Hydrogen’s Thermal Challenge: Q&A with Simon Coburn, AMSL Aero

Hydrogen is seen as the future of sustainable aviation due to its potential for zero carbon emissions and high energy density. It offers a transformative solution to drastically cut aviation’s environmental impact. But beyond the fuel itself, a key technical challenge lies in managing the ‘low-grade’ waste heat generated by hydrogen fuel cells. That heat must be efficiently dissipated even in hot ambient conditions without relying on large, drag-inducing radiators. This thermal management hurdle is one of the defining technical obstacles for hydrogen-powered flight.

To explore both the opportunities and hurdles, we sat down with Simon Coburn, Hydrogen Systems Lead at AMSL Aero, to discuss fuel cells, cooling strategies and what it will take for hydrogen to scale.

Simon Coburn is the Hydrogen Systems Lead at AMSL Aero, an Australian aerospace company developing zero-emissions aircraft. With deep expertise in hydrogen propulsion and thermal management, Simon is at the forefront of next-generation aviation. His work bridges the gap between research and flight-ready technology, making him the ideal person to unpack why hydrogen fuel cells are the right technology for next-generation aviation.

What Makes Hydrogen the Right Choice for Next Gen Aviation?

Simon Coburn: It is useful to think of hydrogen as an energy carrier, rather than a fuel. We use it to store electricity. If you take the carbon out of hydrocarbons, you finish up with hydrogen, the most energetic gas we know.

For aviation, that’s critical. A chemical battery has very high-power output, but it’s not a high-energy device. If you want to fly 50 kilometres, use batteries. But if you want to fly 1,000 kilometres, you need hydrogen fuel cells because it’s the lightest way to do it.

This isn’t new technology either. The fuel cell principle was first demonstrated 200 years ago and the technology was applied for the first time in the 20th century, notably for NASA’s Apollo missions. Fuel cells were developed for the space program. Neil Armstrong didn’t take a big battery to the moon. He took hydrogen fuel cells. So we’re not talking about something experimental or unproven.

Synthetic aviation fuels also have a place, especially for airlines that want to keep existing fleets running. But they’ll cost four to eight times more than kerosene refined from crude oil. Hydrogen offers true zero emissions propulsion and can be produced locally from water and electricity.

How do Hydrogen Fuel Cells and Hydrogen Combustion Compare?

SC: Hydrogen combustion runs hot, well above 1,200°C. That’s the temperature at which nitrogen oxides (NOx) form, which are greenhouse gases. And there’s not currently a way to remove it from an exhaust plume, though micro mixing hydrogen and air in gas turbine engines looks promising. A fuel cell, by contrast, produces only water in the exhaust.

The challenge comes from the heat management. A fuel cell can’t throw much heat out its exhaust. The cooling fluid emerges from the fuel cell at around 80°C, and if it’s 40°C outside, you’ve only got 40 degrees to work with. Compare that with a car engine running at 120°C, where you’ve got an 80 degree difference.

With a fuel cell, it’s half that, and if you use a conventional radiator the aircraft won’t even take off. We built a ground test unit with one; it weighed 150 kilos. Massive and unflyable due to both the weight and the size.

From ‘Functional and Safety Challenges of Hydrogen Fuel Cell Systems for Application in Electrified Regional Aircraft, Stefan Kazula et al 2023 J. Phys.: Conf. Ser. 2526 012063

How Does Liquid Hydrogen Storage Shape Aircraft Design?

SC: Liquid hydrogen forms at about 20 Kelvin, that’s minus 253°C, the second coldest cryogenic liquid after helium. Cryogenic engineering like this is also well understood and mature. The reason we use liquid hydrogen is because large quantities can be stored onboard at low pressure. To store the same amount of hydrogen gas, you’d have to compress it to a very high pressure, which makes the tanks heavy. We use fully composite liquid hydrogen tanks that are light because they operate at low pressure.

The irony is that the fuel doesn’t need cooling; it needs heating. We use waste heat from the fuel cell to turn liquid hydrogen into gas before feeding it into the stack. That’s an elegant solution; the fuel cell warms its own fuel.

At AMSL Aero, this principle has shaped our design philosophy. We keep all the hydrogen, high-voltage systems and hot coolant in the wing pods rather than the fuselage. Passengers sit in a central fuselage with no high voltage, no hydrogen, no hot coolant, which we expect will make it safer and simpler to certify. That architecture reflects our approach of building practical, certifiable aircraft from day one.

AMSL Aero’s Vertiia in untethered flight. Hydrogen test flights are planned for 2026.

Why is Thermal Management so Critical for Hydrogen Aviation?

SC: Stack cooling dominates the thermal load. Compressors, humidifiers and electronics add more heat, but the stacks are the main source. In automotive, you can afford a heavy radiator, but not in aviation.

Thermal management isn’t just an auxiliary function on this aircraft; it’s a central design challenge. A conventional cooling setup for an aircraft like this could easily weigh more than 200 kilos. With advanced heat exchangers like Conflux’s heat exchangers, we can reduce that significantly, to say as little as 100 kilos. That saving is enough to carry one or two extra passengers.

You also want to fly like a shark swims – slicing through the air, with minimal drag. Every square centimetre of radiator is drag. The finer you make your cooling fins the more heat you can reject, but the pressure drop goes up. When you’re flying at 300 km per hour, drag becomes a major performance trade-off. Balancing heat transfer, drag and pressure drop defines the efficiency of the entire cooling system.

Is Hydrogen Aviation Safe? How is it being Certified?

SC: Liquid hydrogen has been used for 70 years by NASA, ESA and JAXA. It’s cryogenic, so you need proper training, procedures and anti-static equipment. But it’s not experimental, it’s routine engineering.

Certification is where the frontier lies. Regulators now need to think about things like cryogenic boil-off and cooling loop failure modes. That’s where digital twins and predictive analytics might play a major role in demonstrating safety over time.

For procurement and qualification, it’s not enough to show how a single prototype works. Every component must demonstrate repeatability, quality assurance and compliance with aerospace standards. Adoption will only accelerate once suppliers can prove that consistently at scale.

From: Flight test validation of the dynamic model of a fuel cell system for ultra-light aircraft. Correa G, Santarelli M, Borello F, Cestino E, Romeo G. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. 2014;229(5):917-932.

Strategic Outlook: Who Adopts Hydrogen First? Can Hydrogen Aircraft Really Work?

SC: The first adopters will be eVTOL and regional aircraft. They’re light, short-range and don’t need to cross oceans.

Boeing and Airbus are already studying long-range liquid hydrogen aircraft, but the issue is volume, the space needed to carry that much fuel.

AMSL Aero is focused on the existing general aviation market with our long range eVTOL aircraft, Vertiia. Within that segment, Vertiia has the versatility to appeal to various sectors such as aeromedical, freight and passenger transport. These are the missions where hydrogen fuel cell aircraft can create real social and economic value, not just carbon savings.

The technology already works. The physics are sound. The challenge isn’t whether hydrogen aircraft can fly, they can. The challenges are configuring a commercially viable aircraft, building supporting infrastructure and achieving certification. Once these happen, hydrogen will transform aviation where it matters most, connecting people and services without the carbon bill. AMSL Aero is making this a reality.

What does Hydrogen Aviation Need Next?

SC: The opportunity is enormous. Green hydrogen can be produced anywhere there is zero emissions electricity. That means even remote towns can generate their own aviation fuel on site, creating a decentralised and resilient network for sustainable aviation.

If a town or community has electricity and water, it can make its own hydrogen. You can now make your own fuel where you are, instead of relying on fossil fuel imports. Twenty years ago Australia produced 90 percent of its kerosene; now we produce 10 percent and import the rest. Hydrogen restores that equation.

The Road Ahead for Hydrogen-Powered Flight

Hydrogen aviation is entering a decisive phase. The technology works and the benefits are clear: zero emissions at the point of use, long ranges that batteries cannot achieve, and aircraft architectures re-imagined for safety and efficiency. The next step is scaling — building out refuelling networks, proving certification pathways and deploying thermal technologies that make hydrogen practical in everyday operations.

eVTOL technology is the primary way forward to hydrogen aviation and AMSL Aero is positioning itself at the centre of this shift. By focusing on regional and eVTOL aircraft, where the business case is strongest, we are helping demonstrate how hydrogen can connect communities, enable critical services and reduce aviation’s carbon footprint all at the same time. What was once a future vision is now a race to deliver sustainable, long-range flight.