The lift, drag, and center of pressure characteristics of a model of the Fowler variable-area wing were measured in the NACA 7 by 10 foot wind tunnel. The Fowler wing consists of a combination of a main wing and an extension surface, also of airfoil section. The extension surface can be entirely retracted within the lower rear portion of the main wing or it can be moved to the rear and downward. The tests were made with the nose of the extension airfoil in various positions near the trailing edge of the main wing and with the surface at various angular deflections. The highest lift coefficient obtained was C(sub L) = 3.17 as compared with 1.27 for the main wing alone

Platt, Robert C

Weick, Fred E

English

NASA Technical Reports Server

, 
CASE 
CO 
TE CHN ICAL NOTZS 
FI~E 
Py 
NATIONAL ADVISORY COMAITTEE FOR AERONAUTICS 
No . 419 
WIND- TUN~EL TESTS OF TEE FOViLER VARI ABLE- AREA WING 
By Fred E . Weick and Robert C. Platt 
Langley Me morial Aeronautical Laboratory 
Washin g ton 
Ma y, 19 32 
Reproduced by 
NATIONAL TECHNICAL 
INFORMATION SERVICE 
Springfield, Va. 22151 
https://ntrs.nasa.gov/search.jsp?R=19930081218 2020-03-17T04:01:49+00:00Z
NAT IONAL ADV I SORY COM~H T'TEE 'FOR itEROHAUT I CS 
TECHNICAL NOTE ~O!~l~ 
WIND-TUNNEL TESTS OF THE FOWLER VARIABLE-AREA WING ' 
By Fred E. Weick and Robert ' C~ Platt 
SUMMARY 
The lift, dr'ag, and center of pressure' cnaracteris-
tics of a model of "tne Fowler variab1e·~area win g were 
measured in the N.A.C.A. ,7 by 10 foot wind tunnel. The ' 
Fowler wing consists of a combination of a main wing and 
an extension' surface, also of a irfoil sec t ion. The exten-
sion surface can be entirely retracted ' within the lower 
rear portion of the main wing or it c an be moved to the 
rear and downward . The tests were made with t h e nose 
of ~he exterisiori "airfoil in vario~s positions near the 
tr ai ling edge 'of ' the mai n wing and wi t:o. the surf a ce at 
various angul a~ def~ections; Tlie highest lift coe ff icient 
o bt aine'd was 0L'= 3.17 as C'ompar ed wi th 1.27 f or the 
main wing alone~ 
I NTRODUCTION 
The Fowler wing, developed by Harlan D. Fowler, is 
the result of an attemp t to combine three different meth-
ods of increasing the maximum lift. 
, , 
1. 
2. 
Increasing the area 'by me an s of an ext in-
sion surface. 
Increasing the effective camber by means of 
a flap. 
Providrng a slot to h elp maintain unbur b1ed 
flow at ~igh angles of attack. 
The combining ' of th~se 'methods is accomplished by means 
of ' an eX,tension s,urface, which is a sort of flap having 
an airfo'i'l 'section. The e xtension a irfoil is retracted 
into the lower rear p ortion ' of the wing wh e n not in us e 
but is extended to the, re a r , and downward. when, high lift 
is desired. CFi,g. 1 ~) ' The ,gap that is l 'eft between the 
main wing and the extension ' airfoi1 f orms ' a slot to main-
2 ,rr • A. C • A • T~. c h.:tl i cal .. Not e H o. 419 
tain unburbled air flow over the rear airfoil at the high 
angles of attack. 
Previous wind- tunn el tests on models of 3 - inch chord 
at both Massachusetts Institute of Technology and New York 
University, and ful l-scale flight tests have all shown ex-
ceptionally high lift coeffici ents with ,the Fowler wing 
a rrang ement. (Reference 1 . ) The present tests were made 
as part of a series on high-lift devices in the 7 by 10 
foot wind tunne l of the National Advisory Committee for 
Aeronautics . The Cl ark Y a.irfoil section was used for 
bo~h the basic w~ng and the extension airfoil and the 
tests were mad e to co~er , ~ range of ~lots and angular de-
flections of the extensio~ airfoil. ' 
APPARATUS AND METHOD, 
The Fowler wing model used in these - t 'ests consisted 
of a basic Clark Y wing with a 10-inch 6hotd and 60-inch 
span , and a ,Clark Y extension airfoil havi 'ng a chord 40 
per cent that of the mai n wing . (~ee iigs. 1 and 2 and 
Table I.) The' extension airfoil and the forward portion 
of the main wing were c onstructed of laminated mahogany . 
The rear portion of the m~in wing, which followed only tne 
upper c ontou r of the Clark Y p ro file , was made of a 1/32 
inch stee l p l at e rolled to the proper curvature and stiff-
ened by ribs spaced 5 inches apart. The extension air-
foil was supp o'rted by means o f five e'qually spaced metal 
plates attached to fi ve of the ribs, and capable of ad-
justment to give different positions and an gular deflec-
tions of the rear airfoil. 
The extension airf oil coul d not be comp letely retract-
ed into the model wing because of interference with the 
ribs; therefore , in the tests representing the retracted 
condition the main wing was fitted with a p late covering 
the rear 4 inches of the lower surface. 
Tests'were made with the nose of the extension air-
foil in nine positions (shown in fig . 1) covering the 
range giving the b est slots. At each of these nose loca-
tions t .he ,angular deflection of the extension airfoil was 
varied throughout .the require d range. 
The 7 by 1 0 ~oot ' wind turinel, which is of t e open-
,jet type, is described .in detail tog'ether with. the bal ... 
N.A.C.A: "'1"echni"ccil ' Hote No~ 419 ·· ·· 3 
ances and standard test proce dur~ in reference 2. Be-
caus~ of the ,high lift obt-a~ned vi'ith ' the Fowler wing mod-
el , . i t . was supported by a;fi,ne wire , at each wing tip in 
addition to "the usual C6:ntE3T support. 
The tests were mad e at an air s~eed of 80 m.p.h., 
corresponding to 'a Reynolq.s Number of 609,00 0. First t :'1C 
v alues of CL max were fbund f or the various angular de-
flections at each, location of the nose. Tnen comp lete 
lift, dr a g, and center of press~re tests were made for 
the six p osi tions giving the highest m~xim~m lift coeffi-
cients . Corroctions were not made for tunnel wall e f f6c~ • 
. 
RESULTS AND DISCUSSION 
Curve s of CL m.aX (based on the area of the basi c 
wing) a g ainst flap angle are g iven for each location of 
the nose of the extension airfoil in Fi gures 3 to 5. From 
the n aximum values in' these curves contour lines were p re-
pared Which show the various p ositions giving t h e same 
value of maxi mum lift . · (Fig. 6 .) Tile v a lues in Fi gure 6 
represent the deflection which g ave the hi gnest value of 
CL max at each location. 
The highest value of CL u~x' 3 .17, was obtained 
with the nose of the extensfoti airfoil i n p osition 5. 
(Soe fi g . 1.) This is the loc a tion sug~~sted by Mr. Fow-
ler. It is believed t hat t h e lift coefficient of 3 .17 is 
the highest that h a s been . ob tained to date from a d evico 
readily applicable to norma l airp lane con struction. 
Curve s of CL ' CD ' and c. P . are g i ven in Fi gure s 
7 to 12 for the best positions of the extension airfoil 
and are comp ared with similar curves for the case wit h th e 
extension airfoil retracted . Th e maxi mum lift coe ff i c ien t 
obtaine d with the p lain wing was 1.27 as comp are d wit h 
3.17 with t h e best exten d ed position . 
The mini mum drag coef ficient f or t h e retracted co nd i-
tion Wa s 0.01 56 . (Ho e~;:ternal fl ap supp orts were in p l a ce 
for this t ,est.) , T ~l e sp eed rang e ratio , CL ,max/CD min' . t l'l e 
maximum' 'lift coefficient bei ng t a ken wit h t h e , r'lap' down ' a t 
the best Idcation and the mi~imum drAg cQeffi~ien t wit h the 
fl ap retracted, Was 203 as comp ared with 87 for the main 
Clark Y wing alone. 
4 N.A.C,A. Technical Note No.419 
, At angles of a t tack a b ove 0 0 t h e center of pressure 
with the extensio~ airfoil ext~nded Was about 25 per cent 
of the chord behind tne center of pressure for the plain 
Clark Y. Although this difference may seem excessive, it 
is no't 'li1cely to lead to great trouble in connection with 
the balance 'of an airplane be·caus'e the dOiTnwash is suo-
stantially great~r with the surface extended, which in-
creases the download on the tail. 
To investigate the possibi lit y of redu cing the Elotion 
' of the c.p. caused by extendin g the surface, a comp lete 
test a~ the best positi on of the nose of the ' exten~ion 
airfoil Was made ~ith a reduced flap angle (25 0 ). The 
curves for flap angles at 25 0 and 40 0 (fig. 11), ho wev e r, 
show very little difference in c. p . for t h e two setting s, 
Effect on airp~~~~erfo~m~~£~o- If the wing of an 
average parasol monop lane were mo d i f ied to include t h e 
FOWler· extension airfoil arrange ;"1 ent, the g ross wei gh t be-
ing assumed unchanged for .;:;implicity, t h e p resent tests 
indicate that the minimum glidi~g s p eed wou ld be decreased 
to less than 2/3 of the origiiai valu s. If the extension 
device required . no exterh~l ~upport~ or mech~nism, the 
high speed would of course remain t h e same. 
If the ::o·ri g inal landing speed "Were desired and the 
ori ginal gr 0 s s weight main t ai ned, t h e basi c 10'>71 er wing 
could be reduced to 40 per cent of t h e original area, and 
the high speed would be increased some what (in the n ei gh-
borhood of 5 per cent for an average presen t~dai airp lane). 
CONCLUSIONS 
1. With the extension airfoil in the be 'st position 
a maximum lift coefficient of 3 , 17 wa s obtained for t h e 
Fowler wing model as compared. with 1027 for the basic wing. 
2 . To obtain the high maxi mu m lift coefficien ts Df 
which this combination is capable, t he extension airfoil 
must be located within close limits of the b est position. 
Langley Memorial Aeronautical Lab oratory, 
National Advisory Committee for Aeron autics, 
Langley Field , Va., April 12, 1 93 2. 
N.A.C.A. Technical Not e No. 419 
REFERENCES 
1. Fowler, Harlan D.: Variable Lift. Western Flying, 
November, 1931. 
2. Harris, Thomas A.: The 7 by 10 Foot rrind Tunnel of 
the National Advisory Committee for Aeronautics. 
T.R. No. 412, N.A. C. A., 1931. 
/ 
5 
• 
N .A. C.A. Techn i cal Note No . 4 1 9 6 
TAB LE I 
AIRFOIL OF-DINA-TES 
(All values in per cent airfoi l cho r d ) 
Clark Y 
Ste.tion Or dinate Ordinate Upper Lower 
0 3 . 50 3.50 
1 . 25 5 . 45 1.93 
2 . 50 6 . 50 1 . 47 
5.00 7.90 .93 
7.50 ~ . ~5 . 63 
10.00 9 . 60 . 42 
15·00 10 . 69 . 15 
20.00 11 . 36 . 03 
30 . 00 11 . 70 0 
40 . 00 11 . 40 0 
50 .00 10 . 52 0 
60.00 9 . 15 0 
70 . 00 7 . 35 0 
80 . 00 5 . 22 0 
90 . 00 2 . 80 0 
95 . 00 1 . 49 0 
100.00 . 12 0 
Leading edge r adius = 1.50 
z 
~ 
0 
. 
~ 
. c ------- --
8 
CD 
,----- --- -----l -------I 
Position A% c + E% c 1 
r-1-- - ~~ __ 1. 2~~ r= 2 ·· 5 . 00 ; 2 . 5~_1 
-- 3 - 5 ~g~_~_-~-!..?5 _ 
4 O. 00 I 1. 25 I 
I 
A -, 
0 
::r 
::s 
1-" 
0 
E 
p 
f-' 
I ~ 0 ci-
CD 
I 
z 
I 
0 
,p.. 
f-' 
lD 
~--- 40% c -- -
- ~---_Iy~~.~ ~-----~"cI 9 A 
,- - - - - u - -- - ).=-----:::;8 ( 0 _~~
-- - ;/4 16 1 
l-I 
Both airfoil sections a r e Clark Y 
Extended fl ap posi tions 
5 I 0 . 00 i~ 2 . 50 ~ 
\==6 0 . 06- 3 . 75 I 
1--=7-~-5 .OO-f- 1 . 25 =~~-- ~-- -;~ 6t-i - - -~ : ~~ 
FiG.l Section of Fo~ler wing. 
b;l 
1-'-
aq 
f-' 
R.A.C.A. Technical Note No.419 Fig.2 
N.A. C.A. Technical ~Jote No . 4:19 Fig . 3 
I I I -n 3 .0~-J ~I I 
-.-+--~.--+~ .. -:~--~ -----+~. x-'\- -_~ I 
/ I \ !-- I -.~---...j,L---f ---\"+ j 
/ . \l I 
_J I f-----j V I I I 
--- / --t---~---
) 2. 5 ---I-~--i 
----~. I I ~----
I I I Pos~lt ion ~f ' ~=I-.-:t f----f--- t-T 3-n~-
~--+--+'--I I I . 
I I I I I ' ------1--·.......f---~----j--i-_l 
I I I ' 
2. c ---+-----+---I·--·-r--·i-~--l 
I I I 
I I -t--
I i! 
- - _.+----1-
25 35 45 
Flap angl e , degr ee s 
Fi g . 3 Varia tion of CL with fl ap angle. max 
N.A.C.A. Technical Hote No . 419 
1- ---r--' -I-----T-- ----' 
1------1-- - , -- '- f :----t--~ 
~------ ,------~---------1 
I ____ -i\----r Ii 
, 7/ --- t\I ----i 
·-++-l - + +-, 
, - \ I I 
-----1------. I ---+--\t-----I 
3 . 0 
I . i \ I Ji 
, -- --1-t-- i 
} 2 . 5 ----1--- - .---- -- ----:---T--' 
--.--+-~. --- -- -:- -T--I 
1-----+----+-.-- - - __ --+-_J_ ----,--1 
. i I I I Po s ~ t jLOl1 :rJo 4 -+- -~--+x I 
11 1 11 5 1 -+o~ +-----+--11 --" 6 u--I=-fo i 
---I----i-----L--~ 
I I I ! ! -+-------l---~ - - ' ---l---- f --- I 1 
I I I I I I I----s~_jjj=~tj 
2. 0 
25 35 45 55 
Flap angl e , degrees 
Fi g . 4 Varia t i on or Cr. wi th f l ap angl e . 
~ax 
Fig . 4 
N.A.C.A. Technical Note 1To . 4l9 
25 35 45 55 
Fl ap angle, degree s 
Fig . 5 Variation of CT_ with flap ~~gl e . ~lHax 
Fig . 5 
Chord line ~ 
v 
Dimens ion B 
Posi tio~s shown thus 5 o 
1. 25 -
2.50 -
3 . 75 -
5 . 00 L 
1 
° 
3 (0 
- 5 
T raili~g edge of ba sic airfoil 
I 
/ 
v 
~:__ 4;~~\\ 6 c,,~_ ~~\\~ 
~ / ' ) I} \\~~ 3 .0~2.~ ~~ .,1 \).40 
I 12 • 00 1 
o 2.60 5 
Dimension .A 
Fig . 6 Contours showi ng varia tion of CT. VIi th position of nose of extension airfoil. lIlax 
z: 
. 
:t> 
o 
. 
:t> 
1-3 
CD 
o 
::r 
~ 
1-'. 
o 
III 
I-' 
z: 
o 
c+ 
CD 
~ 
o 
,p> 
I-' 
~o 
boj 
1-'. 
()q 
en 
B.A .C.A. Technica l Note No. 419 
___ -=- -lr 5% c C ____ .J--~ ____ _ .1. 
Posi tion 1 --x- 4~?F\, ~-;25-% c 
2--' Basic wing--.-
. 
Pi }'! I 
o 80~4--+--+--+---~~~--4--
-10 o 10 20 30 
(t., degrees 
Fig . 7 CL,CD and c . p . curves for position 1. 
Fig . 7 
N.A.C.A. Technical Note No.419 Fig . S 
~r--5% c 
---- -- II I ~ ~--"-'''''" . -..:!L 
Position 2--~ - ~~ 2Jo% c 
Basic wing-- .. '\ 
. 
-b-LLJ::--"-l 
V/
i '-:~ i 
I vq~e--- ___ [;V 1 ~--¢- I 
I VI I j ±~ .. - ._--I [1 
--j I I 
--
r%.J 20 
H 
S 
0 
H 
Cj..j 40 
() 
..j-> 
~ 
(]) 
() 60 
H 
(]) 
p., 
~ 
~~ SO 
() 
2. S 
I V I I I TI- ' ~ . - -~-i / ! II I _ _ J_ f--- .-- t--- 1\ I I / 
2.4 
2.0 
. S 
--I / 1\ i , 
I I ! ~ J 
~~_/ --~~ C ' 4- " L ,.-L .. ,'-~:' - --
il 
--+ 
V \ ~ 
I ( I " . ~ 
I /j ("\.~: ~L /. -~- --~-.-.1 
! I ~ i !/ . 
I ! j,T --=, I / .7r 
c'/==: Jd . -+ --~-;:.-.'" .+-. I .. _ , 
1. 6 
. 4 ~r-
oLI L tr~i - leD [ 
-10 0 10 20 30 
0" degrees 
Fig . S CL,CD and c .p . curve s for po sition 2. 
N.A.C.A. Technical Note No . 419 C-==r=Jr- s% ~ 
Posi tion 3 --[)--
Basic wi!lg __ 4--
! 
'----:1 35~ 3 .75% c 
CL 
f--- --+---1----+--7 ~ 
2.8~ --~-+-~--~v~~--+--~~ 
! 
-10 o 10 20 
0., degre es 
Fig.9 CL,CD and c.p. curves for positio!l 3. 
Fig.9 
N.A.C.A. Technical Note No. 419 Fig .lO 
.- - I C _ __ .. ~ _____ 'J.. 
Posi tion 4--x- 5~~/~\ 1.1&fo c 
Basic wing--.- "--
a.. , degr ees 
Fig .l0 CL,CD and c. p . curves for position 4 
N.A.C.A. Technical Note No.4l 9 ::i'ig.ll 
2· --··-r -
(X, , degrees 
Fig.ll CL,CD and c.p. curves for position 5. 
N.A.C.A. Technical Note No.4l9 
Position 6 <;~~ -=4 
Basic wing ---.-- 3Q~:L"-".~ 3.7ff/o c 
j 201---'__ '--.l-~lm-___ 
--l _.-....... -.'-......! 
S / ,- "-~ 401---+---+-- .:::,.... i 60:-~ / yn~~ -~= ~ lv' =i~ 
ill f-o I 1./ -t 0 
P.I !I 
. 801---i----4-L.-+--+---+-+__ -+---+-- --1 
p, 
o CL iJ f- --~--+--+-~-~~+_-~~ 
i 2 . 8--+-~--~+--+1I~~~-+---
~ o_ ~~4--+--~~~--+--~ 
/ 2. 4~---+'-+--+-+1/----f--!1---+-+-+-+---
1---i--+--+--4L-f---+--+-l--- .-
j 
2. Ol---+--+-+c-+--/+ ---t-o---Jf-----!i'o\-t---f--.--
/ ----
1\ 
CL 1.6 / 
and II C 
CD 1. 2'1-~-/-A----+--l--~+~~''''f--~-''-'':+----+---1 
'
II \ 
"-. 
8 
-10 0 10 20 30 
cx" degrees 
Fig.12 CL,CD and c. p . curves for position 6. 
Fig.12 


Wind-tunnel Tests of the Fowler Variable-area Wing

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