A hydrogen Bonanza?

Testing taking place in Australia

July 1, 2025 By Sarah Deener

An Australian company aims to replace fossil fuels in aviation with its hydrogen electric propulsion system—starting with the Beechcraft Bonanza.

Stralis Aircraft conducted a propeller spin test on its hydrogen-electric ground demonstrator Bonanza A36, Clyde, in late 2024. Image courtesy of Stralis Aircraft

Stralis Aircraft’s vision is for hydrogen to replace jet fuel for turboprop regional airliners like the de Havilland Canada Dash 8. But first, the company will test the technology on Bonanza A36s named Bonnie and Clyde.

Stuart Johnstone, co-founder and chief technology officer, said he and co-founder and CEO Bob Criner worked together at companies developing battery-electric and hybrid-electric solutions for aviation before turning their attention to hydrogen. Batteries can work for short routes, Johnstone said, but they’re not practical for longer flights—and he described hybrid as “the worst of both worlds.”

Hydrogen power has its own challenges: It’s explosive, it leaks, it needs new infrastructure to supply the fuel, and it needs to be cooled to minus-250 degrees Celsius for storage. But, Johnstone says, those challenges can be mitigated.

“If you agree that we have to decarbonize, then this is the best solution,” he said. “And we think that our whole mission is to decarbonize air travel.”

The system comprises the fuel cell, tanks, and an electric motor. Liquefied hydrogen can be stored at around atmospheric pressure, so Stralis uses hydrogen that has been cooled to about minus-250 degrees C. The fuel in the tanks stays cold for about 24 hours, Johnstone said; as it warms, pressure slowly builds, but it goes back down as the fuel is consumed. If the airplane sits out on the ramp for longer, Johnstone said the pressure relief valve will vent the hydrogen at about 1 percent per day. He said that although hydrogen is highly flammable, proper ventilation minimizes the risk: Leaks just disperse into the air, traveling upward at 40 meters per second.

Initial testing will use low-temperature proton exchange membrane (PEM) fuel cells, with a target for first flight in the fourth quarter of 2025. Stralis also is developing high-temperature PEM fuel cells, which Johnstone said are about six times lighter than a low temperature automotive system. Johnstone expects the hydrogen-electric Bonanza will have a range of more than 500 kilometers (311 miles) with a 45-minute reserve.

From the electric motor to gas supply, Stralis’ hybrid-electric engines will be similar weight to a comparable piston engine and not quite as light as a turbine engine, according to Johnstone. Comparing the weight of the fuel is more complicated. Liquid hydrogen is three times lighter than kerosene, but add in the tank and it doubles that weight. The fuel cells are twice as efficient as the turboprop engine, however, so now you’re back at three times lighter, he explained. He estimates that if liquid hydrogen gets down to about $5 per kilogram, Stralis can make a 50-percent cost per available seat savings on a Dash-8.

“We reckon we can make a major cost saving there, but those sub-3,000-kilometer flights, they contribute about half of the world’s carbon emissions from aviation,” Johnstone said. “So if we’d swapped all those we’d be making a pretty big dent in the total emissions.”