Solar Plane Lasts All Night Long

Swiss researchers yesterday marked a major milestone in the development of a solar-powered, single-pilot aircraft that they hope will eventually circumnavigate the globe. They kept their craft aloft through an entire night on stored solar energy.

In the wake of the event, the pilot, André Borschberg--CEO and cofounder of the Solar Impulse project--declared: "I have just flown more than 26 hours without using a drop of fuel and without causing any pollution!" The plane took off from a Swiss airbase early Wednesday and landed there at dawn Thursday.

Of course, it is a long way from this stunt to an aviation industry that isn't reliant on energy-dense jet fuel to hoist hundreds of thousands of pounds of cargo and passengers to cruising altitude. Unlike cars--which can today drive respectable distances on stored electrical energy--commercial aircraft will be dependent on liquid fuels for a long time.

But the Solar Impulse plane does include some novel engineering feats. Its wings are covered with 11,000 solar cells, and it uses lightweight composite structural parts and has a wingspan of 210 feet, not far from that of the world's biggest commercial jet, the Airbus A380, which has a wingspan of 260 feet. Keeping the plane's weight down to 3,500 pounds required optimizing electrical components in order to keep battery size as small as possible. The design was honed with computer modeling help from the European Space Agency and the Swiss Federal Institute of Technology. Still, the plane must fly at a pokey 28 miles per hour to save electricity. The lessons learned from the test flight will be used to develop an improved version of the plane that would attempt to fly around the world.

"It's good engineering, as you would expect from a Swiss team," said John Hansman, professor of aeronautics at MIT. But while the project is interesting, he says: "Solar will be a niche application for aircraft. It's hard to have enough energy capture to use for transportation, and solar cell efficiency is not high enough."

Despite their dubious commercial potential, lightweight solar-powered planes could be crucial to conducting long-term surveillance, and that's why various governments, including that of the United States, have been researching the technology. NASA's solar-powered Helios aircraft, one such unmanned effort, disintegrated due to turbulence during a 2003 test flight.

The unmanned solar powered record, set by QinetiQ's Zephyr UAV in 2008, stands at 82 hours 37 minutes or 3 1/2 days, exceeding the current official world record for unmanned flight which stands at 30 hours 24 minutes set by Global Hawk in 2001.

In 1999, the leader of the Solar Impulse project, Swiss adventurer Bertrand Piccard, became the first person (along with his copilot) to fly nonstop around the world in a balloon. "This is a highly symbolic moment," he said in a statement yesterday. "Flying by night using solely solar power is a stunning manifestation of the potential that clean technologies offer today to reduce the dependency of our society on fossil fuels."

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