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This study investigates the effect of piezoceramic actuator hysteresis on helicopter vibration control using dual trailing-edge flaps. Piezoceramic stack actuators are promising candidates for trailing-edge flap actuation in full-scale helicopters. However, they are inherently nonlinear in response to an applied electric field and exhibit hysteretic behavior between the applied electric field and displacement. In this study, bench-top tests are conducted on a commercially available piezoceramic stack actuator, and its dynamic hysteretic behavior is studied. A Preisach-type dynamic hysteresis model is used to describe the hysteresis in the stack actuator. The unknown coefficients in the model are obtained through identification from experimental data. An aeroelastic model of the helicopter with multiple trailing-edge flaps is then used to predict the hub vibration levels under different flight conditions. The optimal actuator control input for hub vibration suppression in the presence of actuator hysteresis is considerably different from the case of an ideal-linear actuator. Numerical results show the importance of modeling actuator hysteresis in helicopter vibration control using trailing-edge flaps. Ignoring or inaccurate modeling of hysteresis in the piezoceramic actuator can lead to inaccurate phasing of the trailing-edge flap motion which directly affects the performance of the vibration control system.

This study aims to determine optimal locations of dual trailing-edge flaps to achieve minimum hub vibration levels in a helicopter, while incurring low penalty in terms of required trailing-edge flap control power. An aeroelastic analysis based on finite elements in space and time is used in conjunction with an optimal control algorithm to determine the flap time history for vibration minimization. The reduced hub vibration levels and required flap control power (due to flap motion) are the two objectives considered in this study and the flap locations along the blade are the design variables. It is found that second order polynomial response surfaces based on the central composite design of the theory of design of experiments describe both objectives adequately. Numerical studies for a four-bladed hingeless rotor show that both objectives are more sensitive to outboard flap location compared to the inboard flap location by an order of magnitude. Optimization results show a disjoint Pareto surface between the two objectives. Two interesting design points are obtained. The first design gives 77 percent vibration reduction from baseline conditions (no flap motion) with a 7 percent increase in flap power compared to the initial design. The second design yields 70 percent reduction in hub vibration with a 27 percent reduction in flap power from the initial design.

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