A strip method for prediction of damping in subsonic wind tunnel andflight flutter tests.

Abstract

A strip method has been developed for the prediction of subcritical damping characteristics for guidance of subsonic wind tunnel and flight flutter tests. The transient aerodynamic coefficients are found from a Fourier transform of the two-dimensional incompressible oscillatory coefficients. A series of transient aerodynamic influence coefficients (AIC's) has been derived including a newly denned matrix of aerodynamic lag AIC's. Compressibility, sweep and finite span effects are included by varying the lift curve slope and aerodynamic center locations on each strip in accord with static wind tunnel data. A collocation formulation of the subcritical flutter eigenvalue problem is presented. A special technique for solving the complex eigenvalue problem is reviewed and illustrated in an example of a restrained (cantilevered) wing with five strips and ten elastic degrees of freedom. Finally, the simplifications that result from reducing the size of the eigenvalue problem by modal methods are discussed.