Design Space Exploration Study and Optimization of a Distributed Turbo-Electric Propulsion System for a Regional Passenger Aircraft

Electric propulsion systems are considered as one possibility to reach the ambitious goals of the European Union’s Flightpath 2050 with regards to greenhouse gas emissions and noise. It has been claimed in several publications that Distributed Electric Propulsion (DEP) offers significant improvement in aerodynamic efficiency and thus a reduction in structural weight of the wing and noise emissions as well as additional degrees of freedom concerning flight control. To not outweigh those advantages by heavier drivetrains, the components within the electric propulsion system have to be extremely lightweight, efficient and reliable at the same time. The German nationally funded project SynergIE evaluates DEP for a 70 PAX regional reference aircaft with two (SE-2), six (DEP-6) and twelve (DEP-12) propulsion units with a turbo-electric drivetrain layout. This study aims to quantify the effect on the specific block fuel consumption for the different numbers of propulsors based on Top Level Aircraft Requirements (TLARs). The approach contains a coupled electric drivetrain system model which is based on physically derived, analytical models for each component linking specific subdomains, e.g., electromagnetics, structural mechanics and thermal analysis. A genetic algorithm is applied to optimise the key performance indicators (KPIs) of the electric system, before the results are fed back to the aircraft sizing process. It has been identified that constraints such as installation space or architectural decisions such as the number of propulsors have significant influence on the drivetrain weight and efficiency and interact with the whole aircraft sizing process, esp. with reference to nacelle weight and drag and thus the block fuel consumption. The study shows that the DEP-6 and DEP-12 project aircraft both have a potential of reducing the specific block fuel consumption by approx. 4.2 % and 5.8 % respectively in case of direct driven propellers, while for a geared-drive scenario a total reduction of up to 7.6 % in case of DEP-6 and 8.5 % in case of DEP-12 is possible, all compared to the direct-driven baseline (BSL) aircraft SE-2.