Having proposed the re-launch of its X-plane programme earlier this year, NASA’s Aeronautics division has recently unveiled its latest innovation: the all-electric X-57
With a spate of recent announcements, progress in electric aviation is really beginning to take off.
NASA in particular has shown renewed efforts this year, having announced in February that its latest budget included provision for New Aviation Horizons, a programme to design and build new demonstrator aircraft, designated “X-planes.”
As many as five large, “transport-scale” X-planes are planned for development over the next decade, with various possible concepts from electric distributed propulsion, to quiet supersonic flight and hybrid wing aircraft.
The latest of these, the X-57, was unveiled in June. Featuring 14 electric motors and nicknamed “Maxwell” – after the 19th Century Scottish physicist – the aircraft will be based on a modified Italian-designed Tecnam P2006T twin-engine light aircraft.
NASA’s Scalable Convergent Electric Propulsion Technology Operations Research project will replace the wings and two gas-fuelled piston engines with a long, skinny wing embedded with 14 electric motors – 12 on the leading edge for take-offs and landings, and one larger motor on each wing tip for use while at cruise altitude.
In a press release, NASA noted that: “Distributing electric power across a number of motors integrated with an aircraft in this way will result in a five-time reduction in the energy required for a private plane to cruise at 175 mph.”
The Agency is keen to emphasise the aircraft’s pedigree. Reportedly, the X-57 designation was assigned by the US Air Force, following NASA’s request. The first X-plane was the X-1, which in 1947 became the first airplane to fly faster than the speed of sound.
NASA Administrator Charles Bolden added that the X-57 “will take the first step in opening a new era of aviation.”
For now, prototyping appears to be some way away. Late June saw NASA issue an update on the engine test stand it has created for the X-57. Tests in 2015 used a 40kW Pipistrel motor –commonly used in gliders – and powered by lithium polymer batteries. Late summer will see tests expanded to include the Joby Aviation JM-1 motor (which looks to run to about 18 kW).
Less has been stated about the power sources for these motors. Vice’s Motherboard suggests the aircraft will need around 800 lbs (360kg) of batteries (although we’re not sure how that figure was reached).
Certainly, this remains the greatest hurdle of electric flight. Our feature on Lilium’s VTOL aircraft noted that its creators would probably need a roughly tenfold increase in battery energy density to make their stated design work. Based on current specifications and the best available li-polymer batteries (around 0.25 kWh/kg), 360kg would allow the X-57 batteries of around 90kWh.
Based on the stated equipment so far, running the 12 wing motors at roughly full power for take-off – perhaps 20 minutes or so – would require around 65kWh. Once airborne, the two 40kW Pipistrels motors might need a further 20kWh to cruise comfortably at 25% power for an hour. That doesn’t leave a great deal more juice in the tank for landing and emergencies, so it’s likely that a larger payload or greater density will be needed to get the X-57 in the sky for longer.
Nevertheless, NASA is perhaps better equipped than most to tackle the problem, so it will be interesting to see what its engineers can come up with.
That said, even with slow progress on batteries, improvements in other areas may well help maintain the pace of electric aircraft. Siemens, for example, recently completed the first flight of its ultra-lightweight aircraft motor – a 50kg motor with 260kW of output – a major stride for electric aviation. [We’ll be covering more on this in a separate article].
For now though, it seems as though NASA has a great deal of X-planing to do.