Full Flight Regime Controller Design for a Lift+Cruise eVTOL Aircraft

At present, the vast majority of control design work on winged eVTOLs focuses primarily on a specific flight regime, usually hover or cruise. Transition, however, is an equally critical flight regime that requires a combination of both rotorcraft and airplane control effectors to maintain trim and execute maneuvers. Full flight regime trim strategies are examined for a Lift+Cruise eVTOL aircraft. Control laws are designed for hover, transition, and cruise conditions to satisfy standard flying-qualities requirements based on the characteristic behavior of the vehicle (rotorcraft vs. fixed wing) while ensuring realistic motor limits (peak and continuous) are satisfied. CONDUIT® is used to optimize control laws to minimize actuator activity while meeting flying-qualities constraints. Variable-RPM control is shown to be sufficient to satisfy Level 1 flying-qualities requirements in hover and low-speed flight, where control surfaces have inadequate control authority. Time domain simulations are presented to verify controller performance and ensure actuator limits are not violated while following step commands. The aircraft is able to follow commands well in all axes and flight regimes. Successful simulation of transition through the full flight regime (hover-to-cruise and cruise-to-hover) is achieved using a quasi-linear parameter varying stitched model. It was found that elevator sizing and choice of transition speed are strongly linked, and that either a transition speed very near the cruise speed or a large elevator is warranted.