If everything goes right one of the first solar-powered aircraft will take to the skies in 2009 in an attempt to fly around the world with nothing but the sun for fuel.
The Swiss-based Solar Impulse team planning the trip this week showed off the $94 million Solar Impulse Alpha prototype that will be flown in 2008 as proof of concept. The aircraft has a 201-ft wingspan, only 7 feet shorter than an Airbus A340 airliner, and weighs just 3300 pounds thanks to its carbon-fiber body. The Solar Impulse will carry 880 pounds of lithium batteries powered by hundreds of solar cells stretched across its enormous wing. It will be powered by four electric motors producing a maximum of 10 horsepower apiece and should be able to fly for 36 hours at a maximum altitude of about 28,000 ft., at 28 mph said project CEO, André Borschberg.
The prototype “will be a first approach to optimizing the balance between energy consumption, weight, performance and controllability”, Solar Impulse stated.Ultimately the plan calls for the final version of the single-pilot aircraft to take off with its batteries fully charged, climb to about 28,000 ft. during the day under solar power and descend to 3,300 ft, during night under battery power. The goal is to have enough power remaining to begin the cycle again the next day, said Borschberg. There is no heat on board but there will be some dried food for the pilot and of course a bunch of avionics to help control the plane. The pilots, Borschberg and adventurer Bertrand Piccard, the initiator and president of the project will alternate days of flying.
As you might imagine, the aircraft faces a number of key challenges for its multinational 50 engineer development group. From the Solar Impulse Web site: Stretching carbon sheet just a few tenths of millimeters thick over the wing is a challenge. The fragile solar panels also have to be flexible in flight. How do we use cells as both energy generators and wing surface, without breaking when the airplane encounters turbulence? How do we succeed with a mission like this, when we know that with present-day technologies and performances, every square meter of photovoltaic cells can supply only 28 watts – the equivalent of an electric light bulb – to the propeller continuously over a 24-hour period? In other words, how can an airplane fly on the energy consumed by a supermarket window?
Solar aviation has some varied history. The Gossamer Penguin flew in 1980. It had a 71-foot wingspan and weighed only 68 pounds without a pilot, it had a low power requirement and thus was an excellent test bed for solar power. The Solar Challenger crossed the English Channel in 1981 and made several long-distance flights throughout Europe. American Eric Raymond flew Sunseeker across the United States, hopping across the country in 21 stages during two months in 1990. His longest lap was 250 miles, according to a Wired.com article.
The most famous solar aircraft might be NASA’s Helios, the $15 million solar-powered by day, fuel cell-powered by night unmanned aircraft with a wingspan of 247 feet. It made several flights between 1999 and 2003, when it crashed in the Pacific Ocean.
One of the problems with solar flight has been speed. Despite a 247-foot wingspan and 62,000 solar cells gathering energy to propel it, the Helios only ever managed to reach speeds of 19-27 miles per hour, with takeoff and landing speeds comparable to that of a bicycle, according to Treehugger.com.
