Army AH-64 Apaches alsowent stealthy, but only on theground. Brunswick-developeddesert-camouflage nettingdelivered in November 1990 wasdesigned to absorb radarfrequencies from 6-140GHz. Fivehundred two-piece 78 x 100ft(23.75 x 30.5m) covers wereordered to protect parkedaircraft.

SIGINTDuring the Vietnam War, theUSAF and US Navy had eachrun its own air campaign, anarrangement which fosteredinter-service rivalry, and whichmade co-ordination difficult. Theair campaign against Iraq wouldbe fought to a single integratedplan devised by two men.Lieutenant-General Charles

Homer was GeneralSchwarzkopf s air commander,while Brigadier-General BusterC. Glosson, commander of 14thAir Division became US CentralCommand's principal USAFtarget planner. Under theircommand, intelligence officersdrew information from USAFtarget files, supplemented by the

Below: The SA-8 Geckoreplaced the 57mm towedanti-aircraft gun and is inservice in two versions, theSA-8a shown here, withmissiles on openlaunchers, and the SA-8b,which has the missiles inlong boxes for bothtransport and launch. Iraquses both SA-8a and SA-8b.

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results of a massive intelligence-gathering effort. As USreconnaissance satellitesphotographed Iraqi militarypositions, Lockheed TR-lsequipped with the AdvancedSynthetic Aperture RadarSystem (ASARS) gathereddetailed sideways-looking radarimagery of terrain up to 35 miles(56km) to one side of its flightpath.

Sigint aircraft such as theRC-135 sampled Iraqicommunications signals,identifying the location of thetransmitters, and listened to Iraqiradar signals as Allied fightersmade high-speed dashestowards Iraq to test the defences.To counter such elint probing,the Iraqis began to shut downparts of their early-warningradar network for extendedperiods of time. It was a habitthat would help the Allies whenthey finally attacked.

It is possible that some F-117Asslipped across the border atnight to take ELJR imagery ofhigh-value targets such aschemical-weapons sites andnuclear installations, but anyoperations of this type wouldhave been kept highly classified.

As the months wore on, thestrategic plan for the air war wasexpanded to include about 300targets. US and Alliedintelligence officers drew up notjust lists of targets to be attacked,but also the floor plans offacilities such as hardenedconcrete command centreswhich in some cases had beendesigned or even built byWestern companies. As plans touse the unique capabilities ofthe F-117A were drawn up, the

USAF faced the prospect thatone of these highly classifiedaircraft might be shot down overIraqi territory. If this happened,strike aircraft would have to beassigned the task ofsystematically and intensivelybombing the wreckage, toensure that no usefulinformation reached Iraqi (orRussian) hands.

The Iraqi air defences facingthe Coalition looked formidableon paper. SAM systems weremostly Soviet-supplied, andincluded the S-75 (SA-2"Guideline"), S-125 (SA-3 "Goa"),Kub (SA-6 "Gainful"), 9K33 Osa(SA-8 "Gecko"), 9K31 Strela 1 (SA-9 "Gaskin"), S-10M Strela (SA-13"Gopher"), and the man-portableStrela (SA-7 "Grail"), Strela 3 (SA-14 "Gremlin"), plus Franco-German Roland 2s and ChineseHN-5A. To some US planners itmust have seemed more than alittle reminiscent of the NorthVietnamese defences that theUS had faced around quarter ofa century earlier.

Iraq had purchased what was

widely described as a state-of-the-art integrated air defencesystem (IADS) from France.Codenamed Kari (Iraq spelledbackward in French), it was acomputerised and highly-centralised network whichlinked the national air-defenceoperations center (ADOC) inBaghdad to four sectoroperations centres (SOC), one foreach of the four sectors intowhich the country was divided.These SOC were linked to atotal of 17 intercept operationscentres (IOC) -which wereconnected to observer and early-warning reporting posts. Around500 radars were located atapproximately 100 sites. ThelOCs controlled air bases withinterceptor aircraft, more than 50surface-to-air missile sites, pluswidely-deployed antiaircraftartillery sites. The system wasequipped with multiple andredundant communicationmodes, so in theory couldrapidly detect attacking aircraft,and direct fighter, missile, orantiaircraft artillery fire against

them.The Iraqi Air Force had 24

main operating bases and 30dispersal fields, many equippedwith the latest types ofhardened aircraft shelter. Mostpotent fighter in the 750-strongforce of combat aircraft was theMiG-29, but Iraq also had theMiG-25, the older MiG-23 and-21, plus Mirage Fls.

The most heavily defendedareas of Iraq were Baghdad,Basrah, Tallil/Jalibah, H-2 and H-3 airfields, and Mosul/Kirkuk.These were protected by fivetypes of SAM system. The S-75,S-125, Kub, and 9K33 Osa hadbeen supplied by the SovietUnion, while France andGermany had supplied theshort-range Euromissile Roland.

More radar-guided SAMsystems were deployed to theBaghdad area than any otherpart of Iraq, and were dispensedthroughout the Baghdad area (aswere the targets they wereprotecting). The greatestconcentrations of radar-guidedSAMs were not in the centre of

Number and location of Iraqi SAM batteriesLocation

Baghdad

Mosul/Kirkuk

Basrah

H-2 &H-3 airfields

Talil/Jalibah

Total number operational

SA-2

10

1

2

1

1

15

SA-3

16

12

0

0

0

28

SA-6

8

0

8

6

0

22

SA-8

15

1

0

0

0

16

Roland

9

2

5

6

2

24

Total inarea

58

16

15

13

3

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the city but in its outlyingregions. The lethal range ofthese defences extended overthe general Baghdad area,covering up to 60 miles (100km)outside the city.

The maximum engagementranges of the systems variedfrom 3.5 miles (5.6km) for theRoland to 27 miles (43km) for theSA-2, so their firepower did notconverge over the downtownarea. Indeed only the elderlySA-2 had sufficient range for thefirepower of individual batteriesto converge over the centre ofthe city. As a result of thisdispersed deployment pattern,the densest concentrations ofoverlapping radar SAMdefences were outsidedowntown Baghdad, and thelatter had no greater protectionthan the overall metropolitanarea.

A critical weakness in Iraq'sSAM defences was that the SA-2and SA-3 had been firstdeployed around 30 yearsearlier, so were at the end oftheir operational lifespan. As theresult of combat experience inVietnam and the Middle East,their characteristics andoperational limitations were wellknown, and the USAF and otherCoalition air forces had long-established countermeasures tothese systems.

The short-range Strela-2Mand Strela-3 shoulder-firedSAMs were used by field unitsof the Iraqi Army. Most of theseinfra-red guided weapons weredeployed in the area of Kuwait.None was used aroundBaghdad.

A total of around 4,000 anti-aircraft guns (mostly 23mm ZSU-23 towed guns and ZSU-23-4Shilka self-propelled guns werein Iraqi service. There weremore anti-aircraft artillery (AAA)sites in the Baghdad area thanelsewhere in Iraq. Like the SAMsystems, they were positionedthroughout the greatermetropolitan Baghdad area, not

just downtown. Although finkedto the IADS, few of the AAAguns were radar-guided. Mostrelied on barrage-style firing,and posed a threat which wouldrequire attacking aircraft to fly ataltitudes of more than 12,000ft(3,660m) for most of the war.

The entire system had beendesigned to counter threats fromIsrael or Iran, so was deployed tocope with attacks coming fromthe east or west. The air forcesnow poised to strike Iraq wouldbe attacking from the south andnorth, and on a much largerscale than the defences hadbeen designed to cope with. Thedefences could track only alimited number of threats, andhad very limited capabilitiesagainst stealth aircraft.

The Coalition had six monthsto gather intelligence on targets,develop its war plans, deploy thenecessary assets to the theatre,allow aircrew to become familiarwith the operating environment,and practise strikes anddeception measures. SinceFrance was a member of theCoalition preparing to liberateKuwait, it was able to provideAllied planners with full detailsof the Kari computer system.,allowing them to identify thekey IADS nodes whose earlydestruction would inflict thequickest and heaviestdegradation of the Iraqi airdefences. Before attacks began,the US Navy's Strike ProjectionEvaluation and Anti-AirResearch (SPEAR) departmentconcluded that "the commandelements of the Iraqi air defenseorganization are unlikely tofunction well under the stress ofa concerted air campaign."

In early January, the UKmagazine Flight Internationaldescribed the Iraqi air force as"no match for the forcesarraigned against it - not at anylevel, not in any role. It is hard tosee how the IrAF can retain anyresemblance of cohesion afterthe first three allied sorties."

Before that issue had a chance toreach IrAF crew rooms, thevalidity of these commentswould have been cruellyestablished.

DESERT STORMhi late November, the UN hadgiven Iraq until 15 January towithdraw from Kuwait, but byearly January it was becomingobvious that this would nothappen. Even before the UNdeadline ran out, President Bushconsulted with Coalition allies,obtained formal permission fromKing Fahd of Saudi Arabia tobegin hostilities from Sauditerritory, then signed theexecutive order which wouldbegin Desert Storm.

The night of 16 January wasclear, with a new moon givingnear-total darkness - near-perfect conditions for the FLIRsystems of the F-117A and otherAllied fighter-bombers. Themonths of pre-war intelligencegathering had paid off. At pre-flight briefings, pilots were insome cases assigned targets thatwere not just the building itself,but the key area within thesebuildings that was to bedestroyed.

First off the ground, at 12.50amlocal time, were the USAF F-15EEagles from Tabuk, the mostdistant of the Allies' forwardbases. Stripped of their long-range fuel tanks to increasetheir weapon load, theyrefuelled in the air en route toIraq. Starting at 1.30am, TornadoGR.ls of the Royal Air Force andRoyal Saudi Air Force took offfrom Muharraq in Bahrain andfrom bases in Saudi Arabia.Other strike aircraft followedfrom bases in the Gulf states andthe flight decks of US carriers.

At 2.38am on 17 January 1991,AGM-114 Heltfire missiles firedby AH-64 Apache helicoptersslammed into two Iraqi early-warning radar sites in WesternIraq. These were the first shots of

Left: These are GBU-15 guidedbombs before loading onto aCoalition aircraft. The GBU-15was spectacularly successful inprecision air strikes.

Desert Storm. Having fired 27missiles, 100 70mm unguidedrockets, and 4,000 rounds of30mm cannon ammunition, thetwo four-helo formations headedback to base. Within minutes,more than 100 Allied aircraft hadslipped through the gap blownin the Iraqi radar network. Themost intense air bombardmentsince the 1972 Linebacker IIB-52raids on North Vietnam wasabout to begin.

Ahead of this armada ofwarplanes flew around 30F-117A fighters of the"Nightstalkers" and"Ghostriders". The first aircraftto cross into Iraqi airspace, theyhad been assigned the task ofknocking out key enemycommunications facilities, andwere about to bring war to thecapital of Iraq.

On the ground far below, Iraqiradars scanned the skies, butsaw nothing of the US aircraft.The powerful radar pulses thatshould have reflected back fromthe US fighters to indicate thepresence of a target wereinstead being largely absorbedby the black coating on theF-117As, while the remainderwere deflected at bizarre angleswhich matched those of theoddly-shaped aircraft. Invisible tothe defenders, the F-117s couldfly at will over the city atmedium altitudes that wouldhave been suicidal in any otherwarplane, giving pilots plenty oftime to identify their targets.

Carefully, the pilot of the firstaircraft aligned the crosshairs ofthe night-vision system mountedunder the belly of his aircraftwith a carefully selectedbuilding close to the Tigris river.Satisfied that all was correct, hepressed a switch to activate alaser built into the same turret asthe FLIR. The bomb doors underthe centre fuselage opened, anda 2,0001b (900kg) laser-guidedbomb (LGB) fell away into thedarkness, its seeker following apatch of laser light reflectedfrom the building far below.Crashing into the roof of theIraq's most importantcommunications centre, theweapon plunged throughseveral floors, exploding deepwithin the structure, throwingdebris from the windows, andsmashing the central telephonesystem of the city. Withinminutes, LGBs began falling onother command and controlfacilities such as microwaverepeater stations, early-warningradars, and undergroundcommand bunkers.

As the main Coalition forceswept in to begin striking their

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own targets, the Iraqi air defencesystem was already near-impotent. Anti-aircraft guns andsurface-to-air missile (SAM) sitesfired into the sky aboveBaghdad, vainly trying to findthe attackers.

In the opening hours of DesertStorm, the F-117s attacked 80targets, including the Iraqi AirForce headquarters in Baghdad,and an air-defence headquartersnear the city. Videotapes takenby the attackers showed a directhit on the multi-storey IrAFheadquarters, with the LGBlanding almost dead-centre onthe roof. The attack on the air-defence HQ was even moreimpressive, with the bombentering one of the bunker'sthree rooftop ventilation shafts,then demohshing the interior ofthe structure, the blast blowingout the NBC-protectedbuilding's airlock door. Some ofthe best-protected targets wereburied under so much concretethat several bombs had to bedropped in order to breakthrough the thick roof.

Their job done, the F-117Asleft the skies over Baghdad. Asthey did so, the first wave ofTomahawk cruise missileslaunched from US warshipsstruck heavily defended targetssuch as Saddam Hussein'spalace, the Ba'ath Partyheadquarters, and the IraqiMinistry of Defence. The onlysupport needed by thedeparting F-117As had beenflight refuelling, but almost 30minutes ahead of the lead attackaircraft of the massive strikeformations that now approachedtheir targets were dedicatedsupport aircraft such as theUSAF EF-111A Raven and USNavy EA-6 Prowler electronic-warfare platforms. These hadthe task of confusing Iraqi early-warning, surface-to-air missileand ground-control interceptradars until the arrival of theF-4G Wild Weasel anti-radarfighter armed with AGM-88HARM anti-radiation missiles,and Tornadoes equipped withthe lighter-weight Alarm anti-radar missile.

Almost half the sorties flownwere support missions bytankers, fighter escorts, jammingaircraft, and defence-suppressionplanes. The speeds and timingsof the attacks mounted byaircraft such as F-15Es,Tornadoes, F/A-18 Hornets andA-6E Intruders had beenarranged so that severalincoming waves should sharethe services of the supportaircraft. Some Iraqi MiG-29 andMiG-25 fighters were airbornethat night, but failed to interceptthe EW aircraft, or the strikeformations that followed.

The Allied attack achievedtotal tactical surprise, and all theaircraft taking part in that first

Above: False target generationis a technique which reduces aplan position indicator (PPI)display to an unusable mess. Allbut one of these blips could be a

false target, and somewhereamong them is the true target.This declassified photo showsonly a fraction of thetechnique's capability.

Below: The Gulf War was theswan-song for the EF-111 Raven.The USAF now relies on USNavy Prowlers for stand-offjamming coverage.

153

wave of air strikes returnedsafely to base. USAF officialswere quick to credit the successto the effects of the initial F-117Astrike. By the time that theF-117As had attacked all 80targets, Iraq's air defence systemwas near helpless. Radar sites,command centres, air andmissile control facilities all lay inruins, along with thecommunications needed toallow these to function. Longbefore dawn, the Royal Air Forceand Royal Saudi Air ForceTornadoes had completed theirinitial series of dangerous low-level sorties against Iraq's majorair bases. The sun rose on anIraqi Air Force that had beenvirtually decapitated. It wouldnever recover.

Describing the F-117A attackas a brilliant success, 37th TFWcommander Col. Alton C.Whitley told reporters that thishad been the result of stealthhaving allowed the aircraft toreach their targets undetected,plus the split-second timing -withwhich the strike had beenexecuted.

Through the day of 17 January,the 37th TFW pilots slept, in thevampire-like lifestyle to whichthey were accustomed, whilethe rest of the Coalition air forceflew by day to pound moretargets in Iraq and occupiedKuwait. Rising between 3 and4pm, pilots were briefed on thenext night's targets and routes inand out of Iraq, spending several

hours studying the information.Once darkness had fallen, theywere airborne once again, alongwith the British and SaudiTornado crews, flying sortiesuntil just before dawn.

Target list for the 37th TFWthat second night of the warincluded one of Iraq's nuclearreactors, but this was initiallykept secret. NBC reporter RickDavis, part of the press pool atthe F-117A base in Saudi Arabia,found himself with a story hecouldn't file. The returning pilotswouldn't divulge where thereactor was located, Davis laterreported. "They didn't say... justthat it was a nuclear reactor." inan interview with CBS on 20January, Gen. Schwarzkopfstated that four nuclear facilitiesin Iraq had been destroyed.

Each day and night theprocess would be repeated, theF-117As taking to the air eachnight, while by night and daythe rest of the Coahtion air forceflew to a daily battle plan whosecomplexity and detail requiredup to 700 pages of daily taskingorders. Within a few days, Iraqiradar activity had declined toaround a quarter of the peaklevel that had been attainedwhen war broke out. A weekinto the war, it had declined by95 per cent. By night, thedefences could do little morethan to fixe AA shells, SAMs,and even 762mm AK-47 assaultrifles blindly into the darkness inthe hope of hitting an attacker.

Despite the threat posed bythese massive barrages, theF-117As were able to loiter overthe target area, sometimes forseveral minutes, in order topositively identify difficulttargets such as undergroundbunkers.

The stealth fighters weregiven standoff jamming support,but experience soon showedthat this was best kept for thepost-strike portion of themission, when the defenderswould fire for up to five minutesin an attempt to hit the attackers.Jamming support prior to

Above: The view over Baghdadon the morning of 17 January,1991. Tracer fire shoots upwardsat unseen aircraft as Alliedbombs hit key strategic targets.

Above right: From the TVtargeting display of an Alliedaircraft, this remarkable imageshows an Iraqi target secondsbefore destruction by an LGB.

Below: Within a month of the59th and last F-117A to bedelivered by Lockheed to the USAir Force, the type wasperforming well in the Gulf War.

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weapon release did help protectthe F-117As, but also warned theIraqis that an attack wasimminent.

The initial goal of the plandevised by Lt Gen. Homer andBrig. Gen. Glosson was thedestruction of Iraq's commandand control system, nuclear,chemical and biologicalfacilities, its main militaryinstallations, and the supportingmilitary-industrial infrastructure.Almost as important were theattacks on enemy airfields andair-defence sites. The mountingtoll of destruction inflicted onthese allowed US and Coalitionaircraft to operate freely overever-growing areas of Iraqiterritory, beginning the task ofsevering the lines of supply tothe Iraqi Army in Kuwait andsouthern Iraq, and attackingfront-line units such as theRepublican Guard divisionslocated between the Rumailaoilfields and the city of Basra.

DIVERSE TARGETS

As the war progressed, thetargets attacked by the F-117sbecame more diverse. Accordingto an F-117 after-action report,the doctrinal target list for the F-117 "went out the window".Although the F-117s were usedagainst at least one example ofeach of the 12 target categoriesdevised by the planners, theyconcentrated on a narrow rangeof target types within eachcategory. These were typicallyfixed, small, and deeply buriedor protected by concrete, andwere at known locations. F-117sconducted relatively few strikesagainst area or mobile targets.

Within 10 days of offensiveoperations, 10,000 combat sortieshad been flown. By the time thatGen. Schwarzkopf gave theworld's press an hour-longsummary of the first 14 days ofcombat, the air war hadachieved much. Iraq's airdefences had been shattered tothe point where the only IrAF

aircraft taking off were thoseattempting to flee to sanctuaryin Iran, while the Army'scommunications was sodegraded that corpscommanders sometimes couldnot speak directly to theirdivisional subordinates.

One reason for the IrAF'sexodus to Iran was the nightlyattacks by F-117 As on Iraqiairfields. With the IrAF aircraftlargely unwilling (and oftenunable) to come up and fight inair-to-air combat, on 25 Januarythe Allies had started thesystematic destruction of thehardened shelters in whichthese were hiding. Muchstronger and thicker-roofed thanNATO shelters, many of thesehad been designed by Britishcompanies, who passed theplans to the USAF Thestrongest, built by Yugoslaviancontractors, had roofs between1042ft (3.0-3.65m) thick. Study ofthe plans had shown that thebest way of knocking out these

super-hardened shelters wouldbe to attack them with LGBs. Aspecial shelter needed a specialbomb, and the USAF had theideal shelter-busting weapon athand in the form of the 1-2000warhead.

A conventional LGB uses add-on guidance and fin sectionsplus a standard high-explosivebomb. Bomb casings arenormally cast, but the engineersat Eglin AFB who designed the1-2000 created a lin (2.5cm) thickbomb case which was forgedfrom a single piece of high-gradesteel. It is an expensive way tomake a bomb, but whenassembled into a GBU-24 LGB,this hard shell gave the 2,0001b(900kg) weapon the ability topenetrate several feet ofconcrete before detonating.Alternate patterns of TV IR orlaser guidance allowed this 8ft(2.4m) long bomb to beconfigured for day or night usefrom high or low altitude.

The task of delivering the

1-2000 was passed to the 37thTFW. Within 24 hours of the firstanti-shelter missions, Iraqiaircraft began fleeing to Iran,another major victory for theF-117A and its pilots. Detonatedwithin a bunker or shelter, the1-2000 warhead "does a good jobof destroying almost anythingthat's in it," an Eglin officialboasted. If aircraft were in thebunker, the resulting secondaryexplosion of fuel and ordnanceadded to the destructive effects,as could be seen in videotapesof anti-shelter attacks releasedby the USAF in late January.

F-111F, B-52G and Mirage Flsalso flew anti-shelter missions,attacking with the GBU-27s(another LGB fitted with a steel-cased penetration warhead),GBU-15 smart bombs, Paveway IIand m LGBs, and AS.30L laser-guided missiles. By day 14 of thewar, 100 of the 300 shelters hadbeen destroyed, around 70 bythe 37th TFW. By the end ofhostilities, 375 of Iraq's 594hardened aircraft shelters hadbeen damaged or destroyed byCoalition bombing, and anestimated 141 aircraft withinthese shelters had beendestroyed, while 122 had flownto Iran.

Describing the F-117 A's recordseveral days later, Secretary ofDefense Richard Cheney saidthat "we found it comes andgoes pretty much as it pleases,and in all of the missions thathave been flown to date, it'sbeen virtually invisible to enemyradar."

The only airborne radar in

Left: As darkness falls, theF-117 As head for the runway tobegin their mission. The nightand their stealth capability willallow them to penetrate defences.

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Iraqi service that seemed to haveany chance of glimpsing anF-117A was the huge Fox Fire setcarried by the MiG-25. This hasa maximum power output of600kW a level intended to burnthrough massive amounts ofjamming. At close range, itmight have obtained a faint butusable echo from a stealthfighter, but the IrAF commandand control system had no wayof vectoring one of these steel-built Mach 3 jets close enoughto its target. At least one of Iraq's20 Foxbats was shot down in air-to-air combat, while five moreare thought to have fled to Iran.

One Iraqi Cyrano-radarequipped FIE did manage todetect an F-117A, but it was notable to track the stealthyintruder. The F-117A pilot whoreported encountering what hedescribed as a Mirage Flequipped with a searchlightmay have been the intendedvictim. The light in question wasprobably the retractable landinglight mounted beneath the noseof the Mirage FIE, and the Iraqipilot seems to have beenattempting to catch theLockheed aircraft in the beam.The F-117A pilot changed courseby a few degrees, giving the

Mirage the slip.Baghdad remained a major

target throughout the war. Byearly February, Iraq wasinstalling increasing numbers ofanti-aircraft batteries on civilianrooftops in Baghdad and KuwaitCity. Given the Allies' tactic oftrying to avoid unnecessarycivilian casualties, this protectedthe guns from attack, but thiscould do nothing to halt theonslaught. Around 80 per cent ofthe air strikes against the capitalwere being made at night by thetwo F-117A squadrons.

In February the USAFattacked a hardened bunker inthe suburbs of Baghdad. To avoidthe risk to civilians using amosque and a school in the nextblock, US planners opted toattack the bunker at night, whenneither would be in use. The jobwas assigned to the 37th TFW.Two LGBs were delivered in thesort of attack pattern found bestagainst such heavily armouredtargets - one weapon to breakopen the roof, a second toplunge deep inside to destroythe interior. The bombs hit ataround 4.30am on Wednesday 13February, at a time when thebunker was being used as a civilair raid shelter. More than 300

people sheltering inside werekilled. However, US officialsclaimed it had another use as ashelter for military personneland command/communicationsequipment actively engaged inthe defence of Iraq.

A senior Pentagon officialclaimed that another Iraqicommand centre "was operatingfrom the basement of the AlRashid Hotel in Baghdad, thebuilding in which Westernreporters and other foreignerswere staying. The presence ofthe latter had prevented it beingtargeted, he said. Journalistsinvited to tour the basementfound only one room equippedwith relatively simpleequipment consoles andmanned by two operators. It was,they were told, the hotel'stelephone exchange. If Iraq wereindeed reduced to depending onsuch simple communicationshardware to maintain links to itsarmed forces, the idea of a dual-use bunker becomes morefeasible.

GROUND FORCES ATTACK

After 38 days and nights ofbombing, it was the turn of theground forces. At 8pm on

Sunday 24 February, Allied unitsrolled over the border into Iraqand Kuwait. The land attack wasnine days behind the scheduleoriginally planned. The weatherin the early stages of the air warhad been the worst everrecorded in the Gulf, and hadslowed the campaign, while thediversion of aircraft to huntdown and destroy mobile Scudlaunchers had contributedfurther delays.

Instead of the "Mother of AllBattles" promised by SaddamHussein, the land war against ademoralised Iraqi Army rapidlydeteriorated into a rout. Afterless than 100 hours of groundcombat, Allied forces were onthe Euphrates river, and Iraq'selite Republican Guardformations south of Basra hadbeen reduced to a singleretreating division, plus thebattered remains of severalothers. President Bush appearedon US television to announcethat "Kuwait is liberated, Iraq'sarmy is defeated. I am pleased toannounce that at midnighttonight, exactly 100 hours sinceground operations commenced,and six weeks since the start ofOperation Desert Storm, allUnited States and Coalition

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Above: Pre-flight checks arecarried out on an F-117ANighthawk at Langley Air Base,prior to the 15-hour flight to theGuli.

Left: Many US air strikesagainst Iraqi targets displayedhigh precision. These facilitiesat Abu Ghurayb show no signsof collateral damage

forces will suspend offensivecombat operations."

Iraq's collapse after 43 days ofwar was due in large part towhat had been the most intenseaerial bombardment evermounted. The F-117A had madeup less than 3 per cent of theAllied aircraft numbers, but wastasked with attacking more than40 per cent of the targets. Thestealth fighter force had flownsome 1,270 sorties, with eachaircraft flying around 30missions. In more than 6,900flying hours, the force haddropped more than 2,000 tons ofbombs. LGBs accounted for only6,520 of 88,500 tons of bombsdropped on Iraq and occupiedKuwait by US aircraft during 43days of air attacks. This wasaround 7 per cent of the total,and one and a half times thenumber used during the eight-year-long Vietnam War. Successrate was around 90 per cent,compared with around 30 percent for the 81,980 tons of

unguided bombs used in actionin Southeast Asia. Circular ErrorProbability (CEP) of ordnancedelivered by aircraft such as theF-15E, F-16 and F/A-18 wasaround 30-40ft (9-12m) - a fifth ofthat achieved during theVietnam War. CEP of LGB andIR-guided bombs was in theorder of a few feet (less than 1metre).

In the weeks that followed theceasefire, the Iraqi Army wasagain in action, this timeengaged in suppressing revoltsby Iraq's Shi'ite and Kurdishpopulation. The Coalition forcestook no action to prevent this,beyond downing several Iraqifixed-wing aircraft that broke theceasefire conditions byattempting to fly. For most of theAllied air force, and for theF-117As, the war was over. On 1April, eight of the first 14 stealthfighters to leave the Gulf landedback at Nellis, the others flyingto Tonopah.

THE F-117A LEGEND

By the mid-1990s, the exploits ofthe F-117 force during the GulfWar had been boosted into whatcould be called "The F-117Legend", earning the aircraft areputation which itsmanufacturer and user didmuch to encourage. Newspaperstories, magazine articles andbooks recounted how the F-117A

had been the only aircraft toattack central Baghdad, and theaircraft that smashed the Iraqiaid-defence system in a singlenight, opening up holes thatnon-stealthy aircraft then usedto successfully attack othertargets. It was the aircraft thatshattered Iraq's nuclear reactorsin a single strike after massiveattacks by conventional aircrafthad failed. It managed all thiswithout the intensive supportformations needed byconventional aircraft, deliveringits weapons with pin-pointaccuracy.

Like most legends, the onesurrounding the F-117 did notstand up to detailed scrutiny.When the General AccountingOffice (GAO), the investigativearm of the US Congress,prepared a report on "OperationDesert Storm: Evaluation of theALT Campaign" this originallyappeared in classified form, butin response to GAO concernsthe DoD unclassifiedapproximately 85 per cent of theoriginally classified material inthe in the report. When theresulting declassified report waspublished in June 1997, itprovided an unprecedentedglimpse of the achievementsand limitations of the F-117 A.

The aircraft casualty rateduring Desert Storm was verylow compared to historicexperience from earlier wars,

and the planners' expectations.It was only 0.17 per cent - 1.7aircraft per 1,000 strikes. TheGAO believed that this lowcasualty rate was due to threefactors:• the ban on low-altitude tacticsafter day two,• the degradation of radar SAMsand the IADS in the early daysof the war,• a high proportion of strikeswere flown at night

The F-117 was the only aircraftto sustain no losses or evencombat damage. "However,these aircraft recorded fewersorties than any other air-to-ground platforms and flewexclusively at night and atmedium altitudes - an operatingenvironment in which thefewest casualties occurredamong all types of aircraft," saidthe GAO. "Moreover, given theoverall casualty rate of 1.7 per1,000 strikes, the most probablenumber of losses for any aircraft,stealthy or conventional, flyingthe same number of missions asthe F-117 would have been zero."

According to the USAF DesertStorm white paper, "the F-117was the only airplane that theplanners dared risk overdowntown Baghdad", and theAir Force has also stated that "sodangerous was downtownBaghdad that the air campaignplanners excluded all otherattackers, except F-117s and

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cruise missiles, from striking it."In joint testimony to the US

Congress on stealth and DesertStorm, Generals Horner andGlosson stated, "F-117s were theonly aircraft that attackeddowntown Baghdad targets - bymost accounts more heavilydefended than any EasternEurope target at the height ofthe Cold War." The GAOdisagreed, saying, "we found thatfive other types of aircraft maderepeated strikes in the Baghdadregion - F-16s, F/A-18s, F-lllFs,F-15Es, and B-52s. Largepackages of F-16s were explicitlytasked to "downtown" targets inthe first week of the aircampaign, but these taskingswere stopped after two F-16swere lost to radar SAMs overthe Baghdad area duringdaytime." It stated that "after thethird day, planners concludedthat for the types of targets anddefenses found in Baghdad, theF-117 was more effective."

Although US Congressionalresearchers tasked withcompiling the official USGovernment "after-action" reporton the Gulf War were given thewidespread access to classifiedinformation that their taskrequired, one highly classifiedreport stayed firmly closed to

them - the study of all Iraqiattempts to engage stealthfighters. The GAO was alsounable to obtain thisinformation, so the topic ofstealth aircraft vulnerability wasto remain a closed book foralmost a decade.

IRAQ DEFIANTIraq was to remain a thorn in theside of the United Nations.Although required to admit UNinspectors whose task it was tolocate and destroy all Iraqi long-range missiles, chemical andbiological weapons, and thefacilities used to develop andmanufacture these, Iraqpersistently harassed theseteams, and launched a majorprogramme of concealment,moving and hiding equipmentand records. In August 1996Saddam Hussein sent forces intonorthern Iraq and captured thecity of Irbil, a key city inside theKurdish haven established abovethe 36th parallel in 1991. InSeptember, US ships and aircraftattacked military targets in Iraqin response to this militaryoperation.

In October 1997, Iraq accusedUS members of the UNinspection teams operating

inside Iraq as being spies, andexpelled them. In November itexpelled the remaining six USinspectors and the UnitedNations withdrew the rest of theteam. This was to be start of aprotracted confrontation withSaddam Hussein. UN inspectorswere re-admitted to Iraq afterthe US and UK began a militarybuild-up in the Gulf, but Iraqannounced that it would notallow them to visit sitesdesignated as "palaces andofficial residences." Such siteswere suspected of being used toconceal possible weapons.

Angered that the UN seemedto be making no moves to endits economic sanctions, inAugust 1998 Iraq ended its co-operation with the inspectors,and on 31 October stopped theiroperations. The US and UKwarned of possible militarystrikes, and started a newmilitary build-up in the region.

B-1B IN ACTIONThe B-1B had not been usedagainst Iraq during the 1991 GulfWar. There were not enoughcrews qualified to deliverconventional weapons, and B-1Boperations had been suspendedfollowing the loss of an aircraft

on 19 December 1990 due to anin-flight engine fire.Modifications had been deemednecessary to improve engine fanblade containment, and the fleethad been grounded until 6February 1991.

In November 1998, two B-lBsfrom Ellsworth AFB and twofrom Dyess AFB were deployedto a their forward operating basein Oman for possible militaryaction against Iraq. On 11November the UN withdrewmost of its staff from Iraq. By thetime on the 14th that SaddamHussein agreed to re-admitinspectors, B-52s were in the airand within about 20 minutes'flying time of their targets. Theywere recalled, while two moreB-lBs already en-route to theGulf were diverted to PeaseAFB, New Hampshire.

The respite was short-lived.On 8 December the chief UNweapons inspector RichardButler reported that Iraq was stillpreventing effective inspections,and the UN teams once morewithdrew. On 15 December aformal UN report accused Iraq ofnot allowing access to recordsand inspections sites, and ofmoving equipment records andequipment from one to siteanother. A day later, the US and

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UK began Operation Desert Fox,an air campaign against militarytargets in Iraq.

During the course of the four-day campaign, US and Britishcombat aircraft flew more than650 strike and strike supportsorties. USAF B-52s launchedmore than 90 cruise missiles,while naval vessels launchedmore than 325 Tomahawk cruisemissiles. On the first night,around 50 targets "were attackedby US and British air and navalforces and, by the end of the four

Above: A UK-based B-1B isprepared for a strike missionagainst Yugoslavia, fa 74missions, the aircraft deliveredmore than 1,100 tonnes ofbombs.

Left: Three days into DesertStorm, planners decided thatthe F-117A was the mosteffective strike aircraft forBaghdad operations.

Below:A500lbconventional bomb about tobe loaded into a B-1B duringOperation Desert Fox,which saw the bomber'soperational debut.

nights of strikes, had attackedabout 100 targets.

The strike forces werefollowing a plan that had beendeveloped and refined over theprevious year. The main targetswere:• Iraq's air defense system• The military command andcontrol system• The security forces andfacilities involved inconcealment operations• The industrial base for Iraq'sWMD (Weapons of Mass

Destruction) and missileprogrammes• The military infrastructure,including the elite RepublicanGuard forces• A refinery used to produce oilproducts to be smuggled out ofIraq in violation of economicsanctions.

On 18 December, the B-1B hadits combat debut when twoaircraft from Dyess Air ForceBase, Texas, and Ellsworth AirForce Base, South Dakota, tookpart in air raids over Iraq. 86-0135Watchdog was from the 9th BSat Dyess, while 86-0096 WolfPack was from the 37th BS atEllsworth. The target for this firstB-l strike included a RepublicanGuard barracks in the Al Kutarea. This was attacked not withPGMs, but with conventionalMk 82 SOOlb (225kg) "iron"bombs, said Rear AdmiralThomas R. Wilson, USN. "Thispilot walked a stick of bombsacross this barracks facility." Onthe following night 86-0135 flewa second mission, accompaniedby 86-0102 Black Hills Sentinelfrom the 37th BS. Although afourth aircraft (85-0067 from the7th BW) had been deployed tothe region, it was unserviceable,so flew no combat missions.

On both nights, the aircraftflew at an altitude of around21,000ft (6,400m), and reported"heavy" AAA fire. Iraq madelittle use of its surface-to-airmissile systems. "These systemsare important to suppress,degrade, or in some casesdestroy to support the strike...These are mobile targets,"Admiral Wilson told reporterson 19 December. "They get upand move sometimes every 12-24hours... But the main thing aboutthe SAMs and integrated airdefense system is that to date,we have been able to fly in thesystem and not beensuccessfully engaged by any ofthe Iraq air defense systems."

On 18 December each base

despatched a single B-1B to theregion, raising the total numberof B-lBs available to Desert Foxplanners to three from eachbase. They arrived too late to seeany action.

CRISIS IN THE BALKANSThe next crisis that would seeUS stealth aircraft in actionoccurred in Europe. The Balkansis a region that has been abattleground for millennia, acrossroads between cultures andreligions and an area whichformed the frontier for at leastfour empires. Following WorldWar II, during -which the countrywas occupied by Germany, theYugoslav monarchy wasabolished and the SocialistFederal Republic of Yugoslaviawas set up. When thisdisintegrated in 1992, wars brokeout in the former republics ofSlovenia, Croatia, and Bosnia-Herzegovina. In the latter two,Serbs seized control ofsignificant parts of the countryand in a process dubbed "ethniccleansing" tried to expel thenon-Serb portion of thepopulace.

This process of conflict drewattention away from a mountingcrisis in Kosovo, a provincewithin Serbia. In 1974 theConstitution had been amendedto grant greater autonomy toKosovo, giving the ethnicAlbanian majority -who livedthere bilingual public education,bilingual public signs, and analternate judicial system. In 1989the Serbian Parliament voted toalter the constitution to reduceKosovo's autonomy to the federalstandards that had existed priorto 1974. Coming as it did on the600th anniversary of the loss ofKosovo to the Ottoman Empire,this decision created angeramong the Albanian Kosovars.In response to rising separatismin the Albanian Kosovarcommunity in 1991 Serbia

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dissolved the Kosovo Assemblyand all Albanian-run schools, hithe following year, separatistsproclaimed the Republic ofKosovo, but this was recognisedonly by Albania. When theCommunist regime in Albaniacollapsed in 1996, AlbanianKosovar separatists found iteasier to obtain weapons, aprocess which speeded the riseof an armed group calling itselfthe Kosovo Liberation Army(KT.A). As the process of violencespiralled, Kosovo and a newcampaign of "ethnic cleansing"formed an ever-growing part ofnews reports, and a source ofinternational concern.

Fighting between Albanianseparatists and Yugoslav forcesescalated in March 1998,creating new waves of refugees.By September 350,000 peoplewere estimated to have becomeinternally displaced or fledabroad. In May 1998, NATO

Below: A B-1B takes off fromRAF Fair!ord to begin a combatmission against Yugoslaviantargets. The base also housedALCM-armed B-52s.

planners started to study a widerange of military options forintervening in the growingcrisis, including the use of bothair and ground forces. As thesituation in Kosovo deteriorated,these plans gradually evolved.

On 23 September 1998 the UNSecurity Council approvedResolution 1199, demanding acessation of hostilities in Kosovoand warning that, "should themeasures demanded in thisresolution... not be taken...additional measures to maintainor restore peace and stability inthe region" would be considered.Next day, NATO threatenedmilitary intervention in Kosovo,and approved two contingencyoperation plans, one formonitoring and maintaining anycease-fire agreement whichmight emerge, and a secondinvolving air strikes againstYugoslavian forces operatingwithin Kosovo.

On 6 February 1999, peacetalks intended to halt ethnicviolence in Kosovo opened inRambouillet, France. As thesecontinued, NATO wasassembling the air forces

needed to conduct an aircampaign against Yugoslavia.These would eventually includeaircraft from the USAF, USN,Royal Air Force, and French AirForce, and for the first time sinceWorld War II would involveLuftwaffe aircraft in a combatrole.

Most of the strike aircraft -weretactical fighters or fighter-bombers, but a key ingredient ofany large-scale bombingcampaign would be the veteranB-52 bomber and the F-117ANighthawk. On 17 February, sixB-52s from Barksdale AFB,Louisiana, were redeployed toRoyal Air Force Fairford,England, and four days later thefirst F-117As began arriving atAviano Air Base in Italy. Duringthe flight of almost 14 hours fromHolloman AFB to Italy, eachNighthawk had been refuelled18 times by three differentgroups of tankers during thejourney - KC-135 Stratotankersfrom Grand Forks AFB, NorthDakota; KC-10 Extenders fromMcGuire AFB, New Jersey; andforward-deployed KC-135s fromFairchild AFB, Washington.

Around 250 maintainers andsupport personnel were alreadyin position at Aviano, havingbeen flown there aboard C-17transports.

The F-117s found themselvesat a crowded base which wasalready playing host to F-16sfrom Spangdahlem Air Base,Germany; F-15Es from RAFLakenheath, England; EA-6Bsfrom Marine Corps Air StationCherry Point, North Carolina;EC-130s from Davis-MonthanAFB, Arizona; A-lOs fromSpangdahlem; KC-135s from theMississippi Air National Guard;Portuguese F-16s; SpanishEF-18s; and Canadian CF-18s.

By late February, the USAFhad committed two air wings tothe growing forces. The 16th Air& Space Expeditionary TaskForce included the 16th and 31stAir Expeditionary Wings (AEW).The 16th AEW included B-52s,U-2s, F-15C/E, and KC-135s,while the 31st operatedF-16CJ/CG fighters, O/A-10ground attack aircraft, and thegrowing F-117 force, plusEC-130E airborne battlefieldcommand and control centres,

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EC-130H electronic warfareaircraft, and KC-135 and KC-10tankers. By the end of themonth, a third wing wasassigned to the region. The100th AEW included RC-135reconnaissance aircraft andKC-135s.

The Rambouillet talks werefinally abandoned in failure on19 March. By this time, around40,000 Yugoslav army (VJ) andspecial police (MUP) troops, andaround 300 tanks had beendeployed in and around Kosovo.On 20 March, these unitslaunched an offensive in Kosovo,driving thousands of ethnicAlbanians out of their homesand villages, summarilyexecuting some, displacingmany others, and setting fire tomany houses.

AIR DEFENCENATO faced a two-levelintegrated air-defence system.The Yugoslav Air and ProtectiveDefence force (JRV i PVO) - alargely volunteer force - wasresponsible for the early-warning radar network, thefighter force, and most of theheavy and medium SAMs, aswell as the command, control,and communications networkwhich controlled them. Thefixed SAM sites included eightbattalions of Russian-built S-75MVolkov (SA-2F) with 60launchers, and 15 battalions ofS-125 Pechora M (SA-3B), againwith 60 (mostly guad) launchers.Locally produced electronic

decoys were available to protectsome of the early-warningradars and SAM sites fromattack by ARMs.

An unknown portion of the"Low-Blow" target-engagementradars associated with the S-125system were fitted with a 15-mile(25km) range TV camera whichcould act as a fair-weathersubstitute for the radar. This add-on TV system was probablydevised by Nis ElectronicIndustry and the MilitaryTechnical Institute in Belgrade.At least some of the S-125systems were thought to havebeen upgraded. Yugoimport-SDPR was known to havedeveloped an upgrade andoverhaul package incorporatingdigital sub-systems includingdigital MTI, and other retrofitschemes were being marketedby Russia, China, Poland andUkraine.

The Army (VJ) controlledsome mobile medium SAMs,plus organic air-defence assetsincluding most short-range andman-portable missile systems,and self-propelled AAA. Missilesystems in VJ service included asmall number of 9M33M Osa-AK (SA-8b), 130 9K31 Strela 1(SA-9), plus a large number ofthe local S-10M2J version of the9K35 Strela 10M (SA-13). Man-portable SAMs included around300 9K310 Igla-1 (SA-16) andStrela 3 (Sa-14) and over 500variants of the SA-7, includingthe locally producedYugoimport-SDPR Strela 2M/A.

To prepare the way for the air

campaign, NATO mounted amajor electronic intelligence-gathering operation using USAFRC-135U Combat Sent andRC-135S Rivet Joint aircraft, theUS Navy's little-known EP-3Reef Point Orions and the RoyalAir Force Nimrod R.l.

During the final 72 hoursbefore hostilities, the JRV i PVOand VJ displayed a highstandard of electronic silenceand emission control. Theresulting lack of transmissionsfrom air-defence radars made itdifficult to locate Yugoslavia'smobile SAM systems.

With a total of 214 US and 130allied aircraft ready for action,late in the evening of 23 March,NATO Secretary General JavierSolatia gave NATO's SupremeAllied Commander Europe, USArmy General Wesley Clark,authority to launch OperationAllied Force. Its goals were todemonstrate NATO's resolve toend the crisis, and to degradeYugoslavia's military

Above: In March 1999, B-2sfrom Whiteman Air Force Base,Minnesota, began bombingraids on hardened targets inYugoslavia.

capabilities to carry out futureattacks against Albanians inKosovo.

B-2s IN ACTIONAttacks began with on the nightof Wednesday 24 March withthe firing of RGM/UGM-109Cand D Block 3109 TomahawkLand Attack Missiles (TLAM)from US Navy ships, and thelaunching of 27 AGM-86C Block1 Improved CALCMs fromB-52H aircraft operating fromRAF Fairford. In the earlymorning hours of 24 March, two

Below:Fiom the United Statesto the Balkans was a 31-hourround-trip mission, includingover-target loiter, involving airrefueUing.

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Block 30 B-2s of the USAF's 509Bomb Wing left Whiteman AirForce Base, Minnesota, to takepart in operation Noble Anvil.Each was armed with 16 2,0001b(900kg) Mk84 or BLU-109warhead variant Boeing JointDirect Attack Munitions (JDAM).Following several midairrefuellings, the two bombersspent several hours loitering inYugoslavian airspace andsuccessfully attacked multiplehardened targets, includingcommand bunkers and air-defence systems. The twoaircraft landed safely back atWhiteman AFB after 31 hours

aloft. A similar mission wasflown the following night,setting a pattern for nightlyraids. Often, the aircraft wereback in the air to begin anothermission as soon as they hadbeen refuelled and given a newload of bombs.

Using rotary launchers intheir internal weapons bays,each B-2 was able to carry anddeliver up to 16 JDAMs. Aselectable fuse on each JDAMwas set before the munition wasloaded, and allowed for a varietyof time delays - before or afterimpact - for the weapon'sexplosion. It took 30 minutes to

convert each "dumb" bomb intoa smart bomb. Ten technicianshad to work for four hours tobuild a full load of 16 JDAMs foran awaiting B-2. Since JDAMcan be dropped from up to 15miles (24km) from the target, itsuse reduced the risk to the B-2.Immediately after releasingweapons, the aircraft couldretreat, leaving the self-contained guidance systemwithin each bomb to guide theround to its specific target Aninertial navigational system,updated by GPS, steered thebomb by way of movable tail fins.

Four phases of military

operations were originallyplanned. Phase 1 was intendedto establish air superiority overKosovo, and to degradecommand and control and theintegrated air-defence systemover the whole of the FederalRepublic of Yugoslavia. Phase 2would attack military targets inKosovo and Yugoslav forces thatwere providing reinforcement toSerbian forces in Kosovo. Phase3 would expand air operationsagainst a wide range of high-value military and security forcetargets throughout the FederalRepublic of Yugoslavia. Phase 4"would redeploy the available

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forces as required.The air-defence system did its

best to resist the effects of theNATO attacks, and to avoidbeing engaged. JRV i PVO fireand signature-control disciplineis reported to have remainedgood. Following early strikesagainst the IADS, NATOspokesman Air Cdre DavidWilby, RAF, stated that".. wehave degraded it hard, there's nodoubt in our minds that it isshaky. I'm not saying it's down,I'm not saying it's a totallyneutralised threat, there willalways be a threat from that airdefence."

F-117A DOWNED

At about 8:45pm on 27 March,the IADS was to demonstratethat is was still functioning bydowning an F-117A. Aircraft AF82 806 had attacked a targetnear Belgrade and was headingback to base, when it was struckby a missile. As the aircraftentered an uncontrolled dive,the pilot struggled againststrong negative g-forces. "Theone fragment of this whole eventI can't remember is pulling thehandles. God took my handsand pulled," he said.

Left: The General AtomicsPredator UAV was used tomonitor Yugoslavian forcemovements. Several were shotdown.

After landing in a freshlyploughed field approximately 50yards (45m) from a road and railtrack intersection, he buried thelife raft and other items ofsurvival equipment which hadautomatically deployed duringthe ejection sequence. The pilotspent the next six hourshunkered down in a "hold-upsite" in a shallow culvert 200yards (180m) away from wherehe had landed, and waited inhope of rescue. More than sixhours after the bale-out a USspecial operations unit reachedthe area. After a careful anddiscreet authentication of hisidentity, search and rescuespecialists trained to recovercombat air crews rescued him.

F-117A WRECKAGEIn downing the F-117A, theYugoslavians scored apropaganda boost. Serbiantelevision showed video of theburning wreckage, and in othernews footage Yugoslaviancivilians danced triumphantlyon the aircraft's wing. For thefirst time, the legendary stealthfighter had proved vulnerable.

"We are fairly confident weknow what happened thatcaused the loss of this airplane,"Maj. Gen. Bruce Carlson, USAFDirector of OperationalRequirements, told journalistsshortly after the incident. "Butbecause of the fact that this is anongoing operation - I'mconcerned about the safety ofthe air crews - I'm not preparedto divulge it... Any furthercomments of the cause of theF-117 loss are unlikely to bemade until the current combatand high-threat operations haveended," he added. "And then if•we think that there's anoperational advantage to nottelling you, we probably won'ttell you." This tight-lippedapproach was echoed at a 26April press conference, whenNATO spokeman Major GeneralWald bluntly said, "We're notgoing to tell you whathappened."

The damage visible on theF-117 wreckage included whatpress reports have described as"bullet holes", plus a pittingvisible in areas such as the wingsurface. "Both are classicexamples of the type of damagewhich would result from a near-miss detonation of ablast/fragmentation warhead ofthe type frequently employed onearly Soviet heavy/mediumSAM systems," reported Jane'sMissiles & Rockets. At first sight,the distribution and condition of

the wreckage seemedincompatible with a direct orproximity-fused hit at typicalF-117 operating altitudes.However, the crash of an F-117Aat a US air show in Maryland inSeptember 1997 showed that theaircraft behaves oddly when outof control, descending in afluttering flight path similar tothat of a sycamore seed.

Press reports have suggestedthat the stealth fighter wasdowned by a lucky shot from anS-125 battery which hadobtained some idea of theaircraft's position from short-lived temporary tracks that hadbeen established by widelydistributed radars or haddetected the aircraft by using itsback-up electro-optical trackingchannel. In practice, the aircraft'sroute may have taken it over aYugoslavian test site used forradar or missile trials, givingexperienced crews equippedwith upgraded systems thechance to obtain a useful radarreturn.

Whenever stealth fighters hadcrashed in the USA, the crashsite had been sealed off and allfragments of the aircraftgathered up, but here was awreck in distinctly unfriendlyhands. Asked if he wasconcerned that parts of thewreckage of the F-117 mighthave been shipped to Russia foranalysis, USAF Director ofOperational Requirements Maj.Gen. Bruce Carlson said, "If theyshipped the parts to Russia,would that concern us? Sure, itconcerns us. We don't like togive anything away." However,he added, the F-117A is " whatwe called second generationstealth. And we've put a lot ofdistance between secondgeneration and the airplanesthat we're building now. Wethink that the result of thatmaterial, should it have gone toRussian hands... we think thatthe loss is minimal." Hedefended the decision not tobomb the wreckage. "Theairplane was lost and crashed ina rather remote location. It takestime to find those things. AndI'm not sure that the commanderin the field felt it was worth therisk to go in there and try tobomb it."

At least one piece of F-117Awreckage is still in Yugoslavia.The canopy of AF 82 806 is ondisplay in a new section of theYugoslav Aeronautical Museum.Inaugurated by Gen. SpasojeSmiljani, Commander-in-Chief ofthe Yugoslav Air Force, theexhibition features NATOaircraft and weaponry shotdown during Operation AlliedForce. Other exhibits includeparts of an F-16CG lost on 2 May1999, an RQ-la Predatorunmanned air vehicle (UAV)rebuilt from parts recovered

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Above: During the bombingcampaign against Yugoslaviantargets, the B-1B operated fromRAF Fairford, flying more than80 missions.

from two of the downed UAVs,the wreckage of a LuftwaffeCL289 UAV, and a near-intactexample of the RaytheonAGM-145 JSOW.

On the day that the USannounced the rescue of theF-117 pilot, NATO SecretaryGeneral Javier Solana statedthat NATO was moving intophase two of the air campaign.Air strikes would be focus moreon the Yugoslav Army andspecial police forces operating inKosovo. There the campaignagainst the Albanian populationwas growing in intensity, andwould continue to do so. In earlyApril, 13 more F-117 As deployedfrom Holloman AFB to take partin Operation Allied Force. Onewould replace the Nighthawklost on 27 March, and the otherswould increase the number ofF-117 As available in the treatre.

B-lBs DEPLOY

By this time, the USAF's thirdmodel of heavy bomber was inaction. On 29 March, B-1Bbombers were ordered to deployto Europe in support of NATOoperations over Yugoslavia.Before the aircraft could bedespatched to Europe, they

required a block-cycle softwareupdate to their defensiveavionics system. Carried out inless than 100 hours with theassistance of the 53rd Wing atEglin AFB, this would allow theaircraft to accurately identifyand jam Yugoslavian radars

Five B-lBs from the 28th BW atEllsworth arrived at RAFFairford, England, on 1 April.Four were from the 77th BombSquadron, and one from the37th BS. That night, two flewtheir first combat mission,dropping munitions overYugoslav military targets inKosovo. The targets for this firstB-1B mission were a series ofstaging areas that the YugoslavArmy had set up to bringtogether fuel, repair andprovisioning trucks in order tore-supply tank, armouredpersonnel carrier, and artilleryunits. "These staging areas arenot constant places, explained aPentagon spokesman. "Theymove around. They're indifferent places every day, andobviously we look hard for thesestaging areas. The B-l is wellequipped to deal with thosetypes of wide-area targets."

Speaking at a Pentagon pressconference on 14 May, Gen JohnJumper, Commanding Generalof US Air Forces in Europe,revealed that on that first night,the B-l bomber "was shot at andtargeted very precisely by SA-6s.The defensive systems on the

airplane worked exactly asadvertised." Later reportscredited the aircraft's RaytheonAN/ALE-50 towed decoy ashaving successfully lured awaymissiles that had been fired atthe aircraft. By the end of thecampaign, the AN/ALE-50 wasreported to have lured around 10missiles away from B-l bombers.

B-2 missions were stillcontinuing, and by 5 April atotal of 384 JDAMs had beendropped by B-2s against Serbiantargets. This total suggests thattwo aircraft had flown sorties on12 consecutive nights. Thecomposite skin of the aircraftwas "holding up very well",509th Logistics Groupcommander Col. Bill Hood saidon 5 April. "This should lay torest concerns people may haveabout the aircraft's stealthiness."

The degradation of theYugoslav defences was nowsevere. As early as the first weekin April, the Yugoslav airdefences were firing SAMs inballistic rather than radar-guided mode in order to avoidbeing counterattacked by aHARM. Speaking inWashington on 22 April, USJoint Staff Director ofIntelligence Adm. Wilsonannounced the results of thebombing on the Yugoslav forcesoperating in Kosovo. All four ofthe main lines of communicationinto Kosovo had been inter-dicted, reducing movements into

that region by around 50 percent. Damage to ammunitionproduction facilities had resultedin Yugoslav attempts to importmore and different kinds ofammunition, said Wilson."They're not having any successin that regard." The end result ofthe NATO air campaign was toleave Yugoslavia with "...a forcewhich has been in the field forsix weeks, seven weeks, eightweeks conducting operations,low on fuel, low on ammunition,low on food."

NATO Supreme CommanderEurope (SACEUR), GeneralWesley Clark, reported thataround 4,400 strike sorties hadbeen flown. Although theweather was average for thetime of the year, it was creatingproblems. "On about two-thirdsof the days we have had morethan half of the strike sortiescancelled," said Gen. Clark.Nevertheless, attacks on militaryindustries, and in particularammunition production weresaid to have been effective. "Wehave had some very goodsuccess against ammunitionstocks and we have done veryserious damage to his ability to

Bight: A view of one of the twocapacious internal weaponsbays of the B-2A. While thesecould carry a load of 50r0001b(22,680kg) on rotary launchers,the most likely warload is less,about 40,0001b (18,144kg).

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repair and maintain his aircraft,military vehicles, armamentsand munitions."

The F-117 may have been hardat work, but the headlines in thefield of stealth were going to theB-2. By early May, the B-2 forcehad dropped more than 1 millionpounds (450,000kg) of ordnanceon Yugoslav targets. Thiswarload had included more than500 JDAMs. Since each B-2 cancarry up to 32,0001b (14,500kg) ofordnance (16 JDAMs), this meansthat at least 32 missions had beenflown. "The jet's performancereally has exceeded all of ourexpectations," Brig. Gen. LeroyBarnidge Jr., 509th Bomb Wingcommander, told the press on 5May. On a typical sortie, eachbomber carried up to 16 2,0001b(900kg) JDAMs instead of thetwo carried by the Nighthawk.As a result, "A B-2 is eguivalentto eight F-117s. We can take thisthing thousands of miles; we cango into very lethal environments,and we can put the bombsexactly where we want them.Then we bring the guys home,turn the jets and do it again."The combination of the B-2 andJDAM was highly accurate. "I'veseen zero collateral damagefrom our strikes," Barnidge said,"and that's a pretty good record."

It was inevitable that this highoperational tempo wouldhighlight problems with whatwas still a relatively new aircraftBecause of an airflow-coolingproblem, the actuator remoteterminal (ART) which works thevarious control surfaces was oneof the high-failure items, but thiswas repaired on the spot.

By mid-May, NATO had flownaround 20,000 sorties againsttargets in Yugoslavia, andestimated that the defences hadfired more than 600 SAMs.Although Yugoslavia claimedthe destruction of more than 80NATO fixed-wing aircraft,helicopters, and UAVs, in factthe total NATO losses ofmanned aircraft had been onlytwo - the F-117 A, plus anF-16CJ shot down on 2 May. Asmall number of NATO aircraft- estimated by a NATO

Top left: The GBU-30 JDAM isthe weapon of choice for theB-2A, and about 500 weredropped on Yugoslavia in thespring of 1999, using the CPStargeting system. Thisamounted to over 450 tons ofmunitions.

Far left: to USAF post-strikeimagery, Craters mark theposition of what had been aYugoslavian SAM site at IvoSabac.

Left: to the hours of darkness, aB-2 is prepared for the longflight to attack targets inYugoslavia.

spokesman as "about five toten" - had received somecombat damage, but the USDoD would not comment on areport that an F-117 hadsustained damage following anear-miss from an SA-3 round.Spokesman Major GeneralChuck Wald would only say,"We have no indicationwhatsoever that they can track[F-]117s."

In previous wars, airdefences equipped withmissiles such as the S-75 (SA-2)and S-125 (SA-3) had achievedhit rates of only a few per cent.Before the conflict, Yugoslaviais reported to have beenconfident that it would be ableto inflict attrition rates of aboutsix per cent on NATO strikeaircraft. In practice, they hadmanaged a SAM kill rate of 0.3per cent (two aircraft for 600missiles launched), and anoverall attrition rate of around0.01 per cent (two aircraftdowned from more than 20,000hostile sorties). These figuresmade Yugoslavia's air defencesthe least successful of anymajor missile-equipped forceused in recent wars.

The first week of June saw theeffective collapse of theYugoslavian air-defence systemas a result of sustained NATOattacks, and on 9 JuneYugoslavia finally agreed toaccept the NATO demand towithdraw its forces from Kosovo.

By the end of the campaign,NATO had mounted 38,004strikes in 10,484 sorties. TheFairford-based B-lBs had flown81 combat mission. On the 74missions in which weaponswere released, the force droppedmore than 1,100 tonnes of bombs,mostly Mk 82 bombs and CBU-87 cluster bombs.

The B-2 force had set its ownrecord, with 51 of the 53 pilotsof the 509th having flowncombat missions. Eight B-2swere used, flying a total ofmore than 45 missions withonly one turn-back. Althoughthe stealth bomber flew only 1per cent of the total number ofAllied missions flown, itdelivered 8 per cent of thebombs dropped.

During a 21 October hearingof the Senate Armed ServicesCommittee hearing, Gen.Wesley Clark stated that Alliedcrews delivered more than23,000 bombs and othermunitions with less than 20incidents of collateral damage."That's an incident rate of lessthan one-tenth of 1 percent,"Clark said. "There's never beenanything like it in the history ofa military campaign, and Ithink it's a real tribute to theskill and proficiency of themen and women who flew andexecuted this campaign, toachieve that kind of precision."

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COUNTERSTOSTEAITHHaving created the first

stealth aircraft, it is hardlysurprising that the US DoD hasfunded the development ofcounter-stealth technologies.This has required a dualapproach. An effective anti-stealth defence will requiresensors able to detect low-RCStargets, along with weaponsable to attack these elusiveopponents.

The primary sensor is stillradar, which can be inproved inthree ways - increasing poweroutput to obtain stronger radarreturns form stealthy targets,using improved digitalprocessing techniques to detectfaint returns in the presence ofbackground clutter and hostilejamming, and moving to lowerfrequencies where today'sstealth technology is lesseffective.

Claims by radarmanufacturers that theirequipment have detected USstealth aircraft must be treatedwith scepticism. When not incombat, the F-117 is fitted withradar reflectors so that it showsup on air traffic control radars,and the same probably appliestotheB-2.

To strip away the protectionoffered by a low RCS involvesplacing more energy on target,and having a more sensitivereceiver to detect this energy.Both measures create their ownproblems. Greater power can bedelivered on target by using alarger radar antenna and a morepowerful transmitter, but theseincrease the size, weight and

cost of the radar, and reduce itsmobility. Increasing thesensitivity of a radar receiverbrings its own problems, sincethe output can contain enoughclutter and other false targets toplace a massive load on theprocessing hardware.

Rather than pursue such"brute force" solutions to theproblem of detecting low-RCStargets, radar designers aretrying new operating modes. Forexample, the fast scanningspeeds possible with anelectronically scanned array

Below: Early test flightsconfirmed the flyingcharacteristics of the B-2, buttesting of its stealth capabilitieswas to be prolonged.

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Right: The E-3A was designedbefore the era of stealthytargets but a planned upgradeprogramme will improve itseffectiveness.

Below: The Boeing E-3 Sentryis operated by the USA, UK,France, and collaboratively byother members of the NATOalliance.

Left: A variant of Marconi'sMartello radar was a candidatein the mid-1980s competition toselect a radar for a jointmilitary/civil US radarnetwork.

Below: The MiG-25 Foxbat wasdesigned to intercept high-flying bombers, but by 1977missile firing trials againstsimulated cruise missiles hadbegun.

make it possible for the radar totake note of suspect signalswhose value lies below thethreshold set for a true target, thenre-examine them once the rest ofthe scan has been completed

This is the approach whichEricsson Microwave Systems hasadopted with its Giraffe and SeaGiraffe Agile Multi-Beam (AMB)3-D radars. Intended for use withthe RBS 23 Bamse SAM system,Giraffe uses a "priority tracking"

scheme against difficult targets,and can detect a 1.08sq ft (O.lsq m)target at around a third of theradar's normal range. Sea Giraffeuses a single "omnibus"transmitter beam, plus a series ofreceive beams which give aroundfour times the time budgetpossible with a single beam. Thisallows the radar to spend moretime observing targets of interest.

Several years ago researchers atthe Mitre Corporation revealed a

novel operating mode whichshows how computing-intensivealgorithms may help with thedetection of stealthy targets."Track-before-detect" wasproposed as an aid to air-to-airradars, but could be applied toground-based sets. Instead ofmeasuring suspected signalsagainst a pre-defined threshold todetermine whether theyrepresented a target, a "track-before-detect" radar treats all

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signals as potentially genuineand attempts to build these intotentative tracks. A true targetwill gradually result in a"sensible" track, while falsetracks can soon be eliminateddue to their unreasonable andunrealistic behaviour.

One way of degrading theeffects of stealth technology is touse radars which operate atVHP and UHF frequencies,rather than in the microwaveband. Most Western long-rangesurveillance radars operate in D-band (l-2GHz), E-band (2-3Ghz)or F-band (3-4Ghz), but Russiahas long preferred to use C-band(0.5-lGHz), B-taand (250-500MHz)or even A-band (100-250MHz).Similar low frequencies are alsoused in some Chinesesurveillance radars. In the past,these equipments have often beendismissed as examples of Soviettechnological backwardness. VHFand UHF radars are relativelyeasy to design and manufacture,the reason why all the earlySecond World War radars wereof this type.

The need for smaller size,better low-altitude coverageand improved targetdiscrimination soon led tomost radars being built tooperate at microwavefrequencies but, even today,UHF and VHF frequenciesstill have some militaryadvantages. For one thing,their antennas tend to bebulky. This is a problem forthe user but it does givevirtual immunity from attackby anti-radar missiles - it isjust not possible to cram aVHF homing antenna into amissile seeker. They also offergood long-rangeperformance. To see thereason for this requires adetour into basic radio theory.

High frequency microwaveradio signals require a directline of sight between thetransmitter and receiver. Thustransmitted signals can beobscured by terrain featuresand maximum range isconstrained by the curvatureof the Earth. Operating at suchfrequencies makes long rangecommunications difficult, andthe first radio stations usedthe much lower LF or MFbands. At these frequenciesthe "surface -wave" effectbecomes apparent. The signalemanating from the antennatends to hug the Earth'ssurface, travelling well beyondthe horizon.

At the still higher VHF andUHF bands, the skywave isnot refracted back to theground and is lost. There isstill a useful degree ofground-hugging surface wave,however, which allows radioreception some way over thehorizon. The previously

Above: The envelope of a non-rigid airship makes a near-perfect radome for asurveillance radar, and thehelium atmosphere will notaffect performance.

BeIow:The model shows thegondola of one proposed USNsolution to the problem ofdetecting low-RCS targets - theAirship Industries/Westinghouse YEZ-2A.

Top right: Developed byRussia's Nizhny NovgorodRadio Technical Institute, the1L13 is a mobile two-dimensional radar operating inthe VHF band.

Right: The massive antennasof the Cape Dyer station ofthe DEW line lookimpressive, but this networkof North-facing radarstations is obsolescent.

mentioned "obsolete" UHFand VHF radars also makeuse of this effect, giving muchlonger ranges than directline-of-sight microwavesystems.

VHF PROBLEMSIn designing a stealth aircraft,RCS engineers work to defeatthe 1 - 20GHz microwavefrequencies used by mostradars. Equipments operatingat lower frequencies will beless affected by RAM andother RCS-reductionmeasures, giving them someability to detect and trackstealth aircraft.

Luckily for the operators ofstealth aircraft, UHF and VHFradars are no panacea, so they

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still make up a small portionof the total number of threats.Long wavelengths create theirown tactical and engineeringproblems.

For instance, such radarstend to be physically big,since large antennas areneeded in order to obtainadaguately-narrow beam-widths and high antennagains. A side effect of therelatively wide beam createdby even a large VHP antennais that the radar's resolution inazimuth is poor.

When the designer sets outto combine VHP operatingfrequencies with mobileoperation, the resultingsystems are often reminiscentof the Second World WarGerman Freya and arecumbersome to deploy.

Russian electronics companyNitel and research organisation.

Above: General Electric's FPS-118 over-the-horizon radarbounces HF signals off theionosphere hi order to trackaircraft flying far out over theAtlantic. The beam can be

electronically steered inazimuth, while range isadjusted by varying thefrequency (and ionosphericbounce behaviour) of thetransmitted signal.

Nizhny Novgorod RadioTechnical Institute are confidentthat they have cracked theproblem of tracking stealthaircraft. Nitel's 55G6 family ofVHP-band radars are physicallylarge, but can track low-RCStargets such as cruise missilesand stealth aircraft, says thecompany. According to Nitel, thebasic advantages of VHF-bandradars are low cost, good all-weather performance, andresistance to jamming. Since adirectional antenna at such longwavelengths must be very largein order to achieve a narrowbeamwidth, it cannot be fitted toan anti-radiation missile, so theradar is invulnerable to ARMattacks. Nitel claims that VHPradars were the only Iraqi air-defence sensors to survive the1991 Gulf War, but says it doesnot know what success (if any)the Iraqis had in detecting ortracking USAF F-117 stealthfighters. Given the scale of theRussian post-conflict analysis ofearlier military campaigns inwhich its equipment was used,this professed ignorance seemsstrange, unless hag is refusingto provide feedback.

In the past, Western analystshave often dismissed RussianVHP radars as primitive, but ina 1997 discussion with theNizhny Novgorod RadioTechnical Institute's DrAlexandr Zatchchepitsky(General Designer) and ValeryMarskin (Deputy Director ofResearch, and Chief Engineer)the author learned that asurprising degree ofsophistication is built intothese huge radars. In earlyVHF-band radars, the signaldetected by each antennaelement was carried at radiofrequency down to a centralreceiver, but the 55G6-TJ hasanalogue to digital convertersbuilt into each of the individualelements which make up thevertical and horizontal array.Although the huge inverted-T-shaped antenna of this radar hasvertical and horizontal legs 100ft(30m) long, and an azimuthbeamwidth of three degrees, theRussians claim a performancesimilar to that of the USAN/TPS-70 E/F-band radar,with an accuracy of 33ft (100m)in range, 0.2 deg in a Tin-ruth, and1,970ft (600m) in altitude.Keeping the signal to noise ratioof the radar as low as possiblewas the key to achievingangular accuracies of around1/15 of the beam width inazimuth, and between 1/15 and1/25 of the beam width inelevation.

France's Parasol alerting radaroperates at even lowerfrequencies in the HF band (3 to30MHz). Built under a contractfrom the French ministry ofdefence, Parasol was developed

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OTH Radar System

by Thomson-CSF to detectstealthy threats and anti-radiation missiles. It was testedin the mid-1990s.

Under contract from theGerman Federal Office forDefence Technology andProcurement, Alcatel DefenseSystems is developing ademonstration UHF cueingradar for missile-defenceapplications. The primary role ofthis radar is the detection oftactical ballistic missile (TBM)threats, and at UHF frequenciesthe radar cross-section of these istypically 10 to 100 times greaterthan that at microwavefrequencies, while atmosphericloss and clutter are considerablylower. However, Alcatel SEL hascommented that at UHFfrequencies the use of stealthtechnology (what Alcatel SELterms "radar camouflage" ofmissile targets) is practicallyimpossible.

Surface-to-air missile systemsuse radars which scan largeareas of sky and carry outseveral air-defence taskssimultaneously. The cueingradar is able to handle the taskof searching for incomingthreats, then hand over newly

detected targets to the weaponsystem radar. By concentrating itsradar energy into the 5deg x 5degcueing window defined by thecueing radar, the weapon-systemradar will be able to acquire thetarget at the earliest possible time.

The USAF insists that thestealth features designed into theF-117 and B-2 cannot becircumvented by long-wavelengthradar, but during the 1991 GulfWar a Royal Navy warship isreported to have picked up radarechoes form F-117 stealth fighters.If true, this may be due to therelatively long wavelengths usedby older British naval surveillanceradars. The now-obsolete MarconiType 965 operated at metricwavelengths, presumably A or Bband.

OTH RADARSOne of the most promisingmethods of detecting a stealthaircraft is by means of over-the-horizon (OTH) radars. Inthe United States, research onequipment of this type hasbeen under way for about 25years, with the aim ofdeveloping better defencesagainst conventional bomber

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US Defensive Radar Coverage

Above: The Pave Paws phased-arrayradar on the US East and West coastsare anti-SLBM systems, intended todetect sneak attacks by missile firingsubmarines.

AboverighfcEy the 1970s, the USradar early-warning radarnetwork had shrunk to thisemasculated form. Although thedevelopment by the then SovietUnion of the Tu-26 "Backfire" andTu-160 "Blackjack" bombersprovided the impetus forimprovements, the collapse of theSoviet Union ended most of these.

left-Based at Shemya in theAleutian Islands, the Cobra Daneradar covers the Eastern tip of theUSSR, including the strategicKamchatka Peninsula.

threats. The aim was to createlong-range radars able totrack aircraft which aremasked from the view ofconventional ground-basedradars by the curvature of theearth's surface.

Radars of this type direct apowerful sky wave towardsthe earth's ionosphere. This isrefracted and returnedtowards the earth's surface,

illuminating a distant patch ofterrain or sea. Any targetspresent in this area createradar echoes which follow thereverse route back up to theionosphere and thus back tothe receiver of the OTH radar.

One problem in suchdependence on sky waves isthat the signal is redirectednot by reflection but byrefraction, so propagationconditions cannot becalculated by simplegeometry. The amount ofrefraction experienceddepends on the frequency ofthe signal and the density ofthe ionosphere. The lattervaries with time, as does theheight of the ionosphere.Variations occur on both dailyand annual cycles and cannotbe predicted accurately. As theamount of refraction beingexperienced alters, so alsodoes the distance between thetransmitter and the locationwhere the sky wave returns tothe earth's surface a distanceknow to radio operators asthe "skip distance".

Studies of a possible USOTH system began in theearly 1970s and systemdefinition work wascompleted by November 1973.The contract to develop aprototype of what was thencalled the over-the-horizonbackscatter (OTH-B) radar was

awarded in March 1975 butthe programme soon ran intodifficulties with both cost andtimescale. A restructuringbegan in December 1976which put the effort on a morerealistic basis, allowingtechnical feasibility tests fouryears later.

The initial goal of theprogramme was to developand test a limited coverageprototype radar. Based inMaine, this was used to assessthe level of technicalperformance required by anoperational system. At thesame time, further work wascarried out on basic OTHradar technology in order toincrease the effectiveness ofthe final system. Areasexplored by this researcheffort included ionosphericmodelling and prediction,adaptive beam-forming, low-sidelobe antennas andcomputer algorithms forsignal processing and radarcontrol.

The prototype system washanded over to the USAF inMay 1980, allowing the startof nine months of systemperformance tests. These gavethe confidence needed tomake the decision in October1981 to proceed with thedevelopment and deploymentof an operational system, acontract for which was

awarded to General Electricin June 1982. This called forthe upgrading of theexperimental system inMaine to a fully operational60 degree azimuth coverageInitial Operating Sector (IOS)of the East Coast RadarSystem.

US COVERAGEOfficial designation of thesystem is AN/FPS-118.Transmission frequency is5-28MHz, with an output powerof l,200kW A system with foursites was planned. One wouldbe in Maine, the other three onthe US West coast, Central USAand Alaska. Intended to provideearly-warning of aircraft ormissile threats approaching thecontinental USA, it haseffectively been closed downwith the ending of the Cold War.

The Raytheon AN/TPS-71Relocatable OTH Radar(ROTHR) is much smaller thanthe FPS-118, and is designed toallow rapid deployment toprepared sites. Developed for theUS Navy, it consists of two sites- a transmitter and a combinedoperations centre/receiver -spaced up to 110 miles (180km)apart. It transmits at frequenciesof 5-28MHz, and has a poweroutput of 200kW. Maximumrange is 1,875 miles (3,000km).

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The possibility that OTHradars could be used to trackstealth aircraft emerged in thesummer of 1986 when Dr. D.H.Sinnott, a senior principalresearch scientist of theAustralian Department ofDefence's Research Centre atSalisbury, stated during adefence conference inCanberra that the entireairframe of a stealth aircraftwould reflect energy at HFfrequencies.

An OTH radar system has asevere limitation in terms ofminimum range. Since theradar signal must reach theionosphere, reflect and thenreturn to the earth's surface,an OTH radar cannot detecttargets operating within aradius of about SOOnm(900km). Aware of this fact, thecrew of a stealth aircraftwould be able to initiate achange in course or otherevasive tactics once they wereconfident that their aircraftwas no longer visible to theOTH radar.

Russia has an equivalent tothe AN/FPS-118. Known asOTH-B, this has been in servicesince the 1970s. It transmits at afrequency of 4-30MHz, and has apower output of 30MW An OTHradar system is also being

developed in China. Expected tohave a range of 2,190 miles(3,500km), it operates between5-28MHZ, and emits lOOOkW ofpower.

On the other side of theglobe, Australia has the needfor an OTH system and vasttracts of desert in which tolocate antennas. Under theJindalee programme, a singletest site has been built atAlice Springs in the centre ofthe country. This will laterform part of a three-siteoperation system due to enterservice in the mid-1990s. Theother sites will be in thenorth-east and the south-west.

It remains to be seen just howeffectively OTH and VHP radarscould "hand over" stealthytargets to microwave bandradars. Much of the secret testflying of the F-117A and earlierXST stealth fighters in Nevadaagainst threat systems will havebeen intended to investigate thisproblem.

"Can the F-117 or B-2 betracked by radar? The answer tothat question is yes," says USAFDirector of OperationalRequirements Maj. Gen. BruceCarlson. "All vehicles can betracked by radar. However, thekey here is to know when you'rebeing tracked by radar, what

radars are tracking you andwhat the fidelity of that track is.For instance, a very lowfrequency radar - whether it'stracking a conventional, first-generation or a third-generationstealth airplane - has very littlecapability to track it withprecision. They know thegeneral area that the airplanemay be in, but they can't track itwith precision needed to guideeither another airplane to it or aSAM to it. So what you needthen is the target-tracking

radars, the higher frequencyradars that are much moreaccurate, and that's where thestealth airplanes that aredesigned from the bottom uphave their significantadvantages."

Another possible techniquefor detecting stealth aircraftinvolves inter-netting a seriesof fixed-site and mobileradars, using themintermittently as active searchsystems and for the rest of thetime as passive direction-

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left Upgrades have allowedthis US Army Patriot radarstation to control improvedversions of the Patriot missile,including the PAC-3 anti-missile variant.

Right: Triangulation locates theposition of a hostile emitter.Stealth aircraft must remainradar- and radio-silent while inrange of enemy ESM stations.

finders. This was first done asa way of avoiding ARMattacks. The enemy is facedwith a series of blinkingemitters which ESMs andARMs "see" as onlyintermittent signals whoselocation and characteristicschange rapidly. Even if one ormore sites can be attackedand knocked out, the networkwill continue to function.

Detection of stealth targetswould involve the use of agroup of netted radars able totransmit on a wide range offrequencies. As a result of theinevitable compromises in thedesign process, stealthmeasures cannot be equallyeffective at all angles andfrequencies. The greater thenumber of frequencies anddirections of the signalsarriving at a stealth aircraft,the greater the chances thatone or more might create ausable echo.

One promisingcountermeasure to stealth isbi-static radar. In a normal(mono-static) radar, thetransmitter and receiver are atthe same location and oftenshare a common antenna. In abi-static radar, they arelocated some distance apartand several receivers mayshare a single transmitter. An

Below: The Ballistic MissileEarly Warning System atFylingdales in the UK has beenupgraded to deal with newthreats, which may includestealthy re-entry vehicles.

aircraft which relies onshaping or faceting to reduceits RCS is designed to ensurethat an incoming radar signalis not reflected directly backto the radar. This works wellagainst a conventionalmono-static radar but couldresult in the incoming radarenergy being "dumped" in thedirection of a listeningreceiver forming part of abi-static system.

In France, Thomson-CSF hasdeveloped the D-Fence bi-staticwarning radar to detect stealthythreats. Like the Parasol radarmentioned earlier, this operatesin the HF band (3 to 30MHz),and was built under contractfrom the French MoD. D-Fenceis reported to be able to detectstealth aircraft, UAVs and cruisemissiles, and to have a range oftens of kilometres.

Being passive, receiver sitesare immune to the attentions ofthreats such a directionaljammers, anti-radiationmissiles and "Wild Weasel"aircraft. In a bi-static radar,there are several potentialways of protecting thetransmitter. The conceptknown as "sanctuary radar"involves installing thetransmitter in a safe locationfrom which it may serve anumber of front-line receivingsites. Suitable locations for thetransmitter could be far backfrom the battle area, either ata ground location heavilyprotected by air defences orin a high-flying aircraft.Another possibility wouldinvolve mounting thetransmitter unit in ageo-stationary satellite.

Bi-static radar systems neednot incorporate a transmitter, butcould exploit the RF energyfrom other emitters. LockheedMartin's Silent Sentry systemuses a passive receiver to detectand track airborne targets viathe reflected energy fromtelevision and FM radio stations.

Since these signal sourcesbroadcast at VHP and UHFfrequencies, their transmissionsmay be strongly reflected bystealth aircraft.

During tests of this concept,Lockheed Martin is reported tohave used signals from FM radiostations in Gaithersburg,Maryland, to track commercialaircraft flying in and out ofBaltimore-WashingtonInternational Airport. However,like VHF and UHF radars, SilentSentry is not accurate enough tobe used for targeting. It can beused only to detect a target, andto alert a separate tracking radar.

ADVANCED RADARS

Perhaps the best prospect foran anti-stealth radar is atechnique only just emergingfrom the laboratory. This isknown as a "carrierless radar".Tiny low-powered radars ofthis type are already used forsome commercial applicationssuch as creating images of theinterior of concrete structures.However, larger and vastlymore powerful systems couldbe developed for airsurveillance and targettracking.

At first sight, the concept ofa carrierless radar seems likea contradiction in terms.Engineers use the word"carrier" to describe the basicradio-frequency signal towhich modulation is applied.Such modulation can bespeech or data (in the case ofa communications link),pulses (in the case of pulsedradar) or variations infrequency (in the case of acontinuous-wave radar).Remove the carrier and itmight seem that nothing isleft to carry the modulation.

All the radar engineerneeds is a pulse (probably ofrectangular shape) with whichto illuminate his target. Usinga mathematical technique

known as Fourier Expansion,any waveform can be brokendown into a series ofsinusoidal components - amain component, known asthe fundamental, andmultiples of this fundamental,known as harmonics. Vary theshape and frequency of thewaveform being analysed andthe resulting "mix" offundamental and harmonicswill also change. For everyshape of waveform, a"cocktail" of these componentscan be obtained.

The exact operatingprinciples of carrierless radarare classified but the broadidea seems to be to reversethe process. Instead oftransmitting the desiredwaveform, transmit the correctmix of frequencies which willrecreate it. These could mostlybe of low power and couldstretch across most or even allof the frequency bands usedfor radar. The resultingsynthesised pulse would notbe affected by radar-absorbentmaterials.

OPTICAL SYSTEMSStealth technology may also bepartially nullified by the use ofsensors operating at frequenciesfar above those of traditionalmicrowave radars. For decades,the highest frequencies used formilitary radars were in J-band(10-20GHz), but growing use isnow being made of K band (20-40GHz) and M band (40-lOOGHz). Strictly speaking, theterm "millimetre-wave" shouldbe reserved for M band andhigher, but in practice it is oftenapplied to a growing number ofsystems operating at or near35GHz.

An early application formillimetre-wave radar was inshort-range air-defence.Hoflandse Signaalapparatenoffers several 35GHz radars suchas the ASADS gun-mountedradar for AA weapons such as40mm guns, Spear 35GHzradar/TV fire-control system forlow-level air-defence units, andLIROD (LightweightRadar/Optronic Detector) navalfire-control system.

Ericsson chose K-band for itsEagle fire-control radar so that theresulting narrow beam, high-gainantenna, and minimal sidelobeswould help give the equipment alow radar signature. Their successlead to an improved version beingselected as part of the RBS 23BAMSE SAM system. Radars thatcombined millimetric andconventional microwavefrequencies in a single trackercould use the lower frequency todetect targets, and the higherfrequency for subsequenttracking. A common combinationteams I-band and K-band.

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Above: SAM systems whichdon't use radar will pose athreat to stealth aircraft. Shorts'Javelin is command guided andhas an IR surveillance system.

Hollandse Signaalapparatenis probably the best-knownmanufacturer of this type ofdual-frequency radar, offering itsFlycatcher radar, Sting radar/EOnaval fire-control system, andSTfR naval tracking radar.However, the concept has alsobeen used by other companiesincluding Elta ElectronicIndustries in the EL/M-221 navalfire-control radar, and BharatDynamics in the PIW 519weapon control radar. Russiandesigners used I and K-band inthe radar controlling the Kinzhal(SA-N-9) naval SAM system, andare thought to have used thesame dual frequencies in theMR-114, -145, and -185 radars for100mm AK-100 naval gunmount.

The ability of a laser radar(lidar) to detect hydrocarbons inthe atmosphere could provide auseful anti-stealth sensor.According to a paper on remotelaser sensing published by Carlo

Right: One possible stealthdetector is bi-static radar, asystem whose transmitter andreceiver are in differentlocations. The "sanctuary"concept shown here is probablythe ultimate bi-static system.Ground-based receiving sitesoperate in conjunction with atransmitter in a high-flyingaircraft (whose position ismeasured using ground-basedDME stations), or even in asatellite.

Kopp in Air Chronicles, "a jetaircraft exhaust trail will containconcentrations of hydrocarbonsof the order of parts per million,which can be 100 or more timesthe background atmosphericconcentration. Should we see aproliferation of stealthtechnology in the next century,the ability to track such aircrafteven under VFR conditionswould significantly limit anopponent's opportunities to usehis stealth aircraft productively.By constraining hostile stealthaircraft operations to IFRconditions where lidar isineffective, an opponent will beat the mercy of the weather andthus more predictable in termsof operational activity." Sincehelicopters in NOE (Nap-Of-the-Earth) flight and hover are in amoderate to high engine powerregime, and generating largeamounts of exhaust gas, Koppbelieves that a battlefield-surveillance lidar could alsodetect stealthy battlefield

helicopters in the class of theRAH-66 Comanche.

IR DETECTIONTechniques such as directshielding, active cooling andpassive surface treatments suchas special paints and coatingshave reduced the IR signature ofstealthy aircraft and missiles, butnot to the degree that RFsignatures have been reduced.IR thus remains a viable methodof detecting threats. The long-term goal of stealth engineersmust be to reduce IRdetectabihty in the 3-5 and 8-12micron bands to levels whichwould make IR sensors asblunted in range as their RFcounterparts, but until this hasbeen achieved, IR and other EOsensors may prove valuableshort-range anti-stealth sensors,particularly against missilethreats. Their usefulness againstmanned aircraft may be limited,since high-value stealth aircraft

are likely to stay well above thecombat ceiling of point-defencesystems, attacking using guidedmunitions such as laser-guidedbombs, or well away from thedefences and attacking withstand-off missiles.

The ability of an EO system totrack a stealth aircraft wasshown at the 1996 FarnboroughAir Show when a military crewdemonstrating the BAe (nowMatra BAe Dynamics) Jernasversion of Rapier used thesystem's EO tracking system toacquire and track the NorthropGrumman B-2 Spirit stealthbomber at a range of 3.75 miles(6km). In practice, a B-2 taskedwith attacking Farnboroughwould never have come withinRapier range of the airfield, sothe entire exercise said nothingabout the aircraft's potentialvulnerability to ground-basedsensors.

The B-2 may have some IRsuppression tricks up its sleeve.Northrop Grumman's only

Bi-Static "Sanctuary" Concept

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comment on the Farnboroughincident was that, "It's easier todetect the B-2 at air shows thanin combat," so it is possible thatany IR-suppression system fittedto the aircraft would not beactivated while the bombercould be observed by non-USsensors.

Some idea of the currentlevel of Western capabilitiescan be gleaned from theAN/AAS-42. This has a 911b(41kg) chin-mounted sensorhead that contains the opticsand detector assembly, plus athree-axis internally stabilisedgimbal system. It operates inconjunction with a 371b (16.3kg)

Left: The Antey 9K33 Osa (SA-8"Gecko") uses radar guidancebut has a back-up opticaltracking mode which could beused against stealth aircraft.

Below: Advanced IR-guidedweapons such as the StingerSAM (seen here in vehicle-mounted form) might be able tohome in on the jetpipes ofstealth fighters.

controller/processor unitmounted within the aircraft.Unofficially reported to be adual-band device operating at3-5 microns and 8-12 microns,the system has six operatingmodes, which are similar tothose of the aircraft's HughesAN/APG-71 radar. Azimuthand elevation scan volumesare selectable, and separatelycontrolled by the aircrew.Scanning can be donemanually or under the controlof the pilot.

The MiG bureau areenthusiastic proponents of EOsensors, and the stabilised EOsystem carried by the MiG-29and Su-27 combines an infra-red search and track (IRST)sensor and a laser rangefinderwhich share a commonstabilised Cassegrain optionalsystem. The Sukhoi team takesa more conservative view ofthe virtues of EO sensors, butinstalled a similar system onthe Su-27

EO sensors are also carriedby the Eurofighter 2000, Rafale,and the Mitsubishi F-2. The

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proposed dual-band IRSToriginally planned forEurofighter 2000 proved tooexpensive, so the specificationwas relaxed, allowingcontractors to offer single-bandor dual-band systems. In August1992, a development contractwas finally awarded to theEurofist consortium for thePirate (Passive Infra-RedAirborne Tracking Equipment)single-band system. FIAR acts aslead contractor, while ThornEMI is the system designauthority. Spanish team memberwas Eurotronica, which hassince been replaced by Tecnobit.

The Defence Optronicsdivision of Thomson-CSF isworking with SAT to developthe forward-looking optronicsystem for Rafale. The system ismounted behind the radar, andhas two sensor heads on theupper fuselage just ahead of thecanopy. The IR search andimaging unit uses infra-red andhigh-definition CCD technology,and is mounted to port. Theidentification and rangefindingunit (based on an eye-safe laserrangefinder) is to starboard,while a common processing unitis located in the lower fuselage.The combined system will allowpassive detection, visualidentification, and damageassessment of targets in air-to-aircombat.

Relatively little is knownabout the Japan AviationElectronics laser/EO system onthe Mitsubishi F-2. It is probablya dual-band (3-5 micron and 8-18micron) sensor suitable for air-to-air and air-to-ground use.

The range at which aircraftcan be detected by today'sfighter-mounted EO systems isclassified, but some clues can beobtained from the publishedperformance of the IR-guidedVympel R-27T1 and R-27ET1 air-to-air missiles. These lack the

Ranges of Russian SAM Systems

mid-course updating facility ofthe semi-active radar-guided R-27R1 and R-27ER1 models, somust be locked on before launch,yet have maximum ranges of 45miles (72km) and 81 miles(130km), respectively.

In 1997 press reportssuggested that Iraq was about toobtain the ability to track USstealth fighters by purchasingTesla-Pardubice Tamara ESMsystems from the CzechRepublic. A year earlier Maj.Gen. Oldrizhikh Barak,president of the Tesla-Pardubice,told the Russian newspaperPravda that a Tamara systemconsisting of three units spacedseveral miles apart can trackstealth or similar low-signatureaircraft from distances of about12 miles (19km).

Tamara monitors the spectrumfrom 820MHz to ISGHz, andnormally consists of three

Above left: The Teal Ruby infra-red sensor was devised as aresearch tool into the problemsof detecting air targets byobserving their IR signaturefrom orbit.

Left:The Almaz S-300PM(SA-lOb "Grumble") uses aTrack-Via-Missile (TVM)guidance system which mayhave been designed with low-RCS targets in mind.

Be/ow:The likely operatingaltitude and location ofWestern surveillance aircraftwould bring them within thefirepower of long-rangesurface-to-air systems such asthose operated by theRussians. This diagram wasprepared before thedeployment of the US AirForce's E-8 Joint Stars andretirement of the EF-111, butthe potential problemremains. Plans to develop astealthy aircraft in place of theE-8 were abandoned.

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Right: The Improved Hawk isNATO's most commonmedium range SAM. Furtherupgrades are needed tocounter future stealth aircraftdevelopments.

stations mounted on Tatra 8158x8 trucks. By comparing thetime of arrival of detectedsignals at the three stations, thesystem is able to derive thebearing of the emitter, thenidentify it by comparison with abuilt-in threat library. Tamaraprovides coverage over a 100degree arc, while its maximumrange is determined by theradar horizon. The Czechcompany has been promotingTamara as an anti-stealthmeasure, but has not identifiedthe nature of the RF signalemitted from stealth aircraftwhich would allow these to betracked. The range of 12 milesmentioned above suggests arelatively low level signal.

It is unlikely that any onesingle technology willdramatically decrease thevulnerability of steath aircraft.By pooling the information fromseveral sensors, no one of whichis giving reliable data, the"signal-to-noise" ratio may beimproved to the point werestealthy targets can bedistinguished.

MULTI-SENSORS

Much of the effort currentlybeing devoted to developingnext-generation air defences isconcentrating on the idea ofnetting different sensors, andparticularly different types ofsensor, then fusing the data fromall sources to create a tacticalpicture. This technique isalready being used on somemodern air-defence trackingsystem such as OerlikonContraves Skyshield, whichfuses data from the radar, TVand IR channels to help trackdifficult targets.

The Surveillance andWarning Systems Departmentof BodenseewerkeGeratetechnik is testing atechnology demonstrator for amulti-sensor system able todetect aircraft, helicopters,UAVs, and missiles. Developedunder Germany's Aufklarungund Bekampfung nicht-ballisticher Flugkorper (ABF)research and developmentprogramme, this will use acombination of IR and UVsensors that will scan an entirehemisphere. Fusing the targetfeatures seen in the two bands isexpected to sort out potentialtargets from clutter and noise. Averification system consisting ofa high-resolution IR sensor and alaser rangefinder will be used toexamine these potential targets,obtaining additional information

Bight:The massive Antey S-300V (SA-12a "Gladiator") ispart of a Russian SAM systemdesigned to counter low-RCSmissile targets.

such as range, velocity and IRfeatures. The equipment willthen create three-dimensionaltracks which will allowdiscrimination between realtargets and clutter.

Conventional targetassociation and trackingtechniques such as probabilisticdata association (PDA) and jointprobabilistic data association(JPDA) work well given gooddata from a single tracking

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sensor, but are less effectiveagainst the sort of poor-qualityand intermittent data likely to beobtained when attempting totrack a low-RCS target. Researchwork carried out at the NationalUniversity of DefenseTechnology, in Hunan, China,has devised track initiation, dataassociation, and trackingtechniques suitable for use witha network of distributedtracking sensors. Such anetwork might be able tomaintain a reliable track bycombining individual detectionsor fragmentary tracks fromevery sensor in the system.Work has also been carried outat the Tsinghua University inChina to develop new data-fusion techniques which wouldallow stealthy targets to betracked by netted radars.

ANTI-STEALTH SAMS

The latest generation of

Above: Jamming strobesdesigned to mask large targetswill be even more effectivewhen used to protect stealthaircraft.

medium-range SAM systemsoffer anti-stealth capability.Following Desert Storm, therequirement for Patriot PAC-3was extended to cover not onlyconventional aircraft, UAVs, andballistic missiles, but also tacticalair-to-surface missiles, anti-radiation missiles, tacticalballistic missiles, and what aFiscal Year 97 report by the USDirector, Operational Test andEvaluation (DOT&E), describedas "additional performancerequirements needed to counteradvanced stealth technology".The minimum RCS Patriot PAC-3 can engage has never beenreleased - Russian sources claim1.08sq ft (Olsq m), but this figuremay not be reliable.

The previous chapter (Stealthin Action) described howYugoslavian S-125 Pechora (SA-3"Goa") surface-to-air missilesystems had been upgraded toimprove their anti-stealthcapability. This did not mark theend of S-125 upgrades. Under aprogramme in which Russia'sRosvooruzheniye organisation isto upgrade 50 Egyptian Pechorasystems to the Pechora-2standard, the detection rangeagainst stealth aircraft is beingincreased from up to 10 miles(16km) to more than 19 miles(30km), say the system'sdesigners.

Since the USA has been

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left: In the absence of stealthythreats, the US is focusingfuture developments of theStandard naval SAM on theanti-ballistic missile role.

COUNTERS TO STEALTH

openly developing small cruisemissiles since the mid-1970s, itis only to be expected that thelatest generation of SovietSAMs has been designed todeal with such low-RCStargets. One of the first was theSA-10 Grumble, a weaponwhose development may havebeen protracted by the need tocope with cruise missiles.

According to the USDepartment of Defense, atleast 500 SA-10 sites would beneeded in order to create aneffective defence againstcruise missiles. A system ofthis size would have at leastsome capability against stealthaircraft. The SA-10 systems areinter-netted (a techniguedescribed earlier whendescribing anti-stealth radaroperations) and in 1987 the USDoD confirmed that theweapons have "a capabilityagainst low-altitude targetswith small radar cross-sectionssuch as cruise missiles".

The Antey S-300V (SA-12aGladiator) will be a much moresignificant threat, particularly toB-2 operations. Like the SA-lObthis is a mobile system, in thiscase with tracked rather thanwheeled vehicles, and was firstfielded in the mid-1980s.

The S-300 and S-300Vsystems were extensivelymodernised during the 1990s, to

Above: The display of a Patriotfire-control system showsseveral air targets. How wellwill the system cope withstealth aircraft?

Left: The original Patriot wasdesigned to deal with aircrafttargets. Improved versions willbe used in the planned MEADSinternational SAM system.

create new and more combat-effective variants. The 96L6Ephased-array target designationradar and 30N6E2 illuminationand guidance radar of theAlmaz/Fakel S-300PMU2 FavoritSAM system (an upgradedS-300) are able to detect cruisemissiles flying at extremely lowaltitude, and the manufacturersclaim an improved capability toengage stealthy targets.

The most recent Russian SAMsystems to be announced arethe Antey 2500 and the S-400.Both are based on existingsystems and were designed tocounter low-RCS targets, butneither is able to deal with truestealth aircraft. The Antey 2500is based on the earlier S-300V(SA-12 "Giant/Gladiator"), butuses the improved 9M82M and9M83M missiles in place of theearlier 9M82 and 9M83, while itsground eqnipment has beenupgraded to incorporateimproved radar signalprocessing technigues.

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In a magazine articledescribing the Antey 2500SAM system, Antey GeneralDesigner Veniamin ^yfefremovand Yuri Svirin, directorgeneral of the MariyskyMashinostroitel ProductionAssociation, say that the systemis intended to counter"battlefield and theatre missilesand other high-speed, 'stealth'highly manoeuvrable and hard-to-hit targets". In practice,however, its anti-stealthcapability seems limited. Whilethe Antey S300V could dealwith targets whose RCS was aslow as 1.08 to 0.54 sq ft (0.1 -O.OSsq m), the minimum size oftarget which can be engagedby the Antey 2500 is 0.22sq ft(0.02sq m).

By 1999 Russia had beguntrials of the S-400. Little isknown about this system,which the Russians say can fireat least two types of missiles -one for use against aircraft, theother against ballistic missiletargets. Like the Antey 2500, itmay be based in part onimproved versions of existinghardware.

THE SOLUTIONAt present, the only realisticsolution to the problem ofengaging low-observabletargets at other than shortrange is the use of multi-modeguidance coupled to data linksfor mid-course updating. Oncea target has been located and a

missile (-whether surface-to-airor air-to-air) is launched againstit, the weapon must be able tofly towards the target underautopilot/inertial control,relying on mid-course updatesto get it close enough to itsquarry to allow the seeker tolock on. This technique is usedby all the SAM systemsmentioned so far, and by theEuropean Family of Anti-airMissile Systems (FAMS) basedon the two-stage Aster 15 andAster 30 missiles. This is due tobe deployed in land-based andship-board forms. Both systemswill use Aerospatiale verticallylaunched missiles, a Thomson-CSFArabell/Jbandmultifunction phased-arrayradar, plus common computersand displays. The radar isexpected to be able to handleapproximately 50 tracks, and toengage up to 10 targets at thesame time.with rounds beingfired at rates of up to one persecond.

Two types of round areplanned, both vertical launchedand ramjet powered. Aster 15missile will have a range ofbetween 6 and 10.5 miles (10-17km), while the Aster 30 - alsoknown as Aster ER (ExtendedRange) - will have a tandembooster and greater range.During the initial stages offlight, the missiles will beinertially guided, receivingtarget updates via the Arabelradar. Once close to the target,the J-band Electronique Serge

Dassault AD4A active pulse-Doppler seeker will beactivated.

The US has no all-new long-range SAM on the drawingboard, but the latest PAC-3version of Patriot has animproved capability againstballistic missiles, stealth aircraftand stand-off jammers. It has abetter radar, larger rocketmotor giving greater range, anew 35GHz (K-band) seekerwith three operating modes(including fully-active), and animproved warhead and fuze.

IMPROVED MISSILESStealth threats also demand theintroduction of improved oreven all-new air-to-air missiles.By the mid- to late-1990s, theability to fly close to a targetbefore engaging a terminalguidance mode was becomingan essential feature in the AJMsof all nations facing the threatof stealth aircraft or missiles.This capability first becameavailable to USAF and otherNATO air arms with thefielding of the Hughes (nowRaytheon) AIM-120 AMRAAM,a missile -which combines anactive radar seeker withupdateable inertial mid-courseguidance. Developed to replacethe ATM-7 Sparrow, AMRAAMis smaller and lighter, yet has arange of between 30 and 40nm(55-75km).

Matra BAe Dynamics saysthat its MICA (Missile

Above: The AIM-120AMRAAM missile (seen hereon test below the wing of anF-16) is now in service with theUS and its main allies.

Right:The Rafale A prototypedemonstrates an air-to-airarmament of four Matra BAeDynamics MICA "fire-and-forget" missiles and twowingtip-mounted Magics.

Below: Early test firings of theMatra BAe Dynamics MICAwere from ground launchers. Itis apparently in the sameperformance class as the USAMRAAM.

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Intermediat de Combat Aerien)will match the performance ofthe US missile. Two alternativemodels of seeker are offered - apassive IR unit for air-combatmissions, and an active-radarseeker for interception sorties.

In short-range combat, MICAis locked on to its target beforelaunch. Medium-rangeengagements would be flownunder strap-down inertialguidance, with the seeker beingactivated later in the flight.During long-range shots, theinertial system would be given anin-flight update. MCA is 10.17ft(3.1m) long and weighs around2401b (110kg). Its solid-propeUantrocket motor gives a maximumrange of between 31 to 37 miles(50-60km), and its aerodynamiccontrol surfaces are supplementedby a thrust-vectoring system toensure high agility.

The Russian equivalent ofthe AMRAAM is the R-77. Inits basic form, this is poweredby a solid-propellant rocketmotor, but a ramjet-poweredRV-AAE version is known tobe under development. It isunlikely that Russia will beable to afford to field the RV-AAE in the near future, butChina is reported to befunding the project.

Even for these high-performance missiles, downinga stealthy aircraft or cruisemissile will not be easy. Newpatterns of multispectralseeker may be needed. Forexample, one US project isdeveloping a seeker intendedto detect the small amount ofenergy emitted by the radaraltimeter and engine of cruisemissiles.

In the late 1980s Gen. LarryD. Welch, then the US AirForce chief of staff, predictedthat, "It would take anincredible density of radars" tocreate a workable defenceagainst the B-1B and B-2. In awar, the US bombers would flythrough gaps in radarcoverage, potentialweaknesses that are plottedand regularly monitored by USintelhgence-gatherrng.

STEALTHY CRUISEIn the absence of any Russianstealth aircraft, the US DoD seesstealthy cruise missiles as amore likely future threat. Suchmissiles could appear in theinventories of Russia, China, andseveral Middle Eastern nations,either as the result of exports ofthe weapons themselves, or as a

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result of stealth technologybeing sold to nations engaged indeveloping ballistic or cruisemissiles.

During 1997 hearings of theUS Senate Armed ServicesCommittee, General Howell M.Estes HI, Commander in Chiefof the North AmericanAerospace Defense Command(NORAD), and the Commanderin Chief of the United StatesSpace Command(USSPACECOM), said, "We areworking on issues to give usbetter defensive capabilitiesagainst the cruise missile threat.Fighter upgrades and nextgeneration fighters, such as theF-22, wiH improve our ability todefend against such weapons.We do not have the capabilitytoday that we would like tohave to defend North Americaagainst cruise missiles ... we willneed to ensure we have thenecessary defensive systems inplace before the threat becomespainfully real in the future."

Under the Radar SystemImprovement Program (RSIP),USAF E-3 Sentry AWACSaircraft are being given anupgraded and more reliableradar. A new pulse-compressedwaveform will improve itsability to detect low-RCStargets, while other classifiedimprovements will help theaircraft detect and track cruisemissiles. When all the planned

modifications are completed,the upgraded E-3 should beable to detect a stealthy cruisemissile at a range of more than100 miles (160km), passing thisdata to an E-8 Joint Starsaircraft. Originally developed todetect and track ground targets(a capability used to great effectduring the 1991 Gulf War), theE-8 will be given the ability totrack low-flying aircraft,helicopters and missilesattempting to hide in groundclutter. It should be able todetect and track stealthy cruisemissiles, and direct the fire ofair- or ground-launchedmissiles. Fighters or SAM siteswould not have to acquire thetarget, but would launchmissiles into a "basket" in thesky so that the E-8 could takecontrol of the weapon anddirect the interception.

Similar upgrades are beingplanned by the US Navy toimprove its E-2C early-warningaircraft. The RadarModernization Program (RMP)will fit the aircraft with a new 18-radar-channel ADS-18 antenna,solid-state transmitters, anddigital receivers. The upgradedradar will offer improved target

RighkThis MiG-29 Fulcrumfighter is armed with a pair ofmedium-range AA-10 Alamomissiles, plus four short-rangeAA-8 Aphid dogfight weapons.

Above: Another electronicplatform that made animpressive debut in the GullWar was the E-8 Joint-

Surveilance Target AttackRadar System (J-STARS),subsequently used over theformer Yugoslavia.

184

COUNTERS TO STEALTH

tracking in high-clutterenvironments and over land. Inthe longer term, the USN hopesto replace the ADS-18 antennawith a new UHF electronicallyscanned array (UESA). Bothchanges will allow the radar toconcentrate its RF energyagainst specific high-prioritytargets, so should improveperformance against low-RCSthreats.

Many of the techniquesneeded to detect and trackstealth aircraft and missileshave been tested at the PacificMissile Range Facility in Kauai,Hawaii. A project designatedMountain Top has investigatedmethods of extracting the tinyradar returns from stealthytargets from background clutter.This effort was expected to leadto a follow-on Mountain Top 2series of experiments intendedto prove the techniques neededto deal with stealth aircraft andstealthy cruise missiles.

Russia is carrying out its owninvestigation of potential anti-stealth techniques. Scientistshave successfully tracked low-observable targets against aforest background, and a newversion of at least one air-to-airmissile has been developed forthe anti-stealth role.

Similar work is under way inother countries, but on asmaller scale. Late in 2000, theUK announced that ThomsonRacal Defence, the DefenceEvaluation and ResearchAgency (DERA) and University

College London 'would beundertaking a three yearprogramme into "innovativeradar research related tocounterstealth". This workwould include 10 individualprojects, and covers detection,tracking and classification of"difficult" and stealthy targets inland, sea and air environments.

For the foreseeable future,stealthy targets and smallmissiles will pose problems forair-defence systems. Mostdefence systems cost more thanthe weapon they are intendedto counter, and coping withstealth technology is noexception to this rule. A late-

1990s article in the magazineLockheed Horizons warned, "Itwill, in all probability, take ageneration for the world to re-arm with yet undeveloped anti-stealth weapons. And, in thattime, stealth technology willlikewise continue to improve."

As the defences improve, thedesigners of stealth aircraft arebeginning to react "There hasbeen continuous improvementin both analytical andexperimental methods,particularly with respect tointegration of shaping andmaterials," F-117A projectmanager Alan Brown noted ina technical paper. "At the same

AAove:The Vympel R-33 (AA-9"Amos") missile was designedfor use on the MiG-31"Foxhound" but may be used toarm the Su-27 "Flanker". UnlikeAMRAAM, it does not useactive-radar guidance.

time, the counter stealth factionis developing an increasingunderstanding of itsrequirements, forcing thestealth community into anotherround of improvements. Themessage is, that with all thedramatic improvements of thelast two decades, there is littleevidence of leveling off incapability."

185

INDEXA-12 Avenger n, 86 et seqAdvance Technology Fighter(ATF), 13

Advanced Combat experimentalprogramme (ACX), 114

Advanced Cruise Missile (ACM),77 et seq

Advanced Manned StrategicAircraft, 63

Advanced Tactical Aircraft (ATA),86 et seq

Advanced Tactical Fighter (ATF),56,78 et seq

Advanced Technology Bomber(ATB), 67 et seq, 73 et seq

"Advanced Transport TechnologyMission Analysis", 93AGM-129A, 77 et seqAGM-28 Hound Dog missile, 61,62Aircraft factories, 22,23Airfields, 22,23Airframe heat, 50Airship Industries/WestinghouseYEZ-2A airship, 170

Alcatel Defense Systems missile-defence radar, 172

ALCMs (Air-Launched CruiseMissiles), 76 et seq

Anti-stealth air-to-air missiles, 182Anti-stealth SAMs, 180Aurora, 90 et seqAvro (Hawker Siddeley) Vulcan, 56AX (AFX) programme, 86

BBAe Experimental AircraftProgramme H, 100,112

BAe UAV101Balkans, 159 et seqBeUAH-1G, 35AH-1J, 35AH-1S Cobra, 35,36Model 67 (X-16), 59OH-58D Stealth Kiowa Warrior,95,96

Bi-static radar, 175"Black Manta", 93"Black" programmes, 68 et seqBoeingAGM-86B ALSM, 35

B-52,35,56,57E-3 Sentry, 131,169X-32 JSF, 89 et seq, 122X-45A UCAV, 104

Boeing Sikorsky RAH-66Comanche, 96,128

"B-X bomber", 94

CCamouflage and markings, 14 et seqCanberra bomber, 18Cancellation systems, 48 et seq"Carrierless" radar, 175Cavities, 36Chaff and flares, 139Chain Home early-warningradars, 27,29

Chinese stealth technology, 100CIA (Central Intelligence Agency),58,60,106,108

Circuit Analogue Absorbers, 47Cobra Dane radar system, 173Cockpits, 38"Combat Dawn" programme, 102"Compass Arrow" programme, 102Composites, 42Contrails, 22Convair F-102 Delta Dagger, 40Counter-stealth technology, 168etseq

Cruise missiles, 75 et seqCuban Missile Crisis, 63

DDallenbach Layer, 43DASA (FADS) Mako (Shark), 101Dassault Aviation Aeronef deValidation Experirnentale

(AVE) UAV, 105Dassault Mirage 2000,35Dassault-Breguet Rafale, 48,52,100,114

Dazzle camouflage, 17de Havilland Mosquito, 42Decoy RPVs, 144Decoys, 138Desert Fox, Operation, PersianGulf, 159

Desert Shield, Operation, PersianGulf, 148 et seq

Desert Storm, Operation, PersianGulf, 152 et seq

DEW line radar network, 170Diffraction, 30Dihedrals, 31

Dornier LA-2000,100

EEl Dorado Canyon, Operation,Libya, 146

Electromagnetic waves, 24Electronic aids to stealth, 130 et seqElectro-optical detection of stealthaircraft, 176

Electro-optical systems, 133Engine inlets, 37 et seqEngine noise, 51Engine nozzles, 49,50Eurocopter Deutschlandhelicopter blade control, 95

Eurofighter Typhoon, 100,112,178European stealth technology, 100European UAVs, 105

F"F-19", 11, 69,116Faceting, 11,36,69Fairchild A-10,20,21,50Fan Song radar, 61Ferris, Chris, 20,21Ferrite paint, 46,47, 60,106FI-X (Japanese next-generationfighter), 99

Folland Gnat, 56FS-X (Japanese Fighter, Supportexperimental) project, 99

Fuhs, Professor Allen E, 12,56Future Airborne Weapon System(FAWS, Germany), 105

GGeneral Atomics Predator UAV, 163General Dynamics F-16,20General Dynamics/McDonnellDouglas A-12 ATA, 86 et seqGerman stealth technology, 100Gotha Go.229,59"Granger" electronic warfareunit, 60

"Grassblade" stealth helicopter, 97Groom Lake test facility, 90GrummanA-6 Intruder, 33A-6F Intruder, 86EA-6B Prowler, 38EF-111A, 57F-14 Tomcat, 18,21,40FB-111H, 67

Gulf War, 21,143,148 et seq"Gusto" (CIA project), 60

186

INDEX

HHandley Page0/400,15Hampden, 15Victor, 36

Harrier GR3,19,22Harrier, 37"Have Rust" programme, 75Hawker Hunter, 56Hertz, Heinrich, 25HMS Revenge, 16Horten Ho IX, 59"Hot spots", 52 et seqHunting 126 research aircraft, 50Hyper-X UAY 90 et seqHyTech project, 91

IIndian stealth technology, 100Infrareddetection of stealth aircraft, 176emissions, 48 et seqjammers, 140

Iraq, 13,21,148 et seqIraqi air defences in Gulf War, 151etseq

Israel Aircraft Industries HA-10UAY 105

Italian stealth technology, 100Izmaylov, Col. Vladimir, 97

JJamming aircraft, 141 et seqJamming of SAMs, 57Japanese stealth technology, 99Jaumann absorber, 45Johnson, Clarence "Kelly", 59Joint Air-to-Surface Stand-OffMissile (JASSM), 78Joint STARS, 88Joint Strike Fighter, 88 et seq, 122Just Cause, Operation, Panama,146 et seq

KKamov Ka-60 Kasatka, 97Keldysh Research Centre, 48,124Kongsberg Nytt Sjomalsmissile, 71Kosovo, 141,159 et seq

LLampyridae (Firefly) programme, 10:Laser radar, 133Laser radar anti-stealth sensors, 176Lebanon, 146

LFI (Russian lightweight front-linefighter), 98

LFS (Russian lightweight frontalaircraft), 98

Light Helicopter Experimental(LHX) programme, 96

LMFI (Russian lightweightmultifunctional front-line fighter), 98

LockheedA-series aircraft, 60A-ll, 61,108A-12,58, 61, 68,108ATF, 35CL-282 (variant of F-104Starfighter), 59

CL-400 "Suntan", 60D-21 reconnaissance RPY 62Echo 1RCS predictionprogramme, 53

F-117 Nighthawk, 11 et seq, 34,36,37,39,49,53,56,64,68 et seq, 79,90,116,132,146

Have Blue, 13,21,40,49,53,63, 68,78Mach 5 stealth concept, 52Q-Star, 53Senior Prom, 64 et seq"Skunk Works", 59 et seqSR-71 Blackbird, 35,46,51,60,90,108Tier E and Tier m UAV103TR-1,47,59,106,108U-2 series, 18,45,60 et seq, 68,106U-2R, 59,106U-2S, 59,106YF-12A, 61YMQM-105 Acquila RPV, 102,103YO-3A, 53

Lockheed Martin A/F-117X, 69F-22 A Raptor, 42,47,80,120,132X-35 JSF, 89 et seq, 122

Lockheed Martin/BoeingDarkStar UAV, 103

Long Range Cruise Missile(LRCM), 78

MMartin 294 (RB-57D), 59Martin Marietta X-24,64Matra Apache, 77Matra BAe Dynamics StormShadow, 78

MCA (Indian Medium CombatAircraft), 100

McDonnell Douglas (Boeing)F-4 Phantom, 21,22-15 Eagle, 19F-15 Eagle STOL demonstrator, 50

F/A-18E/F Super Hornet, 87McDonnell Douglas Harpoonmissile, 38

McDonnell Douglas No Tail Rotar(NOTAR), 95

McDonnell Douglas/Bell LHX, 95MC-X transport, 93Messerschmitt Bf 109,15Mikoyan 1.42 and 1.44 MFI, 98,124Mikoyan 1-2000, 98Mikoyan-GurevichMiG-3,16MiG-25,53,169MiG-29 Fulcrum, 33

Mission Adaptive Whig, 40Mitsubishi F-2,47 99,178Mountain Top stealth detectionprogramme, 185

Multi-sensor stealth-trackingsystems, 179

NNASA/Boeing X-36 UAV, 104Navaids,134 *Night colours, 15Night vision goggles (NVG), 134Nitel stealth-detecting radar, 171Noriega, General ManuelAntonio, 146,147

North AmericanF-107A, 52,53F-108, 61XB-70, 60 et seqYF-93A, 38,39

NorthropB-2 Spirit, 12,13,36,39,48,49,54,64,67, 70 et seq, 92,94,118,132,161 et seq, 168

N-1M, 66Tacit Blue, 13,88.90Tacit Rainbow drone, 143,144YB-49/XB-49, 66YF-23,49, 80 et seq

Northrop GrummanGlobal Hawk, 103 et seqPegasus UAY 102

OOver the horizon (OTH) radarsystems, 171 et seq

Overholser, Denys, 63

PP-50 Barlock radar, 63Panama, 13,146

187

Panavia Tornado IDS, 39Parasol alerting radar, 171Patriot radar system, 175Pave Paws radar system, 173Plasma cloud, 48,124Powers, Francis Gary, 18, 60, 62,106"Prime Chance" operation, 96Pulse detonation engines, 91

RRadarand radar cross-section, 24 et seqbeam shapes, 131counters to stealth, 168 et seqcross-section (RCS) and aircraftsize, 57

cross-section (RCS) reduction, 56cross-section (RCS) test ranges(indoor/outdoor), 54,55

ranges, 56 et seqwaveforms, 130wavelengths, 30waves, 24

Radar-Absorbent Structural (RAS)materials, 47

Radar-absorbing (and radar-absorbent) materials (RAM), 11,24

Rainbow (CIA project), 60RAM, 36, 42 et seqRayleigh scattering, 29Raytheon AIM-120A AMRAAM, 42"Red Wagon" project, 62Rich, Ben R., 63 et seq, 70 et seq, 116Rickenbacker, Eddie, 14Rockwell InternationalATF proposal, 78B-l, 35,38,39, 63,67B-1A, 49,56,58,59,108B-1B, 44,49,56,57, 66, 72,110,137,158,164 et seq

B-1C, 72RPVs (remotely piloted vehicles),101 et seq

Russian stealth technology, 97 et seqRyan"Lucy Lee" project, 62Model 136, 62Model 147A Fire Fly RPV, 62Model 147B Fire Fly RPV, 62,101Q-2 Firebee target drone, 62

SSaabJ35 Draken, 36JAS-39 Gripen, 39

"Saber Penetrator" programme, 65Salisbury Screen, 43 et seq, 60SAMs against stealth aircraft, 57Schwarzkopf, General NormanH., 148

Secrecy 68 eq seq"Senior Citzen" transport, 93"Senior CJ", 71"Senior Ice", 65,71"Senior Peg", 65"Senior Trend", 68,116"Shamu", 88"Skyquake", 90"Smart skins", 145Smoke and light, 22Sopwith Snipe, 15Spad fighter, 14Spad Xffl C.1,15Special Access Programs (SAPs),68 et seq

Stealth aircraft "sightings", 93,94Stealth helicopters, 95, 96Stealthy cruise missiles, 183SukhoiS-37 Berkut (Golden Eagle), 98,126T-60S (S-60), 98

Supermarine Spitfire, 16Surveillance radars, 170Swedish Highly AdvancedResearch Configuration (SHARC)UAV105

Sweetman, Bill, 12,91,109SX-3 (Japanese stealth aircraftproject), 99

TTamara ESM system, 178"Teal Dawn" programme, 65,76"Teal Ruby" space-based infraredsensor, 51,178

TeledyneModel 147T RPV 102Model 154 (AQM-91A CompassArrow) RPV, 35,102

Model 324 RPV, 35Model 350 RPV 35RPVs, 61

Teledyne Ryan Tier II Plus UAV, 103Terrain reference navigation(TRN), 133 et seq

Testor/Italeri "F-19" kit, 11,12Thermal signatures, 48 et seqThomson-CSFRCS-prediction software, 53TRS-22XX radar, 25

Thorn EMI RCS prediction polardiagram, 54

Tier 3A, 93"TR-3A', 93

Travelling Waves, 30, 39 et seqTupolevTu-95 and -142 Bear, 132Tu-160 Blackjack bomber, 96 et seq

UUAVs (unmanned air vehicles), 101etseq

UCAVs (Unmanned combat airvehicles), 104

Ufmitsev, Pyotr, 33, 63Urgent Fury, Operation, Grenada, 146

VVietnam War, 18,19,22,28, 42,61,63, 95,101

WWatson-Watt, Sir Robert, 27Wavelengths, 25Weapons carriage, 41"Wild Weasel" anti-radar aircraft, 143WindeckerAC-7 Eagle 1, 63YE-5A, 63

Wing sweep angle, 36World War II stealth aircraft, 59

XX-30 National Aerospace Plane(NASP), 91

XST (Experimental StealthTactical aircraft), 59, 64,66

Y"Yehudi" rights, 22YF-113G. 93Yugoslav air defences, 56,161Yugoslavia, 161 et seq

ZZuiho (Japanese carrier), 18

188

An up-to-date,illustrated

analysis of thefighters andbombers that use

incredible stealthtechnology todefeat enemydefences