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MAT I OBAL ADVISORY COPIII.IITTEI FOR. BZRONAV$I c s ADVANCE CONFIDENT I A L R3PORT = , % " '- * - L * . < . .
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OF A HIGHLY CAl4B3B3D LOW-3RAG-AIRFOIL S E C T I O N WITH k LIFT-CONTROL YLAP
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Bg I r a E. h b b o t t a n d R a l p h 3 . > t i l l e r L a n g l e y M e m o r i a l h e r o n a u t i c a l L a b o r a t o r y L a n g l e y F i e l d , Va, Unclassified - Notice remarked 4/17/09
i I December 1 9 4 2
I $ I W A T I O X h L ADVISORY COMMITTEX FOR BZRONAUTICS ADVANCE CONFI DSNT I A L REPORT T3STS OF A HIGHLY CATlIBZRED LOW-DRAG-AIRFOIL SPCTIOM W I T 3 A LIFT-COMTROL FLAP - - By XHa H. A b b o t t and R a l p h B . ' I i l l e r - .
SUMMARY T a * s t s were made i n t h e IqACA t w o - d i m e n s i o n a l low- t u r b u l e n c e p r e s s u r e t u n n e l of a h i g h l y cambered l o w - d r a g a i r f o i l (NACA 6 5 , 3 - 6 1 8 ) w i t h a p l a i n f l a p d e s i g n e d f o r l i f t c o n t r o l . The r e s u l t s i n d i c a t e t h a t s u c h a cambina- t i o n o f f e r s a t t r a c t i v e p o s s i b i l i t i e s f o r o b t a i n i n g a l o w p r o f i l e - d r a g c o e f f i c f e n t s o v e r a wide r a n g e of l i f t c o c f - f i c i c n t s ~ l r i t h o u t l a r g e r e d u c t i o n s of c r i t i c a l s p e e d . . .
INTRODUCT I OR The a b i l i t y of c e r t a i n f l a p s t o s h i f t t h e low-drag h i - r q n g c of t h e NACA low-drag a i r f o i l s s h o u l d h a v e i m p o r t a n t a p p l i - c a t P o n s i n i m p r o v i n g a i r p l a n e performa,nce. Such f l a p 5 . sccm - t o o f f o r adv3nta,ges f o r t a k e - o f f , c l i m b , maneu- v a r i n g , a n d p e r h a p s , c r u i s i n g st h i g h a l t i t u d e s . They a l s o f a c i l i t 8 , t e t h 2 d e s i g n of n o s e a i r - i n t a k e s l o t s t o be e f f i c i e n t f o r b o t h h i g h s p e e d a n d c l i m b .
Such a d v ~ n t a g e s , however, a p p e a r t o be a t l e a s t p a r t - l y depen?-ent upon t h e u s e of f u l l - s p a n f l E p s o r d r o o p e d a i l e r o n s w i t h p a r t i s l - s p a n f l q p s t o a v o i d d r a g i n c r e m e n t s l s s o c i a t e d w i t h t h e f l a p e n d s s n d t h e d i s t o r t i o n of t h e s p a n - l o a d d i s t r i b u t i o n . I t was s u g g e s t e d i n r e f e r e n c e 1 t h s t s u c h d i f f i c u l t i e s might b e p a r t l y overcome by d e s i g n - i n g t h e wing i n i t i a l l y f o r t h e h i g h l i f t - c o e f f i c i e n t r a n g e .
The h i g h camber of t h e r e s u l t i n g wing c o u l d t h e n be r e - duced t h r o u g h t h e u s e of upward f l a p d - e f l e c t i o n s s n d n e g a - t i v e a i l e r o n a r b a p f o r t h e l o w - l i f t or high-speecl f l i g h t c o n d i t i o n s . ' The u p w r r d f 1 n p 5 d e f l e c t i o n would a l s o r e d u c e t h e r a t h e r l a r g e mament c o e f f i c i e n t s of t h e h i g h l y cam- b e r e d a i r f o i l f o r t h e " high-speefi r a n g e of l i f t c o e f f i - c i e n t s .
The p r e s e n t t - e s t s were t h e r e f o r e made t o o b t a i n s e c - t i o n c h a r a c t e r i s t i c s of A h i g h l y cqmbercd l o w - d r a g sir- f o i l ( U C k 65,3-618) w i t h s u c h a f l a p , P l a i n f l s p s s u i t - ~ b l e f o r - t h i s ' ~ p p l f c ~ t i 0 n h ~ v e been shown t o be e f f e c t i v e i n s h i f t i n g t h e l o w - d r a g r p n g e , have r e a s o n n b l y good maxi- mum l i f t s f o r mrcny a p p l - i c a t i o n s , 'snd r e q u i r e s mininum of m e c h a n i c n l c o m p l e x i t y . Such f l a p s s l s o e l i m i n q t e t h e n e c e s s i t y f o r d i s c o n t i n u i t f e s a t t h e - f l - a p end f o r s m ~ l l d o f l c c t i o n s when u s s d w i t h d r o o p e d a i l e r o n s , -.
. .
METHODS AIVD APTBRATUS The t e s t $ we're mpde i n t h e NkCA % n o - d i m e n s i o n a l low- t u r b u l e n c e ' p r e s s u r e t C n n e l by t h e niexhods d e s c r i b e d i n re.feren'ce 1. Drag c o e f f i c i e n t s were o b t n i n s d by t h e wake- s u r v e y method aind l i f t c o e f f i c i e n t s w e r e o b t a i n e d by meas- u r e m c n t of t h e l i f t r e ' d c t i o n 'on t h e - f l o o r a,nd c e i l i n g of t h e b u n n e l . Nomen% c o e f f i c i e n t s '*ere measured by means' o f n s i m p l e b a l a n c e , A l l r e s u l t s 2 r e f u l l y c o r r a c t e d .
T2e inodel W R S b u i l t o f ' w o o d w i t h a 2 4 - i n c h c h o r d . I t - 1 w q s p~ i n t ed 2nd s2.nded t o p r o d u c e s e r o d y n n m i c a l l y smooth s u r f a , c e s . The model was e q u i p p e d w i t h p r e s s u r e o r i f i c e s f o r tost's rn8,de 3.0 o b t s i n p r e s s u r s d i s t r i b u k i o ' n s , b u t t h e s e - ._
o r i ' f i c e s wero f i l l e d and smoothed far q21 - o t h e r t e s t s . -
Tho f38-p ,~,.rr~ngc%ient i s shown i n figxmo: 1, : Unpublksh'ud t e s t s i n d i - c x t e d t h s t - t h o s k i r t . sh,'ipa u s e d f o r t h e m t o s t s ( f i g . 1) .was s d v ? n t ~ g e ' o u s ili e x t ' o n & i n g t h e - low-drag r a n g e r n d i n o b t a i n i ~ g ' s u i t s b l e hinge-moment c h n r a c t c r i s t i c - s f o r i n t e r n a l l y b a l a n c e d s i l e r o n s . The gap a r o u n d t h e f l q p l e ~ , d i n g c a g e was f i l l e d w i t h m o d e l i n g c l a y v i t h o u t chang- i n g t h e e x t c r n ~ l c o n t o u r . A i r f o i l o r d i n s t o s may be 0%- t ~ i n e d f r o m t h ~ d a t a i n r e f ~ r 2 n c e 1.
RESULTS k J D DISCUSSIOW L i f t c h a r a c t c r i s t i c s f o r t h e combin%-t;ion. a r e p r e s e n t - ed i n f i g u r e 2 f o r a R e y n o l d s number of ~ p p r o x i m a t e l y
6 X 18. The i n c r e m e n t i n maximurn l i f t c o e f f i c i e n t i s
a b o u t 0'.8 f o r a f l a p d e f l e c t i o n of 40'. H i g h e r maximum l i f t c o e f f i c i e n t s p r o b a b l y c o u l d be o b t a i n o d by s l i g h t m o d i . f i c a ' t i o n o f t h e s k i r t on t h a 'lower s u r f a c e t o p e r m i t l ~ r g d r f l a p d e f l e c t i o n s . C h a r a c t e r i s t i c j o g s i n t h e l i f t c u r v e s ni3pcnr a t l i f t c o e f f i c i a n t s of a b o u t 1.1 t o 1.3 f o r s i n a l l p o s i t i v e f l a p d e f l e c t i o n s . Those j o g s ~ " r c com- monly f o u n d i n t h c characteristics of n i l c r o n s 2nd p l n i n f l - p s r n d n r c a t t r i b u t e d t o r a t h e r sudden f l o w breskdowns o v e r t h e f l a p . Sneh j o g s do n o t o c c u r a t l a r g e positive, n e u t r a l , o r sma,ll n e g a t i v e f l a p d e f l e c t i o n s .
D r a g a,nd moment c h a r a c t e r 9 s t C c s f o r t h e c o m b i n a t f on a r c presented i n f i g u r e 3. The f l a p i.s v e r y e f f e c t i v e i n s h i f t i n g t h e low-drag r a n g e t o l o w s r l i f t c o e f f i c i e n t s w i t h p r a c t i c a l l y no i n c r e a s e i n d r a g a n d t o h i g h e r l i f t c o c f f i c i e n t s w i t h o n l y m o d e r a t e d r a g increases. T h u s , w i t h p r o p e r s e l e c t i o n of f l a p d o f l c c t i o n s , c o n p a r a t i t e l y low s e c t i o n d r a g c o o f f i c i e n t s I r e o b t a i n a b l e o v e r a r a n g e of l i f t c o e f f i c i c n t s from bzlow 0 t o a b o u t 1 . 2 . T h i s r a n g e of l i f t c o e f f i c i e n t s i s t h o u g h t t o be s u f f i c i e n t l y b r o ~ , d t o c o v c r t h e most i m p o r t a n t f l i g h t c o n d i t i o n s , ex- c e p t c o n d i t i o n s f o r t s k e - o f f a n d l a n d i n g , f o r most n i r - p l a n o s . A c o m p a r i s o n w i t h t h e d a t a of r e f e r e n c e 1 i n d i - c n t o s t h a t t h e d r a g c o c f f i c i o n t s of t h ~ f l a p p c d a i r f o i l i n t h e low-drag r a n g e a r e p r o b q b l y s l i g h t l y h i g h e r t h a n t h o s e f o r t h e p l n i n n i r f o i l .
- T h o ' r q t h e r 1 2 r g e ?itching-mornont c o e f f i c i e n t s of t h e
* -
p.re r e d u c o d t o v a l u s s 8 f o n l y n i r f o i l w i t h f l a p n e u t r a l
f l a p d e f l e c t i o n of -10 . S m a l l
r b o u t -0.02 ( f i g . 3 ) b y s &+ . p i t c h i n g - g o c q e n t c o e f f i c i e n t s t o g e t h e r w i t h l o w d r a g c o e f - f i c i e n t s a r e t h u s a v s i l n b l c f o r t h e h i g h - s p e e d f l i g h t c o n d i t i o n , Bonc l o s s of c r i t i c a l s p e e d iflust, of c o u r s e p be R C - c e p t c d i n t h e u s e of n n n i r f o i l n o t ~ p e c i f i c ~ l l y d-esigned f o r t h e h i g h - s p e e d c o n d i t i o n . ExZ:xinntion of t h e p r e s - s u r e c o c 9 f i c i e n t s S ( r e f e r e n c e 1 ) p r e s e n t e d i n f i g u r e s 4 t o 7 shows, h o w e v e r , t h n t t h i s l o s s n e e d n o t be v e r y l n r g c . The i ~ a x i n u a p r c s s u r o c o e f f i c i e n t shown i n f i g u r e
5 f o r a f l a p deflection of - l o 0 a n d R l i f t c o e f f i c i e n t
of 0.2 i s s l i g h t l y h i g h e r t h a n t h a t f o r t h e c o n p a s a b l e a i r f o i l c a n b o r c d f o r u s e a t t h e s g n e l i f t c o e f f i c i e n t (wACA 6 5 , s - 2 1 8 ) a s e s t i n a t e d f r o n n e n n - l i n e t h e o r y ( r e f e r - e n c e 1 ) a n d u n p u b l i s h e d p r e s s u r e d i s t r i b u t i o n s on t h e s y m m e t r i c a l ( N A C A 6 5 , 3 - 0 1 8 ) a i r f o i l . The d i f f e r e n c e c o r - r e s p o n d s t o a l o s s i n c r i t i c a l s p e e d of a b o u t 6 t o 1 0 m i l e s p e r h o u r t o a va,lue of a b o u t 44'7 m i l e s p e r h o u r f o r t h e f l a p p e d a i r f o i l a t a n a l t i t u d e of 2 5 , 0 0 0 f e e t .
While s u c h a l o s s would n o t be t o l e r a t e d f o r a n a i r p l a n e f o r which a h i g h c r i t i c a l Xach number was o f prime i m - p o r t a n c e , such a r e d u c t i o n of c r i t i c a l s p e e d i s t h o u g h t t o be of l i t t l e i m p o r t a n c e f o r many a i r p l a n e s .
CONGLUSI ONS
- A p l a i n f l a p on a h i g h l y cambered NhCA low-drag-
a i r f o i l s e c t i o n a p p e a r s t o o f f e r a t t r a c t i v e p o s s i b i l i - t i e s f o r o b t a i n i n g low p r o f i l e - d r a g c o e f f i c i e n t s o v a r a wide r a n g e of l i f t - c o e f f i c i e n t s w i t h o u t l a r g e r e d u c t i o n s of c r i t i c a l speed - f o r t h e h i g h - s p e e d ' f l i g h t c o n d i t i o n s .
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L a n g l e y Nemorial A e r o n a u t i c a l ~ a b o r a t o r y , Hat i o n a l Bdyi s o r y Cammitt c e f o r k e r o n 8 u t i c s , Langley F i e l d , Va.
. - " - > ,.
- , 1, J a c o b s , E a s t n a n IT., Abbott , I r a IT., and Davidson, M i l t o n : P r e l i m i n a r y Low-Drag-Airfoil an-d F l a p D a t a from T e s t s a t Large Reynolds Numbers and Low Tur- b u l e n c e , and Supplement. MhCk X.C.R., March 1942, . C., - . . . C . . .
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