Analysis of Wingless eVTOL Dynamics and Design Low-Level Controller

Abstract

Urban Air Mobility (UAM) is a new type flying vehicle that transports people and goods around urban cities. The major electric vertical take-off and landing (eVTOL) concepts being studied and developed currently are 3-types, “Vectored Thrust”, “Lift + Cruise”, and “Wingless”. This paper focuses on the Wingless eVTOL because it has effective performances for short-range flight operation that will take the main role of Japanese UAM. Conventionally, a heavy rotor aircraft such as helicopter uses variable pitch to control thrust quickly, and heavy Wingless eVTOLs are suggested to have variable pitch as well. However, owing to the development of strong electric motors, the Wingless eVTOL like CityAirbus and VoloCity is controllable by variable speed method as well as UAV. The advantage of variable speed is significant regarding simplicity and maintenance cost. We analyzed the Wingless eVTOL detailed dynamics with rotor aerodynamics (blade element theory and momentum theory) and simple electric motor model. We took care of an additional counter torque by rotor inertia. UAV has the same effect, but it is so relatively small to air drag torque that it can be ignored. For the Wingless eVTOL, the angular acceleration of rotor brings large effect to control yaw. In order to overcome rotor inertia, we used many small propellers and the existing latest motor. This paper includes eVTOL dynamics that has unique behaviors and characteristics including both conventional helicopter and UAV. Moreover, our control architecture includes the command filtering, the reference model, the linear feedback and feedforward controller, the incremental dynamics inversion, and the mixer of 8 coaxial rotor with taking the rotor inertia. Finally, we applied the pilot command (attitude command) to the closed-loop system, and checked if hover and low speed requirements for small and moderate attitude change satisfy the ADS-33E.