Nonlinear dynamic inversion control for urban air mobility aircraft with distributed electric propulsion

In this work the use of a Nonlinear Dynamic Inversion flight control system is investigated for use on electric-VTOL aircraft. This included studying the use of an airspeed scheduled switching system that would switch the aircraft's control architecture from a low speed helicopter control system to a high speed airplane control system. Additionally, a novel thrust control allocation scheme is presented. This new scheme combines the variable collective pitch and variable rotor speed allocation schemes into a unified, complimentary filtering based, control allocation scheme. This new scheme is compared against the original constituent schemes on the basis of time simulations, stability margins and handling qualities. The successful operation of the control architecture switching system, was demonstrated via time domain simulations. It was also found that the combined control allocation scheme did not have better performance than the variable collective pitch scheme. However, the combined scheme did offer some improved performance over the variable rotor speed scheme. Especially when electric motor torque limits are enforced. The combined control allocation scheme was able to perform maneuvers that the variable rotor speed scheme could not.