06/03/2013

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Solar Impulse project designs new zero fuel plane for launch in 2015

The founders of the Solar Impulse (SI) project, doctor and psychiatrist Bertrand Piccard and former fighter pilot André Borschberg, were represented by Piccard, who described the challenges associated with the development of the first aircraft, which weighs only 1,600 kg and is only 21.85 m in length, but with a wingspan of 63.4 m, equivalent to that of an Airbus A340. The new aircraft SI2 will incorporate Bayer's Baytube carbon nanotubes (CNTs) in epoxide resin-impregnated composite structures, allowing an even wider wingspan without suffering a high weight penalty. Wingspan is also important: wind causes a vortex on the tips, resulting in drag. This can be reduced slightly by using PU winglets to move the vortex away from the wing. CNTs also make the SI2's battery 30 % lighter, producing 240 Wh/kg instead of 160 Wh/kg produced by the first aircraft. This is extremely important, as electricity storage is the bottleneck.[image_0] Earlier solar planes had no batteries, but were not manned: "If we really want to have an impact, we have to put a pilot on board, also for communication,” Piccard observed. "When we announced the aim of manned flight with a solar power plane, we held a press conference. There was so much coverage on worldwide news networks that, we said now we must start and can't go back”. The Solar Impulse cockpit, displayed on the Bayer MS stand at K2010 was made with rigid PU foam and was clad in a silver effect Bayer Makrofol polycarbonate film. Other Bayer PU products included viscoelastic foam seating, Impranil textile coating under the wing and hull, rigid foam for the motor nacelle lining. Desmodur, Baymer and Desmorapid products are also used for the rigid foam wing tips. SI2 also features PU rigid foam: Baytherm Microcell foam with 40 % smaller pores than conventional PU foam but providing 10 % better heat insulation, an important feature with temperatures ranging from -50 °C at night and 50 °C during the day. Conventional polyurethane rigid foam would need to be thicker to achieve the same level of thermal insulation and this would be more restrictive on the pilot's freedom of movement. An upper carbon fibre-reinforced plastic (CFRP) panel, with Microcell PU rigid foam cladding on top of it, is located behind the IR and UV-resistant polycarbonate canopy glazing and the SI2 also has a carbon fibre filament wound PU composite nose cone.[image_1_right] BMS designed the resin transfer moulding (RTM) equipment using a Hennecke MN10 mixing head. Hooks to hold the PC canopy should be made in PU-based CFRP, as should the "lower eggshell”. The front section of the hatched 3D eggshell-shape cockpit needs insulation, but the rear fuselage section should be made just from "special” plastic foil, without insulation, but reinforced by a structure adapted to it. Relating to his aviation and ballooning experiences to day-to-day life, Piccard said "We should switch off the auto-pilot in our heads and throw ballast overboard.” He has been influenced here by his experience of almost running out of fuel when ballooning, leading to his interest in flying without fuel. Hence the Solar Impulse aircraft flies using electricity collected during the day by solar panels on the wings and at night using power stored in the batteries. "The more we fly, the more energy we have,” Piccard said, "but the pilot is not replaceable,” explaining that flight times were limited, to come extent, by the pilot's ability to fly alone for 24 hours continuously and in a cramped space, rather than the aircraft's batteries. The Solar Impulse project aims to demonstrate the possibilities of innovative thinking to overcome the challenges of reduced mobility, economic growth and less job security by simply reducing fuel consumption and using clean technologies. Piccard is convinced that the use of technical expertise can save 50 % of the world's energy, the rest can be supplied by renewably sourced energy. The Solar Impulse project creates solutions, humanistic and philosophic ones, as well as technical solutions, he claimed. Of the 80 partners, only privately owned Dassault is the only aviation industry company to participate in the project and illustrating its pioneering spirit. New ideas for the project have come from outside of the aviation industry. There is one insurance company partner, Swiss Re, interestingly, as Piccard's great grandfather Auguste Piccard was refused insurance before flying into the stratosphere in 1932 in a balloon-held capsule - on the grounds that suicide was uninsurable. Piccard continued, "When we had the first plastic model, we thought aircraft companies would fight to make it, but none responded, so we found a boat builder with carbon fibre experience.” The result was a 50 kg structure weighing ten times less than a typical sailplane. Many were sceptical and while admitting its existence, some said it would never fly. But the first Solar Impulse took off in July 2010, equipped with four engines. The HB-SIA flew as guest of honour to the Le Bourget air show. A flight from Switzerland to Morocco helped promote the project for the world's largest solar electricity plant. This happened while some large electrical and oil companies were withdrawing from solar initiatives, Piccard noted. The next project is to fly coast to coast across the US from San Francisco to New York during 2013. This adventure will be a great opportunity to showcase the technology used in Solar Impulse, even though the aircraft is being dismantled and shipped to the US in a Jumbo Jet. Looking ahead, Piccard concluded "We say solar energy will never transport 200 people - but maybe we are wrong. If it is possible, it will be due to you,” he said jokingly while looking at Bayer MaterialScience staff, "so maybe you should start to work on it.” - DV -

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