Diamond Aircraft is coordinating a pathbreaking Austrian Research Promotion Agency (FFG) funded project to advance understanding of gaseous H₂’s potential as a fuel source for hybrid powertrains in general aviation. The ‘H2EDT’ (H₂-based Twin-engine Electrification and Digitalization Testbed) project consortium – which unites researchers from FH JOANNEUM (Institute of Aviation and Electronic Engineering), TU Graz (ITnA), HyCentA and IESTA – is designing an experimental, hybrid testbed to explore the challenges H₂ poses as a fuel for aviation. Research will continue at Diamond Aircraft’s Wiener Neustadt facilities until the end of 2025, including manufacturing and testing.

H₂ is a zero-carbon fuel that could play a decisive role in the future of sustainable aviation. It can be used either in fuel cells, where electrochemical reactions produce energy from H₂ and oxygen with only water as a byproduct, or in internal combustion engines. Through either method, H₂ does not produce carbon dioxide. Only in the case of high temperature reactions – such as H₂ combustion – can nitrogen oxides emissions in some cases develop.

The zero-emission profile of low temperature fuel cells and their quieter operation are among the reasons why this technology is gaining traction, not only in the automotive and maritime sectors, but also for aviation applications. In addition, H₂ powertrains offer higher system-level energy density compared to purely electrical ones, allowing greater range and endurance for zero emission aircraft.

However, relying on H₂ alone for aircraft propulsion poses major challenges. These include the low power-to-weight ratio of H₂ fuel cells – which would make them too heavy to cover peak power demands – and the storage of H₂, which requires significant volume due to its low density, within the limits of an aircraft airframe. Another challenge is the safety and certification aspect due to H₂’s propensity to leak and its low ignition energy, as well as safety challenges introduced by high pressure or cryogenic H₂ storage systems.

For these reasons, the research team is implementing a hybrid H₂-electric architecture. They see this as a key to leveraging both the high-power density of batteries and the high energy density of the H₂ fuel cell powertrain. This architecture also offers increased redundancy as an added benefit.

The testbed will be a scaled General Aviation platform and will include a fuselage, sets of independent batteries, H₂ fuel cell and H₂ storage system and up to 10 electric motors and propellers. The research team had originally planned to develop a testbed that mirrors powertrains typically used in a General Aviation twin-engine aircraft. However, given the fast-growing interest in Advanced Air Mobility, the team has adapted its design to enable testing of a VTOL (vertical takeoff and landing) platform with up to 10 motors.

With the H2EDT testbed, the project has set about testing a holistic approach to energy management and heat recovery, while investigating the performance and reliability of H₂ fuel cells and storage and distribution systems for aviation applications.

What sets the H2EDT apart is its digital power management system, implemented via a power distribution board developed by FH JOANNEUM, as well as its ‘parallel’ hybrid architecture, where batteries and H₂ fuel cells can both directly power any motor in the system. The innovative H2EDT system leverages digital sensors and multiple power sources to automatically combine electric and H₂ power as required, greatly improving efficiency and safety.

An essential part of the project has been the design of a digital twin assembling both detailed CAD geometry and performance simulations, the latter thanks to a model developed in cooperation with TU Graz. This model will be calibrated using test data and provide insights beyond the scope of the H2EDT testing. These will include simulations of failure modes and different environmental conditions, such as a high-altitude flight or high air temperatures.

Another project goal is to define certification and design guidelines for a possible follow-up H₂ project on a full-scale General Aviation platform such as a DA40 or a DA42. Certification and design challenges specific to H₂ storage and distribution systems are also being investigated.

H2EDT marks another important milestone for Diamond Aircraft in H₂ propulsion research. Previous achievements include Boeing Phantom Works integration of a fuel cell system in a Diamond HK36 and participation in the AH2AS (Austrian H₂ Aviation Study) and concurrent FFG funded projects like the Austro Engine-TU Wien conversion of a diesel engine into a dual fuel Jet-A1/H₂-powered engine. Presentation of the H2EDT results is anticipated for the first half of 2026.

The pictures below show the H2EDT testbed components integrated within a complete half-scale CS-23 VTOL aircraft. The testbed will provide valuable experience in hybrid H₂-electric architecture on a simplified yet representative platform, accelerating development cycles and ensuring the safety of future hybrid aircraft.

This project has received funding from the Austrian research funding program Take Off. Take Off is a Research, Technology and Innovation Funding Program of the Republic of Austria, Ministry for Innovation, Mobility, and Infrastructure (BMIMI). The Austrian Research Promotion Agency (FFG) has been authorized for the Program Management.