Use of rotor state feedback to improve closed loop stability and handling qualities

A rotorcraft control law which 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 of a utility helicopter over its entire operating envelope and over a large range of rotor speeds. The RSF control law is designed to integrate seamlessly with the baseline control law and can be readily engaged or disengaged. The RSF control gains are designed using LQR synthesis on an augmented plant model that includes the baseline controller feedback loops. Linear analysis of the controller show that RSF allows much larger feedback gains, which can be used to improve the disturbance rejection properties of the rotorcraft. Results show that without RSF, increasing feedback gains can results in closed-loop instability, especially when operating at a reduced rotor speed. The controller was tested in non-linear simulation, and the RSF control law was shown to effectively eliminate closed-loop instabilities in the presences of high feedback gains. Piloted simulations were conducted and show that handling qualities are improved with high feedback gains, which are only feasible with the use of RSF.