High-Performance Composites

NOV 2014

High-Performance Composites is read by qualified composites industry professionals in the fields of continuous carbon fiber and other high-performance composites as well as the associated end-markets of aerospace, military, and automotive.

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N O V E M B E R 2 0 1 4 | 4 7 N O V E M B E R 2 0 1 4 | 4 7 stop, round-the-world balloon fight and came up with the Solar Impulse concept. The venture is led by Piccard, and CEO André Borschberg, whose curriculum vitae includes engineering, a graduate degree in management science and experience as a fghter pilot and a professional air- craft and helicopter pilot. They describe Solar Impulse 2, the sec- ond generation of the company's frst solar-powered aircraft, as "the only air- plane of perpetual endurance, able to fy day and night on solar power, without a drop of fuel." To make that possible, Solar Impulse enlisted the aid of North Thin Ply Technology (NTPT, Penthalaz, Switzerland). NTPT has successfully developed very thin unidirectional pre- pregs using spread tow that comprises intermediate-modulus carbon fbers with an areal weight reportedly as low as 18 g/m 2 (0.4 oz/inch 2 ). From sails to wings NTPT's parent company, North Technol- ogy Group (Milford, Conn.), made news previously with another spread-tow, thin-ply development, its patented 3Di process, which produces monolithic yacht sails (see "Learn More"). But un- like 3Di, which is designed to produce fexible material at the North Technology Group facility in Minden, Nev., that can function like, but perform better than, more conventional sailmaking material, the system developed by North Thin Ply Technology, and registered under the trademark TPT, is "100 percent dedicat- ed to rigid composite applications," says NTPT's sales and marketing manager Gilles Rocher. "NTPT offers outstanding composite strength, homogeneity and machinability for rigid commercial ap- plications demanding high performance and low weight." Solar Impulse 2 ( Si2 ) was designed with TPT materials in mind by Solar Impulse in conjunction with its airframe manu- facturer, Decision SA — a member, with Multiplast SAS (Vannes, France), of Groupe Carboman SA (Ecublens, Swit- zerland). Decision constructed the Si2 airframe in its Ecublens facility. Launched in 1984, Decision focuses on production of innovative compos- ite structures that include not only the Solar Impulse airframe but the internal structures of the Volvo Ocean 65 high- performance monohull racing yacht. In July 2010, Decision built the prototype model, Solar Impulse 1 ( Si1 ), the frst air- craft in solar aviation history to stay in the air after dark (26 hours of continu- ous solar-powered fight). "Construction of Si2 began in 2011 and lessons learned from the prototype are incorporated into this second air- plane," says Bertrand Cardis, Decision's general manager. "Designated HB-SIB, it will have an increased payload, its elec- trical circuitry will be isolated to enable fights in light rain, and system redun- dancy will improve reliability. Important- ly, its more spacious cockpit will enable the pilot to fully recline during fights lasting up to fve days and fve nights." Weight has been decreased "gram by gram" for the Si2 venture, largely through the use of the NTPT materials and process in the construction of all of the airframe's structural components, which includes the main and rear wing spars, the fuselage and cockpit, the tail structure and the vertical and horizontal stabilizers. Solar Impulse airframe structure As the frst step in the manufacturing process for the Si2 , NTPT spread M46J 12K ultrahigh-modulus PAN carbon tow, a 440-GPa fber supplied by Toray Indus- tries (Tokyo, Japan), using NTPT's pro- prietary technology. Depending on the carbon fber, the process can yield tapes with areal weights of 100 g/m 2 (2.3 oz/ inch 2 ), 50 g/m 2 (1.1 oz/inch 2 ) and as little as 25 g/m 2 (0.6 oz/inch 2 ) . Eight spools of M46J 12K tow feed the technology's spreading unit. Rocher points out that NTPT typically spreads a 3- to 4-mm (0.12- to 0.16-inch) tow of 12K to 18 mm/0.71 inch width for a 25-g/ m 2 (0.6-oz/inch 2 ) unidirectional tape. For the Si2 , however, it produced a 25-g/m 2 unidirectional tape with a width of 300 mm/11.8 inches. As it came out of the spreading unit, the unidirectional tape was impregnat- ed using NTPT's custom-formulated Round-the-clock flight around the world The all-composite airframe of the Solar Impulse 2 (Si2) supports 17,000 solar panels that not only power the craft's four electric prop engines by day, but collect enough additional energy to charge onboard batteries that can power those engines after the sun sets, making Si2 and its predecessor (Si1) the world's only aircraft able to fly nonstop, day and night, on solar power, without a drop of fuel. Si2 is in preparations now to circumnavigate the globe in 2015. Source: Solar Impulse/Photo: Ackermann The NTPT materials and process were used to construct the Solar Impulse 2's main and rear wing spars and other airframe components.

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