A year into the development of its H2GEAR hydrogen-electric powertrain, GKN Aerospace has seen a subtle shift in the UK government-backed project.
When the £54 million ($72.5 million) initiative was launched in January 2021, GKN had a goal of delivering to ground test by 2026 an entire 1MW powertrain, including the hydrogen storage, fuel cells, power management system and an electric motor.
That goal has not changed, but what has become apparent over the last 12 months, says GKN Aerospace chief technology officer Russ Dunn, is that in order to progress its design, the project also needs a reasonably firm idea of the aircraft the system is intended to power.
“We knew this already to a degree, but we have now realised to an even greater extent just how integrated the propulsion system, the hydrogen-electric system, is to the overall aircraft,” he says.
“Depending on what you are targeting the system for, that will have a significant effect on the size and complexity of the system and the amount of heat that needs to be dissipated. The fact is, you almost need to design the aircraft in order to design the system.”
Dunn says the process has been “almost the inverse of a classic aircraft programme”. In that case, an iron bird ground test rig would validate and inform the final aircraft design, while with H2GEAR the reverse is true: as only ground testing is envisaged, different potential aircraft designs are feeding into the development of what is essentially an iron bird.
2021 has also been about “building our capability” – from a human resource perspective – to allow GKN to deliver the programme; it has seen an influx of highly qualified people from elsewhere in the industry, says Dunn.
GKN has additionally been “building the roadmap – the master schedule if you like – about how we deliver against the programme goals” and setting the top-level requirements for the system.
That means it ended 2021 in a “pretty good place” in terms of those requirements; “we understand what the overall system has to do”, says Dunn.
“What we have progressed through  and we are getting a lot more clarity on what the unknowns are. We have realised just how important the overall aircraft integration is.”
GKN has now begun the process of analysing the various “ingredients” for the system and working through the trade-offs between power, weight and complexity to begin driving down “to the solution we are going to take forward” and “making some of the bigger architecture decisions”.
The overall system architecture should be “locked down” by the end of 2022, leading to a preliminary design review milestone in 2023, followed by a critical design review the following year. Overlaying all of this is the need for a clear path to “validation and verification”, or “how we prove the system does what it is supposed to”.
But with considerable opportunity for innovation – its academic partners on H2GEAR are opening up several avenues, Dunn says – there is a balance to be struck: the question, he says, is “how much innovation to baseline into the plan and how much to take the safe option”.
It is, of course, a trade-off that all development programmes wrestle with. Prior to joining GKN, Dunn was head of wing engineering at Airbus and worked on both the A380 and A350. He says both involved high degrees of complexity and innovation – the fuel system on the former and the airframe and high-lift system on the latter – the risk of which was mitigated by chosing simpler options in other areas.
“We are having a similar debate: what’s the best overall solution to give us credibility, confidence and a route to market?” he says.
H2GEAR is designed around a 19-seat sub-regional aircraft, although the system should be scalable to larger and smaller designs. As the powertrain grows it should become “more competitive”, says Dunn, but also more complex: multiple fuel cell stacks will generate more heat, necessitating cooling solutions beyond the usual air- or water-cooled systems.
Dunn contends that dealing with that heat generation is likely to remain one of the biggest issues to overcome. “With any complex system there are a whole series of problems to solve, but heat dissipation is the one that we look at that’s the big challenge and need to spend more time on that area.”
However, given that the whole H2GEAR programme is a step into relatively uncharted territory for GKN “our biggest challenge is the unknown unknowns”.
“Ultimately this is why we have gone down the ground-based demonstrator route – we want to push the boundaries to really inspire the industry,” says Dunn.
The fuel cells themselves are being provided by Midlands-based Intelligent Energy, with other partners including electrical controls specialist Aeristech and the universities of Birmingham, Manchester and Newcastle.
In addition, GKN is able to draw on other parts of its aerospace business: its operation in Trollhattan, Sweden specialises in engine technology while its Dutch unit has strong expertise in high-voltage power distribution.
As an example, GKN is working with the Swedish Royal Institute of Technology on EleFanT – an 18-month-long project to develop electric-powered ducted fan technology – essentially a thruster – for smaller regional aircraft. In other words, aircraft not unlike those being used to shape the design of H2GEAR. Ultimately that means GKN could offer an end-to-end system to the market.
The Aerospace Technology Institute is providing £27 million for the H2GEAR programme, a figure matched by GKN and its partners. It is a core project being undertaken at the company’s new Global Technology Centre in Bristol.