Hydrogen Fuel Cell Plane Tests: Liquid Hydrogen Breakthroughs

The aviation industry is facing its biggest shift since the invention of the jet engine. As pressure mounts to reduce carbon emissions, engineers are turning to hydrogen as a clean alternative to fossil fuels. Recent successful tests by aviation startups have proven that flying entirely on liquid hydrogen is not just a theory. It is a reality that could soon change how we travel.

The Historic Liquid Hydrogen Flight

The most significant recent development comes from H2FLY, a German company acquired by Joby Aviation. In September 2023, the company completed the world’s first piloted flight of an electric aircraft powered by liquid hydrogen.

The test flights took place in Maribor, Slovenia, using their demonstrator aircraft, the HY4. While hydrogen planes have flown before using gaseous hydrogen, the switch to liquid is a critical technological leap. By using liquid hydrogen, H2FLY was able to double the maximum range of the HY4 aircraft from 750 kilometers (466 miles) to 1,500 kilometers (932 miles).

This test proved that cryogenic liquid hydrogen can be safely stored and used onboard a passenger aircraft. It validates the technology needed to make zero-emission medium-haul flights commercially viable.

Liquid vs. Gaseous Hydrogen: Why It Matters

To understand the significance of these tests, you have to look at the physics of fuel storage. Hydrogen is incredibly light, but it takes up a lot of space.

The Volume Problem

Gaseous hydrogen must be stored in heavy, high-pressure tanks. Even under high pressure, the gas requires a massive amount of storage volume. This limits aircraft design because there is simply not enough room in the fuselage to carry enough fuel for long trips.

The Liquid Solution

Turning hydrogen into a liquid solves the volume issue. However, it presents a new engineering challenge. Hydrogen only turns into a liquid at extremely low temperatures: -253°C (-423°F).

Keeping fuel this cold requires specialized cryogenic tanks. The successful tests by H2FLY demonstrated that these tanks can be integrated into an airframe without making the plane too heavy to fly efficiently. Liquid hydrogen stores much more energy per unit of volume than gas. This density is the key to unlocking flights that can travel between major European cities or across US states without stopping.

Key Players in Hydrogen Aviation

While H2FLY made headlines with their liquid hydrogen success, other major players are racing to certify hydrogen powertrains.

ZeroAvia

Based in the UK and US, ZeroAvia is aggressively testing hydrogen-electric engines. They are currently testing a 19-seat Dornier 228 aircraft retrofitted with their ZA600 hydrogen-electric engine.

ZeroAvia aims to certify a 600kW engine for 9-19 seat aircraft by 2025. They have secured orders from major carriers like American Airlines and United Airlines. Unlike the liquid hydrogen tests, ZeroAvia initially focused on gaseous hydrogen for shorter regional flights but is moving toward liquid hydrogen for larger engines (ZA2000) designed for 40-80 seat planes.

Airbus ZEROe

The aerospace giant Airbus is not a startup, but they are a massive force in this space. They have committed to developing the world’s first zero-emission commercial aircraft by 2035 through their ZEROe concept.

Airbus is building a dedicated “Iron Pod” test center to test hydrogen fuel cell propulsion systems. They are exploring three different concepts:

• A turboprop for regional flights.
• A blended-wing body design (looks like a flying V) to maximize fuel storage.
• A turbofan design for transcontinental range.

How Hydrogen Fuel Cells Work

The technology powering these prototypes is fundamentally different from a standard jet engine. A jet engine burns kerosene to create thrust. A hydrogen fuel cell creates electricity through a chemical reaction.

1. Storage: Liquid hydrogen is stored in cryogenic tanks onboard.
2. Conversion: The hydrogen is fed into a fuel cell stack where it mixes with oxygen taken from the outside air.
3. Reaction: This mixture creates a chemical reaction that generates electricity.
4. Propulsion: The electricity powers an electric motor, which spins the propeller.
5. Exhaust: The only byproduct released from the back of the plane is pure water vapor.

This process is quiet, efficient, and produces zero carbon dioxide or nitrogen oxides.

Remaining Challenges for Commercial Use

Despite the successful flight of the HY4 and other prototypes, several hurdles remain before you can buy a ticket on a hydrogen plane.

Infrastructure is the biggest bottleneck. Airports currently do not have the facilities to store or pump liquid hydrogen. Handling fuel at -253°C requires new safety protocols, pipelines, and refueling trucks.

Tank weight is another issue. While liquid hydrogen is light, the vacuum-insulated tanks required to keep it cold are heavy. Engineers are working on using lightweight composite materials to keep the overall aircraft weight down.

Cost remains high. Green hydrogen (produced using renewable energy) is currently more expensive than jet fuel. For airlines to switch, the cost of hydrogen production needs to drop significantly.

The Path Forward

The successful flight of liquid hydrogen prototypes marks the end of the “science fiction” phase of hydrogen aviation. It is now an engineering problem. Companies like H2FLY and ZeroAvia are moving from proving the science works to proving they can build engines reliable enough for daily commercial service.

With regulators in Europe and the US creating pathways for certification, we will likely see small hydrogen cargo planes or air taxis entering service before 2030, followed by regional passenger planes shortly after.

Frequently Asked Questions

Is flying with hydrogen safe? Yes. Hydrogen has been used in industrial applications for decades. Aviation tanks are designed to be crash-resistant. In some ways, hydrogen is safer than jet fuel because it rises and disperses quickly if it leaks, rather than pooling on the ground and burning.

How far can hydrogen planes fly? Current prototypes like the HY4 have demonstrated ranges up to 1,500 km (932 miles). This covers many popular regional routes, such as London to Berlin or Los Angeles to San Francisco. Long-haul international flights are still years away.

Will hydrogen tickets be more expensive? Initially, yes. New technology and infrastructure costs will likely result in higher prices. However, as green hydrogen production scales up and fossil fuel taxes increase, hydrogen flights could eventually become cost-competitive with traditional flights.

What is the difference between hydrogen combustion and fuel cells? Hydrogen combustion involves burning hydrogen in a modified jet engine (similar to how cars burn gas). Fuel cells use a chemical process to create electricity without burning anything. Fuel cells are generally more efficient for smaller planes, while combustion might be used for very large jets.