Could hydrogen-powered zero-carbon commuter flights be just around the corner? TIM ROBINSON speaks to stealth start-up ZeroAvia – which this year will test a six-seat Piper single-engined piston aircraft converted to use a hydrogen powertrain in the skies of the UK.

Hydrogen as a fuel has many advantages. Energy-rich and easy to make, it nevertheless has failed to take off for many reasons. The need for volume to store means that liquid hydrogen requires cryogenic tanks – adding substantially to an aircraft’s drag. Additionally, memories of the Hindenburg disaster and complex fuelling of rocket launches has kept it away from adoption in mainstream aviation. However, a new US start-up, ZeroAvia, plans to change that by using hydrogen as the fuel for a new hybrid powertrain system for small regional airliners.

Enter ZeroAvia

Flight tests of ZeroAvia's hydrogen-powertrain have already taken place in the US. (ZeroAvia)

Founder and CEO of ZeroAvia, Val Miftakhov, comes from a highly interesting background, for someone looking to introduce a new logistics and fuel infrastructure to the aviation industry – and understanding the need for scale and ‘range anxiety’. A physicist by training, he previously pioneered electric charging stations for cars with a company called Electric MotorWerks which was sold off in 2017. A private pilot himself in helicopters and fixed-wing aircraft, he said the idea for ZeroAvia came from these two themes – “That’s when I started thinking about what’s next, it was naturally a combination of these three: zero emission mobility, sustainable mobility and aviation”. says Miftakhov. However, he was keen that any start-up should be able to bring benefits quickly: “I wanted to have impact as soon as possible on the sustainability of the emissions trajectory in aviation. That meant, to me at least, that we should focus on the segments that already exist, like short-haul regional aviation, instead of starting yet another flying drone company, for example.”



He conducted market research on potential demand for zero-emission aircraft. “We went around and talked to a number of operators, regional airlines mostly, and asked them what would be the type of aircraft and type of mission profile that they would be willing to actually fly once we bring the product to the market. That’s how we ended up focussing on our 19-passenger, 500-mile mission profile in the fixed-wing twin-engined aircraft.” ZeroAvia believes that, with 50% of all trips worldwide being covered by the 500mile range, this is the sweet spot for a new disruptive regional aircraft.

However, despite ‘flightshaming’ and the growth of climate change awareness – the interest from airlines is not purely altruistic – it is the economics of electric that also provide a powerful pull – with an estimated 50% reduction in operating costs compared to a traditional turbine powerplant. Says Miftakhov: “We think we can deliver this type of mission at a significantly lower cost than a jet fuel-based mission in the small aircraft that flies today. That’s really one of the most exciting pieces in this whole equation for me, that we can actually not only have zero emissions, which is nice of course and personally motivating. However, we can also have better economics.”

The powertrain

ZeroAvia has replaced the piston Lycoming TIO-540-AE2A engine in a Piper Matrix with its electric-hydrogen powerplant. (ZeroAvia)

With a growing number of electric and hybrid-electric propulsion projects (Eviation Alice, Project Fresson Twin Islander and MagniX electric Beavers) why did ZeroAvia settle on a hydrogen-based system? Miftakhov explains that, having decided on the 19 passenger, 500mile target, “It was pretty clear that batteries will not get us there anytime soon. We did not want to use turbine hybrids, because the efficiency improvements are pretty minimal. You’re still utilising liquid fuels, so you have all the pollution and the cost associated with that. So that pushed us pretty quickly into the hydrogen fuel-cell-based battery.”

Miftakov notes that, despite the excitement over electric battery-powered flight, “those who have done their due diligence looking at the operating parameters have decided that probably it will take some time before they can meaningfully fly those things.” Meanwhile, he argues there has been a ‘muted market response’ to hybrid-electric flight: “over the last 12 months, the operators, aircraft manufacturers and some of the third-party aviation existing players, such as leasing agencies and such, have realised that the actual benefits from the hybridisation are probably not as big as originally expected.”

He explains: “In ground transportation, hybridisation makes a lot of sense because of the standard sort of stop and go type usage profile. You have a lot of acceleration and deceleration during a typical trip. In aviation, in the typical regional aircraft utilisation profile, you do not have an opportunity to save anything through something like this. You can’t really regenerate much on descent. You’re still operating at certain power levels on the descent and it’s definitely not helpful during a climb and cruise. So the impact is relatively minimal.”

He believes that now the time is right for hydrogen to step in: “Once people see that there is an option like this hydrogen-powered option that could deliver higher range, they actually get quite interested.”

Explaining the approach of ZeroAvia, he says: “We’ve positioned the company as a powertrain company. We’re a company delivering initially a PT6 turbine style and size powertrain to the market. We think we can do it in the next three years, in a fixed-wing airframe that would be coming from one of the existing manufacturers.” Miftakhov reveals that the company is initially targeting platforms such as the Viking Air Twin Otter, Dornier 228 and Cessna SkyCourier as potential conversions to its ZA600 hydrogen powertrain.

The system uses compressed hydrogen – which then goes to a proton exchange membrane (PEM) fuel cell. This converts chemical energy from the hydrogen and ambient oxygen to power an electric motor providing rotational energy for the propeller. Miftakhov admits that, for initial applications, the compressed hydrogen fuel may need to be stored in ‘drop’ or wing tip tanks mounted externally on the airframe, saying: “depending on the airframe, we might actually have these tanks mounted outside of the airframe. For some airframes, it might be possible to integrate altogether. This is one of the factors for selecting which airframe we will go with for the initial introduction.”

By using compressed hydrogen instead of liquid hydrogen (as in rocket fuel and other cryogenic hydrogen airliner projects) ZeroAvia aims to simplify the certification process. “We decided to focus initially, on compressed hydrogen because liquid hydrogen, which is more dense, has less volume and definitely weighs less; the problem is the system becomes more complex and harder to certify for commercial use. We think that we’ll be able to deliver 500 miles of range with compressed gas and it’s much simpler to push through certification.” Says Miftakhov: “However, going from there, for longer distances and a larger aircraft, we would have to go liquid at some point.”

He notes that the hydrogen system incurs a weight penalty relative to a kerosene-powered PT6 equivalent – with the hydrogen powertrain delivering one-third of the max fuel range. However, “With the technology improvements that we are expecting to have in the next three years, we’ll be able to deliver about half of the liquid range of a fossil fuel. So that’s where the 500 miles become realistic on a three-year time horizon.”

The demonstrator

The aircraft may need external ‘drop tanks’ to accommodate the compressed hydrogen. (ZeroAvia)

However, this zero-emission powertrain is no theoretical model – it has already taken to the air using a converted Piper-M class single-engine aircraft that the company is using as a technology demonstrator. The M-class piston aircraft was chosen as it is highly efficient, requires at least 250/300kW of power and has sufficient space for the components. “Using this test aircraft,” says ZeroAvia, is also cheaper than going directly to the 19-seat aircraft.

Initial test flights have already taken place in Hollister, California and, in early 2020, the company is set to transfer flight testing to the UK at Cranfield ahead of long-range 250-300mile demonstration flights in the Orkney lslands. The aircraft was converted to a hydrogen powertrain at the end of 2018 and received a FAA experimental certification in February 2019. In 2019 the company also received a £2.7m grant from the UK’s Aerospace Technology Institute under the HyFlyer project.

Initial flight testing is set to begin this month from Cranfield, with the 300-mile demonstration flights to Kirkwall Airport in the Orkney Islands taking place around September. Although the aircraft will not be commercially certificated, ZeroAvia then plans to start doing commercial demonstrations of the technology using the six-seater Piper M. Says Miftakhov: “We expect to start doing what we call commercial spec demonstrations where we say, ‘Okay, we’ve got the aircraft technology figured out to get it to 300m range. Let’s now demonstrate that we can use that aircraft to fly actual commercial missions.’ Obviously, it’s not going to be certified yet, so we cannot actually put it in commercial operation. However, we can go to the operators and say that we want to fly the same missions that you fly commercially today to demonstrate the refuelling times, to demonstrate the dispatchability, demonstrate the payloads, capacity, and all those things, ability to manage weather situations, and all the other things that would be required for commercial operations.”

Another selling point for a zero-emission 19-seat electric regional airliner is also likely to be its noise – or lack thereof, compared to turboprop aircraft. Miftakhov explains: ‘you still have the prop noise. We think that we can reduce the prop noise quite a bit and we will be doing a good amount of testing around that.” He adds: “The fundamental reason why we can reduce the noise from the propeller is that, with the electric motors, it’s easier to deliver maximum power at lower rotational speed. Just the power band is much wider on the electric motors compared to internal combustion engines, whether turbines or reciprocating engines. We plan to utilise the benefit to reduce the tip speeds and therefore reduce the noise output of the aircraft while still providing thrust. We believe we can get to 10 to 15dB reduction of the noise outputs of the typical sort of turboprop of that size, which is going to be quite substantial improvements. Hopefully, that will make the integration of this additional traffic an easier proposition. “

Why test in the UK?

ZeroAvia will be testing its demonstrator in the UK this year. (ZeroAvia)

Some might wonder, given the vast airspace of the US with its test facilities such as those found in Mojave or Moses Lake, why ZeroAvia has decided to flight test its zero-carbon demonstrator in the UK.

The first reason, says Miftakhov, is the high level of support for greener aviation initiatives from Whitehall through funding tools like the Aerospace Technology Institute (ATI). “It was pretty clear that UK aerospace is definitely a key industry and there is a huge amount of attention to zero emission aviation, to the point that they recently announced the Future of Flight programme that is specifically targeting zero emission aviation. There is nothing like that in the US and probably will not be for a bit, under the current administration anyway, on the federal level.”

Miftakhov singles out the ATI for its approach in fostering innovation from a US start-up. “In my experience, they were probably right up top there in terms of how organised and structured they are and how helpful they are in the submission process, giving you the feedback and really trying to make you successful. This is very different from some of my other experiences elsewhere. It was really, really good to work with them”.

“The second reason was the ecosystem perspective” says Miftakhov, “with target partners and potential joint venture partners as we go along. Rolls-Royce is here. Airbus has a huge operation, GKN Aerospace and other major players in aerospace are here. Again, the government is quite supportive of new technologies and wants to keep the place of UK in the global aerospace industry, which is great.”

Finally, he notes that a UK flight test campaign and base places ZeroAvia closer to its expected market for short-haul zero-carbon regional flights – Europe. “The third reason was that Europe in general, we see as a pretty attractive market, probably more attractive than the US market in some ways because of a lot of these short-range routes. Again, generally a better environment for zero-emission transportation with more awareness of the impact that aviation has.”

Infrastructure

ZeroAvia carbon-free infrastructure. (ZeroAvia)

Despite the lower operating costs and green credentials, one challenge confronting hydrogen as aviation fuel is the logistics and infrastructure footprint needed to make this feasible for everyday operations. Miftakhov, with a background in electric charging stations for cars, is aware of the issue. “It’s a very good question. One of the partners in the demonstration project that was funded by Innovate UK, is the European Marine Energy Centre (EMEC) based in Orkney, which which has a lot of experience with renewable hydrogen, especially in producing it from renewable power. EMEC are going to be responsible for figuring out the fuel infrastructure side of things for us in this project. So right now it is working with Cranfield Airport, for instance, to understand the safety requirements, to understand how to bring the fuel into the airport, how to refuel the aircraft at the airport and what kind of requirements are around that, with an eye towards scaling it to other airports once the first one is figured out.”

Miftakhov reveals that he has already several large companies involved in fuels and hydrogen that are quite interested in becoming involved but says, “I want to provide enough certainty to the fuelling infrastructure players that they will invest in it – we need to show them that there is economic sense in them doing so, because I don’t want to be building fuelling infrastructure.”

The future

ZeroAvia joins other electric and hybrid-electric regional/commuter aircraft projects - such as Germany's Scylax E10. (ScyLax)

Beyond the Piper M demonstrator, the company plans to start work on the powertrain for a 19-seat regional aircraft, scaling up the 260kW system to a 800kW one with certification planned for 2022. ZeroAvia says that this timeline includes a ‘buffer’ to take into account extra scrutiny from the regulators of this new propulsion architecture – especially in the wake of the Boeing 737 MAX. “I don’t think there will be a significant impact on our expected timeline, which already includes sort of a buffer for new technology and new risks that we would have to kind of go through with the FAA, the CAA and EASA. If we were just building perhaps a new version of a turbine tech, the timeline would have been quicker than the three, four years we’re projecting now.”

ZeroAvia is aware that, despite offering a quieter, zero-emission aircraft promising half the running costs – airlines are by nature conservative beasts when it comes to buying new aircraft. To therefore incentivise operators and accelerate the introduction of this technology, Miftakhov says the company is mulling a powertrain ‘zero-emission power by the hour’ leasing model. “The operators, when you’re looking to de-risk their operation and probably asking them to buy into the technology outright, limit the initial ramp rate of how fast we can get those things out there and in fact delay our impact, which is something I care about quite a bit. So probably the best way to do this is to accelerate the ramp up to offer a lower risk option to the operators where they pay on the ongoing basis and pay less than what they pay today for the turboprop operation. So you can think about a fully-baked, wet lease of the power plants.” Power by the hour will also provide additional savings for ZeroAvia too, “We want to capture part of the savings that we’re generating and still deliver a significant part of the savings to the operator.”

Summary

Previous hydrogen-powered aircraft studies - including this German/Russian project from the 1990s failed to get off the ground. (Airbus/DASA)

Could hydrogen then become the zero-emission aviation fuel of the future? Many challenges still remain but what is true is that ZeroAvia, alongside Project Fresson, E-FanX and Rolls-Royce’s acquisition of Siemens eAircraft, has catapulted the UK into a prime position in the fast-changing electric ‘Third Revolution’ in aerospace. With quieter electric aircraft offering game-changing economics, smaller, long neglected regional and GA airports may now be at the forefront of a revolution in affordable, green point-to-point travel.

Tim Robinson

