State of play of hydrogen in aviation
Hydrogen aviation remains a technology of the future – it won’t always be.
By Dominic Weeks, Strategic Partnerships Director for Aerospace
Today, on the other side of the Atlantic, is National Hydrogen Day, a date which perhaps attracted more fanfare and attention two years ago than it does today. Developing a hydrogen economy, for the first half of the decade, was seen as a vital tool in the path to net zero, with major Biden-era policy interventions in the U.S. even driving fears over European competitiveness in H2. Since the last presidential election, however, the H2 story has cleaved to the familiar narrative of the Gartner “Hype Cycle”, with a corresponding market correction that has similarly affected the UK industry and perception of hydrogen here.
Given the contribution that UK industry and government has made in pioneering hydrogen flight, it is worth reflecting on the path ahead.
Balancing priorities in UK aerospace R&D
At the start of last month, the UK’s Hydrogen in Aviation Alliance (HIA) – made up of some of the UK’s most important aerospace sector players - launched a new report in Parliament, exploring the pathway to growth. The mood was one of optimism after a challenging 18 months where some large programmes slowed or halted. The alliance members – including NCC Tier 1 members Airbus, Rolls-Royce and GKN Aerospace – pledge £188m in collective investment over the next year or two.
However, with the pursuit of next-generation single-aisle aircraft opportunities very much front of mind and clearly articulated as the strategic priority in the ATI’s Engineering Growth strategy, can the UK also effectively maintain a strong hydrogen positioning over the next few years?
The HIA report spelled out the commonly articulated hurdles to hydrogen aviation adoption – abundant supply of low-carbon hydrogen, airport refuelling infrastructure and progressing the technology and supporting regulatory frameworks to allow adoption and passenger air travel on hydrogen aircraft. Engineering hydrogen aircraft to fly commercial routes is not seen by leading players as the primary challenge.
It is worth saying that there is still significant growth: to see it viscerally, you can plug in to the International Energy Agency(IEA)’s hydrogen project tracker and roll forward the years from 2020-2026 and see around 100 electrolytic hydrogen projects pop up as operational across Europe, including a spate of UK Hydrogen Allocation Rounds (HAR) projects.
The pace of UK and global clean hydrogen production capacity growth has not met projections, of course. A quintessential chicken and egg scenario. If aviation hoped to be the fast follower, the lack of clear demand pull from other sectors forces a re-evaluation.
Aviation as a critical driver
Aviation may itself be the critical vector to accelerate a hydrogen economy, precisely because, even with a slowing and re-evaluation of aircraft technology programmes, the fundamental promise remains strong for one of the hardest to abate sectors. The date selected by the U.S. Department of Energy to celebrate National Hydrogen Day (10/08 – October 8) refers to the atomic weight of the element 1.008. As the lightest element, there are clear advantages for this fuel in the weight-sensitive context of aviation.
Hydrogen gas turbine aircraft will be zero-carbon in flight, significantly reducing the climate change impact. If using fuel cell power for a hydrogen-electric aircraft, other emissions with climate and air quality impacts, such as NOx and soot, could also be eliminated. In one scenario for H2 aircraft entry-in-service, the Aviation Impact Accelerator at Cambridge projects a 30-70% reduction of emissions by 2060.
For smaller aircraft deploying hydrogen-electric systems, the efficiency of these propulsion systems and theoretically lower hydrogen prices over time could offer airlines lower operating costs. For larger, long-haul aircraft the comparative low weight of hydrogen (weighing half as much as jet fuel) could be an enormous efficiency gain. Nearly half of the take-off weight of today’s longest-range aircraft is fuel. Hydrogen-powered aircraft could also achieve 10% lower energy consumption per passenger kilometre on long-haul flights. And a key virtue of targeting long-haul first would be the focus on hub airports, reducing the dispersed infrastructure required.
So fuel cell or combustion, the environmental and business cases are attractive. This wasn’t lost within the ATI’s Fly Zero project when it declared in its seminal reports five years ago that liquid hydrogen is the fuel of aviation’s future.
Of course, opinions about the maturity of technology and the viability of hydrogen aviation projects vary wildly, and debate can be heated (hard hats at the ready for the comments section). While there are exciting, high visibility achievements to point to (the flight test breakthroughs of Joby and ZeroAvia, hydrogen combustion engine testing by Rolls-Royce or the commercial and design advancements of private jet player Beyond Aero), the reality is that much intensive groundwork must be done to prove out individual components that can be certified, manufactured and maintained in the field.
Building on UK advantage
The Hydrogen in Aviation Alliance report argued that pioneering research and technology initiatives have outlined the technologies that can follow the path to successful commercial introduction.
Much of this has been developed and demonstrated in the UK. Airbus continues to work on hydrogen fuel systems at the Zero-Emission Delivery Centre in Bristol. ZeroAvia continues work on a 200kW modular fuel cell system that can support small UAV and ultimately scale for commercial aircraft propulsion. UK fuel cell developer Intelligent Energy is working on a £17 million project to develop a 300kW fuel cell system. Similarly, Bristol-based Zero Emissions Aerospace (ZeAero%) is pioneering a design for a hydrogen-electric propulsion system using LH2 to retrofit into a Cessna Caravan retrofit. The recently UK Department of Transport-funded Project CHOSAN (cryogenic hydrogen optimised systems for aviation) targets delivery of zero-emission flights from a commercial airport.
At NCC, we have made our own contributions in designing, manufacturing and testing composite pressure vessels and cryogenic storage. Current metallic tanks do not enable a system weight reduction when compared to conventional kerosene fuel systems, but switching to carbon fibre reinforced plastic (CFRP) significantly improves the gravimetric storage efficiency. For storage of liquid hydrogen, there are hopes that CFRP systems could mean that the fuel itself is 50% of the overall system weight (which is not bad going, given liquid hydrogen is around 3 times lighter than kerosene).
Our work to date at NCC has pushed the boundaries of fuel system design for both gaseous and liquid hydrogen storage, testing different methods of manufacture and designs and developing towards the long cycles required by commercial aviation. We have innovated alongside industry to build unique UK capability for future hydrogen aircraft platforms, and also developed a raft of training courses to advance UK capability. At the same time, the UK Civil Aviation Authority (CAA) has invested in capability and understanding of hydrogen systems to provide the UK an attractive environment to innovate, progress and ultimately adopt hydrogen technologies.
New propulsion systems drive airframe innovations
While fuel and propulsion system advances can bring lighter systems long-term, early hydrogen powertrains are likely to be heavier, space hungry and, due to the poorer energy density compared with hydrocarbons, offer shorter range or reduced payload. New airframes are mooted, designed to accommodate hydrogen storage and enhance aerodynamics to minimise range compromise.
This endeavour will likely be supported by use of revolutionary composite aerostructure technologies, such as thermoplastics which enable more ultra-smooth, tight-tolerance aerodynamic surfaces that support laminar flow. Thermoplastics can offer the opportunity to eliminate fasteners, relying instead on advanced joining techniques and thus avoiding micro airflow disruptions. In the shorter term, using more conventional thermoset composites, hydrogen and batter-electric aircraft will require even higher composite content than seen in the latest commercial aircraft to minimise range compromise.
The early signs of this revolution in airframe design, driven by hydrogen propulsion, are apparent. French private jet disruptor Beyond Aero is designing the One aircraft, which will depend heavily on CFRP wings, fuselage and storage vessels. Airbus ultimately plans a regional hydrogen-electric aircraft, with the concept now at TRL3. Blended Wing Body designs such as those favoured by Jet Zero can both improve conventional fuel burn, but also offer more storage space for hydrogen.
If the UK can take the essential steps to acquire greater content on single aisle aircraft, the economic boost will provide further leeway to invest in what comes next. But mothballing H2 capability in the meantime could create a major competitive disadvantage. Maintaining UK H2 aerospace capability, while advancing the wider fuel ecosystem through patient endeavour are necessary foundational actions, even if the primary focus must necessarily fall elsewhere in the short term.
Learn more about how NCC is supporting the priorities of today for UK aerospace, as well as the solutions of the future.