Transition between Level Flight and Hovering of a Tail-Sitter Vertical Takeoff and Landing Aerial Robot

This paper presents the vertical takeoff, landing and transition between level flight and hovering of a tail-sitter vertical takeoff and landing (VTOL) aerial robot. The tail-sitter is suitable for micro aerial vehicles because it does not need any extra equipment for the VTOL maneuver. The developed tail-sitter aerial robot is equipped with four actuators for controlling ailerons, an elevator, a rudder and a propeller. A micro computer, various sensors and a battery are mounted on the aerial robot for autonomous flight without any support from a ground system. A transition flight strategy is constructed so that the transition finishes in the shortest time restricting an altitude change. In order to achieve the transition strategy, the reference trajectory of the pitch angle is computed offline by using an optimization technique. In the transition flight control system, a PID feedback controller is applied to attitude control, while a feedforward controller is applied to altitude control. The gain scheduling is applied to the control of the rudder and aileron. The experimental results on the transition between level flight and hovering, takeoff, and landing are presented.