To help build the Boeing 787's composite fuselage, Italy spends a bundle.
- By Joe Pappalardo
- Air & Space magazine, July 2007
(Page 5 of 5)
The placement and orientation of the fiber strips are not the only way to handle stresses caused by openings in the fuselage structure—doors, windows, and other holes. The composite skin is reinforced by composite ribs called stringers, which run longitudinally to stiffen the weaker areas adjacent to the openings. An automated system of cranes within the towering fiber placement machine places the long carbon fiber stringers on the mandrel before “lay up” of the fibers. There are more than 100 stringers in each fuselage component.
Between uses, the mandrel stands as passive as an Easter Island statue. It is made from a nickel alloy, which is stable in extreme temperatures. When the composite piece is fired at 350 degrees Fahrenheit, the mandrel will be heated too, and it must not bend or buckle during the process. “In all other materials there is deformation, and we must be very precise,” Rosini says. All pieces must be within a tolerance of 0.3 millimeter.
An automated vehicle ferries the composite form and mandrel slowly toward the autoclave. Before leaving the clean room, the form is covered by a bag to keep impurities out. At 64 feet long, the autoclave is Europe’s largest. The barrel slips into the oven like a shotgun shell into a chamber. The oven’s round door looks like it belongs at the blast-hardened entrance of a NORAD bunker. It is, of course, painted Alenia blue.
The strips of carbon fiber material are impregnated with resin, which will ooze out when heated in the autoclave to form the matrix—the binding substance in a composite that holds the reinforcing elements, in this case polymer resin that holds the strips of carbon fiber. In the finished product, the resin matrix will serve as a bridge to ferry the stress of a load across a break if the carbon fibers snap. The heat and pressure of the autoclave are vital for the stability of the final product. The heat melts the resin, which is designed to retain its form when it softens, unlike a common plastic. The pressure drives out air pockets by pushing the resin into any microscopic voids that may lie between the carbon strands. Air pockets could create weak spots, forming cracks that could spread and jeopardize the entire piece.
After a 16-hour bake, the mandrel is removed from the autoclave, and the heat-resistant bag is removed.
The mandrel and now-cured fuselage section stay connected as they are brought to a 160-foot-long machine that shaves away composite to create openings for windows and doors. Several days after the process started, the form is placed into two fuselage-size rings—think Stargate—that will preserve its shape once the mandrel is collapsed and removed. The rings hold the not-yet-rigid airplane section while the work continues and quality control inspections begin.
When the sections are finished, Boeing’s modified 747 freighter, the unsightly Dreamlifter, will fly them to the new Alenia-Vought plant in North Charleston, South Carolina. There, approximately 350 workers will assemble, integrate, test, and apply surface finishes before sending joined sections on to Everett, where all the pieces will be put together.
As Alenia begins production of 787 parts, it is also negotiating a role on the 787’s rival, the Airbus A350. For the Boeing contract, the company benefits from a happy accident of geography. The 787 project demands time-zone straddling conference calls between South Carolina, Japan, Everett, and Italy. The best time to get all the partners together at once, Caruso notes, turns out to be daytime in Italy. “We are in the best location for conference calls,” he says. In other words, he feels Alenia is right in the middle. Just where it wants to be.