CORRECTED: Confidence grows as solar plane cruises to historic flight

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Confidence soared among the crew of an experimental solar-powered aircraft on Wednesday as it cruised above Switzerland in a historic bid to fly around the clock and prove the value of solar energy.

More than five hours into the ambitious 25 hour flight, the crew's chief weather forecaster said the threat of strong high altitude winds and late thunderstorms above the Swiss Alps was receding.

And team chief Bertrand Piccard reported that the pilot had to switch off solar collectors charging the onboard batteries for overnight power because they were working too well.

"Until now, let's cross our fingers, everything is going extremely well. Over the mountains we have... no clouds, the sky is completely clear," added Piccard, who made the first non-stop round-the-world flight in a balloon in 1999.

Solar Impulse whirred along the runway at Payerne in western Switzerland shortly after daybreak, reaching 35 kilometres per hour (22 mph) as lone pilot Andre Borschberg gently took off into clear summer skies at 6:51 am (0451 GMT).

"Conditions are really beautiful up here, I feel great," Borschberg told AFP by radio a few hours later, as he cruised over the Jura hills in northern Switzerland.

"I've been dreaming about this for seven years since we started the project, everybody on the team was looking forward to this very special day and I can tell you I'm really enjoying it," he added.

The Swiss pilot's take-off run took barely 90 metres, testimony to the light weight and giant airliner-size wingspan of the single seater craft, which relies totally on 12,000 solar cells and nearly half a tonne of batteries.

"The goal is to take to the air with no fuel. The goal is to show that we can be much more independent from fossil energy than people usually think," Piccard said.

The aircraft was flying at 4,075 metres (13,000 feet), slowly gaining altitude to reach an apogee of 8,500 metres at sundown, before a slow night-time descent.

The space mission-like ground control crew were due to decide shortly before dusk whether Borschberg should test his own limits of endurance by pressing on with a pioneering flight through darkness and landing at Payerne shortly after dawn on Thursday morning.

"If we have a problem -- weather, technology or energy -- then we have to bring the plane down so that he lands before 10:00 local time tonight. That will be the moment of decision," explained Piccard.

Joint flight control chief and former astronaut Claude Nicollier said: "We're confident the plane can do it."

The overnight flight by the prototype is the first major hurdle for the project since it was set up seven years ago, with the aim of flying around the world by 2013 or 2014.

Solar Impulse relies on the sun to power the engines and charge the batteries, in theory storing enough energy to last through some seven to eight hours of darkness.

A first round the clock attempt was called off an hour before scheduled take-off last Thursday after an electronic component failed, but the aircraft has flown for up to 14 hours straight in daylight in recent weeks.

The single seater shaped like a giant dragonfly is clad with solar panels across a wingspan the size of an Airbus A340 airliner (63 metres).

But the high tech craft is powered by just four small electric motors and propellors -- as the crew put it, the "power of a scooter" -- and weighs little more than a saloon car.

Success on Thursday would set the stage for ocean crossings, transcontinental and round-the-world flights over the coming years.

The pioneering bid is being monitored by the international aeronautical federation (FIA), which oversees aviation records.

© 2010 AFP

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