Hybrid feedforward-feedback control for active helicopter vibration suppression

Emerging technology in rotorcraft design and the increasing demand for maximum vibration suppression during both the steady-state and transient flight conditions create the need to design and evaluate new strategies for vibration control in helicopters. In this research, a hybrid feedforward-feedback control scheme is developed and implemented in an active airframe configuration using PZT stack actuators to effectively suppress vibration within the helicopter fuselage. Using finite element analysis to develop the mass and stiffness matrices, a scaled Apache AH-64A tail boom structure with four PZT actuators placed in parallel as frame members is modeled. Eigenanalysis is conducted and a reduced order model is developed using the first ten system modes. The hybrid feedforward-feedback controller is developed utilizing a Linear Quadratic Gaussian (LQG) feedback controller and an adaptive feedforward controller combined in series. Using MATLAB and SIMULINK simulation, it is shown that the hybrid control scheme outperforms the current state of the art adaptive feedforward control scheme during tail boom vibration disturbance conditions based upon previous flight test data and new emerging rotorcraft design. The hybrid control scheme suppresses vibration below the accepted standard of 0.05 g throughout all disturbance conditions.