Solar plane: From San Francisco to Phoenix in 18 hours!

The solar-powered airplane from San Francisco to Phoenix took 18 hours and 18 minutes on Saturday - and didn't use a drop of fuel.

A solar-powered airplane that developers hope eventually to pilot around the world landed safely in Phoenix on the first leg of an attempt to fly across the United States using only the sun's energy, project organisers said.

The plane, dubbed the Solar Impulse, took 18 hours and 18 minutes to reach Phoenix on the slow-speed flight, completing the first of five legs with planned stops in Dallas, St. Louis and Washington on the way to a final stop in New York.

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The spindly-looking plane barely hummed as it took off Friday morning from Moffett Field, a joint civil-military airport near San Francisco.

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It landed in predawn darkness at Sky Harbor International Airport in Phoenix, according to a statement on the Solar Impulse's website.

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The flight crew plans pauses at each stop to wait for favorable weather. It hopes to reach John F. Kennedy International Airport in New York in about two months.

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Swiss pilots and co-founders of the project, Bertrand Piccard and Andre Borschberg, will take turns flying the plane, built with a single-seat cockpit. Piccard was at the controls for the first flight to Arizona.

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The lightweight carbon fiber Solar Impulse has a wingspan of a jumbo jet and the weight of a small car and from a distance resembles a giant floating insect.

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The plane was designed for flights of up to 24 hours at a time and is a test model for a more advanced aircraft the team plans to build to circumnavigate the globe in 2015.

It made its first intercontinental flight, from Spain to Morocco, last June.

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The aircraft is propelled by energy collected from 12,000 solar cells built into the wings that simultaneously recharge four large batteries with a storage capacity equivalent to a Tesla electric car that allow it to fly after dark.

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The lightweight design and wingspan allow the plane to conserve energy, but make it vulnerable. It cannot fly in strong wind, fog, rain or clouds.

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The plane can climb to 28,000 feet and flies at an average of 43 miles per hour (69 km per hour).

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The project began in 2003 with a 10-year budget of 90 million euros ($112 million) and has involved engineers from Swiss escalator maker Schindler and research aid from Belgian chemicals group Solvay.

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A Solar Impulse crew member stands beneath an engine on the runway at Moffett Field before the first leg of the aircraft's 2013 Across America Mission, piloted by Bertrand Piccard, in Mountain View, California.