The effect of structural damping on binary flutter

Abstract

The paper describes an investigation of the effect of structural damping in the torsion mode on wing flutter with the object of finding circumstances in which damping reduces the flutter speed. The drop in flutter speed can be considerable (25 per cent) and extend to very large values of structural damping. The effect is most apparent when the relative density (wing to air) is high, and when the wing bending mode involves a relatively large aerodynamic stiffness. The rate of decrease of flutter speed with damping in small, and for the amounts of damping normally encountered in practice the effect is unlikely to be important. Possible practical cases are, however, part-full under-wing fuel tanks, which can supplyhigh structural damping, and large tailplane amplitudes in the wing torsion mode, which can supply considerable aerodynamic damping; in both cases the effect could be appreciably adverse.