Robust hover control of thrust-vectored unmanned tail-sitter aircraft against gust load

Vertical take-off and landing (VTOL) aircraft has the merits of both fixed-wing and rotary-wing aircraft. Tail-sitter is the simplest way for the VTOL maneuver since it does not need extra actuators. However, conventional tail-sitting airplanes made by propellers or duct fans have less thrust and efficiency. In this paper a conceptual thrust-vectored unmanned tail-sitter (CTUT) aircraft which is controlled by no control surfaces but only with two thrust vectors is introduced. However, the system of hovering control for a tail-sitter UAV is like a 3-D inverse pendulum, which is unstable and quite difficult to control against the gust load in traditional PID controllers. In this paper, the synthesized system model including thrust-vectored tail-sitter aircraft model, actuator system and gust model is developed. The LQG/LTR control for robust hovering against gust load is proposed. The results show that the controller designed successfully compensates the errors generated by gust.