Distributed actuator approach for active control of helicopter airframe vibrations

Active control of helicopter vibrations, with actuators in the airframe structure, is appealing in terms of simplicity, airworthiness, and effectiveness. The actuator locations of current active control systems are centrally located in the cabin or near the main rotor. A new approach to advance the state-of-the-art in helicopter active vibration control is proposed and explored in this research. The approach uses an optimization process to distribute a set of actuators throughout the airframe. A reduced order airframe dynamic model is utilized for the design methodology synthesis and system analysis. Actuator models are formulated and integrated with the airframe dynamic model. A novel optimization methodology is formulated to simultaneously determine optimal actuator placement and control actions. The optimization process couples an optimal control formulation with a non-gradient based optimization routine. An analytical study is performed comparing distributed actuator configurations to a representative state-of-the-art centralized actuator configuration. Actuation requirements are evaluated to aid the realization of an active airframe configuration. When compared to a representative state-of-the-art control configuration, a distributed actuator configuration achieves greater vibration reduction and requires less control effort. For example, one distributed actuator configuration produced an additional vibration reduction of 57% and a 15% control effort reduction.