UK research lab Qinetiq is claiming a world duration record for its solar-powered Zephyr unmanned aircraft.

"This is the longest flight for a UAV [unmanned aerial vehicle]," Qinetiq business development manager Paul Davey told EW. "Zephyr flew for 82 hours 37 minutes."

Zephyr is high tech design with all the stops pulled out.

The aeroplane has a 20 metre wingspan but a mass of only 32kg thanks to its carbon fibre construction.

"We are using everything we have learned about lightweight structures. It weighs nothing and can withstand 5G," said Davey.

Along with liquid crystal displays, carbon fibre was originally invented at Qinetiq when it was still a UK Government military research centre.

The methods of ‘laying-up’ the carbon fibre as the plane is firmed remains proprietary to lab, said Davey.

Zephyr was tested last year, but its flight was curtailed by a faulty motor-gearbox assembly. "We didn’t look into which part failed in great detail, we went to Newcastle University and they came up with a new design of direct drive motor without a gearbox," said Davey.

Power comes from 1.6kW of 9% efficient flexible amorphous silicon solar cells bonded to the upper wing surface.

This is fed to the motors and payload, and a lithium-sulphur battery from US firm Sion that runs everything at night.

"At the moment, the battery’s energy density is getting on for twice lithium polymer," said Davey. "We are seeing better than 350Wh/kg and I think 600Wh/kg is not impossible eventually."

It is actually the same pack that was used for the 2007 trail, weighing 10kg with 576 cells in a 12series-48parallel configuration.

External temperatures have been measured down to -68 deg C, which means the battery has to have a built-in heater to keep it above 0 deg C.

According to Davey, straight and level flight requires only a couple of hundred Watts, rising to 400-500W for each of the two motors when climbing.

During the record flight the plane reached 20km altitude, far above the jetstream, where wind speeds are low and station-keeping is not difficult. "Flying around 50 to 70 knots is fast enough for most weather," he said.

Launch is by hand, with three people supporting the aircraft which running into the wind until it lifts off.

As no judges were present, the firm is not attempting to claim an official world record.

The flight, in the Arizona desert, could have been longer. "This was not a straightforward attempt to keep the aircraft up," said Davey. "It was a system trial with the customer and it was mutually convenient to bring the aircraft back when we did."

The MoD has funded the development of Zephyr to date and has partnered with the US Department of Defense under the Joint Capability Technology Demonstration Programme - aimed at getting technology to US troops.

"The US DoD funded the demonstration flight under the Programme and this was the first time the two governments have participated in a joint demonstration of a HALE UAV," said Qinetiq.

Potential applications for Zephyr include military and civil earth observation and communications relay.