AEROELASTIC AND AERO-VISCOELASTIC FLUTTER ISSUES IN THE AGE OF HIGHLY FLEXIBLE FLIGHT VEHICLES

Abstract

Aeroelastic and aero-viscoelastic phenomena arising from the high flexibility of modern flight vehicles are examined, and governing relations are formulated and solved. In particu- lar, the time dependent flight velocities associated with maneuvers and with in-plane bending are considered, which necessitate new derivations of the Theodorsen function, unsteady aero- dynamic relations and equations of motion. Under these conditions, simple harmonic motion (SHM) is no longer achievable and different flutter criteria based directly on motion stability are presented. The viscoelastic problem, of importance to composites and other media, is for- mulated in terms of integral partial differential equations with variable nonlinear coefficients. Their solutions and evaluations are discussed in detail. One interesting departure from linear elastic and/or viscoelastic constant flight velocity responses emerged which, for some configu- rations. indicates the presence of flutter in the in-plane bending mode while the other bending (plunging) and torsional modes both remain stable.