Flight Control of Quad Tilt Wing Unmanned Aerial Vehicle : Objective and Difficulty in Development

This paper is concerned with the flight controller design of Quad Tilt Wing (QTW) Unmanned Aerial Vehicle (UAV) which has Vertical Take-Off and Landing (VTOL) capability as well as high speed cruise performance. The flight controller is composed of Stability Augmentation System (SAS), which feedbacks angular velocity, and Control Augmentation System (CAS), which feedbacks the difference between attitude commands and current attitude angles. The gains of S/CAS are both scheduled by the tilt angle of the main wings of the QTWUAV since its airspeed and flight dynamics drastically change in accordance with the tilt angle. The S/CAS are designed by three steps; we first select several design points, then design the controller gains at those design points, and finally connect the gains by linear interpolation. In the design process of the controller gains, perturbed models are introduced in addition to the nominal models, and common gains for those models are designed to ensure robust control performance against modeling errors. Full transition flight from vertical take-off to horizontal cruise was successfully accomplished using our controllers.