58 September/October 2023 | E-Mobility Engineering Developments in motors for e-aircraft are becoming intertwined with issues of energy storage and certification. Nick Flaherty reports In the line of flight There are many different designs for motors being developed for a variety of electric aircraft platforms, from vertical take-off air taxis to 100-seaters with a flying time of an hour or so for regional flights. This is leading to a range of design architectures to reach and exceed the 13 kW/kg power density needed for flight. However, the challenge remains for long-range, large-capacity aircraft. The challenge is not so much the motor, more the energy storage and the certification, says motor supplier MagniX. “With hydrogen, for example, it’s more a question of certification than the technology, it’s about how to build the technology in a way that is appropriate for certification,” says Riona Armesmith, CTO at MagniX. “It’s a lot of work to certify the system, which means a lot of cost.” MagniX is working on motor designs targeting 350 and 650 kW of power. “These are representative of the size of aircraft we are working with, whether single or twin-engine with up to 19 seats, and that’s driven by the energy storage available,” she says. Motor makers are working to increase the efficiency of the systems, increasing the power of the magnets, reducing the weight of the rotors and stators and using new materials such as carbon fibre to reduce the weight. All this delivers more power with less weight, but these new designs require more detailed certification. “If you can increase the efficiency you reduce the kilowatts you need and the amount of energy storage,” says Armesmith. “Because of that, we are moving to integrated powertrains.” “Small gas turbines with hydrogen are at most 30% efficient, fuel cells offer potential efficiency improvements, and low-temperature PEM fuel cells are 50% efficient,” she says. “But when you add in a lot of the extras, that efficiency has yet to be proven as you need power to run the compressor, and that takes energy away from the efficiency of the system.” The Alice is a ground-up design for a nine-seater electric aircraft with a range of 250 nautical miles using two 700 kW motors (Courtesy of Eviation)
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