A multimodal flight control design and flight test of a tail-sitter UAV

Abstract

Aircraft capable of vertical take-off/landing (VTOL) have attracted considerable attention owing to their greater operability and high-speed horizontal flight capability for maximal mission range. A possible solution for such application is tail-sitters, which takes off vertically and transitions to horizontal flight. During its mission, a tail-sitter goes through largely varying dynamic characteristics from take-off to landing. In particular, the transition mode between vertical and horizontal flight is a critical part of its flight profile. In this study, I proposes a comprehensive multimodal flight control system for horizontal, vertical, and transition flight regimes. In conjunction with conventional multi-loop feedback, I uses $L_1$ adaptive control with quaternion feedback to supplement the linear controllers whose feedback gains are insufficiently tuned. Furthermore, a transition flight strategy to control the flight trajectory is proposed to improve the reliability and repeatability of these maneuvers. The key to a controlled maneuver is to maintain the vehicle’s desired path angle and flight velocity using a dynamic inversion technique. An adaptive system and a dynamic inversion technique can be used to reduce the gap between the simulation and the flight test. The proposed controller was first validated using simulation models and then through actual flight tests to successfully demonstrate its capability to control the vehicle over the entire operating range.