Investigation of departure transition noise for lift-plus-cruise eVTOL aircraft

This paper investigates the acoustics and performance during departure transition maneuvers for an eVTOL aircraft design of lift-plus-cruise configuration. A variable pitch lift rotor thrust control scheme with an airspeed-dependent schedule of rotor RPMs was used to fly the transition maneuvers. Parametric sweeps at different flight speeds were used to develop a schedule that would meet the goals of low noise and low power consumption. The aircraft forces and moments were studied throughout the departure transition maneuver and significant, unsymmetrical rotor-wing interaction occurred in the range of 40-70 knots. A change in the control mixer was found to reduce the impact of rotor-wing interactions on motor power consumption, improving the power margin and safety of the aircraft. Three departure transition maneuvers were studied to compare the power and energy required and the acoustic impact. First, a level acceleration maneuver prioritized airspeed gain; second, an axial climb maneuver prioritized altitude gain; and third a continuous climb maneuver was a combination of both strategies, as it accelerated and climbed at the same rate as the other two maneuvers. In general, it was observed that transitioning to wing-borne flight as quickly as possible reduced both acoustic impact and energy consumption during the departure maneuvers.