The Economist: Solar-powered manned flight: Flying for ever
WHEN an airliner takes off for a transatlantic flight it needs to carry some 80 tonnes of fuel, which accounts for around one-fifth of its weight. On really long flights, fuel can account for 40% of a plane’s take-off weight, so that around 20% of the fuel is used to carry the rest of the fuel. Each tonne of fuel burned also produces 3.2 tonnes of carbon dioxide. Yet inside a hanger at a Swiss airfield is the prototype of an aircraft (illustrated above) that does not use any fuel at all. The wings of this aircraft are almost as big as those of an airliner, but they are covered in a film of solar cells that convert sunlight into electricity to drive its engines.
Solar-powered aircraft have flown before. The pioneer was Paul MacCready, whose Gossamer Penguin made the first manned flight in 1980 in California, with his then 13-year-old son at the controls. A derivative, Solar Challenger, crossed the English Channel in 1981. But nothing like HB-SIA, as the Swiss aircraft is known, has ever taken to the air. If it works as expected, another version will be built and this will take off, climb to 10,000 metres and, by storing some of the electricity generated during the day, continue flying through the night. Its pilots, Bertrand Piccard and André Borschberg, plan to cross the Atlantic in it and later to fly it around the world.
The prototype will be unveiled on June 26th by Solar Impulse, a project the aviators run. ...