Altman, John M

Rose, Leonard M

English

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NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
TECHNICAL NOTE 1934 
LOW-SPEED EXPERIMENTAL INVESTIGATION OF A THIN,
FAIRED, DOUBLE-WEDGE AIRFOIL SECTION WITH 
NOSE AND TRAILING-EDGE FLAPS 
By Leonard M. Rose and John M. Altman 
Ames Aeronautical Laboratory
Moffett Field, Calif. 
'^7^
Washington 
August 1949
https://ntrs.nasa.gov/search.jsp?R=19930082610 2020-06-17T22:16:48+00:00Z
NATIONAL ADVISORY CO4i'rna FOR AERONAUTICS

TECHNICAL NOTE 1934 
LOW-SPEED EXPERIMENTAL INVESTIGATION OF A THIN,

FAIRED, DOUBLE-WEDGE AIRFOIL SECTION WITH

NOSE AND TRAILING--EDGE FLAPS 
By Leonard M. Rose and John M. Altman 
OMM 
A faired, double-wedge airfoil section, 14.23 percent thick, was 
investigated with plain nose and trailing-edge flaps. The nose flap was 
0.16 of the airfoil chord and the trailing-edge flap was 0.25 of the 
airfoil chord. Section lift, drag, and pitching-moment data are pre-
sented for a Reynolds number of 5,800,000 and a Mach number of 0.17. 
A maximum lift coefficient of 1.96 was obtained with combined nose 
and trailing-edge flap deflections of 300 and 600, respectively. The 
maximum lift coefficient of the basic section with flaps undeflected was 
0.814.
The possibility of a considerable reduction in profile drag at high 
lift coefficients over that of the plain airfoil was indicated for suit-
able combinations of nose and trailing-edge flap deflections. 
INTRODUCTION 
Although thin, sharp-edged airfoil sections are intended primarily 
for operation at supersonic speeds, the safe operation of piloted 
aircraft equipped with such sections requires a knowledge of the charac-
teristics of these sections at low speeds. Thin airfoil sections gener-
ally develop low maximum lift coefficients, and sharp-edged sections are 
further characterized by large variations of profile drag with lift. To 
overcome these deficiencies, both nose and trailing-edge flaps have been 
proposed for use with such airfoils. 
As there are presently available little data as to the characteris-
tics of thin, sharp-edged airfoil sections, an investigation of a faired, 
double -iredge airfoil with plain nose and trailing-edge flaps was under-
taken. The force and moment characteristics obtained with a 16-percent-
chord nose flap and a 25-percent-chord trailing-edge flap are presented
2
	
NACA TN 1934 
herein. The tests were made in the Ames 7- by 10-foot wind, tunnel No. 1. 
NOTATION 
The results are presented in the form of standard NACA coefficients 
which are defined as follows: 
c	 section profile-drag coefficient (D/q,c) 
c 2	 section lift coefficient (L/qc) 
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 -stream dynamic pressure,pounds per square foot 
Mo section angle of attack, degrees 
MODEL AND TESTS 
The airfoil section tested was obtained by rounding the midsection 
of a symmetrical double wedge with an arc tangent to the gurface at 42.5 
and 57.5 percent of the chord. The resulting airfoil had a thickness of 
4.23 percent of the chord. A plain nose flap of 16-percent chord and a 
plain trailing-edge flap of 25-percent chord were incorporated on the 
model. A section drawing of the model is shown in figure 1. Both the 
nose and trailing-edge flaps were made of metal in order to make the 
leading- and trailing-edge thicknesses as small as possible. The remain-
der of the model was built of wood on a steel spar and covered with a 
thin aluminum skin. The flaps were connected to the central portion of 
the model by a continuous hinge, and rubbing contact was maintained 
between the radius of the deflected flap and the skirt on the fixed 
portion of the airfoil. 
Lift, drag, and pitching-moment data were obtained from the wind-
tunnel balance system. The results thus obtained included the forces 
acting on the turntables at either end of the model (fig. 2). It has 
been found in previous investigations that, with the exception of the 
drag, the effect of these turntables on the results obtained is negligi-
ble. Some additional drag data were obtained by surveys of the wake
NACA TN 1934
	
3 
behind the model, but these results were 
wake was wider than the available survey 
of angles of attack and flap deflections. 
obtained by the two methods of measuremen 
was not possible to establish the tare of 
tions, the drag results obtained from the 
for indicating, qualitatively, the effect 
of the model.
limited in extent because the 
rake except for a small range 
Comparison of the drag results 
t indicated that, although it 
the turntables for all condi-
balance system are satisfactory 
s of flap deflection on the drag 
The tests were carried beyond maximum lift except for certain combi-
nations of nose and trailing-edge flap deflections where severe shaking 
or buffeting of the model occurred near maximum lift. When this condition 
was encountered, it was impossible to determine the maximum.lift coeffi-
cient. However, it is believed that the highest lift coefficient meas-
red, before buffeting made it impossible to obtain further results, was 
very nearly the maximum. 
The tests were made at a Reynolds number of approximately 5,800,000 
and a Mach number of approximately 0.17. The results were corrected for 
constraint of the tunnel walls by the methods outlined in reference 1. 
RESULTS AND DISCUSSION 
The lift and pitching-moment characteristics of the model with var-
ious flap deflections are presented in figure 3. The drag results 
obtained from wake surveys are shown in figure 4, and additional drag 
results from the balance system for a greater range of flap deflections 
and lift coefficients are shown in figure 5. The variation of maximum 
lift coefficient with nose flap deflection for various deflections of the 
trailing-edge flap is shown in figure 6. 
Maximum Lift Characteristics 
The maximum lift coefficient of the basic airfoil section was 0.814, 
and, as shown in figure 3(a), the lift varied linearly with angle of 
attack to nearly maximum lift. There were no discontinuities evident in 
this lift curve. A maximum lift coefficient of 1.73 was obtained for a 
600 deflection of the trailing-edge flap with the nose flap urideflected. 
It is possible that a slightly higher maximum lift coefficient might have 
been obtained for greater trailing-edge flap deflections; however, a flap 
deflection of 600 was the maximum tested. With the nose flap alone 
deflected, a maximum lift coefficient of 1.28 was obtained with 300 
deflection. For combined deflections of the nose and trailing-edge flaps 
of 300 and 600 , respectively, a maximum lift coefficient of 1.96 was 
obtained. The variation of maximum lift coefficient with nose flap 
deflection, as shown in figure 6, indicates that the nose flap was more 
effective in increasing maximum lift for the smaller trailing-edge flap 
deflections.
4	 NACA TN 1934 
For all of the nose flap defle 'ctions investigated, except 350, the 
results could be repeated without difficulty. With the nose flap at 
350, however, a considerable range of maximum lift values was obtained 
on repeated runs. An attempt was made to find an indication of the 
cause of this inconsistency in results by the application of roughness 
at several locations on the nose flap.' The results of this investiga-
tion are shown in figure 7 and indicate no conclusive information as to 
the reason for the diverse maximum lift characteristics. 
Pitching-Moment Characteristics 
The variation of pitching-moment coefficient with lift coefficient 
for the basic airfoil section with flaps undeflected, shown in figure 
3(a), indicates that the aerodynamic center moved forward from the 
quarter-chord point until a lift coefficient of approximately 0.5 was 
attained. • The aerodynamic center above this lift coefficient moved 
rearward at an increasing rate as the lift coefficient was further 
increased. Trailing-edge flap deflection resulted in large negative 
pitching moments and a pronounced variation of the location of aerodyna-
mic center with lift coefficient. Deflection of the nose flap resulted 
in moderate negative pitching moments and delayed the rearward movement 
of the aerodynamic center to higher lift coefficients. 
Drag Characteristics 
Although it was not possible to correct the drag results obtained 
from the balance system for the tare of the end plates, the drag resultb 
obtained by both the wake survey and balance system clearly indicate the 
usefulness of the nose flap, and, to a lesser extent, the trailing.-edge 
flap, in reducing-the drag at high lift coefficients (figs. 4 and 5). The drag results shown in figure 4 indicate that by the use of suitable com-
binations of nose and trailing-edge flap deflections it is possible to 
obtain profile-drag coefficients of the same order of magnitude as those 
obtained for thicker conventional airfoil sections not equipped with nose 
flaps. The drag results presented in figure 5 indicate similar beneficial 
effects of nose flap deflection with even the largest trailing-edge flap 
deflections tested.
CONCLUDING REMARKS 
The results obtained in this investigation of a faired, double-wedge 
airfoil section with plain nose and trailing-edge flaps are suininarized.as 
follows: 
1The roughness applied extended over approximately 1 percent of the chord 
with number 60 carborund.um grains distributed as uniformly as possible 
over this length.
NACA TN 1934	 5 
1. A maxiim'm lift coefficient of 0.84 was obtained for the basic 
airfoil. For individual deflections of the nose and trailing-edge flaps 
of 300 and 600, respectively, ma iim,Tn lift coefficients of 1.28 and 1.73 
were obtained. Simultaneously deflecting the nose flap 300 and the 
trailing-edge flap 600
 produced a maximum lift coefficient of 1.96. 
2. The aerodynamic center of the basic airfoil section moved 
forward slightly from the quarter-chord point as the lift coefficient 
was increased to about 0.5. At higher lifts an increasingly rapid rearward 
movement of the aerodynamic center occurred. Deflection of the trailing-
edge flap resulted In much more negative pitching moments and accentuated 
the variation of aerodynamic-center location with lift coefficient. 
Deflection of the nose flap resulted in slightly more negative pitching 
moments and delayed the rearward movement of the aerodynamic center to 
higher lift coefficients. 
3. Considerable reduction in drag at high lift coefficients was 
noted for suitable combinations of nose and trailing-edge flap deflec-
tions. 
Ames Aeronautical Laboratory, 
National Advisory Committee for Aeronautics, 
Moffett Field, Calif., June 13, 1949. 
REFERENCE 
1. Allen, H. Julian, and Vincenti, Walter G.: Wall Interference in a 
Two-Dimensional-Flow Wind Tunnel with Consideration of the Effect 
of Compressibility. NACA Rep. 782, 1944.
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NACA TN 1934 
Figure 2.— The faired, double—wedge airfoil model installed in the 
wind tunnel.
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Low-speed experimental investigation of a thin, faired, double-wedge airfoil section with nose and trailing-edge flaps

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