Solar Impulse: Zero-fuel plane begins final flight

[nitpicker]

http://www.bbc.com/news/science-environment-36867613

Solar Impulse: Zero-fuel plane begins final flight

By Jonathan Amos
BBC Science Correspondent

24 July 2016
Take-off occurred at 23:30 GMT. The flight should last about 48 hours

The zero-fuel aeroplane, Solar Impulse, has left the Egyptian capital, Cairo, on the last leg of its global tour. The aircraft should take about 48 hours to reach Abu Dhabi, UAE - the place it began the circumnavigation in March 2015.

Pilot Bertrand Piccard is at the controls one final time. His flight ought to be fairly straightforward, although his team has some concerns about how the heat in the Middle East may affect the plane. Mr Piccard is likely to have to spend a lot of time at high altitude on oxygen to get above the thermals and the turbulence they induce.

The warmer, thinner air above the Saudi desert also means Solar Impulse's motors will have to work harder to propel the vehicle forward. This will require careful management of the energy reserves in the plane's lithium polymer batteries, to be sure they can sustain the aircraft through the night hours.

"We thought it was going to be an easy flight because it's always good weather between Egypt and Abu Dhabi across Saudi. But actually, it's extremely difficult to find a good strategy," Mr Piccard told BBC News.
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