July 19, 2024


At a somewhat small and unassuming airport in Maribor, Slovenia, German hydrogen propulsion startup H2FLY has quietly been building up to a major milestone in zero-emission aviation over the summer. And all the hard work has come to fruition, with the successful completion of the world’s first crewed liquid hydrogen-powered flights. 

Before any aviation history enthusiast out there goes “but what about the Tupolev Tu-155?” — yes, the Soviets did try out liquid hydrogen as fuel 35 years ago, but only for one of the three engines. In contrast, H2FLY’s HY4 has now operated using only liquid hydrogen (as opposed to the gaseous kind) as fuel, relying solely on the hydrogen fuel-cell powertrain for the entire flight.

On Thursday, this TNW reporter was present for the fourth in a series of test flights. The event marked the culmination of Project HEAVEN, an EU-funded partnership undertaking to demonstrate the feasibility of using liquid, cryogenic hydrogen in aircraft. (That is short for High powEr density FC System for Aerial Passenger VEhicle fueled by liquid HydrogeN, just FYI.)

Liquid vs. gaseous hydrogen as aircraft fuel

While yesterday’s demonstration flight lasted somewhere around the 10-minute mark, a few days prior, the HY4 and its two pilots stayed in the air for 3 hours and 1 minute — a feat that required 10kg of hydrogen. If using up the aircraft’s full storage capacity of 24kg, it could stay up for 8 hours. 

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“It feels really amazing, it is the perfect teamwork coming to life,” said one of the pilots, Johannes Garbino-Anton, after the flight. He added that the technology “works perfectly,” and that the biggest difference to a normal aircraft is the lack of vibrations and noise. And, the lack of carbon dioxide emissions. 

The two test pilots after the flight