The influence of thickness/chord ratio on supersonic derivatives for oscillating aerofoils

Abstract

By the use of Temple and Jahn's theory for the oscillating flat plate and Busemann's theory for aerofoils in steady motion, derivatives are obtained for symmetrical circular-arc and double-wedge aerofoils describing low frequency oscillations at supersonic speeds. It is known that theoretically the torsional aerodynamic damping for a flat plate oscillating about an axis forward of the two-thirds chord position is negative at low frequencies for a limited range of supersonic speeds. In this report, however, it is shown that the effect of increasing thickness/chord ratio is to decrease the range of speeds for which the aerodynamic damping is negative, and for which one degree of freedom flutter is possible. The present theory also allows for the forward movement of the centre of pressure from the half-chord position as the aerofoil thickness is increased, and leads to better estimates of the stiffness derivatives for an actual aerofoil. In practice, the centre of pressure is not at half-chord as predicted by linear theory.