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

This hydrogen-electric aircraft powertrain developer has lights of less than 500 nautical miles – and their emissions – in its sights. Rory Jackson reports Short haul fromhere A s detailed in the first issue of this magazine (Winter 2018) through our discussions with Pipistrel about its Alpha Electro aircraft, it is just as feasible to develop (and certify) a two-to-four seater plane to run on battery power as it is with a roadcar. While serious optimisation of the battery and overall system weight must be undertaken to make small battery-electric planes flightworthy, it is empirically achievable. However, when trying to transport anything much heavier than four seated passengers, an aircraft manufacturer will run into the same problem as large truck or train manufacturers: the power density needed for very heavy vehicles cannot be supported simply by stringing together ever-higher numbers of packs in series. The gravimetric energy density of current battery technology simply isn’t high enough, and eventually the powertrain ends up being so heavy that it cannot carry itself. That is why hydrogen-electric power appeals greatly to vehicle developers looking to bring mass-transport or large- scale freight applications to e-mobility. The specific energy of hydrogen gas is around 33.3 kWh/kg, more than 200 times that of lithium-ion batteries (around 0.15 kWh/kg). And although arguments against investing r&d in hydrogen power are often circulated in the media, many companies continue developing and proving solutions oriented around hydrogen-electric mobility. UK-based ZeroAvia has rapidly taken the lead in manned hydrogen-electric flight, having successfully flown its first test aircraft – a Piper Malibu Mirage six- seater – using a hydrogen PEM fuel cell configuration in September last year. It is now developing larger platforms for the powertrain. With the aim of greater optimisation now in mind, ZeroAvia has announced partnerships with several other companies for r&d of specialised components to maximise the power and energy density in its powertrain. This will boost its capabilities beyond the aircraft used in its maiden flight towards the dozens and hundreds of seats it hopes to offer commercially in the future. Aircraft roadmap ZeroAvia’s research into aerospace emissions has determined that most CO 2 is produced (during normal, pandemic-free operations) by narrow- body passenger aircraft: planes carrying between 100 and 200 passengers, typically for 2-3 hours. “Most flights are typically of about 500 nautical miles, so flying those aircraft without emissions is really our endgame, and we’re convinced hydrogen is how we get there,” says ZeroAvia is developing hydrogen-electric passenger aircraft, using a Piper Malibu Mirage for testing (Images courtesy of ZeroAvia) 50 Autumn 2021 | E-Mobility Engineering