Summary: The effect of Reynolds number on the aerodynamic characteristics of a low-drag airfoil section tested under conditions of relatively high stream turbulence was determined by tests in the LMAL 7- by 10-foot tunnel of the NACA 653-418, a = 1.0 airfoil section with a split flap having a chord 20 percent of the airfoil chord. The Reynolds number ranged from 0.19 to 2.99 x 106; the Mach number attained was never greater than 0.10. The data are presented as curves of section angle of attack, section profile-drag coefficient, and section pitching-moment coefficient against section lift coefficient for various flap deflections. The maximum lift coefficient increased with Reynolds number. Deflecting the flap added an increment of maximum lift coefficient that seemed to be almost constant at all Reynolds numbers. The slope of the section lift curve with flap deflected showed no consistent variation with Reynolds number, although the slope of the section lift curve for the plain airfoil increased up to a Reynolds number of about 1.0 x 10 6 and then remained nearly constant up to a Reynolds number of about 3.0 x 106, the limit of the tests. For flap deflections about 15°, the slope of the section lift curve decreased with increase in flap deflection. The section drag coefficient with flap deflected remained almost constant with Reynolds number of about 0.8 x 106 and then remained nearly constant to a Reynolds number of about 3.0 x 106.

Summary: An investigation in two NACA wind tunnels has determined the effect of Reynolds number and stream turbulence on the lift and drag characteristics of a low-drag airfoil, the NACA 653-418, a=1.0 section, particularly at low Reynolds numbers, to give an indication of the performance of low-drag wings in low-scale tests. The results are correlated with similar data for the same airfoil section in the NACA two-dimensional low-turbulence pressure tunnel to provide data over a range of Reynolds number from 0.19 to 9.0 x 106. Large increases in minimum drag coefficient were found as the Reynolds number decreased. This effect was particularly marked at Reynolds numbers below 1.5 x 106. At Reynolds numbers below 1.5 x 106, stream turbulence had little effect on the drag characteristics of the NACA 653-418 airfoil section when compared on the basis of test Reynolds number but, at higher Reynolds numbers, stream turbulence had a detrimental effect on drag. Large decreases in maximum lift coefficient were found with decreasing Reynolds number; most of this decrease was encountered at Reynolds numbers above 2.0 x 106. Marked differences in maximum lift were apparent between the results obtained at high and low turbulence. When compared on the basis of effective Reynolds number, however, fair agreement was reached between the data obtained under both turbulence conditions.

A theoretical analysis, based on the linearized equation for supersonic flow, of characteristics of triangular-tip control surfaces on thin triangular wings. By restriction to case for which Mach lines from wing apex lie behind the leading edge, a simplified treatment was possible; results of previous work on lift of triangular wings could be used to derive expressions for lift effectiveness, pitching moment, rolling-moment effectiveness, hinge moment due to control deflection, and hinge moment due to angle of attack. Comparisons were made with two-dimensional case.

Because of the complexity of the equations resulting from the analysis, numerical calculations from the equations are presented in a series of figures. A computational form is provided to be used in conjunction with these figures so that calculations can be made without reference to the analysis.

The effect of Reynolds number on the aerodynamic characteristics of a low-drag airfoil section tested under conditions of relatively high stream turbulence was determined by tests in the LMAL 7- by 10-foot tunnel of the NACA 65(sub-3)-418, a = 1.0 airfoil section with a split flap having a chord 20 percent of the airfoil chord. The Reynolds number ranged from 190,000 to 2,990,000; the Mach number attained was never greater than 0.10. The data are presented as curves of section angle of attack, section profile-drag coefficient, and section pitching-moment coefficient against section lift coefficient for various flap deflections.

The results of the investigation indicate that: (1) The structure temperatures that prevail in a thermal ice-prevention system are of sufficient magnitude to require some consideration in the design of stressed members (2) heated-air temperature is the primary variable affecting the structure temperatures.