Solar plane to cross America

SOURCE:  Jonathan Jay (
SUBHEAD: Solar-powered airplane breaks world record for distance traveled aloft.

By Jason Paur on 23 May 2013 for Wired Magazine -

Image above: The Solar Impulse in flight. From (

Solar Impulse pilot André Borschberg completed a record-setting flight in the wee hours this morning after flying more than 950 miles on solar power alone, even if he was, strictly speaking, going backward for part of the trip.

His impressive flight from Phoenix to Dallas completed the second leg of the Solar Impulse team’s “Across America” trip which is expected to end in New York in early July. The enormous solar airplane, known simply by its Swiss registration HB-SIA — has roughly the same wingspan of a Boeing 747 yet weighs about as much as a Honda Accord and uses four 10-horsepower electric motors for propulsion.

We got to chat with Borschberg as he soared high over Texas en route to Dallas. He’s is a veteran pilot who flew fighter jets in the Swiss Air Force, but things are going just a bit more slowly on this trip. HB-SIA can’t even keep up with the cars zipping along on the highways below, as it typically cruises at about 30 mph.

That slow pace helps optimize its range. The four motors draw power from nearly 12,000 photovoltaic cells mounted on the wings and tail of the carbon fiber airplane. The cells also charge the batteries that power HB-SIA at night. Borschberg landed in Dallas with his batteries at about 60 percent, and will use that juice to begin the third leg of his journey.

The flight to Dallas was fairly smooth, with just a few sections of turbulence. Flying 832 nautical miles (957 miles) broke the team’s own distance record for a solar powered airplane (and for any electric airplane). It also provided valuable experience and expand the Solar Impulse team’s flight techniques for future flights — including their planned circumnavigation of the world in a larger aircraft in 2015.

“I think we learned more about how to steer this airplane in meteorology that is not entirely optimum,” Borschberg told us from the cockpit.

The experienced glider pilot says there were several times when he found himself in “waves of air” that caused the airplane to rise and descend. Unlike a glider, he says, it is difficult to take advantage of the free lift in HB-SIA. Still, he did learn a lot about how to avoid downdrafts that steal valuable altitude.

Another problem he faced was overcoming the speed of the wind moving against the airplane. Anybody who has experienced headwinds on an airliner knows fighting the wind lengthens your trip. For Borschberg, flying along at 30 mph in a strong headwind severely impaired forward motion.

“We had a strong wind at a certain stage, and we had been approaching backward our next waypoint,” he says.

Yes, as the headwind exceeded the speed of the airplane, Borschberg traveled backward relative to the ground.

After wrapping up our interview, Borschberg began preparing for the landing in Dallas. After more than 15 hours in the air, he was looking forward to being back on the ground. The plane is quite cramped. At one point, a little less than three hours before he actually landed, he was only 20 miles or so from Dallas/Fort Worth International Airport and found himself lined up with runway 13L, where he planned to touchdown.

“Can I just lower the gear and make the approach?” Borschberg jokingly asked his team on the ground.

Unfortunately it wasn’t in the cards. He had to wait, and wait, and wait some more. Landing on 13L required closing the runway, and there was simply too much commercial traffic. It was after midnight before air traffic control allowed him to land, so he spent the intervening hours in a holding pattern above the runway.

The team knew the landing in Dallas would be tricky, and strong winds at lower altitudes made it an unusual landing. As he descended, the windspeed increased and he encountered a 25- to 30-knot wind at 2,000 to 3,000 feet. This meant Borschberg had to be careful not to turn downwind, because he would be blown too far north and would have to make another approach to land, covering the ground at less than five miles per hour with the headwind. Borschberg kept HB-SIA pointed into the southeasterly wind as he moved toward 13L.

“I was lined up with 13R,” he says referring to the parallel runway he had been circling over. “I was just moving sideways, I was only doing a translation.”

Fellow pilot and Solar Impulse co-founder Bertrand Piccard says Borschberg’s technique was an impressive feat of piloting.

“It’s not a normal airplane approach,” he said of his colleague’s sideways flying over the airport. “If a student was doing that in an exam, he would fail.”

The sideways translation eventually brought him over the top of runway 13L, where he touched down at 1:08 a.m. local time, 18 hours and 21 minutes after departing Phoenix.

The Solar Impulse team will be in Dallas at least through the holiday weekend before continuing on to St. Louis. The trip across America is a prelude to the team’s ultimate goal, a flight around the world in a new solar-powered airplane currently under construction in Switzerland..

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