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Solar Impulse, a solar-powered plane designed and built at the Ecole Polytechnique Fédérale de Lausanne, a Swiss University, recently flew from Switzerland to Morocco, a 48-hr journey. The flight included a stopover in Madrid to change pilots and was scheduled to coincide with the start of construction of a 2,000-MW solar project in Morocco.
The aircraft has a wingspan of 208 ft, about the same as that of an Airbus A340. The tops of the wing and horizontal stabilizer carry 11,628 photovoltaic cells which cover 2,200 ft2. The solar cells generate enough electricity to power the plane’s four 10-hp brushless motors and charge a bank of lithiumpolymer batteries. Each motor turns a 11.5-ft two-bladed propeller at about 400 rpm. The batteries provide power for night-time flying.
The plane weighs only 3,500 lb, including crew, and the batteries account for a quarter of the total weight. To keep the aircraft light, the cabin, wings, and nacelles are made of engineered polymers from Bayer MaterialScience, Pittsburgh.
The aircraft has a 22-mph take-off speed, cruises at 43 mph, and can fly as high as 39,000 ft. To keep the batteries functioning at that height, where temperatures can be -40°F, thermal insulation conserves heat the batteries radiate.
The Swiss team is now working on a follow-on aircraft that will attempt to circumnavigate the Earth on solar power. Unfortunately, the 236-ft composite spar that stretches the entire wingspan cracked during construction, pushing back the planned flight from 2014 to at least 2015.