Abstract: The flight control strategy for vertical take-off and landing(VTOL) unmanned aerial vehicle(UAV) in mode transition is essential to ensure a safe and reliable flight. This paper studies the flight control strategy in the transition mode of tail-mounted VTOL UAV, and proposes a strategy of the fastest transition speed with constant altitude control. Simulation and experiment are used to analyze and compare the flight effect of this strategy, classical proportion-intergration-differentiation(PID) control and the fastest transition speed control. Strategy of the fastest transition speed with constant altitude control optimizes the change of flight speed and altitude, synchronizes the time of cruise attack angle and cruise speed, and maintains the vertical force balance of UAV in the mode transition. The simulation results show that the fastest transition speed with constant altitude control’s time decreases by 0.98 and 0.48s than that of the classical PID control and the fastest transition speed control, while the change of altitude decreases by 2.27 and 0.91m. The flight control effect of the fastest transition speed with constant altitude control is obviously superior to the classical PID control and the fastest transition speed control. The proposed control strategy solved the problem of large altitude change during the mode transition, and ensured the rapid and steady flight mode transition of UAV in the transition mode.

Key words: multiple flight mode, vertical take-off and landing (VTOL), unmanned aerial vehicle (UAV), transition mode, the fastest transition speed with constant altitude control