Optimization Approach to Vibration Reduction in Rotorcraft Airframes Using Individual Blade Control

Vibrations of helicopter airframes are a major concern in rotorcraft design. They can impair crew performance, reduce passenger comfort, and cause fatigue damage of structural components. Recently considerable effort has been undertaken to reduce rotor-induced vibrations by means of actively controlled rotor blade trailing edge flaps. Several methods for developing control laws for the efficient actuation of the trailing edge flaps have been proposed. In this paper, the feedback gains are computed using a multi-objective parameter synthesis tool. With this approach, it is possible to significantly drive down airframe vibrations at specific locations of interest while limiting hub loads to a predefined value. Since the optimization tool allows to prescribe a certain controller structure, it is possible to limit the control law complexity to a for practical purposes acceptable level. Controller robustness is shown by application of the vibration controller to an off-design flight condition and evaluation of its efficiency to drive down airframe vibrations in this non-nominal case. Alternative formulations of the optimization problem are briefly discussed.