The project “Evaluation of (hybrid‑)electric propulsion systems for small aircraft” was carried out at the Institute for Jet Propulsion and Turbomachinery (IST) of RWTH Aachen University from 1 August 2020 to 31 December 2022. It was part of the joint research initiative IVekLu, funded by the German Ministry of Education and Research. The consortium comprised IST, the aircraft design organisation Bauhaus Luftfahrt e.V. (BHL), and the propulsion‑software company GasTurb GmbH. IST led the overall coordination, BHL was responsible for the aircraft design, and GasTurb supplied its established software for modelling jet engines and hybrid propulsion systems.
The scientific work was organised into seven work packages. In the first package a comprehensive map of hybrid‑electric aircraft concepts was produced, followed by the definition of overarching system requirements such as payload, range, cruise speed, altitude, and a projected market entry date. These requirements guided the selection of representative aircraft configurations and propulsion architectures in work package 1.3. Using the IST’s modelling tools, BHL identified a set of technically feasible aircraft layouts and evaluated several propulsion options—including fuel‑cell, piston‑engine, and battery‑driven hybrids—against the mission profiles defined earlier. A joint workshop finalized the choice of configurations for the subsequent system studies.
Work package 2.1 focused on the identification and specification of the mechanical, electrical, and thermal components needed for the propulsion models. This included small‑power fuel cells, supporting hardware, piston engines, and batteries. IST and GasTurb agreed on the required detail level and interface definitions. In work package 2.3 the newly created component models were verified by IST. Reference data were gathered from higher‑detail models and, where available, experimental measurements. The component outputs were compared to these references, and the models were calibrated to ensure accuracy.
Thermal management, addressed in work package 3.3, was modelled in collaboration with BHL for two small aircraft equipped with (hybrid‑)electric drives. IST first quantified the cooling demand of the propulsion components, paying particular attention to the thermal coupling of electronic power switches and the cooling of PEM fuel cells and batteries operating at low temperatures. Interfaces to the aircraft’s overall thermal system were defined, and key parameters such as heat fluxes and maximum allowable component temperatures were established.
In work package 4.2 the drivetrain models were synthesised. IST, together with GasTurb, integrated the propulsion system models with the aircraft models provided by BHL, ensuring consistent control volumes and interface compliance. Error‑handling strategies developed by GasTurb were reviewed and refined by IST to improve reliability.
The final work package, 4.3, combined the propulsion and aircraft models to perform full system studies for both a vertical‑take‑off and landing (VTOL) and a conventional take‑off and landing (CTOL) aircraft. Evaluation criteria were defined, and the suitability of the hybrid‑electric propulsion concepts for the specified mission requirements was assessed. The studies demonstrated the feasibility of the proposed design methods, highlighted the advantages and disadvantages of different propulsion architectures, and produced actionable insights for future research and development of small hybrid‑electric aircraft.
Overall, the project delivered a validated methodology for early‑stage design of hybrid‑electric propulsion systems, a set of verified component models, and comprehensive system‑level performance assessments for two representative aircraft configurations. The collaboration between IST, BHL, and GasTurb combined academic modelling expertise, practical aircraft design experience, and commercial propulsion software, ensuring that the results are both scientifically robust and directly applicable to industry‑driven development programmes.