Solar Powered Aircraft's Night Flight

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Solar Impulse HB-SIA began its 24-hour flight at 6:51 a.m. local time, Wednesday, seeking to finish it Thursday, after surviving the night over Payerne, Switzerland, on stored solar power and aerodynamic efficiency. The aircraft climbed all day to about 28,500 feet. It began that trip using stored battery power, but as the sun rose the aircraft's 12,000 solar cells kicked in. They overcame the four electric motors' energy drain and fully charged the batteries even while the airplane climbed. As darkness fell, the aircraft transitioned to conservation mode. It spent about four hours and thirty minutes in a slow descent, reaching about 4,500 feet at roughly 11 p.m.. At that height, pilot Andre Borschberg put the juice to the motors to maintain altitude. He would loiter there until about 7:30 a.m. when the sun again rose high enough to build charge in the aircraft's batteries, proving it could complete the cycle. At the time AVweb went to press, the aircraft had flown through the night until dawn and the solar energy it was collecting had just made the aircraft "energy neutral." It appeared the flight would conclude sometime after it turned the corner to show positive total energy gain, marking the flight as a success.

For the entirety of the flight, Borschberg was tasked with hand flying the aircraft and for a full ten-hour period, cockpit temperatures were below minus 20 degrees Celsius. He did have a heater, which he could use, sparingly. The aircraft's wing spans 63.4 meters and it carries 400kg worth of batteries. Running the aircraft's four motors to sustain altitude uses approximately 10-percent of the aircraft's battery capacity per hour. That means the aircraft can maintain altitude for about ten hours on batteries alone. For this flight, it needed about eight and a half hours (from 11 p.m. to 7:30 a.m.) of endurance before the sun rose high enough to begin charging the batteries, again. Aside from performing while sleep deprived, Borschberg encountered environmental challenges. The cold temperatures froze his drinking water system and caused his iPod to fail, but we understand he filled some of his downtime with singing. For the latest update and details, check the Solar Impulse blog, by clicking here.