A

N A T I ONAL ADVISORY COUMI TTTEE FOR AERONAUT1 CS - I ,

TECHNI CAL XEKORANDUti NO. 631

By P i e r r e LQgl i se

In a v i a t i o n t h e supercharger h a s h i t h e r t o been con- s ide red as an "accessory" of Che gaso l ine engine , de- signed t o mainta in t h e p r e s s u r e at h i g h a l t i t u d e s . As long 2,s t h i s view p r e v a i l s , however, i t w i l l not cons t i - t u t e ' so i n p o r t a n t an element of p r o g r e s s a s i t i s capable of doing. 'P1ze sugercharger should be cons idered , at l e a s t f o r s ingle-engine a i r p l a n e s and f o r cu r r en t a l t i t u d e s of 5000 t o 6000 m (16404-19685 f t ,) a s an e s s e n t i a l p a r t of t he enz ine and not a s a rernova,ble accessory.

I t seems ha rd ly necessary t o u se a supercharger near s ea l e v e l sirnply t o mix the gases . The importance of t h e supercharger w i l l i nc ' rease , however, wi th t h e u s e of heavy f u e l s , Before long me s h a l l probably be u s ing two- s t roke -cyc l e and four - s t roke-cyc le scavenging engines on a i r p l a n e s . I n accord w i t h t he p r e s e c t tendency, we s h a l l he re p r e s e n t t he French s o l u t i o n s of t h e problem i n a p r a c t i c a l r a t h e r t han i n a p u r e l y t h e o r e t i c a l manner,

I . Turbo-Superchargers

Seve ra l yea r s ago the Rateax Company made t h r e e turbo-supcrchargcrs f o r engines of 175 hp, 300 hp, and 450 hp, r c s p e c t i t e l y . The manufacture of t h e f i r s t one has bcen d i scont inxed f o r t h e p r e s e n t . The second one has a maximum speed of 32,000 r.p.m., which r e s t o r e s t h e atmospheric p ros su re at 5500 m (18045 f t .) , t h e r a t i o ' of t h e d e n s i t i e s being 2 : l . I n t h i s cese t ho t a n g e n t i a l v e l o c i t y of tho r o t o r i s about 400 n / s (1312 f t . / s e c . ) . The 450 hp supercharger , being l a r g e r , r o t a t e s l e s s rap- i d l y (about 24,000 r.p,m.).

Thc s h a f t i s f l e x i b l e and r e s t s on two b a l l bear- i ngs . The t u r b i n e h a s 92 vanes ( f i g . 1 ) and t h e f a n h a s 10 r a d i a l vanes. A t p r e s e n t t h e t u r b i n e vanes a r e s e t i n

---.--- -- * ~ r o m ' ~ ' ~ d r o n a u t i ~ u e , LIarch, 1931, pp. 101-109, and A p r i l , 1931, pp. 141-149.

t h e Gisk by means of tenons; I n f u t u r e they w i l l be dove ta i led . The end of the s h a f t n e a r e s t t h e f a n i s sup- p o r t e d by a two-piece t h r u s t b e a r i n g , which absorbs t h e l a t e r a l r e a c t i o n s . The o the r end i s supported By a p l a i n bea r ing and c a r r i e s a w o r m gear f o r t h e tachometer d r i v e ( r educ t ion r a t i o 20 : l ) .

The t u r b i n e and f a n a r e bo th n a b of chrome-nickel s t e e l , t r e a t e a t o o b t a i n g r e a t r e s i l i e n c e . The s h a f t h a s a n i c k e l con ten t of 8$. The t u r b i n e vanes a r e made o f t o o l s t c c l . Thc bushings a r e l o a d bronze or regul-as 88:12, The d i r e c t i v e vanes a r e chrome-tungsten s t e e l .

There a r e e i t h e r two or t h r e e i n l e t s f o r t h e exhaust gases , according t o whether t he engine i s a V or W. The exhax~st gases e n t e r t h e t u r b i n e through t u y e r e s , which p l a y an extremely importent r o l e (problem of i n j e c - t i o n ) . The gases t hen expand a g a i n s t t h c vanes and a r e evacuatsd through one o r two o r i f i c c c according t o the engine type . The r o t o r , which m u s t bc perf c c t l y ba laaced , i s des igned t o f u n c t i o n above t h e f i r s t c r i t i c a l s ~ e c d , i n tho neighborhood of S O 0 0 r.p,ni,

The opers t i n g c o n d i t i o n s of turbo- superchargers a r c sevcrc , 'some of t h e i r p a r t s having t o work a t n ' tompera- t u r e . o f about 75!1°c, while o the r p z r t s a r e sub jec t ed t o t h e temperature of fhc surrouniling n i r , Under such con- d i t i o n s t h e t reztment of s t e e l s i s d i f f i c u l t and the problem of t h e turbo-supercharger becomes a m e t a l l u r g i c a l problem, A t p r e s e n t t h e l i f e of such a mechanism i s s h o r t e r t hcn t h a t of t h e engine.

The f a n i s l i g h t and compact, I t can bc r o t a t o d very r a p i d l y . I n 1 9 1 7 , Mr. Rstocu, whilc i n v e s t i g a t i n g t h e r u p t u r e l i n i t of r a p i d l y r o t a t i n g p a r t s , a t t a i n e d s spccd of 52,000 r.p,m. w i t h a turbo-supercharger f o r t h e 175 'ny: eagixe, I t s r o t a t i o n p rope r absorbs ve ry l i t t l e energ?, s i n c e tho za in t cnance of t h e r o t a r y n o t i o n docs no t , l i k e r e c i p r o c a t i n g motions, ~ c r i o d i c a l l y des t roy t h e momentum of t h e moving masses. . ,

I t i s wel l t o no t e , however, t h a t the f a n i s i n con- s t a n t communication x i t h t h e compressed-air r e c e i v e r and t o r e f e r , i n t h f s connec t ion , t o a recent , r e p o r t of t he

X.A..C,A. . Technical ,l,femor andun. ITo. 631. 3

X,ational Advisory Committee T o r Aeronautics* ( r e l a t i v e t o a Boots t y p e supercharger and not t o a f a n , though t h e conc lus ions a r e perhaps t r a n s f e r a b l e ) . This r o p o r t e s t i - mates at 26% t h e sav ing i n pomer ( f i g . 2) at 20,000 f e e t from ti19 u s e of' v e l v c s nh ich do no t open u n t i l t h e i n t a k e air h a s been compressed t o the d e s i r e d p r e s s u r e .

head of t h e cy l inde r at t h e l e f t i n F igure 2 i s provided w i t h a c a l i b r a t e d va lve . The p i s t o n f i r s t com- p r e s s e s t h e a i r t o t h e d e s i r e d p r e s s u r e ( c u r v i l i n e a r p a r t of diagram: PI, or PV = c ~ n s t a n t ) . The c y l i n d e r zt t h e r i g h t h a s no c z l i b r a t e d valve. The p i s t o n hoad i s con- t i n u o u s l y sub jec ted t o the p r e s s u r e p r e v a i l i n g i n t h e r c - ce iver . Eence i t works a g a i n s t a cons tan t p r e s s u r e dur- i n g i t s whole s t roke . The s-itpplcmentary ex2end i t a r e of energy i s re?rbsonted by t h e ha tched a rea , I t i s quos- t i oned whether such v a l v e s which, i n tho terms of the sa-20 r o p o r t , add tho complicat ion of xoving p a r t s t o sim- p l e mechanisms, can be advantageously rno~~.nte& i n the v i c i n i t y of t he fan.

Tho t u r b i n e produces a brak ing e f f e c t on t h e ex- haus t . Vhen t h e evacua t ion of t 3 e exLaust gases i n t o r a r e f i e d a taosphere i n c r e a s e s t h e engine ou t2u t t o t he p o i n t t h a t tLe ga in i n power ( f i g . 3) cons ide rab ly ex- ceeds (accord ing t o c e r t a i n w r i t e r s ) t he l o s s duo t o t h e ope ra t ion of t he supercharger , t h e i n t e r p o s i t i o n of a t u r b i n e c r e a t e s a coun te rp re s su re on the p i s t o n s . Vith- out dcnging t h i s coun tc rp re s su rc , t h e Bateau Company c la ims t h ~ t i t i s mani fes ted n a i n l y nenr s e a l e v e l , w%cra t h e t u r S i n e exhaust , c r e a t i n g a p r e s s u r e nonr t h e atmos- p h r i c p r e s s u r e , p r e v e n t s tho expansion of t h e gases from having i t s maximum o f f c c t .

Gains g r e a t e r than those i n d i c a t e d by t h e t heo rc t - i c a l curvc i u F igure 3 have been ob ta ined i n p r a c t i c e . 'Posts were mado i n 1928 at Chalais-lieudon on a Fczrman' automobile engine rrh'ich y ie ldod 80 hp at 2400 repem. The e x h m s t .of t h i s engine n s s connected n i t h a box i n rshich a c e n t r i f u g a l n s ~ i r a t o r p r o d ~ c e d c negz t ivo pres- su re of about 300 mm (11.81 i n , ) of mercury, The engine, ;?hi& then func t ioned under c o n d i t i o n s of exhaust corre-

*Technical Report No, 303 (1928): "An I n v e s t i g a t i o n of t h e Use of Dischz-rge Valves end en In take Control f o r I m - p rov ing t h e Perfornance of N.A.C.A? Roots Type S-&per- chnrger , l t by Osczr V, Schey tmd Eraest E. B i l son ,

spondfngLto : an & t i t u d e of ' about 5500 m (about 18000 f t . ) , developed LOO hp, a g a i n of 25$ i n s t e a d of 95 a s ind i - ca t ed by t h e curve i n . F i g n r e 3. Under t hese cond i t i ons i t mas found by ex tkapo la t ion t h a t a 500 hp engine, a t whose f n t a k e 9 p r e s s u r e of 1 kg/cm2 (14.22 l 'b, /sq. in,) i s m a i ~ t a i n e a , would develop 625 hp at 5500 m. If t h e 80 hp r e q u i r e d f o r running t h e supercharger mere deducted, tho a v a i l a b l e power would be 545 hp, o r z n e t g a i n of 45 hp.

hwo reasons a r e given by lir. Baseige i n explana t ion of t h i s gz,in: I) The 'gases expand quicker and' a r e cooled more; t h e i r tkm-jjerature d-ro$ nay amount t o 2 5 0 ' ~ (450~F . ) . The danger of s e l f - i g n i t i o n i s t h e r e f o r e reduced and t h e charge can be increased . 2) The exhaust gases r e h a i n i n g i n t h e c y l i n d e r have a lower p r e s s u r e than t h e f r e s h g a s ; mhen r e t u r n e d t o t he same p r e s s u r e a s t he l a t t e r , they t h e r e f o r e occupy i e s s space and l e a v e more space f o r t h e f r e s h gas.

l.I.:r, Ea teau observes t h a t t h e r e a r e t w o phases of t h e exhaust s t r o k e t o be considered.* F i r s t , t h e very sho r t phase nh ich fo l lows i m e d i a t e l y a f t e r t h e opening of t h e v a l v e , whi le t h e p i s t o n , being nea r i t s bottom dead, cen- t e r , ha s a very l o w speed, As soon 9,s t he v a l s e opens, tho gases , boing under a p r e s s u r e of 2 t o 3 kg/cm2, (28.45 t o 42.67 lb . / sq . i n . ) , escape at a v o l o c i t y of sev- e r a l hundred metors p e r second, This p r e s s u r e drops al- most i n s ~ a n t a n e o u s l y . I t i s t he flpuff.fl The r e s i s t a n c e o f f e r e d by t h e t u r b i n e dur ing t h e s e sho r t i n t e r v a l s p re - s e n t s ho disadvantage* The gases a r e supported by t he p i s t o n head, ct t h i s moment a l m o s t s t a t i o n a r y , and per- f o r m a 3 d i t i o n a l work.** Then, i n t h e second phase , tho

--. - *This i n t e r e s t i n g i d e a mas exp la ined by Ur, Anxionnaz, t h e d i s t i n g u f s h e d c o l l a b o r a t o r of 1.Ir. Rateau, i n a l ec - ' t u r e b e f o r e t h e " ~ o e i e ' t e ' F ranca i s e de Xavigat i o n ~ G r i e n n e . **This i s , from ano the r viewpoint , an analogous concep- t i o n p r e s e n t e d by tire Rowledge on t h e u t i l i z a t i o n of t h e gas expans ion . in t he tvo-s t roke cyc le . During t h e f i r s t s t r o k e , t h e gases nork i n a h igh-pressare c y l i n d e r and, dur ing t h e secocd s t r o k e , i n a lov-pressure c y l i n d e r . Hsre, t ho u t i l i z a t i o n at low p r e s s u r e i s r e p r e s e n t e d by the t u r b i n e , and t h e h igh p r e s s u r e i s only a mean p re s - su-re, s i n c e g a s o l i n e does hot a l low compr@ssions above 6 , nor maximum p r e s s u r e s above 30,

1T.A. C .A. Technical liemorandum IXo. 631 5

p i s t o n d r i v e s t h e gases i n t o t h e t u r b i n e , o p e r a t i n g a s o r t of pneumatic power t r ansmis s ion wifh a l l t h e corre- sponding lo s se s . The t u r b i n e e v i d e n t l y r ecove r s only a p a r t of t h e p i s t o n energy.

I t i s t h e r e f o r e obvious t h a t t h e a d d i t i o n o f a turbo-supercharger t o a given engine , as an a c ~ 6 s s d r y , f a l l s f a r s h o r t of r e a l i z i n g t h e h ighes t p o s s i b l e e f f i - ciency. The c y l i n d e r s of a modern engine, des igned f o r t h e u se of a supercharger d r iven by a gas t u r b i n e , should t h e r e f o r e , according t o M r . Rateau, have t h r e e o r i f i c e s , naiaely, i n t a k e , exhaust-puff i n t o t h e t u r b i n e and exhaust i n t o t h e open a i r , The t u r b i n e would then f u n c t i o n i n p e r i o d i c p u l s a t i o n s and mould produce a v a r i a b l e p re s su ro , Due t o tLo estx:emcly sho r t d u r a t i o n of the p u f f , a va,lve- l e s s system mould seem dos i r ab l e . Such engines do not yot e x i s t , tho supcrchargors now used being m6chanically con t ro l lod .

11. Rateau Supercharger w i t h Farman Mechanical Control ( ~ i g u r c s 4-6, 11-13)

This suporcharger , mhosc f i r s t mhdel weighed 50 kg (110.2 1 3 , ) , r e s t o r e s t ho a tmospher ic p re s su ro at GOO0 m (about 20,000 f t , ) . Since the mechanical c o n t r o l has t o t r ansmi t 80 hp f r o m t h e engine, which has a speed of 2150 r.p.n,, t o t he supercharger , which t u r n s a t about 20,000 r.p.m., no c l u t c h of the o rd ina ry automobile type ' can be used. I t i s necessary , however, t o throw i n t o and out o f > g e a r without reduc ing t h e engine speed.

A "free-wheelt t system enab le s t h e f a n t o r un a t t h e speed of t h e engine, oven when t h e c o n t r o l gear i s re- l eased . Tkc drawings ( f i g s . 5 , 5 a t o 5j), which show t h e p a r t s i n t h e i r order of assembly, mere made be fo re t h e " f r e e wheeln ha,d been added, The l a t t e r i s i n d i c a t e d , hornever, i n Tigure 5 and shown i n F igure 6.

The step-up g e a r ( f i g s . 5b and 5 c ) , c o n s i s t s essen- t i a l l y of a p l a t e n i t h t h r e e p i n s on w'ni.ch a r e mouilted t h r e e s a t e l l i t e gea r s , These mesh, on the one hand, n i t h a f i x e d r i n g gear ( f i g , 5a) and, on the o the r hand, w i t h a c e n t r a l 2 i n i o n ( f i g . 5b) keyed d i r e c t l y t o t h e f a n shaf t . Thore Ps t h u s ob ta ined , i n a small space, a speed i n c r e a s e of 9:1 f o r t h e Farman 1 2 W.E. engine. The p i n s c a r r g i n g the s a t e l l i t e s a r e s e t 120' a p a r t and a r e h e l d by a p e r f o r a t e d t r f s i ~ g u l a r p i e c e ( f i g . 5b). Their combined a c t i o a , whi le f u n c t i o n i n g , produce a s i n g l e mo-

6 E'.A.. ~ b . 8 . Technical Hemorar-durn Bo. 631 - . . _

meat d i s t r i b u t e d ovor a l a r g o number o f t e o t h , a condi- t i o n f a v o r a b l e t o t h o mcar of t h e l a t t e r . Tne l u b r i c a - t i o o of t h o s a t e l l i t e bear ings i s e f f e c t a d 3y d e f l e c t o r s which form groovos f o r tho o i l ~ r o j o c t e d o u t s i d e tho bushings, Tho tcct 'h a r c l u b r i c a t e d by p r o j e c t i o n and by a s p e c i a l devico f o r tho d e l i v e r y o f o i l d i r e c t f r o n t h o cngino. Tho s z t c l l i t e s ara a l s o providcd w i t h groovos f o r rccoi-r ing t h e p r o j e c t e d o i l and wi th p e r f o r a t i o n s i n t h e i r r i n g s through which t h e o i l passes t o t h o t e e t h ,

The automatic c l u t c h c o n s i s t s e s s e n t i a l l y of a mova- b l e d i s k ( f ig , 5d) on a s p e c i a l Sea r ing indepenaent of t h e engine, This d i s k , c o n t i n u a l l y &r iven by t h e engine,

' by means of a s h a f t w i th a u n i v e r s a l j o i n t , t n r n s setmeen t ~ o f r i c t i o n p l a t e s c a r r i e d by t h e p a r t s b, c , an2 e, These g l a t e s Exe p r e s s e d toge the r sr'aon t h e c l u t c h c o n t r o l i s operatod, The nova32e r i n g gear ( f i g , 5c) i s cen torod i n t ho >ar t b ( f i g , 51, t b c t o o t h f o r n i n g [;uido groovos f o r t ho l o n g i t u d t n a l movemcnts.

The c l u t c h i s opera ted 537 means o l a v e r t i c a x l e d o r v i a i b l e i n t he goar ca se j, To t k l s lever t h e r e a r e keyed two a r k s ( f i g , 5i3 which engage i n t h e c a v i t i e s of t'le t h r u s t %lock ' h, The ope ra t ion of tkrowing i n t o gear advances block h toward t h e engine aad r e l e a s e s tiie t i p s of t h e mcight s ( f i g . . 5g ) , which a r e n o s n z l l y he ld at r e s t by block ' h. . * .

The n o i g h t s a ro rnountca on p a r t f in' such nanner that %hair- ccnt r i f i aga l f o r c e , when t h e p l a t e ' r evo lves , t ends t o m a k e them t i l t o r rock about t h e i r p i v o t s , Un- de r t h e s e c o n d i t i o r s t h e case-hardened lug ileer t h o p i v o t of each weight i s 'crought i n t o c o n t a c t wi th t h e rfm.of t h e movable r i n g gear (fig, ,5%) which c o n t r o l s t h e c l u t c 2 , %y gradual a c t i o n on d i s k d, vhich i s d r i v e n 5y the engine.

I n o rde r t o s t a r t p l a t e f , each weight i s a c t u a t e d by a f l a t spr ing , e x soon as t h e block h r ~ l e a s o s t h e t i p of t h e weight. A c e r t a i n p r e s s a r e i s t h a r e f o r e t r a n s m i t f e d 3g t h e s e q s i n g s t o t h o r&ov~tblc r i n g gear o, whicll e f f e c t s t h e i n i t i a l t i g h t e g i n g of disk d and con- sequent ly t k e s t a r t i n g or" . the mhote neclzanism, c o n s i s t i n g of t h e s l a t e suppor t ing $he n e i g h t s , t h e r e v o l v i n g r i n g , t h e s a t e l l i t e - s u 5 9 o r t f n g p l a t e and the fan.

As. t h e speed of t h e weight-support ing p l a t e in- c r e a s e s , t h e c e n t ~ f f u g a 2 f o r c e af so increases and t i g h t -

N.A.C.A. Technicax Momorandum No. 631 . ,

ens tho gear disk . The r e l a t i v e s l i p p i n g of t h i s d i s k w i t h r e s p e c t t o i t s mount g r a d u a l l y d imin ishes , and t h e automat ic engagement tprminate s when the wei ght-support- i n g p l a t e and the r i n g gear acqui*o the same speed as t h e d i sk . This ope ra t ion r e q u i r e s only 8 t o 1 0 seconds. I n t h e p r o c e s s o f throwing out of g e a r , t he arms i el imi- n a t e t h e c e n t r i f u g a l e f f e c t of t h o weights on t h e sup- p o r t i n g p l a t e of t ho c l u t c h , and tho weight-support ing p l a t e g rndua l ly l o s e s speed x n t i l i t s tops a l t ogo the r .

The c e n t r i f u g a l c l u t c h enbodies sound p r i n c i p l e s un- de r an apparent mechanical complication. I t i s f l e x i b l e and very gradua l , because the p r e s s u r e on t h e movable r i n g gear i s s l i g h t a t f i r s t and does not r each i t s maxi- m u m va lue so snddenly a s t he o rd ina ry sp r ing mecillinism, The d r i v i n g ,moment v a r i e s p r o p o r t i o n a l l y t o t h e square of t h e momentary speed of t ho wet ght-support ing p l s t c . Since t h e r g s i s t i n g moment of t h e supercharger f o l l o r s p r a c t i c a l l y t he same l a w , t h e c a p a c i t y of tho c l u t c h t o absorb t h e v i b r a t i o n s and the v a r i a t i o n s i n t k e moment t r a n s m i t t e d by the c r anksha f t and by d i s k d remains p r a c t i c a l l y cons tan t at a l l speeds. This i s ar. e s s e n t i a l c h a r a c t e r i s t i c .

I n p a r t i c u l a r , f o r low engine speeds a t which the moment t r a n s m i t t e d by t h e . c r anksha f t i s g e n e r a l l y very i r r e g u l a r , t he c l u t c h i s s t i l l capable of s l i pp ing . The t o r s i o n a l v i b r a t i o n s o r o s c i l l a t i o n s a r e not there - f o r e t r a n s m i t t e d t o t h e s t e p u p g e a r s , a s would 3e t he case i f t h o p r e s s u r e on tho c l u t c h p l a t c were cons tan t aid maintained i t s maxinum vz lue at a l l sgceds.

The s t r e s s e s on tho weights off s e t one another and do not d.ovelop any r a d i a l coaponent on t h e bear ings , Ncithor a r c t h e r e any a x i a l r e a c t i o n s dur ing tho automat- i c o p e r a t i o n of t he c lu t ch . The woigllts a c t s e p a r a t e l y , wi thout stressing t h e c l u t c h o r i t s opore t ing l e v e r wiiilc i r gear. Ebc f o r c c r e q u i r e d t o ovcrcamc t h c c e n t r i f u g a l f o r c e whi le thr,oming oint of gear ceases as soon a s t h i s h a s been axcompli shed,

The body of t he supercharger c o n s i s t s of t w o p a r t s made of lfalpaxfl (an aluminum a l l o y ) . A i r i s admi-lted t o t h e cent0.r of t h e supercharger through an o r i f i c e i n t h e f i r s t p a r t , called. t h e i n t a k e sgir?"Lc Ilf ' tcr be ing con- p re s sed by t h e f i r s t r a d i a l wheel, i t i s f o r c e d i n t o a second s p i r a l , , where i t i s aga in c o m p ~ ~ e ~ s e d 3y another nhee l be fo re reacLing the i n t a k e p ipes , Packings a r e

8 N.A. G..A. Technical 14emorandurn N O * 631 . .

p laced a t bo th ends of the sp i r a , l s t o i n s u r e t h e i r t i g h t - ness , The , r o t a t i n g s h a f t r e s t s ct both 'ends on bushed bear ings , The vases, of very r e s i l i e n t chrone-nickel s t e e l , a r e dove ta i l ed i n t o the ,whee l . Being s t r i c t l y r a d i a l , t hey ;d.eld no component p a r a l l e l t o t h e a x i s of r o t a t i o n .

I n t h e f i r s t superchargers inade, tho f a n was sta- t i o n a r y when t h e mechanical c 6 n t r o l w a s r e l e a s e d , Con- c u r r e n t l y w i th t h e i n s t a l l a t i o n of exces s ive ly long t u y e r e s on c e r t a i n engines , t h e r e was in t roduced i n t o t h e i n t a k e 2" brak ing e f f e c t , which caused a l o s s of 5 t o 8% i n power, Since i t was important t o avoid t h i s l o s s and t o produce a thorough mixing, even at a l o w a l t i t u d o , tho Farman Company in t roduced a [If rcc-n'ncol" coupl ing 'device, vh i ch i s slzown i n d e t a i l i n F igure 6. Tho i m - proved, ,~a rbu rcz t ion from tho mixing o f f s o t s t h o power r e - qu i r ed t o operr . tc t h o f an ,

The pa.wls o f t h e " f r e e nhee'lit ( f i g , 6) a r e provided wi th s m a l l weights, Then tho c l u t c h i s thronn out of g e a r , t h e pawls are engaged and consequent ly d r i v e the supercharger s h a f t , %!he t i p s of t h e weights S ( f i g , 5) being ax-rested by b lock h , t ha coupl ing cannot t ake p l a c e and t h o r o t a t i o n a l speod i s t h e s m o as t h a t of t h o cngins , When thronn i n t o g e a r , tho movablc p a r t s gradu- a l l y Bass f r o n tho low t o t h e h i g h speed. Each pawl i s then disengaged from i t s notch and f r e e d from a l l f r i c - t i o n , r h e a the c e n t r i f u g a l f o r c e h a s acqui red a c e r t a i n va lue , The wear i s t h u s g r e a t l y reduced.

When thrown out of gea r , t h e speed of t h e f a n dimin- i s h e s g radua l ly . The pawls engage i n t h e i r no tches under t he a c t i o n of t h e i r r e c a l l s p r i n g s , then "free-wheel" t i l l the speed of t h e f a n s h a f t f a l l s s l i g h t l y below t h a t of t he onginc, The pawls then engago and tho r o t o r i s d r iven a t t h e speed of t he enkine.

The Rateau-Farman supercharger ( f i g , 4) i s now a well-developed u n i t , I t s c h a r a c t e r i s t i c s a r e def ined by F igu res 7 , 8 and 9. Ta'bles I and I1 and F igu re 1 0 g ive the r e s u l t s of t he t e s t s made on t h e Breguet 2 9 B.2 a i r - p l ane by Cousin and Burt in . A f t e r t he f i r s t t e s t s , i m - provements werg made i n t h e n schan ica l c o n t r o l . Tho d r i v i n g d i s k nov r o t a t e s sore r a p i d l y than t h o crank- shaf t (7000 r .p,in,), nh ich has enabled a r e d u c t i o n i n t ho ~ e i g k t and s i z e of t ho c e r t r i f u g a l c lu tch . On t h e o the r

-* a .A. 3 .A. Technical Xorcornndum Ro. 631

h a d , t h e s u ~ e r c h a r ~ c r now bas on ly a s i n g l e stago. We w i l l g i ve a fern d e t z i l s l a t e r r e g a r d i n g t h i s p o i n t .

F i g u r e 7 shows t h e sir ou tpu t of a Rzteau-Farman sxpcrcharger i n g r m s p e r secoad i n terms of t ho a l t i - t udes p l o t t e d as o r d i n a t e s f o r f a n speeds of 10,000 t o 2C,000 r,p.ri, The dash-dot I l n e s a r e curves of equal e f - f i c i e n c y .

F i g u r e 8 shows t h e c h a r a c t e r i s t i c curves 6 a.~d 6P of t h e Rate2,u-Farman supercharger . 6,, outpll t ; , t h e o r e t i c a l p r e s s u r e ; P, e f f i c i e n c y .

F igu re 9 shoas t h e maintenance of t h e power wi th i n - c r e a s e o f a1t i tud.e by ncans of t h e throe-speed mechanical con t ro l . Wotc t h a t t h o power zt 5800 m (19030 f t , ) i s s l i g h t l y g r c s t e r t han at 3000 m (9840 f t , ) - (a gai-n due t o t h e exhaust i n t o t h e r a r e f i e d . a tnosphero) .

F i g u r e 1 0 consa re s t h e speeds of a 3 regue t 19 air- p lxne equipped wi th a 500 bp Farman engine , bo th w i t h and wi thout s u ~ e r c h a r g s r .

111. T:lree-Speed 15echanZcal Control

When the s ~ q e r c h a r g e r i s i n ope ra t i on , i t i s not p o s s i b l e t o open t h e valve wide a t lorn a l t i t u d e s , and t j c r c i s always cons idc rab lo masto of energy, I n o rder t o remedy t h i s d i sadvantage , t h e Farmrwl Company i n t r o - d.uccd a thrcc-speed mechanical con"vo1.

Alii, tude

Test No. 9 arch 22, 1929). Pilot, J. Burtin. Observer, Cousin. 3regue.t 1932 airplane. Farman 12WE engine. Rateau supercharger with mechanical control. Levasseur two-bladed propeller of 4 m (13.12 ft.) diameter. Total load, 2500 kg (5511.6 lb.)

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G.A. C.A. Technical liomorandum 170, 631 12

The f i r s t speed i s used only f o r t he ground mixture and absorbs 5 t o 8 hp, The second and t h i r d speeds ab- sorb, r e s p e c t i v e l y , 22 and 80 llp i n r e s t o r i n g t h e pres- su re st 3C00 n (s30nt 10,090 Tt.) and at 5600 m (18,373 f t , ) . For each of %he f i r s t t w o speeds t h e r e i s a f r e e wheel p rov ided wi th pawls o p e r s t i n g ur,3er t h e a c t i o n of t h e c e n t r i f u g a l f o r c e , This f r e e mheel enab le s t h e gear- i n g i n v h i c h i t i s mounted t o r evo lve more r a p i d l y than t h e mechanism which d r i v e s i t , There i s t h e r e f o r e no :.:oc& of any t h r o t t l i n g or gear r e l e a s e i n p a s s i n g from one spezd t o another. A s i n g l e l e v e r i n t h r e e p o s i t i o n s r ende r s f t p o s s i b l e t o r e l e a s e t h e g e a r s sncces s ive ly , F i g u r e s 11, 12 , and 1 3 and t h e i r l egends oxp lz in t h e op- o r a t i o n o f t h i s remarkable mechani sn, The Tarman Company cozs fde r s t h a t tho t h r e e speeds a f f o r d a s u f f i c i e n t rango f o r nor:;al a i r p l a n e s .

Diagrams of t h e Farman Throe-Spced IJochanical Control

z + ~ t s p e e & , so -ca l l ed n i x i n g speed [upper ha l f of Figure 12).- 1Plneel d , keyed t o t h e engine s h a f t , ac tu- a t e s wheel a by t h e i n t e rmed ia t ion of the s l i d i n g j o i n t f , and p i n i o n b d r i v e s wheel a wi th t h e a i d of r a t c h e t c and pawls p. ( i 1 ) Ti:c pawls can be r ep l aced by r o l l e r s a c t i n g on t h e n r i n c i p l e of a medge, The supercharger 3hccL i s then geared t o 11,000 r.p,m. f o r a n o z i n a l engine speod of 2500 r.p,n, and produces an excess p r e s s u r e of about 5$ i n t h e i n t a k e p ipes . A t t h i s i n s t a n t t h e gea r s a r e r e l e a s e d , i.e., the b a l l bea r ing k i s i n c o n t a c t wi th t h e t i p s of t h e n e i g h t s g ( f i g . 12) and re vents t h e l a t t e r f r o n p r e s s i n g on t h e f r i c t i o n d i s k near p l a t e h .

Second speed (lower h a l f ' of Bigure 12) .- When t h e --- - n e i g h t s g a r e f r e e d by moving l e v e r j , t h e r i n g gear I i s engaged by t h e p r e s s u r e w i t h p l a t e h , and the swoercharger wheel t u r n s at 17,000 r.p,m. r e s t o r i n g t h e p r e s s u r e of 760 m a (29.92 i n , ) Hg up t o 3000 n (9842 f t , ) . Yhi le running a t speed 2 , t h e supercharger mheel r evo lves f a s t e r than at speed 1, and t h e gear wheels l ikcmi so t u r n f a s t e r . The pawls p of speed 1 a r c t hen actua,ted by t h e c e n t r i f u g a l i o r c e and f r e e d from t h e r a t c h e t c , t h u s Sreak ing tho connect ion between p i n i o n b and mheel a. The geaxing of speed Y. i s then s a i d t o bo i n t:lo l l freo-whcelg posf t ion .

W,A,C.A. Technical Memorendun .Eo, 631 1 3

Thi rd speed ( f i g . 13).- Continning the ope ra t ion of --- l e v e r j , t he weights o f each of ' t h e two c l u t c h e s a r e l i b e r a t e d . The r i n g g e a r s n a r e d r iven , w i t h t h e a i d of g e a r s d and n, at a r i u l t i p l e of t h e c r anksha f t speed, The supercharger wheel t hen t u r n s a t 27,000 r,p,m, and a n r e s s n r e of 760 mn (23.92 i n , ) 9g i s main- t a i n e d up t o ' ebout 5800 m (19029 f t , ) , T n i l e running a t specd 3, t h e f r e e wheel of speed 2 a c t s t h e same a s t h a t of speed 1 and t h e connect ion i s l i kewise broken between t h e c o n t r o l s h a f t and t h e second speed gear , Contrary maneuvers enable running at speed 2 and then at speed 1, Notc, on F igure 1 1 , t h a t t h c ?;ears of speed 3 a r e two i n number. This mothod was adopted p a r t l y t o enab le t he transmi s s i o n of tho maximum power of the supercharger w i th in a small , space and p a r t l y t o b ~ l a n c c t h e s t r e s s e s on tho bea r ings of t h o supercharger whcol.

The p rocoss of t h rov ing i n and out of geer cons5s t s simply i n moving l e v e r j from one p o s i t i o n t o ano ther , without any s p e c i a l p r ecau t ion , The con%rol Sever of t h e supercharger can be s e t a s d e s i r e d , The maximum f o r c e f o r r e l e a s i n g t h e c o n t r o l l e v e r i s about 1 5 kg (33,l 13 , ) . This f o r c e ceases a s soon a s t h e r e l e a s e h a s been e f f e c t - ed,

IT. Other ldechmiical Cont ro l s

Before d e s c r i b i n g t h e nem volumet r ic s i l~3crchargers , -it i s i n t e r e s t i n g t o examine o t h c r mechanical c o n t r o l s , which cannot be thrown out of g e a r , f o r c e n t r i f u g a l su- pcrchakgors. As t y p i c a l exaclples, pac n i l 1 cons idor , on t h e one hand, t h e c o n t r o l o r i g i n a t e d by t h e B r i s t o l Con- pany f o r th'e well-known J u p i t e r engine, which combines ve ry s a t i s f a c t o r y s o l u t i o n s of t h e problems posed ( g r e a t a u i t i p l i c a t i o n , g radua lness of engagement, e l a s t i c i t y of c o n t r o l ) and, on t h e o the r hand, t h e more r e c e n t and simple Benault c o n t r o l on t h e i r 700-850 hp engine,

Mechanicd c o n t r o l of the B r & ~ > o l super charge8rrOm The f a n r evo lves normal ly at 17 ,750 r.p,m,, t h e mt l l t ip l i - c a t i o n of 1 0 : l being ob ta ined ill two ste.ees. Tilo e l a s t i c c o n t r o l ( f i g s . 14, 15 , 16) comprisc:~ a s t e e l + h u b h h e l d on a con ice l bea r ing of t11e c r a rkzLaf t , This h i ~ b a c t u a t e s wheel f ( o r A, f i g , 16) FJy of ~0111- p r e s s i o n s p r i n g s g seen endwise i n F i r - ~ r o 14. The sp r ings a r e l o c a t e d Setmoen s i x p a i r s o f f centering notches ( s i x notchcs on tho hub and siqiothers on t h e niieol) . This device 6eadcns t he t o r s i onsl v i b r a t i o n s a t

1 4 l?.A.C.A. Toclinical Llcmora~durn Wo, 631

t h c end of the c r anksha f t and prcvont s t h o i r t r ansmis s ion t o tho s tep-?~p gears . Bronze r i n g s i cen to r t ho nhocl f o n i t s h u b h,

Wheel f engages t h reo p i n i o n s d , which revolve on r o l l e r bear ings c a r r i e d by f i x e d a x l e s o (whieh a r e h e l d by grooves i n t h e i r heads and p e n e t r a t e t h e aJuqi7 num c a s i n g n a), Ring e connec ts t be :iea,ds of t h e s e a x l e s . The t e e t h o f p i n i o n s d a r e lomered at c and form grooves t o which a r e keyed t h e hubs b of t h e t h r e e r e tu rn .whee l s , one of which i s s lovn at k. These t h r e e n h e e l s d r i v e t h e p i n i o n at t h e end of t h e f a n s h a f t u and con ta in t h e c e n t r i f u g a l c l u t c h e s which l i m i t t h e m.oment ,

The hubs b a f t ho r e c e l l wheols have , a c e n t r a l . p a r t i t i o n cu t i n such a way a s t o form socke t s f o r t he bronze engaging b locks a. Those b locks , which a r e s h ~ p e d l i k e t h e segments of a r i n g , can move only i n t h e r a d i a l d i r e c t i o n , P r o j e c t e d ou taa rd 5y tho c e n t r i f u g a l f o r c o at t h o moment of s t a r t i n g , t hcy e x e r t a s t rong p r e s s u r e i n s i d e t h e wheels k. Tne r e s u l t i n g f r i c t i o n s u f f i c e s t o i n s u r e f i r s t t h e s t a r t i n g and then t h e t r ans - miss ion of t h e moment t o t h e vane wheel.

B'ncn t h e cnkine i s sub jec t ed t o sudden a c c e l e r a t i o n s which may prodncc v e r y v i o l e n t s t r e s s e s on t h e t ransmis- s ion gea r , t h e cngzging b locks s l i d e , On t h e o thc r hand, thcy uniformly d i s t r i b u t e t h e s t r o s s o s between t h e t h r e e r e t u r n wheels, s ince t ho c l u t c h , tLus a c c i d e n t a l l y loadod, s l i d o s u n t i l uniform d i s t r i b u t i o ~ . i s r e e s t a b l i s h e d ,

The vane whccl p , of fo rged s t c c l ( f i g , 27) , h a s 1 6 r a d i a l vanes which t a p e r at t h e i r t i p s . I t i s mounted by means of grooves r on s h a f t u which r o t a t e s con- c e n t r i c a l l y mith t he c rankshaf t v i thout be ing supported by i t , Tile legend o f 7 igu re 1 4 ( ~ r i s t o l supercharger) d e f i n e s c e r t a i n o t h e r d e t a i l s , as fo l lows: a., bronze en- gaging b lock ; b , hub of r e t u r n wheel enmeshed at c by grooves on r e t u r n p i n i o n d; e , crown of r e t u r n a x l e s ; f , d r i i e wheel; g , sp r ing of e l a s t i c c o n t r o l ; h, hub of & < i ~ e wheel; i , bronze hub r i n g s ( c e n t e r i n g wheel f) j j , i n t a k e ahamber from which the , in ta lce p i p e s go t o t h e c y l i n d e r s ; k , r e t u r n wheel which con- t a i n s t h e engaging b locks a; E, crankcase r i b ; m, vane d i sk . ( I t i s between these d i s k s , whose divergcnco determines the g r a d u a l . i n c r e a s e i n t he s e c t i o n s of pas- sage, - t h a t t he k i n e t i c energy of t h e a i r i s conver ted - -

N.A.C.A. Technical Xemorandun No. 631 1 5

i n t o p r e s s u r e ) ; n and q , c a s i n g ; o, a x l e of r e t u r n whcol; p , vane mhecl mounted by grooves at r on s h a f t u ; s , r i n g f o r ho ld ing o i l ; v, o i l c o l l e c t o r ; w , supercharger ca se ; x , i n t a k e s p i r a l .

Mechanical -.-...-- c o n t r o l on the 700-800 hp Benaul t engine. - The r o t o r being r e q u i r e d t o produce an excess p r e s s u r e of only 150g/cm" (2.13 lk . / sq . in . ) , i t s r o t a t i o n a l speed was l i m i t e d t o about 15,500 r.p,m, Under t h e s e cond i t i ons , Renault thought b c s t t o u s e neiCher a c e n t r i f u g a l c l u t c h nor a s l i d i n g j o i n t , i n order t o make h i s nechznica l con- t r o l a s simple a s p o s s i b l e . I t s c o n s t r u c t i o n i s i l l u s - t r a t e d by F igure 17 wi th i t s l egend , a s fo l lows:

a ) Front viem of step-up o r a u l t i p l y i n g g e a r s , v i x s i b l e through the cutaway near t h e bottom of tho case . Here $he c a l i b r a t e d p i n i o n i s keyed t o t h e end of t h e c r anksha f t , The mul- t i p l i c a t i o n of about 7 : l i s e f f e k t e d i~ two s t a g e s by simple s t r a i g h t gear ing . I t i s known t h a t Ronault u s e s a s i m i l a r system i n h i s r e d u c t i o n g e a r s , of course , w i t h p a r t s p ropor t ioned t o t he moment t o Se t r ansmi t t ed .

b) Srlpercharger cover con ta in ing t w o h o r i z o n t a l o r - i f i c e s (only one of which i s v i s i b l e ) , t o which t h e c a r b u r e t o r s a r e a t t ached . These or- i f i c e s expand i n s i d e t h e cover i n i o two cham- b e r s , whose s l i g h t l y h e l i c o i d a l ? a r t i t i o n i s v i s i b l e , through t h e c e n t r a l opening.

c ) Rear view of t h e f a n o r blower i n i t s cas ing , The r o t o r i s duralurnin, I t s vanes a r e sup- po r t ed by me'bs inc luded i n t h e ca s t i ng . The hollom o u t s i d e vanes a r e supported by a d i s k which i s secured by n i n e b o l t s , o'ne f o r each vane, There a r e shonn at the top t h e t h r e e o r i f i c e s , each of which s u p p l i e s e group of f o u r c y l i n d e r s , The p e r s p e c t i v e r e n d e r s i t

. ha rd ly p o s s i b l e t o d i s c e r n t h e boss i n which t u r n s t h e p i n i o n keyed t o t he end of t he c r anksha f t , which i s s i t u a t e d on t h e oppos i te f ace , The cas ing i s c lo sed at t h e r e a r by t h e cover b,

V , Volumetric Superchargers

These superchargers a r c now t h e subJect of i n t e n s i v e rcsearch . Two vcry ingenious exac~p lc s have bccn prosen t - ad: one wi th p i s t o n s ( ~ u ~ e l a ~ - ~ o r t h i n g t o d ~ tho o thcr

16 N.A.C.A. Technical Memorandum No. 631

wi th r o t a t i n g b l ades (P .Z . ) , We. s h a l l now cons ider only t h e s t r u c t u r e of t h e superchargers and not t h a t of t h e i r c o a t r o l s , They a r e , i n f a c t , designed f o r d i r e c t d r i v e ,

The Dugelag-WorthYngton s _ u ~ e _ r c h a r ~ e r ( f i g , 1 8 ) , now being t e s t e d by the Se rv i ces Techniques, h a s two hori- ' z o n t z l r e c i p r o c a t i n g c y l i n d e r s , The f i r s t type made was designed t o be a t t a c h e d d i r e c t l y t o t he s h a f t of an en- g ine having a c y l i n d e r displacement o f 22 l i t e r s (1342 cue in , ) and t o develop a power of 350. t o 400 hp a t 7000 m (about 25000 f t , ) , The nos t modern dev ices were employed i n i t s c o i s t r u c t i o n (need le bea r ings , f l e x i b l e b lades i n s t e a d of va lves , otc.'). I t has , moreover, been l i g h t - ened t o t h e maximum by the u se o f magnesium, e l e k t r o n and duralumin, so t h a t i t s t o t a l . weight i s only 26 kg (57.3 13.);

The c ranksha f t c a r r i e s a p l a t e k w i t h needlo bear- i ngs , The bear ing s h a f t s a r e of G l T 5 s t e e l , t r e a t e d 'and d r i l l e d , The connec t ing rods 1 , i n t he f o r m of equal- r e s i s t a n c e s o l i d s , a r e of n i t r i d e d s t e e l ,

Tho p i s t o n s g , of l i g l i t metal c a s t under p r e s s u r e , a r e hollow. wi th i n t e r i o r r e i n f o r c i n g r i b s , The i r he igh t has been reguced t o t h e minimum i n order t o e l i m i n a t e dead spaces i n so f a r a s p r a c t i c a b l e , Since jamming might occur under t h e s e cond i t i ons , two guide r o d s e , ar

N..A. C . A . Techn ica l Memorandum No, 631 1 7 i . . . . . ,

The customary i n t a k e and exhaus t v a l v e s a r e r e p l a c e d by e l a s t i c d i s k s of v e r y smal l i n e r t i a . . Only t h e i n t a k e d i s k s c , a r e c o n t r o l l e d by a system of c a a s and push r o d s of po l i sGed n i t r i d e d s t e e l an3 duralurnin r o c k e r s ( i h, 3 ) . The s e n s ' i t i v e au toma t i c exhav-sf v a l v e s a r e mounted ' i n e a s i l y a c c e s s i b l e removable hous ings ,

The ba lgac ing was g iven s p e c i a l at t e n t i o n , Since t h e c y l i n d e r s had a comnon a x i s , t h e p i s t o n r e a c t i o n s ba lanced one ano the r , Tile b i g ends of t he connec t ing r o d s arle ba lanced by coun te rmeigh t s , The connect ing-rod bod i e s a l o n e hevelop a soment which can be l a r g e l y e l im i - n a t e d by an a d j u s t n e n t of t h e m'asses.

The l u b r i c 4 a t i o n of t h e cam c o n t r b ~ s i s t i g h t and h a s , a t t h e b o t t o n , a t a n k of o i l i n c o n t a c t w i t h t h e ca,IiZs. A v o l u m e t r i c pump, c o n t r o l l e d by ;.,'b.'orrn gea r and d e l i v - e r i a s :one drop a minu te , s u p p l i e s t h e connec t ing rods.

-- Charac t e r i q t i c s . - Bore, 260 mm (9.84 i n . ) ; s t r o g e , 160 mm (6.3 in,*) ; voXume of one c y l i n d e r , 7.85 l i t e r s (479 c u m i n , ) ; t o t 2 1 c y l i n d e r d i sp lacement p e r r e v o l u t i o n , 31.4 l i t e r s (1916 cu.in.) ; p e r minute at 1700 r epam, , 53.38 n2 (1885 c u , f t ,) . The v o l u n e t r i c e f f i c i e n c y be ing 85$ , t h e v-olulne drawn i n st t h e p r e s s u r e of t h e surround- i n g a tnosphe re i s 45.37 ma (1602 c u , f t , ) ,

Iaf we now cons ide r an eng ine of 22 l i t e r s (1342 cu. in,) c y l i n d e r d i splacoement, rum1 ng u n i f orrnly at 1700 r,p,m, a t 85$ v o l u m e t r i c e f f i c i e n c y , t h e volume a c t u a l l y drawn in; i s 15.89 rnS (551.15 cu . f t . ) . The r a t i o of t h e d i s p l a c e d volurnes i s t h e n

The exhaus t a b i l i t y of t h i s supercharger exceeds 700 am (27.56 i n , ) Hg. The power absorbed wi thou t fond i s about 6 hp. The power absorbed w i t h l o a d at 7000 y (about . 23,000 f t , ) , e n a b l i n g t h e ' r e s t o r a t i o n of a p r e s s u r e 1 ,037 kg /cn2 (14.15 l b , / sq . i s . ) t o t h e eng ine i n atrnas- phero r a r e f i e d t o 38$, i s about 35 hp, ~ h e ' o v e r - a l l e f - f i c i e n c y i s 55 t o 60$.

The 1fP.Z." s u p g ~ ~ h - a r ~ e r , - ' The numbers and l e t t e r s --- ----.--- r e f e r , r e s p e c t i v e l y , t o F i g u r e s 22 and 23-24. Three pho tographs a,re shovn i n F i g u r e s 1 9 , 20, 214.

.18 N.A.,C.A. Technical .!8emorandum No, 631

Tlie P,Z, supercharger c o n s i s t s of n c y l i n d e r , i n which r o t a t o two 3,blade systoms such as m s o t a t 120' and i n t e g r a l wi th two coax ia l s h a f t s k and 1 .. These s h a f t s c a r r y , r e s p e c t i v e l y , tho crankpins M1 and M a t o which a r e a t t ached by yokes t h o connect ing r.ods , Bi. and B2 o r j. The l a r g o cnds of thoso r o d s a r e j o i n t e d at e t o two p i n i o n s , such a s c , which t u r n i n s i d e a fixod. double-toothed r i n g a. The p i n i o n s , having a diam- e t e r one- thi rd t h a t of s a i d r i n g , a r e borne by a d r i v e r f r evo lv ing on r o l l e r s a t g and on b a l l s a t g t . If f o r c e i s a p p l i e d t o t h e motion p i e c e by means of t h e groowes h , t he two three-bladed systems, i n revolvring, approach and recede from each o t h e r t h r e e t imes p e r rev- o l u t i o n , due t o t he hypocycloidal motion of t h e l a r g e ends of t h e connect ing rods B1 and B2. I n s h o r t , t h e blade assembly i s endowed with a l t e r n a t i n g r o t a r y motions w i t h r e s p e c t t o t he f i u t i v e b l ades which revolve uniform- l y $nsido t h e cy l inde r . (The over -a l l l e n g t h i s 315 mm.)

The p o s i t i o n s of n e a r e s t approach of t h e b l ades a r e s i t u e t e d at t h r e e p o i n t s a, 8 , 'Y ( f i g . 23 ) , spaced at 120° on t h e f i x e d cy l inde r . On each s i d e of t h e s e t h r e e p o i n t s t h e r e a r e p l a c e d t h r e e s e t s of p o r t s A, R,, . A 2 R2, A, R, (A2 and AB not shown.), There i s always a b lade between these p o r t s , If t h e i n t a k e p o r t s 81, A2, and 83, on the one hand, and t h e ephanst p o r t s R,, R 2 , and Rg, on the o t h e r hand, a re jo ined by manifolds , we have a l i f t purnp and w f o r c e pump.

. . The s i x b lades d e f i n e s i x chambers of v a r i a b l e vol-

ume. Since each b lade occupies. a d ihed ra l . ang le of 20°, the maximum volume of a chamber corresponds t o a d i h e d r a l of 80°. Thr ice du r ing each r o v o l u t i o n t h i s dShedral c l o s e s and then resumes i t s maximum volume, d e l i v e r i n g a volume of a i r corresponding t o a r o t a t i o n of 80° X 3 = 240°, that i s , t o two-thirds of t h e cy l inde r . The s i x chambers t h e r e f o r e supply a volume equal t o f o u r t imes t h a t of t h e cy l inde r t angent t o t h e b lades , An. apparent- l y d i f f i c u l t p rob len h a s t h u s been succes s fu l ly solved, n m o l y , t o make a supercharger d e l i v e r , pe r rovo lu t ion , s eve ra l t imes i t s own volume.

The legends accompanying F i g u r e s 22 t o 24 i n d i c a t e a l l tho d e t a i l s , a s fo l lows:

F i ~ ~ z r e 22.- Longi tud ina l s ec t ion , - a, f i x e d dou- b l e r i n g gea r ; b , cove r ; c , double p i n i o n borne by

i7.B. C , A . Techn ica l Memorandum No. 633 1 9

t h e d . r ive r (at t h e bot tom, t h e c o u n t e r p q i s e s of t h e l a r g e ends of t h e c o n n e c t i n g r o d s ) ; d , b e a r i n g of double p i n - i o n , mounted on n e e d l e s and ha-ving, i n t h e c e n t e r , a case-hardened s t u d ; e , l a r g e end of c o n n e c t i n g r o d mounted on n e e d l e s ; f , d r i v e r r e v o l v i n g on r o l l e r s a t g and on b a l l s a t g t ; h , g rooves f o r t r a n s m i t t i n g mo- t i o n t o d r i v e r ; i , r i n g g e a r h o l d i n g s e t of b l a d e s a l o n g a x i s of r o t a t i o n his g e a r h o l d s a s h o u l d e r of s h a f t I ) ; j , l a r g e end of c o n n e c t i n g r o d inounted by a yoke a n d n e e d l e s on a c r a n k p i n i n t e g r a l w i t h s h a f t k; k , l ~ o l l o w s h a f t r o t a t i n g 5nsid.e s h a f t 1 which it SUP- p o r t s (k r o t a t e s on two n e e d l e b e a r i n g s a t i t s ends , one S e i n g c o n t c r e d i n c a r r i e r f , t h e o t h e r c l e a r t o t h e r e a r , an& 1 ~ o t a t o s about k on two n e e d l e b e a r i n g s ) ; m, bla6.e assembly and i n t e r s e c t i o n of i n s i a e r i b s ; n , as - sembly of b l a d e on a l o n g i t u d i n a l s t u d of hub p ; o, grooves t r a c e d oa a s h o u l d e r of s h a f t k f o r d r i v i n g t h e hub c a r r y i n g s t u d p ; a, p r e s s u r e - r e g u l a t i n g v a l v e , h e l d by s p r i n g s and c o n t r o l l e d . by l e v e r r o p e r a t e d by t h e p i l o t ,

FX'ure23-. Cross s e c t i o n showing t 3 e two 3?bladed systems.- a, $, and Y, l i a e s a l o n g which t h e b l a d e s approach t h e ? l e a r e s t ; A1, A2, and AS, i n t a k e p o r t s of 19' a p e r t u r e ; R l , R z , and R J , e x h a u s t p o r t s of 15' ap- e r h u r e ; ZZl, a r c of 12' a s t r i d e t h e l i n e a , a long v h i c h t h e b l a d e s form a p r a c t i c a l l y consta.nt d i h e d r a l of 2'. Note asseinbly of b l a d e s on t e n o n s of one of t h e hub s .

l ? f ~ u _ g g . ~ . Cross s e c t i o n showing d r i v i n g mechani s m of c o a x i a l sha f t s . - The s a t e l l i t e p i n i o n s , whose a x i s i s borne by t h e c a r r i e r , ro ta , t e i n s i d e t h e f i x e d r i n g . The l a r g e ends 02 t h e c o n n e c t i n g r o d s B1 and B2 d e s c r i b e th ree - loop h g p o c y c l o i d s , which communicate t o t h e crank- p i n s M L and 1/12 a motion r e s u l t i n g from t h e superpo- s i t i o n of o s c i l l a t i o n s on a u n i f o r m r o t a r y motion. The c o a x i a l shafts k and I a r e h e r e shovn endwise , sepa- r a t e d by t h e n e e d l e b e a r i n g ,

Ye m i l l h e r e c a l l s p e c i a l a t t e n t i o n t o c e r t a i n s t r u c t u r a l d e t a i l s , I t w a s sought t o l i g h t e n a s much as p o s s i b l e t h e r e v o l v i n g p a r t s s u b j e c t e d t o v a r i a b l e p e r i - o d i c a c c e l e r a t i o n s .

The e l e k t r o n .b lades , . f o r g e d nlld r e i n f o r c e d on t h e i n s i d e , c o n s i s t of two s h e l l s r i v e t e d t o t h e l o n g i t u d i n a l

20 N.A.C.A. Technical Memorandum No, 631

tenons of t h e hubs, The t h i c k n e s s of t h e i r walls and r i m s v a r i e s between 1.5 .and 2 mm (0.06 and 0.08 i n , ) , Each b l ade weighs on ly 130. g(0 ,287 lb.), Moreover, t h e l a r g e r p a r t of t h e m a t e r i a l i s n e a r . t h e .hub, so t h a t , a t 2000 r,p,m, t h e maximum f o r c e e x e r t e d on a connec t ing rod i s only 800 kg (1763.7 l b , ) , d i s r e g a r d i n g r e a c t i o n s due t o t h e compressed air . This f o r c e i s small i n compari- son w i t h t h e f o r c e s e x e r t e d on t h e connect ing rod of an a i r c r a f t engine , bu t i t i s s t i l l f u r t h e r X-educed i n oper- a t i o n . I t has been found, i n f a c t , that t h e compression s t r e s s e s a r e d i r e c t l y opposed t o t h e i n e r t i a f o r c e s and, under a d i s cha rg ing f o r c e of 500 g/cm2 (7.11 lb , / sq . in . ) , f o r exEmple, t h e r e l i e f t o t h e connect ing r o d s amounts t o 40$,

Moreover, knowing t h a t t h e i n e r t i a s t r e s s e s a r e . g r e a t e s t when t h e b l a d e s a r e nea r t o g e t h e r , we can, by s u i t a b l y a d j u s t i n g t h e b i g ends of t h e connec t ing rods a n ' t h e p i n i o n s , o b t a i n an acccmpanying movement of t h e b l a d e s which e l i m i n a t e s t h e e f f e c t s of t he p o i n t of p r e s - su re , I t i s at an ang le of about 12O, a f f e ~ t i n g t h e a r c ZZ' ( f i g , 23) as r e g a r d s t h e direct iorzl a , t h a t t he b l ades come the n e a r e s t t o g e t h e r and have p r a c t i c a l l y equal spoeds. The a i r cushion between the:, & cushion which cor responds t o a d i h e d r a l o f about 2 , and which i s ob ta ined by an i n t e n t i o n a l s t a g g e r i n g of t h e i n t a k e and exhaust p o r t s , t ends t o r e t a r d t h e blade which i s slowing down and t o a c c e l e r a t e t h e one which i s p i c k i n g up, A supplementary r e l i e f of t h e connec t ing rods i s t h u s ob- t a ined . The loss i n ou tpu t , due t o t h e b l a d e s no t coming e x a c t l y i n c o n t a c t , i s only about 3$, A t o r d i n a r y en- g ine speeds t h e supercharger r u n s wi thout v i b r a t i o n and g i v e s t h e same impress ion as a mechanism w i t h a uniform r o t a t i o n a l motion,

I n o rde r t o avo id a l l overhang, t h e r i n g g e a r , w i t h which t h e p i n i o n s mesh, i s double , t he p i n i o n s them- s e l v e s a r e double and t h e connec t ing rods a r e forked, The j o i n t s and t h e ' coax i a l s h a f t s a r e mounted on Nade l la need le b e a r i n g s r e q u i r i n g ve ry l i t t l e o i l and w e l l s u i t - ed f o r t h e contemplated l o a d s and speeds, - .

The wid th o f t h e b l ades a t t h e i r ends i s f avo rab l e t o t i g h t n e s s , Desp i te t h e a n t i c i p a t e d expansion, t he l o s s e s a r e cons ide rab ly reduced, even i f t h e a i r drawn i n t o t h e superchcrger i s d ry and, i f i t i s c a rbu re t ed , t h e t i g h t n e s s becomes p e r f e c t , t h e s m a l l d r o p l e t s d i s -

N.A.C.A. T e c h n i c a l Memorandum'No. 631 21

t r i b u t e d over a l a r g e . s u r f ace fo rming a h y d r a u l i c s e a l .

The ad jus tment i s by means of t h e I n t e r n a l c i r c u l a - t5on. The r e a r end of t h e c y l i n d e r i s c l o s e d by a p l a t e q, w i t h a c o n i c a l b a s e a g a i n s t which t h e b l a d e s r e v o l v e . Th i s p l a t s i s normal ly h e l d a g a i n s t i t s s e a t by a s p r i n g s. A l e v e r makes i t p o s s i b l e , by opposing t h e a c t i o n of t h i s s p r i n g , t o r a i s e t h e p l a t e f rom i t s s e a t and es tab- l i s h d i r e c t communication between t h e chambers a l t e r n a t e - l y s u b j e c t e d t o compress ion and s u c t i o n .

The v a l v e i s wide open a t s e a l e v e l , t h e s u p e r c h a r g e r on ly s e r v i n g t o mix t h e g a s e s w i t h t h e l e a s t e x p e n d i t u r e of power. The g r a d u a l c l o s i n g of t h e p l a t e makes i t p o s e s i b l e t o i n c r e a s e t h e p r e s s u r e w i t h a l l t h e p r e c i s i o n ded s i r e d , L a s t l y , t h e sys tem a c t s a s a ' s a f e t y v a l v e a g a i n s t back-f i r i n g .

The p r o t o t y p e of t h e P.Z. s u p e r c h a r g e r was des igned t o be g e a r e d d i r e c t l y t o t h e s h a f t of a 350 hp engine r e - v o l v i n g a t 2000 r.p,m. The c y l i n d e r h a s a b o r e of 190 mm (7.48 in . ) and a l e n g t h of 200 mm ('7.87 in . ) . The b l a d e s cover 20'. The t h e o r e t i c a l o u t p u t i s 21.4 l i t e r s (1306

. cu.in.) p e r r e v o l u t i o n , Length, 315 mm (12.4 i n , ) ; maxi - mum d i a m e t e r , 270 rnn (10.63 in . ) ; weigh t , 1 7 kg (37.48 ) The P.Z. s u p e r c h a r g e r i s now undergo ing t e s t s f o r p l o t t k n g t h e e f f i c i e n c y curves .

TI. Comparison of D i f f e r e n t Supercharger Types

I t i s r a t h e r d i f f i c u l t t o a p p l y a c o e f f i c i e n t of q u a l i t y t o t h e v a r i o u s formulas . The e f f i c i e n c y and t h e r e q u i s i t e power do n o t s u f f i c e . The weight and t h e i n - s t a l l a t i o n d e t a i l s must a l s o be c o n s i d e r e d ,

Turbo-superchargers .- Idany t h i n k t h e e x h a u s t g a s e s --- c o n s t i t u t e an u n d e s i r a b l e r e s i d u e and t h a t t h e u t i l i za - t i o n of t h e i r ene rgy , i n t e r e s t i n g i n t h e o r y , g i v e s r i s e , i n p r a c t i c e , t o more t r o u b l e t h a n p r o f i t . I n any c a s e , t h e t u r b o - s u p e r c h a r g e r h a s no t y e t s a i d i t s l a s t word, e s p e c i a l l y on l a r g e e n g i n e s ,

The c e n t r i f u g a l - superchue I s compact. I t i s es- p e c i a l l y s u i t a b l e f o r r a a i s l e n g i n e s ( f i g s . 25-28), i n which i t g e n e r a l l y s u f f i c e s t o improve t h e s tep-up g e a r , a s t h e f a n i s a l r e a d y p r e s e n t and pe r fo rming t h e o f f i c e

22 N.A.C.A. Technical idemorandurn No, 631

of mixer.* I t ' must revolve very r a p i d l y , however, and the q u e s t i o n s of b a l l bear ings and l u b r i c a t i o n become q u i t e troublesome.

Evolu t ion o f Armstrong-Siddeley Superchargers

F igu re 25, type I (1925) .- From l e f t t o r i g h t : l n t a k e b l ades ; supercharger i n ca s ing , r o t o r , I n t ake ' b lades w e f i x e d , Rotor i s duralumin, mounted on engine . s h a f t by f i n e grooves, Ex i t b l ades a r e s t r a i g h t , Note l a r g e number of b l a d e s and space between them and the r o t o r ,

F igu re 26, type I11 (1930) ,- Rotor has more b lades than i n type I. ' They a r e r e i n f o r c e d by a d i s k c a s t i n one p i e c e wi th them. Tho s t e e l i n t a k e b l ades a r e incor- po ra t ed i n t he r o t o r and form incurved e lements f o r de- f l e c t i n g t h e a i r toward t h e i r r o o t s . Doveta i led i n t o t ho mass, thoy adre ho ld i n p l a c e by p r e s s u r e on t h e hub. The p e n e t r a t i o n of t h e bases of t h e s t e e l b l ades i n t o t h o f r o n t edges of . t he d u s a l u m i ~ b l a d e s u n i t o s t h e two p i e c e s i n t ima te ly ,

, " "

The p r e s s u r e suppl ied by i t v a r i e s much more wi th the speed thah t h a t produced by v-olurnetric superchargers . Siiice a i r c r a f t enkines revolve a t m,ore uniform speed than automobi lo engines , t h i s o b j e c t i o p mould be more app l i ca - b l e t o ' t h e l a t t e r , The f a n works c o n s t a n t l y under the cond i t i ons of counte rpressure a l r e a d y i n d i c a t e d , The mechanical c o n t r o l s and c l u t c h e s a r e s t i l l d e l i c a t e in - s t ruments , d e s p i t e a l l t h e ca re e x e r c i s e d i n t h e i r con- s t r u c t i o n . Their e f f i c i e n c y i s of t h e order of 60-65$,

The v-olurnetric supercharger appears t o have -a h ighe r e f f i c i e n c y , but i t i s more cumbersome, The h i g h compres- s ion r a t i o s , made p o s s i b l e , at v e r y h i g h a l t i t u d e s , seem t o o f f e r decided advantages , e.g., f l i g h t s at 15,000 m

*Note, i n t h i s connect ion a remark by Mr. Easeige. he- p r o s p e c t s f o r superchargers seem more promising on water- cooled engines , where t h e coo l ing capac i ty can be i n r c reased , than on a i r -cooled engines , where a l l t h e a v a i l - ab l e s u r f a c e o f t h e c y l i n d e r s i s a l r e a d y covered w i t h f i n s and does not seem a b l e t o i n s u r e , wi thout complica- t i o n s i n t h e v e n t i l a t i o n at very h i g h a l t i t u d e s , tho sup- plementary cool ing n e c e s s i t a t e d by t h e conserva t ion of t h e power, Howovcr, i t i s only f a i r t o r e c a l l t h a t tho world a l t i t u d e rocord was won by an a i r -cooled engine.

(49200 f t , ) , i f such f l i g h t s a r c 3 o s s i b l 0 , which has no t Been proved, t h e r e be ing ve ry few d a t a on t h e e f f i c i e n c y of p r o p e l l e r s at spceds above t h e v e l o c i t y o f sound i n t he cir.

I t can bc fo re seen t h a t , o n l a r g e mult i-engine ai-r- p l a n e s , . the supplying of t he c c r b a r e t o r s and a i r cab ins . at one atmosphere w i l l be t he o b j e c t of t e s t s of d i s t r f - bu t ion by a c e n t r a l p l a n t . For t h e s o l u t i o n of t h i s problem, r e have tho explosion engine , whose c y l i n d e r s and movable a c c e s s o r i e s a r e immediately t ransposab le .

A 500 hp four-s t roke-cycle engine consumes about 500 l i t e r s (17.66 cu,ft.) of f u e l mix ture p e r second. I n f u n c t i o n i n g a s a two-stroke-cycle pump, i t would d e l i v e r , at 5500 m ( 1 8 0 ~ 0 f t ,) , a p r a c t i c a l l y equ iva l en t volume 4 of air a t a tnosphe r i c p re s su re . The d e l i v e r 9 might b3 doubled by us ing r e c i p r o c a t i n g c y l i n d e r s ,

The s t r u c t u r a l weight of such a supercharger , a s i d e f r o m t h e engine, might be cons iderab ly reduced by the e l i m i n a t i o n of a l l t h e a c c e s s o r i e s and a g r e a t r educ t ion i n t h e weight of a l u l t h e p a r t s c a l c u l a t e d E o r t h e maxi- mumepressure o f 2 kg/cm2 (28.45 lb . / sqefn . ) , i n s t e a d of 30 kg/cm2 (426.7 lb . / sg . in , ) . ( 1 t i s only necessary t o r e c a l l t h e remarkable r e s u l t s ob t a ined i n t h i s way by t h e Dugelay-Tiorthington supercharger .) The speed i n c r e a s e would be made p o s s i b l e by l i g h t e n i n g tho movable accesso- r i e s , We would then have, f o r a bulk comparable t o t h a t of a 500 hp engine, i f i t be assumed t h a t t h e r o t a t i o n a l speed can be doubled (which a?pears q u i t e p o s s i b l e under t h e contemplated working p r e s s u r e ) , a supercharging p l a n t capable o f supplyi'ng f o u r 500 hp engines a t 5500 m (18045 f t , ) . This p l a n t would be operated by a s p e c i a l engine w i t h change-speed gea r , The weight cannot be *accu- r a t e l y computed, 'but would probably be l e s s t han t h e weight of f o u r o rd ina ry superchargers .

V I I . Problems f nvolxing t h e Accessor ies

The maintenance of t he p r e s s u r e at h i g h a l t i t u d e s e n t a i l s n o d i f i c a t i o n s i n t h e i n s t a l l a t i o n of t h e accesso- r i e s , which a r e rendered i n c r e a s i n g l y necessary as t h e cornpression r a t i o i n c r e a s e s ,

There being only one a i r i n t a k e ; i t i s important t o P

24 N , A , C , A . Technical Memoraniturn No, 631

g i v e i t t h e bes t f o r n t o conver t t h e v e l o c i t y of t he a i r i n t o p r e s s u r e , an expedient which i s i n c r e a s i n g l y produc- t i v e a s t h e spced of t h e a i r p l a n e + i n c r e a s e s ,

If t h e c a r b u r e t o r i s p l aced between t h e supercharger and t h e c y l i n d e r s (fig. 31), communfcation must be ektab- Lished between the f l o a t chamber and the c o l l e c t o r . This method o f mounting does no t p r o f i t from the e f f e c t of t h e mixing and r e q u i r e s s p e c i a l adjustment of t h e f u e l pump which must supply t h e f l o a t chamber at excess p re s su re , I f , on t h e o the r hand, c a r b u r e t i o n t a k e s p l a c e before compression, a s i n g l e ca rbu re to r s u f f i c e s , and o rd ina ry f u e l punps can be used. A c a r b u r e t o r , however, which i s suppl ied a t a h igh a l t i t u d e by a i r of small d e n s i t y , a must have a lar'ge gas sage , which i s too l a r g e a t sea l ev - e l . I n t h i s case an automatdc a l t i t u d e c o n t r o l would be of s p e c i a l i n t e r e s t ,

Backmfiring must be avoided i n ' t h e l a r g e exhaust man- i f o ld of t h e supercharger , which always c o n t a i n s s eve ra l l i t e r s of t h e f u e l mixture , The Farman Company uses , I n a d d i t i o n t o t h e customary nan re tu rn va lve on each cy l in - der i n t a k e p i p e , a c o l l e c t o r va lve ( f i g , 29). L a s t l y , i t i s neces sa ry t o p rov ide an i n l e t va lve a t t h e en t r ance t o t h e supercharger and c a l i b r a t e d v a l v e s f o r t h e exhaus t , i n o rder t o avoid any a c c i d e n t a l overpressure i n the pipea.

The r i s e i n t o a p e r a t u r o due t o compression is ex- p re s sed by the formola

-,-

n

!I? = Po (8) w i t h n = 1.4. 0

corresponding t o an a d i a b a t i c compression. Thg air does not l e a v e tho p r e s e n t superchargers at a temperaturo above 7 5 ' ~ (167'E'.), Rad ia to r s w i t h l a r g e aluminum tubes g ive s a t i s f a c t i o n ,

I t i s necessary t o overdimension tho wate r and o i l r a d i a t o r s , s i nce t h e r a d i a t i n g a r e a s o r d i n a r i l y provided may be i n s u f f i c i e n t i n r a r e f i e d a i r , no twi ths tanding t h e i n c r e a s e i n speed,

I n a supercharger wi th t h e Farnan mechanical c o n t r o l , t he o i l promision i s ve ry l a r g e , 150-180 l i t e r s (39,6- 47,6 gal.) p e r hour. I t n e c e s s f t a t e s a s p e c i a l mounting,

'@.'A. C*. E . ' ~ g c h i i i c a l hIemor andum NL*.: 633 25

a s shown i n F i g u r e £50,' which h a s t h e f o l l o w i n g legend,

F i g u r e 30.- O i l c i r c u l a t i o n of Farnan 1 2 WX e n g i n e , equipped w i t h a m e c h a n i c a l l y c o n t r o l l e d Ra teau snper- cha rger . a , o i l r a d i a t o r ; b , i n t a k e of d r a i n pump connected w i t h sump h ; c , o i l f i l t e r ; d , excess- p r e s s u r e v a l v e ; e , o i l d i s t r i b u t o r ; f , p l u g f o r em- emptying o i l ; g , o i l p i p o t o c l u t c h of s tep-up g e a r and t o bush ing i n f r o n t of s u p e r c h a r g e r ; i , r e t u r n of o i l f rom d r a i n pum oto t a n k n ; j , o i l p i p e from t a n k t o pump; k, p i p e 7 manometer Id; 1 , o i l p i p e t o ad- j u s t a b l e conne.ction m .and t h r u s t 3 e a r i n g of supor- c h a r g e r ; A, l e v e r of mechanica l c o n t r o l .

FJ-g:?r.g-?J.-' Diagram of f u e l sy'stem on. Farman 12TE eng ine equipped w i t h a Rateau m e c h a n i c a l l y c o n t r o l l e d s u p e r c h a r g e r ( a i r blown p a s t c a r b u r e t o r ) . The a i r p i p e s a r e h a t c h e d , whi le t h e f u e l p i p e s a r e i n d i c a t e d by heavy p a r a l l e l l i n e s , A, f rom f u e l t a n k ; C, c a r b u r e t o r Z e n i t h 60 D.J.P., t i g h t ; D , D ' , a i r d i s t r i b u t o r s ; .K, . s u p e r c h a r g e r ; Ed, compensated manome.ter; P ,Pi, Amble f u e l pnmps; R,R,, a i r c o o l e r s ; T , e q u i l i b r i u m tuloe; am, i n l e t f o r compressed a i r g o i n g t o manometer; &s, i n l e t f o r compressed a i r go ing t o d i s t r i b u t s r s D and Dl t h r o u g h r a d i a t o r s R and R'; d, opt ' ional f u e l - p r e s s u r e r e g u l a t o r ; , pump f o r i n j e c t i n g f u e l i n t o t h e i n t a k e p i p e s ; v , f u e l c l e a n e r ,

The c a r b u r e t o r C i s t i g h t , - The e q u i l i b r i u m tube T c o n n e c t s t h e . f r e e space abovo t h e f l o a t chamber w i t h t h e c o r ~ p r c s s e d - a i r c u r r e n t i n f r o n t of t h e V e n t u r i tube . Withov-t t h i s p roca ,u t ion , t h e p r e s s u r e i n t h e V c n t u r i t u b e mould b e g r e a t e r t h a n t h a t above t h e f l o a t chamber, and t h o f u e l monld n o t bc drawn i n . The f l o a t chamber b e i n g t h u s under excess p r e s s u r e , t h e A.M. f u e l pumps (normal ly a d j u s t e d t o work under a p r e s s u r e of 250 g/cm2 (3.56 ~ b . / sq , in . ) would n o t be a b l e , above a c e r t a i n l i m i t , t o r a i s e t h e n e e d l e v a l v e and i n s u r e t h e f u e l f low. A p i p e

c o n d u c t s comgressed air t o t h e d i s t r i b u t o r s D zgd This a i r i s a d m i t t e d t o t h e i n s i d e of t h e e l a s - t i c deformable p i s t o n of each pump and augments t h e ac- t i o n of t h e d i s c h a r g e s p r i n g , However, b e i n g h o t , t h e r e i s danger of c a u s i n g , th rough t h e n e t a l w a l l of t h e p i s - t o n , a v a n o r i z a t i o n of t h e f u e l which would d i s t u r b t h e c i r c u l a t i o n , I t i s c o o l e d , t h e r e f o r e , i n two small r a d i - a t o r s R,R', These do n o t , t h e r e f o r e , r e p r e s e n t i n any nay t h e r a d i a t o r th rough which p a s s e s t h e a i r g o i n g t o

t h e engine and which i s not shown he re ,

b Ma~ne tos , - The r e s i s t a n c e betnoen the e l e c t r o d e s of t h e spark p lug remaining cons t an t , t h e c u r r e n t has j u s t so x u c h ' g r e a t e r tendency t o p a s s t o t h e spark a r r e s t o r as the d e n s i t y o f t h e d i e l e c t r i c surrounding a i r dimin- i s h e s . This d i f f i c u l t y i's remedied by s h i e l d i n g tho magneto ( o r . a t l e a s t t h e spark a r r e s t e r , -which than f u n c t i o n s i n an atmosphere under cons tan t p r e s s u r e ) , o r by mcking t h e d i s t a n c e .between t h e e l e c t r o d e s of t h e spark a r r e s t e r a d j u s t a b l e , For f u r t h e r d e t a i l s , see a z a l y s i s of tho French p d e n t 648,361 by M r . ~ o i n c a r g (No. 126, page 3'72):

Propel lers ; - In order t o main ta in t he maximum e f f i - c iency, i t i s p o s s i b l e t o a c t 6n t h r e e parameters - D , n, and h, One dreads t o contemplate t h e c o n s t r u c t i o n of p r o p e l l e r s wi th d iameter v a r i a b l e i n f l i g h t , A s r ega rds n, t h e p rob lem-mer i t s t he a t t e n t i o n of t e c h n i c i a n s , T. B, Barbaroux has invented a two-speed r e d u c t i o n gear f o r a i r c r a f t engines , which shows t h a t t he .p~oble rn i s be- ilg s t u d i e d , So fa r as we know, however, i t has not y e t been solved. The n o s t a c c e s s i b l e parameter a t t h e pres - en t t i a e i s h. I t i s evident t h a t p r o p e l l e r s w i t h p i t c h v a r i a b l e du r ing f l i g h t a r e neces sa ry f o r h i g h - a l t i t u d e engines.

T r a n s l a t i o n by Dwight Id. Miner, Nat iona l Advisory Committee f o r Aeronaut ics .

.h.~. C.A. Technical Xemorandun No. 631

Section A B 1 &=a

Fig.1, Tellon mounting of Rateau turbine vanes

I - - L , I . . 1.-

L L

Fig.2, .Co~qarative curves of the work of compression

Power

Fig.3, Calculatec! gain in pomer resulting f r o m efiaust into rarefied atmosphere.

N.A. C.A. Technical Memorandun: No. 631

Altitude

0 250 500 750 1000 1250

Air, g/sac. Fig. 8

Fig. 7

Altitude

Fig. 9

Figs. 7,8,9,10

........+... 'i.'esf cf 1?./25/26 12 W.2. nitbout superchareer

-,....-..--Test of 11/12/30 12 W.1, with sugerch,rger

Fig. 10

Fig, 11 Front view of pinions ---

Fig. 12 Median vertical section of Farman control

g S Portion of horirontal oeotf on

Fig. 17 a,b,c, Supercharger of 700- 850 hrp.Renault engine

fig. 18 m e l a y - vol'tric supr- charger with pistons

Fig. 22 P.Z. supercharger, longitudinal section

Yig.30, 31 Oil and fuel system8 on Farman

o f aoaxiail ahai'to

Slddeley superchargers

%?Jupf terR engine)

( on is'911aspt¶ engine)