World’s largest solar-powered aircraft, Solar Impulse 2 has left Cairo on last leg of its round-the-world tour. Aircraft should take about 48 hours to reach Abu Dhabi – the place it began the circumnavigation in 2015. “We thought it was going to be an easy flight because it’s always good weather between Egypt and Abu Dhabi. But actually, it’s extremely difficult to find a good strategy,” Piccard said. He added that the warmer, thinner air above the Saudi desert also means Solar Impulse’s motors will have to work harder to propel the vehicle forward.