Hydrogen-powered planes almost ready for takeoff

A complete hydrogen fuel cell powertrain assembly occupied the pride of place in the pavilion of Beyond Aero at the recently concluded Paris Air Show. That a fuel cell system was the Toulouse-based startup’s centerpiece at the biennial aero event is an indication of the steps being taken by a range of companies, from startups to multinational corporations, toward realizing the goal of using hydrogen as fuel in the aviation sector.

“This 85 kilowatt subscale demonstrator was successfully tested a few months ago. Even though in its current form, it serves only ultralight aviation, the successful test of the powertrain is a crucial step in our technical development path for designing and building a business aircraft,” Beyond Aero co-founder Hugo Tarlé told Ars Technica.

Tarlé said that the business aircraft would have a range of 800 nautical miles and will be powered by a 1 MW powertrain. “For generating this power, there won’t be one big megawatt fuel cell. Instead, it will be multiple fuel cells. It will be based on the same technical choices that we made on the subscale demonstrator—i.e. gaseous hydrogen, fuel cell, hybridization of batteries and electric motors."

Beyond Aero stays small

Tarlé listed the reasons behind developing a CS23 category aircraft using hydrogen. “The CS23 is a EASA (European Union Aviation Safety Agency) certification for small aircraft with a low Maximum Take-off Weight. The requirements for this certification are lower than for CS25 certification (larger aircraft). So it's more realistic for a start-up.”

In the case of Beyond Aero, their first aircraft will have a Maximum Take-off Weight of under 8.5 tonnes with a seating capacity between 4 and 8.

“With hydrogen fuel cell technology we could reach a certain performance in terms of the range of our aircraft. We realized that with a range of 800 nautical miles, we could cover 80 percent of the business aircraft market.” He said electric batteries alone were not considered, as they are too heavy for aircraft.

“Batteries alone are not an option, due to their low mass-energy density. With batteries alone, the range of the aircraft is very low. However, there will be hybridization of the fuel cell with batteries for phases where extra power is required, such as during take offs. ”

Tarlé also stressed there is an urgent need to decarbonize business aircraft because of its CO2 emissions. “The CO2] emissions per passenger in a business aircraft is 10 times more than an airliner passenger,” he said.

Another important factor for choosing a relatively smaller sized aircraft was the certification process. “As a young startup, it’s more realistic to aim for a CS 23 category certification than a certification for an airliner,” Tarlé said.

Speaking about the design challenges, Tarlé said mastering the characteristics of hydrogen and oxygen inside the fuel cell was a critical task. “For achieving the best efficiency of the fuel cell, we are considering several factors such as using a compressor, an intercooler and filter, as well as changing the characteristic(s) of hydrogen (for example, increasing its temperature) before it reaches the anode of the fuel cell,” he said.

The other challenge, according to Tarlé, was related to the cooling system. “We need to evacuate a lot of thermal energy, which adds plenty of weight. Mastering the complexity of the cooling system is therefore critical,” he said, adding Beyond Aero has patented a solution in this regard.

ZeroAvia’s half-hydrogen aircraft

While Beyond Aero aims to launch its first aircraft in 2030, a British/American startup is confident it can bring hydrogen power to the skies as early as 2025. To achieve this aim, ZeroAvia is developing engines that can be retrofitted onto existing aircraft. “There is a large fleet of aircraft which can be retrofitted with fuel cell powertrains. This is a quicker way of putting the technology into service,” ZeroAvia’s chief strategy officer, James McMicking, said.

He added that, although retrofitting may not allow the aircraft to travel its full design range, it will still be adequate for the customers. “We think we can actually deliver the cost reduction for the customers because many of these airframes have been designed to fly a lot further than they ever used to.”

“When we retrofit an aircraft, we add some weight because the first generation of these engines is heavier than the turbine. We compensate for the extra weight by reducing its range.” McMicking said the range of a Donner 228 retrofitted with a hydrogen fuel cell will be in the order of 250 to 300 nautical miles, which is one half of a standard aircraft. “But even the reduced range is still adequate for 98 percent of all the missions that these aircraft fly,” he explained.

ZeroAvia’s first product will be a 600 kilowatt hydrogen fuel cell engine, a prototype of which is currently being tested on a 19-seater Dornier 228 aircraft. “One engine of the aircraft uses a 600 kilowatt fuel cell that matches the performance of a stock turboprop on the other side of the aircraft. We have done so because when you're experimenting with any new technology in this industry, you want to ensure maximum level of safety. So in case we need to shut down the engine for any reason, we can do so and yet still have power from the other at the same time,” he said.

“To get the experimental certificate for the aircraft, we had to demonstrate to the regulator that the aircraft could climb out of the takeoff on the hydrogen electric engine, in case the turboprop had to be shut down,” he added.

According to McMicking, this engine produces enough power for 19 seater aircraft. “We are partnering with OEMs such as Textron and Hindustan Aeronautics Limited. We will start the certification program at the beginning of next year and aim to get the first product in the market by the end of 2025,” he said.

McMicking said that the new powertrain will match the turbine performance in terms of power and thrust. “The pilot will be able to operate it close to the standard performance of the aircraft. There are some compromises involved in the retrofit approach. But, you end up with an economically advantageous solution on a per-seat basis and obviously zero emissions,” he said.

He said the company is also ensuring that its sources of hydrogen are the cleanest possible. "We are offering our customers engine contracts that include hydrogen. That means we will be responsible for sourcing the hydrogen. We are doing a lot of research and development in green hydrogen infrastructure. We have a demonstrator that uses solar power to produce hydrogen,” he said.

McMicking said that ZeroAvia’s next offering would be a bigger engine and liquid hydrogen storage systems for ATR 72  and Dash 8 aircraft, turboprops that carry up to 78 passengers.

Airbus plans in-flight testing

Meanwhile, aviation giant Airbus is also busy developing its fuel cell engine demonstrator, which could have its inaugural flight test in 2026.

According to Hauke Lüdders, who is the head of fuel cell propulsion systems for Airbus’ ZEROe research project. ZEROe’s first A380 aircraft (A380 MSN1) will be transformed into a flight lab demonstrator in order to allow hydrogen engine testing.

“Hydrogen will be stored in liquefied form in a cryogenic tank. It will be converted into gaseous form before being fed into the megawatt-class fuel cell engine,” Lüdders said.

He said the fuel cell engine won’t be used to operate the A380 demonstrator. “It will be an attached engine whose thrust will be measured in different flight phases and during different maneuvers. We want to test it with regards to its behavior under different environmental conditions,” he said.

“These tests could form the basis for developing fuel cell engines for a regional 100 seater aircraft, which is one of the three ZEROe concepts,” he added. Luedders said that the other ZEROe concepts will be powered by hybrid hydrogen engines that use hydrogen combustion, or electric motors powered by fuel cells.

Airbus has also funded a startup, UpNext, that is developing a hydrogen fuel cell engine demonstrator for the Auxiliary Power Unit (APU) of an A330 aircraft.

The APU is mostly used for powering cabin air conditioning and lighting, as well as for controlling the hydraulics and pneumatics of an aircraft when it is on the ground.

According to Giulio Zamboni, who is the head of the HyPower demonstrator, the program's main objective is to explore what it takes to integrate new non-propulsive energy systems based on hydrogen.

"The fuel cell comes with a given thermal efficiency. When you bring a fuel cell version on board an aircraft, you need to make provision for a cooling system which is not present on board an aircraft. We are trying to learn such system requirements for the integration of the fuel cell engine on the aircraft," he said.

Zamboni said the HyPower demonstrator, which isn't linked to a direct product development, will also be tested in flight.

"The aircraft modification will begin next year along with the ground test support. This will be followed by the inaugural flight test by the end of 2025," he said.

It’s not clear whether hydrogen will be central to the decarbonization of aviation—other companies are betting on battery improvements, and biofuels are already powering some flights. But the efforts made by these companies are likely to give us a much clearer idea of what hydrogen is capable of before the decade is out.

Dhananjay Khadilkar is a journalist based in Paris.