Effects of Independent Variations of Mach Number and Reynolds Number on the Maximum Lift Coefficients of Four NACA 6-Series Airfoil Sections

An investigation has been made in the Langley low-turbulence pressure tunnel to determine the effects of Mach number and Reynolds number on the maximum-lift characteristics of the NACA 65-006, 64-009, 64-210, and 642-215 airfoil sections in the smooth condition and in the condition with leading-edge roughness. The section lift characteristics were determined for Mach numbers ranging from 0.1 to approximately 0.5 at constant values of the Reynolds number. The Reynolds number range extended from 1.5 x 10(exp 6) to 9.0 x 10(exp 6). For the airfoil sections with abrupt stalls, such as the NACA 64-210 at low Mach numbers, increases in Mach number (Reynolds number held constant) generally resulted in gradual stalls; whereas; variations of Mach number generally caused only small changes in the stalls for those airfoil sections, such as the NACA 642-215 with gradual stalls at low Mach numbers. With leading-edge roughness, the stall for each airfoil section was gradual and generally unaffected by variations of Mach number. The reduction in maximum section lift coefficient resulting from increasing the Mach number from 0.1 to 0.4 (Reynolds number held constant) may be as large as 0.4) depending upon the airfoil section. With leading-edge roughness, the maximum section lift coefficient was only slightly affected by variations of the Mach number between 0.1 and approximately 0.5. The Reynolds number effects as indicated by experimental data for smooth airfoil sections are dependent, in many cases, upon the manner in which the Mach number varies with Reynolds number. The prediction of aircraft low-speed performance characteristics from experimental data should include considerations of the interrelated effects of Mach number and Reynolds number on maximum lift if wing maximum lift coefficients approaching those of the smooth airfoil section are anticipated.