Solar Impulse 2's final 48-hour flight from Cairo to Abu Dhabi may take begin on Sunday at 1:00 AM Cairo time, a "provisional time" for a trip that will be the most technically challenging of the round-the-world tour, Solar Impulse announced Friday. The flight was postponed last Saturday due to pilot Bertrand Piccard's sickness and worsening conditions in Cairo, as winds were too strong for the solar-powered airplane to be taken out of its tent. "Conditions are tricky with winds challenging Si2's limitations on the runway," Solar Impulse said on Friday. "We are therefore getting ready for an attempt, but there is a risk that we will need to postpone the flight at the last minute." The Control Center has been in discussions over the choice of the time that will allow the plane to overcome high temperatures in Riyadh. "We have never had to deal with temperatures so high before on our round-the-world tour, but a little challenge at the end of our mission is always good," Solar Impulse said on Thursday on their blog. The temperature at sea level is approximately 15°C in the standard atmospheric model, while in Saudi Arabia, the temperature at sea level in 3 times this temperature, Solar Impulse explained. Heat is bad for Solar Impulse because it makes it less energy-efficient. "Because hot air is less dense, the airplane requires more energy to remain level and climb to higher altitudes. Think of it this way, with lower air density, the propellers have to shovel thinner air, therefore requiring more energy to fly towards its destination," the Solar Impulse team explained. The groundbreaking aircraft uses solar energy to charge batteries that power propellers. The plane makes it climb to its highest altitude (about 28,000 feet) and is able to produce enough energy for nighttime cruising. Solar Impulse 2's round-the-world tour started in March 2015 in Abu Dhabi and was aimed at promoting clean technology by founders Betrand Piccard and André Borschberg. The Monaco-based Mission Control Center identified Sunday at 1:00 AM as a time that could allow the airplane to overcome Saudi Arabia's high temperatures during the voyage's final leg. "We are likely to have to adapt timings - so, as always with Solar Impulse, stay on your toes," the statement said. source: Ahram Online
