INGENIEUR
INGENIEUR
photovoltaic( PV) cells. The entire project from its beginning in 2003 until mid-2015 had cost € 150 million. It raised another € 20 million in late 2015 to continue the round-the-world flight.
FLIGHT PATH
Two solar powered planes, Solar Impulse 1 and Solar Impulse 2 were manufactured. Prototype Solar Impulse 1 made its maiden flight in 2009 and its first inter-continental 19-hour flight in 2012 from Madrid, Spain to Rabat, Morocco.
Solar Impulse 2 began its round-the-world journey in March 2015 starting and ending in Abu Dhabi, UAE( with stops in 16 legs). By the end of May 2015, the plane had traversed Asia. It made an unscheduled stop in Japan to await favourable weather over the Pacific. With Borschberg in the cockpit, it reached Hawaii on July 3, 2015 setting new records for the world’ s longest solar-powered flight both by time( 117 hours, 52 minutes) and distance( 7,212 km). During that leg, however, the plane’ s batteries were damaged by overheating. The plane was grounded in Hawaii until new batteries were made and installed. Test flights began in February 2016 and the plane resumed its journey landing in California in April, 2016. Additional legs of the flight were added in the US with the Solar Impulse 2 arriving in New York City on June 11, 2016. Piccard then piloted the aircraft across the Atlantic Ocean, arriving in Seville, Spain, on June 23, 2016. The final stop was in Cairo, Egypt, on July 13, 2016 before returning to Abu Dhabi.
TECHNICAL CHALLENGES
Solar Impulse’ s engineers and technicians, under André Borschberg’ s leadership, had to apply innovative solutions to create the unique solar-powered plane. They faced many technical challenges before being able to make a plane as big as a Boeing 747 but as light as a car, and one that could fly without fuel over long distances.
Energy to cross oceans and continents During the day, the plane flies only by the energy from the sun. But in the morning and evening, when sunshine is not so strong, and especially at night, it must tap into its reserve of energy stored in its batteries. So every evening, the pilot must make sure that the plane’ s batteries are 100 % charged so that it can fly until the next sunrise.
To ensure energy supply, 17,248 monocrystalline silicon cells each 135 microns thick was mounted on the wings, fuselage and horizontal tail plane, providing the best compromise between lightness, flexibility and efficiency. Each solar cell was tested three times.
The energy collected by the solar cells is stored in lithium polymer batteries, whose energy density is optimised to 260 Wh / kg. The batteries are insulated by high density foam and mounted in the four engine nacelles, with a system to control charging thresholds and temperature. Their total mass amounts to 633 kg, or just over a quarter of the aircraft’ s all-up weight.
During the first ascent on day one of the flight from Nagoya to Hawaii, the battery temperature increased due to a high climb rate and an over
Flight route of the Solar Impulse 2
28 VOL 67 JULY-SEPTEMBER 2016