Hydrogen fuel could change the way aircraft work, and look

Last month, Airbus announced plans to overhaul an A380 airliner by adding an additional hydrogen-combustion engine to the outside of the plane and installing monitoring equipment. With the changes, the company will be able to test hydrogen-powered flight in real-world conditions.  

The move is part of a broader industry goal to reach net-zero carbon emissions by 2050.  Passenger air travel is a growing contributor to climate change, making up about three percent of carbon emissions worldwide in 2021. While flying less and investing in more efficient planes can help reduce emissions, new technologies will likely be needed to reach net zero.

Other solutions, like battery-powered air taxis and sustainable aviation fuels, may help cut emissions, but hydrogen in particular might be one of the major paths forward to net zero because it could be used widely in the industry, from shorter regional hops to longer flights with larger planes.

Airbus’s test plane is actually the first-ever A380, with a serial number of one, says Amanda Simpson, vice president of research and technology for Airbus Americas. The aircraft was originally used for certification of both the original A380 and the engine for the A350. Now, Airbus plans to modify it by adding an extra engine on top that will burn hydrogen instead of traditional jet fuel.

The A380 is the largest passenger airliner in service, leaving plenty of room to install monitoring equipment, as well as store the 400 kilograms (880 pounds) of liquid hydrogen that the plane will carry on board for fuel. (Airbus announced in 2019 that it would stop producing the A380, as the industry moves towards two-engine airliners with greater fuel efficiency.)

The placement of this engine, at the top of the plane and in the back, just in front of the tail, is significant, Simpson says. Because it’s separated from the four engines on the wings that will burn traditional jet fuel, Airbus will be able to fly another plane behind the A380 in flight and sample only the emissions from the hydrogen fuel.

Understanding emissions from hydrogen combustion in real-air conditions is one of the major goals of this testing program, Simpson says. While burning liquid hydrogen doesn’t produce CO2, the most abundant greenhouse gas, researchers are still eager to learn more about emissions from hydrogen-powered flight. Hydrogen engines will still produce some nitrous oxides, which are common pollutants, as well as water vapor, which acts as a greenhouse gas in the atmosphere.

The test engine will also allow Airbus to learn more about how best to run hydrogen combustion in flight. Researchers can change the operating conditions of the engine, like the fuel-to-air ratio it burns, and the temperature it runs at, to learn more about how to most efficiently power a hydrogen-powered plane.

Ultimately, these tests are part of the overall plan for Airbus to have a zero-emissions aircraft in service by 2035, Simpson says. In order to meet that deadline, major design decisions will have to be made around 2026, the same year this test craft is expected to take to the sky.

While hydrogen combustion is one of the main possibilities for such a plane, there’s still a chance Airbus will select another technology, Simpson explains. For example, instead of burning hydrogen, it could be combined with oxygen to generate electricity in hydrogen fuel cells. Automotive makers like Toyota and Daimler have been working on developing fuel cells for vehicles, and Simpson says that Airbus is considering the technology, or a hybrid system with both a fuel cell and a combustion engine.  

The design of the aircraft these engines might attach to are still being worked out, too. Last year, Airbus revealed three different potential designs for hydrogen-powered aircraft: a prop plane, a small regional jet, and a concept plane that’s a different shape from most commercial aircraft today. It’s a blended-wing body.

This range of designs says something about the future of hydrogen-powered planes, as well as one of the major challenges of hydrogen-powered planes: fuel storage, says Jayant Mukhopadhaya, an analyst at the International Council for Clean Transportation.

Hydrogen is much less dense than traditional jet fuel, even when it’s compressed at high pressures. Comparing the amount of jet fuel and hydrogen needed to generate the same power, hydrogen takes up at least about four times more space. 

The storage protocols are different, too. In most planes today, jet fuel lives in the wings. However, hydrogen needs to be contained at high pressures and low temperatures, so it tends to be kept in larger, cylindrical tanks. These tanks can’t fit in the wings of traditional aircraft designs, and instead need to be in the body. The volume of hydrogen needed to fuel a plane can severely limit the remaining space, reducing passenger capacity by a third or more.

Aircraft would likely need to be totally redesigned in order to better fit hydrogen inside. One of the concept planes Airbus revealed last year, the blended-wing body design, is an example of a configuration that would better use space for fuel storage. This model in particular may also have other benefits over traditional plane designs, like increasing the aerodynamic efficiency by ten percent or more, Simpson says.

Trying out totally new shapes likely won’t happen fast enough for the first hydrogen-powered planes, Mukhopadhaya says, so companies will probably have to retrofit existing designs to carry large tanks of hydrogen fuel. But eventually, hydrogen combustion could reconfigure what we think of as airplanes.

While these new aircraft could overhaul the industry, even just the two more familiar designs that Airbus released could have a major impact on aviation—the small regional jet and prop plane would together be able to service about a third of all passenger miles flown today, according to a recent ICCT analysis that Mukhopadhaya co-authored.

There are still major challenges to implementing hydrogen-combustion planes, including limited fueling infrastructure, higher costs, and concerns about how sustainable the hydrogen supply is. And longer flights on larger planes will likely take longer to switch over to hydrogen, because of the limited space on board for fuel.

But testing hydrogen-powered engines in real flight conditions could be a major step to legitimizing the technology, and could bring aviation one step closer to reaching net-zero emissions. For now, we’ll have to wait for 2026 to learn more from Airbus’s A380 flight tests.