Flight Simulation of a Hybrid Electric Propulsion VTOL UAV for Mission Performance Assessment

Hybrid Electric Propulsion Systems (HEPS) have grown to be a promising topic of research for Unmanned Aerial Vehicles (UAVs) applications as they combine the complimentary benefits of internal combustion engine and electric propulsion systems while reducing pollutant emissions. Controlling UAVs in any flight condition is essential for its successful application in practical missions. In general, hybrid-electric UAVs exhibit three flight modes: vertical flight mode, fixed-wing mode and transition mode. The transition control design from vertical and hover flights to fixed-wing flight mode or vice versa still remains a challenge due to the multiple nonlinearities in the model and the optimal design results have a strong effect on mission performance. In the present study, a numerical model was developed to enhance the flight performance and the transition control of a hybrid electric multi-rotor UAV during a specific flight mission. This model is based on the control of forward thrust, lift thrust, and pitch angle to achieve the speed, altitude, and position defined in the mission profile of the flight simulation. The simulation results show that, of the two applied control strategies, the one that separates the segment into one below stall speed and another above stall speed provides better performance and faster response during transition from vertical flight mode (VTOL) to horizontal fight mode (fixed-wing) and vice versa, where significant changes in speed and pitching angle occur.