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