Solar Impulse sets off for Washington DC via Cincinnati
Solar Impulse plane reaches Washington Dulles
(2 days later)
A solar-powered plane aiming to cross the US coast-to-coast has set off on its fourth leg, from St Louis, Missouri, to Washington DC.
A solar-powered plane has touched down in Washington DC, ending the penultimate leg of a first-of-its-kind bid to cross the US on solar power.
But the Solar Impulse team made a last-minute decision to stop over briefly in Cincinnati, Ohio, because of strong winds expected on the journey.
The Solar Impulse vehicle landed at the capital's Dulles airport at 00:15 local time (04:15 GMT).
That would have pushed the travel time beyond the limit of 24 hours that has been set for the single-pilot craft.
The plane will remain in Washington until early July, when it will take off bound for New York - the final leg of the "Across America" project.
After the 16-hour flight to Cincinnati, the team plans a pilot change.
On Sunday, the plane will be on view to the public at Dulles Airport.
The pilot duties on the "Across America" bid are being shared by the two leaders of the project - Swiss nationals Bertrand Piccard and Andre Borschberg.
This is the location of the US National Air and Space Museum's Steven F Udvar-Hazy Center.
Mr Borschberg will fly the St Louis-Cincinnati leg, with Mr Piccard taking over from there, landing some time after midnight local time (04:00 GMT).
The fourth leg of the journey from St Louis was re-routed via Cincinnati at the last minute, as high winds and air traffic would have made the direct journey longer than the team's prescribed limit of 24 hours for one pilot to be at the controls.
The prior part of the journey, from Dallas to St Louis, was piloted by Mr Piccard, representing his longest flight in the vehicle to date at 21 hours, 22 minutes.
After a 15-hour, 14-minute hop, the HB-SIA prototype craft landed at Cincinnati's Municipal Lunken airport on Friday evening in order to allow a change of pilots - Bertrand Piccard taking over from Andre Borschberg.
The craft holds the world record for the longest solar-powered flight at 26 hours, but the team has limited journeys in the Across America bid - billed as the first cross-continental, solar-powered flight - to 24 hours.
The segment from Cincinnati's Municipal Lunken airport to Dulles lasted 14 hours and four minutes.
Heavy air traffic as well as strong head winds and cross winds expected over the Appalachian mountain range have pushed the expected full travel time to Washington beyond that limit.
On landing, Andre Borschberg said that "with the successful completion of these last four US flights, we have shown that we are capable of coping with challenging meteorological conditions for our weather-sensitive plane and for our ground operations, and that we could find each time the right solutions to move forward. It has been a succession of fruitful learnings preparing us for the 2015 world tour."
It is not the first weather-related change to the project. Storms in the St Louis area prior to the plane's arrival damaged the hangar that was meant to house it, so the team was forced to erect a novel, inflatable hangar there.
Piccard's and Borschberg's intention is to build a bigger plane than the HB-SIA prototype and fly it first across an ocean and then around the globe.
The HB-SIA craft has the same wingspan as an Airbus A340 but weighs just 1.6 tonnes. Its propellers are powered by an array of lithium-ion batteries, which in the hours of daylight are charged by 12,000 solar cells that cover the craft's wings and stabiliser.
The HB-SIA craft already holds the world record for the longest manned solar-powered flight at 26 hours. The aeroplane's other records include the first international flight of a manned solar-powered plane in 2011, and first inter-continental flight in 2012.
The Across America project is the last showpiece with the prototype HB-SIA aircraft before Mr Piccard and Mr Borschberg attempt a trans-oceanic flight and an eventual around-the-world flight in 2015 in the two-seat HB-SIB.
The Across America project coincides with Piccard's and Borschberg's Clean Generation Initiative, an effort to encourage policy-makers and businesses to develop and adopt sustainable energy technologies.
The aeroplane's other records include the first international flight of a manned solar-powered plane in 2011, and first inter-continental flight in 2012.
The aircraft completed the first leg of its trans-American bid - between San Francisco and Phoenix - in early May, in a flight lasting 18 hours.
The second leg - from Phoenix to Dallas - was completed in late May. This trip covered a distance of 1,541km (958mi) - again, a record for a manned solar-powered plane.
The Across America project coincides with the Piccard's and Borschberg's Clean Generation Initiative, an effort to encourage policy-makers and businesses to develop and adopt sustainable energy technologies.
