Adjustable cowling flaps, an adjustable-length cowling skirt, and a bottom opening with adjustable flap were tested as means of controlling the rate of cooling-air flow through an air-cooled radial-engine cowling. The devices were tested in the NACA 20-foot tunnel on a model wing-nacelle-propeller combination, through an airspeed range of 20 to 80 miles per hour, and with the propeller blade angle set 23 degrees at 0.75 of the tip radius. The resistance of the engine to air flow through the cowling was simulated by a perforated plate. The results indicated that the adjustable cowling flap and the bottom opening with adjustable flap were about equally effective on the basis of pressure drop obtainable and that both were more effective means of increasing the pressure drop through the cowling than the adjustable-length skirt. At conditions of equal cooling-air flow, the net efficiency obtained with the adjustable cowling flaps and the adjustable-length cowling skirt was about 1% greater than the net efficiency obtained with the bottom opening with adjustable flap

McHugh, James G.

NASA Technical Reports Server

I 
.i 
i 
NAqIQgdL ADVISOBY COMMITTEE FOB ABBo%AUTEC~ 
COMPARTSOB OF TRREE EXIT-AREA COSTROL DZVI  CES 
OD AN N , A ,  C,A. COWLIWG 
By James G. McHuqh 
Langley Hernor ia l  Aeronautical Laboratory 
May 1940 
https://ntrs.nasa.gov/search.jsp?R=20090015113 2019-08-30T06:38:32+00:00Z
COMPARISOB CB THREE EXIT-AREA CONTXOL DEVICES 
By J a n e s  G. XcHugh 
SUMMARY 
A d j u s t a b l e  c o w l i n g  f l a p s ,  a n  a d j u s t a b l e - l e n g t h  cowl- 
i n g  s B i r . t ,  sad a  b o t t o n ,  o p e n i n g  w i t h  a d j u s t a b l e  f l a p  were  
t e s t e d  a s  means of c o n t r o l l i n g  t h e  r a t e  of c o o l i n g - a i r  
f l o w  t h r o u g h  an  a i r - c o o l e d  r a d i a l - e n g i n e  cowl ing .  The 
d e v i c e s  were t e s t e d  i n  t h e  N.B.C.R. 20-foot  t u n n e l  on a 
model w i n g - n a c e l l e - p r o p e l l e r '  c o m b i n a t i o n ,  t h r o u g h  an  a ir-  
s p e e d  r a n g e  of  20 t o  80 c i l e s  p e r  hou.r, and w i t h  t h e  pro-  
p e l l e r  b l a d o  a n g l e  s e t  23O a t  0.75 of t h e  t i p  r a d i u s .  
Tlie r e s i s t a n c e  of . t h e  o n g i n e  t o  a i r  f l o w  t h r o u g h  t h e  cowl- 
i n g  was s i m u l a t e d  by a p e r f o r a t e d  p l a t e .  
The r e s u l t s  i n d  icai;ed t h a t  t h e  a d j u s t a b l e  c o w l i n g  
f l a p  and t h e  bo t tom o p e n i n g  w i t 1 1  a d j u s t a b l e  f l a p  were  
ab,out e q u a l l y  e f f e c t i v e  on t l ie b a s i s  of p r e s s u r e  d r o p  ob- 
t a i n a b l e  and t h a t  b o t h  were  more e f f e c t i v e  means of i n -  
c r e a s i n g  t h e  p r e s s u r e  d r o p  t h r o u g h  t h e  c o w l i n g  t h a n  was 
t h e  a d j u s t a b l e - l e n g t h  s k i r t .  A t  c o n d i t i o n s  of e q u a l  coo l -  
i n g - a i r  f l o w ,  t h e  n e t  e f f i c i e p c y  o b t a i n e d  w i t h  t h e  a d j u s t -  
a b l e  c o w l i n g  f l a p s  and  t h e  a d j u s t a b l e - l e n g t h  c o w l i n g  s k i r t  
was abou t  1 p e r c e n t  g r e a t e r  t h a n  t h e  n e t  e f f i c i e n c y  ob- 
t a i n e d  w i t h  t h e  bo t tom o p a n i n g  w i t h  a d j u s t a b l e  f l a p ,  
INTRODUCTION 
I t  i s  g e n e r a l l y  r e c o g n i z e d  t h a t  a means of c o n t r o l -  
l i n g  t h e  c o o l i n g  a i r  f l o w i n g  t h r o u g h  t h e  b a f f l e s  of r a d i a l  
e n g i n e s  e q u i p p e d  w i t h  ig.8,C.A. c a w l i n g s  i s  n e c e s s a r y  f o r  
o b t a i n i n g  maximun a i r p l a n e  per furmhnce .  The c o n t r o l l i n g  
m.eans, i n  c o n J u n c t i o n  w i t h  t h e  e n t i r e  c o w l i n g ,  s h o u l d  b e  
c a p a b l e  of p r o d u c i n g  s u f f i c i e n t  c o o l i n g  a i r  t o  f u l f i l l  
c e r t a i n  ground o p e r a t i n g  r o q u i r e r n e n t s  and y e t  b e  c a p a b l e  
of 1 i : n i t i n g  t h z  f l ow t o  t l i e  needs  of t h e  e n g i n e  f o r  t h e  
c r u i s i n g  and  t h e  h i g h - s p e e d  c o n d i t i o n s  of f l i g h t .  
A d j u s t a b l e  f l a p s  l o c a t e d  a round  t h e  c i r c u n f e r e n c e  of 1 
a c o w l i n g  a r e  o f t e n  enpXoyod a s  a menns of c o n t r o l l i n g  
a i r  f l o ~ ;  t h e  mechanism, however ,  i s  c o n p l i c a t e d  and t h e  
n a i n 5 e n a n c e  i s  d i f f i c u l t .  Doors e x t e n d i n g  o v e r  s m a l l  po r -  
t i o n s  of t h e  c o w l i n g  c i r c u n f e r e n c e  a r e  s o m e t i n e s  employed 
t o  reg-uce m e c h a n i c a l  c o n p l i c a t i o n s .  R e q u e s t s  f o r  i n f  o rna-  
t i o n  have  b e e n  r e c e i v e d  r e g a r d i n g  t h e  r e l ~ t i v e  m e r i t s  of 
d o o r s  f o r  c o w l i n g - e x i t  c o n t r o l .  
Compara t ive  t e s t s  wore t h e r e f o r e  made of a wing- 
n a c e l l e - p r o p e l l e r  c o m b i n a t i o n  equ ipped  w i t h  t h r e e  t y p e s  
of c o w l i n g  e x i t  opan ing :  conven t  i o n a l  a d j u s t a b l e  f l c p s ,  
a d j u s t a b l e - l e n g t h  s k i r t ,  a n d  a s p e c i a l  bo t tom o p e n i n g  w i t h  
adjustable f l a p .  Mcasurononts  were nade of t h o  n e t  p r o -  
p u l s i v e  e f f i c i e n c y ,  b a s e d  on t h e  d r a g  of a s t r e a m l i n e  
n a c e l l e - w i n g  c o n b i n a t i o n ,  and of t h e  c o o l i n g - a i r  f l ow.  
APPARATUS AND WETHOD S 
The M . A . C . A .  20 - foo t  t u n n e l ,  i n  which t h o s e  t e s t s  
, wero conr?.ucted, i s  d e s c r i b e d  i n  d e t a i l  i n  r e f c r c n c e  1. 
S k e t c h e s  of t h e  model a r e  shown i n  f i g u r e s  1 and 2. Pho- 
t o g r a p h s  of t h e  t e s t  s e t - u p s  a r e  shown i n  f i g u r e s  3 t o  5, 
The wing h a s  a  span  of 1 5  f e e t ,  a c h o r d  of 7.2 f e e t ,  
and i s  of N . A . C . A .  23019.5 a i r f o i l  s e c t i o n .  A 1 1  t e s t s  
were  r u n  a t  z e r o  a n g l e  of a t t a c k .  
The n a c e l l e  u s e d  i n  t h e  i n v e s t i g a t i o n  was 2_0_&& i n c h e s  
i n  d i a m e t e r  a n 6  was f i t t a d  w i t h  an  i n t e r n a l  p e r f o r a t e d  
p l a t o  t o  s i n u l a t e  t h e  r e s i s t a n c e  of a r a d i a l  e n g i n e  t o  t h e  
a i r  f l o w  t h r o u g h  t h e  cowl ing .  The r e s i s t a n c e  of t h e  pe r -  
f o r c t e d  p l a t e  was a d j u s t e d  t o  g i v e  a v a l u e  of c o n d u c t a n c e  
of O d O .  Th i s  q u a n t i t y  i s  p r o p b r t i o n a l  t o  t h e  r a t i o  of 
> 4.b- ,. 
t h e  e n g l n e  o r i f i c e  a r e a  t o  t h e  f r o n t a l  a r o a  of t h e  cowl- 
i n g .  (See  r e f o r e f i c e  2 . )  With t h i s  v a l u e  of c o n d u c t a n c e ,  
t h o  p r e s s u r e  d r o p  a c r o s s  t h e  e n g i n e  o r i f i c e  p l a t e  v e r i e d  
f rom a v a l u e  of h p j q  of 0 . 1 0  t o  a v a l u e  of h p l q '  of 0.70 
f o r  d i f f e r e n t  e x i t  o p e n i n ~ ; ~ .  
b 
A t h r e s - b l a d e  p r o p e l l e r ,  5.75 f e e t  i n  d i a n e t e r ,  was 
c o n s t r u c t e d  f r o n  C u r t i s s  p r o p e l l e r  d rawings  nos .  88980 
and  88981 and t h e  b l a d e s  were s e t  a t  23O a t  0.75 of t h e  - 1 
t i p  r a d i u s .  A s c a l l  sp i 'hner  was f i t t e c ?  Co t h e  p r o p e l l e r  
hub t o  i n p r o v e  t h e  c o o l i n g  c h a r a c t e r i s t i c s  of t h e  cowl ings .  
The e l e c t r i c  motor  u s e d  t o  d r i v e  t h e  p r o p e l l e r  d e v e l -  
o p s  1 5  horsepower  a t  1 , 1 5 0  rpm. I t  n s s  mounted i n s i d e  t h e  
wing ,  and  t h e  p r o ? e l l e r  w a s  d r i v e n  t h r o u g h  a n  e x t e n s i o n  
s h a f t .  
Each c o w l i n s  a r r angemen t  was t e s t e d  a t  s e v e r a l  d i f -  
f e r e n e  v a l u e s  of  t h e  c o w l i n g - e x i t  a r e a .  For  c o n v e n i e n c e ,  
t h e  t e s t  c o n d i t i o n s  a r e  t a b u l a t e d  a s  f o l l o w s .  
# 
Type of e x i t -  
a r e a  c o n t r o l  
C o n t r o l l a b l e  
cowl ing  f l a p s  
V a r i a b l e -  
l e n q t h  c o k l -  
i n g  s k i r t  
Bot tom open ing  
w i t h  a d j u s t -  
a b l e  f l a p  
I 
C o n l i n g - e x i t  l E x i t  a r e a  
F l a p  a n g l e  ( d e g ) :  
0 
9 
20 , ' 
30 
40  
50  
R a t i o  of  e x i t  
a r e a  t o  n a c e l l e  
I 
--------I---------- - - - ---- + ----- ----- 
F l a p  a n s l e  ( d e g )  : I i 
0  15 .9  1 I 0.049 1 0  4 2 . 0  , 130  
One t e s t  was n:ade w i t h  t h e  p r o p e l l e r  removed, t h e  , 
e x i t  s e a l e d ,  a n d  v i t h  a  l a r g e  nose  f a i r i n g  added  t o  t h e  
n a c e l l e  ( f i g .  2 )  t o  e s t a b l i s h  a  b a s i s  f o r  computing t h e  
n e t  e f f i c i e n c y .  
c o ~ l d i t i o n  I ( s q  i n .  ) I  c r o s s - s e c t i o n a . 1  
a r e a  
20 1 65.6 
30 i 94.0  
RESULTS AiJD DISCVSSIOil 
. 203  
- 2 9 1  
A l l  d z t a  a r e  r edu -ed  t o  s t a n d a r d  nondin icns iona l  c o e f -  
f i c i e n t  s .  The s ~ m b o l s  and  c o e f f i c i e n t s  i n v o l v e d  a r e  de- 
f i n e d  a s  f o l l o w s :  
E x i t  zap  ( i n . ) :  
0.25 ' 15.9 I I .049 
. 78  49 .0  . I 5 2  
1 .50  1 81.1 1 . 2 9 1  
q  dynamic p r e s s u r e  of a i r  ( 1 / 2  p  v'). 
p  mass d e n s i t y  of a i r .  
V v e l o c i t y  of a i r  s t r e a m .  
n  p r o p e i l e r  r e v o l u t i o n  speed .  
D c  d r a g  of s t r e a m l i n e  nace l le -win .$  c o m b i n a t i o n  t a k e n  
f rom d r a q  t e s t  a t  same v a l u e  of q.  
B n e t  f o r c e  on t h r u s t  b ~ , l a , n c e .  
D d i a m e t e r  of p r o a e l l e r ;  
P power supp l - i ed  t o  p r o p e l l e r .  
V / ~ D  advance -d i ame te r  r a t i o  of p r o p e l l e r .  
maxlnnrn qo f r o &  p l o t  o f  To a g a i n s t  v / ~ D .  
'0IEax 
Ap p r e s s u r e  d r o p  a c r o s s  e n q i n e  o r i f i c e  p l a t e .  
-- --...--- 
~ P I P ~ '  2 p r e s s u r e  c o e f f i c i e n t .  
coivl in<-exi  t a r e a ,  
-__-___-___-___-_-_--_-I-.---- -- . 
'l n a c e l l e  c r o s s - s e c t i o n a l  a r e a  
' K conduc tanca  o f  e n q i n e  /-.?!!J-- 
Q q u a n t i t y  o f  c o o l i n g - a i r  f l o w .  
F mnxi~::un c r o s s - ' s e c t i o n a l  a r e a  of n a c e l l e .  
F o i r e d  c u r v e s  of qo a r a i n s t  V / ~ D  a t  d i f f e r e n t  
e x i t  c o n d i t i o n s  a r p  shovn f o r  t h e  a d j u s t a b l e  c o a l i n g  f l a p s ,  
t h e  a d j u s t a b l e - l e n g t h  cowl ing  s k i r t ,  and  t h e  bo t tom open- 
i n s  w i t h  a d j u s t a b l e  f l a p  i n  f i q u r e s  6 ,  7 ,  a ~ i l  8 ,  r e s p e c -  
t i v e l y ,  These f i g u r e s  s h o ~  a p r o g r e s s i v e  d e c r e a s e  i n  
v i t h  i n c r e - t s e  i n  c o w l i p q - e x i t  a r e a .  '?::is e f f e c t  i s  - I 
'omax 
l a r g e l y  due t o  t?te i n c r e a s e  i n  c o o l i n y - a i r - f l o w  d r a q  w i t h  
i n c r e a s e  i n  c o w l i n g - e x i t  a r e a .  - . a  
/--I----- The v a r i a t i o n  of p r e s s u r e  c o e f f i c i e n t  ,, ~ p / ~ n ' D '  
w i t h  K 1  f o r  s i x  v a l u e s  of V / ~ D  i s  shown f o r  t h e  ad- 
j u s t a b l e  cowl in% f l a p s ,  t h e  a d j u s t a b l e - l e n g t h  c o w l i n s  
s k i r t ,  a n d  t h e  bo t tom o ~ e n i a g  w i t h  a d j u s t a b l e  f l a p  i n  
f i g u r e s  9 ,  1 0 ,  a n 8  11, r e s p e c t i v e l y .  The v a l u e s  t h e r e i n  
g i v e n  a r e  a v e r a g e  ~ r a l n e s ;  no measurements  n e r e  made of 
t h e  d i s t r i b u t i o n  of f l o r  t h r o u g h  t h e  c o r l i n s .  
Comparison of t h e  r e s u l t s  r e v e a l s  t h a t ,  w i t h  t h e  p a r -  
t i c u l a r  d imens ions  c3osen ,  t h e  cornling f l a p  and  t h e  b o t -  
tom o p e n i n g  a r e  a p p r o x i m a t e l y  e q u a l  i n  m e r i t  on  t h e  b a s i s  
of p r e s s u r e  d rog  o b t a i n a b l e  a n d  t h a t  b o t h  p r o v i d e  h i 3 h e r  
v a l u e s  of ? r e s s u r e  d r o p  t h a n  t h e  a d j u s t a b l e - l e n g t h  coivlin? 
s k i r t .  I t  i s  t h e r e f o r e  p o s s i b l e  t h a t ,  f o r  o t h e r  a r r a n q e -  
men t s  I n  which t h e  f l a n  c h o r d  i s  l o n q e r ,  t h e  a d j u s t a b l e  
c o w l i n g  f l a p  mi.$ht y i e l d  g r e a t e r  v a l u e s  of F r e s s u r e  d r o p  
t h a n  e i t h e r  of t h e  o t h e r  tmo a r r a n g e m e n t s .  
I n  o r d e r  t o  make compar i sons  of V O m a x  f o r  c o n d i t i o n s  
of e q u a l  c o o l i n $ - a i r  f i o w ,  t h e  v a l u e s  of Tomax  a n d  V / ~ D  
a t  " ~ m a x  Tor e a c h  a r r a n g e n e n t  t e s . t e d  were o b t a i n e d  from 
f i g u r e s  6 ,  7 ,  a n d  6.  The corres:)onding v a l u e s  of 
------- 
f i p / p n 2 D "  were  o b t a i i ~ e d  from f i g u r e s  9 ,  1 0 ,  a n d  11. F o r  
e a c h  a r rang ,e rnent ,  t h e  v a l u e  of ~ p / ~  o b t a i n e d  a t  t h e  con- 
d i t i o n  of Tomax was computed from t h e  r e l a t i o n  
T3.e r e s u l t s  of t h i s  c o m p u t a t i o n  a r e  g i v e n  i n  f i g u r e  
1 2 ,  w h e r e i n  
'om,x 
i s  p l o t t e d  a s  a f u n c t i o n  of Ap/q 
f o r  t h e  t h r e e  e x i t - a r e a  c o n t r o l  d e v i c e s .  Throuqhout  t h e  
r R n g e  of v a l u e s  of a t  which  cornTayisons can  be 
, .  made, t h e  v a l u e s  of Q o m X  o d t a i n e d  a - i t h '  t h e  bot tom open- 
i n s  m i t h  2 d J u s t a b l . e  f l a p  a r e  a p p r o x i m a t e l y  1 p e r c e n t  l ower  
t h a n  t h o s e  o b t a i n e d  w i t h  t h e  a d j u s t a b l e  c o v l i n g  f l a p  and  
t h e  a d j u s t a b l e - l e n g t h  cowl ing  s k i r t .  I n  a l l   case^, t h e  
v a l u e  of q O m a x  d e c r e 2 s e s  w i t h  i n c r e s s i n <  v a l u e  of A p / q ,  
a s  would - ~ e  e x s e c t e d .  T3rou.ghcvt t h e  g r e a t e r  u o r t i o n  of 
t h e  r n n q e ,  t h e  decre:?-se i n  w i t h  i n c r e a s l n :  v a l u e  
'Qomnx 
o f  ~ p / ~  i s  m a i n l y  due t o  t h e ,  i n c r e a s e  i n  c o o l i n g - a i r -  
f l o w  d r a s  t h a t  o c c u r s  v i t h  i n c r e a s e  i n  apIq.  A t  h i g h  
v a l u e s  of d p I q ,  however ,  t h e  r a p i d  d e c r e a s e  i n  
'omax 
i s  l a r ~ e l y  chr\ .r%eable t o  t h e  f a c t  t h a t  l a r s e  e x i t  a r e a s  
i n c r e ? s e  t h a  form d r a ?  by d i s t u r b i n g  t h e  f l o w  o v e r  t h e  
n a c e l l e .  
CON CLUDIRG BE3hABK.S 
The r e s u l t s  i n d . i c z t e  tkfiat t h e  a d j u s t a b l e  comlinq f l a p  
a n d  t h e  bot tom o v e n i a g  m i t h  a d j u s t a b l e  f l a p  a r e  a b o u t  
e q u n l  i n  m e r i t  on t h e  b s s i s  of p r e s s u r e  o b t a i n a b l e  a n d  
t h a t  b o t h  a r e  more e f f e c t i v e  t h a n  t h e  a d j u s t a b l e - l e n g t h  
c o w l i n g  s k i r t .  
Fo r  e q u n l  c o o l i n g - a i r  f l o m ,  t h e  maximum n e t  e f f i -  
c i e n c y  o b t a i n e d  f o r  t h e  a d j u s t a b l e  cowl in$  f l a p s  a n d  f o r  
t h e  a d j u s t a b i o - l e n g t h  cowl ing  s k i r t  mas a b o u t  1 p e r c e n t  
s r e ~ t e r  t h a n  t h a t  o b t a i n e d  f o r  t h e  5 o t t o n  open ing  w i t h  
a d j u s t a b l e  f l a p .  
No ~ x ~ e a s u r c m e n t s  were made o f  t h e  d i s t r i b u t i o n  o f  f lom 
t h r o u q h  t h e  cowl ing .  Such measurements  m i l l  be n e c e s s a r y  
b e f o r e  d e f i n i t e  c o n c l u s i o n s  c a n  be d.ravn concerning t h e  
r e l a t i v e  c o o l i n g  q u a l i t i e s  of t h e  a r r a n g e m e n t s  t e s t e d .  
L a n ~ l e y  I ~ i e n o r i n l  Aeronnu-t i  c n l  L a b o r a t o r y ,  
N a t i o n a l  A d v i s o r y  Committee f o r  A e r o n a u t i c s ,  
L ~ n g l e g  F i e l d ,  Va., March 1 2 ,  1940.  
1, V e i c k ,  F r e d  E . ,  and  Wood, DonTld H . :  Tho Tmenty-Foot 
P r o g e l l e r  R e s e a r c h  Ttxnnel. of t h e  R a t i o n a l  A d v i s o r y  
Committee f o r  A c r o n n u t i c s .  T . B .  No. 3 0 0 ,  X . B * C * A * ,  
1928. 
2 .  Theodor sen ,  ~ h e o d o r e ,  B r e v o o r t ,  M. J., 2nd S t i c k l e ,  
George W .  : F u l l - S c n l e  T e s t s  of U . A . C . A .  Cowlings.  
T . R .  No. 5 9 2 ,  B.A.G.A., 1 9 3 7 .  
Figs. 1,2 
To fa/ pressure 
Per forofed plate ; 
I ,  E / ~ c ~ ~ / c  for ~ f ~ f i c  pressure : : A - -- - - , ,-- 
g 
t ~ 3  
Sec fion of hinge axis 
Figare 1.- Wing-nacelle combination with cowliag 
for tes t  of bottwn epeniag with adjuetablo ffzp. 
Tofal pressure 
Perforated plate . , ::' 
Static pressure ;; 
I Section A - A  
Figure 2.  - Wiag-mcsPPe combimation with uowlir@ art 
for t a r t  s f  cowling flaps and adjustable-le-h 
cowling ski l t t .  
Figtare 3.- Adjuetebla cowling flap s@l-up. 
H.A.C.A. 
Figwe 6.- Comparison of 
net efficiency 
obtained with various 
cowling flap angles. 
N.A.C.A. e m l e d  nacelle 
with adjustable cowling 
flaps. 
Figure 7.- Comparison of 
net efficiency 
obtained with various 
skirt lengths. N.A.C.A. 
cowled nacelle with 
adjustable-length skirt. 
Figure 8.- Comparison of 
net efficiency 
abtained with various 
exit flap settings. 
Bottom opening with 
adjustable flap. 
1.6.C.A.  Figs. 9,10 
Figure 9 . -  Variakicn o f  pssswre eoetffieient with emit area. 
Adjustable cowling f lape.  
Figure 10.- Variation of pressure coefficient with axit area. 
Adjustable-length cowling skirt. 
Fige. 11,12 
F i e x w  12.- Variation of prsasure eoeff'ieient with exit arm. 
Bottm speniplg with adjustable flap. 
B 12,- Variatisn of q vi%h Ap/q for nvims t y p e  
af cowling exit-area control. 


Comparison of Three Exit-Area Control Devices on an N.A.C.A. Cowling, Special Report

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