NACA Research Memorandums

A two-dimensional wind-tunnel investigation of the flow and force characteristics of four NACA 6A-series airfoils with thickness ratios of 4, 6, and 9 percent has been conducted in the Langley airfoil test apparatus at at transonic Mach numbers between 0.8 and 1.25. The Reynolds number range for these tests varied from 2.6 x 10(6) to 2.8 x 10(6). As was expected, the airfoils exhibited a smooth transition in force coefficients from a Mach number of 1.0 to the values obtained at the higher speeds. Lift-curve slope and maximum lift-drag ratio correlated very well on a basis of the transonic similarity laws at Mach numbers above 1.0, but below that value the correlation was not good. The measured effect of thickness on the drag coefficient at supersonic speeds was less than that predicted by the transonic similarity laws. Good correlation of the drag coefficients was obtained by reducing the exponent of the thickness term from the theoretical value of 1.67 to 1.50. This change did not affect the correlation at subsonic speeds, which was good for either case