Suppression of bending-torsion flutter in accelerated flight with aero-servo-viscoelastic controls

The Theodorsen function [1] is generalized to non simple harmonic motion and for time dependent flight velocities encountered during maneuvers, changes in altitude, landings, takeoffs, etc. A formulation and examination is undertaken of the dynamic responses of flexible linear viscoelastic lifting surfaces in potential flow and under the influences of unsteady aerodynamic forces, non-simple harmonic motion and time dependent flight velocities. Differential, integral or proportional servo-controllers are added in order to stabilize the system and extend its lifetime. Parametric studies of servo-controllers led to no general conclusions because of the highly complicated phase relations. However, computational simulations indicate that a continual increase in servo control parameters does not necessarily culminate in utter velocity increases, but actually may decrease such thresholds after a maximum control condition has been achieved. The presence of flight maneuvers introduces time de- pendent velocities and coefficients in the governing integro-differential relations. These are solved analytically by piecewise averaging of the coefficients over selected time intervals. Expanded necessary and sufficient utter conditions beyond the customary simple harmonic motion definition are also formulated.