H2FLY, the Stuttgart-based developer of H₂ fuel cell systems for aircraft, announced it has successfully passed liquid H₂ on-ground filling tests with the newly developed liquid H₂ tank which is integrated into its HY4 aircraft. The efforts are part of the European project HEAVEN, a consortium of five partners to demonstrate the feasibility of using liquid, cryogenic H₂-powered fuel cell powertrain in aircraft, led by H2FLY.

H2FLY has successfully passed the filling tests of the new liquid H₂ storage system which is designed and supplied by its project partner Air Liquide based on H2FLY’s requirements. The filling procedure took place in preparation for the forthcoming coupling tests in which the liquid H₂ storage system will be coupled with the fuel cell system to form a complete H₂-electric powertrain. H2FLY led the test campaign on Air Liquide’s Campus Technologies Grenoble, in Sassenage, France.

By reaching this milestone, the consortium demonstrates experience in liquid H₂ refueling operations and liquid H₂ handling on board an aircraft. Prof. Dr. Josef Kallo, co-founder and CEO of H2FLY said, “The successful on-ground filling tests today mark the next milestone in our pursuit to doubling the range of our HY4 aircraft. It is a critical step for our upcoming flight test campaign this summer, which will demonstrate the feasibility of liquid H₂ as a fuel for medium and long-haul flight.”

This filling milestone follows the company’s announcement in November 2022 that it had started the mechanical integration of Air Liquide’s liquid H₂ tank into H2FLY’s fuel cell powered aircraft HY4 after the tank passed the vibration and LH₂ leakage tests in September 2022.

For more than 10 years, H2FLY has been researching, testing and refining, resulting in the development of the HY4, a four-seat aircraft with H₂-electric propulsion, that first took flight in 2016. There have been several key milestones across the past three years, including:

• In 2020 H2FLY was granted a permit to fly the latest generation of the HY4 aircraft, which featured a fully redundant powertrain architecture. Across more than 100 take-offs the company successfully demonstrated the applicability of H₂-electric propulsion solutions in aviation.
• In 2021 the company signed a strategic partnership with aircraft manufacturer Deutsche Aircraft that will see the companies work together to fly a CS25 class aircraft powered by H2FLY’s H₂ fuel cell technology. The climate-neutral regional aircraft demonstrator is expected to fly in 2025.
• Earlier last year, the company completed a cross-country flight, from Stuttgart, Germany to Friedrichshafen, covering 77 miles, marking the first time a H₂-powered passenger plane has flown between two commercial airports.
• Also last year, the company set what is believed to be a world altitude record for a H₂ aircraft, flying at 7,230 feet, confirming the company’s position as a leader in this new category.