Solar Impulse is a Swiss long-range, experimental, solar-powered aircraft project which has been running for a number of years and is used to promote the use of alternative renewable energy sources related to new technologies to allow decreased dependence on fossil fuels.
Solar Impulse 2 (SI2) has been built in an attempt to achieve the first round-the-world flight powered solely by energy from the sun.
SI2 is a single seater aircraft made from carbon fibre and has a wingspan of 72m, which is wider than a Boeing 747 jet. It has a compact cockpit space of only 3.8 cubic metres to accommodate a single pilot. The overall weight of the aircraft is 2300kg.
A total of 17,248 solar cells are built into the wings, fuselage and horizontal tailplane covering a total surface area of 269.5 m2. They collect up to 340kWh of solar energy per day to drive 4 electric motors and to charge the lithium polymer batteries. The batteries are used to allow SI2 to fly during the night.
The four engines, each generating a maximum power of 17.5hp, are mounted below the wings and each have a 2 blade propeller with a diameter of 4m. The entire system has an efficiency of 94%.
There are 4 batteries which have an energy density optimized to 260 Wh/kg and are insulated using high density foam. They are mounted in the four engine housings and weigh a total of 633kg which is slightly more than 25% of the overall aircraft weight.
SI2 flies at a speed between 20 and 77 kts. Energy usage is optimised by using a combination of solar energy with the potential energy created from the aircraft height.
During the day the pilot slowly ascends to a high altitude using solar energy to drive the aircraft and charge the batteries. As the sun sets, the pilot reduces the power to the engines and begins a gentle descent of around 0.4m/s to an altitude of between 1000-1500m where level flight is maintained at around 25kts. This cycle is repeated for each day and night of flight.
The driving force behind the project are also the 2 pilots.
Bertrand Piccard, a doctor, psychiatrist, explorer and aeronaut, who made the first non-stop round-the-world balloon flight, is the initiator and chairman.
André Borschberg, an engineer and graduate in management science, a fighter pilot and a professional airplane and helicopter pilot, is the co-founder and CEO.
SI2 set off from Abu Dhabi in March 2015 in a multi-leg attempt to fly around the world powered by the sun’s energy.
The flight started from Abu Dhabi, on March 9 2015. The route includes stop-overs in Oman, India, Myanmar and China. Crossing the Pacific Ocean with a stopover in Hawaii then flying across the U.S.A. and over the Atlantic Ocean, before heading back to Abu Dhabi.
Andre has just completed one of the most challenging legs of the round-the-world flight consisting of a journey which was to last 5 days and nights
SI2 left Nagoya (Japan) on June 28 2015 at 18:03 (UTC) and arrived in Hawaii on July 3 2015 at 15:55 (UTC). The total flight time was 4 days 21 hours and 53 minutes travelling 7212km at a maximum altitude of just over 23000ft and an average ground speed of 38 mph.
Full details about this leg of the journey can be found at
During maintenance and checks after landing in Hawaii it was discovered that the batteries had suffered irreversible damage caused by overheating. Repairs will take several months and the round-the-world trip has been postponed until spring 2016.
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