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.
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.
That would have pushed the travel time beyond the limit of 24 hours that has been set for the single-pilot craft.
After the 16-hour flight to Cincinnati, the team plans a pilot change.
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.
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 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.
Continue reading the main storyThe Solar Impulse HB-SIA
- Wingspan - 63m (208ft)
- Weight - 1,600kg (3,500lb)
- Covered with 11,628 solar cells
- Carries 400kg (900lb) of lithium-ion batteries
- Maximum cruising altitude of 8,500m (28,000ft)
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.
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.
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.
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 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 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.
Source: http://www.bbc.co.uk/news/science-environment-22902402#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
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