Aeroelastic control of non-rotating and rotating wings using the dynamic stiffness modulation principle via piezoelectric actuators

Carleton University’s Rotorcraft Research Group is working on the development of an active rotor control system that incorporates a mechanism for helicopter blade pitch dynamic stiffness modulation at the root, the Active Pitch Link. This system overcomes stroke limitations of smart material and attains superior performance for helicopter rotor-induced vibration reduction. The system was tested at the whirl tower facility and this article reports the achievements obtained with a dynamically similar hinged rotor blade model. Up to 100% reduction in the transmitted loads occurred at the target 2/rev frequency when the blade was excited by a transversal jet to mimic the asymmetric flow of the helicopter rotor in forward flight. An open-loop control algorithm optimized to a target higher-harmonic frequency of the rotor also minimized the impact on the rotor fundamental cyclic control frequency at 1/rev. In another experiment at University of São Paulo, semi-passive control techniques using shunted piezoelectric materials were investigated for the aeroelastic control of fixed wings. Flutter oscillations of a typical section were controlled out over a range of airflow speeds. Finally, the similarity between both control techniques is discussed and recognized that they are based on a dynamic stiffness modulation control principle.