WASHINGTON - The solar-powered Solar Impulse aircraft landed near the US capital early Sunday on the second to last leg of its cross-country journey, organizers said. The single-seater plane, which runs on four electric propellers powered by 12,000 solar cells mounted on its 63-meter wingspan, touched down smoothly in the dark at Dulles International Airport at 12:15 am (0415 GMT). The Solar Impulse usually lands in the middle of the night, when airport traffic has subsided. At the controls was Swiss pilot Bertrand Piccard, who is taking turns with compatriot Andre Borschberg on the various legs of the flight across the United States. "It might seem easy, but it's the result of a lot of work," Piccard said shortly after landing, highlighting a decade of effort, including developing the plane and studying historical and current weather records.

He said the flight has shown "we can achieve unbelievable things" with renewable energy, saying his plane is "so efficient, so reliable it can fly without any fuel day and night."

The plane will spend around two weeks in the Washington area and will be available for public visits at the Udvar-Hazy wing of Smithsonian Air and Space Museum.

"To be hosted by the Smithsonian Institution is an honor for Solar Impulse," Piccard said, adding that he hoped his plane might join the museum's permanent collection.

"Congrats & welcome!" the museum said on its Twitter feed shortly after the plane touched down, in a landing broadcast live on the organizer's website, live.solarimpulse.com.

The final leg of the cross-country journey will take the plane to New York City.

The aircraft can fly at night by reaching a high elevation of 27,000 feet (8,230 meters) and then gently gliding downward, using almost no power until the sun comes up to begin recharging the solar cells.

The flight from Cincinatti, Ohio took about 14 hours, after a 14-hour pit stop in the midwestern US city prompted by difficult weather.

The organizers had planned for the solar craft to fly directly from St. Louis, Missouri to Washington DC, but they said strong cross and head winds slowed down the aircraft.

Conditions were such that the flight to Washington would have taken longer than the self-imposed 24-hour time limit set for the pilot in the cramped cockpit.

The Solar Impulse project, founded and led by Piccard and Borschberg, aims to showcase what can be accomplished without fossil fuels, and has set as its "ultimate goal" a round-the-world flight in 2015.

The first leg of Solar Impulse's US tour took place on May 3, when Piccard flew the aircraft from San Francisco, California, to Phoenix, Arizona.

St. Louis was chosen as the Midwest stopover as a homage to aviation pioneer Charles Lindbergh and his "Spirit of St. Louis," the first plane to fly from New York to Paris non-stop. AFP