Engineers in Switzerland have successfully completed the first test flight of an aircraft designed to fly round the world using only solar power.
The Solar Impulse flew to an altitude of 4,000ft in an 87-minute flight to check stability and manoeuvrability ahead of a global circumnavigation attempt in 2012.
"This first mission was the most risky phase of the entire project," said André Borschberg, chief executive and co-founder of Solar Impulse.
"Never has an airplane as large and light ever flown before. The aim was to verify the prototype's behaviour in flight, and to test its reaction to various manoeuvres. The success of this first flight allows us to envisage the programme with greater serenity."
The aircraft has a wingspan wider than a Boeing 787, and carries 12,000 solar panels. It weighs just 3.5 tons fully loaded, and is powered by four 10-horsepower engines. Cruising speed is around 45mph.
"We still have a long way to go until the night flights, and an even longer way before flying round the world, but today, thanks to the extraordinary work of an entire team, an essential step towards achieving our vision has been taken," said Solar Impulse co-founder Bertrand Piccard.
"Our future depends on our ability to convert rapidly to the use of renewable energies. Solar Impulse is intended to demonstrate what can be done already by using these energies, and applying new technologies that can save natural resources."
The planned flight in 2012 will take off in the Middle East and head east in five stages lasting three to four days each. Pilots will have to gain altitude and charge the aircraft's batteries during the day, and then glide downwards at night.
The project's co-founders, who were awarded the 2009 Brunswick Research Prize for their work, suggested that improvements in battery technology could eventually allow a non-stop circumnavigation of the world.
"Piccard and Borschberg are true pioneers and ambassadors of flights propelled only by solar energy, searching for opportunities to meet tomorrow's mobility challenges by developing alternative propulsion solutions," noted the Brunswick Prize jury.
"They push the limits of technical feasibility, and convince us of their determination and their outstanding commitment.
"The outcome of their achievements has given us new and fundamental expertise in man-machine interfacing, aircraft construction technology and alternative energies."
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