- Associated Press - Wednesday, July 7, 2010

GENEVA (AP) - An experimental solar-powered plane took off from western Switzerland on Wednesday for a 24-hour test flight _ a key step in a historic effort to one day circle the globe using only energy collected from the sun.

The plane with its 207-foot (63-meter) wingspan left Payerne airfield shortly before 7 a.m. after overcoming an equipment problem that delayed a previous attempt, the Solar Impulse team said.

Clear blue skies on Wednesday allowed the prototype aircraft to soak up plenty of solar energy as it flew over the Jura mountains west of the Swiss Alps. The big question, however, was whether the plane’s 12,000 solar cells could fill up its batteries with enough energy so the plane could fly through the night.

The flight is going “extremely well,” said team co-founder Bertrand Piccard, a record-breaking balloonist whose father and grandfather also accomplished pioneering airborne and submarine feats.

“The goal of the project is to have a solar-powered plane flying day and night without fuel,” Piccard said. “This flight is crucial for the credibility of the project.”

By late afternoon, pilot Andre Borschberg had his oxygen mask on and was cruising at almost 29,500 feet (9,000 meters), having earlier dodged low-level turbulence and thermal winds that are frequent in the mountains.

At 3 p.m. engineers posted a message on the project’s Twitter page saying the batteries were fully loaded. “Sun rays are now for climbing only,” they wrote.

Borschberg will have to decide Wednesday evening whether to continue through the night using solar power stored in the plane’s batteries.

Piccard told The Associated Press he was confident but its energy efficiency hadn’t yet been tested under real life conditions.

“We will most probably take the decision to go through the night,” he said. “We’ll have to be very careful, because then we have to see if the energy that we have in the batteries will be enough.”

The plane is flying loops in Swiss airspace and within gliding range of Payerne airport, so it can land if it runs out of energy, he said. The solar plane needs a wide, concrete runway because of its massive wingspan, which is similar to a large passenger jet.

Every aspect of the aircraft is monitored by engineers on the ground, with much of it fed onto the team’s website and Twitter page.

If Borschberg, the plane’s only pilot, decides to fly through the night, the plane will slowly descend to 4,920 feet (1,500 meters) before midnight and stay there until he attempts a dawn landing.

The 57-year old Swiss, a former fighter jet pilot, is wearing a parachute.

Piccard said Wednesday’s test flight _ the third major step after its first ‘flea hop’ and an extended flight earlier this year _ will demonstrate whether the ultimate plan is feasible: to fly the plane around the world.

The team had hoped to make their 24-hour test flight last week when days in the northern hemisphere were even longer. But there was a problem with a key piece of communications equipment, forcing the team to ground the plane while modifications were made.

Piccard, who achieved the first nonstop circumnavigation of the globe in a balloon, the Breitling Orbiter III in 1999, said if successful, the next step will be a solar Atlantic crossing. That will be done in a second, lighter prototype, because it will involve new challenges and dangers, he said.

Although the goal is to show that emissions-free air travel is possible, the team says it doesn’t see solar technology replacing conventional jet propulsion any time soon. Instead, the project is designed to test and promote new energy-efficient technologies.

____

On the Web:

Solar Impulse night flight page: https://www.solarimpulse.com/nightFlights/

Solar Impulse Twitter page: https://twitter.com/solarimpulse

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