Socata studies liquid-resin composite fuselage process

NBAA Convention News » 2007
September 21, 2007, 6:44 AM

EADS Socata (Booth No. 3871) has started exploring a liquid-resin infusion (LRI) process for composite fuselage construction. The French company this month launched a $12.5 million, four-year research and development program, dubbed Fuscomp, which eventually is expected to yield a composite fuselage demonstrator. Its current business aircraft offering, the single-turboprop Socata TBM 850, uses mainly metal construction.

“Fuscomp is a feasibility study for using the infusion process in primary structures,” project manager Pierrick Venisse told NBAA Convention News. The demonstrator airplane will take the shape of a TBM 850 fuselage. The technology, however, will be applicable across Socata’s three market segments: aerostructures in business aircraft (not only the TBM series but also Falcon business jet subassemblies), airliners and helicopters.

Venisse distinguished between two kinds of resin-infusion processes. Resin-film infusion (RFI), more common in aerospace, is a process whereby the resin is used in a solid rather than liquid form. An autoclave is generally used to cure the components. RFI is more appropriate for large parts with simple geometry.

Although an infusion process as well, LRI is somewhat different, Venisse explained. “At the beginning of the LRI process, the resin is outside the mold. The latter holds dry fibers under a vacuum bag. The pressure differential allows the resin to be sucked into it,” he said. The part is then cured without an autoclave. Compared to the more usual “prepregs” (pre-impregnated fibers), LRI enables more complex and integrated parts in one operation.

LRI is already used for parts that are smaller or less complex than those Socata is aiming at. For example, components for flap tracks on the Airbus A380 are made using LRI. Socata wants to manufacture structure panels with numerous functions integrated into a single piece. “They will integrate frames, stringers and window and door contours,” Venisse said.

As a result, the part count can be greatly reduced. This will translate to lower manufacturing costs, notably because the process is less labor-intensive. In addition, cycle times will be shortened.

Program Goals
Socata R&D engineers believe LRI better suits the company’s business. “Fiber placement involves major investments–notably for big autoclaves–that can be substantiated with larger fuselages and/or higher production rates,” Venisse said. Moreover, fiber placement does not lend itself to small, complex shapes.

The biggest challenge is in finding the perfect set of parameters for each part. Production engineers have to determine the best placement for the intake of resin into the mold, for example. They have to choose the right resin temperature to allow a smooth flow. They also have to find the best way to shape the fibers themselves.
The four-year research program will be broken down into two years of studies and two years of manufacturing. So does this mean that Socata could launch a composite-fuselage aircraft program in 2011? “Our design office will not necessarily wait until then–they could start a new design earlier, using what has been done so far in Fuscomp,” a Socata spokesman said.

And why not study a composite wing? “A wing offers fewer opportunities to integrate multiple functions,” he said.

Socata has several partners in the Fuscomp R&D program. One of them is
boat material specialist Sicomin. “They make resins for boat construction, and infusion is already used in this industry,” the spokesman explained. “We are going to develop a resin for our applications. Aircraft materials have to withstand higher temperatures, up to 120 to 180 degrees Celsius [250 to 360 degrees Fahrenheit] because they can spend a long time on the apron on a hot day or be close to
the engine.”

Another partner is Aerovac, a company that specializes in composite part manufacturing equipment, especially infusion processes. Socata and its Fuscomp partners will fund 32 percent of the program. The French state and local authorities will fund the remaining 68 percent.   

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