Altman, John M

Rose, Leonard M

English

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NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
TECHNICAL NOTE 2018 
LOW-SPEED INVESTIGATION OF A THIN, FAIRED, 
DOUBLE-WEDGE AIRFOIL SECTION WITH NOSE 
FLAPS OF VARIOUS CHORDS 
By Leonard M. Rose and John M. Altman 
Ames Aeronautical Laboratory 
Moffett Field, Calif. 
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https://ntrs.nasa.gov/search.jsp?R=19930082677 2020-06-17T22:12:41+00:00Z

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
TECHNICAL NOTE 2018 
LOW-SPEED INVESTIGATION OF A WIN, FAIRED, 
DOUBLE-wEDGE AIRFOIL SECTION WITH NOSE 
FLAPS OF VARIOUS CHORDS 
By Leonard M. Rose and John M. Altman 
SUMMARY 
A thin, faired, double-wedge airfoil section was investigated with 
plain nose flaps having chords e~ual to 12, 16, 20, and 25 percent of the 
airfoil chord. Section lift, drag, and pitching-moment data were obtained 
at a Reynolds number of 5.8 million and a Mach number of 0.17. 
A greater positive shift in the angle of attack for zero lift and 
more negative pitching moments resulted from increased chord of the nose 
flap. Little effect of nose-flap chord on the maximum lift was found. 
Increased chord of the nose flap produced the least drag at high lift 
coefficients. 
INTRODUCTION 
Although thin, sharp-edged airfoil sections offer considerable 
promise for certain supersonic aircraft, the low maximum lift and extreme 
variation of drag with lift, characteristic of thin sections at low speeds ; 
have reduced the attractiveness of such sections for piloted aircraft. 
Several low-epeed investigations have indicated the benefit of nose flaps 
in improving the maximum lift and in reducing the drag at high lift coef-
ficients. Such benefits were shown in reference 1, wherein the results 
obtained for a thin, faired, double-wedge airfoil with a 16-percent-chord 
nose flap were presented. 
Most of the low-epeed investigations of sharp-edged airfoils that 
have been undertaken to date have, been primarily concerned with one 
combination of airfoil and nose flap; consequently, there are available 
few systematic results from which the effects of variation of the nose-
flap chord can be assessed. For this reason, it was thought desirable 
to extend the investigation reported in reference 1 to include variation 
of nose-flap chord. In this report, the force and moment characteristics 
of the faired, double-wedge airfoil with 12-, 16-, 20-, and 25-percent-
chord nose flaps are presented. The investigation was conducted in the 
Ames 7- by 10-foot wind tunnel No. 1. 
2 NACA TN 2018 
NOTATION 
The results are presented in the form of standard NACA coefficients 
which are defined as follows: 
Cd section profile~rag coefficient (D) 
o qc 
c 1 section lift coefficient (~c) 
cm section pitching-moment coefficient, referred to the quarter-
chord point (M) 
qc2 
c airfoil chord, feet 
D drag per unit span, pounds per foot 
L lift per unit span, pounds per foot 
M pitching moment per unit span, pound-feet per foot 
q free-etream dynamiC pressure, pounds per square foot 
ao section angle of attack, degrees 
MODEL AND TESTS 
The model used in this investigation was the one that is described 
in reference 1. For these tests, additional flaps of 12- and 20-percent 
chord were constructedj in order that the 25-percent-chord trailing-edge 
flap could be investigated as a nose flap, the model was reversed in the 
wind tunnel. The airfoil section tested was obtai~ed by rounding the 
midsection of a symmetrical double wedge with an arc tangent to the surface 
at 42.5 and 57.5 percent of the chord. This amount of rounding was 
believed sufficient to alleviate the adverse pressures resulting from the 
ridge of the double-wedge section. The resulting airfoil had a thickness 
of 4.23 percent of the chord. A section drawing of the model is shown in 
figure 1 . 
Lift and pitching-moment data were obtained by the use of the wind-
tunnel balance system. The model completely spannei the 7- foot dimension 
of the tunnel between two 6-foot-diameter turntable~ (fig. 2); conse-
quently, these results include the air forces acting on these turntables. 
Although the forces acting on the turntables affect the f orce and moment 
data obtained with the balance system, previous investigations have 
--- ~--- -~--
I 
I 
J 
NACA TN 2018 3 
indicated that, with the exception of the drag, the turntable tare is 
negligible. The drag results presented were obtained from surveys of the 
wake behind the model. These surveys were limited to a small range of lift 
coefficients near minimum drag by the width of the survey rake available 
for the tests. 
For some nose-flap deflections, severe buffeting of the model was 
encountered near maximum lift. When this occurred, it was not possible 
to determine the maximum lift coefficient. 
The tests were made at a Reynolds number of 5.8 million and a Mach 
number of approximately 0.17. The results were corrected for constraint 
of the tunnel walls by the methods outlined in reference 2. 
RE3Ul/IS AND DISCUSSION 
The aerodynamic characteristics for the basic airfoil are presented 
in figure 3. The lift and pitching~oment characteristics of the air-
foil for various deflections of the four nose flaps are presented in 
figure 4. The drag results for corresponding conditions are shown in 
figure 5. In figure 6 are the lift and moment results obtained with the 
12-, 16-, and 20-percent-chord nOSe flaps deflected 300 and the 25-percent-
chord trailing-edge flap deflected 500 and 600• Pres ented in figures 7 
and 8 is a summary of the variation of some of the characteristics with 
nose-flap chord. In these figures, the results for 50 and 150 nose-flap 
deflections have been extended to 25-percent chor~although test results 
were not obtained for those two deflections. 
Lift Characteristics 
The primary effect of increasing nose-flap chord on the lift charac-
teristics of the airfoil was an increase in the angle of attack for zero 
lift. This shift in angle of attack was nearly linea r in variation with 
both length of the nose flap and flap deflection. These results are 
summarized in figure 7. Also shown in figure 7 is the variation of 
maximum lift coefficient for various flap deflections with nose-flap 
chord. These results indicate a slight tendency toward increasing maJi-
mum lift coefficient with increasing flap chord. The results shown in 
figure 6 for the model with the 12-, 16-, and 20-percent-chord nose flaps 
at 300 and the 25-percent-chord trailing-edge flap at 500 and 600 indicate 
the Bame general effects of nose-flap-chord variation as were found with 
the trailing-edge flap undeflected. 
It should be noted that the erratic force characteristics encountered 
previously with the 16-percent-chord flap deflected 350 (reference 1) were 
also found for the other flap-chord lengths investigated. As may be seen 
4 NACA TN 2018 
in figure 4(g), the discontinuities in the lift curves show no consistent 
variation with flap length for the range investigated. 
Pitching-Moment Characteristics 
Increasing the chord of the nose flap made the pitching moments 
generally more negative. (See fig. 4.) It should be noted in connection 
with the pitching-moment characteristics that the variation of pitching 
moment with lift at the stall was adversely affected by large nose-flap 
deflections as well as by increased flap chord. For small flap deflect-
ions~ large negative moments were encountered at maximum lift. However, 
for larger flap deflections, the negative moment at the stall became 
less and with 300 nose-flap deflection there was little variation of 
pitching moment with lift near maximum lift. It is possible that for 
some applications such an effect would result in poor stalling character-
istics of the airplane with nose flaps deflected. 
Drag Characteristics 
The variation of drag with lift for the various flap chords shown 
in figure 5 indicates little difference in ndnimum drag for a particular 
flap deflection in the low lift-coefficient range for any of the flaps. 
At the higher lift coefficients, some reduction in drag may be noted for 
the larger-chord flaps, although extensive results could not be obtained 
from the wake surveys. This advantage resulted primarily from the 
increase in lift coefficient for minimum drag with constant flap defleo-
tion obtained for the larger-chord flaps. The variation of lift coef-
ficient for minimum drag with nose-flap chord 1s shown in figure 8. 
CONCLUSIONS 
Tests of a faired, double-wedge airfoil section with nose flaps 
having chords of 12-, 16-, 20-, and 25-percent chord indicated the 
following conclusions: 
1. The primary effect of variation of nose-flap chord upon the 
lift characteristics was an increase in the angle of attack for zero 
lift with increased flap chord. Little variation of maximum lift with 
flap chord was obtained. 
2. The principal effect of increased flap chord on the pitching 
moments was to make these moments generally more negative. Large 
deflections of the nose flap and increased flap chord had an adverse 
• 
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NACA TN 2018 5 
effect on the Yariation of pitching moment with the lift at the stall. 
3. With constant flap deflection, the lift coefficient for minimum 
drag increased with increased flap chord. The net result was that the 
larger-chord flaps produced the least drag at the higher lift coeffi-
cients. 
Ames Aeronautical Laboratory, 
National Advisory Committee for Aeronautics, 
Moffett Field, Calif., Nov. 17,1949. 
REFERENCES 
1. Rose, Leonard M., and Altman, John M.: Low-Speed Experimental 
Investigation of a Thi~Faired, Doubl~edge Airfoil Section 
with Nose and Trailing-Edge Flaps. NACA TN 1934, 1949. 
2. Allen H. Julian, and Vincenti, Walter G.; Wall Interference in a 
Two-Dimensional-Flow Wind Tunnel with Consideration of the Effects 
of Compressibility. NACA Rep. 782, 1945. 
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NACA TN 2018 
Figure 2.- The faired, double-wedge airfoil model installed in the 
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NACA TN 2018 19 
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21 
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NACA-Langley - 2-3 - 50 - 775 
~~------- ~------~--
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• 


Low-speed Investigation of a Thin, Faired, Double-wedge Airfoil Section with Nose Flaps of Various Chords

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