This study compares a hybrid-electric aircraft featuring a propulsive empennage and overthe-wing, distributed-propulsion to a conventional regional turboprop. The impact of multiple design parameters, mission requirements, and technology assumptions on maximum takeoff 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 hybridelectric 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.

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This paper presents a synthesis of aero-propulsive interaction studies performed at Delft University of Technology, applied to conceptual aircraft designs with distributed hybrid-electric propulsion (DHEP). The studied aero-propulsive interactions include tip-mounted propulsion, wing leading-edge distributed propulsion and boundary-layer ingestion, combined with different primary propulsion-system arrangements. This paper starts with a description of the applied design framework and an overview of the aero-propulsive interactions. Subsequently, the different aircraft configurations are sized for a set of top-level requirements covering the range between regional turboprop to typical narrow-body turbofan aircraft. Results indicate that lower shaft power ratios show better performance, with the unoptimized DHEP concepts showing values of maximum takeoff mass (MTOM) and payload-range energy efficiency (PREE) comparable to their reference aircraft. It was shown that beyond 20% shaft power ratio, the PREE decreases and MTOM increases much more than between 10% and 20%, indicating a possible local optimum between these values since even lower values did not yield any significant improvements. The benefits of tip-mounted propulsion are found to be constrained by the propeller blade tip Mach number in this particular analysis for the selected reference blade loading distribution. At the high range case for Mach 0.5, it can be seen that the distributed propulsion systems show the largest improvement.