Document
• _k. 7_!!,i_ _ /_ !. _ _ _ _ !•_ i _ k '¸'_ • H • ..... / -" TECHNICAL NOTES NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS No. 808 WIND-TUNNEL INVESTIGATION OF AN NACA 23012 AIRFOIL WITH SEVERAL ARRANGEMENTS OF SLOTTED FLAPS WITH EXTENDED LIPS By John G. Lowry Langley Memorial Aeronautical Laboratory
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Washington May 1941
NAT 0NAL ADVIS0RY COMM E FOR A
TECHN c L NOTE NO.SO8
WIleD-TUNNEL INVESTIGATION OF AN NACA 23012 SEVERAL ARRA_GEI,E±_TS OF SLOTTED FLAPS WITH EXTENDED LIPS By John G. Lok_ry l SUMMARY _ An investigation was made in the NACA 7- by 10-foot wind tunnel to determine the effect of slot-lip location on the _aerodynamic section characteristics of an NACA 23012 airfoil with.a 30-percent-chord Slotted flap.
Tests were made with slot llps located at 90 and 100 per- cent of the airfoil Chord and with two differen% flap shapes.
The results are compared with a slotted flap previ- ously developed by the National Advisory Committee for Aeronautics with a slot lip located at 83 percent of the airfoil • chord, The extension of the slot lip, to the rear increased the section lift and pitching-moment coefficients.
Comparisons made on a basis of pitching moment for a glve n tail• length show that the Fowler type flap, lip extended to' trailing edge of the airfoil, has the greatest section lift coefficient. For moderate tail lengths, 2 to 3 chord 1.engths, 'there was only a slight difference between the_previQusly developed slotted flap and the slot- ted f%ap with zslot lip extended to 90 percent of the air- foil chord. Of the three flaps tested, the Fowler flap had the lowest drag coefficient at high_iift coefficients.
The extenslon, of the lower surface at the leading edge of the slot:had a negligible effect on the profile drag of the airfoil-flip arrangemen t witl_ the flap deflected when the lip terminate _ at 90 percent of the airfoil chord,
.... N ODUCT
• _I I0N The Nati0nal iAdVisory Committe_ for Aeronautics has undertaken an extensive investigation of high-lift devices to furnish information applioable to the design of more efficient and safer airplanes. Some of the desirable aero- ,' . • NACAi, Techn.ical,,?Not'e_..',N,Q., ._808", dynamic features of high-l_fto @eViceS are: high lift with variable drag for landing, high lift with low drag for take-off and initial' climb, no increase in drag with the device neutral, and small change in pitching moment with the device in operation. One of the most promising devices developed up to the present time is an airfoil _ in combination with a slotted_flap. Aerodynamic and load data are available o_ 12-p_rcent thick airfoil-flap com- binations in references 1 to 8; references 1 and 2 give aerodynamic data for slotted flaps with a short lip exten- sion developed by the NACA; and references 3 and 4 give aerodynamic data for Fowler flaps on which the slot lip extends to the trailing edge of the airfoil. Load data are given in reference 5 for one of the slotted flaps and in reference 6 for the Fowler flap.
The present te_ts broad ened_the investigation to in- clude slotted flaps with slot-lip extensions between slot- ted flap 2-h (reference l) with the slot lip extended to 83 percent of the airfoil chord and the Fowler type flap.
MODELS The airfoil model used in these tests has a chord of 3 feet and a span of 7 feet; it conforms to the NACA 23012 airfoil profile (table I) and is/made of mahogany and waterproofed wallboard. The basic model is provided with a removable trailing-edge section that allows easy chang- ing of slot-lip• length andslot shape. • Three flap arrange- ments were used in the tests:• Two of them have slot lips terminating at 0._0c (90 percent of the basic airfoil with flap retracted) and will be called slotted flaps 1-a and l-b; the third one has the slot lip•terminating at 1.00c and is a Fowler flaP. (See fig. i.)
The full,span flaps were built of laminated mahogany with a cher]_ of 0.30c (10,8 in.) and were fastened to the airfoil with seweral thin-steel fittings. The Fowler flap (fig. l) conforms to the Clark Y airfoil profile (table I).
The two slotted flaps (fig. l) have a Clark Y profile modi- fied to conform to the NACA 23012 airfoil back of the slot lip with the flap in the fully retracted position and faired to the nose radius of the flap by progressive vari- ation of the Clark Y _ppe_r s?urfa_ce_ ordinates (table I_.
All the flaps could be_ mo:ve&_ normal_to the airfoil chord, Jglj\I 5: n),,' I NACA Technical Note No. 808 _tWS I the slotted flaps along a line 0.0025c ahead of the slot lip and the" Fowler iflap along a line at the 1.00c station.
Flap deflections of 80 ° in l0 o increments were possible with all arrangements. No arrangement _was made for fully retracting the flaps, ,_ The slot shapes for the two slotted flaps follow the same general profile (table I); for slotted flap l-a, how- ever, the lower surface of the airf011 extended 0.020c back of the slot entry for slotted flap l-b, forming a seal when the flap was fully retracted. (See fig. ]..)
The slot shape for the Fowler flap is made to clear the flap in the fully retracted position, as shown in figure 1.
TESTS The models were so mounted in the closed test section of the NACA°7- by 10-foot wind tunnel that they completely spanned the jet except for small clearances at each end.
(See references I and 7.) The main.airfoil was rigidly attached to the balance frame by torque tubes eitending through the upper and the lower boundaries of the test section. The angle of attack was changed from outside the tunnel by a calibrated electric drive connected to the torque tubes. Approximately two-dimensional flow is ob- tained with this test installation and the section charac- teristics of the model under test can be determined.
For all the tests a dynamic pressure of 16.37 pounds per square foot was maintained; this pressure corresponds to a velocity of about 80 miles per hour under standard conditions and to an average test Reynolds number of about 2,190,000. Because of turbulence in the air stream the effective Reynolds number, based,on the chord of the air- foil with flap retracted and a turbulence factor for the tunnel of 1.6, was approximately 3,500,000, (See refer- ence 8.)
Tests were made with the Fowler flap and slotted flap 1-a to determine the optimum gap for conditions of low drag coefficient throughout the llft range and for maximum lift coefficient. Tests were made on slotted flap 1-b with the flap located at the optimum position for slotted flap 1-a. Lift, drag, and pitching moment were measured for the slotted flaps throughout the lift range from ap- proximately zero lift to the stall and for flap deflection
4 NACA'_Technica'! N.ote _o_ 808
from 0 ° to the de fle'ctlon fo_ max im_m lift at I0° incre -
ments. On the F6wler flap similar,data were Obtained
throughout t_e angle-of-attack range from -6 ° to the stall
and for flap deflections at 100 increments_ No tests _ere
made above the stall because of unsteady conditions of the
model.
- RESULTS AND DISCUSSION
•_ ...... COefficient s
All test results are given in standard nondimensional
section coefficient form corrected as explained in refer-
ence i.
section lift coefficient (_/qc)
c I
section profile-drag coefficient (do/qc) C d'o: section pit'ching-moment coefficient about Cm(a'c" )'0" aerodynamic c, enter of.plain airfoil (m(a.C.)o/qC _) , • where section lift section profile drag
ao
section pitching moment m(a.C.)o dynamic pressure (I_2 pV2) ' q C chord of basic airfoil with flap retracted and angle of attack corrected to infinite aspect O_ o rat_io.
flap deflection, measured between airfoil 8f chord line an_d flap chord l_ne
NACA Technical Note No. 808 5
Precision
The _ccuracy of the various measurements in the tests
is believed to be within the following limits:
• . _0.0006
_'o • • .... _0"l°
Cd°(c = 1.0)" . . _0.002
C%max. . . . , _0.03
Cd°(c = 2.5)"
. . _0.003
6f ........ • 0.20
Cm(a.C.)o"
.... _ 0. 0003
Flap position. • • _0.001c
Cdomi n
No attempt was made to determine the effect of hinge fittings because the effect is believed to be small. The relative merits of the several flap arrangements should not be appreciably affected by hinge-fitting drag because similar hinge fittings were used for all.
Plain Airfoil The complete aerodynamic section characteristics of the plain NACA 23012 airfoil are given in figure 2. These data have beeH discussed in reference 1 and therefore re- quire no further discussion here.
Fowler Flap The aerodynamic section characteristics of the NACA 23012 airfoil with a 0.30c Fowler flap at the optimum gap are given in figure 3. The maximum lift coefficient, C_max = 3.30, is much higher than that reported in refer- ence l, where the flap was also of NACA 23012 profile. The pitching moment of this flap arrangement is very high and might limit the use of this flap in some designs.
The effect of slot gap on the aerodynamic section characteristics of the NAC_ 23012 airfoil with a 0.30c Fowler flap is given in figure 4, _ The effect of either increasing or decreasing the gap from 0.015c was to de- crease 'the maximum lift and increase the profile drag.
These results show the optimum gap to be smaller than for the arrangement reported in reference 1.
No tests _rere made to determine the adverse effect of 6 NACA Technical Note No. 808 a break in the lower surface with flap retracted because a simple member could be made to cover this gap and seal the slot.
Slotted Flaps The aerodynamic section characteristics of the NACA 23012 airfoil with the two arrangements of slotted flaps with extended lips are given in figures 5 to 10. Figures 5 to 8 give the characteristics for the airfoil-flap ar- rangements tested and figures 9 and l0 are comparisons of the different arrangements.
The effect of the slot gap on the maximum section lift coefficient of these arrangements is given in figure 9. The maximum values of AClmax for slotted flap 1-a with the 0.01c gap were about the same as for flap 1-a with the 0.02c gap; with the 0.01c gap a flap deflection of 50 ° was required, whereas a deflection of only 40o was required with the 0.02c gap. Flap 1-a with the 0.30c gap gave maximum lift at a flap deflection of 30 ° but with a loss of 0.17 in Clmax from the values for the smaller gaps. Slotted flap 1-b with a gap of 0.02c gave a slight- ly lower value of maximum section lift coefficient than slotted flap 1-a with the same gap.
A comparison of profile-drag characteristics for the various arrangements of slotted flaps with extended lips is given in figure 10. Figure 10(a) shows that, through- out the lift range of slotted flap l-b, there is no appre- ciable difference in the profile drag for the two flaps but that the profile drag of slotted flap 1-a increases rapidly above the maximum lift of flap 1-b. Figure 10(b) shows that slotted flap 1-a with a gap of 0.O2c appears tobe most desirable if the criterion of low drag and high lift is used. Slotted flap 1-a with the 0.03c gap had approximately the same profile drag as with the 0.02c gap for values of the lift coefficient less than 2.3. Slotted flap 1-a with the 0.01c gap gave lov_er profile drags for values of the lift coefficient above 2.8 but had much higher profile drag than the arrangements with larger gaps over the lift range from cl = 1_4 to c_ = 2.8.
No tests were made to determine the effect of the break in the lower surface of the airfoil with flap re- tracted because the effect is thoughtto be small for
NACA Techn_ical Note No,. 808 7
slatted flap 1-a, as the lower surface _ould be sealed un-
der such conditions. Inasmuch as the _ change in slot shape had no adverse effect on the airfoil-flap charac- teristics,; such tests wo_ld have little value.
From the results of these tests it would appear _that the Fowlez ty_e flap could have a similar seal with no adverse effects on the aerodynamicsection character- istics.
Comparison of Three Slotted Flaps A comparison of increments of section maximum lift coefficients is given in figure ll for the two flaps tested and for a 0.2566c slotted flap '2-h. (See refer- ence 1.) For the arrangements tested, the maximum lift coefficient increases as the slot lip is moved toward the rear, reaching a maximum value of 3.30 for the Fowler flap.
In order to get a more comprehensive comparison of the three flaps, the value of pitching moment should be accounted for because the pitching moment also increases as the slot lip is moved toward tile trailing edge. Tail loads necessary to compensate for the adverse pitching moment were therefore computed, and the effective section maximum lift coefficients as a function of tail length % are shown in figure 12. The tail length in this paper is the distance fromthe aerodynamic center of the airfoil %o theL center of pressure of the tail, expressed in air- foil chords. These values are based on a theoretical cen- ter of gravity at _ the aerodynamic center of the wing with the flap fully retracted. If the center of gravity is ahead of the aerodynamic center of the _irfoil, the tail load will increase as some function of the_ increase in tail length and the lift of the w_ing; but, if the center of gravity is back of the aerodynamic center of airfoil, the tail load will decrease by a similar function. With this method of comparison the Fowler flap also gives greater maximum effective section lift coefficients than the other two flaps, but %he slotted flap with extended slot lip ,is _not _ appreciably better than slotted flap 2-h (reference l) for a tail length of 2 airfoil chords. For tail lengths of 2.5 chords or more the slotted flap with extended slot lip gives a greater maximum effective sec- tion lift coefficient than slotted flap 2-h. It might be possible with a flap of different camber and a gap of 8 NACA Technical Note No. 808 0.015c to obtain higher maximum effective section lift coefficients with the extended-lip slotted flap.
A comparison of profile-drag characteristics for the three flaps is given in figure 13. The plain airfoil has the lowest profile-drag coefficients for lift coefficients less than 0.90. The slotted flap 2-h (reference l) has the lowest profile-drag coefficients for values from cl = 0.9 to c I = 1.9. Above a value of c_ = 1.9, the Fowler flap has the lowest profile-drag coefficients. In cases where high lift with high drag is needed to make safe landings, the slotted flap with extended lip would be the most satisfactory. Here again by changing the camber and the gap, it might be possible to obtain values of profile- drag coefficient lower than those shown for the slotted flap with extended lip.
CONCLUSIONS For the arrangements tested, the extension of the slot lip to the rear increased the section coefficients of lift and pitching moment of an NACA 23012 airfoil with slotted flap. The Fowler arrangementgave the largest effective maximum lift coefficient and the lowest drag coefficient at high lift. For tail lengths greater than 2 chord lengths the slotted flap with extended lip gave slightly higher maximum lift coefficients than the slot- ted flap with a shorter lip extension previously devel- oped by the NACA. The extension of the lower surface at the leading edge of the slot had no appreciable effect on theprofile drag of the airfoil-flap arrangement with flap deflected and slightly increased the maximum lift coefficient. Such an arrangement could probably be added to the Fowler flap with little or no effect on the profile- drag characteristics.
Langley Memorial Aeronautical Laboratory, National Advisory Committee for Aeronautics, Langley Field, Va., April 12, 1941.
NACA Technical Note No. 808 9
REFERENCES
1. Wenzinger, Carl J., and Harris, Thomas A.: Wind-Tunnel
Investigation of an N.A,C.A. 23012 Airfoil with
Various Arrangements of Slotted Flaps. Rep. No. 664, NACA, 1939.
2. Harris, Thomas A.: Wind-Tunnel Investigation of an
N.A.C.A. 23012 Airfoil with Two Arrangements of a
Wide-Chord Slotted Flap. T.N. No. 715, NACA, 1939.
3. Platt, Robert C.: Aerodynamic Characteristics of a
Wing with Fowler Flaps Including Flap Loads, Down-
wash, and Calculated Effect on Take-0ff. Rep. No.
534, NACA, 1935.
4. Weick, Fred E., and Platt, Robert C.: Wind-Tunnel
Tests of the Fowler Varlable-Area Wing. T.N. No.
419, NACA, 1932.
5. Wenzinger, Carl J., and Delano, James B.: Pressur$
Distribution over an N.A.C.A. 23012 Airfoil with a
Slotted and a Plain Flap. Rep. No. 633, NACA, 1938.
6. Wenzinger, Carl J., and Anderson, Walter B.: Pressure
Distribution over Airfoils with Fowler Flaps. Rep.
No. 620, NACA, 1938.
7. Harris, Thomas A.: The 7 by l0 Foot Wind Tunnel of
the National Advisory Committee for Aeronautics.
Rep. No. 412, NACA, 1931.
8. Jacobs, Eastman N., and Sherman, Albert: Airfoil Sec-
tion Characteristics as Affected by Variations of
the Reynolds Number. Rep. No. 586, NACA, 1937.
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Figure 2°- Aerodynamic section characteristics of NACA 25012 plain airfoil.
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Or,,I @o I I Fig. 5 IACA Teohnlcal ]lore No, 808 J D Figure 5.- Aerodynamic section ohar&oteristlo8 of _n NAOA 23012 airfoil with a 0.030c slotted flap I-_.
Slot gap = O.Olc.
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81oi _p = O.O_c.
/8 /.8 ....
/ _m i/ I Gap 51'o f
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I i / I / I I i I I 0 /0 20 30 40 50 EO I0 2O 30 40 SO Flop clef/eel/on, _/, dog T/up def/ecHon, 6/, de W Figure II.- Oomparieon of increments of section maximum llft Figure 9.- Oompazison of increments of section coefficient for three flaps on an NACA 23012 aid- maximum lift coefficient for _lotted foil.
flaps with extended slot llp at three himge locations.
_o NACA Technical Note NO. 808 I .08 3.g ,2.2 extended slot lip_
NACA Technic_l No%e No. 808, F!Eso 18,1S
j.24 .u .20 o./6 I • _.. 08 .0 u .04 .4 .8 /.2 /.S 2.0 2.4 2.8 3.2 .Sect/on lift coeffzbieng c z Ti_e I_,- 0om_rison 3._ of three slo%_ed fl_ps on an
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_AQA 33012 _Azfoil.
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is y
b r_ o ....... 02566c slotted f/up 2-h, c_o, =f.Sf /ref.l] ¥&_e i_.- _ffeotive 0.30c Fowler- flop, O.Ol_c pc,p, cz .... =t30 -- 0.30c slotted f/c/9 /-c7, O. OZc_ Cz_= =2.SI section foz NACA _ZOI_ airfoil ¢, (n <°o0,0,)0,..
u .4 0 2 3 .4 S I [_Jl length, Z, o/Pfoi/ chords