A balance of plan: Inside ZeroAvia’s UK HQ
December 3, 2024
As ZeroAvia looks to scale and commercialise its retrofit product offering – with an upcoming inaugural A to B flight another major milestone and its type certification application well underway – the company continues to move at pace towards the entry into service of its ZA600 and ZA2000 powerplants, due in 2026 and 2028 respectively. With R&D ongoing across its flight test campaign supported by work in its fuel cell labs and hydrogen infrastructure developments, just what makes ZeroAvia’s Cotswold base a forerunner in disruptive propulsion technology?
Flying the flags
The row of flags festooning the ceiling of ZeroAvia’s UK facility (at Cotswold Airport, Gloucestershire) highlights the global nature not just of ZeroAvia’s UK staff but also the company’s international ambitions. Founded in California in 2017 by cleantech startup veteran and company CEO Val Miftakhov, ZeroAvia has nevertheless had a strong UK presence since 2019; attracted by UK Aerospace Technology Institute (ATI) funding and a favourable environment for innovative initiatives.
Despite development progressing at pace across both US and UK sites, work conducted stateside is more focused on electric propulsion unit elements, explains VP of strategy James McMicking. Although ZeroAvia “made some very early gains” in developing this technology in the US (most notably with some of the earliest electric retrofit flight testing), he says the UK site is more focused on the hydrogen elements; resulting in a “natural split in core capabilities between these locations” – with the UK having been very proactive in its support for the hydrogen piece of the equation.
And ZeroAvia has picked a prime spot to base from. Cotswold Airport (formerly RAF Kemble, commissioned in 1936), is a location steeped in aviation history; with the black and yellow tape around a shelter hatch in the floor of ZeroAvia’s World War 2-era hangar further juxtaposing old and new. Neither the secret bunker beneath, nor the 1940s conflict driving aerospace innovation forward at pace, remain active today – although as ZeroAvia head of external affairs and marketing Dominic Weeks explains, the urgent need to address aviation’s carbon emissions brings its own international imperative.
Although the company initially performed flight testing of a Piper Malibu retrofitted with a battery-electric concept, it had already identified hydrogen-electric as its path to progress, with an initial 250kW hydrogen-electric system (fitted to the blue Piper Malibu on display and flown on occasion by passionate pilot Miftakhov himself) making over 35 sorties in 2020 and 2021.
Dornier 228 testbed
However, ZeroAvia’s current flight testing work is featured around the Dornier 228, which completed the first round of tests with its prototype ZA600 powerplant in July 2023. Chosen for its twin-engine specification and good single-engine performance, the aircraft reached 5,000ft in altitude and durations of 25 minutes over the course of 14 sorties. A second Dornier recently ferried in from Nevada will also augment the ongoing flight test programme.
Running on gaseous hydrogen, the modified experimental airframe G-HFZA features a tank along the right hand side of the fuselage, fuel cell systems towards the rear generating electricity from the hydrogen fuel, and high-voltage electrical cabling running along the wing and through the nacelle to connect to the electric propulsion system fit which has replaced the existing engine. This configuration includes batteries powering two of the four electric motors in the prototype system, providing additional redundancy for testing the fuel cell systems, on top of the combustion engine on the left hand side.
An upcoming inaugural A to B flight will further “build confidence, performance, and highlight the duration of the systems,” explained Weeks, with McMicking nevertheless adding the upcoming months will entail “a lot of hard work going on inside the business that’s not necessarily as glamorous” – including “hard graft on documenting [ZeroAvia’s] engine and demonstrating that it meets all regulatory requirements to progress with certification”.
Caravan STC
With the 1950s de Havilland Vampire unexpectedly lurking in a corner of the hangar reassuringly not a candidate for hydrogen conversion, the adjacent single-engine Cessna Caravan is forming the focus of ZeroAvia’s inaugural retrofit remit. “The whole [ZA600] engine is being built with that in mind and will come towards the end of next year as a retrofit project,” explained McMicking.
Weeks added that the market for the nine-seat, rugged utility aircraft provides some “interesting use cases,” with potential ZA600 applications (to be covered by an STC) also extending to the DHC Twin Otter and Dornier 228. “We sequence those things according to a number of factors,” he added, although noting that a Dash 8-400 picture on the wall (an airframe based in Seattle and donated by Alaska Airlines) serving as a daily reminder for the team to dream bigger – quite literally.
“It’s great to have airlines backing this agenda – but it’s also great that they approve of our strategy of the ‘stepping stone’ approach,” McMicking ventured. “This involves very practical first steps into the community segment technology, building knowledge and confidence about how it works, before taking a step into Part 25 bigger commercial aircraft. I think this will benefit not just us but the whole industry.”
Fuel cell build lab: scaling stacks
However, with progressively larger aircraft such as the Dash 8 expected to receive supplemental type certification by the end of the decade, ZeroAvia’s work at Kemble to build the test rig (accompanying ongoing build work conducted at its Sandwich, UK facility) progresses at pace.
A fuel cell works a lot like a battery in theory, with an anode and cathode separated by an electrolyte, but with hydrogen gas fed into the anone and compressed air fed to the cathode to deliver oxygen. In the case of the Proton Exchange Membranes, the fuel cell leverages the reaction of combining hydrogen and oxygen to generate electricity. The membrane allows hydrogen protons to pass through, but not electrons, with the latter funnelled off to create an electrical current.
The voltage is determined on the number of cells, while ampage depends on the surface area of the membranes. The low temperature fuel stacks used for the ZA600 (such as the example pictured here) are 455 cell stacks (featuring two banks in series, providing a total output of around 130kW), and uses water to cool the 65 deg C produced by the system.
However, with heat exchange one of the main challenges, cells operating at higher temperatures are critical for higher power outputs at a commercially viable weight. This is because increasing the temperature differential between the exhaust from the system and the ambient air makes it easier to remove the heat, thus simplifying the ‘balance of plan’ (humidification, thermal management and compression of air) and reducing the overall weight. Additionally, high-temperature fuel stacks will employ phosphoric acid as an electrolyte. (Not as dangerous as it may sound, this common food preservative is contained within the stack and bound into each membrane).
Fuelling solution
However, prior to a product’s certification and entry into service, it’s equally imperative to have a sufficiently mature airport fuelling ecosystem aligned with the system’s needs. “We’re not planning to be hydrogen producers ourselves at scale, but we’re developing solutions to support gaseous and liquid storage and supply,” explained Weeks.
Around the corner from the company’s Toyota Mirai (which can be refuelled using the same apparatus as its aircraft), low-temperature and high-temperature fuel cell test labs are fed by rooftop hydrogen tanks. An adjacent Enaptera electrolyser housed in a shipping container provides the hydrogen, which can also be piped to the apron. Alternatively, 400 bar hydrogen can also be provided by a refuelling truck – something to be deployed by road to the upcoming A-B flight.
Something the size of a Cessna Caravan (with fuel for a 250nm range) would need around 60kg of hydrogen, which takes around 40-60 minutes to refuel at 350 bar. However, as ZeroAvia continues to develop its monitoring and observation system, it’s anticipated these refuelling times will drop to around 20 minutes in commercial service.
Progressing at pace
“The climate agenda is very real, and you’re seeing more venture funding being made available for these sorts of projects, because people recognise that this is the direction we need to solve these problems,” suggested McMicking. (Last month, ZeroAvia successfully completed its Series C finding round, with a total of $150 million including a $20 million investment from the Scottish National Investment Bank – and following previously funding from American Airlines and IAG).
In terms of the appetite to risk profile between US and UK investors, he believes there was initially more response from the US markets. However, “having burned down a lot of that risk” through flying the aircraft and building up the order book, “the next phase is going to require a different sort of investor to come in and engage with industrialisation”.
However, ZeroAvia’s ongoing partnership with the UK ATI remains “essential to the ability run more R&D at a higher pace” – alongside providing “a partner in helping [ZeroAvia] shape and perform our approaches to some of these technology challenges” with its “broad overview of what’s going on within industry, a broad understanding of the technology and the application of that technology”. Having received around £12 million from UK funding sources to date (yet having invested seven times that into the UK), “the company’s here because of the ATI, simple as that,” he added.
Ultimately, if ZeroAvia proves successful in commercialising the technology being developed here, “we’ve got airports, operators, insurance, the whole supply chain of hydrogen figured out before anyone has to take a massive gamble on designing a hydrogen narrowbody,” McMicking concluded. “The value of derisking these exercise by starting in these segments is billions”.
