Use of Rotor State Feedback to Improve Closed-Loop Stability and Handling Qualities

Abstract

A rotorcraft control law that uses rotor state feedback (RSF) is presented and demonstrated in simulation. The baseline control law uses a model following/dynamic inversion approach to control the roll, pitch, and yaw axes. The RSF control law was designed to integrate seamlessly with the baseline control law and can be readily engaged or disengaged. The RSF control gains were designed using linear quadratic regulator synthesis. Linear analyses showed that RSF could allow for the feedback gains on rates and attitude to be increased to values that would result in closed-loop instability without the use of RSF. The increased gains can be used to increase bandwidth and improve disturbance rejection. The controller was tested on a nonlinear model in both non–real-time and piloted simulations, and results confirmed the linear analysis. The RSF control law design has potential to improve handling qualities by allowing higher bandwidth and better disturbance rejection with reduced risk of closed-loop instability.