Attitude and Cruise Control of a VTOL Tiltwing UAV

This letter presents the mathematical modeling, controller design, and flight testing of an overactuated vertical take-off and landing tiltwing unmanned aerial vehicle (UAV). Based on simplified aerodynamics and first principles, a dynamical model of the UAV is developed which captures key aerodynamic effects including propeller slipstream on the wing and poststall characteristics of the airfoils. The model-based steady-state flight envelope and the corresponding trim-actuation is analyzed and the overactuation of the UAV solved by optimizing for, e.g., power-optimal trims. The developed control system is composed of two controllers. First, a low-level attitude controller based on dynamic inversion and a daisy-chaining approach to handle allocation of redundant actuators. Second, a higher level cruise controller to track a desired vertical velocity. It is based on a linearization of the system and lookup tables to determine the strong and nonlinear variation of the trims throughout the flight envelope. We demonstrate the performance of the control system for all flight phases (hover, transition, cruise) in extensive flight tests.