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.
Nomenclature
Controllability and stability of ducted fan air vehicles is a challenging problem due to their complex nonlinear aerodynamics and dynamic behavior. At the same time, the combination of vanes and rotor pitch controls can provide unique control characteristics for these vehicles. A dynamic inversion controller is designed for a tandem ducted fan air vehicle to achieve desired response characteristics across the flight envelope. The controller includes an inner loop that controls the attitude and an outer loop that controls translational motion. In this study, it is desired for the vehicle to perform translational maneuvers with minimum pitch and roll angles. This is obtained by modifying the control mixing and the model inversion controller to use a combination of cyclic pitch and vanes to generate a lateral or longitudinal propulsive force. Simulation results of the controller show that the use of vanes decreased the pitch and roll angles considerably for lateral and longitudinal translation maneuvers.
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