A Feedback-Feedforward Controller for Hybrid Flight Regimes in Transitioning Aerial Vehicles

This paper presents a guidance and control methodology for transitioning unmanned aerial vehicles (UAS) designed around hybrid flight, i.e., flight states purely in the transition regime. The control architecture, designed for a tailsitter vehicle, consists of a trajectory planner, an outer loop position controller, an inner loop attitude controller, and a control allocator. The trajectory planner uses a simplified vehicle model with aerodynamic and wake effects for generating optimal trajectories and associated aerodynamic feedforward information for minimum time transition between flight modes. The outer loop position controller then uses these approximate aerodynamic forces computed by the trajectory planner in feedforward along with feedback linearization of the outer loop dynamics. The inner loop attitude controller is a standard nonlinear dynamic inversion control law that generates the desired pitch, roll and yaw moments, which are then used to compute rotor angular velocity commands. We derive analytical conditions that guarantee robust stability of the outer loop position controller, in the presence of uncertainty in the feedforward aerodynamic force compensation. Finally, the performance of the control architecture is evaluated on a high fidelity flight dynamics simulation of a quadrotor biplane tailsitter for various transitioning flight missions that demand high maneuverability.