H2FLY completes first liquid hydrogen flight tests

Germany’s H2FLY has run a series of successful flight tests on its HY4 demonstrator aircraft using liquid hydrogen, claimed to be the first time liquid H2 has powered piloted flights.


According to the Stuttgart-based company, a total of four flights were completed using cryogenically stored liquified H2 (LH2) to power HY4’s hydrogen-electric fuel cell propulsion system. With one of the flights lasting in excess of three hours, H2FLY is hailing the achievement as a major milestone on the road to emissions-free passenger flight. It’s claimed the results indicate that using LH2 in place of gaseous hydrogen (GH2) will double the maximum range of the HY4 aircraft from 750 km to 1,500 km.

“This achievement marks a watershed moment in the use of hydrogen to power aircraft,” said Professor Josef Kallo, co-founder of H2FLY. “Together with our partners, we have demonstrated the viability of liquid hydrogen to support medium and long-range emissions-free flight.”

“We are now looking ahead to scaling up our technology for regional aircraft and other applications, beginning the critical mission of decarbonising commercial aviation.”

The LH2 flight tests are the latest instalment of Project HEAVEN, a European-government-supported consortium assembled to demonstrate the feasibility of using liquid, cryogenic hydrogen in aircraft. Compared with pressurised GH2, the use of LH2 enables significantly lower tank weights and volume, leading to increased aircraft range and payload. Led by H2FLY, the consortium includes partners Air Liquide, Pipistrel Vertical Solutions, the German Aerospace Centre (DLR), EKPO Fuel Cell Technologies, and Fundación Ayesa.

“Air Liquide is proud to have designed, manufactured and integrated, together with H2FLY, the liquid hydrogen tank that enabled to power the HY4 aircraft,” said Pierre Crespi, innovation director at Air Liquide Advanced Technologies.

“Today’s success demonstrates the full potential of liquid hydrogen for aviation. Liquid hydrogen can be stored onboard and transported. Hydrogen is key to the energy transition and this new step proves that it’s already becoming a reality.”

In June 2023, H2FLY announced the development of its new H2F-175 fuel cell systems which will be capable of providing their full power range in flight altitudes of up to 27,000 ft. In 2024, H2FLY is set to open its Hydrogen Aviation Centre at Stuttgart Airport, which is planned to become a focal point for the future of Europe’s hydrogen aviation industry.