Preliminary Sizing of a Hybrid-Electric Passenger Aircraft Featuring Over-the-Wing Distributed-Propulsion

This study compares a hybrid-electric aircraft featuring a propulsive empennage and over-the- wing, distributed-propulsion to a conventional regional turboprop. The impact of multiple design parameters, mission requirements, and technology assumptions on maximum take-off mass and payload-range energy efficiency is evaluated, in order to illustrate the sensitivities of the design. A preliminary sizing method that incorporates aero-propulsive interaction effects is used to obtain rapid estimations. Results show that, for the baseline mission, the hybrid electric variant is 2.5% heavier and consumes 2.5% more energy than the reference aircraft. In this process, several key design guidelines and challenges for distributed-propulsion aircraft are identified. Firstly, when comparing a hybrid-electric configuration to a conventional one, each aircraft must be sized at its optimum cruise altitude for the same payload and range requirements. Secondly, the hypothetical advantages of distributed propulsion described in literature do not easily lead to a benefit at aircraft level, if the aero-propulsive interaction effects and associated dependencies are incorporated in the design process. Thirdly, the power-control parameters affect practically all characteristics of the aircraft, and the optimal control strategy is highly dependent on the aero-propulsive interaction. The results suggest that the proposed configuration can constitute a low-noise alternative for the regional transport market if the performance of the over-the-wing distributed-propulsion system is optimized.