Airplane landing gear

AIRPLUE L A W 3 8 8 G33A2 3 y Salvatore Maiorca NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS , . . ,

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TECHNICAL MEhfORANDUM NO. 627

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AIRPLANE LANDING GEAR* By Salvatore 1.taiorca ~ h ' e landing gear serves the dual pdrpose of absorbing the shock of impact on landing and of dissipating the energy so absorbzd. For this reason the wheels are generally equipped with pneumatic tires and attached to the aircraft by means of a n undercarriage and some suitable elastic system called shock absorbers.

The airplane is equipped,with a landing gear and two or more wheels having the same geometrical axis of rotation.

The third point of support is the tail skid at the rear end of the fuselage.

Prom the viewpoint of load distribution over the fuselage the position of the landing gear with respect to the C.G. of the aircraft assumes a special significance. While the dif- ferent installations have a tendency to raise the position of the C.G., on one hand,it is imperative to have the fuselage as low a s possible on the other, so as to bring the C . O . of the F airplane close to the ground. But the minimum clearance is contingent upon the propeller in such a way that its size and I mounting govern the proportions and tha arrangement of the whole.

An airplane equipped.with a large propeller in the front of the fuselage Fresents, in this respect, the most unfavorable conditions.. Mounting the 3ropellers on both sides of the fuse- lage makes it possible to use a smaller landing gear, favors landing itself, and reduces the taxiing run.

At first sight it would seem as if a maximum clearance between the C.G. and the axis of the wheels (one to the rear and the other as far ahead as possible) would result in greater protect ion against bouncing or dangerous one-wheel landing, but experience has proved it to be othernise.

Placing the landing gear unduly far forward with respect to the C.G. tends to induce dangerous rebound which imperils the aircraft structure. If the C.G. is too far back and very high the a i r ~ l a n o is very unstable during the take-off run.

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*I1Sui Carrelli Per Acroplani," L'Aerotecnica, Vol. 10, Nos. 9 and 1.0, Sept.-Oct., 1930, pp. 689-745.

With r e s p e c t t o t h a h e i g h t of t h e C..G. t71e l a n d i n g g e a r s h o u l d move tcward t h i s c e n t e r a s nuch a s p o s s i b l e as c o n s i s t e n t m i t h t h e moment of t h e p r o p e l l e r t h r u s t a g a i n s t t h e p o i n t of c o n t a c t of t h e wkeels n i t h t b e gr.ound. T o . b e t t e r r e s i s t t h e t r a n s v e r s e s t r e s s e s t h e a x l e s h o u l d b e r a t h e r l a r g e . I n s i n g l e - e n g i n e a , i r c r a f t i t a v e r a g e s a r o u n d 0.18 of t h e wing span; i n t h e tmin- e n g i n e t y p e s t h e wheels a r e always p l a c e d d i r e c t l y u n d e r t h e e n g i n e s ( f i g . 1 ) ; i n t h r e e - c n g i n e and o t h c r v e r y heavy a i r c r a f t one o r more l a n d i n g g e a r s a r e u s e d a i t h u r i n d e p e n d e n t l y ( f i g . 2 ) a r c o n j o i n t l y (fig. 3 ) .

C h a s s i s o r u n d e r c a r r i a g g . - Tho w h e s l s may b e i n d e p e n d e n t 1 . - - - 1 - - 1 - 3 - _ - 1 1 - - - _ C - - - - - - - - o r mounted on an a x l e , t h u s f o r m i n g one o f t v o t y p e s of l a n d i n g g a a r s , i . e . , v i t h o r w i t h o u t a x l e . Tho a x l e , u s u a l l y of s t e e l , may be co~:tinaous ( f i g . 4) o r h i n g e d a t i t s c e n t e r ( f i g . 5) ; whcn e n c l o s e d i n a f a i r i n g i t 2 8 c a l l e d f a l s e a x l e a n d s e r v e s t o r e i n f o r c e t h e c h a s s i s .

O r d - i n a r i l y t h e a x l e i s g u i d e d i n a c a s i n g which s e r v e s t.o j o i n t 2 s l a n d i n g g e a r s t r u t s . T h i s h o u s i n g h a s a n e l o n g a t e d o p e l i n g p r o v i d e d m i t h b r o n z e g u i d e s i n which t h e a x l e s l i d e s ; i t l i n i t s t h e t r a v e l i n c a s e t h e shock a b s o r b e r f a i l s . I n c a s e t h i s arrzngernent i s n o t u s e d , some o t h e r s u i t a b l e means s h o u l d b e p r o v i d e d t o liinit t h e t r a v e l of t h e s h o c k a b s o r b e r .

Xu t h e ' c a s e c f t h e a x l e l e s s l a n d i n g g e a r , t h o c h a s s i s i s formed by one o r more s t r u t s ' w h i c b may be i n t e r c o n n e c t e d a n d f i x e d t o t h e a i r c r a f t by r i g i d b r a c e s o r h i n g e d J o i n t s . ( ~ i g s .

6 , 7 aizd 8 . ) The s t r a t s s h o u l d 3 e s t r e a m l i n e d . They may be of one s o l i d p i e c e of mood o r plywood. I n c e r t a i n c a s e s t h e two s t r u t s m a ; ' hie: com'biiled i n t o one and made of plynrood.

I t i s a d v i s a b l e t o c o v e r t h e tvllole w i t h f a b r i c f o r r e a s o n s of s t r e n g t h . Hard wood, such a s beech o r o a k , i s p r e f e r a b l e a.lthoug:n sprlzce i s i n g e n e r a l u s e t o d a y due t o t h e s c a r c i t y of t h e f o r m e r . Q11.ite o f t e n t h e s t r u t s a r e of m e t a l ( s t e e l , d u r a l - umin) t u b i n g , e i t h e r round o r o v a l shaped. The h a l f c h a s s i s formed by one s t r u t c o n s t i t u t e s a n i n t e r n a l l y b r a c e d m e t a l box.

Theso l a t t e r t y p o (fig. 9 ) l a n d i n g g e a r s h a v e u n q u e s t i o n a b l y % o t t e r aerod.gnamic c h a r a c t e r i s t i c s t h a n the o l d e r t y p e s .

x&gg&g.- The d i a m e t e r of t h e wheels r a n g e s from 0.60 t o 1.50 In (1.97 t o 4.92 f t . ) as f o r CxariQle i n t h e Linke-Hofmann t y p e , B a t t h e r e a r e o t h e r s w i t h 2 m ( 5 . 5 6 f t . ) d i a m e t e r , as t h e S p i g a w i t h 2000 s 400 mm ( 7 8 . 7 4 x 1 5 . 7 5 i n . ) . The wheels a r e u s n a l l y f a i r e d w i t h f a b r i c ( f i g . 1 0 ) ; i n some c a s e s w i t h d u r a l - umin s h e e t .

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I B . B . C . A , T e c h n i c a l Memorandum l?o. 627 I n s e v e r a l c o u n t r i e s t h e d i s k wheel ( f i g . 1 1 ) h a s come i n t o f a v o r , and seems t o be d e s t i n e d t o w i d e s p r e a d u s e b e c a u s e of i t s good ~ h a ~ a c t e r i s t i c s . T h i s t y p e o f mheel i s c l e a n e r i n a p p e a r - a n c e , i n s u r e s b e t t e r s t r e a m l i n e shape t h a n t h o s e h a v i n g s p o k e s , i s l i g h t e r i n weight and c h e a p e r t o m a n u f a c t u r e . Another f e a - t u r e i s t h e s p a c e a v a i l a b l c f o r i n s t a . l l i n g t h e b r a k e a n d p a r t s o f shock a b s o r b e r s .

Normally t h e wheels a r e f i t t e d w i t h t i r e s . Siemens and Linke-Hof~tlanii s u b s t i t u t e d wood. f o r r u b b e r d u r i n g t h e e x i g e n c i e s of t h e morld w a r , even m a r k e t i n g one c e r t a i n t y p e made of i r o n t h r o u g h o u t . ( ~ i g . 1 2 . ) But t h e mheel r e a l l y s h o u l d b e e l a s t i c a n d t h i s i s i n s u r e d only n i t 3 pneumatic t i r e s . The a d v a n t a g e s of t h e s e v11.ee3.s o v e r t h e o t h e r s i n c l a d e s l o n e r moment of i n e r - t i a of t h e mass a b o u t t h e i r p r o p e r a x i s and s m a l l e r f r i c t i o n of r o l l i n g . The p r e s s u r e of t h e n l ~ e e l s on t h e ground s h o u l d n o t

e x c e e d 4 kg/cms ( 5 7 l b . 2 . ) , a l t h o u g h one i i a n u f a c t u r e r

a d v e r t i s e s t i r e s f o r 6 kg cm (85.3 l b . / s q . i n . ) i n f l a t i o n p r e s - s u r e , which d o e s n o t p e r m i t a n a i r p l a n e t o l a n d o r t a k e o f f u n l e s s t h e ground i s dry a n d h a r d .

To r a i s e t h e l o a d i b i l i t y of t h e l a n d i n g g e a r w i t h o u t any p r o p o r t i o n a l i n c r e a s e i n wheel d i a m e t e r t h e double wheel h a s been d e v e l o p e d . ( p i g . 1 3 . ) Such a w h e e l , n o r m a l l y c o n s t r u c t e d w i t h 3000 nm ( 1 1 8 . 1 i n . ) d i a m e t e r and 1 7 5 mm (6.89 i n . ) pneumatic t i r e s , n e i g h s 106 kg (233.69 l b . ) w i t h f a i r i n g c o v e r .

A s i n g l e wheel of t h c s a n e d i n e n s i o n s n e i g h s 55 kg (116.84 l b , ) .

A s a m a t t e r of r e c o r d t h e r e a r e n h c e l s which can s u p p o r t a l o a d of f o u r t o n s .

T i r e s . - ----- The o l d c l i n c h e r t y p e ( f i g . 1 4 ) i s 2 r a c t i c a l l y o b s o l e t e . T3e most n i d e l y u s e d t i r e i n America and which a l s o f i n d s f a v o r h e r e i n Europe i s tile s o - c a l l e d s t r a i g h t - s i d e t i r e .

( F i g . 1 5 . ) 1 3 I t a l y t h e a i r p l a n e n 3 e e l h a s been s t a n d a r d i z e d . ( ~ i g .

1 6 . ) B,A,C.A. T e c h n i c a l Momorandun No. 627 TABZE I A i r p l a n e Wheels ( ~ o v e r n m e n t s t a n d a r d ) ---A VIII

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12 50 Outside diameter mm Diameter, t i r e section I t 250 Diameter, groove of r i m 12 7 Length, groove of r i m Length of hub 11 Diameter of hub 11 Airplane weight Average weight o f

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inner tube I I 0.590 Average weight of I I 1.850

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outer t i r e cover I n f l a t i o n p r e s s u r e kg/cm2 3 L

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nn X .03937 = in.

kg X 2.20462 = lb.

kg/cma X 14.2235 = lb./sq.ic, Ben X 7.2333 = f t . l b .

N.11.c . A , T e c h n i c a l Memorandum No. 6 2 7 TABLE I1 T i r e s ' ( T e n t a t i v e s t a n d a r d ) s i z e s i n mm - t i r e s w i t h w i r e i n s e r t ITominal diam. Diameter 510 X 65 510 4 10 610 X 75 610 4 10 710 X 8 5 710 rt 1 0 760 X 100 760 4 10 100 f. 5 810 X 1 2 5 810 4 1 0 1 2 5 rt 5 975 4 10 150 4 5 975 X 150 1,020 f. 10 ( 1 , 0 2 0 X 1 7 5 ) 1 7 5 f 5 1 , 1 0 0 f_ 1 0 220 -C_ 5 1,130 X 220 1,250 4 10 1 , 2 5 0 X 250 250 -4. 5 (1,300 X 300) 1 , 3 0 0 k 10 300 % 5 The s i z e s w i t h i n p a r e n t h e s i s may be e l i m i n a t e d .

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N . A . C .A. Technical Monorandurn No. 627 Fig .l8 R i m s (~entative standard)

sizes in mm - rims with straigh& sides

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Width Fitting For I1Dinel 19" ---I-------T------------- of rim ference D n D I I Regular ' Oversize r ------- 1670 45 7 . 5 710 X 85 1730 50 8 760 X 100 810 X 125

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810 X 125 1730 60 8 . 5 810 X 125

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2065 75 10 965 X 150 2075 120 13.5 1 . 1 0 0 X 220 (1200 X 250) 2075 150 17 (1200 X 250) 1300 X 300 -- -.----- ---.--------------------- W . A . C . A . T e c h n i c a l hfemorandu-n 170. 627 TABLE IV ( T e n t a t i v e s t a n d a r d ) A: a h e e l s w i t h s p o k e s B: d i s k wheels ...............................................

19" t i r e s Theel For I1Dinel .....................

Oversize

~o--r Hub Remlar

size Size

---- ----.------------- ------ - - - - - - - - - - - - - - - - - * - - - -

1 30 -

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710 X 85 710 X 85 42 x 160

(2) - (0)

3 11 - ( 4) 760 X 100 760 X 100

- (0)

(6) 810 X 125 810 X 125 5 5 X 160

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(7)

11 -

(9) - ("1 - 11 965 X 150 965 X 150 40 - 65 X 225 - 11 (11) I )

11 -

(I3) (1200 X 250) 1100 X 220 1100 X 220 80 X 220

- 11

I' -

80 X 220 (15) 1300 x 300

1 1200 x 250 1200 x 250

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10OX 250

- - - - - - - - - , - , . . . . - - -

S i z e s i n p z r e n t h o s i s may be e l i m i n a t e d .

F r a a c e h a s a l s o s t a n d a r d i z e d t h i s t y y e of m'ileel. The p r e s e n t - d a y t e n d e n c y i s t o v a r d l a r g e t i r e s and low i n f l a t i o n pressv-re. The c h a r a c t e r i s t i c s o f t h e vlzeel r e c e n t l y p r o p o s e d a r e a s f o l l o n s : N.A.C.A. Techcical Menorandurn Bo. 627 TABLE V Dimension I of wheel: Hub : length bore %eel bare : min. length of outer r i ~ ?

radial stress Q static stress laterally applied at a distance from edge of hub k ' f m Wheel mounted : max. pressure of static test P kg height of tire in- flated a t Tressurc P RWC. width of flw (inflation pres- sure P of tire) total might kg min. static energy to flatten tire k t , m sax. 2ressure on tire kg

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These specifications also include a lateral stress expressed in form of a moment, which is not found in the Italian standard.

Shock absorbers,- In order to 'eliminate thp snocKs between

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the wheels and the fuselage it is customary to ira.terpose elas- tic units which absorb at the moment of landj-ng the vertical component of the energy of the airplano which the tires have not dissipated.

These elastic units commonly known as shock absorbers may be mounted between landing gear axle and chassis, between chassis and fuselage, or between the wheel and the axle. I n tho latter case me have tho internally sprung or olastic wheel.

Tho shock absorbers may consist of rubbor cords acting in tcnsion, rubber disks acting in compression or steel springs acting in tension or in compression.

Lastly there is the oleopneunatic type in wh:ich the oil is forced through a, series of holoe.

In the first thre& types enumerated the absorption of the kinetic energy results in a number of lesser shocks which make the airplane bounce. The additional stresses set up by those repeated rebounds endanger the strength of the airplane and the safety in landing to such an extent that the airplane commences to bounce from tho first impact if the initial tension of the springs is abnormal.

The importance of shock absorbers was soon recognized during the late mar. England decided on rubber,cord in con- junction with oil shock absorbers, while Prance equipped the Goliath bombers with BQchereau oleopneumatic shock absorbers along with rubber cord.

Ordinarily the rubber cord is said to function satisfac- torily. A steel spring serves the same purpose as was proved by Germany during the war when the lack of raw materials be- came a vital factor. Rubber cords, even though subject to rapid wear and tear, are preferable to steel springs becauae they dissipate bg friction a large part of the energy absorbed.

In normal landings the direction of the shock is toward the rear.

Pormerly this inclination w a s disregarded; the return was verti- cal in such a way that only this component of the shoclr was absorbed. The axle of the wheels should be mounted so as to be ' able to travel normally as well as parallel tow&rd.t2ie fuselage.

Moreover, heavy and rather long airplanes are materially affected by the wind as their speed increases, and it is'vsry important to have the landing gear elastic in the transverse direction also.

Rubber disk shock absorbers,- In order to deform an elastic body, say to compress'a flat disk by means of stresses evenly distributed over its bases and acting along its axis, a certain amount- ox" ezlergy i s exgesded v h i c h i s t r a n s f ~ r r n e d i n t o p o t . e n t i a l e l a s t i c energy:: The e n e r g y which a n e l a s t i c bcdy c n c a b s o r b r r o v i d e d t h e e l a s t i c l i n i t B i s n o t e x c e e d e d , i s p r o p o r t i o n a l t o i t s volume a n d t o t h e sq-&are of t h e s p e c i f i c p r e s s u r e .

33t 0 = - o r , w i t h p a r f t g of vol~.me, t h e work n h i c h t h i s 3 ' ' boay c r y a-kisorb i n c r e a s e s as t h e s e c t i o n d i m i n i s h e s , o r i n o t h e r n o r d s an e l a s t i c body i s i n S e s t s o n d i t i ~ n t o d i s s i p a t e energy nkex i t i s n a r r o n 2nd l o n g .

On t h e o t h e r h a n d , a bodg o f the d e s i r e d p r o p o r t i o n s and l o a d e d a t the end bends l a t e r a l l y w i t h t h e r e s u l t t h a t i n some s e c t i o n s t h e s t r e s s e s exceed t h e e l a s t i c l i n i t a z d n a y even r e s u l t i n a rzFi.4 dcc$ease i n t e n s i o n i n t h e g r e P t e r p o s t i 3 n of t h e s e c t i o n s a n d i n consequence of t k e energ;>- a b s o r b e d .

Then a g a i n , t h e i::crease i n l e n g t h I may r e s u l t i n f i g u r e s u n s u i t a b l e t o a i r p l a n e shock a b s o r b e r s mhose t r a v e l s k ~ o u l d be d e f i n e d n i t L i n s t a t e d l i m i t s .

Tl:.e i ' l r s t n a y be remedied by t h e u s e of r u b b e r d i s k s i n t e r - s p a c e d w i t h p l a t e s i n such a manner a s t o a v o i d a l l f l e x u r e of t h e column nkich o t h e r w i s e n i g h t f o r c e t h e l a n d i n g g e a r s t r u t t o g i v e z a y u n d e r any a c c i d e n t a l a s y m m e t r i c a l s t r e s s .

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i n t r i o n o s t e l e m e n t a r 7 k i n & of shoclc absorbers o f t h i s t y p e t L e s p a c e r s a n d t h e c e n t e r i n g p l a t e a r e stamped i n one p i e c e i r o n alnnir,v-m s h e e t . ( F i g . 13.) I n t h e P a r n a l l . t y p e (fig. 2 0 ) t h e s t e m p e 3 ~ , l a t e s g l i d e i n c o i l t a c t w i t h t!ie i n s i d e c g l i n c l r i c n l s u r f a c e o f t h c s t r u t . I n t h o G l o s t e r t y p e ( f i g .

2 1 ) , dis?:s aiid 2 l a t e s a r e botli y e l l s t r e a m l i n e d and even d i s - t r i b u t i o n o f i o $ < i s tnsnre?. by t h e c o c t a c t of t h e r u j b e r o n two g u i d e t u b e s . These s 3 a c i n g and c e n t e r i n g p l a t e s s h o u l d be l o n g e r thac t h e r u b b e r d i s k s s o as t a t a k e c a r e of t h e e x p a n s i o n mhen u n d e r c o r n ~ r e s s i o n .

i2 o r d e r t o d e c r e a s a t h e t r a v e l o f t h e shock a b s o r b s r a t t h e moment of impact t h e sllock a b s o r b e r i t s e l f i s s u 3 j e c t e d t o

a n i n i t i a l t e n s i o n . I n f a c t , conformably t o L = -$ W A I t h e

work i s d e f i n e d i n t h e t r i a n g l e ( f i g . 2 2 ) n i t h t h e t r a v e l a s b a s e and t h e h.eight a s t % e l o a d s .

L e t 3 C r e p r e s e n t t h e p e r m i s s i b l e n i n i m u ~ l s t a t i c l o a d , which f o r r u b b e r . d i s k s i s a r o u n d 17.!zg/cm2 (241.8 l b . / s q . i n . ) .

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* . .I - - - - - - N .A.C .A. Technical liernorandum Bo. ' 627'' ' When it exceeds this figure the rubber becomes hard and soon loses its elasticity. Figure 22 sbons that for a stated travel a b, naturally less than the complete path A 33, a maximum and B coincide.

amount of energy is dissipated when b Likenise, for the dissipation of a stated- amount of energy (the cxact amount'to be given 2a.ter) the minimum travel may be o b t a h e d if one commences with the calculation of the area C B .

The work diagram is thus transforned from a triangle into a trapezoid, the smallest base of nhich yields the value of the initial tension. (The rubSer shock absorbers are also put under initial tension.)

- ~ i g u r e 23 illustrates a Potez landing gear equipped with rubber disks working under initial cosilpression by means of a spring, nhile Figure 24 shons a shcck a b s ~ : ~ b i n g strut of the Blackburn-Bluebird airplane. The elastic system consists of a steel spring, the disadvantages -f which mere pointed out above.

For this type of' spring as for the rubber disks aild for any other type of shock absorber mhich becopes deforr-led when con- pressed along its own axis; the struts as well as the axles must be hinge jointed. The hinges represent nearly always dangdrous points of rupture and materially contribute to diminish the aerodynamic charactertstics o-f a landtng gear.

Rubber ....................... cord shock absorbers.- They are formed by a stated

number of 1 X 1 mn ( . 0 4 X ,04 in.) square rubber strands wrapped in a double webbing of cotton. The threads are continuous over their entire length and should stretch..600$ under a 500 g (1.1 lb.) stress. 'Phe threads break under 1000 g-(2.2 lb.) and stretch about 700$.

The texture of the cotton webbing should permit the threads to stretch evenly, be of woven fabric and of first grade cotton so as not to deteriorate too quickly.

These shock absorbers are in rings or twisted strands. In the latter case the ends terminate in special rings and attach- ment hooks shown in Pigures 25, 26 and 27. Their installation should be such that all rubber rings work evenly and be as paral- lel as possible to the direction of motion of the axle. It is very important to cover the parts on nhich the shock absorbers rest nith heavy leather and to avold all sharp angles nhich inevitably cut them in two.

The whole should be protected against mud and oil by a leather covering or casing.

T e c h n i c a l Mez~oran&-~.z No. 527 N.A.C

-There : a r e v a r i o n s 17~;;s i: rILfc;rL rubber cord shock a b s o r b e r s *

:my be 03e t y p e , sho~:: ia 3 i g u r e 2 8 , - i s p a r t .of t h e Yorane-Saulnier . s 9 l i t - a x l e landin,? gear i n v h i c h t h e s t r a n d s a r e

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n o t t i e d ; t h e one i n F i g u r e 29 i s ~ h n i l a r but h a s a s h o r t e r t ~ a v e l . F i g u r e 30 shovs t h e JvLiZ::$rs t y p e , mhich f e a t u r e s t h r e e shock-absorbing s t r u t s . The s t r r t s and t h e a x l e a r e i n t e r c o n - a ~ ~ t e d and hinged t o t h e f u s e l a g e . Fvo o r i g i n a l arrangements G T C s e e 2 i 9 F i g a r e s 31 and 32, v i z : t h e Zokker t r i n o t o r and t h e Sermard t y 9 o . In t h e Fokker t h e wheel s u p p o r t s t h e f u s e l a g e by a e a n s o f as e l a s t i c system which j o i n s a f i x ~ d . h o l l o n Body t o a strll-t which g l i d e s along t h i s body aad n ~ l h c h i s ' h . i a g e d t o t h e f z s r l a g e . %lie body a t t h e same time s e r v e s a s t r a v e l stop. I n t h e S e r x a r d t y p e t h e s t r u t i s c o a a e c t e d t o t h e n h c e l . Another n e r l knoma t y p e , y a r - l i c u l a r l y on heavy a i r c r a f t , i s shonn iil n 2 i g u r e 33. S e r e t h e nlieels c a n a l s o s h i f t h o r i z o n t a l l y . Note 2- 7 ~...xe l e s t h e r c o v e r i n g .

I n $ig.c-res 24 ax3 35 i s shonn a type riith s t e e l s p r i n g s n h e r e aany s r ~ a l l s p r i 3 g s a r e p r o f e r r e d t o f e n l a r g e ones, It -:;.ill be n c t e d t h a t one ea6. i s f a s t e n e d t o a n 'iipper box n'ilich r e s t s o a t h e wheel hub and t h e o t h e r t o a l o n e r box. The s p r i n g s tire n o t a l l g a r a l l e l ; t h e y a r e i n t n o s o t s and form a s h a r p a r g l a . Tbis arrangement 3 1 ~ 4 e ? s i t p o s s i b l e t o a b s o r b shocks i n - c l i r e d t c t h e v e r t i c a i .

D l e ~ n e a m a t i c skock abxorBers - Yor o r d i n a r y l a n d i n g t h e

--.----.--- & ---------.-- - *

- _._

shock absoi-3cr s ? ~ ~ a l & , a s a r u l e , be f l e x i b l e i n o r d e r t h a t the shocks be a s l i g b t ~ . s p c s s i b l e ' a p d t h e rebound which i s a l v a y s daxgersus moderate.

Oa t?le o t h e r hand, i3 q i o l e n t l a z d i n g s t-he shocg a b s o r b e r should be c n l ~ a b l e of a b s o r b i n g a maxiriv-m anount o f energy a i t h - o u t excee5ing t h o p e r n i s s i b l e s t a t i c load.

. * KitL t h e p r e s e n t day &b5er-cord and c ~ m ~ r e s ~ i o n - d i s k g e a r s t b e s t a t i c l o a d ctrrve > l o t t e d a g a i n s t t h e t r z v e l sholns a n upward c o n v e x i t y and tz:is a ~ 2 2 l i e s t o g e a r s cei3aSI.c sf a b s o r b i n g a g r e a t rmqy k i l o g r a ~ s . I f the g e a r s a r e v e r y f l e x i b l e t h e c o n v e x i t y of t h e c u r v e i s downward.

? h i r e ol.eopnev.r,tatic g e a r s o l v e s t h e d i i f i c u l t f (fig. 38).

I t c o n s i s t s o f a s t e e l c y l i n d e r n l t 5 t v c chambers and a v a l v e .

The upger chamber c o n t a i n s a p i s t o n mhicl~ bottoms a g a i n s t t h e v a l v e -0-:;clef nprnaf l o a d . The space above t h e ? i s t o n i s f i l l e d zri.tk c c r q r e s s e d a i r ( 5 0 kg,! (120.23 Ib.). The lower c h a ~ ~ b e r i s c f a s o d a t t h e b o t t o u 3g a sec3nd p i s t o n equipped mith a rod ~ h L c k f'firi,zs t l r s o o n n e c t i s n - w i t 9 t 5 e a x l e a f t h e wheel. The spacc j e t n e e 2 t h o tno > i s t o n s i s f i l l e d n i t h a n t i f r e e z i n g o k l o r g l y e c r i n e . Then, under t h e e f f e c t o f t h e s3ocBs t r a n s n i t t e ~ ~ - \ - ~3 t h e a x l c , t h e l o a e r p i s t o n e x p e l s t % e c i l , a 3 i c h p a s s i n g N.d.C .A. T e c h n i c a l Elemorandun No. 627 a c r o s s xne sFace p r o v i d e d by t h e v a l v e l i f t a c t s i n i t s t u r n on t h e p i s t o n and compresses t h e a l r i n t h e o t h e r chamber. When t h e s t r e s s h a s d i s a p p e a r e d t h e ctinpressed a i r r e l a x e s and r e - c o i l s t h e top g i s t o n , t h e v a l v e c l o s e s and l i m i t s t h e r e t u r n f l o w of o i l t o a b l e e d e r h o l e 52 t h e v a l v e .

I n t h i s t y p e of a b s o r b e r t h e t y p i c a l s t a t i c l o a d e l o u g a t i o n c u r v e embodies t h e curve of t h e c o m p r e s s i b i l i t y of t h e a i r and a n o t h e r t h e r e s i s t a n c e due t o h y d r a u l i c r e s t r a i n t which grows w i t h t h e p i s t o 3 speed. But sucb a g e a r shoas a n a l m o s t c o 3 s t a n t d e f o r m a t i o n c u r v e no n a t t e r what t h e impulsion of t h e a i r p l a n e on t h e grourrd. The r a t e of o i l outflow d u r i n g t h e compression o r d u r i n g t h e expansioa of t h e a i r can be s u i t a b l y graphed from the normal l o a d s u p g o r t e d by t h e wheels. T o make t h e l a n d i n g g e a r of a heavy a i r p l a n e more e l a s t i c t h e o i l flow may b e a d j u s t e d t o t h e l o a d v a r i a t i o m by v a r y i n g t h e a i r p r e s s u r e i n t h e c y l i n d e r .

The a t t e m p t s t a inprove t h i s t y p e of shock a b s o r b e r s have been many.

1 3 t h e EgssLgy g e a r t h e p a s s a g e of t h a o i l i s a c r o s s a r e c t a n g u l a r o r i f i c e which houses a s l i d e v a l v e of v a r i a b l e s e c t i o a ; %30 c u r v e c o r r e s p ~ n d i a g t o h y d r a u l i c r e t a r d a t i o n v a r i e s w i t h t h e s i z e of t h i s v a l v e . Tho appeaded diagram ( f i g . 39) shows t h e c u r v e f o r t h e L l e s s i e r - t r p e .E 3 g e a r d u r i n g t h e compres- s i o n s t r o k s . Ourve C r e p r e s e n t s t h e c o n p r e s s i b i l i t y of t h e a i r ; a t h e d e c e l e r a t i o n of t h e o i l f a r a 3 ra/s (9.84 f t . / s e c . ) v e r t i c e l v e l a c i t y on c o n t a c t ; 2 f o r 1 n / s (3.28 f t . / s e c . ) and A B t h e r e s u l t a n t curve.

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Thus, t h e adjustment o r o t h e r s i m i l a r d e v i c e of t h e o u t l e t o r i f i c o e n a b l e s u s t o a p p l y t h e l o a d g r a d - ~ a l l y u n t i l a maxinum i s reacheG v h i c h remains c o n s t a n t throughout t h e s t r o k e . A s a r e s u l t t h e s t r e s s e s on t h e a i r y l a n e s t r u c t u r e a r e k e p t a t a m i n i ~ x i n . This uinimun i s , la c e r t a i n c a s e s , l o n e r by h a l f t h a n t h a t o b t a i n a b l e 3g a f i x e d o r i f i c e a c c o r d i n g t o G. H. Domty who a t t e n p t e d t o f i n d some means c a p a b l e - o f a b s o r b i n g t h e k i n e t i c eEergy of a n a i r p l a n e c o n f o r n a b l y t o t h e s a n e laa of v a r i a t i o n of t h i s e l e r g y , i . e . , p r o p o r t i o n a l t o t h e square of t h e speed, Re i s s a i d t o have found t h e s o l u t i o n of t h e p r o b l e n by u s i n g a n e e d l e v a l v e , and i n p a r t i c u l a r by t h e s e l e c t i o n of a n e e d l e so t h a t t h e s q u a r e r o o t of tzie weight r a t i o s af a i l p l a n e and o i l t o be d i s p l a c e d mas e q u a l iz r a t i c ~ of p i s t o n a r e a t o f l o n o r i f i c e

----

/ - = l a n e d e i g h t = a r e a of pis to:^ a weight of o i l o u t f l o w o r i f i c e I? . A , C .A. Technical Uenorandun No. 627 a too long taxiing run. Braking itself is difficult to regulatw and sets us rebounds very easily as shown ia the C~.proni air- planes nhich, however, seens tc have been temporarily abandoned.

Angiiibiaa gear.- The fuselage is built as a llull to provide alighting on water. In addition it is equipped with two re- tractable vheels as in the Irelanii "NeptuneN (fig. 48) or as ia the American Tonle W. C.

The landing gears vith lateral shock absorbers merit spe- cial mention. (Figs. 49 and 50.) Others are the De Havilland 54 and the Levasseur gear. The disappearing type is relatively well represented by the Bellanca, Burnelli, etc.

Lastly, there are the various caterpillar s y s t e m bbf which the Trench L. Viuay type is a representative. This nas intended to be substituted for the orthodox types of landing gear, but the iaherezt drawbacks seem to outreigh its alleged advantages.

Brakes.- The use of wheel brakes presents numerous ad- vantages. The high value attached to quickness of pull-up, or time to stick is apparent. Aircraft for deck landing benefits by braking owing t~ the very limited length of run available.

Independently operated mheel brakes give the single-engine air- craft maneuverability on the ground, thus augmenting in a great measure its safety in rough terrain, unfavorable winds or right operation. Lastly, they pernit landing at higher speeds and the elimination of mheel cliocks for the preliminary starting and runxing up of the engine.

Because of all these advantages, wheyel brakes are becoming normal equipment in America on military as well as on commercial aircraft. The brakes do not differ very much from automobile brakes and the gilots have found them satisfactory.

In Europe, on the other hand, the use of brakes has found no widespread favor.

Adnittsdly their use has always boen associated with additional weight and complications cansequent to their adoption, and in t3e search for a suitable method many schemes have been suggested and tried. The following present some of the most popular types: The Bendix _>eel and brake nl-rich is of t3e expanding two-sector type, t2e operating can and lever being visible in Figure 51. The brake dram is entirely contained within the

wheel. The primary shoe A is articulated to the seccndary

shoe B at the point C and is not anchored to the brake drum.

The location of pin S and anchor pin 2 have been carefully

B .A, C . A . T e c h a i c a l 1deworandv.rn No. 627 ., ..

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s e l e c t e n I,O provide e f f c c t i v c ; r a k i n g . Cast aluniaum i s u s e d - a l n o s t e x c l u n l v e l y . T i g u r e 52 skomc t l e i a s t a l l a t i o n a n d o p e r a t i F o l l o n i n g a r e t h e n e i g l i t s ax?- t11e d e f l e c t i o l s of v a r i o u s - s i z e eels TABLE V I

----- --------- ------------------- ,------------ ---------

T i r e s i z e T i r e d e l l e c t i o n C a p a c i t y [ A i r p l a n e

4 of ;:eel n o i g h t reac!j 3x1

% .

iar-1 Sii

------------- ---I------- - - - - - L - , - - ---=&----

t

t

T k e t ? r q u c r e a c t i s n S a s e d - q o n tz:e bra,king e f f o r t and t h e a x i a l s t r o ; s a s i s cs;mate2 f r o n t h o f o r r a ~ l a p = c o c f f i c i e : ~ t s f f r i c t i c l n = 0.55, 8 = a i r p l a z e n e i g h t , R = r a d i u s of ~ r h c e l , h = t i r e d e f l e c t i o n .

d 750 X 1 2 7 nn (29.92 X 5 i n . ) s i z e a k e e l n i t ~ ~ s t a n d s a r a d i a l l o a d o f 5900 l:g ( 1 ~ , ~ 0 0 l t . ) a n d a s i d e l o a d af 1820 BE (4012 l b . ) ; a 915 X 203 nn ( 3 3 , 0 2 X 8 i n , ) mheel a r a d i a l l o a d o f 9080 ( 2 0 , 0 1 5 1 5 . ) ~ i ~ d a s i d e l r a d of 2800 k g (6173 l b . ] .

I t w i l l b e s e e u t 2 a t eacL ~7Leel i s o p e r a t e d independeiztly, A l t k o u g l t h i s s y s t e a docs n o t p r e s e a t any s p e c i a l f e a t u r e s , it seems t o have f s u n d t7idcsprea.d f a v o r .

rii- ~ - - e &aczadde n l e c l a n d b r a k c 3 a s a spoke a r r a s g e n e a t ; t 3 e 3 r a k e i s L k c SRI.^IC a s ill a u t r j r ~ o b i l e s ; t L e b r a k e n e c h a n i s n i s iasidc t k e rr:rccl and >as fins a l o ~ l g t h e c i r c x n f e r e n c e of t h e d r a n t o d i n s i 2 a t c t i e lieat g c n e r a t e d a s a r o s a l t of f r i c t i ~ n .

The Sra!ze of e a c l ~ ~ l ~ a e l i s c p e r a t e d by a s e p a r a t e f o c t p e d a l .

Co:-;pared t o t!lc Bendix m ' l e c l , t k e Sav-zedde wl"lee1 i s riuc!~ n o r e c o n ~ l i c ~ ~ t c d - , l e s s r c l i a b l e a n d L e a v i e r .

E.A. C . A . Teckn-lcal Menorandm Xo. 627'.

-___d_____I-____-_d____-___~------ -----------------

S i z e of wheel wei&t of mh2&&th-- - - - - Veight --_ of -,----- b r a k e

I - - g ~ d i ~ b r a k e Sanzedde b r a k e 1 l3e;di; 1 Sauzedde

----_--___-_--- _---_----__ ---__------- ----11-1 ---------

T

The V i c k e r s v h e e l a n d b r a k e ( f i g . 53) i s of t h e e x p a n s i o n .'

t y p e L y d r a u l i c a l l y o p e r a t e d . The t h r e e b r a k e shoes a r e o p e r a t e d by a s i n p l e h y d r a u l i c c y l i n d e r and p l u n g e r . The b r a k e drum i s i n s i d e t h e iyheel; t h e b r a k e s a r e c o m p l e t e l y e n c l o s e d and w e l l p r o t e c t e d a g a i n s t s a n d , mud and w a t e r . The n h e e l i s r e a d i l y removed. w i t h o u t i n any nay d i s t u r b i n g t h e b r a k e s . The b r a k i n g s y s t e n i s e x c e e d i n g l y s i m p l e . The p i l o t h a s a b r a k e l e v e r n h i c h o p e r a t e s a s m l l h y d r a u l i c pump. Two backward and f o r w a r d move-

ments of t 3 i s l e v e r r a i s e tile p r e s s u r e t o 1 4 kg/cm2 ( 1 9 9 171.1

sq. i n . ) and t a k e up a l l t h e bra?:e c l e a r a n c e s . The t h i r d s t r o k e

r a i s e s t h e r r e s s u r c t o 55 - 70 lcg/cm2 (782.3 - 995.6 l b . / s q . i n . )

and t h o Brakes a r e a y p l i e d f n d i r e c t ~ r o p o r t i o n t o t h e movement of t h e l e v e r . The o i l c i r c n l a t i o n p i p e s a r e of s t e e l . To i n - s u r e i n d e p e n d e n t b r a k e o p e r a t i o n of e a c h n h e e l a s p e c i a l v a l v e ( p i l o t ' s c o n t r o l ) i s p r o v i d e d . When t h e c o n t r o l s t i c k i s i n n e u t r a l p o s i . t i o n t h e S r a k e s z u t o m n t i c a l l y b a l a n c e one anotzier.

A ' p r e s s u r e gav-ge mounLed on t h e dashboard i n d i c a t e s t h e p r e s - s u r e e x i s t i n g i n t h e system.

T h i s b r a k i n g s y s t e n h a s been f i t t e d on t h e V i c k e r s Vanguard n h i c 4 i s i n t 3 e s e r v i c e of tF.e I m p e r i a l .Airways; and t h e s y s t e m h a s been found v e r y e f f e c t i v e . I t p e r m i t s of p u l l i n g up t 3 e a i r p l a i i e , v 2 i c h vfeigf1s 8125 kg (16,000 l b . ) l o a d e d , i n some 70 - 90 m (230 - 328 f t . ) w i t h o u t t h a t s c a r i f y i n g e f f e c t on t h e l a n d i n g f i s i d s u r f a c e produced br t L c u s u a l t a i l s k i d .

B u t i n s p i t e of t h e i n d i s p u t a b l e a d v a n t a g e s of h y d r a u l i c o p e r a t i o n t h e f o l l o v i n g d i s a d v a n t a g e s must n o t be l o s t s i g h t o f : g r e a t n e i g h t , and danger of l e a k a g e a t t h e i n e v i t a b l e s o l d e r e d j o i n t s .

Tlie E n g i n e e r i n g D i v i s i o n b r a k e s . - The f i r s t e x p e r i m e n t a l

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b r a k e ( f i g . 54) oras of t h e d o u b l e - d i s k t y p e and s e p a r a t e l y con- t r o l l e d . TLe b r a k i n g u n i t c o i l s i s t e d of two superimposed d i s k s a t t a c h e d t o e a c h n h c c l , t h e l a r g e r b e i n g r i q e t e d t o t h o w3eel N .A. C . A . Technical Memorandum 1 1 0 . 627 parallel wit11 tbe outer row of spokes. The braking disk is actuated by means of three cams mounted concentric with the axle, the brake being applied by depressing a pedal in the *cockpit conascted to the cams by cables runsing inside the axle.

The next brake (fig. 55), a9 independently controlled unit of the'intornal expanding hydraulic type was incorporated in a disk w : z e e l with built-in brake drum.

Ic both types the brake is enclosed in tho wlzeels witl~in tho fairing, Tho Palmer a11eel brake.- (~igs. 56 and 5 7 . )- The whoel has wire spokes and tLo latter carry a drum. A disk attached to tho axle carries a castellated channel to nk.,ich a conplete sing of small friction blocks are recessed. Below these blocks is an annular expansion chamber; when air is forced into this chamber, this expands and byings the blocks into frictional contact w i t h the revolving drum. The castellated channel prevents the blocks from revolving with the drum. This arrangement is novel and exceedingly simple.

On airplanes not equipped with a con-pression starter the air supply for working tho brako is obtained from a flexible air cylinder (rubber), roinf orced with Palmor cord, and although but a fraction of .the weight of the usual steel cylinder, it has an ample nargin of strength.

, Automatic release devices.- These may be grouped into three categories: 1) Those controlled by the reaction of the ground on the tail skid; 2) Those in which braking is regulated as a function of the angle of the vertical passing through the C . G . and the straight line which connects this center in the point of contact of the wheels with the ground; 3) Those controlled by the reaction of the ground on the landiag gear.

The second and third systems have,' moreover, the advantage of brakiug the airplane even when it travels on the ground in line of flight.

The Iiessier device belongs to tho first category, becanse it is operated by tho tail skid. It is applicable to a brakc..

operated By an hydraulic servo brake. The oil prossure is

X . A . c . A . T e c h n i c a l Memorandum :To. 6 2 7 '

s u b j e c t t o v a r i o u s f a c t o r s : a c t i o n of p i l o t , r e a c t i o n of ground, and t h e time element.

f".e r e g u l a t i n g d e v i c e , which quickly opposes a t o o s u d d ~ n d e c e l e r a t i o n and i n s u r e s i n s t a n t a n e o u s r e l e a s e of t h e b r a k e s as soon a s t h e t a i l s k i d no l o n g e r t o u c h e s t h e ground, c o n s i s t s of: A pump b a r r e l w11icIi sends o i l under p r e s s u r e i n t o a p i p e emptying f n t o two r e g u l a t o r s , one t o each m l ~ e e l ( f i g . 58).

T2e r e g u l a t o r which i s t h e organ of t h e brake c o n t r o l ( f i g .

59) c o n s i s t s of i v o pump b a r r e l s , o'ne f o r t h e iilcoming compressed o i l and t h e o t h e r f o r s e n d i n g t h c o i l under p r e s s u r e t o t h e b r a k e shoe. The l e v e r which o p e r a t e s t h e p l u n g e r of t h e l a t t e r purap Bar,rel and which i s l i k e w i s e connected w i t h t h e o t h e r , i s manip- u l a t e d 'oy t 2 e p i l o t . FI11eli t h e p i s t o n , due t o l a c k of o i l , i s c o m p l e t e l y extended (fig. 6 2 ) , i t cannot b r a k e evon i f t h e p i l o t s t e p s on t 3 e p e d a l bccause t h e l e v e r i s i n o p e r a t i v e . A d e v i c e i n s e r t e d i n t h e o i l i n l e t p i p e s of t h e brake and i n f r o n t of t h e r e g u l a t o r f o r c e s t h e a i l tlirough a s m a l l n e t e r i n g o r i f i c e w h i l e p e r m i t t i n g ' t h e o i l t o flow tZlroug3 a l a r g e opening i n t h e oppo- s i t e d i r e c t i o n .

The ~ k a i n a u t - ~ a 7 1 v o l i & r e system ( f i g . 60) belongs i n t h e second c a t e g o r y . I t r e l e a s o s t h o brake when t h e a i r p l a n e s t r i k e s any o b s t r u c t i o n , roug2 ground, o r any o t h e r o b j e c t wbich might s e t up f r o n t a l o r l a t e r a l rebound. S p r i n g m a c t s on l e v e r & mhick o p e r a t e s t h e can of t h e shoes and keeps t h e wheel braked undcr normal c o n d i t i o n s . Elen t k e p i l o t , f o r taking-off o r any otLor ma;lcizvcr, w a ~ t s t o r c l e a s e tlie Bra!ces Bo p u l l s c a b l e c

which t u r u s 03 A s o t h a t l e v e r S c o n t a c t s w i t h l u g , allich

c o n p r c s s e s s p r i n g and r e l c a s c s t h e bralccs. i s t h e a h e e l fiub .

Dnring ax o r d i n a r y naneuver of t h e a i r p l a n e on t h e ground, t h e w3eel b e i n g braked, t h e s p r i n g moves backward and s t o p s i n a n e q u i l i b r i u n p o s i t i o n so t h a t i f i s t h e b r a k i n g e f f o r t and C t k e l o a d o;i t h e wheel F =. C t a a a o r u i s t ? ~ e a n g l e formed by s t r a i g k t l i n e M_f w i t h t h e v e r t i c a l .

T5e r e l a t i v e p o s i t i o n of and i s iadependent of t h e i n c l i n a t i o l l o f t2ie a i r p l a n e , b u t t h e d i s t a n c e from B_ t o 2 i s n o t . Thus, whei t h e n h e e l moves e x c e s s i v e l y backward, whether due t o abnormal b r a k i n g e f f o r t i n s o f t ground o r any o t h e r c a a s o , o r vSen tLe f u s e l a g e s l o p e s beyond a s t a t e d l i n i t , 2 c o n t a c t s n i t 3 &, c o n p r c s s e s t h e s p r i n g and r c l o a s c s t h c brake shoes.

The s g s t c n i s t r u l y simple a n d o r i g i n a l .

X.A. C .A. T o c h s i c a l M~norandtu3 No. 627

Xydraulic-ggrvo b r a k e s . - - L ~ i g . G I . 2- A r i n w i t h f o u r cams

i s boused. on t 3 e 'sotton of t h e b r a k e drum. Tao s n a l l o i l pumps a r e c o n a e c t e d t o a r o l l e r a r e n i t k p i v c t s a t t h e ends and d r i v e n by c a n s . The o i l i s p u t u n d e r p r e s s u r e and f e d i n t o a s m a l l c y l i n d e r h a v i n g t ~ o p i s t o n s w2ish a c t d i r e c t l y on t h e b r a k e s h o e s .

Tlxe b r a k e a c t i o n I s c o n t r o l l e d bg a v a l v e from t h e p i l o t ' s s e a t .

Otker t y p e s of s e r v o b r a k e s n t i l i z e a hand l e v e r c o n n e c t e d t o t h e c y l i n d e r of an o i l p i s t o n . The o i l i s f o r c e d t h r o u g h p i p e s t o t h o bra?ce c y l i n d e r , t h e c y l i n d e r of which i s T a s t e n e d t o n s c t of s p e c i a l l e v e r s a n d t r a n s m i t s t h e p r e s s u r e o f t b e c.ocDressed cril t o t h e b r a k e slxoe.

- rr: R e v e r s r n g the l e v e r f o r c e s tke compressed o i l t h r o u g h t h e - o r i f i c e of a v a l v e i n t o a s n a l l tank. When t h e p r e s s u r e i s l o w e r e d i n t h e b r a k e c y l i n d e r a r e t u r n s p r i n g r e t u r n s t h e p i s t o n a n d t b u s r e l e a s e s t h e s h o e s . The m u l t i p l i e d f o r c e of t h i s s e r v o b r a k e i s c o n t i n g e n t a n t h e r a t i o of Brake c y l i n d e r d i a n e t e r t o c o a t r o l c y l i n d e r d i a a e t e r .

B r a k e - c o n t r o l , d e v i c e s . ( F i g . 62. )- Brake c o l i t r o l i s c a r r i e d o u t by t w o S u t t o n s on t h e 2 e d a l s o f t 3 c r - ~ d d o r b a r . Pashed down these-batto::s t i g k t e n t h e c a b l e o f t h e > r a k e cam. The t r a v e l depends on t h e a i r p l a n e w e i g h t , 3 r a k e d i a m e t e r a n d r e d x c t i o n g e a r r a t i o .

T o t a l weight S r a k e d i a m e t e r 500 P e d a l movement 110 140

------

1 n t e r n a l l ~ - s p r u n c - o r e l a s t i c i e e s A t t h e b e g i n n i n g o f --.------ t h i s s t u d ~ ~ c e 2ut I n e v i d e n c e t h e c h a r a c t e r i s t i c s and t h e ad- v a n t a g e s a t t e n a n l i t t o t h i s t y p e .

AdmitteS-ly t h e ? r e s e n t day methods a r e f a r from b e i n g p e r f e c t , b u t t h e s t u d i e s of t h i s problem a r e n o t v i t h o n t b e n e f i t a n d x o d e r n t e c h y w i l l a r r i v e a t a s a t i s f a c t o r y s o l a t i o n .

The B l e r i ~ t e l a s t i c hub n h e e l .. 63.1- The w h e e l p r o p e r

------,,,--,,,,,,,, ,,--L.-LEA&L t u r n s gn a drTm a:iich p l a y s t h e r.::10 of t h e a x l e . The l a n d i n g g e a r a x l e i s c o n n e c t e d t o t h i s d r u n 7 2 7 e l a s t i c r i n g s . I t h a s o n l y r o t a t i n g p a r t s , no s l i d i n g novenent.

The Bvimeta v7ieel.- F i g u r e 54 s h o n s t2le f r a n e a t t h e bottom -p----~L- of t h e drum v h i c b , as i n tlie B l e r i o t n % e o l , i s s t a t i o n a r y n i t h r e s p e c t t o t h e wheel. Rubber c o r d s f r o n t h i s f r a m e e x t e n d t o a s c c o n d frane On v h i c h t h e a x l e nay b e s u p p o r t e d .

65 66 and 67.1- I@, t 3 i s d i s k n h e o l

~ ) . o ~ - ~ ; ~ ~ ~ L - - L Z L ~ ~ ~ -.----_-

t h e s l c c s a b s c r S i n g p a r t s e n b r a c e t n o s s t s of s o l i d r u b b e r d i s k s n i t h f l n i d & a s h p o t i n t h e c e n t e r . T 3 e r e a r e t h r e e d i s t i n c t m o t i o n s : 1 ) The u n i t s n h i c L turr: abo-at t h e hubs -and move v e r t i c a l l y r e l a t i v e t o t h e landi:;g g e a r , - t i r e , r i m , s i d e d i s k and b r a k e drum; 2 ) Tlie p a r t s n h i c h rnove up a:?& donil,- t3.e s i d e f l a n g e s of ;1-a7z, t h e b r a k e s h o e s , t h e compression r u b b e r colanns, l o n e r S e a n s a n d d a s k p o t p i s t o n ; 3) "he u n i t s r i g i d l y a t t a c h e d t o t h e a i r p l a n e , - d a s k p o t c y l i n d e r , t o p beam, c e n t r a l g u i d e member a n d liub f i t t t n g .

The d a s h p o t i s enclosefi ia a secoxd c y l i n d e r b u i l t i n t e g r a l n i t h i t . Vhcn, u a d e r t h e a c t i o n of a s h o c k , t k e c y l i n d e r of t h e sLoclr absor1;cr c o n e s t o t;ie e:~d of thc? donu s t r o l r e , t h e o u t e r c r l i a d - e r , 57 e c t i n g 021 a p l a t e , a c t o r n i n e s t > e comy.ressio% of t h e t a o r u 5 5 c r c o l u n a s . T h e i x f l a t i o n v a l v e of t h e o f c o p n e m a t i c s h a c k a b s o r b e r i s of t h e n e e d l e t y p e s o t h e a b s o r p t i o n of t h e shock can b e r e g u l a t e d . T h i s ivheel nay b e b r a k e d once i t s i n v e n t o r h a s o v e r c o n e t h e f o l l o v i n g d i f f i c u l t y : any i n t e r n a l l y i n s t a l l e d b r a k i n g system i s c o n t i n u a l l y r a i s e d a n d lomered w i t h r e s p e c t t o t h e s t r u c t u r e . I t i s i n p o s s i b l e t o s e e how t h i s a r r a n g e n e n t c a n a b s o r b t h e h o r i z o n t a l c o q ~ o n e n t of t h e shock a n d t h e i d c z c e r t a i n l p does n o t s t a n d f o r t h a.s a n exi30nent of e x c a s s i v e s i ~ p l i c i t y ,

Thee1 s i t h i n s i d e t u b e -

b~aIcablfl.~-Lf&g. 6 8 ------- a c c o r d i n g -- t o

qy invt:ution.- A t u b e i s p l a c e d noar t h o hub b e t n e c n t w o r i n s , one i n t e g r a l w i t h the hub and t h e o t h e r n i t h t h o v h c e l p r o p e r .

T h i s vlleel i s e s s e n t i a l l y l i k e t h e ' o r d i n a r y n h e e l e x c e p t f o r i t s l a r g e r hub d i a n c t e r . The r e s i s t a n c e t o a x i a l s t r e s s e s i s i n s u r e d by t n o s i & e d i s k s , ~ h i c h a r e n o u n t e d l o o s e on t h e a x l e , c o v c r t h e a h o l c n h c e l and b r i n g t h e l e n g t h of t h e t n o round r i a s i n c o a t a c t v i t h i t . Thore i s sonc c l e a r a n c e b e t n c c n t h e n ~ l e e l ". .

, 5 .

N . A . C . A . T e c h n i c a l ~danorandun No. 627 and t h e d i s k s t o e n a b l e t h e wheel t o s l i d e when, under t h e ef- f e c t o f a shock, i t i s pushed a g a i h s t t h e a x l e .

T o r b r a k i n g t h e v h e e l one of t h e d-isks i s bloclced and ap- p l i e d t o t h e n h e e l which i n t h i s manner i s g r i p p e d between t h e two r i n s l i n e d n i t h Ferodo. This movement i s produced by a m u l t i p l e f r i c t i o n d i s k asserably. ( p i g . 69.) The o u t e r p a r t s o r f e n a l e d i s k s nesh i n t h e grooves of a d r u n i n t e g r a l n i t h t h e d i s k ; t h e y t u r n a i t h it. The i n s i d e o r n a l e d i s k s r e c e s s i n t o t h e grooves of t h e ' a x l e and d o n o t r o t a t e . ~ h ' i s p a r t h a s a s n a l l e r i n s i d e d i a n e t e r s o as t o s u p p o r t t h o d i s k ; i t a l s o c a r r i e s a szall ?.run on which t h e d i s k r e s t s and t u r n s .

A t t h e uonent of b r a k i n g a d i s k - l o c k i n g s l e e v e n o r n a l l y k e p t i x p l a c e by a s p r i n g ( n o t sbonn i n t h e f i g u r e ) noves t o v a r d t h e d i s k a s s e n b l y and a c t u a t e s by t h e f i r s t novenent t h e b l o c 4 of t h e b r a k e d i s k s , and by a second t h e a x i a l n o t i o n of t h e l a t t e r c a l e f r i c t i o n d i s k , and through i t tho brake d i s k .

Thus t h e wheel i s braked.

T h e s a l i e n t f e a t u r e s of t h i s wheel a r e : i a s i d e t u b e , s h o n l d e r d i s k s and brake. I t s advantages a r e n o t a b l e s i n p l i c - i t y , and in consequence l i g h t eight w i t h r e s p e c t t o wheels n i t h i n t e r n a l s p r i n g s ; t h e a c t u a l a b s o r p t i o n of shocks, t h e s i d e d i s k s and t h e wheel f l a n g e s f u n c t i o n l i k e t h e H a r t f o r d f r i c t i o n shoclz a b s o r b e r .

-%'igure 68 r e p r e s e n t s t h i s v h e e l d e f l e c t e d under a x i a l l o a d ; F i g u r e 70, t h e wheel w i t h o u t t h e u s u a l o u t s i d e t i r e .

T r a n s l a t i o n by J. Vanier, R a t i o n a l Advisory Comr~ittee f o r A e r o n a u t i c s .

N.A.C.A. Technical Memorandum No. 627 Bibliography Buch, M. and Schmidt, R.: Reifen, Felgen und ~ k d e r .

liknchen. ) Doubrovin, A. A.: Application des freins aux avions. ( ~ u p p l 6 - ment a u journal Les Ailes, No. 401, Feb. 21, 1929.)

Dowty, George H.: Internally-Sprung Wheels for Aircraft. h he

Aeroplane, Vol. XXXVI, I T o . 9, Feb. 27, 1929.)

Ferrari, Luigi G.: Nota sugli organi di atterraggio degli aeronobili. (Notiziario Tecnico d'aeronautica, No, 5, March, 1929.)

Guglielmetti, A. and Ferrari, L. G,: Condizioni di lavoro delle ruote unificate per aeroplano, endic icon ti Tecnici, Vol.

XV, 370. 4.)

Guillemin, J.: Prdcis de construction, calcul et essais des avions et hydravions. (Gauthier-Villars et Co., Paris, 1929.)

Offermann, Riesenflugzeuge.

~ u f f r i n - ~ d b e r t , M.: Etudes nouvelles sur les trains dfatterrissage.

( ~ e v u e ~ 6 n g r a l e de llAeronai~tique, Ho, 9. ) Review: L'Ala d'Italia, April, 1929.

S.A.E. Journal, U.S.A., l~farcl~, 1929.

N.A. C .A. Technical Mernor~.adum No.. 6.27 Fig. 1 Fig. 2 Fig. 4 Fig. 5 Fig. 8 N.A.C.A. Technical Memorz,ndum No.627 Figs. 10,14,15 Fig. 10 I Fig. 15 Fig. 14 W.A.C.A. Technical llemorandum 30.627 Fig. 19 Fig, 20 Fig .22 Fig .25 N . A . C . A . Technical Memorandum lJ0.627 Figs .31,32,33

N . A . c .A. Technical Mezlorandm No. 627

', , Fig .32

c , !

Fig .33 - Figs .35,38,42,43,46,51,54 N,A,C.A. Technical Memorandum 10.627 Fig 43 Fig. 40 Fig. 4 1 N . A . C.A. Technical 3emorsndum 1Jo. 627 Fig. 44 Fig. 45 Fig. 48 Fig. 47 N.A. C.A.

Fig. 49 Fig. 50 - I . A . C . A . Technical Memorandum No.627 N.A.C.A. Technical ::emorandm No.627 Figs. 55,57 Fig .57 Fiaa .60,61,62 N.A.C.A. Technical Memorandum No.627 Big. 61 rig. 62 Pig. 64 Fig. 66 Fig 65 Fig. 67

w

Fig. 68 Fig, 70