Takeoff and Performance Trade-Offs of Retrofit Distributed Electric Propulsion for Urban Transport

While vertical takeoff and landing aircraft have shown promise for urban air transport, distributed electric propulsion on existing aircraft may offer immediately implementable alternatives. Distributed electric propulsion could potentially decrease takeoff distances enough to enable thousands of potential intercity runways. This conceptual study explores the effects of a retrofit of open-bladed electric propulsion units. To model and explore the design space, blade element momentum method, vortex lattice method, linear-beam finite element analysis, classical laminate theory, composite failure, empirically based blade noise modeling, motor and motor-controller mass models, and gradient-based optimization are used. With liftoff time of seconds and the safe total field length for this aircraft type undefined, this paper focused on the minimum conceptual takeoff distance. It was found that 16 propellers could reduce the takeoff distance by over 50% compared with the optimal 2-propeller case. This resulted in a conceptual minimum takeoff distance of 20.5 m to clear a 50 ft (15.24 m) obstacle. It was also found that, when decreasing the allowable noise by approximately 10 dBa, the 8-propeller case performed the best with a 43% reduction in takeoff distance compared with the optimal 2-propeller case. This resulted in a noise-restricted conceptual minimum takeoff distance of 95 m.