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A quadrotor equipped with a fixed-wing (hereinafter referred to as the quadrotor tail-sitter UAV) has been developed by authors. The quadrotor tail-sitter UAV can hover like a quadrotor and can fly like a fixed-wing airplane. The remarkable characteristic of the developed quadrotor tail-sitter UAV is that it does not use any control surfaces during any form of flight; hovering, transition flight or level flight. This paper discusses an optimal transition from hovering to level flight for the quadrotor tail-sitter UAV because transition flight is most likely to be unstable throughout flight owing to stalling of the fixed-wing. The paper proposes three transition strategies: (i) normal transition (PID feedback to a step input), (ii) minimizing the transition time, and (iii) minimizing the transition time with keeping altitude constant. To realize the above optimal transition strategies, the aerodynamic parameters of the developed quadrotor tail-sitter UAV are measured by the wind tunnel test in advance. The three strategies are experimentally verified and the comparison among the three strategies is presented. [ABSTRACT FROM AUTHOR]

Quadrotor unmanned aerial vehicles (UAVs) have been actively used in various fields. However, only the altitude and the attitude in three degrees of freedom can be independently controlled since quadrotor UAVs are underactuated systems. A quad tilt rotor UAV solves the problem of an underactuated system in a general quadrotor UAV. The quad tilt rotor UAV can control both position and attitude independently by tilting the directions of the propellers. However, the flight control system in a wide range of attitudes has not been discussed yet, for example a UAV can fly and hover with a 90pitch angle, and it can even flip over when the thrust direction is tilted in a wide enough range. In this paper, we present the attitude transition flight control system for pitch angles ranging from 0to 90since flight conditions with a 90pitch angle significantly differs from that in a conventional quadrotor UAV flight. We construct an adequate control system for a flight with a wide range of attitude conditions. [ABSTRACT FROM AUTHOR]

In this paper, we present the development of a quad-rotor tail-sitter unmanned aerial vehicle (UAV) that is composed of quad rotors and a fixed wing. The developed UAV can hover like a quad-rotor helicopter and can fly long distance like a fixed-wing airplane. The main wing of the developed UAV is taken from a commercially available radio-controlled airplane and other parts such as the body frame are newly developed. A microcomputer, various sensors and a battery are mounted on the UAV for autonomous flight without any support from a ground system. Attitude and altitude control systems are developed for the UAV. In order to verify the designed controller, a three-dimensional flight simulator of a quad-rotor tail-sitter UAV is developed by use of MATLAB/Simulink. This paper also describes attitude control experiments. The results show that the propeller slipstream has a negative influence on attitude control. Solutions for the negative influence of the propeller slipstream are also discussed in this paper. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]