Piezoelectric Actuators in Helicopter Active Vibration Control

Abstract

Vibration is a major problem for helicopters due to flexible rotating blades, an airspeed varying radially and temporally at each rotor blade section, and a highly unsteady aerodynamic environment due to nonuniform wake and dynamic stall. The complexity of the forcing means that efforts to reduce vibration through vibration absorbers and isolators yield only meager vibration reduction and lead to a large weight penalty. The performance of such passive devices also degenerates quickly away from the tuned flight condition. Piezoelectric stack actuators offer the possibility of active vibration control in helicopter rotors, through the actuation of judiciously placed trailing edge flaps at appropriate higher harmonic multiples of the main rotor speed. Such actuators need to be coupled with amplification mechanisms to generate sufficient rotary motion of about 2 degrees which is needed to dramatically reduce vibration by 70–90 %. However, hysteresis is inherent in stack actuators, and this complicates their use in helicopter vibration control. In this chapter, we look at hysteresis compensation methods which can be used along with harmonic optimal control for vibration reduction in periodic rotating systems. The danger of ignoring hysteresis effects on the controller is also highlighted.