Composites are at the beginning of their evolution, but metals are not yielding the field
The true test of whether composites can replace metals as the dominant raw materials from which aircraft are manufactured has still to come. Whether it is an all-new aircraft from before 2020 or after 2025, the next-generation single-aisle airliner will determine the balance of materials.
Composites are here to stay, but there could be a swing back to metals for the next-generation single aisle. It's a matter of timing, says Rich Oldfield, director of technology with GKN Aerospace, a leading supplier of both composite and metallic aerostructures.
“Everything being done today has a 'black metal' design philosophy,” says Oldfield. “A lot of compromises are made in using design rules evolved over decades for metals. To fully unlock the potential of composites, we must move . . . to design concepts optimized for carbon.”
“To change the design philosophy we have to build up a huge body of evidence and conduct large-scale demonstrations, and do so way in advance of any program or take an enormous risk. That's the dilemma. Is there enough time before the next program comes along?” If it comes soon, he says, composites content will stay where it is on the Airbusand , around 50%. “If it comes along in the 2020s, there is far greater opportunity for more radical concepts.”
The metals industry is ready with new aluminum-lithium alloys and advanced structural concepts. “New alloys fit into the existing metallic infrastructure, and offer less risk and cost versus a new supply chain for composites,” says Mick Wallis, president of North American rolled products for aluminum manufacturer Alcoa. “We can provide up to 10% weight saving, up to 30% less cost to manufacture and be ready for the next single-aisle entering service after 2015.”
Third-generation aluminum-lithium provides the full 7% lower density with corrosion and fatigue resistance. This allows metals to match the advantages of carbon fiber in the high-stress lower skins of thin, stiff wings with advanced aerodynamics, enables higher humidity, more comfortable cabins and meets the extended 12-year heavy check cycle possible with carbon-fiber composites, he says.
“There is always going to be a balance between composites and metallics, but it will depend on the size and architecture of the aircraft,” says Oldfield. “It's possible we will see more metallics on the next-generation single aisle, because it has to land eight or 10 times a day, versus one or two for a widebody, and the increased risk of 'ramp rash' during loading and unloading changes the design trades.”
The biggest issue for composites is the readiness of the supply chain to meet simultaneous demand from Airbus and Boeing to support production of 40-plus single-aisle airliners a month. “To switch from rate 40 in metals to rate 40 in composites is a huge challenge. It is the key question: How do you get to rate in time?” asks Oldfield, who says composites in commercial aircraft are still at “generation 1.5.”
“To be able to manufacture at high volumes and rates will require improvements to every step in the process to really bring the manufacturing cycle down dramatically and reduce both investment required and recurring costs,” he says. “There is still a large cost gap [between composites and metals].”
Research into advanced composites, meanwhile, is threatened by spending reviews in all the major economies. “Just when investment needs to be dramatically increased for the next generation, it is difficult for government and industry to make the investment,” says Oldfield.
Whichever material dominates, new virtual design techniques could reduce costs. “Immersive reality” modeling and simulation tools now give specialists the opportunity to challenge design choices in the manufacturing and support phases, says Pierre Marchadier, vice president of aerospace and defense for leading engineering software developerSystemes. Changes can be made early, saving time and cost, he says.
Extensions to 3-D design systems enable high-fidelity simulations for use with virtual-reality visual displays and haptic devices. This allows production lines to be simulated in advance, for example to make adjustments to accommodate the different sizes of U.S. and Japanese workers. “More and more we are moving into support and service,” he says. Accessibility is key. Experts working on virtual aircraft can lead to issues being found while there is still time to change the design.