The HeRKoLus project set out to design a hybrid‑electric propulsion system for the Zeppelin NT airship, aiming to cut emissions and operating costs while preserving the aircraft’s existing mission profile. The study defined three reference missions that the new system must support: a 45‑minute sightseeing flight that can be repeated many times a day, a long‑range transfer flight of roughly 11 hours covering 300–350 nautical miles, and an advertising flight that includes a two‑hour outbound and return leg of about 75 nautical miles plus a multi‑hour hovering segment. Each mission incorporates a reserve period—two hours for the sightseeing flight and four hours for the transfer and advertising flights—during which the airship flies slowly at low power. The required thrust and shaft power for each of the four propellers are summarized in the project’s performance table; the cruise power demand is only 75 kW, but the system must also deliver the higher peak powers needed for take‑off, maneuvering, and reserve operations. The existing propulsion system’s mass and detailed mass breakdown were supplied by Zeppelin Luftschifftechnik (ZLT), enabling a realistic comparison and weight optimisation.

To explore the design space, the team employed a morphological box that encoded 113,400 possible hybrid configurations. By applying plausibility rules—such as excluding combinations that would pair a piston engine with a battery—the list was narrowed to 58 viable variants. This systematic approach ensured that no promising architecture was prematurely discarded. The selected hybrid architecture will be detailed further and subjected to ground‑based testing in a dedicated test rig, as outlined in the project’s next phase. The anticipated benefits include reduced fuel consumption, lower noise, and a smaller, more efficient central power unit that can be shut down when not needed, thereby improving overall reliability and lowering maintenance demands.

Collaboration was central to the project’s success. Zeppelin Luftschifftechnik, the sole partner and consortium leader, provided the type certificate for the Zeppelin NT and supplied critical data on the current propulsion system. The research was conducted at the University of Stuttgart’s Institute for Aircraft Design under Prof. Dr.-Ing. Andreas Strohmayer, with key contributions from research group members Jonas Lay and Andreas Bender. The project was funded under the German aviation research programme LuFo VI‑1. Meetings were held online until mid‑2022 because of the COVID‑19 pandemic, after which in‑person sessions resumed. The project’s timeline spanned several years, with the initial design and analysis phase completed before the planned test‑rig validation. The partnership leveraged ZLT’s operational experience and the university’s expertise in hybrid‑electric flight to create a comprehensive design that balances performance, cost, and environmental impact.