Powertrain System Analysis for an Urban Air Mobility Tiltwing Concept Vehicle

In support of research and development for Urban Air Mobility (UAM) operations, the National Aeronautics and Space Administration (NASA) is developing a fleet of Vertical Takeoff and Landing (VTOL) concept vehicles. These vehicles aim to identify key areas for technological growth and provide reference data to the UAM community. A six-passenger Tiltwing concept recently added to the fleet offers new opportunities to explore the UAM design space through trade studies of the power and propulsion systems. In this paper, a turboelectric powertrain is designed and analyzed using the Numerical Propulsion System Simulation (NPSS) tool, the NPSS Power System Library, and a motor drivetrain optimization tool. Direct and geared motor drivetrains are designed and compared across a UAM design mission. Sensitivity of the Tiltwing maximum takeoff weight to motor drivetrain weights and efficiencies is estimated and used to inform optimal motor and gearbox selection. Results indicate that direct-drive and geared-drive configurations are comparable for this vehicle, with slight advantages to direct-drive when the radius of the drivetrain is unconstrained. When the drivetrain radius is constrained, a geared-drive system becomes more optimal.