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Source of Acquls~t~on CASI Acqu~red NATIOSAL ADVISORY COUi4ITTEB FOR AZBOXAUTICS #
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P R E L I M I ~ A R Y WIiqD-TUMBEL AND PLIGHT TESTS OF A BALAM CED SPLIT FLAP B y Fred E, lsick and 2 l o g d L. Thompson Lsngl ey Kexaorial Aeronautical Laborat osy A u g u s t 1934 PREL I i 4 I iTARY ABD F L I G H T TESTS BALANCED SPLIT F L A P By F r e d E, Weick and Floyd L, Thompson One d i s a d v a n t a g e t h a t h a s been a p p a r e n t i n tlie opera- t i o n of s p l i t f l a p s ass u s e d t o d a t e i s t h e t i m e and e f f o r t r e q u i r e d t o o p e r a t e them. I n t h i s c o n n e c t i o n a n i n v e s t i - g a t i o n i s b e i n g made o f p o s s i b l e means f o r b a l a n c i n g them a e r o d y n ~ t ~ n i c a , l l y t o make t h e i r o p e r a t i o n e a s i e r . S e v e r a l a.rraagerne:lts h a v e bcten t e s t e d i n t h e 7 by 1 0 f o o t wind t n i i n e l , and t h o r o s u l t s of t h e wind-tunnel t o s t s a s w e l l a s p r e l i m i n a r y f l i g h t t e s t s on one of t h o more p r o m i s i n g forms a r o g i v e n i n t h i s p a p e r .
W I X D - T U E N E L TESTS &~~ar_t.tu~_-s~d__.~:?!7_gtt.g.-- T110 7 b y 1 0 f o o t wind t ~ z n n o l i s d e s c r i b e d i n r o f e r c n c o 1 t o g c t h c r w i t h t h e b a l a n c e and s t a n d a r d t e s t p r o c e d u r e . For t h e s e t e s t s a s p e c i a l model a r r a n g e n e n t mas use$- v i t L mhich c h a n g e s i n t h e f l a p s c o u l d b e mado c o n v e n i e n t l y . Tile main a i r f o i l had a chord of 20 i n c h e s and a span of 20 i n c b e s , and was l o c a t e d between t w o l o n g i t u d i n a l v e r t i c a l p l a n e s , o r end p l a t e s , e x t e n d i n g 1 4 i n c h e s ahead of and 1 4 i n c h e s b e h i n d t h e model and en- t i r e l y t h r o u g h t h e j e t v e r t i c a l l y . Thus t h e f l o w o v e r t h e a , i r f o i l w a s a p p r o x i m a t e l y two-dirneasional i n c h a r a c t e r .
The main a i r f o i l had t h e C l a r k Y s e c t i o n , and t h e d i m e n s i o n s of t h e f l a p s a r e shown i n f i g u r e 1, The e n t i r e s e r i e s of t e s t s , which a r e s t i l l under way, i n c l u d e b o t h s p l i t f l a p s and u p p e r - s u r f a c e a , i l e r o n s w i t h many h i n g e - a x i s l o c a t i o n s . O n l ~ one of t h e more p r o m i s i n g f o r m s , which h a s a l s o b e e n t e s t e d i n f l i g h t , i s c o n s i d e r e d h e r e and t h e r e s u l t s a r e compared w i t h t h o s e f o r a p l a i n u n b a l a n c e d s p l i t f l a s of t h e same s i z e .
The t e s t s were mads a t d y n a p i c p r e s s u r e c o r r e s p o n d - i n g t o a t u n n e l speed. of 8 0 m i l e s p e r hour i n s t a n d a r d ' d i r , g i v i n g a Reynolds Eunber of a p p r o x i m a t e l y 1 , 2 1 8 , 0 0 0 . Ths r e s u l t s a r e u n c o r r e c t e d f o r wind-tunnel w a l l e f f e c t .
R e s u 1 a . - Curves of l i f t , d r a g , and c e n t e r of p r e s - .
s u r e a r e g i v e n f o r t @ e b a l a n c e d s p l i t f l a p i n f i g u r e 2 and f o r t h e u n b a l a n c e d one i n f j - g a r e 3., V i t h t h e f l a p n e u t r a l t h e maximum l i f t c o e f f i c i e n t w i t h t h e p r e s e n t t e s t a r r a n g e - ment mas a p p r o x i m a t e l y t h e sa.me as t h a t w i t h t h e u s u a l mod- e l of a s p e c t r a t i o 6 b u t w i t h t h e u n b a l a n c e d s p l i t f l a p , f o r which a d i r e c t comparison i s a v a i l a b l e , i t w a s about '-5' p e r c e n t l o w e r ( r e f e r e n c e s 2 and 3 ) . I n t h e p r e s e n t t e s t s , '"the maximum l i f t c o e f f i c i e n t was 1 2 p e r c e n t h i g h e r w i t h t h e ' b k l a n c e d s p l i t f l a p t h a n v i t h t h e u n b a l a n c e d one.
The s h i f t i n t h e c e n t e r of p r e s s u r e due t o f l a p de- f l e c t i o n w a s a b o u t t h e s a v e w i t h b o t h t y p e s of f l a p . The pitching-moment c o e f f i c i e n t s a r e g i v e n f o r b o t h t y p e s i n f i g u r e 4 , and t h e hinge-moment c o e f f i c i e n t s i n f i g u r e 5.
The h i n g e moments were a b o q t 50 p e r c e n t g r e a t e r f o r t h e u n b a l a n c e d f l a p t h a n f o r t h e b a l a n c e d one.
F L I G B T TESTS A~a_raws..- The b a l a n c e d s p l i t f l a p w a s t e s t e d i n f l i g h t on a s p e c i a l wing of a n F-22 a i r p l a n e . T h i s wing i s r e c t a n g u l a r i n form w i t h a span of 30 f e e t and a chord of 6 6 i n c h e s . F o r l a t e r a l c o n t r o l t h i s wing i s f i t t e d w i t h t h e r e t r a c t a b l o a i l e r o n s d e s c r i b e d i n r e f o r o n c e 4.
The f l a p ( f i g s . 6 t o 8 ) e x t e n d e d a c r o s s t h e f u l l span of t h e wing w i t h t h e e x c e p t i o n of a 3 - f o o t c u t - o u t a t t h e c e n t e r . The arra,ngement of t h e f l a p w a s g e o m t r i c a l l y s i m - f l a r t o t h a t of t h e model. On t h e f u l l - s i z e d a i r p l a n e ' t h e f l a p c h o r d w a s 10.7 i n c h e s and t h e h i n g e a x i s w a s l o - c a t e d 1.6 i n c h e s below t h e lower s u r f a c e of t h e f l a p and 2 . 1 i n c h e s behind t h e i e a d i n g edge of t h e f l a p . The max- . i m u m d e f l e c t i a n w a s 56 . C o n t r o l of t h e f l a p w a s o b t a i n e d by means of a 22-inch l e v e r i n t h e c o c k p i t moving t h r a u g h a n a r c of 48'. T h i s l e v e r w a s c o n n e c t e d w i t h t h e fiap"by p u s h - p u l l r o d s , equipped w i t h b a l $ m b e a ~ . i n g - ' j o i n t s i n ovdor t o e l i m i n a t e f r i c t i o n . T ~ Q f l a p was c o n s t r u c t e d of L a m i - n a t e d s p r u c e w i t h q i f a b n i c c o v e r .
. ' Tests and result_g,- Tile f i r s t f l i g h t t e s t s showed -I.-- tbat t h e f o r c e r e q u i r e d t o o p e r a t e t h e f l a p w a s s a t i s f a c - t o r y . ' I t was found t h a t t h e f l a p c o u l d be o p e r a t e d r e a d i - l y a t a i r s p e e d s of t h o o r d e r of 6 5 m.p.h., which i s t h e d e s i r a b l e a i r specd f o r o p e r a t i n g t h e f l a p on t h i s a i r p l a n e .
A t t h i s s p e e d t h e p i l o v s e s t i m a t e d t h a t a f o r c e of about 2 5 pounds was r e q u i r e d t o d e f l e c t t h o f l a p . A t t h e o u t s e t t h e f l a p w a s o p e r a t e d s e v e r a l t i m e s a s t h e a i r p l s n e ap- p r o a c h e d t h e ground f o r l a n a i n g s . F a r t h e r t e s t i n g d i s - c l o s e d , however, t h a t t h e a i r p l a n e d i d n o t b a l a n c e l o n g i - t u d i n a l l y w i t h t h e c o n t r o l s t i c k f r s e when t h e f l a p w a s down and t h a t i t would be a a v i s a b l e t o c o r r e c t t h i s condi- t i o n f o r more e x t e n s i v e t e s t s .
P r e c i s e measurements t o d.etermine t h e e f f e c t of t h e f l a p on maximum l i f t i n f l i g h t h a v e n o t beon mado up t o t h e p r a s o n t t i m e . Tho r o n d i n g s o f t h e a i r - s p c o & motor set minimum s p e e d were n o t e d , b n t t h o r e i s somo doubt as t o t h e p r o c i s i o n of t h e r e a d i n g s a t v e r y l o w s p e e d s . Thc wind-tunnel r e s u l t s i n d i c a t e t h a t t h e minimum s p c c d s h o u l d b e rcdnccd nbout 20 p e r c e n t by t h e uso of t h e flap. Tho minirnum s p e c d of t h e 3'122 as flown i n t h o s o t e s t s w i t h the f l a p up i s a p p r o x i m a t e l y 53 m.p.h. Thus, t h e f l a p s h o u l d r c d u c o t h e minimum s p e c d t o a b o u t 43 m.p,h.
Tho c h i e f i n t e r e s t i n t o s t s w i t h t h o s o f l a p s l a y i n d e t e r m i n i n g t h e e f f o c t and t h e d e s i r a b i l i t y of q u i c k oper- a t i o n . I n o r d o r t o mako f u r t h e r t e s t s t o d e t e r m i n o t h e b e h a v i o r of t h e a i r p l a n e m i t h t h o f l a p o p s r a t o d q u i c k l y u n d e r v a r i o u s f l i g h t c o n d i t i o n s , i t w a s d e s i r a b l e t o ob- t a i n l o n g i t u d i n a l b a l a n c o and s t a t i c s t a b i l i t y at lorn speods w i t h t h o s t i c k f r o c . The c o n t o r of g r a v i t y of t h e a i r p l a n e mas s h i f t o d w i t h o u t s a t i s f a c t o r y r e s u l t s and a l a r g e r s t a b i l i z e r was t r i a d (25 p e r c e n t o v e r s i z e ) , Tho l a t t e r m o d i f i c a t i o n had t o be d i s c a r d e d b e c a u s e of s e v e r e t a i l v i b r a t i o n w i t h f l a p s down. A c o n d i t i o n of s t a b i l i t y w i t h s t i c k f r e e and power o f f b o t h w i t h f l a p s up and f l a p s down was f i n a l l y a t t a i n e d by a t t a c h i n g t a b s t o t h e e l e v a - t o r s , These t a b s had a c h o r d of 2 i n c h e s , a s p a n of 2 5 i n c h e s , and were d e f l e c t e d 10' m i t h r e s p e c t t o t h e e l o v a - t o r . Ths a i r p l a n e w i t h power o f f t h e n b a l a n c e d at a speod of 62 m.p,ii. m i t h t h e f l a p s down and a t a spocd of 57 m,p,h, w i t h t h e f l a p s up. I more s a t i s f a c t o r y c o n d i t i o n would be o n e i n v h i c h t h e o r d o r of t h o s p o e d s w a s r e v e r s e d , b u t w i t h t h e b a l a n c c o b t a i n e d i t w a s p o s s i b l e t o p r o c e e d w i t h t h o a d d i t i o n a l t e s t s d e s i r e d .
S e v e r a l t e s t s mere made t o d.etormine t h e b e h a v i o r of t h e a i r p l a u e when t h e f l a p was o p e r a t e d q u i c k l y . With t h e a i r p l a n e g l i d i n g s t e a d i l y at 57 m.p,h. m i t h t h e f l a p %p and s t i c k f r e e , i t =as f o u n d t h a t q u i c k o p e r a t f o n of t h e f l a p c a u s e d a smooth t r a n s i t i o n t o a s t e a d y g l i d e at 62 mop ,he w i t h c o r r e s p o n d i n g changes i n a t t i t u d e and ' f l i g h t p a t h , With t h e a i r g l a n e g l i d i n g s t e a d i l y at 62 rn,p.h.
w i t h t h e f l a p down and s t i c k f r e e , q u i c k o p e r a t i o n of t h e f l a p caused a momentary i n c r e a s e i n speed w i t h one o r two o s c i l l a t i o n s ~ . d u r i n g t h e t , r a n s i t i o n t o a s t e a d y g l i d e a t 57 m.p.h. ' . .
Another t y p e of t e s t was made w i t h t h e s t i c k h e l d back t o o b t a i n a s t e a d y g l i d e at c l o s e t o minimum speed w i t h t h e f l a p s down. The f l a p s were t h e n c l o s e d q u i c k l y and t h e s t i c k r e l e a s e d s o t h a t i t was f r e e t o assume t h e p o s i t i o n c o r r e s p o n d i n g t o a g l i d i n g speed o f 57 m.p.h.
w i t i i t h e f l a p up. T h i s p r o c e d u r e would seem t o be a b o u t t h e worst p o s s i b l e t h a t a p i l o t c o u l d a t t e m p t w i t h f l a p s f o r ' i t l e a v s s t h e a i r p l a n e f l y i n g a t a speed c o n s i d e r a b l y l e s s t h a n . t h e s t a l l i n g speed w i t h ' t h e f l a p s c l o s e d . The ' e f f e c t as o b s e r v e d by t h e p i l o t was t h a t t h e a i r p l a n e seemed t o d r o p a p p r e c i a b l y , t h e n n o s e o v e r , p i c k up speed r a p i d l y , and o s c i l l a t e s e v e r a l t i m e s b e f o r e t h e new s t e a d y glkd'ing c o n d i t i o n w i t h f l a p s up was a t t a i n e d . T h i s t y p e o f o p e r a t i o n m a s re.peated s e v e r a l t i m e s a t a n a l t i t u d e of a b o u t 500 f e e t so t h a t t h e e n s u i n g motion c o u l d b e ob- s e r v e d f f o m t h e ground. The d e c i d e d change i n a t t i t u d e and r a p i d i n c r a a s ' c i n s p e e d were o b v i o u s f e a t u r e s that c o u l d be d e t e c t e d w i t h o u t d i f f i c u l t y . The most i n t e r e s t - i n g f e a t u r e of . t h o ground o b s e r v a t i o n s c o n c e r n s t h o change i n f l i g h t p a t h . By s i g h t i n g a l o n g a s t r a i g h t e&ge h e l d p a r a l l e l t'o t h e o r i g i n a l f l i g h t p a t h w i t h f l a p down an ob- s e r v e r c o u l d t e l l t h a t t b e r e mas v e r y l i t t l e , if a n y , i n - c r e a s e i n s t e e p n e s s of t h e g l i d e a n g l e over t h a t c o r r e - s p o n d i n g t o t h e flap-down c o n d i t i o n . Tne o r i g i n a l f l i g h t p a t h was a p p a r e n t l y m a i n t a i n e d f o r a c o n s i d e r a b l e d i s t a n c e w h i l e t h e a i r p l a n e p i c k e d up s p e e d , s o t h a t t h e r a t e of ' d e s k c n t a c t u a l l y w a s c o n s i d e r a b l y i n c r e a s e d . A s t h e i n - c r e a s e i n aPr speed w a s o b s e r v e d t o be of t h a o p l e r of 50 p o r c a n t , t h e i n c r e a s e i n r a t e o f d o s c e n t , would a p p e a r t o be of t h e samo o r d e r . F o l l o w i n g t h e p h a s e of t h e motion w h e r e i n t h e speed i n c r e a s e d , t h e r e a p p e a r e d t o be a f a i r l y smooth t r a n s i t i o n t o t h e f l a t t e r g l i d i n g p a t h c o r r e s p o n d - i n g t o t h e c o n d i t i o n of f l a p s up. F u r t h e r e x p e r i m e n t s t h e n showed that by t h e u s e of t h e e l e v a t o r s t h e change i n a t t i t u d e a n d a i r s p e e d c o u l d be g r e a t l y r ~ d u c e d and t h e o s c i l l a t i o n s e l i m i n a t e d , t h e e n t i r e t r a n s i t i o n t o t h e now g l i d i n g c o n d i t i o n b e i n g made f a i r l y smoothly.
DiscussLon.- I t s h o u l d be a p p r e c i a t e d t h a t t h e a t t a i n - ment of h i n g e momeqtq. p e r m i t t i n g t h e f l a p t o b e o ~ e r a k e d q u i c k l y by means of a s i m p l e l e v e r w a s a c h i e v e d t o some e x t o n t by t h o u s e of a narrow-chord f l a p a s w e l l a s . b y o f f - s e t t i n g t h e h i n g e a x i s f r o m t h e l e a d i n g edge o f t h e f l a p .
The wind-tunnel t e s t . s i n d i c a t e , bowever,, t h a t tbg flag i s a s e f f e c t i v e a s a p l a i n s p l i t f l a p of a p p r e c i a b l y g r e a t e r c h o r d so t h a t t h e s m a l l h i n g e moments a t t a i n e d f r o m b o t h s o u r c e s a r e a t t r i b u t a b l e t o t h e b a l a n c e d t y p e of f l a p .
From t h e t e s t s of q u i c k o p e r a t i o n of t h e f l a p i t was concluded t h a t d e f l e c t i n g t h e f l a p q u i c k l y f ram i t s c l o s e d p o s i t i o n h a s no d a n z e r o u s r e s u l t s i f t h e t a i l i s d e s i g n e d t o t a k e c a r e of t h e new c o n d i t i o n s of l o n g i t u d i n a l b a l a n c e , The a t t a i n m e n t of l o n g i t u d i n a l b a l a n c e and s t a b i l i t y w i t h f l a . p s i s , however, n o t a s p e c i f i c problem concornod w i t h t h e u s e of a q u i c k l y o p e r a t e d f l a p . A sudden c l o s i n g of t h e f l a p a t mininum speed w i t h f l a p s down i s , of c o u r s e , p o t c n f i a l l y dangerous mhen performed a t vory low a l t i t u d e s .
With t h o a x o r c i s o of r e a s o n a b l e judgment, however, i t seems u n l i k e l y t h a t q u i c k o p e r a t i o n of t h o f l a p ca.n b e r e g s r d c d a,s a n y t h i n g b u t an u n q u a l i f i e d a d v a n t a g e o v e r t h o t y p e of o p e r a t i o n t h a t r c q u i r e s c o n s i d n r a b l o t i m e and e f f o r t . A t t h e F r a s c n t timo i t i s p l a n n e d t o p r o c a o d w i t h f u r t b o r t e s t s i n which a c t u x l measurements of t h e motion f o l l o w i n g q u i c k o p e r a t i o n of t h o f l a p w i l l be m a d e .
Langloy M e n o r i a l A e r o n a u t i c a l L a b o r n t o r r , N a t i o n a l Advisory C o n a i t t o o f o r A e r o n a u t i c s , L a n g l e y F i e l d , V a . , Angust 2 0 , 1934, REFEREFCXS 1. X a r r i s , Thomas A , : The 7 by 1 0 Foot Wind Tunnel of t h e B a t i o n a l Advisory Committee f o r A e r o n a u t i c s . T . R .
N o . 412, X,A,C.R., 1931, 2 . Wenzinger, C a r l J . : !find-Tunnel ideasurement s of A i r ~ o a d $ on S p l i t F l a p s . T . N . No. 498, N . A . C . A . , 1934.
3 . Weick, F r e d E . , and Wenzinger, C a r l 3 , : Wind-Tunnel R e s e a r c h Comparing L a t e r a l , C o n t r o l D e v i c e s , P a r t i c u -
l a r l y a t High Angles of A t t a c k . X I 1 - Upper-Surface
A i l e r o n s on Wings w i t h S p l i t F l a p s . T . R . No. 499, X . A . C . A . , 1934.
4 . Thonpson, Floyd 5.: R e t r a c t a b l e A i l e r o n s f o r Use w i t h Y l a p s . W ..Q,C.h. ( C o n f i d e n t i a l ) Memo. R e p o r t , Docom- b s r 1333.
N . A . C . A .
a , degrees a , degrees Figure 2.- Lift, drag, and o.p. for wing with Figure 3.- Lift, drag, and o.p. for wing with unbalanoed eplit flap.
balanced s p l i t flap.
Figure 6.- Hinge-moment ooeffioient varletion with flap defleoiiion for balanced and unbalanoed flape.
Figs. 7,8 Figure 7,- Flap retraoted.