The Solar Impulse solar-powered airplane made history in 2010 when it embarked on the first-ever solar-powered night flight, and again in 2012 when it made the first intercontinental solar-powered flight (Europe to North Africa)
With a wingspan of 63.4 metres, which is as big as a jumbo jet’s. It weighs no more than a car, with a fuselage is as slender as a glider’s and a cramped single-person cockpit. The wings are covered in almost 12,000 photovoltaic cells, which can simultaneously run four electrically driven propellers while charging four packs of lithium-polymer batteries. The batteries are needed because the aircraft has to be able to fly through the night.
Swiss co-founders Bertrand Piccard and André Borschberg began working on Solar Impulse in 2003 after a feasibility study at the Swiss Federal Institute of Technology in Lausanne suggested a round-the-world trip by solar airplane would become possible as solar cell power efficiency improved. The idea was not to suggest that aviation should switch to solar power, but rather to use the aircraft as a mobile showcase for solar cell efficiency.
Now the co-founders and pilots of Solar Impulse will conduct the first solar-powered coast-to-coast United States flight – Solar Impulse Across America – taking flight from May 1st. The Solar Impulse manages a speed of just 64 kilometres per hour so, although it can stay aloft for 36 hours, it will stop over a number of times: at Phoenix, Arizona; at Dallas, Texas; at St Louis, Missouri (or Atlanta, Georgia); and at Washington DC en route to New York City.
A typical flight involves taking off in the early morning, when winds are light, and ascending to 10,000 metres to stay above any storm clouds. The air is thin at this altitude, though,and an oxygen supply is needed. The pilot has to wear an oxygen mask because pressurising the cockpit is not possible. The team do not want to carry heavy oxygen cylinders so Air Liquide, an industrial-gases firm, has developed a solar-powered system to generate oxygen.
At night the pilot descends slowly, carefully using up the power until dawn. Once the sun returns the batteries can recharge in three hours as the plane ascends again. Landings are also left until the early evening, when winds are light.
“We want to show that with clean technologies, a passionate team and a far-reaching pioneering vision one can achieve the impossible,” said Piccard at last month’s announcement of the Solar Impulse Across America trip. “If we all challenge certitudes by driving change and being pioneers in our everyday lives, we can create innovative solutions for society’s biggest challenges.”
Ross Aimer, CEO of Aero Consulting Experts, told ABC News that he believes Solar Impulse’s Across America flight is “a big step, but also a baby step.“When it comes to a commercial craft, you would need more power. … You’d probably need something like two football fields of solar panels,” said Aimer, a retired United Airlines captain.
But the flight expert is confident. Seeing advances in solar flights and some new airplanes using biofuel encourages Aimer. “Anything to get us away from burning kerosene,” he said. Some commercial planes are already using electric battery backup systems, although that technology is still in its early stages, Aimer said.
“Hopefully, the [Across America] flight will get some people’s attention. I’m optimistic that the future can be solar and electric,” said Aimer.
The next Solar Impulse challenge is to fly around the world, the attempt is already slated for 2015. This will be much more challenging due to long ocean flights, the pilot will have to fly non-stop for five-to-six days at a time only catnapping for 20 minutes at a time. Therefore to give the pilots Piccard and Borschberg room to exercise and lie down, the next aircraft will be about 15% bigger than the prototype, which tips the scales at just 1,600kg (3,527lb). The Solar Impulse’s ultimate range will be limited by the physical ability of the pilot to remain alert, with little room to move or to store much food and water. With current technology, the team reckon, a two-person solar plane would be too heavy so the pilots will take turns to fly the aircraft.
The ability to stay awake for long periods of time will be vital as installing a full autopilot system is currently unfeasible due to its weight. However, Altran, an engineering consultancy based in France and one of the project’s supporters, is developing a partial system. In calm weather, it will keep the aircraft pointing in the right direction. And if turbulence causes a wing to dip by more than five degrees, a cuff on the pilot’s right or left arm will vibrate to tell him which way to correct course. He must react quickly to keep control. This system will be tried out on the prototype flight in America.
Sources include: New Scientist, BBC, The Economist, solarimpulse.com
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