Unmanned solar air vehicles have been around for years, but on April 7 while a crowd of spectators watched the human-piloted Solar Impulse HB-SIA took off from Switzerland's Payerne airfield, climbed to nearly 4,000 ft (1,200 m), and went through various flight exercises for the next 87 minutes. We'd love to provide details, but the project website is long on speculation (environmental niceties, a planned nonstop flight around the world, and so on) and strangely short on specs. However, various sources have tagged the plane as about 72 ft (22 m) long with a wingspan of 208 ft (63.4 m), and powered by nearly 12,000 photovoltaic cells and a pack of lithium batteries.
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