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Source of Acquisition CASI Acquired Unclassified - Notice remarked 4/17/09 By Thomas 0, Bvss an4 Robert E, Heely L a ~ g l e g &smo rial Aeronaa%%cal LabasaLoPg F [ . ' Y $ jz:; -[; ? l > < < Sept ember 1991 WIND-TUWNEL XNVESTIQATZON OP AN NACA 6692-216 LOW-DRBQ WING WITH S P L I T TLBPS OF VARIOUS SIZES By Thomas C. Uuse and Robert H . Weely An i n v e s t i g a t i o n was conducted i n t h e BACA 19-foot p r e s s u r e wind t u q n e l of a r e c t a n g u l a r wing h a v i n g MACA 66,21216 low-drag a i r f o i l s e c t i o n s and v a r i o u s s i z e s of s i m p l e s p l i t f l a p s . The purpose of t h e i n v e s t i g a t i o n was, p r i m a r i l y , t a d e t e r m i n e t h e i n f l u e n c e of t h e s e f l a p in- s t a l l a t i o n s on t h e aerodynamic c h a r a c t e r i s t i c s of t h e wing. Complete h i f t , d r a g , and pitchine-moment charac- t . e r i s t i c s were d e t e r m i n e d f o r a range of t e s t Reynolds numbers from about 2,600,000 t o 4,SOO,C00 f o r each o f t h e i n s t a l l a t i o n s and f o r t h e p l a i n wing.
The r e s u l t s of t h i s i n v e s t i g a t , i o n i n d i c a t e t h a t v a l - u e s of maximum l i f t . c o e f f i c i e n t s i m i l a r t o t h o e e of wings w i t h c o n v e n t i o n a l a i r f o i l s e c t i o n s and s p l i t f l a p s can be e x p e c t e d of wings having t h e BACA 66.2-216 low-drag sec- tioxrs. The increment of rnaxirnum l i f t due t o t h e e p l i t f l a p was found t o be p r a c t i c a l l y . i n d e p e n d e n t of t h e Reynolds number o v e r t h e range i n v e s t i g a t e d . The o p t f aum s p l f t f l a p - o n t h e b a s i s o f maximum l i f t a p p e a r s t o have a chord about 20 p e r c e n t of t h e wing chord and a d e f l e c t i o n of 60°. The 0- of t h e wing w i t h t h e 0.200 p a r t i a l - Lmax span f l a g d e f l e c t e d 60' is 2.07 at a Reynolds number .of 4,600,000 w h i l e w i t h t h e f u l l - s p a n f l a p i t i s approximate- l y 2.83; t h e increment of t h e maximuin l i f t c o e f f i c i e n t d a e t o t h e f l a p i s approximately p r o p o r t i o n a l t o t h e f l a p span.
Although t h e a d d i t i o n of a spXft f l a p t e n d s t o h a s t e n t h e s t a l l and t o c a u s e i t t o o c c u r more a b r u p t l y , l i t t l e change i n p a t t e r n i s evidenced by o b s e r v a t i o n s of t h e be- h a v i o r o f wool t u f t s on t h e wing.
INTRODUCTIOW .The p r e s e n t n a t i o n a l energency h a s , among o t h e r t h i n g s , g i v e n impetus t o t h e demands f o r h i g h e r sp.eed a i r - c r a f t . However, s e v e r a l p r e s k i n g aero&ynamic problems a r e encountered t h a t have an i n c r e a s i n g l y a d v e r s e e f f e c t on performance a s t h e a i r c r a f t speed r i s e s . One of t h e s e problems i s p r e s e n t e d by t h e c o m p r e s s i b i l i t y b u r b l e which h a s been s o l v e d t o a g r e a t e x t e n t f0.r t h e p r e s e n t neecls by t h e development of t h e EACA low-drag a i r f o i l s e c t i o n s .
These a i r f o i 1 s have, however, proved t o be somewhat s e n s i - t i v e t o s u r f a c e i r r e g u l a r i t i e s and some doubt e x i s t s a s t o t h e e f f e c t i v e n e s s of v a r i o u s h i g h - l i f t d e v i c e s used i n c o n j u n c t i o n w i t h them.
T o d a t e very l i t t l e da,ta a r e a v a i l a b l e on t h e aero- dynamic c h a r a c t e r i s t i c s of low-drag wings w i t h h i g h - l i f t d.evices, a l l b o u g h .some i s o l a t e d t e s t s f o r two-dimensional flow have been made. These t e s t s were not e x t e n s i v e and o n l y a f e a %ypes o f f l a p were t e s t e d .
I n t h e NAbA 29-foot p r e s s u r e t u n n e l , some t e s t s have been made of complete a i r p l a n e models w i t h wings having NACA low-drag a i r f o i l s e c t i o n s . I n t h e s e t e s t s a 20- p e r c e n t - c h o r d s p l i t f l a p and a n e x t e n s i b l e t r a i l i n g - e d g e f l a p mer'e i n v e s t i g a t e d . Although t,hese t e s t s have been f a r from c o n c l u s i v e , t h e r e s u l t ' s , n e v e r t h e l e s s , i n d i c a t e t h a t v a l u e s of s i m i l a r t o t h o s e of c o n v e n t i o n a l c ~ m a x s e c t t g n s mith s p l i t f l a p s can be expected from wings hav- i n g t h e NACA low-drag @ a c t i o n s .
T h i s p a p e r , p r e s e a t s t h e f i r s t p a r t of a n e x t e n s i v e i n v e s t i g a t i o z t o d e t ermiae t h e e f f e c t of v a r i o u s high- l i f t a e v i c e s gn t h e aerodynamic c h a r a c t e r i s t i c s . o f . wings h a v i n g ZJACA low-drag a i r f o i l s e c t i o n s . fn t h e p r e s e n t t e ' o t s t h e s i m p l e s t p h a s e of t h e i n v e s t i g a t i o n was c a r r i e d o u t . That -is, s p l i t f l a p s of v a r i o u s chbrds. and spans were t e s t e d o n a p l a i n wing of r e c t a n g u l a r ' p l a n fbrm. and t h e o h a r a c t e r i s t i c s of t h e combination determined. The remaining p o r t i o n of t h e program w i l l Be devoted t o t h e d e t e r m i n a t f a n of t h e aerodynamic c h a r a c t e r i s t i c s of wings of v a r i o n s p l a n forms u s i n g XBCA low-drag s e c t i o n s i n combination w i t h s e v e r a l d i f f e r e n t t y p e s of h i g h - l i f t d e v i c e s .
UODELS P l a i n Ring The p l a i n wing o r b a s i c model ( f i g . 1) was c o n s t r u c t e d of l a m i n a t e d mahogany, r e i n f o r c e d w i t h s t e e l s p a r s , t o t h e BBCA 66,20216 low-drag a i r f o i l s e c t ion ( f i g . 2 ) . The model, r e c t a n g u l a r i n p l a n form w i t h e l l i p t i c a l t i p s , h a s no d i - h e d r a l o r geometric t w i s t . The span i s 1 5 f e e t , t h e a s p e c t r a t i o 7.0, and t h e a r e a 32.14 s q u a r e f e e t . &n I1aerodynan- i c a l l y smoothn s u r f a c e was o b t a i n e d by s p r a y i n g t h e wing w i t h a number o f c o a t s of l a c q u e r and t h e n rubbing u n t i l smooth w i t h No. 500 w a t e r ' c l o t h .
F l a p s S.imple s p l i t f l a p s of 1 0 , 2 0 , and 30 p e r c e n t of t h e These f l a p s v e r e made of 1/16.
wing chord were t e s t e d .
i n c h g a l v a n i z e d s h e e t s t e e l curved t o approximate t h e con- t o u r o f t h e f l a p p o r t i o n of t h e a i n g l o v e r s u r f a c e .
IVooden b l o c k s , c u t t o t h e a p p r o p r i a t e ehape, were a t t a c h e d t o t h e wing lower s u r f a c e and t h e f l a p t o obtain: each of t h e dersired f l a p def i e c t i o n s . For t h e p a r t i a l - span con- d i t i o n t h e f l a p s extended o v e r 5 3 - p e r c e n t of t h e wing span.
.(See f i g . 1.) T h i s d i s t a n c e was determined a s t h e d i s - t a n c e t h a t e x i s t s between t h e inboard enEs of 0 . 3 ' 7 ; con- ventiona.1 - a i l e r o n s , should t h e y be t2sed. The f u l l - span arrangement of t h e f l a p s extended a l o n g 90 p e r c e n t of t h e o v e r - a l l wing span.
TESTS The t e s t s were conducted i n t h e %ACB 19-foot p r e s s u r e wind t ~ ~ n n e s l a t . a n a b s o l u t e p r e s s u r e of 35 pounds p e r s g a a r e i n c h w i t h the model mounted on t h e s t a n d a r d wing supports.
( s e e f i g . - 3 . ) ' S i n c e t h e p l a i n wing i s used a s t h e b a s i s f o r compar- i n g t h e m e r i t s of t h e v a r i o u s f l a p arrangements, a s e t of complete p o l a r runs was f i r s t made f o r t h i s c o n d i t i o n .
F o r t h e s e r u n s t h e a n g l e of a t t a c k was v a r i e d from -5' t h r o u g h t h e s t a l l f o r dynamic p r e s s u r e s of 13, 20, 40, 70, and LOO pou-nds p e r s q u a r e f o o t c o r r e s p o n d i n g t o t e s t Reynolds numbers'of about 2,100,000; 2,600,000; 3,600,000; 4,600,000; and 5, 600,000. Simultaneous measurements of l i f t and d r a g were recorded by a six-component e l e c t r i c a l - r e c o r d i n g balance. I n a d d i t i o n t o t h e complete p o l a r s , measurements of l i f t and d r a g were made through t h e low- l i f t range f o r dynamic p r e s s u r e s o f 150 and 175 pounds p e r s q u a r e f o o t .
I n o r d e r t o p r o v i d e a b a s i s f o r some comparisori of aerodynamic c h a r a c t e r i s t i c s o b t a i n e d i n t h e s e t e s t s w i t h s e c t i o n c h a r a c t e r i s t i c s o b t a i n e d i n two-dimeasion&l-flow t e s t s , momentum s u r v e y s were rnade i n t h e wing wake a t dynamic p r e s s u r e s of 20 and 49 gound.s p e r s q u a r e f o o t .
These s u r v e y s were made w i t h k r a k e composed of a number of s t a t i c and t o t a l head t u b e s . Measurements were made a t 1 - f o o t i n t e r v a l s a l o n g t h e span except n e a r t h e wing t i p s , w h e r e i n t e r v a l s of about 2 i n c h e s v e r e used. A t each of t h e s e s t a t i o n s t b e a n g l e of a t t a c k was v a r i e d s u f f i - c i e n t l y t o p r o p e r l y bracket t 5 e ainimum- d r a g r e g i o n * For t h e p a r t i a l - s p a n arrangement of t h e 10-percent- chord f l a p s , complete p o l a r r u n s mere a a d e f o r f l a p de- f l e c t i o n s o f f5O, 30°, 4 s 0 , and 60O a t dynamic p r e s s u r e s o f 2 0 , 40, and 70 pounds p e r s q u a r e f o o t . Complete p o l a r r u n s were made f o r t h e f u l l - s p a n f l a p arrangement but o n l y (.
a t t h e 60' d e f l e c t i o n . S i m i l a r l y , t h e v i n g was t e s t e d w i t h 20- and 30-percent chord f l a p s a t t h e v a r i o u s d e f l e c - t i o n s and dynamic p r e s s u r e s . .
I n o r d e r .to study t h e wing s t a l l i n g c h a z a c t e r i s t i c s , w o o l t u f t s were f a s t e n e d w i t h c e l l u l o s e t a p e t o t h e w i n g I u p p e r s u r f a c e a t t t h e 20-, 30-, 40-, 5 0 r , 60-, 700, 800, and 90-percent-chord p o i n t s . These t u f t s were a r r a n g e d i n p a r a l l e l rows spaced a p p r o x i m a t e l y 7 i n c h e s a p a r t a l o n g t h e w i n g span. S l i g h t l y c l o s e r spacing was u s e d n e a r t h e t i p s . S k e t c h e s were drawn from v i s u a l o b s e r v a t i o n s of t h e a e h a v i o r of t h e t u f t s a t v a r i o u s a n g l e s of a t t a c k through
t h e s t a l l f o r t h e ' p l a i n wing, and f a r each of t h e lo-, 20-a
and 30-percent-chord f l a p s def l e c t e d 60' i n t h e p a s t i a l - s p a n arrangement . o n l y . Ths t u f t o b s e r v a t i o n s were made a t a dynamic p r e s s u r e of 70 pounds p e r s q u a r e f0o.t.
C o e f f i c i e n t s The d a t a p r e s e n t e d i n t h i s r e p o r t a r e g i v e n i n stand- a r d nond,imensional c o e f f i c i e n t form c o r r e c t e d f o r t h e e f - f e c t of model support t a r e and i n t e r f e r e n c e , and f o r j e t - boandary e f f e c t s.
The c o e f f i c i e n t s and s ; j b o l s used h e r e i n a r e d e f i n e d a s follovis: 3 . - , . .. - b i L
CL l i f t c o e f f f c i e n t --
qs D
CD d r a g c o e f f i c i e n t --
9s Cm pitching-moment c o e f f i c i e n t about t h e q u a r t e r - U L ~ 4 Be
chord p o i n t of t h e p l a i n wing --
9Sc wing p r o f i l e - d r a g c o e f f i c i e n t C% do
s e c t ion prof i3.e-drag c o e f f i c i e n t -
q c Cao where q , d-yngrpic p r e s s u r e in t h e u n d i s t a r b e d a i r s t r e a m S w i n g a r e a (32.14 sq f t ) c mean r i n g chord (2.14 f t ) b b wing span ' ( 1 5 f t ) p mass d e n s i t y o f a i r , s l u g s p e r c u b i c f o o t and 6f f l a p d e f l e c t i o n measured between t h e lower ' s u r f a c e of tile wtng and t h e f l a p a ' g e o m e t r i c a n g l e between t h e r o o t c h o r d and t h e h o r i z o n t a l a x i s o f t h e t u n n e l a a n g l e o f a t t a c k of r o o t chord c o r r e c t e d f o r j e t - boundary i n t e r f e r e n c e R t e s t Reynolds number based on mean wing c h o r d , & c o e f f i c i e n t o f v i s c o s i t y . - i XI-* *.*/ , > " ' # 1 < * *a , ',. $ 6 , : , y P r e c i s i o n The a c c i d e n t a l e x p e r i m e n t a l e r r o r s a s d e t e r m i n e d f r o m r e p e a t t e s t s are b e l i e v e d t o b e m i t h i n t h e f o l l o w i n g l i m i t s : i 0.0002 .
C d O ( c l = 0 ) wake F l a 2 p o s i t i o n f 0 . 0 0 2 ~ The c o e f f i c i e n t s given a r e c o r r e c t e d f o r t b e e f f e c t of s u p p o r t t a r e and i r t e r f s r e a c e a s determined f o r %be p l a i n wing. Eo s ~ d d i t i ~ n a l t a r e t e s t s were a a d e fai. t h e f l a p i n s t a l l a t i o n s , a s t h e t a r e i a c o e a e n t i s beiiieveCk t o be saall.
The aerodynamic c h a r a c t e r i s t i c s of t h e b a s i c model as determined i n t h e s e t e s t s a r e g i v e n i n f i g u r e s 4 t h r o u g h 6 as t h e z e r o f l a p ' d e f l e c t i o n c o n d i t i o n . By re- f e r r i n g t o t h e l i f t c u r v e s , i t can be seen t h a t up t o a CL of a b o u t 0.1 t h e l t f t c u r v e i s s t r a f g ' a t , but Eetween C L of 0 , l and 0.5 t h e r e i s a clef i n i t e change. Above CL o f a p p r o x i m a t e i y 0.5 t h e l i f t - c u r v e s l o p e becomes progres- s i v e l y l e s s up t o t h e s t a l l . The s l o p e o? t h i s p o r t i o n of t h e l i f t c u r v e i n c r e a s e s and t h e change i n s l o p e , a s mentione,& above, t e n d s t o d i s a p p e a r as t h e Beynolds sum- ber i n c r e a s e s . A l s o , w i t h i n c r e a s e d Reynolds number t h e a n g l e of s t a l l i s i n c r e a s e d .
, d .. .
,a Because of t h e v a r i a t i o a o f t h e p o s i t i o n of t h e aero-+j dynamic c e n t e r w i t h CL, t h e pitching-moment . c o e f f i c i e n S was computed about t h e ving q u a r t e r - c h o r d p o i n t . E,xami- n a t i o n of t h e s e c u r v e i r e v e a l s t h a t t h e pitching-moment c o e f f i c i e n t becoges g r e a t e r p o s i t i v e l y a s t h e a n g l e of a t t a c k i s i q c r e a s e d and t h a t ' t h e r e ' i s a slig2lt s c a l e ef- f e c t , the v a l u e of t a e p i t &ing-nosent c o e f f f c i e n t in- c r e a s i n g p o s i t i v e l y w i t h a n i n c r e a s e i n Iieynolds number.
, .
The s e c t i o n p r o f i l e - d r a g c o e f f i c i e n t s aetermined by t h e momentum method a r e shown i n f i g u r e 7 f o r two v a l u e s o f t h e R e ~ n o l d s number. From t h e s e p l o t s , t h e wing pra- . .
f i l e - d r a g c o e f f i c i e n t , , was determined by i n t e g r a t -
i n g t h e v a l u e s .of a c r o s s t.he span a s s u g g e s t e d adO X c i n r e f e r e n c e 1. The minimun wing p r o f i l e - d r a g c o e f f i c i e k t o b t a i n e d from t h e s e t e s t s a t a n approximate t e s t Reanoliis a m b e r of 2,700,000 i s 0.0038. The a i r f a i l s e c t i o n pro- f i l e - d r a g ' c o e f f i c i e n t s shown on t h e ' f i g u r e a r e i n good 4 agreement with t h e v a l u e s o b t a i n e d from wake aeasuremsnt s of a n a i r f o i l w i t h t h e same low-drag s e c t i o n i n t h e WACA two-dZmensiona1 lorn-turbulence t u n n e l . It . should be L p o i n t e d o u t t h a t t h e t u r b u l e n c e of t h e 19-foot p r e s s u r e t u n n e l i s almost a s low a s t h a t of f r e e a i r a t low t e s t s p e e d s , and i n c r e a s e s s l i g h t l y w i t h i n c r e a s e i n t u n n e l t e s t speed.
Values of minimum prof i l e - d r a g c o e f f i c i e n t of t h e wing o b t a i n e d frorn t h e f o r c e - t e s t measlzrements a e r e con- sicierably h i g h e r t h a n t h o s e o b t a i n e d frorn t h e momentum method. The d i f f e r e n c e s a r e b e l i e v e d t o be due t o t h e d i f f i c u l t i e s involved i n a c c u r a t e l y measuring t h e t a r s f o r c e s due t o t h e model s u p p o r t s i n t h e c a s e of t h e low- d r a g wing, and t o some e r r o r i n t h e momentum measurement due t o t h e d i f f i c u l t y of c o r r e c t l y o b t a i n i n g t h e t i p ef- f e c t s of t h e wing.
. - l i n g w i t h F l a p s The l i f t , d r a g , and pitching-moment c b a r a c t e r i s t i c s ' f o r t h e wing w i t h t h e v a r i o u s f l a p i n s t a l l a t i o n s a r e p r e - s e n t e d i n f i g u r e s 4 t o 6 , i n c l u s i v e , where t h e d a t a a r e p l o t t e d a g a i n s t a n g l e of a t t a c k f o r t h r e e v a l u e s of Reynolds number. ! ! ! h e l i f t c v r v e s , i n g e n e r a l , a r e uniform and c o n s i s t e n t but t h e r e i s some v a r i a t i o n i n t h e shape a t t h e peak. However, t h e change i n s l o p e t h a t a p p e a r s %a e x i s t a t low Reynolds numbers i n t h e l i f t c u r v e s of t h e p l a i n wing i s not e v i d e n t wikh f l a p s d e f l e c t a d . Tbe .elimG i i n a t i o n of t h i s e f f e c t may be due t o t h e d e c r e a s e of a c r o s s flow a t t h e t r a i l i q g edge ovqr t h e c e n t e r p o r t i o n of t h e wing when t h e f l a p s a r e d e f l e c t e d . The s l o p e Of t h e
l i f t c u r v e , s, a p p e a r s t o d e c r e a s e w i t h i n c r e a s e i n
d a f l a p d a f l e c t i o n , w h i l e , on t h e o . t h e r h a n d , f o r a g i v e n .
d e f l e c t i o n , i t t e n d s t o i n c r e a s e w i t h a n i n c r e a s e of Reynolds number.
Examlnation of t h e pitching-moment c u r v e s shows t h a t t h e pitching-moment c o e f f i c i e n t about t h e q u a r t e r - c h o r d p o i n t v a r i e s w i t h Reynolds number and a but t h e v a r i a - t i o n i s not c o n s i s t e n t . The pitching-moment c o e f f i c i e n t does, however, i n c r e a s e n e g a t i v e l y a s t h e f l a p d e f l e c t i o n and f l a p chord a r e i n c r e a s e d . A comparison o f t h e p i t c h - ing-moment c o e f f i c i e n t s o b t a f n e d w i t h a 20-percent-chortl s p l i t f l a p on a n WAC& 23012 a i r f o i l ( r e f e p e n c e 2 ) , w i t h t h e r e s u l t s of t h e p r e s e n t t e s t s , w h i l e not s t r i c t l y com- p a r a b l e , does g i v e v a l u e s of t h e same magaitude.
The v a r i a t i o n of w i t h Reynolds number i s 'Laax . + g i v e n f o r t h e wing w i t h v a r i o u s f l a p s i n f i g u r e s 8a, 8 b , and % c . A marked s o a l e e f f e c t i s n o t i c e a b l e both f o r t h e 4 p l a i n wing and f o r t h e wing w i t h f l a p s . The curve for t h e p l a i n ming a p p e a r s t o g i v e a n approximately l i n e a r v a r i a t i o n between Reynolds numbers of 2,000,800 and 6,000,000 w i t h no i n d i c a t i o n of a n immediate l e v e 1 3 a g o f f . The c u r v e s f o r t h e f l a p p e d c o n d i t f o n a p p e a r de- v i a t e somewhat from a l i n e a r v a r i a t ioa but a o c o n s t i s t e a t change can be d e t e r a t n e d , so t h a t , i n g e n e r a l , t h e r e i s
l i t t l e s c a l e e f f e c t on t h e increment of C . The in-
baa: c r e a s e of AC o b t a i n e d w i t h t h e f u l l - s p a n arrangement Lmax o v e r t h a t o b t a i n e d w i t h t h e p a r t i a l - s p a n f l a p i s approxi- mately p r o p o r t i o n a l t o t h e i n c r e a s e i n f l a p span.
The v a r i a t i o n of AC- w i t h f l a p d e f l e c t i o n i s %ax g i v e n i n f i g u r e 9. ~t t h e d e f l e c t i o n of about 60° t h e c u r v e s a r e b e g i ~ n i n g t o l e v e l o f f , i n d f c a t i r r g t h a t v e r y l i t t l e g a i n i n l i f t c,an be expected b e y o n d . t h i s p o i n t . A c r o s s p l o t of t h e s e c u r v e s ( f i g . 10) showing t h e v a r i a t i o n O f A C ~ m a , w i t h f l a p chord r e v e a l s % b a t v e r y l i t t l e ad- d i t i o n a l l i f t i s o b t a i n e d by i n c r e a s i n g t h e f l a p chord be- yond 20 p e r c e n t of t h e wing chord. From a c o n s i d e r a t i o n of t h e s e two s e t s o f Oata, i t would seem t h a t a 20-percent- chord s p l i t f l a p B e f l e c t e d about 60° would be. about t h e optimum arrangement from c o n s i d e r a t i o n o f C Lmax.
S t a l l i n g C h a r a c t e r i s t i c s The s t a l l diagrams f o r t h e p l a i n wing and f o r t h e wing w i t h each of t h e l o - , 20-, and 30-percent-chord f l a p s d e f L e c t e d 60' a r e g i v e n i n f i g u r e s 11 t o 14. These d i a - grams show t h a t t h e s t a l l b e g i n s i n , t h e r e a r - c e n t e r por- t i o n of t h e p l a i n w i r r g , moving forward and outward w i t h i n c r e a s e i n a n g l e of a t t a c k , The movement a p p e a r s t o be f a i r l y uniform and g r a d u a l , i n d i c a t i n g d e s i r a b l e s % a l l i n g c h a r a c t e r i s t i c s . % i t h t h e a d d i t i o n of f l a p s t h e begin- n i n g of t h e s t a l l i s somewhat d e l a y e d ; once s t a r t e d , how- e v e r , i t d e v e l o p s much more r a p i d l y w i t h complete s t a l l o c c u r r i n g a t a lower a n g l e of a t t a c k t h a n f o r t h e p l a i n wing. The diagrams a l s o i n d i c a t e t h a t t h e p a t t e r n of t h e s t a l l i s n o t g r e a t l y a f f e c t e d by i n c r e a s e s of f l a p chord.
From t h e v i s u a l o b s e r v a t i o n s , however, i t appeared t h a t * .
t h e v e l o c i t y o f t h e inflow n e a r t h e wing t i p s w a s sub- s t a n t i a l l y i n c r e a s e d a s t h e . f l a p chord was i n c r e a s e d , The
. s t a l l diagrams g i v e t h e i m p r e s s i o n t h a t t h e l e f t s i d e o f
t h e wing s t a l l s e a r l i e r t h a n t h e r i g h t s i d e , but t h e d i f - f e r e n c e i s s m a l l and may be d u e t o a s l i g h t asymmetry of t h e wing r a t h e r t h a n t o a n aerodyrarnic e f f e c t .
. - 1, The a d d i t i o n o f a s i m p l e s p l i t f l a p t o a r e c t a n - g u l a r wing, w i t h BACA 66,2-216 lowhdrag a i r f o i l s e c t i o n s g i v e s aerodynamic c b a r a c t e r i s t i c s t.hat a r e a p p r o x i m a t e l p t h e same a s t h o s e o b t a i n e d w i t h s i m i l a r f l a p s on wings h a v i n g c o n v e n t i o n a l a i r f o i l s e c t i o n s , 2. The n o s t f a v o r a b l e s p l i t - f l a p i n s t a l l a t i o n from z s t a n d p o i n t o f C a p p e a r s t o b e ' o n e wft;h a c h o r d o f Lmax a b o u t 20 p e r c e n t o f t h e wing c h o r d a n d d e f l e c t e d a b o u t 60'.
3, The increment o f maxinun l i f t h e t o t h e s p l i t f l a p was found t o be p r a c t i c a l l y i n d e p e n d e n t of t h e Reynolds number o v e r t h e range i n v e s t i g a t e d .
4. The C o f t h e wing w i t h t h e 0,200 p a r t i a l - Lmax s p a n f l a p a e f l e c t e a 60' i s 2,07 a t a Reynolds number o f 4,500,000 and r i t h t h e f u l l - s p a n f l a p t h e C s m a x i s 2,53.
The i n c r e m e n t of t h e maximum l i f t c o e f f i c i e n t due t o t h e f l a p i s a p p r o x i m a t e l y p r o p o r t i o n a l t o t h e f l a p span.
5. The a d d i t i o n of t h e s p l i t f l a p t o t h e r e c t a n g u l a r wing, i n g e n e r a l , r e d u c e & t h e a n g l e of a t t a c k a t which t h e s t a l l o c c u r r e d but d i d n o t a p p r e c i a b l y a l t e r t h e p a t t e r n of t h e s t a l l .
L a n g l e y Memorial A e r o n a u t i c a l L a b o r a t o r y , N a t i o n a l Advisory Committee 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 .
2 . Anderson, Raymond I ? . : The Experimental and Calcu- l a t e d C h a r a c t e r i s t i c s of 22 Tapered Wings. Rep.
0 6 2 1 , WACA, 1938.
2. T e n z i n g e r , Carl J., and H a r r i s , Thomas A.: Wind- Tunnel I n v e s t i g a t i o n of an N.A.C.A. 23012 A i r f o i l w i t h Varions Arrangement s of S l o t t e d F l a p s . Rep.
N O . 654, SACA, 3 . 9 3 9 0 Fig. 1 Figure 2.--0Pdinates f o r the EACA 66,2=/ Bow-drag a i r f o i l section, Fig. 4% HACA (a) R = 2,600,000.
Figure 4a to c. - Aerodynamic characteristics of a rectangular NACA 66,2-. 216 low-drag wing w i ~ h 0,lOc split flap, Fig. 4b NACA (b) R = 3,600,000.
Figure 4.- Continued.
Fig. 4c NACA (c) R = 4,600,000.
Figure 4.- Concluded.
Fig, 5a WACk (a) R = 2,600,000, Figure 5a to c,- Aerodynlmic characteristics of a rectangular NACA 66,2- 216 low-drag wing with 0,20c split flap, Fig. 5 b NACA NACA Fig. 5c Angle o f oh'ack, d, deg ( c ) R = 4,600,000.
Figure 5 , - Concluded.
Fig, 6a NACA (a) R = 2,600,000, Figure 6a to c,- Aerodynamic characteristics of a rectangular N A C A 66,2-.216 low-drag wing wic.1 0,30c split flap, N A C A Fig. 6b ( b ) R = 3,600,000.
Figure 6.- Continued.
Fig, 6c NACA ( c ) R = 4,600,000, Figure 6 . - Concluded, Fig. 7 NACA Big. 8 NACA f i g , l Z Fig. 1 3 NACA