Original URL: http://www.theregister.co.uk/2010/01/21/puffin_vtol_pod/

NASA flying-car man designs electric VTOL podcraft

'Puffin' tailsitter offers just 6 minutes' hover, though

By Lewis Page

Posted in Science, 21st January 2010 14:35 GMT

A NASA engineer long obsessed with flying cars has produced a concept design for a one-man, electrically powered helicopter/plane/glider podcraft. However the work was done largely without backing from NASA, and designer Mark Moore admits that battery technology must improve massively before the design becomes practical.

Moore, employed at NASA's Langley research centre in Virginia, is working on the "Puffin" aircraft - so dubbed because both are environmentally friendly and both look as though they can't fly* - with various partner organisations: MIT, Georgia tech, the US National Institute of Aerospace and private firm M-DOT.

Moore has long been a zealot in the cause of Personal Air Vehicles (PAVs, aircraft for everyman - essentially flying cars). He was formerly in charge of an actual NASA PAV project, which had a budget of $10m and was planned to produce a demonstrator "Tailfan" aircraft by last year.

The Tailfan would have been basically a light plane, but powered by a silenced car engine and fitted with a silenced ducted fan rather than a noisy propeller. The quiet Tailfan would have been capable of operating to and from from small airstrip-laybys in residential areas, and with the addition of modern robo-autopilot/air-traffic equipment (and perhaps the ability to drive on roads like the Terrafugia Transition) might have turned into a true PAV in time.

In the event, bosses at Langley "redirected funding" and terminated NASA's PAV activities in 2005. There was a NASA-funded tech prize, the PAV Challenge, but that was subsequently rebranded the "General Aviation Technology Challenge" and has now become the "Green Flight Challenge" - seeking aircraft which are low-carbon rather than ones which anybody could use.

But Moore evidently doesn't give up easily, because here he is back again with the Puffin. The aircraft's cunning landing-gear/tail, cleverly designed wing flaps and fiendish use of the many excellences of electric motors should allow it to operate somewhat like the "Tailsitter" prototypes of yesteryear, as opposed to today's Osprey tiltrotor. Rather than the rotors tilting and fuselage maintaining attitude, the whole lot will tip over into forward flight after making a vertical takeoff; and tip back again for landing to set down on its tail.

Only 6 minutes' hover before flat battery - or just 3 if you want to go somewhere

So cunning is this design that Moore reckons just 45 kilowatts of power will suffice to lift the Puffin and its pilot off the ground. Unfortunately, while electric motors are great they generally mean the use of batteries - which aren't great at all, even today. The Puffin has just 45kg of them, which with present-day lithium phosphate technology means only 4500 watt-hours of juice: in other words the machine can hover for about six minutes before its batteries run flat.

Moore has told the press that the Puffin could fly in tipped-over plane mode for 20 minutes, achieving a range of 80 km. Previous remarks of his have suggested energy consumption of around 7.5 kW in the cruise for such aircraft, indicating that there'd also be juice for around 90 seconds' hovering at each end of such a journey - not much time for dithering, certainly.

As it stands, then, the Puffin is pretty marginal as a means of flying from place to place: though it could make an impressive glider, the more so as its props would be able to act as turbines in forward flight, recharging the batteries as the Puffin glided down. Electric motors don't lose performance with height, but propellors do: however the machine - if not its pilot - would be theoretically capable of reaching 30,000 feet, reportedly.

Even so, in the current state of battery tech the Puffin is no more than a curiosity. Moore and his colleagues hope to have a scaled-down prototype flying within months, and have suggested that military customers might like the design as it stands - it would be no noisier "than a conversation", apparently, and having no exhausts would boast low infrared signatures.

But the Puffin isn't vastly more capable than existing jetpacks or minicopters, and the military has conspicuously failed to embrace them. Hopeful commentary along the lines of "let's not forget who put men on the Moon" is out of place here, too - NASA has shown quite clearly that it is uninterested in PAVs.

Even so, there's hope for aspiring electric hover-pod pilots yet. Moore believes that battery energy densities could triple in coming years, which would make Puffin-style craft much more useful. ®

*Puffins genuinely can't fly in winter, when they moult their flight feathers and become groundbound. Hopefully not an omen. (The puffin is environmentally friendly, according to Moore, "because it hides its poop".)