Cutting-Edge Composites for Solar Impulse

"We will take composite technology two to three times beyond where it is today," asserts Andre Borschberg, a former Swiss air force pilot who wants to combine cutting-edge technology with environmental responsibility. As the CEO of Solar Impulse, Borschberg is in charge of a project whose mission is to design an airplane that can "take off and fly autonomously, day and night, propelled uniquely by solar energy, right around the world without fuel or pollution."

Some of the composite materials for Solar Impulse will be provided by Decision S.A., the Swiss company which supplied lightweight materials for the Alinghi, the yacht that won the America's Cup. According to Design News, the composites used aboard the Alinghi have a weight of 10 kg/m2; the materials for the Solar Impulse must weigh less than one-fifth of that. The solution, Borschberg explains, will be very high-modulus carbon fibers with optimized integration, starting with small-scale prototypes.

Solvay Advanced Polymers, one of the primary sponsors for Solar Impulse, has invested almost $100-million in Borschberg's project. Today, the company is busy developing thermoplastic products for the lightweight aircraft, including a shielded throttle housing made from Radel^® R polyphenylsulfone (PPSU). According to the Solvay Advanced Polymers web site, Radel R has a heat deflection temperature of 405° F (207° C) and can withstand continuous exposure to heat without cracking or breaking.

The solar cells for Solar Impulse will be made of monocrystalline silicone that is about 150 microns thick. This will require 200-m² of wing and tail surface for a low-speed (70 km/h) aircraft that will be difficult to control in flight. The photovoltaic units for Solar Impulse will be encapsulated in a composite "sandwich". To provide high mechanical strength at a very low weight, these structures will be carbon-fiber-reinforced composite skins bonded to a low-density core. One of the major test of Borschberg's solar-powered project includes stretching the carbon sheet just a few tenths of 1-mm thick over lengths of 20-m.

Solar Impulse faces many technical challenges, but Andre Borschberg remains optimistic. Recently, a small prototype was showcased at a Swiss airfield. The first daytime flight is scheduled for year's end, and the first nighttime flight will occurred in 2009. Sometime in 2010, Solar Impulse will attempt is first transatlantic night flight; however, because the aircraft will lack autopilot capabilities, the pilot will need some strong coffee for this voyage over the ocean.