ABOVE: The HY4 aircraft in flight using liquid hydrogen, September 2023

German developer of hydrogen-electric aircraft powertrain systems, H2FLY, has successfully completed the world’s ‘first piloted flight of an electric aircraft powered by liquid hydrogen’.

The hydrogen-electric fuel cell propulsion system fitted to H2FLY’s HY4 demonstrator aircraft was powered by cryogenically stored liquid hydrogen, used to power the aircraft for the entirety of its flight in what co-founder Professor Josef Kallo described as a “watershed moment in the use of hydrogen to power aircraft”.

First flown in 2016 (powered by gaseous hydrogen), the latest round of testing has seen the HY4 conduct ‘multiple flight tests’ from Maribor, Slovenia, including one mission that lasted for over three hours. Results of the test flights indicate that the use of liqueous rather than gaseous hydrogen will double the maximum range of the HY4 aircraft from 466 miles to 932 miles, ‘marking a critical step towards the delivery of emissions-free, medium- and long-haul commercial flights’.

Although liquified cryogenic hydrogen (LH2) enables significantly lower tank volumes than pressurized gaseous hydrogen (GH2), enabling increased range and useful payload, it must be stored at -253 degrees C. Pierre Crespi, Innovation Director at Air Liquide Advanced technologies, noted that his company is “proud to have designed, manufactured and integrated” H2FLY’s liquid hydrogen tanks, believing the momentous first flight to “demonstrate the full potential of liquid hydrogen for aviation”.

As well as marking a ‘significant milestone’ for H2FLY, the successful flight tests also mark the culmination of Project HEAVEN. Led by H2FLY and incorporating various partners, this European government-supported consortium was assembled to ‘demonstrate the feasibility of using liquid, cryogenic hydrogen in aircraft’.

H2FLY now intends to focus on the path to commercialization, with Kallo noting: “We are now looking ahead to scaling up our technology for regional aircraft and other applications”. This includes the development of new H2F-175 fuel cell systems (capable of providing full power in altitudes of up to 27,000ft). H2FLY estimate that ‘in just a few years, hydrogen-electric aircraft are expected to be able to transport 40 passengers of distances of up to 1,240 miles’.

The opening of H2FLY’s Hydrogen Aviation Centre at Stuttgart Airport in 2024 will also ‘become a focal point for the Europe’s aviation industry and its hydrogen economy, providing fuel cell aircraft integration facilities and liquid hydrogen infrastructure’.