British engineers are developing the electric motors that will propel an unmanned solar-powered aircraft with a 120m wingspan that is due to take off in 2014 and could stay airborne for five years at a time. The Solar Eagle craft, backed by $89m of funding from the US Defense Advanced Research Projects Agency (Darpa), is being built by Boeing in collaboration with the UK research contractor, Qinetiq. It will be able to carry a 450kg payload operated from a 5kW power source.
The four permanent-magnet motors that will drive the aircraft (above) are being developed by at team at Newcastle University led by Professor Barrie Mecrow, head of the University’s Centre for Advanced Electric Drives. They will have to be light, efficient, reliable and able to operate at temperatures below –60°C that they will encounter at the Solar Eagle’s cruising altitude of 18–27.4km above the earth’s surface.
“The motors will have to be powerful enough to drive the propellers to get this gigantic plane off the ground while still being super-efficient and incredibly lightweight,” says Mecrow. “The work is particularly challenging because the plane will be flying at a height of more than 60,000 feet where temperatures can be below –60°C and conventional systems stop working.” The motors will incorporate rare-earth magnets and special low-loss steel laminates produced in Japan.
Mecrow says it is “incredibly exciting” to be part of this feat of engineering. “This plane will have the longest wingspan ever – the only thing that comes close is the Airbus A380, which has a wingspan of around 75m,” he points out. “This is more than half as big again – longer than a football pitch.”
In 2010, the Newcastle team helped to develop QinetiQ’s Zephyr – a smaller unmanned aircraft which completed two weeks of non-stop flight powered by solar energy.
The team hopes to have the first two prototype motors for the Solar Eagle ready to test within six months. The first flight, which is likely to last about a month, is planned for 2014. Potential applications for the craft have not been disclosed.