Solar-electric plane to attempt around the world flight

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Solar Impulse Unveils Solar-Powered, Round-The-World Aircraft

Switzerland?s Solar Impulse has unveiled the aircraft with which it will attempt a solar-powered round-the-world flight in 2015.

The 236-ft. wingspan Solar Impulse is scheduled to make its first flight in mid-May.

The aircraft, registered HB-SIB, is larger and heavier than the prototype, HB-SIA, with increased wingspan, solar-cell area and battery capacity. Solar Impulse 2 will have increased endurance and speed, giving it a greater ability to manage weather during the round-the-world attempt.

Unveiled at Payerne airport April 9, the aircraft will be rolled out of the hangar early next week to begin ground tests of the solar energy collection and storage system, Solar Impulse says. Flight testing will be conducted from Payerne.

Where the 1,600-kg (3,530-lb.) gross weight prototype?s longest flight has been more than 26 hr., the 2,300-kg Solar Impulse 2 is designed to fly for four-six days. Changes from HB-SIA include a 14% longer wingspan, increasing the number of solar cells to 17,000 from just less than 12,000.

Energy density of the four lithium-polymer battery packs is increased to 260 kw/kg, from 240 kw/kg in the prototype, and efficiency of the four more-powerful brushless electric motors is increased to 94%. The engines are mounted closer together, to reduce thrust asymmetry in case of a failure.

The round-the-world flight attempt is planned to begin from somewhere in the Middle East so that the aircraft can cross India and China before the monsoon season starts. Solar Impulse co-founders Bertrand Piccard and Andr? Borschberg will take turns flying the single-seat aircraft.

The team is planning to make 8-10 stopovers. The longest flight will be crossing the Pacific from eastern China, which is expected to take up to five days and nights. Solar Impulse has a roomier cockpit than the prototype, to carry more supplies and make it easier for the pilot to take short naps during flight.

Where HB-SIA cruises at 70 km/hr. (39 kt.), Solar Impulse 2 will be capable of speeds up to 170 km/hr., but will have to slow to 25 kt. at night to conserve energy, Piccard says. Crossing the Pacific against trade winds means the aircraft may be going backward at night, he says, adding to the flight time.

Weather will be the major challenge, and Borschberg says there will be a large team of meteorological specialists and simulation experts on the ground working to predict the weather and routing a couple of days in advance of each flight.

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