Investigation of Whirl Flutter Stabilization using Active Trailing Edge Flaps

Within the development of propeller and tiltrotor aircraft, whirl flutter has always been a major concern, as the phenomenon potentially leads to unstable whirling motions of rotors or propellers. The likelihood for the occurrence of whirl flutter is increased by low stiffness values of the structure that is bearing the propeller or rotor which is a typical trend for modern light weight structures used in helicopter design. Common means to stabilize the phenomenon comprise modifications in the stiffness or modeshapes of the propeller/rotor bearing structure and thus a major design amendment. In this paper, the insertion of a whirl flutter-like instability into an aeroelastic model of a generic helicopter by adding artificial support structure modes is presented and a stabilization approach using active trailing edge flaps is proposed. Whereas attempts to stabilize whirl flutter using standard controllers have been performed already, the controller concept presented in this paper explicitly uses the periodicity of rotor systems. It is shown by simulation that whirl flutter can be alleviated by the proposed control approach and that robustness is given with respect to flight speed.