A design of triaxial unmanned rotor aircraft and its adaptive flight control system

A tri-axial unmanned rotor aircraft consisting of three sets of coaxial rotors is designed. The control mechanism of the unmanned rotor aircraft is very much simplified. The rotors are directly driven by DC motors. The speed of each motor is the only regulating variable which could control the attitude and trajectory of the aircraft. In order to verify the design of the flight control system for the triaxial unmanned rotor aircraft, a nonlinear dynamic model of the aircraft is investigated. A computing method of the rotor aerodynamic loads is established by means of the blade element momentum theory. The effect of the rotor inflow characteristics on the rotor aerodynamic load is analyzed. The validity of the rotor aerodynamic load model for the co-axial rotor is tested by experiments. Due to the influence of nonlinearity and un-modeled dynamics, it is quite difficult to establish a very accurate mathematical model, which makes it a challenge to design a flight control system. In this paper, a rotational dynamical model inverse controller and translational dynamical model inverse controller are deduced according to the nonlinear model of the aircraft. The model inverse error is adaptively compensated with an online neural network. The command following error is regulated with a PD/PI controller. A combined maneuver flight mission task element is applied to simulation validation, which included pirouette and vertical maneuvers. A demonstration is conducted to validate the flight control system of the tri-axial unmanned rotor aircraft. Simulation results including an imitation of gust disturbance are provided. The demonstration shows clearly that the designed flight control system has adaptability and robustness, and that it can implement accurate command following control.