Dynamic Inversion based Full Envelope Flight Control for an eVTOL Vehicle using a Unified Framework

Abstract

Urban Air Mobility is a future mode of transportation that will require a revolutionary new vehicle concept. One of the concepts currently being studied and developed are eVTOL (electrical vertical takeoff and landing) vehicles. This paper discusses a nonlinear dynamic inversion based control law that was designed for this vehicle concept. Two advantageous inherent properties of dynamic inversion in this setup are the effective decoupling of the control axes which are by design highly coupled for this kind of vehicle, and its ability to naturally handle changes of operating condition, which removes the need for gain scheduling. These are advantageous for control of VTOL vehicles, due to their wide range of operating conditions which varies from hover to forward flight, and transitioning between them. The inner dynamic inversion control loop, including an optimization based blended control allocation strategy to the rotors as well as to the control surfaces, serves as an inner core flight control system for the full envelope. This setup is complemented with a set of linear controllers, and reference models as well as command filtering for the different manual control modes in the various flight phases. An autoflight mode is included as well. By using Incremental Nonlinear Dynamic Inversion, it was found that the overall controller becomes significantly less dependent on accurate aircraft model properties, especially with respect to the aerodynamic derivatives, of which one can expect limited knowledge for this kind of UAM vehicles.