t I

- U.S. DEPARTMENT OF COMMERCE National Technical Information Service

NACA TM 666

DEVELOPMENT OF TAILLESS AND ALL-WING GLIDERS AND AIRPLANES

R. W. E. Lademann

National Advisory Committee For Aeronautics Washington, D. C.

1932

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NATIONAL AVISORY COMMITTEE FOR AERONAUTICS

TECHI'TCAL HEMORA1TDU r iQ, 666

DEVELQPjAENT OF TAILLESS A TD -IiG GLIDERS AIrD AIRPLAJES*

By 'Robert W. E, Lademann :" '

Tailless airplanes are characterized. by having all their control 'surfaces, especially the elevator, incôrpo-rated ih the wings. If a wing, with the center of gray

-ity of the whole airplane correctly located, is suffi-ciently stable in all directions, i.e., if the airplane, for any analytically infinitely small oscillation, is automatically and. aperiod.ically damped and. returns to its normal position, it Is said. to have inhere2lt stability.

The longitudinal stability of inherently stable wings rests on the fact that thewing tips, due to,an aerody-. namic sweepback, generate a moment which tends to return the airplane to its normal position. The static direc-tional stability is obtained by an'always-present dihe-dral angle due to the taper of the wings and by wing-tip ailerons. The lateral stability is a function of th di-hedral1 and 'sweepback and,also,of the wing contour.

I.herent stability is Rot absolutely ,zestricted. to wing sections or profiles itn a fixed center of pressure, but in many tailless 'airplanes the shifting of the c.p. is utilized for increasing'the restoring moment about the lateral axis, as, for example, in Lipisch's uModel 4U

(1926) with Dunne plan form and..Joükowsky profiles. On the other hand.., the use of profiles' with a fixed' c.p. fa-cilitates constructive 'development, as well as the compu-tations. An inherently stable wing,.according to R. v. Mises, may also be a normal rectangular wine with fixed c,p. and with c.g. located far enOugh back, which is.re-placeable, however, by a sufficiently large dihedral angle.

'...... . . ' .

Most tailless and, inherently stable airp lanes have highly cambered profiles producing the greatest lift in the middleportion of thewing span and, at the wing. tips, slightly ;cam'oered.. and symmetrical profiles with negative

* Il Schwanzlose und Nurf1&gle'." Die Luftwacht, February, 1932, pp. 62-69.

JOSEPH S. AMES COLLECTION.

2 N.A.C.A. Technical Memorand-um iT o. 666

angle of attack. This arrangement also affords the great-est protection against spins. Nevertheless, there are other possible stable systems, e.g., a straight wing hav-ing profiles with a fixed. c.p. and. dihedral angle, that is, with ccg. located.: fáraft, in which case the wing tips also produce lift. The latter have a negative sweepbac-k and may also have a negative dihedral, because a negative sweepback requires a more comp]ete lift distribution. This princilo was well exemplified by Colonel Duchesnets models in 1911, which were alo tested. by Lippiech in 1926 in the 'improved forms corresponding to the aerody-namic develoieit. The induced drag of these tyDes in-creases, esPecially at large angles of attack, this be-ing arësul f the more complete lift distribution. Such wings are yery sensitive to misplacements of the c.g. and. also with respect to diroctiona]. stability.*

Nature provides us with examples of al1-wing aircraft in the winged. seeds of the maple and of the "Zanonia i•akrokarpa (investigated. by Ahiborn), etc., which served as prototypes of inherently stable models for pioneers like Pline (187.0), Igo Etrich. (1390), Caslant and J05 Weiss (1900):;

The British painter and. aviator os Weiss studied. bird flight from 1900 to 1916 at Cornwall on the Atlantic coast and this arrived at the tailless-type of airplane. .&sa result of hIs .ests, he developed the important Weiss law of enlargement, which substitutes a wing loading of

G/P'' 33 for G/P and indicates a great weakening of the Lanchester principle. He accordingly developed tailless mode1s with a thin profile, which had a pronounced posi-tive camber in the central portion and. a negative camber at . the wingtips. These moddls had a high wing .oading. A man-carrying glider, built on these importan princi-ples, was also tried out in the Aumberley Mountains (1908-1916). The models soared to a height of 500 m (1640 ft.)

*This fact is utilized, by soaring sea birds in strong gusts by a similar position of the wings, since they are dependent on the utilization of.the aerodynamic impulses. Compare also the recent investigations of Profesor Uoltschtenof in tt Struktur und Impuismenge der Boen.

N.A0.A. ochnica1 . MmOrandurT 55 3

and. a distance of 9.7 km (6 miles).* There We.S:built,. moreover, a TTeiss two-engine tailless monop lane, which profoundly influenced: the Handley Page airplanes,

In 1905 iTeiss met Igo EtricThiat the in:ternationa].1 model contest in. Paris,where it was fOund that both had. a:ived. independently at thèsamè forinz. Et'1ch bad. de-veloped the. "Taube" .thrugh ti'ansition from, flora to fauna, waich, however, duo to external conditions, did ot re-ceive the merited atte'ntioi, (Since 1928 Etrici. n.as con-

tinued his studies in anotner direction.)

The use ,'.ó' e].atic part-a is cornmon to all these wings, whether eivd'from flora or. fauna. They are therefore suited only for'relative'1' slow flight. ven now this question is entirely open, Energetic advocates of the ':p.rtiall elatic type are Etrich (at least.until veryro-b9tly), Crocco, and also 'irchner with his glider "La Pruve" 'and the new "La Pruvo"mod.el (1931-2).

Since linear outlines and rigid surfaces wer re-quired . for technical and economical reasons, the forms borrowed. from nature were conventionalized., This was firs.tccomplished by Captain Duimne. Sources of weakness in his airpines were the thiii, almost upiform profiles, un'avorable at low speeds, and the pronounced lift educ-tion. at th conically warped wing tips.: Here belongs also the braced. low-wing monoplane P.en6 Anoux (1911) with its pusher propeller and -re'c-tangular. fuselage. The wing had, a low fineness ratio and 'a. symmetrical pro-file., flat, on the bottom and curved. onthe top, with an S ' twist. The 'requisite longitudinal balance was obtained by giving the trailing edge, whic1 constituted ab.dut a third.. of the uniform wing chord, a negative . angle of at-tack,.whereby the altitude control was, tp'be insured. by regulation.of the propeller thrust. In1910-ll Bernet also tried. out an inherently stable and. decid.ed.ly .conical

*Th Veiss enlargement law of mechnica1 creations is ex-plained. In a treatise ".Notes.o .n Giant Aeroplanes" written .with the collaboration of Alexander Keith, It contains the experimental and en1agment' laws UD to very large -'all-wing airp lanes. The life •work of Jose Veiss has been very charmingly d:escribed.. by h1. son Bernhard Jose' 7iss in "Gliding and Soaring 1igh:t.0

4 N.A.C.A, Technical Memorandum No. 666

mod.el wing,* . .. . ,. .

In lll-1913 Robert Mal1e tested a large number of inherently stable wingá with positive and negative dihe-dral and. sweepbacl, which, according to Duc-hesne, exhibit stability for a given form, magnitude and. location of the inerti. ellipsoid.. Similar airplanes with wing tips.ex-

• teide.. forward. were also designed by Lippisch in 1926 and by Dr..Aifred King in 1928. Mallet!s best models h oqounced sweepback and dihedral, tapered..wings with cuea trailing edge and,well-roundedtips. •Ma1letalso' investigated wines, which, according to Dunne's prototype, could bp developed, into, a. right circular cofle., as well as

vitn divided tips like the 'A sgeier" (.g. 1) which were recently tested a'gain.atRossitten.-Mal]et's inheiently stable vings were. surfaces with potential. curves, because they..represented. the dvelopab1e...surfaces of cylindei and-cones. .The models of over.2 m span flew freely, even whQn :captve, in a wind 'of.20 rn/s (66 ft./. sec.). The largest model, with a span of 45 m (14.76 ft.), had tapered wings. with rounded tips anda uniform decrease in the angle of attack with mostly thin profiles. Most' of. the models, weighing 15 to. 20 kg (33. to 44 lb.) flew at a velocity of about 12.5 rn/s (4]. ft./sec.). The Mal1et.-type even with thin profiles, -has good stability.

Accord.i"ig to i llet, tne directional stability o±' flattened M, ..wing (as subsequently . in enk t s model) de.. pends on the . raä. of the .half-span to the height of the wing, i.e6., directional in.st.abil,ity.is produced by a pro-nounced. dihedral of the inner or central port ion of the wing, The best arrangement i for the wing roots and tips to be horizontal. An inherently stable wing, with a forward sweep. and variable angle. of attack, has poor lateral stability, low speed and a.small LID. ratio, but better lift .d.istribution. The .stability can be increased, especially for.wings with forward sweep, by dividing the tips into several parts. Good aileron efficiency with long lQ'er arms is this obtaid w1tot affecting tile inherent stability of the wing asa whole. Mallet's mod.-ole ±'lew without keel- or rudder 0 The model wings were

*Compare also -the . British patents of the Blaire Atholl,. Comiany .accor.d.ing..to. Dunne, as regard.s..tie development of a rectangular wing into a ::r±ght' circular cone , and. Uie ex-periments of G. Eiffel in HLa Rsistance do l t Air et l'A-

viat ion, t(

N.A.C.A. Technical Memorandum i. 66E 5

so designed, with forward sweep, that their roots met at the rear in the plane of symmetry, and. the air flowed. un-der the wings toward. the plane of symmetry (1914 Eiffel laboratory tests) Such models, however, • lew very.slovr-. ly, due to the more perfect circulation distribution,

For historical completeness, the tailless gliders of the painter Sold.enhoff are here mentioned, some of which, of the Ericb and Weiss types, also had. inherently stable wings with very short tails (1913)

The experiments of the students Adaridi, Hschnef and Scherscliewski on the Gulf of Finland, with models of 20 cm to 3 m (?87 to 118 inc) span, were p.rformed more systematically (1911-1916). Tests were made with tailless and "Ente t' airplanes having inherently stable main wings of the Weiss Etrich and Dunne types with Jcukowsky or Eiffel profiles 0 Prom these there wa derived a semi-elastic wing with gradual transition to the fuselage0* The investigation demonstrated the extr-aordi.nary stabili-ty of an inherently stable wing with elastic tips0 Here also directional instability and a tendency to turn into the wind are produced by an ecessive positive dihedral,

The tailless types gradually receded, because the develconent tf more efficient aircraft engines enabled the flight of ae'udynamically less perfect airplanes. The de-sired rapid improvement in flight performances was pref-erably obtained by increasing the efficiency of the en-gines 0 Only a few investigators, like Etrieh, Offermann and Weiss still occupied. themse1'res with ta5.11ess air-planes. Not until 1920 was the work of the pioneers re-sumed at different points, since the post-war time re-quired ëconcmical airplanes0 The science of modern aero-. dynamics has provided the requisite knowledge for con-struction and the preliminary assumptions for stability ca1cu1ations for profiles with fixed c.p6 yielding the maximum lift, and lastly for artificially increasing the circulation by means of slotted w:ngs by removing the boundary layer by pressure or ition and by forward control surfaces with or witbou 1oted wings and their

c omb in at i on s

In Eng1nd in 1920-21 the inherently stable wing U Alula was developed with a measured L/D ratio of 21.

*A similar type was patented by Georg Wojewetzki in Eng-land in 1924 and tested in the wind tunnel of the National. Physics Laboratory.

N.A.IC .A-. Technical ':Ieniorand.um No. 666

The leading edge.had. a negati.ve.'d.ihedral, while the trail-ingedge'had. no dihedral. The whole iag was bent upward at he ti p s, like the. Z,anonia, these tips providing the necessary longitudinal balance. A large airplane was de-signed., and. thenJá pursuit plane was built with Alula wings, which proved to have very poor controllability. In 1921 the racing plane USimp1exI was built on similar lines as a mdial-wingmonoplane with a short fuselage terminat-ing'at the rear in a vertical"edge (keel effect). The tractor propeller was driven by a',300 hp engine. Unfor-tunately this racer was considered. too dangerous to be flown'. . •'....

:' . .

In Germafl the first tailless airplane, the Pe1d-berg, 11. .desiied by Dr.F.. Weik (Weltensegler-Plu.gzeugwerke) with U wing and.: negative angle of ,.sting of,. th,e win tips, was tested at','Sylt. , Tbe very narrow rect.angu1ar winghad a thin seátion 'with a, stiffener ruining its whole length on the undàr side. The short fuselage was,s.tream-lined0 Because of its inherent weakness, it was destroyed in 1921. The thick cantilever high-wing monoplane "Baden-Baden-Stblz" was built in 19.22. Its wing also had. the characteristic' H. shape, tbe central portions having a positive dihedral and the outer portions a decided. taper. Unfortuiately,. this promising type was not developed. fur-ther 0' oceny'; :7olf Hirth and enk have been working on

similar type.' '.:

A. LiDpisch, 'I.' Tscheranowski and. Captain Hill first, and. almost simultaneously, 'applied, the results 0f the more recent 'theory 'of . flow. ' Lippiscil first built a monoplane dëveloed frm the'.Dunne wing wih a pronounced sweepback into', the triangular tapered wing of'his.latest semi-all-Wing "Plying Triangle" having a dissymiietrical, maximum-lift profiIe'witii a fixed. ceftter'of prossure, as worked out by him in 'the .R.R.. . (Rhàn-Rossitten-G'esollschaf) .*

• ' In 1929-30 Captain Latimer Noedham in England built a ti1ies, two-enin'e sport mono1an:e. the ,Ha1ton.Ueto-or, , U provided' with forward. cont.o'L surfaces. for rapidly increasing the leveling-off longitudinal moment. Lippisch

*9hn models (1920) in collaboration with Es p enlaub. Also partially, by derivation from 'the works of Uax 1.iunk for the N'tional Advisory Committee for Aeronautics. The Hunk pro-files have been.i:nown. since 1925, but were first published by Lipp'isch 'ii, 1929. They play an imporant role in the construction, of. the••R.R.G. tailless gliders.

iT,A'.C.A'. TechhicalMembx'an1um To•. 666 '7

is likewise working out' a sstem• of forward control sur-faces based on the Handle'y Page slotted wing. These sur faces might also take the form of auxiliary surfaces over the leading edge of the wing. The introduction of the forward control surfaces from 'submarine construction constitutes an' important innbvati'on, especially for high-sp eed airplanes. The forward control surfaces are nec-essarily similar to the ndley Page system of controls with the trailing edge in the form of an elevator, in oider to affoM 'an' important local increase of the lift cofficient 'in the middle of •thewing', since' the air flow begins'to separate 'at the middle of most inheront-lr s'tab1e wings. A further help is the use of wing. pro-'fj:le& with ' artificial lift increase. Thus far no oxijer-imentC hate' been tried with removal of the boundary lay-'r by pressure 'or suction in the middle df an 'inherently table wing, but'probabiy will be soon.

In 1922 B. Tscheranowski trid.a glider with a wing having the shape of a parabolic'seent, in which the aerodynamic sweepback with corresponding profile devel-opment could exercise' a good stabilizing effect, This all-wing gli'.er- exhibited excellent longitudinal stabil-ity in its trial fli;hts but, unfortunately, developed a considerable diving moment due to the faulty profile. Th9 experiments also demonstrated the possibility of di-recioal control without a regular rudder.* In 1930 the first powered all-wing airplane, the Parabola Bitsch 1tII," appeared with a tractor propeller and a 100 hp Bristol engine. The very thin profiles of this airplane are composed of sections of logarithmic spirals by a sim-pie graphic method. The trailing edge of the wing con-sists of flaps'with slot effect for altitude and lateral. control.

In 1920-23 the'tailless 11 Charlotte I and II of the Berlin Polytechnic Institute appeared, These gliders may be regarded as ' improved "Zanonias." Professor ioff, Par-seval, Tank and Vinter participated in their design. The rectangular fuselage of thó Charlotte was short and point-ed in front with a pronounced keel, 'while the wings had' very thin profiles and were braced by two V struts. Good directional control is obtained by the one-sided opera-tion.of both pairs of ailerons, The stability conditions

*The various models and full-sized •airplanoe had a trian-gulated lattice structure, which was largely indeterni nate,

8 NIA.C.AS Technical órandum.io 666

we±e determined by Professor Parsev'al 'in numerous model tests Both types exhIbited good f1iht.. characteristics, but, unfortunately, were not further developed.

The Swiss, Soldenhoff, after an unsuccessful experi-ment vith a compound wing, built several charact.eris-

tic all-wing airplanes having a very pronounced 'sweepback (so°) and rectangular or tapered wihgs' with a dihedral of only 65'? and ' push'er propôller 0 The wing profiles were cambered. in the middle, symmetrical in the center of each semispán and either' symmetrical or with camber reversed at the wing tips 0 'Fitted with only one pair of ailerons, the first Solenhdff tailless 'áirlanes had no rudder. End plates were used only once '(id that wingly) over the middlQ of 'each .half-*ing. 'Soldenho'ff 'is fundamentally op-posed to end plates, because the con:-.iient'slightdimi-nutien in the induced drag can be off eot 'by a very slight increase ' in span 0 Exper.iments with large models show that turns, can be made very well by means of al 'eron alone without the aid. of wing-tip' r'udders. , '

The ' u Luftfracht tt 'ompany had Langut design an all-wing airplane of 50 rn (16,4'ft.') span with three 420 hp Liberty engines. Peculiar features of this ai±pIane are the us of tc.o pairs of balanced rudders and the d.istri-butioci of the weight along the span so as to correspond. as closely a cssible to the ditributionof the lift, thus reducing to' a minimum the bending moment s.of the spars, Langgut and Lip p isch apparently followed very much the same line of reasoning0 " ' '

Haydn also built a tailless glider on the'plan of the Zanonia and the Jose Weiss His interesting productions wero not continued after 1926.

In. 1928-29 Dr. Alfred' King developed a tailless type with a forward sweep. According to th'o 1930 patent, 'this type' was easy to maneuvor, as demonstrated by tests.

We have showi how practice and theory adequately cov-er he static directio±ial and lateral stability. An in-vestigation. of the dynamic stability of tailless airplanes

*Soldenlloff t s It compound wine was intended to uti1ie the gy•r.oscopic effect of the air vo±tices",'pioduc'd. 'by steps o, n• the pressure 'side of the wing, for rnaiiitain'i the sta-bility. . ' . '

.

N.A.C.A. Technical Memorandum No. 666

by Routh is not yet completed, but is very important on account of the wholly different form and. magnitude of the combined action of the aerodynamic forces and mothents,' as well as the different form of the inertia ellipsoid. The possibility of wing forms with neutral and. with positive longitudinal stability has been demonstrated. Neutral: stability, however, can be of imp ortance only for pursuit planes. Tith the correct weight distribution (according to Fuchs. and corresponding, under certain conditions, to the lift distribution) along the wing and the construction of the wing tips with symmetrical or even lattice profiles, protection against spins is fully insured.* The presence of lattice, profiles my correspond, though not necessarily, o.the '.reuirementsof inher 'á'nt. stability in the so].ec-

tioi of the.piofile, though this is still an open question.

According to the nethod. of Schirmanof's Russian ex-periments,. Lippisch also shows that backswept wings like the ?tSto±chH and tapering wings with a straight trailing edge may possess good directional stability. Even a straight cylindrical wing and, still more, a tapering vrin may have great directional stability, which increases, be-low the separation point, with the ngle of attack. Posi-tive and especially negative dihedral angles, in simple cylindrical and tapering wings, suffer a considerable re-duction in the directional stability.** In the separa-tion phenomeiion, which begins in the middle of inherently stable wings, the longitudinal stability, especially with the use of floating ailerons, is theoretically and experi-mentally but little endangered, due to the wing warping. Al s o the location of the rudders at the wing tips fully insures directional stability, even in the stalled condi-tion.

The experimental airplanes of Dr. A. Kupper must be

*By lattice profiles is here meant, in general, thin pro-files ("plate profiles") provided with transverse slots. They are aerodynamically advantageous, due to the fact that the.normal forces increase almost linearly up to an-gles of attack of 900, so that, according to W. Schmidt, they should have n L/D , r,atio of only 8 (?). **Cf...footnote on page'.2. 'A eabir.dalways flies.froth "' the trough to the crest and must therofore have direction-al stability. This he obtains by giving his wings a neg-ative dihedral. By continually varying his courso he re-acts on the gusts, whi he converts into lifting power.

10 N..A..C,A, Technical Memorandum No. 666

regarded., as 1imitng cases of inhrently stable wings with minimum sweepback, in which the' requisite aerodynamic sta-bilizing moments are kept small by the use of profiles with fixed. c0p, and proiiouiico& variation of the lift mo-inen.t according to the angle of attack (i.e., dca/da iaigo), so that. •srñáll lever arms, that is, a slight sweepback with a borre spending lift reduction at the wing tips, will' suf-fice 1 Though the vertical control surfaces are not at' all necessary according to the experiments, nevertheles's, if they'a"e used, they should take the form of end plates with .ttached wing-tip rudd.ers, which would improve the manuverability.*

Since 1929 Rudolf Schul. has been investigating models with new inherently stable wings charactsrized'by the fac.t that each outer portion of tlie wilig forms a hollow half-cone with its open side down and its vertex coinciding with the end. point of the lading edge of the central portion of the wing. The Gàttingen and Munk profiles are used, including the N.A.C.A. profile lvi 12.' According to the model tests, good lift-drag ratios are obtainable, even with a smaller. aspect ratio, which, according to Schul, is attributable t the favorable effect of the wing tips on the marginal vortices, Schul 1 s models exhibited re-marhablu 'stability in straightening out from any attitude of flight.

The wing of Abrial's gli4er,.at the Rh g n in 1931, 'was similar to the "Plying Triang1e" This cantilever low-wtng monolane has a thick tapered wing of 1,5 to 2 m (4.92 to 6,56 ft.) span, The Lachmann slots are used by both Abrialand Lippisch.

At the Rhn in 1931, a member of the Hessian Academ-ic Aero Club exhibited a. remarkable tajiless all-wing mod-el of about 1 m (3.28 ft.) span *i'th a very thick orofile, small aspect ratio, large wing loeding and consequent high speed. I shape .t resembled the "Parabola," but its

*According to the i±lves'tigationFi of Nagel, the end plates diminish the induced drag in correspondence with the ratio of the height to the span, which is equivalent to increas-ing the span. According to the Russian works of ICras-s'ilschtikof (Z.A.H.I., i/iosccvñ, wing-tip plates have less cffoc cud produce considerable additional drag' when wrongly used, as by' Soldenhoff, Punay and others,,

N.A.C.A. Technical I,Iemorandum No. 666 11

trailing edge had an elliptical cutaway to which a circu-lar elevator was fitted.

Aerodynamically the all-wing type enables a consid-erable shortening of the span, amounting to 30 or 40 per cent as compared with theconventional types, as well as a pronouflced reduction in the wing loading The inherent-ly tab.e wing has many possible applications, due to its many adirant. ages and great diversity of shapes The in-herently stable. tailless, a1l-ving airplane, with great static longitudinal stability, spinproof shape, decentral-ized power distribution and correct weight distribution throughout the span, a high fineness ratio and maximum commercial efficiency, is the ner..ssary and satisfacto-ry airplane for long flights W:ie:a such a wing is de-signed for a low rate of vertical descent, a new and prom-ising type of glider is obtained. In a wing having min imum static longitudinal stability (neutral) and support-ing wing tips witiout wing-tip rudders (King type), with the introduction of bow elevators, a promising form of combat plane is obtained, on which the abser.ce of the cus-tomary tail surfaces leaves a free field of fire toward the rear.

Translation by Dwight M. Miner, Natioial Ad cory Committee for Aeronautics.

iT.A.C.A, Technical Memorandum Ho. 666 12

TABLE I

The Principal Constructors 7ho Participated in the Development of Tailless Gliders and Airplanes

• To i900J 1901-1910 1911-1920 1921-1931

JI Haydn , Nihm, mann, 7inter, Venk,

German,r Friedricxi Berner 'Kircbncr, Iing, Erich Offer- Lippisch, Lang-Arilborn man* - gut, pnul, hup-per, Kohl

Jose' 7eiss Jose Veiss Lathinier-Needham, England with A. with A. Keith, G, T. R. Hill,

Keith, J. . Dunne F. R. and J. Gran-J. 7. Dunne ger

Robert Mallet, C-eorge Abrial, France C. Eiffel, Rena Arnoux

Rend Arnoux, Moreaux**

Switzer-. Alexander Soldenhoff with land Soldenhoff Langgut

United. Twining*** Twining Curtiss State

__________________ Austria Igo Igo Etrich

-________ ------ - Igo Etrich****

Etrich

Boris Adaridi with Alex.

Russia Boris Scher- B. I. Tschera-chewski and nowski

________•

________ __________W. Vischnef __________- _________________

*prevjous to 1914, OUerinann was occupied chiefly with 11 Enten, which had inhernntly stable main wings.

**Moreaux built a tailless high-wing monoplane with pusher propeller. The wing was designed after Mallet and Eiffel. ***The Curtiss Airplane and i'iotor Co. built in 1930 a tailless

biplane of the Dunne type. ****In 1906-12 Professor Twining investigated inherently stable tailless airp lanes, which had a very similar appearance to the subsequent "A1ula t type.

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'5. t.A.C.A. Technical Memorandum No. 666 Figs. 1,

zig. 1 Mallet's "Assgoier" glider with divided viing tips.

Fig. 3 King's tailless air;lane (1928) with negative svieepbac± and d.i1idral.

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LA.C.A. Tec1m1ca1.Memorandm No. 666

Fig. 2