Modeling and control of highly flexible flying-wing uav with multiple elevons and propellers

A coupled and geometrically nonlinear structural/flight dynamics model with unsteady aerodynamics model is developed for a large scale highly flexible solar-powered UAV. Based on the model, the UAV is trimmed with all the all-wing span elevons deflecting conformably. For the longitudinal control, the equation of motion in trimming condition is linearized firstly, then the dynamic model of elevons servo and integral signals are augmented into the control plant. The LQG/LTR method is employed to control the pitch angle. Simulation results show that the controller can provides a quick dynamic response with a very small additional deformation of the wing. For lateral-directional control, the lateral control efficiency of elevons is evaluated. It is found that due to the large lateral and poor directional static stability, the lateral control efficiency is very limited, and an aileron reversal coefficient is proposed and verified. In contrast, the multilateral differential throttles control has higher control efficiency in lat-dir control, but it must be noted that the inertia of propellers and motors will reduce the phase margin and the damping ratio of Dutch mode significantly due to the low cut-off frequency.