torpedoes in naval warfare - radio and ......torpedoes in naval warfare s do not concentrate on war...

TORPEDOES IN NAVAL WARFARE

S

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PRACTICALMECHANICS

Editor: F. J. CAMM

VOL. VII. MARCH, 1940. No. 78

THE INVENTED NEEDBy the Editor

IN walking through one of our largeLondon stores the other day, I

reflected upon the enormous number ofgadgets-a word I use for want of abetter term, gadgets being somethingyou don't want, but must have !-which have been produced on theassumption that people would inventan excuse to use them. The successfulinventor is one who caters for an exist-ing need, whereas most of our un-successful inventors are those whofirst invent the need and then pro-duce an invention for the inventedneed.

Most people possess a large numberof gadgets presented to them on specialoccasions, such as birthdays or atChristmas, which have cost, in toto,quite a large sum of money, but whichhave merely given them temporarypleasure at the time the gifts were made.Thus, these expensive gadgets are nomore than toys which amuse for a shorttime. They are placed by in drawersand seldom looked at again.

Multiple GadgetsONE of the most popular lines for

the inventor is to produce onegadget which does the work of six. Icannot think of any successful multiplegadget or tool. Thus we have lighterswhich combine a watch, a nail file, apocket knife, a pair of scissors, and apencil and a rule. In order to producethe completed design to a size which willmake it fit the vest pocket, not one partof the gadget is really satisfactory.Incidentally, why do inventors liketo make things specially for the vestpocket ? The number of devices, aswell as books, which I possess whichhave been specially designed to fit thevest pocket would fill a van. It is timethat inventors remembered that the vestpocket is already overloaded and cannotcarry further devices.

In engineering there is a very largenumber of combination tools. You donot see a skilled engineer using them,however. They fail in one or moreimportant directions. You rememberthe watches which were sold some yearsago whose dials included a number ofsmaller dials telling the time in mostof the important cities of the world.They failed commercially because theycatered for a need which did not exist.

Era of Cases -THIS is also the era of cases. Directly

something is produced, someoneelse wishes to sell a case for it. Thereare fancy wallets with divisions markedstamps, treasury note, driving licence,insurance certificate, registration card,etc. There are cases marked pyjamasand brushes and collars and ties.Apparently, the producers of thesegadgets have not a high opinion ofpublic intelligence, for they presumethat we need to be told that a collar boxhas collars in it.

One of the queries I sometimesreceive concerns a list of things toinvent. There is no limit to the numberof things still required, and my adviceto the budding inventor is not to wastehis time inventing a need, but to produceinventions which are needed. Needlethreaders exist by the thousand, andthey will never be successful. Patentalarm clocks which wake you up afterthey have boiled the water, made thetea, cooked the breakfast eggs, andoperated the vacuum cleaner have alsobeen produced in large numbers, butnone of them have succeeded commer, 1 -ally. Similarly, time -control switcheswhich switch on the radio at a pre-determined hour and switch off againare also failures. Inventors shouldremember that the human race has notyet reached that stage where it is tootired to move.

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Working on the stern section of ,a torpedo

THE word " torpedo " comes from theLatin, torpere, meaning, " to berigid," the term being originally

applied to denote a certain family ofelectrical fishes of the ray or skate variety.Exactly how the term originally becameused to denote a submarine weapon ofaggression is difficult to ascertain. All weknow is that the notion of the explosivetorpedo arose during the time of theAmerican Civil War in the sixties of thelast century, at which period certaip veryprimitive types of underwater explosivebombs were employed by one or other of theAmerican belligerents, these explosivedevices consisting of a light steel canisterprovided with a percussion cap and filledwith a small quantity of high explosive.This canister was secured to the end of avery long rod which latter was attached to asmall boat which was cautiously steeredtowards the ship to be attacked. Frequentlymuch damage was effected by this crudemethod of marine attack, but often enoughthe attacking vessel was blown to piecesalong with the attacked one. Hence thismode of marine warfare was relinquished,although there were many in Americawho retained the idea that it might bepossible to devise a small vessel filled withexplosives which would be capable of travel-ling of its own accord and steering itselfthrough the waves until it came into

STABILISING VANES

TWIN SCREW PROPELLERS

Torpedoes inAn Insight into the History, Mechanics

There are morethan 6000 separ-ate parts in every

torpedo, and ittakes several -months to makeone. Before being

sent out to HisMajesty's shipsevery torpedo

has to be triedout and passedunder working

conditions

explosive impact with the object of itsattack.Whitehead's Torpedo

The first individual to make practicablethe torpedo was an Englishman namedWhitehead, who was, towards the end of thesixties of the last century, in charge of anengineering company in Fiume, which wasthen an Austrian seaport.

A certain individual named Luppis hadfor some time been working on a torpedodevice which was driven by a clockworkmotor, and which was steered by ropesstretched through the waters. Luppis'sinvention was obviously impracticable, andthe Austrian naval authorities in no meanterms informed him of that fact. Dis-couraged, Luppis, seems to have climbedout of the picture, for we hear nothing moreabout him.

Whitehead, however, who knew Luppisand, also, the details of his invention, founda peculiar fascination and satisfaction inworking upon the details of a torpedo whichwould travel under water and steer itself.He put in a couple of years of hard andpersistent effort and eventually produced acompressed -air driven torpedo which showeditself to be capable of travelling some 700yards at an average speed of seven knots.

After this, Whitehead devised a specialtype of depth control mechanism to keep historpedo at a fixed depth during its travelthrough the water. This was the mechan-ism which gave to the torpedo its firstpractical success.Torpedo Trials

In July, 1870, a number of torpedo trialstook place off Sheerness, and they were

ENGINE. CHAMBER

GYROSCOPE APPARATUS

witnessed by a committee of Admiraltyexperts. In spite of the fact that the resultsof the trials were by nc means satisfactoryin all respects, the panel of Admiralty menreported very favourably on Whitehead'sinvention, with the result that in thefollowing year this inventor sold his patentrights to the British Government for thesum of £15,000.

Other countries, too, purchased torpedo -making rights from Whitehead. The Frenchnation negotiated for such rights withWhitehead in 1872, whilst in the followingyear the German and the Italian Govern-ments acted in like manner.

Whitehead, now a man of position andaffluence, continued to experiment cease-lessly with a view to perfecting his death-dealin ignvention. He introduced oneimprovement after another, until, eventu-ally, the torpedo became an almost in-fallible, albeit an extremely costly device.

Recent improvements in torpedoes have,naturally enough, become the closely -guarded secrets of the nations in which theyhave been effected. Nevertheless, in itsessentials, even the modern naval torpedofunctions on the principles laid down somany years ago by Whitehead, it being,indeed, doubtful whether-short of a modeof utilising atomic power-any moreeffective operating principle for such aweapon could possibly be devised.

Principle of the TorpedoIn principle, the modern torpedo is simple

enough, but in detail it is an extremelycomplicated device. The torpedo, as is now,perhaps, perfectly well known, comprises acigar -shaped metal tube which is fired at aship from a position either above or belowthe water line and which is capable ofpropelling itself in a perfectly straight lineand with a very high velocity towards theobject of its attack. Having made forcibleimpact with the latter, the charge of highexplosives contained in the torpedo isdetonated, resulting in an explosion and theconsequent destruction of both the attackedvessel and the torpedo.

The explosive charge of the torpedo iscarried in its head, beyond which projectsthe percussion device which, on makingimpact with any solid body, immediatelydetonates and so brings the explosive chargeinto violent and destructive action.

Immediately behind the explosive heador compartment of the torpedo is the airreservoir which, in most modern types oftorpedo, comprises a steel tube of very hightensile strength. It is, indeed, virtually, atravelling air cylinder, and into this, purifiedair is pumped to a very high degree ofcompression.

COMPRESSED AIR CHAMBER

DEPTH CONTROLLING APPARATUS

EXPLOSIVE HEAD

PRIMARY CHARGE

Showing, the internal construction of a torpedo


Naval Warfareand uses of a Potent and World-wide Weapon

The Balance ChamberAt the rear of the air reservoir comes the

" balance chamber " of the torpedo, whilstbehind this is situated the engine chamber.Finally, an " after -body " carrying the tailand propellers of the torpedo completes theassembly of this much -used missile of navalwarfare.

The reader may be surprised to know thatbefore the air conies into contact with theengine, it is actually heated by means of apetrol burner. This heating results in thegiving of an increased amount of energy tothe air escaping from compression. Usually,in order to prevent the heating device fromattaining too high a temperature, water isinjected into it, the water being obtainedfrom storage tanks formed around thecompressed -air reservoir.The Engine

The heater operates within a sort ofcombustion chamber into which air escapesfrom the compression reservoir via a delicatetype of reduction valve. Petrol is alsosprayed into this chamber in quantity whichis automatically regulated by the amountof air entering the chamber. In thischamber the petroleum vapour is ignited bymeans of a slow -burning fuse. Thus it isthat a mixture of compressed air, burningpetrol vapour and steam is passed on to theengine cylinders at a considerably hightemperature.

The engine of a modem torpedo is amasterpiece of mechanism. It is frequentlyof a three or four cylinder type, automatic-ally lubricated, and capable of developingabout 500 b.h.p. Many portions of theengine are cooled by a circulation of sea-water which is automatically pumpedthrough it from an opening in the side wallsof the torpedo.Lubrication and Cooling

The greatest attention has to be paid tothe adequate lubrication and cooling of the

torpedo engine, for if, as is many times thecase, the torpedo " breaks " sea by leapingabove the waves for even a few seconds, the

. . . going . . .

gone

engine, were it not adequately lubricatedand cooled, would instantly heat up andfuse into a solid mass even within that shortspace of time.

From the engine, two concentric pro-peller shafts pass through the tail or

after body " of the torpedo, each of theseshafts carrying a propeller. This propellermechanism is so arranged that the twopropellers revolve in opposite directions,this being necessary in order to rid the

Firing a torpedo from a British warship

Going . . .

travelling torpedo of any heeling movement.Perhaps more interesting even than the

amazingly efficient engine which propels thetorpedo through the waves is the delicatemechanism which keeps it on a true courseand, also, the means whereby it is enabledto travel through the water at any requireddepth.

Keeping a True CourseTorpedo inventors and designers experi-

enced their greatest difficulties in keepingthe missile on a true course through thewater. Without such a mechanism thetorpedo might even describe circles in thewater, and, although, in some instances, itmight only stray out of its course by a verysmall amount, such a deviation would besufficient to render it ineffective whenattacking an enemy ship.

Not a few devices were tried out for theabove purpose of keeping a travellingtorpedo in a straight line, but, eventually,the gyroscopic mechanism proved itself tobe the most satisfactory for this purpose.Nowadays, as is well known, a torpedo iskept on its course by means of the revolu-tions of a small gyroscopic flywheel, weigh-ing, perhaps, two or three pounds. Thisgyroscopic wheel is gimbal -mounted, and itis caused to run at extremely high dpeed.

4.


The GyroscopeThe -means by which the gyroscopic wheel

maintains the torpedo on a straight courseis 'really very simple in principle. It isdependent upon the fact that the axis of awell-balanced flywheel tends always topoint in the one direction during therotation of the flywheel, the flywheel itselftending always to rotate in one and the sameplane.

Now, if, during the run of the torpedo.the latter tends to deviate from its course,the high-speed gyroscope flywheel remainsin its original position. By so doing,matters are so arranged within the gyroscopecompartment of the torpedo that thegyroscope makes impact upon a projectingcam which actuates a small valve admittingair to a miniature cylinder. This latteroperates a control yudder and so brings thetorpedo back into line.

The depth control of the torpedo isusually effected by means of a small hydro-static piston operated by the externalpressure of the water. This acts on a valve.which controls the diving fins of the torpedoand so compels the travelling missile toremain at a given depth under the water.This depth control gear is necessarily a verydelicate one, and it has to be very accuratelyadjusted in order that the torpedo may notalternatively leap above the waves and divetoo deeply under them.The Tubes

Torpedoes may, in general, be fired from" tubes " or cylinders which are carried bya ship or submarine below the water line, or,

alternatively, they may be projected fromsimilar tubes which are situated above thewater level. In the latter case, the torpedowill leap from the elevated tube into thewater and, sinking to its predetermineddepth, will travel in a straight line towards,its object with an almost incredible velocityand precision.

Practically the entire wartime utility of atorpedo is dependent upon its ability totravel in a straight line and at a very highspeed towards the object of its attack. It isoften essential, or, at least preferable, thatthe torpedo should travel below the watersurface so that its presence may not berevealed until the fateful moment.

An average run for a torpedo is of theorder of 3,000 yards, and, at a speed of some45 knots, it will perform this journey inabout 120 seconds. The torpedo engine unitmust be so designed and constructed thatit attains maximum speed within a fewseconds after the firing of the torpedo. Thisvital requirement is attained In practice notthrough the existence of any special device,but, rather, in virtue of the great care andthoroughness with which the torpedo isdesigned and constructed.

FiringA torpedo may be fired from a ship or a

submarine either by means of compressedair or through the agency of a small chargeof explosive. Torpedo firing tubes of thesubmerged type are usually fixed in direc-tion, but those of the above -water varietycan be trained on any object as desired.

Just before firing a torpedo which has

been loaded into its tube, the interiorgyroscope flywheel is set into rotation bythe release of a strong spring and/or by acompressed -air jet. As the torpedo isprojected forcibly from its firing or im-pulse " tube, a projection within the tube,automatically engages a lever or arm on theside of the torpedo. This opens the mainair -reservoir valve and thereby sets theengin,e into motion, releasing, at the sametime a number of automatic mechanismswhich all play their part in bringing thetorpedo to bear speedily and accuratelyupon its chosen quarry.

Average Life of a TorpedoThe average " life " of a torpedo, once it

is set into action, is, as we have already seen,about a couple of minutes. Then this closelycompacted assembly of many mechanicalingenuities and automatic devices mustinevitably share the fate of the object of itsattack, which is to be blown to pieta.

It is, indeed, a curious commentary uponthe creative mind of man that it is capableof devising and that it is, indeed, willingto invent some of the most marvellous andefficient trains of automatic, powerful andyet ultra -delicate mechanisms with the fullknowledge that they can only be used fordestruction and that, having destroyed,they will themselves also be annihilated.

There is, indeed, no constructive use foratorpedo. But a motor car normally operat-ing at the efficiency of a modern torpedowould be an article of amazement the worldover, and, as such, would contribute greatlyto the happiness of civilisation generally.

NEWS OF THE MONTHIdeas that are

Conveniently Cleaned KennelA POET has said,' 'Tis sweet to hear the

watchdog's honest bark." This istrue, although not only the burglar but theaverage listener finds too much of thehonest bark disconcerting. Still the loyalanimal deserves to be housed in a mannerwhich ministers both to his health and hiscomfort.

It is a fact that kennels and also hutchesof the usual type are not always easy toclean. One cannot conveniently reach theinterior and scrub the corners and inmostrecesses with that thoroughness which isnecessary in order to do the job completely.

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Coloured Targets for DartsTHE game of darts, during recent years,has become increasingly popular. Ithas also gained in respectability, if I maysay so, without reflecting upon the socialtap -rooms with which at one time it wasalmost entirely associated. To -day, forexample, at A.R.P. posts, the worthywardens-ceaselessly on the qui vire for airattacks-beguile the period of waiting bythrowing feathered missiles at a long-suffering target.

An application has been accepted for apatent in this country relating to aninvention, the purpose of which is to enlargethe possibilities of the game of darts. The

Novel and Newdevice consists in the provision of' a dart-board of a number of individual targetswhich may be of different colours, shapesand sizes. These targets may be colouredafter the manner of the balls used in thegame of snooker. In that case, darts couldbe played to similar rules. There may be,for instance, an outer ring of red targetsand radially arranged yellow, green, brown,blue, pink, and black targets.

Each target is mounted in a cup or shellof metal or some other rigid substance andis composed of material into which a dartcan easily penetrate. The targets are

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detachable, and one object of the inventionis an improved method of attaching thesetargets.

Pocket DartsTHERE hail also appeared another con-

trivance connected with the game ofdarts. The aim of the inventor is to furnisha type of dart which can be convenientlycarried in the pocket or paper containers.The enthusiast who prefers to use his owndart will now be able to convey it to theplace of play without risking damage tohis pocket, his hand or the dart.

According to this invention, when it isproposed to pocket a dart, the nose isdetached, the point is taken out and reversedand the head is reinserted in a recess. Thenose is attached to the main portion of thebody, in a bore of which the point is accom-modated. Thus it can be carried on theprinciple of a pencil protector.

Audible Railway SignalIN the present age, when the ingenuity of

the inventor is so evident in everydepartment of life, one may legitimately beallowed to express surprise that a reallyeffective method of railway fog signallinghas not yet been conceived. What isrequired is a foolproof system, so that evena blind motorman could pilot his train withperfect safety. A patent which appears tobe at least in this direction has been grantedin the United States. The device is officiallyentitled "Audible Railway Signal," andincludes a diaphragm valve. In foggyweather, such a signal, though invisible,would orally authorise a driver to stop orproceed. This would relieve a railwaycompany of the necessity of using theordinary fog signal, whose detonation some-what resembles that of an enemy bomb.Moreover, in war -time, such a signal mighttake the place of lights, which are hostileto the black -out and extend further thana modulated sound would reach.


A WDRIVE

EATN LOC

The Driving Force of the Atmos Clock is asNear Perpetual Motion as we are Likely toAttain. It Relies Upon Changes of Temperature

to Supply the Winding Energy

THE Atmos Clock, strictly speaking, isnot perpetual motion, but to allintents and purposes it can be claimed

as such, because there is no necessity forwinding it by hand, mechanically or elec-trically. It is propelled simply and surelywithout any human intervention by thevariation of temperature and barometricpressure. The variations need only beminute. A change of 21 degrees centigradegives 41 hours winding power. The temper-ature is constantly changing and during 24hours it is probable the clock is energisedwith a fortnight's reserve winding force.Even in centrally heated buildings thisminute variation occurs.

Experience proves that throughout theworld -the daily variation of temperature ismuch greater than 21 degrees, and it isobvious, therefore,becomes accumulated. This is stored in aspecially long mainspring which more or lessremains under constant pressure at itsmaximum working capacity. With thisreserve there is sufficient power to last oneyear even if the clock is placed in a vacuumwhere there is no change of temperature.

The MovementThe originality of the Atmos is not con-

fined to the power unit. The movement it-self is unique in that, owing to the extremelyslow action of the moving parts (there ispractically no wear and tear), together withthe extra fine precision finish, the use of oilhas been eliminated. This removes at onceone of the most serious sources of trouble inthe maintenance of clocks, as oil in timebecomes dry and sticky, thereby necessitat-ing a clock to be periodically cleaned.

A very important advantage of the Atmos11 is the simplicity and precision of themeans of regulation. Owing to the remark.able constancy in the power tension theregulation is very sensitive. One completeturn of the regulating wheel produces avariation of only 12 seconds per 24 hours.It will be seen, therefore, that the adjust-ment is almost micromic. The balanceoscillations of the ordinary escapementclock are 432,000 per 24 hours, but in theAtmos they total only 2,880.

The Temperature MotorThe Atmos motor consists of a drum.

marked (1) in diagram, in the interior ofwhich is assembled a flexible metallicbellows (2). The space between the bellowsand the outer drum casing (4) is hermeticallysealed and contains ether -chlorine in gasform.

With the slightest decrease of temper-ature some of the gas will liquify (at 3),and the interior pressure of the bellows willbe lowered. A spring (5) under compressionis mounted on the central surface of the

bellows (6). This spring tends to keep thebellows in the open position as in thediagram. We will refer to this as the" compression spring."

When, on the other hand, the gas pressureis increased, the spring becomes further com-pressed and the bellows close like anaccordion. When, later, the gas pressuremay fall, the action is reversed-thesprings expand, forcing the bellows openagain.

A sectional view of the motor of the Atmos clock

Barometric PressureThe change in barometric pressure also

comes into play. If it is increased, thecompression spring is assisted in forcing thebellows to the open position. If the baro-metric pressure is decreased the internalpressure of the bellows has less exterioropposition. It will be seen, therefore, thatthe effect of barometric pressure, althoughof secondary importance in providing thewinding power, assists materially in liveningup the accordion -like action of the motor.

Working within the compression spring(5) is a smaller spring which indirectlyprovides the winding power. It is fixedto the body of the clock and the other end isfree. The spring is always under com-pression. At the extremity, adjacent tothe bellows, is fixed a fine chain (8) whichpasses over a pulley (10), and is thenattached to a larger pulley (11). This isfixed with ratchet action on the spindle indirect drive with the mainspring of theclock.

The Atmos II clock which can be obtained inbronze -gilt or chromium. It measures 9+ in. X

8+ in. X 6,* in.

Winding the MainspringA fine coil spring (12) is mounted on the

side of the main pulley drive for the purposeof taking up the slack in the chain when thebellows are being compressed. As thebellows expand again the pull on the chainturns the driving pulley and winds the main-spring.

The centre surface of the bellows has anarea of 80 sq. ems. A difference in temper-ature of 1 degree centigrade will cause avariation in pressure of 50 grms. per sq. cm.The working force, therefore, is 4 kilo-grammes (81 lb.) per 1 degree centigradechange in temperature. The maximumcompression of the bellows is 40 kilo-grammes.

Provision has been made by which theclock cannot be overcharged with power.The maximum power of the intermediatespring (9) is lower than that of the clockmainspring so that if the mainspring iswound to full working pressure the inter-mediate spring can only expand itself to thepoint where it balances the mainspringand there remains. As the clock runs downso does the pressure of the mainspring fall.As there is a reserve in the intermediatespring the power is automatically returnedto the mainspring which, therefore. mustremain at a constant pressure. It could onlybe in artificial conditions that the inter-mediate spring ftilly expanded itself beforethe mainspring had reached its maximumworking pressure. In practice, the tensionof the mainspring is maintained at almostconstant pressure-a very great advantagefor precision timekeeping.

FeaturesThe advantages of the Atmos clock is

that the pendulum is suspended on anElinvar spring which is unaffected b ytemperature changes, thereby assuringaccurate timekeeping in any climate. Theconstant driving force ensures maximumprecision and it eliminates the humanelement-forgetfulness. There is no electri-cal problems as with electric clocks andthere is no wear and tear on movingparts.

The Atmos clock is manufactured byJaegar-Le Coultre, one of the largest andoldest established watch factories in Switzer-land, and the distributers for Great Britainand the colonies are De Travers, Ltd., of88 Regent Street, London, W.1.


REMOVABLESHEET METAL

CASING

WATER power is not available toany considerable extent inEngland, for although there are

plenty of streams, the land is frequentlytoo flat to provide a good head. Also thewater flow is liable to considerable variationbetween wet and dry weather conditions.The picturesque old water mills that arestill to be seen are being superseded bygiant factories, or possibly the water wheelmay be replaced by an oil engine.

A waterfall is always a source of power,but a slow stream flowing through meadow -land is not. If it is possible to raise thelevel of the stream a few feet by building adam without flooding the surroundingcountry, a head of water equal to the heightof the dam is obtained and the streambecomes a source of power.

When considering the question of waterpower, the first step must, of course, be to

... see if the required power is available, andto do this it is necessary to ascertain thequantity of water flowing per second andthe height through which the water canfall, or in other words we want to knowthe " flow " and the " head."A Wooden Dam

The flow of a small stream can be arrivedat by building a wooden dam or weir witha rectangular notch in the top as shownin Fig. 2. The depth of water flowing overthe bottom of the opening will, in conjunc-tion with Table I, give the flow in cu. feetper second. The depth should not bemeasured at the opening itself, but shouldbe measured in still water not too near theopening, as shown in Fig. 2.

" An approximate estimate of the flow can

Harnessing WaterPractical Methods of Obtaining Power

be made withoutthe weir bymeasuring theaverage widthand the averagedepth of thestream over astraight stretchof, say, 20 yd. to30 yd. Then placea well -submergedfloat (a bottlepartly, filled withwater will do) inthe middle of thestream, and timethe rate at whichit moves, thus ob-taining the vel-ocity of the waterin the middle of

Fig. I. -Asimple arrange-ment for aPelton wheel

the stream. The flow and power availablecan be worked out as follows :-

W = Average width of stream in feet.D = Average depth of stream in feet.V = Velocity at centre in feet per second.F = Flow in cubic feet per second.H = Head of water in feet (measured

from surface of water above weirto surface below).

P = Horse -power available.F ---WxDxVx.7

WxDxV)< 43.7550

If the notched weir method is used in

Fig. 2 -A notched weir for measuring water flow

I

conjunction with Table I, the horse -powerwill be :-

P -Fxllx 62.4550

Horse -PowerAs an instance, suppose the stream has an

average width of 9 ft., average depth2 ft. 3 in., flow .8 ft. per second, and youcan arrange a head of 4 ft., then the powerwill work out at 5.15 h.p. But the fullpower cannot be obtained in practice as nowater motor is 100% efficient, so supposewe use a water -wheel with an efficiency of,say, 60%, then we might reasonably expectto obtain about 3 -h.p. Tbis may not seemvery much for a stream of this size, but thisis because there is only a small head. Ifthis same stream were flowing down amountain and a head of 200 ft. were avail-able, one could quite reasonably expect a

WATER JET

L

Fig. 3.-Bucket casting for a Pelton wheel

power output of about 150 horse -power,or even more, because the efficiency wouldbe higher than with a water -wheel.

If the water supply appears to be capableof developing the power required, the nextstep is to consider the type of water -motor.These may broadly be divided into threeclasses as follows :-

(a) Water turbines, of which there aremany different kinds, in all sizes, developingup to tens of thousands of horse -power.When properly designed for the work theyhave to do they are suitable for any headof water from the lowest to the highest.

(b) Pelton wheels, particularly suitablefor high heads and small flows.

(c) Water -wheels of the paddle or buckettype suitable for low heads with a largeflow of water.

Turbine and Water -WheelA turbine may be distinguished from a

water -wheel in that it has two concentricrings of vanes, one ring remaining stationaryand serving to defiect.the water on to thering of moving vanes. As some indicationof the variations in design of this type of

March, 1940 NEWNES PRACTICAL MECHANICS 24)

PowerFrom Small Streams

water -motor, there are inward radial flow,outward radial flow, and axial flow turbines,and these may have horizontal or verticalshafts. Such machines are rather beyondthe capacity of the amateur mechanic, alsoa great deal depends upon their design andthe suitability for the particular purpose inview. The study of water turbines is avery involved affair, and it is recommendedthat the maker's advice be sought and theproper machine purchased from one of thefirms of hydraulic engineers who advertisein the engineering periodicals.

A Pelton wheel, however, should not bebeyond the capability of an amateur toconstruct, but careful consideration shouldbe given to the design before constructionis begun.

Assuming that the supply of water isample, the power developed will dependupon the effective head of water and thesize of the jet. Table II gives this informa-tion for various conditions, all figures forhorse -power being arrived at assuming anefficiency of 75%.

Pelton WheelFig. 1 shows a suggested general arrange-

ment for a Pelton wheel ; it should, of course,be covered in to prevent spray being thrownabout in all directions. The diameter of thewheel should be worked out that will givethe required number of revs. per minute

re"

/1.124141"--.

-041 E A D.-."RAEt4'

.... //Ay'

H

_ -

-411.11.111V..0311V -

when its peri-pheral velocity isas given in TableII. Obviously thesmaller the wheelthe higher ther.p.m.

The number ofbuckets should bearranged so thatthere is alwaysone in line withthe jet; the mini-mum number toachieve this resultshould be used.There is no advan-tage in putting onmore buckets than necessary. A patternshould be made for the buckets (see Fig. 3)and the required number of castings ob-tained. The size of the buckets is not offirst importance, the main point being that

DL

#14- TAIL RACE

Fig. 6.-A breast wheel

PARALLEL

1.4-trj. 60PAPER

Fig. 4.-A nozzle for a Felton wheel

the water shouldflow smoothly andwithout sprayuntil leaving thebucket. Theradius inside eachsemi -bucket maybe, say, about twoto three times thediameter of thejet, the centraldivision sh ouldhave a sharpedge, but the cupsshould be ratherless than a semi-circle in shape sothat the waterwhen dischargedfrom the bucketflows clear of thenext bucket.About a dozensuch castingsbolted to an oldmotor - car wheelshould make asatisfactory Pel-ton wheel provid-ing the diameteris suitable for ther. p. m. required.One-half of a rearaxle could also beadapted to formbearings for thewheel,the drive be-ing taken off of thedifferential end.

Shape of NozzleThe shape of

rJ

Fig. 5.-An undershotwater -wheel

the nozzle is an important detail. Theinside must be smooth and well finished,and there must be no sudden change ofdiameter. Any elbows or junctions inthe supply pipe should also be keptwell away from the nozzle, as also shouldthe stop -valve. A nozzle made of brassor gunmetal on the lines of Fig. 4 shouldgive good results; the constant taperis not theoretically the best shape, but it iseasier to make and there will be very littleloss of power compared with the theoreticalnozzle. A roughly made or makeshiftnozzle will, however, waste a high propor-tion of the power available. Extra nozzlescan be arranged to work on the same wheelif it is desired to increase the power andthere is sufficient water available.

The arrangement of the supply pipe isof great importance if waste of power is tobe avoided. It should as a rule be not lessthan three or four times the diameter of thejet if the pipe is very long, and should be asfree as possible from sharp bends or elbows.It will be noticed in Table II that" effective " head is referred to. The reasonfor this is that there must always be acertain amount of loss of head due to frictionin the supply pipe, and loss of head meansloss of power. Table III is given to showloss of head in feet for various diameters ofpipe and various rates of flow, so that thereader can work out the probable loss forhis own installation. A study of this tablewill indicate the importance of a largesupply pipe.

For low heads of water large quantitieshave to be dealt with and for such conditionsa water -wheel is suitable. These areusually large for the power developed, butas they can be made principally of wood,they may yet be within the capability of anenthusiastic- handyman.

Undershot WheelsUndershot wheels may be used for heads

up to, say, 6 or 7 ft., and should be arrangedas shown in Fig. 5. The thickness of thewater stream should not exceed 10 inchesbut may be of any required width. A sluiceshould be provided to regulate the flow.


h

HEADRACE",;\

41'.1.%1 f,to RACEFASURFACE

Fig. 7. -An overshot wheel maybe used where the head exceeds

10 ft. or so

The paddles should be inclined to theradial line and should be at least twice thedepth of the stream of water. Note thestep below the axis of the wheel to allow thewater to fall clear directly it has done itswork. The velocity of the stream of watercan easily be calculated when the head isknown and its value in feet per second willbe eight times the square root of the headmeasured in feet. The peripheral velocityof the water -wheel should be between halfand .6 of the water velocity for best results,

Fig. 8.-Propor-tions of

buckets forovershot

and breastwheels.There

should be_ _about two

buckets foreach foot

in diameterof the waterwheel, and

the wheelshould bearranged

to deal withthe requiredquantity of

waterwithout

waste overthe tops ofthe buckets

and the wheeldiameter andr.p.m. should bearranged to givethe requiredperipheral speedat full load. Thepower developedmay be cal-culated when thehead and quan-tity are known,as explained atthe beginning ofthis article andan efficiency of50% assumed.

For heads be-tween 6 ft. and12 ft. a " breastwheel " is used(Fig. 6). If thewater enters thewheel above itscentre it is calleda high -breastwheel, or if belowthe centre a low -breast wheel.There are severalvariations in thistype' of wheel,chiefly in themanner in whichthe water is fed tothe wheel. Theycannot be dealtwith fully here,but the samegeneral principles

discussed earlier apply. These wheelswork by the weight of the falling water,and consequently carry a series of bucketson heperiphery to hold as much water aspossible.

Overshot WheelsOvershot wheels (see Fig. 7) may be used

where the head exceeds 10 ft. or so, and inthis case the wheel should be made as largeas conditions allow, as long as it does notdip into the water in the tail race. It willbe seen that this type of wheel rotates in theopposite direction to the undershot andbreast wheels, and being worked chieflyby the weight of the water carried on thewheel it is provided with buckets like thebreast wheel. There should be about twobuckets for each foot in diameter of thewater -wheel, and the proportions shouldbe as shown in Fig. 8. The power can becalculated as already explained and thewidth of the wheel should be arranged todeal with the required quantity of waterwithout waste over the tops of the buckets.

WORKSHOP CALCULATIONSTABLES AND FORMULIE

2nd Editionby F. J. CAMM

A handbook dealing with methods of calculation,solution to workshop problems, and the rules andformula' necessary in various workshop processes.It contains all the information a mechanic normally

requires.From all booksellers, 3/6 net,by post 3/9 from the publisher:

GEORGE NEWNES LTD. (Book Dept.),Tower House, Southampton St., London W.C.2

Flow in cubic feet per second ..

TABLE I

1

Depth of Water in inches

2 3 4 5 6 7 8

.08 .225 .414 .637 1.890 1.17 1.47 1.80

9

2.15

10 11 12

2.52 2.90 3.31

TABLE Il

Dia. ofjet

Effective Head Feet10 20 30 40 50 60 70 80 90 100

I inch.03 .08 .75 .24 .33 .43 .55 .66 .80 .94

Horse PowerE = 75%)

.03 .05 .06 .07 .08 .085 .09 .10 . .105 .11 Cub. ft. per sec.

1 inch.12 .32 .61 .95 1.3 1.7 2.2 2.6 3.2 3.7

Horse PowerE = 75%)

.14 .19 .24 .28 .11 .34 .37 .39 .42 .44 Cub. ft. per sec.

11 inch.27

.31

.5

.72 1.35 1.76 3.0 3.9 5.0 6.0 7.2 8.5Horse Power(E = 75%)

.44 .54 .62 .70 .76 .82 .88 .94 1.0 Cub. ft. per sec.

2 inch1.3 2.4 3.8 5.2 6.0 8.8 10.6 12.8 15

Horse Power(E=75%)

.55 .78 .06 1.10 1.24 1.35 1.46 1.56

36

1.66 1.75 Cub. ft. per sec.

13 18 22 2.i 28 34 34 38 40Peripheral Vel.

Feet per sec.

TABLE 111

Watervelocityin pipefeet

Diameter of Pipe, Inches

persecond 1 2 3 4 5 6 7 8

2 2.37 1.18 .80 .60 .47 .39 .34 .30

3 4.9 2.4 1.6 1.2 1.0 - .80 , .70 .60

4 8.2 4.1 2.7 2.0 1.6 1.4 1.2 1.0 Feet loss ofhead 100 ft.

5 12.3 6.2 4.1 3.1 2.5 2.0 1.3 1.5per

of straight pipe

6 17.2 8.6 5.7 4.3 3.4 2.9 2.5 2.1

7 22.9 11.5 7.6 5.7 4.6 3.8 3.3 2.9


L

The Principles of theSt bm rinePart 2

/ff y R. L. Mwughan, M. Sc., A hist PThe Periscope is the Eye of the Submarine, and In

event Yr ars has eveloped Added Roving Powersso that it can View the Sky as well as the Sea

THE water ballast tanks carried by asubmarine are of two types. Theseare the main water ballast tanks which

are arranged symmetrically about the keelin the spaces between the inner pressurehull and the outer hull, and the smallerauxiliary trimming tanks which are lodgedin the narrow confines at the extreme endsof the hull. The main water ballast tankshave a larger capacity and take the bulk ofthe water necessary to destroy the reservebuoyancy of the boat to bring about itssubmergence. Each tank is fitted with twovalves, one in the tank bottota giving directaccess to the sea and the other in the top ofthe tank to act as an air vent. When thesubmarine is in the normal surface cruisingcondition these tanks are filled with air ator just over the atmospheric pressure, theair valve being closed and the sea valveopen and under the surface. The onrush ofsea water through the open valve is pre-vented by the pressure of the air trapped inthe tank, and any partial flooding of thetank due to an extra surge of water throughthe valve is combated by the automaticcompression of the enclosed air.

DivingA dive is initiated by the simple operation

of opening the air vents in all the mainballast tanks to allow the sea to enter underits own pressure through the lower valve,the air being forced out through the openvents. When the tanks are filled with seawater the air valves are closed and the seavalves left open in readiness for the reverseoperation of discharging the tanks. At theend of the dive the hydroplanes are rotatedinto the neutral position and the submarineenters upon its underwater course in ahorizontal line. Recourse is made if neces-sary to the auxiliary trimming tanks inorder to adjust the boat to a level keel.There are two of these tanks, one at eitherend of the submarine hull, and permanentcommunication is established between themby a tube which traverses the length of theboat. In the normal working conditionthey are shut off from the sea, but hold asmall amount of water which may be trans-ferred wholly or in part from one tank to theother by a water pump operating throughthe connecting tube. A small transferenceof weight in this way from one end of thesubmarine to the other is usually sufficientto correct the delicate poise of the vesseland to bring it to an even keel when in thesubmerged condition, but a continuoustransference is necessary while the boat is

being navigated on the surface under themotive power of its Diesel engines in orderto counterbalance the redistribution ofweight which occurs when fuel oil is removedfrom the storage tanks and consumed by theengines.

The Main TanksThe main tanks are emptied when an

ascent to the surface is to be made by blow-ing the water out through the open seavalves under a blast of air. This air is storedin a highly compressed state in cylindershoused within the hull, and is supplied to theballast tanks through a valve which isdirected towards the pressure hull wall insidethe tank. The strength of this hull is easilysufficient to withstand the impact of the airblast and leaves the less robust wall of thetank formed by the outer hull plates to takethe smaller strain of the pressure difference .between the external sea water and theinternal blown air. The cylinders arerecharged when the submarine rises to thesurface, the air supply being drawn directfrom the atmosphere through open hatchesby an air compressor worked from theDiesel engine drive. As a precaution it iscustomary to store at any one time anadequate supply of air to be able to discharge


the ballast tanks several times over ifnecessary.

Although submarine construction datesfrom the year 1624 when the Dutchman,Cornelius van Drebbel, built a vessel out ofwood and leather and successfully demon-strated its practicability as an under -watercraft by propelling it with oars slottedthrough flexible leather glands in the sides,it was not until 1902 that the periscopebecame a permanent feature of the sub-marine. Previous to that date submarinestravelled Mind and were obliged to makefrequent visits to the surface in order totake cognizance of their whereabouts,

The PeriscopeThe periscope is the eye of the submarine,

and in recent years has developed addedroving powers to enable it to view the skyas well as the sea. In structure a periscopeis really a set of three telescopes arrangedend to end in a vertical tube with a prismat the top and bottom of the tube. Theupper prism serves to reflect the light fromthe sighted object into the top of the tubeand the lower prism from the bottom of thetube into the eye of the observer, while thetelescopic system in between producesthe necessary magnification. The opticalarrangement of the instrument is illustratedin Fig. 6. Any system of lenses, prisms andmirrors which receives a parallel beam oflight at one end and transmits a parallelbeam from the other end after convergingor diverging it in between is said to betelescopic. It will be seen from Fig. 6that by this definition the two lenses C andD form one telescope, the three lenses E, F,and G a second, and the remaining systemHKLMN a third. A telescope is made up

(n) (b)

Fig. 7.-Showing elevation of view operated byupper prism

eEs mtially of two lenses,' the first theobjective to receive the parallel beam oflight from the sighted object, and the secondthe eyepiece to transmit a parallel beam tothe eye of the observer. If the lenses areboth convex the telescope is said to beastronomical and produces an invertedimage of the viewed object. If the objectiveis convex and the eyepiece concave theyform a Galilean telescope which produces anupright image.

Simple InstrumentsIn practice single-lens objectives and

eyepieces are employed only in the verysimplest types of instrument where slightdistortion of the image due to sphericalaberration and slight colouring of the imageedges due to chromatic aberration are notconsidered as serious defects. Where it is ofthe utmost importance to record the trueform and colouring of a sighted object as itis in the periscopic observation from a -sub-marine, objectives and eyepieces each con-sist of a series of convex and concave lensescemented together to form compound lenseswhich are free from colour and distortiondefects, that is they are both achromatic andanastigmatic. Compounds of this type are represented in Fig. 6 by the twin lenses D, E,G, H, N. Since the periscope tube containsthe equivalent of two astronomical telescopes

(EFG andHKLMN),each of whichinverts theimage, andone Galileantelescope(CD), whichkeeps theimage up-right, thefinal imageproduced bythis corn-,bination willalso be up-right. Inadditionthere is aninversion ateach .prismreflection, so

LIGHT ENTERINGEYE OF OBSERVER

b`LIGHT BEING RECEIVEDFROM SIGHTED OBJECT

Fig. 6.-Vertical section of aperiscope showing the opticalsystem and path of the central

beam

that the ulti-mate imageseen by theobserver willstill remainupright. Thetwisting ofthe beam oflight to pro-duce thesesuccessive in-versions maybe traced inFig. 6 in thecourses ofthe extremerays of thebeam mark-ed " a " and

b"GalileanTelescope

The pur-pose of theGalilean tele-scope is toprovide theperiscope

with two different powers of magni-fication. It will be seen from Fig. 6that the Galilean telescope is reversedwith respect to the observer's eye and thetwo other astronomical telescopes, its con-cave eyepiece C being situated between theupper prism B and its convex objective Dwhich is directed towards the objective E,belonging to the middle telescope. Whenall the lenses are aligned along a commonaxis the observer has a view through threesuccessive telescopes, but as the endtelescope is reversed the view obtained hasa low -power magnification and the imageis not much enlarged. The advantage ofthis low -power vision is that rapid recon-naissance may be made over wide tracts ofseascape or sky by rotating the periscopeabout its vertical axis through a relativelysmall angle. When the high -power mag-nification is required the Galilean telescopeis swung out of the line of vision to leave thetwo astronomical telescopes to bear uponthe object with their added powers freedfrom the effect of the reversed Galileantelescope. Under these circumstances, thefield of view is well filled by the highly mag-nified image, and the minute examination ofdetails is possible over a necessarily limitedrange of vision. It will be appreciated thatthe removal of the Galilean telescope toincrease the power of the system rather thana reversed astronomical telescope does notalter the number of inversions of the imageduring the course of the beam from theperiscope window to the observer's eye, andso the final image still remains upright.

In the modern submarine the periscope'srange of vision is made to extend to the skyas well as to the surface of the sea. For thispurpose the upper prism is made to rotateabout a horizontal axis in order to inclineits reflecting surface at a smaller angle tothe vertical. In this position light receivedfrom higher altitudes is received on thesurface of the prism presented to the windowand is reflected from the back surface down

' through the system of telescopes into theeye of the observer. (See Fig. 7.)

Keeping out the SeaThe sea is prevented from entering the

periscope by means of the plate glass win-dow built into the tube head. (A in Fig. 6.)And the remainder of the tube is a water-tight metal casing which passes through awater -tight gland pierced through the hullto emerge above the conning tower. Thetube is raised to its full length when obser-vations are to be made, and withdrawnthrough the gland when the submarinesubmerges, by the power of the boat'selectric motors. The unquestioned import-ance of the periscope as part of the sub-marine's equipment is responsible for thecontinued study and experiment devoted toits design and construction by the expert inmetallurgy as well as in optics and engineer-ing, The metal of the periscope tube is abronze which has, at the same time, theproperty of being able to resist corrosionthrough prolonged contact with sea water,the required rigidity to withstand the strainof being forced broadside on through thewater as the submarine proceeds on itscourse, and the merit of being totally non-magnetic which prevents it from influencingthe boat's navigation by disturbing thecompass card.

Fig. 8 illustrates the external mechanismat the base of the periscope tube by meansof which the observations are controlled.The eyepiece E, with its guard ring of rub-ber, is centred in the base of the tube-which also carries the control screws S andT which are used to move the lenses in theadjustment of the periscope focus. Twoarms AB protrude from the base piece andby means of them the base and the entirecolumn of the periscope above it may beturned about a vertical axis in order tomake the line of vision sweep through anydesired angle in a horizontal plane. Theindicator I, carried by the base, moves overa fixed scale K engraved on the circular rimof the tube containing the periscope, andautomatically registers the angle betweenthe line of vision and the line of the boat'skeel. The handles at the ends of the armsare able to rotate about the common axisAB of the arms themselves, and by turningthe handle A the power of the periscope isadjusted to the high or low value by swing-ing the Galilean telescope out of or into theoptic axis of the lens system, whilst themanipulation of the handle B varies theinclination of the prism in the periscopehead in order to elevate the view from thesea to the sky. When the periscope is notin use the two arms fold upwards into verti-cal rest positions against the periscope baseto economise the space in that part of thecontrol -room.

Fig. 8.-Fieldof view throughperiscope show-ing crossedscales for rang-ing sighted

object


Main FunctionThe main function of the periscope is one

of plain observation, but in addition to thiswork of surveillance it is also used as arange -finder. For this purpose its field ofview is divided into four quadrants by twocross -wires situated in the eyepiece in such aposition that their image is permanently infocus in the circular field of view. (SeeFig. 8.) Superimposed on their image aregauge lines marked along the length of eachcross -wire, and by means of them anestimation may be made of the size of asighted object, its distance from the sub-marine and the speed at which it is moving,while at the same time an inset image of thereading of the main indicator of the peri-scope's angle of observation is projectedinto the field of view. (H in Fig. 8.) Thisdevice enables the observer to consult -thisreading without having to remove his eyefrom the periscope eyepiece. The calcula-tions of the size, speed !and distance aregreatly simplified when the cross -wireobservations may be compared with known

data about the sighted object. If thisobject is a ship whose length is known, itsspeed may be at once gauged from the timeits image takes to move completely acrossthe vertical cross -wire, and if it is viewedbroadside on its length subtends at theobserver's eye an angle indicated on thecross -wire graduations, so that the calcula-tion of its range is made by dividing theship's length by the angle it subtends, inaccordance with the well-known geometricalprinciple.

Fixed Line of SightThe tendency of the motion of the sub-

marine in the sea to upset these calculationsby making it difficult to keep a fixed line ofsight on the object is counteracted by theaction of a small gyroscope situated.in thebottom of the periscope case and set intomotion by the control screw Z. (Fig. 8.)Its effect is to maintain a steady line ofvision from the eyepiece to the sightedobject in spite of the rolling or pitching ofthe boat.

The apparatus of the periscope's base iscentrally situated in the submarine's hullimmediatelynnderneath the conning tower.This region is the control -room, the positidnof which makes it highly adaptable to thecommand and control of the boat's interiorand to the maintenance of communicationswith the outside world. The entire designof the periscope and its controls makes forsimplicity, efficiency and economy ofoperation. The observer stands with aneye applied to the eyepiece and a hand oneach of the arm handles. A turn of the armsrotates the periscope tube and sweeps out aview over the surface of the sea. A twist ofone handle elevates this view and sends itover the sky ; a twist of the other changes themagnification of the view and makespossible the rapid reconnaissance of largeregions or the detailed examination of alocalised region as required, whilst the con-trol screws for varying the focus and- settingthe gyroscope into motion are convenientlyat hand on the casing of the periscopebase.

MANUFACTURING GLASSVarious Processes in Use To -day

GLASS is a soda lime silicate. Thatis, it is made from silica (sand),soda, and lime. If sand is mixed

with soda (in the form of soda ash or salt -cake) and heated, the soda melts and thesand dissolves in the soda. If there is anexcess of soda, on cooling a thick syrupyliquid is obtained, but if more sand isadded a hard, transparent, glassy substanceresults, but this, unfortunately, is solublein water and is known as waterglass. Bythe addition of lime, the solubility of thesodium silicate is reduced, and with a suffi-cient quantity of lime a durable glass is ob-tained which will stand up to the weather andto all strong acids except hydrofluoric acid.

The ProcessesAll processes of manufacture are governed

first by the article which it is required tomake and, secondly, by the physicalproperties of the material employed. In themanufacture of glass the principal physicalproperties which influence the processesare :-

1. Viscosity. Glass has not a definitemelting point. If the glass is heated, itfirst softens so that it can be bent ; as thetemperature rises it reaches a point whenthe glass becomes a thick, syrupy liquid,which can be gathered on the end of apipe and blown, and finally at highertemperatures it becomes a thin, wateryliquid.

2. Devitrification. Although weatheringproperties can be assured by a high limecontent, there is always the danger ofcrystallisation, or devitrification, occur-ring. Above a certain temperature,known as devitrification temperature,glass may be kept in a liquid conditionwithout any change occurring, but if theglass is kept below that temperature forany length of time, crystallisation ordevitrification occurs. It is, therefore,essential in any process that the timetaken to complete the operation shall notallow of devitrification. The tendency todevitrify can be reduced by decreasing theamount of lime and increasing the soda,but this can only be done at the expenseof the weathering properties.

3. Annealing. A hot sheet of glass left

to cool naturally will break, and in orderto obtain whole sheets of glass, the sheetmust be annealed, that, is, cooled downgradually in what is known as a lehr.

4. Melting. The melting process takesplace in three stages : (1) The initialmelting. That is, the chemical reactionbetween the three ingredients, and thisresults in a sticky mass full of bubbles.(2) The next stage is the fining operation,which consists simply of raising thetemperature so that the glass loses itsviscous nature and becomes quite watery,thus allowing the gases forming thebubbles to rise to the surface. At thisstage the glass is so thin that it is quiteunworkable. (3) The third stage con-sists of cooling the glass down to a tem-perature where it is of the correctconsistency to proceed with the particularprocess which is desired.

The Glass BathIn feeding the tank, the raw material,

which consists of the actual ingredients andbroken glass, falls from a hopper carried onan overhead crane, into what is known asthe filling pocket, this pocket being thejutting -out portion of the actual glass bath.A glass tank, which may be as large as120 ft. long by 36 ft. wide and 5 ft. indepth, has sides and bottom made of clayblocks and the roof of silica bricks, andmay contain anything up to 1,000 tons ofmolten glass, with temperatures varyingfrom 1,200° C. to 1,450° C. in differentparts of its length. There is no end to thevariations which may be made to the shapeof the tank so as to melt the " frit " at oneend to produce seedless and homogeneousglass at the other. It is comparatively easyto forecast the convective currents in abeaker, but the convective currents in aglass tank of large dimensions are moredifficult, and to understand them is toknow how to produce good glass. Actually,the amount of glass flowing down themiddle of the tank due to convective cur-rents is about twenty times as much asthat being withdrawn at the working end.

Polished Plate GlassThis was originally made by melting the

frit, i.e. the mixture of sand, soda, saltcake,and limestone in fireclay pots, each holdingapproximately one ton of molten metal,which was heated for 17 hours in a gas -heated furnace at a temperature of approxi-mately 1,600° C. At the end of this periodmechanical tongs gripped the pots andconveyed them to the casting tables madeof iron, on which the molten glass wasslowly poured. A roller covering the wholewidth of the table then moved across it,flattening the molten metal into a plate, thethickness of the glass required being regu-lated by adjustable guides at the side of thecasting table. The resultant glass wastranslucent but not transparent, its surfacebeing rough and coarse, but the insidecrystal clear. This glass was slowly annealedto release any internal strains and thensubjected to a grinding process by which therough surfaces were smoothed down onrotating circular tables by means of revolv-ing iron -shod discs, the abrasive being sandor emery and water. After the grindingprocess the plate was polished on both sidesindividually by means of felt -paddeddiscs, the polishing agent being rouge andwater.

About 1921 a further process was intro-duced called the Bicheroux process, inwhich, although the glass is melted in potsas in the old process, it is rolled into a sheetbetween two rollers instead of being pouredon to a table in front of a single roller, witha resultant flatter sheet, which means lessloss of time in the subsequent grinding andpolishing operation.

This method gave place to a continuousprocess in which the molten glass floweddirectly from the tank between rollers intothe lehr or annealing chamber, from whenceit was cut into lengths and subjected to agrinding and polishing process on a. con-tinuous machine. The length of thismachine was 600 ft. and was evolved atSt. Helens.

The latest adaptation of this method isthe direct flow of the sheet from the tankto the warehouse, where it arrives in apolished state without handling, havingbeen ground and polished on both sidessimultaneously en route.

This is an achievement unsurpassed inthe history of glassmaking and has entailedan expenditure of over one million poundssterling in research and erection of plant.The plant itself, from the melting end of thefurnace to the point of delivery of thefinished product, is over one thousand feetin length.


A Low -Wing PetrolMonoplane

A front view of the model

The Undercarriage and Tail WheelYEARS ago I developed a simple type of

undercarriage for petrol models withtwo main built-up steel wire legs that

are faired with balsa and bound with silk, anddoped. The two rear legs are coil wire springs.

This was fitted to my record -holder." The Blue Dragon." This model has flownfrom 1934 to date and completed an enor-

carriage construction because the elevationis self-explanatory, and if the readerwill refer to the photograph of the modelas shown, on the ground the point to beobserved is that the travel of the under-carriage is first back then upward, and thatthe action is very resilient. This permits themodel to glide into the ground. A model isnot put down 3 -point on to the ground as in

BRASS TUBES ATTACHED TO FUSELAGE

BOUND 2.SOLDERED

CATCHES FORELASTIC BANDS

BALSA FAIRING_BOUND WITH SILK 2 DOPED

SPRING SI LtL WIRE

mous number of flights, and the under-carriage, which is perhaps the most highlystressed p,art, has never had any repair of anysort.

It is not beautiful, but it works, which isthe main essential point. I have developeda better -looking undercarriage since, but it isnot so reliable, although it certainly has theessential back and then upward shock -absorber movement.

In the case of a low -wing model theremust be a limited rearward travel or therear legs will strike the wing. It was, there-fore, decided to revert to the trusty old typeof undercarriage for the " Gull," as flyingresults always come first when there is anyquestion about their clashing with looks.

It is hardly necessary to describe the under -

Fig.5 .-Detailsof the under-

carriage

the case of a full-sized aero-plane.

The recent development ofthe tricycle undercarriages forfull-size aeroplanes is a similaridea, and allows the aeroplane tobe flown and glided at reason-able angles straight into theground without flattening off.This is as it should be.

The Detachable Tail and Detach-.able FinThe shape of the tail is evident

from the drawings of the generalview plan. A full-size drawingmust be made from this. Youshould also refer to Fig. 8,

By Major C. E. Bowden(Concluded from page 222 of last month's issue)

which is a sketch of the tail unit showingconstructional details. You will notice thatthe tail is detachable and placed on therear platform on the fuselage, and is keptin position by elastic bands from the twopegs in front to the wire hooks on eitherside of the fuselage, and also from the hookon the tail end of the fuselage.

The fin is made separate for ease of trans-port, and has two in. round birch dowelpegs glued into it. The bottom ends of thesedowels fit into the 1 mm. 3 -ply covering ofthe tail centre section. Glued below thiscovering there is a block of solid balsa whereeach dowel peg fits to strengthen.

There is a wire hook at the front and atthe rear of the fin. Elastic bands keep thefin hard down to the tailplane. The finsmust be set straight at all times. This willbe explained later. The fin is made of threelaminations of -18, in. sheet balsa cut to theoutline shape, and then hollowed out, so thata proxal outlined remains. The laminationsare glued together and weighted until dry.The outline edge is then streamlined off bythe use of a razor blade and sandpaper.Streamline ribs of in. balsa sheet are then

the centre.The tail and the separate fin are then

covered with thin jap silk, using photo pasteas an adhesive. Now spray the silk withwater when covering, and this will tightenthe silk up when dry.

Now give one coat of clear full-size gliderdope (obtainable from the model shops thatspecialise in petrol models).

The Detachable Wing Built in Two HalvesThe fitting of a low wing to a large and

heavy model is always a knotty problem, as1 he wing must be fairly rigid and yet mustknock off if the model flies into a tree.

On this model the wing is built in twohalves for portability, and the two halvesare kept together by wire hooks and elasticbands. The wire hooks must be not less than16 s.w.g. wire and must be very well boundand glued into position as they have con-siderable loads to carry.

There have been added wire strengthenersto the break in the wooden spars where thedihedral angle comes, and up to the twoNo. 1 3 -ply ribs. -

The hooks are bound and soldiered tothese wire strengtheners and the whole arebound to the main spars with thread andglue.

For the first few bays the top and bottomWIRE CAMERA TIMERSTRIP

SECONDS SCALERELEASELEVER

LEADS 3- PLYWOODEN BASE

Fig. 6.-The flight timer to cut off ignition at a predeterminedtime


LARGEST RIB WINO

X.4 TOP SPAR

Mil 1,2,3, RIBS.(IYets I AND 2 ARE .41 3 -PLY) FRON 1/93 TO /5 RIB WING TAPERS

SOLID BALSA BLOCK ADDED TO TOPS OF CENTRE SECTIONONLY, KEEPS WING FROM MOVING THROUGH VIBRATION

UNDERSIDE OF FUSELAGE BETWEEN N433 AND 4FORMERS SHOULD BE SHAPED 70 TAKE THIS BLOCK

L.E. SPARACXY BOTTOM SPAR

TE SPAR

46 SHEET BALSA STRIPUNDER AND ALONG TE

No/5 SMALLEST RIB OF WINGra

SMALLEST TAIL RIB

LE SPAR%,6 X6 BALSA

TOP AND BOTTOM SPARSBIRCH

re 4IL s BALSALARGEST TAIL RIB BALSA

P10 SHEET STRIP UNDER1:E.

Fig. 7.-The wing and tail sections

main spars are covered in on both sides byis in. sheet balsa glued on. This makes astrong box spar in the centre. The top andbottom main spars are of i in. by g in.spruce. The L.E. and T.E. are also of in.by 18 in. spruce.

Ifirst of all built a platform from match -boarding, upon which to make the winghalves. This platform has the necessarydihedral in it.

The drawing of the wing can be put on tothe platform, with some greaseproof paperover it to prevent glue sticking to the draw-ing. The wing is then built over the full-sized drawing, and when the glue is dry acovering of thin jap silk is put on, usingphotopaste as an adhesive, and damping thesilk with water from a scent spray. As theunder -surface of the wing is concave and itis essential to keep this section, the bottommust be covered first.

The fabric has to be stitched to each ribby large stitches of thread through thefabric, around the rib and back through thefabric.

When the two wing halves are covered,they are left to dry, and then given onegenerous coat of full-strength, full-size, cellonglider dope, as in the case of the fuselage andtail plane.

When the dope is half -dry, and has justlost its tackiness, the wing halves are placedupon the wing bed, and flat irons are usedto weight the wing so that it does not distortwhilst the dope is drying. The idea of using,glider dope is that, once dry, it forms a hardcovering that seldom distorts and is noteasily affected by weather. It also makes avastly morerigid andstrongerwing than ifmany coatsof thin modeldope areused. It dis-penses also'with all in-ternal brac-ing.

It is veryimportant togive the wingtips a few de-grees of wash-out. This isdone by plac-ing smallbalsa wedgesabout + in.thick under

RIGHT HALF WING

the trailing edges at the tips only. Thewashout will set in as the glider dope drieswith its weight and top of the wing halves.When dry, leave several days to really hard-en, with weights on.

LEADING EDGE6X °,5g BALSA

vents distortion de-veloping in the T edge.

The main balsa ribsare spaced every 4 ins.apart, and are cut fromfin. balsa sheet. Every2 ins. and between themain ribs there are Iin. 3 -ply wood, andover the top and bot-tom of these centralribs, a covering of 1mm. 3 -ply wood isglued. This makesstrong wing centres forthe wing halves to buttup against each other.

There are two smalldowels glued into theright wing half and pro-truding I in. only, andtwo holes drilled oppo-site in the left winghalf No. 1 rib. Theseare merely to locatethe two halves. The

wings are otherwise kept together by thetension of the elastic bands.

On this page is shown the largest andsmallest rib of a wing half. From these thetapered wing can be drawn full size.

BAMBOO PEGS FORELASTIC BANDS

TAIL

COVERED IM.M3PLY"" E N T R E SECTION ONLY

A.'8No8ARLISBALERTI SBS

T.E.FROM;""x/ BALSA4/ 3

SILK COVERING

TOP AND BOTTOM 1- /N.SPAR .4-xKe" BIRCH

LAMINATED4.5HEET BALSA

FOR TIPS

Fig. 8.-Method of constructingthe tail and rudder

OUTLINE MADE FROM3 LAMINATIONS OF

SHEET BALSA PEGS FIT'CLUED TOGETHER INTO TAILSTREAMLINED AND CENTRE.SILK COVERED SECTION

It should have been mentioned that underthe trailing edge spars of the wing halves, astrip of flat ,A in. balsa sheet about 14 ins.wide is glued, so that the rear ends of theribs are also glued to this strip. This pre -

WIRE STRENGTHENERSAT DIHEDRAL

/6 S.LIIC HOOKFOR ELASTICBANDS TO FUSELAGEFRONT HOOK

FRONT /6 SWG WIREHOOKS TO TAKE ELASTICBANDS T °KEEP WING

HOOK FOR ELASTIC BANDSTO FUSELAGE REAR HOOKz

LOCATING DOWELS FITINTO HOLES ON

OTHER WING HALF

ROUNDDOWELLING

WIRE NOOK FOR REAR ELASTIC BAND

Flying the ModelIf you are a novice-and this article has

been written for the beginner, and in con-siderable detail-it is suggested that you getto know your engine by running and starting

Fig. 9.-The right and left halves of thewings, showing details of the fittingwhich hold the two halves together

REAR /6 S.W.G. WIRE HOOKSTO TAKE ELASTIC BANDSTO KEEP REAR OF WING

HALVES TOGETHER

LEFT WING HALF

COVER BOTH WING HALVES// HERE WITH 1/4.1,1. 3 -PLY/77 7 ; I BEFORE 5/LK COVERING

TOGETHER TWO BOTTOM /6 S.W G. WIREHOOKS FOR ELASTIC BANDSTO KEEP BOTTOM OFiv/NG HALVES TOGETHER.


it on the bench first, and then on the fuse-lage, whilst you are completing the rest ofthe model. Model engines become simple,when you understand their peculiarities.

Now get the gliding trim of the modelcorrect. The model must be a perfect gliderif you wish to get good power flying followedby flat glides to good landings. Any othertype of flight is not worthy of a decent model,neither should any modern aero modeller besatisfied with less.

To get glide -perfect, see that balance iscorrect. The point of balance when themodel is fully assembled, and with flyingbattery in position, should be approxi-mately one-third back from the leading edgeof the wing. If it is not, moVe the batteryalong the fuselage.

If there is not enough room and yourweight distribution has come out slightlydifferent, you must weight the nose or tailwith a small weight, but the balance mustbe correct.

Glue a + in. packing of balsa under theleading edge of the tailplane for preliminarytests. This may be reduced later.

Fig. 4 shows the ignition system and Fig. 5the chassis construction of the 6 c.c. petrol

model. It will be seen that the chassis is ofthe sprung type which permits the landingshocks to be absorbed, and in conjunctionwith the knock -off engine mounting makesthe model reasonably crash -proof. Therubber band method of securing the wingssafeguards them against damage.

The wiring system is self-explanatory.Now choose a field, if possible, with a slightdownward slope that leads directly into aslight wind. Try gliding the model by hold-ing above the head and throwing direct intothe wind. A straight forward steady throwis necessary, of reasonable but not excessivespeed, into a moderate wind. Do not throwupwards. Throw straight, or only veryslightly downwards like a dart.

If the model dives, reduce the block underthe front. If the model noses up, give alittle more under the front of the tail-plane.

In this way get the glide perfectly flat,with nice wheel landings every time. Onlyslight variations of the C.G. position may bepermitted to assist tail settings. If you havegot your mainplane angle correct, thereshould he very little alteration of tail, etc.,necessary to get the glide correct.

On no account try flying under poweruntil the glide is correct.

Keep the fin set straight so that the modelwill glide straight after the power is off, andit will then not land whilst winding andbanking and with one wing down, and socause a cartwheel landing.

Do not alter these gliding settings on anyaccount for power flight.

Alteration of climb and turn under poweris done by tilting the thrust line of engine onthis model. This is the only safe way.

Now choose a decent piece of grass, and asa safety precaution put a piece of * in.packing in between the top of your enginemounting and the fuselage, to give tempor-ary down -thrust.

Give three-quarter revs. on your tinyengine by controlling the ignition lever.Set the timer for 10 -second hops, and givethe model a slight push directly into wind.She probably will not rise. Reduce thedown -

torpedoes in naval warfare - radio and ......torpedoes in naval warfare s do not concentrate on war...

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