ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

access to electricity for recharging from the grid, ZeroAvia is quick to point out that all the technology needed to make hydrogen gas is available to anyone who actually wants it. Internally, however, Renz acknowledges a key problem for scaling up commercial hydrogen-electric flight: most airports in a short timeframe would be unlikely to have any hydrogen gas to offer aircraft driven by ZeroAvia’s powertrain if they were to land there. To that end, the company is also undertaking r&d for ‘green’ hydrogen production, storage and dispensing infrastructure. The primary demonstrator for this currently sits at Cranfield airport. Water is dispensed into an electrolyser, which produces hydrogen from water using a reversed version of the electrochemical reaction by which PEM fuel cells produce electricity. The electrolyser is powered using electricity from Cranfield University’s own grid, which is partially supplied by solar panel arrays. Dispensing this hydrogen is then carried out by a mobile fuelling truck, which is largely identical to the trucks ferrying jet fuel around most airports. The truck carries Type 4 tanks that are refilled at the electrolyser before it drives over to ZeroAvia’s aircraft. A nozzle is attached to the plane from its storage tanks, and upon opening the valves at each end, hydrogen flows out until 350 bar is reached, typically after just a few minutes. “As we see it, producing hydrogen on-site at airports by using renewable energy and feeding that directly into electrolysis is the cheapest way to access hydrogen gas, as well as the greenest,” Renz says. “Britain has widespread access to wind and wave power, and parts of Oxfordshire provide almost perfect conditions for solar array fields. “There are further practical reasons to turn airports into hubs for a national hydrogen grid. Airports are major transport and logistics hubs, with huge trucks, buses and coaches constantly running to and from them – electrifying these types of vehicles with hydrogen makes much more sense than batteries in terms of weight, cost and range efficiency, so why not gear up airports to act as hydrogen refuelling stations as well?” Future plans Now forging ahead with developing its 600 kW powertrain for commercial use- cases, ZeroAvia has signed an order for a number of 100 kW fuel cells for its 10- and 20-seat demonstrators. Deliveries of these will start later this year. The company is also now working with high-speed electric air compressor developer Aeristech, whose patented motor and control technology is expected to help significantly with improving the power-to-weight and power-to-volume ratios of the overall powertrain. Development of the powertrain for 10-20 seater planes is included in the next phase of the HyFlyer project, HyFlyer II, which is aiming to create a market-ready hydrogen-electric powertrain by 2024. “If we want to see hydrogen-electric commercial flights within the next few years, we have to be practical, which means working with components that are widely available,” Renz says. “We have to fly well-established aircraft models, and fuel them with gaseous hydrogen stored at 350 bar. “But as we move into the future, for the much larger aircraft we might need to design airframes around our powertrain. That will open up opportunities for things such as storing fuel in the wings and using liquid hydrogen, which is stored cryogenically but can provide 3-10 times the energy density of hydrogen gas – in fact, it’s more energy-dense than jet fuel. “That’s really where aviation has to go, once the technology allows it at a large scale.” Speci ications PA 46 350P Malibu Mirage demonstrator Six-seater ixed-wing aircraft Hydrogen-electric powertrain PEM fuel cell MTOW: 1969 kg Wingspan: 13.11 m Length: 8.6 m Fuel capacity: 1.5 15 kg of hydrogen Fuel storage pressure: 350 bar Maximum power output: 250 kW The company is now developing a 600 kW hydrogen-electric powertrain for use on its next demonstrators, which will be 10- and 20-seater aircraft Autumn 2021 | E-Mobility Engineering 55 Digest | ZeroAvia hydrogen-electric aircraft