Solar-Powered Flyers
Head for the U.S.


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A Swiss team has been building up step by step to take a solar-powered airplane on a flight around the world. The next step will be to fly across the U.S. After all, it is the birthplace of powered flight, and the team may be able to pick up some American sponsors along the way.

Last year the team "Solar Impulse" flew the plane on a round trip between Payerne, Switzerland, and Rabat, Morocco, in a series of flights that included a midnight landing in Madrid. This year, the team plans to start in San Francisco, make two stops along the way, and then land in Washington, D.C. After that, it will fly to New York. Solar Impulse is the brainchild of Bertrand Piccard. He is a psychiatrist by training whose father invented a deep-diving vessel and whose grandfather rose 10 miles above Earth in a capsule lifted by a balloon. Bertrand Piccard and Brian Jones were the first team to take a balloon around the world.

When the balloon, the Breitling Orbiter 3, came down in Egypt it had very little propane left in its tank. According to Piccard, the mission almost failed because of the limitation of fuel. That's when he got the idea for a craft that would fly using no fuel at all, which is the way he describes Solar Impulse.

Solar Impulse at Brussels Airport, May 25, 2011. Image: Vyk, Commons.Wikimedia.org

Piccard is the chairman of the Solar Impulse project. His partner, the CEO, is André Borschberg, an engineer and pilot. They take turns flying the airplane. The plane completed a 26-hour flight in 2010. As Borschberg, who was the pilot on that flight, put it, "If you can fly one day and one night, then you can fly a second and a third."

The plan for the North American trip is to ship the plane in parts to San Francisco and reassemble it there. According to Piccard, the plane could fly cross the Atlantic, but the pilot could not. The plane is not equipped to sustain a person for a non-stop flight of several days, which would be required to make the crossing. (A second generation plane, now in the works, will make the global flight.)

The aircraft has an average flying speed of 70 kilometers an hour. Its wingspan, at 63.4 meters, is similar to that of a Boeing 747, but the mass of the plane is 1,600 kilograms, about the same as a car. According to Piccard and Borschberg, many innovations in the ultralight construction and energy efficiency of the airplane derive not from aerospace sources, but from shipbuilding and Formula One racing. The plane is made of carbon fiber composites. The upper surfaces of the wings and horizontal stabilizer are the solar panels, from SunPower Corp. of San Jose, CA.

It is powered by four electric motors with a maximum output of 8 kilowatts, or 10 hp. A quarter of the plane's weight is due to its lithium polymer batteries, which provide part of the power at night. The first few hours of night flight make use of energy stored in altitude. The plane climbs during the day to come near its maximum cruising altitude of 8,500 meters. At sundown, it descends for about four hours as a glider to its night cruising altitude of about 1,500 meters.

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If you can fly one day and one night, then you can fly a second and a third.

André Borschberg, CEO, Solar Impulse

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February 2013

Harry Hutchinson

by Harry Hutchinson, Executive Editor, Mechanical Engineering Magazine