The possibility of developing an airfoil to carry lift without decreasing the critical Mach number below that of the basic thickness form at zero lift has been investigated. Low-speed tests of five NACA 66-series airfoil sections having a thickness-chord ratio of 0.l6 were made in the Langley two-dimensional low-turbulence pressure tunnel. By designing the mean line to carry load over the portions of the airfoil section having low induced velocities an effective design lift coefficient (the lift coefficient corresponding to the center of the range of high critical Mach numbers as obtained from the experimental pressure distribution) of approxi¬mately 0,1 was obtained for several airfoil sections without causing the maximum predicted critical Mach numbers to be appreciably less than the critical Mach number for the basic thickness form at zero lift.
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