The investigation described in this report is concerned with the changes in the aerodynamic characteristics of an airfoil which are produced by a gauze-covered suction slot, located near the leading edge, and connected by an air passage to a split flap at the trailing edge. The tests were conducted at the Langley Memorial Aeronautical Laboratory. At the larger values of lift coefficient where the action of the slot might be expected to be most effective, the pressure differences were such that the air flowed out of the slot rather than in through it, and in consequence, the maximum lift coefficient was decreased

Bamber, Millard J

English

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'IE Cl1!!I CAL l~OT:2:S 
r-i ATIONAL ADVISORY CO l:2a~TEE FOR AEROrAT:'ICS 
To. 324 
~':Lm TU:-~~E1 'I E: STS 01\ A:j AIRFO 11 E~:iIPFLD nTH 
A SPLIT ? LAP A:-: A SLOT 
Bjr :,: i llar d J . :S<:;"!lQe:I' 
:S a.ngley lte:'Jori al Aeronauticll 1 aboratol~Y 
· ~t~nll'.IU " "'-
Octoo er, 1~29 
https://ntrs.nasa.gov/search.jsp?R=19930081089 2020-03-17T04:21:34+00:00Z
~~ ATIONAL ADVISORY COMMITTEZ FOR AERONAUTICS. 
TECHNICAL NOTE NO . 324 
wrm TUNNE L TESTS or AN AIRFOIL EQUIPPED WITH 
A SPLIT FLAP AND A SLOT. 
By Millard J. Bamber . 
Summary 
The investigation described ~n this report is concerned 
wi th the changes in the aerodyna;nic cho..racteristics of an air-
foil vTh i ch ar e produced by a gauze-covered suction slot, located 
near the l eading edge , and connected by an air passage to a 
split f l ap at the trailing edge . The tests were conducted at 
the Langley remol'~oJ. Aeronautical Laboratory. 
At the large r values of lift coefficient where the action 
of the slot might be expected to be most effective, the pres-
sure differences were such that the air flowed out of the slot 
rather thon in through it, and in consequence, the maximum lift 
coefficient was decreased. 
I nt r oduction 
It is known that the lift of airfoils may be increased if 
the ai r of the boundary layer i s removed by suction acting from 
the inside of the a irfo il, and also, that D. suction exists be-
tween the parts of a split flap located at the trailing edge. 
The following tests were made to determine the aerodynamic 
N.A . C. A. Technical Fote No . 324 2 
character istics of an airfoil equipped with <l suction slot and 
a split flap near the trailing edge which were connected by an 
air passage thr ough the interior of the airfoil. The tORts were 
conducted in the Five-Foot Atmospheric ','lind Tur:nel of the L;mg-
ley Memorial Aeronautical Labo r atory. 
The tests described in Reference I indicated th2.t a vridc 
gauze-covered slot l ocated near the leading edge y/ould give the 
be st r esults with small pr essur e differences, although this type 
of slot , with no a ir flow through it, appears to ~ive considera-
ble spo il er action . 
T est s 
The tests we r e conducted in the Five-Foot At '':!1ospheric Wind 
Tunnel on a 15-inch chord , 25-1/4-inch span airfoil which Was 
mounted vertically in the tunnel between large horizontal plane s 
at each end . Figur e 1 shows the airfoil {Jlou:1ted in the tmmel 
between the planes . The ai r foil mounting cons isted of a ver-
tical spindle pass ing through and rigidly fastened to the model 
and the two end disks . The lower end of the sp indle Was pivoted 
and to the upper end were attached the force measuring balances 
by me ans of wir e linkages . Air was prevented from passing be-
tween the disks and the planes b.y means of two liquid seals. 
The Ii . A.C.A . 84- M prof il e VIas used and the ordinates are 
g iven in Table 1. The airfoi l was equipped with a split flap 
and a 3/4-inch slot covered wi th a fine mesh porous cloth. The 
N. A. C. A. Technical 10te No . 324 3 
inside of the ai rfoil Was so constructed that the air had free 
, 
passage f r om the slot to the opening between the parts of the 
split flap . I n Figures 2 and 3, t he airfoil is shown with the 
f l ap , slot, and inter i or ai r passages. 
The l ift , drag, and pressur e on the inside of the airfoil 
were measured at various flap settings with and without the 
slot . For the t ests without the slot a solid leading edge piece 
was used. The planes between which the airfoil Was tested re-
s trained the a ir flow to two dimensions , so that the effect of 
infini te aspect ratio Was approximated. 
The dynamic p re ssure Was hel d constant at 4.06 lb. per sq. 
ft . dur ing the tests . This co rre sponds to a speed of about 
40 m. p . h . and a Reynolds _umber of about 455,000. 
Res u 1 t s 
The results are presented in Figures 4 to 1, in which the 
absolute lift and drag coeff i ci ent s and the pressure Pw inside 
of the airfoil are plotted ver sus angle of attack for the vari-
ous slot ru1d fl ap combinat ions. These results are to be consid-
ered of comp arative value only, due to the limitations of the 
app ar a tus at the time these tests were made. 
The pressure Pw is g iven in terms of the dynamic pressur e 
and is measured with referenoe to the static pressure in the 
t est section of t he tunnel. This pressure was measured with and 
without the slot for each flap setting. The pressure difference 
N. A. C. A. Technical Note No . 324 4 
without the slot was that p r oduced between the open parts of the 
flap by the a ir flow past them. By a comparison of the pressure 
diffe r ences wi th and wi thout the slot the direction of air flow 
thr ough the slot can be deter mined, as indicated on the curves 
Pw ver sus angle of attack ( Fi gs. 5 to 7). 
Dis c u s s ion 
Fi gur es 5 to 7 show, as might be expected , that as long as 
the air flow was in thr ough the slot , the lift was increased 
wit h p r ac tical l y no change i n drag, but that when the flow was 
reversed , the r e Was a consider able decrease in lift and irrcrease 
in drag . As th i s rever sal of flow took place at about 2/3 of 
the maximum. l i ft coefficient of the airfo i l without the slot, 
the max i mum l i ft coefficient with the slot was considerably de-
cre a sed. At the high angles of attack, aft er the complet e bux-
ble of the ai r foil , t he lift coefficient was slightly increased, 
although the pressures indi cated that the air was flowing out 
thr ough the slot . The resul ts of previous tests (Reference 1) 
indicate that onl y small inc r eases in lift may be expected at 
these angles of at tack , even with the h i gher pressures or suc-
tions used in those tests . 
The tests were i"Ilade with the slot in but one location along 
t he chor d and the r e remains the possibility that a better effect 
might have been obtained with some other slot location. However , 
the max i mum suction developed by the flap is of the order of 1 q 
and pr evious tests (Refer ence 1) with suction slots indicate that 
------~----~-----~----------------
N. A. C. A. Technical 1\ ote No . 324 5 
but smal l, i f any , i nc r ea se s i n i:laximu;n 1 i ft may be expec t ed 
with suction s of th i s magni t ude. 
C o n c 1 u s i on s 
I n these test s the max imum lift coeff i c i ent of the airfo il 
wo.. s reduced when the gauze- covered slot Was added because the 
spli t fl o..p d i d not fur nish the p r e ssure diffe~ence requi r ed fo r 
the oper at i on of the slot at the angl es of attack of the larger 
lift coeffic i ents . 
Langley Memor ial Aer onautical Laborator y , 
Nat i onal Advi sory Comm i ttee for Ae ronautics, 
Langl ey Field , Va., August 14, 1929 . 
1. Reid, E . G. 
and 
BeJTIber, M. J . 
R ef ere n c e 
Prel i mi nary I nvest i gation on Boundary 
Laye r by ~~ e ()Jls of Suct ion and Pre s-
sure with t he ~ . S . A . 27 Airfoil. 
'J. A. C. A. Technical Note No. 286, 1928 . 
r .A.C.A. Technic al Note No . 324 6 
TABLE I. 
N. A. C.A. 84- M Profile Ordinates 
station in Ordinat es Ordinates 
pe r cent of chord upp er sur face lO'ner surf:lCe 
per cent of c~ord per cent of chord 
------~----------_1~~-----------------~--0 . 000 
1 . 000 
2. 000 
4 . 000 
6. 000 
8 . 000 
10. 000 
12 . 000 
16. 000 
20 . 000 
25 . 000 
30 . 000 
40 0000 
50 .. 000 
60 . 000 
70 . 000 
80 . 000 
90 . 000 
9 5. 000 
99 . 000 
100 . 000 
2. 920 2.920 
4 0 947 1.366 
5.920 0~858 
7 e 390 O~333 
~ .445 0~087 
90320 00000 
10 . 090 O~OOO 
100750 00000 
11.930 0.000 
120855 00000 
13.680 0.000 
14.160 OGOOO 
14.475 O~OOO 
13. 910 0.000 
12.425 0.000 
10 . 250 0.000 
7 .580 0.000 
4.285 0.000 
2 . 606 0.000 
0 . 993 0.000 
0 . 253 0.253 

_._- .-- ~---~--~--~--------~----~----------, 
N.A .C.A. T ec~nical No t e No . 324 
Fig . 3 N. A. C. A. 84 Airfoil wi th split flap-slot combination . 
~ig . 4 Split flap closed . 
~----~"~" '-----~-------
N. A.O . A. T8chnical Note NO .324 
1.6 
1.4 
1.2 
1.0 
. 8 
. 2 
o 
- . 2 
-.4 
_40 0 0 
Angle of attack 
Fig . 5 Split flap up 30° . 
Fig . 5 
N. A.C.A . 
2.2 1.1 
"J ':)24 1 Note l' 0 ., Te chnica 
2.0 1 . 0 I __ _ 
1. 8 • 91 L if t--l-_ l..---_ _ I 
1.6 . 8
1
' 
1 . 2 
1.0 
.8 
.6 
.2 
o 
Fi g . 6 Spli t f l ap 
Fig.6 
I .A.C.A. Te chnical ~o t e No . 321 Fig .7 
2.2 
2. 0 
1.8 
1.6 
1.4 
.8 
.6 
. 4 
.2 
o 
Angl e of att ack 
Fi g .7 Spl it flap both par t s ope n 30° . 
.. 


Wind Tunnel Tests on an Airfoil Equipped with a Split Flap and a Slot

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