Wall Street Journal — BOEING CO.’S 787 Dreamliner has drawn popular attention as the first commercial plane with skin made of carbon-fiber composites. To the aviation industry, the plane’s less-heralded materials underneath—including highly engineered titanium and a range of cutting-edge aluminum alloys—are equally significant.
Not long ago, passenger jets were built of familiar metals such as aluminum and steel. In 1974, European upstart Airbus pushed the technology envelope with a composite rudder on its first plane, the A300. Since then, plane makers have been steadily increasing their reliance on high-tech materials that are lighter, stronger and less prone to corrosion than the metals they replace.
Now, the new Airbus A350 sets a new mark as the most-composite passenger jet flying. The A350, which began test flights on Friday, is 53% composites by weight compared to 50% for Boeing’s Dreamliner, according to the companies’ own information. “It’s quite an exciting time because a lot of new material combinations are coming on line,” said Ric Parker, director of research and technology at Rolls-Royce PLC, which builds engines for both planes. The British turbine-maker is developing new composites with plastics, ceramics and metals for its products.
Materials have always been critical to aviation. In 1930, Boeing built some of the first all-metal airplanes, which boasted superior strength and aerodynamics over existing wood-and-fabric models. Eight years later, Boeing’s technology enabled it to offer the first fully-pressurized airliner, the propeller-driven 307 Stratoliner.
In the 1950s, Boeing and its engine makers tapped material technologies developed during World War II to build the first commercially successful jetliner, the 707.
Jet engines are at the vanguard of commercial aviation’s push for new materials because the heat, stresses and performance demands on them exceed what nature can offer. General Electric Co., the biggest jet-engine maker and a world leader in advanced materials, is building new factories to create composite engine parts, including from new-wave ceramics. Its GEnx engines on the Dreamliner are the first to use a light but strong alloy of titanium and aluminum that engineers have been developing for more than 20 years.
But featherweight materials can carry hefty price tags. Robert Schafrik, general manager of materials and process engineering at GE Aviation, jokes that an advanced material is “one that costs 10 times as much as the current material.” If that can be cut to just twice the price, he says, other savings in weight and maintenance costs can offset the difference.
“There has to be a very strong value case for going forward with some advanced materials,” said Mr. Schafrik.
Excitement about new materials is also tempered by sobering experience. Rolls-Royce Limited was financially crippled in 1971 because advanced composite fan blades it was developing for new engines failed.
Airbus, now a unit of European Aeronautic Defence & Space Co., in 2005 discovered that composites on its earliest planes didn’t age well after the rudder snapped off a 14-year-old passenger jet in midair. The A310 landed safely.
Boeing and its suppliers have also struggled with the Dreamliner’s carbon-fiber and polymer structures. The plane’s fuselage, for example, consists of barrels made from tape wound around cylindrical molds and then baked. Mastering the process was tough, and several of the first sections produced were rejected. In 2009, Boeing conceded it had to fix wrinkles in the skin of the first 23 barrels.
Headaches with composites and their continued high cost have helped encourage metals companies to push back with new alloys. U.S. giant Alcoa Inc., for example, is supplying Airbus with A350 components that are made for the first time from a new aluminum-lithium alloy that combines benefits of traditional aluminum and composites.
And since materials have different attributes, such as stiffness and elasticity, engineers are getting increasingly specific in not just the shape but also substance of each part. “You tend to have a certain material that is well adapted for a specific environment,” said Charles Champion, Airbus’s executive vice president for engineering.
Blending material characteristics with economics yields some complex decisions. As chief engineer of the Airbus A380 superjumbo a decade ago, Mr. Champion selected a synthetic material of glass fiber and plastic, called Glare (a.k.a. glass laminate aluminum reinforced epoxy), that appeared to have big potential in aviation. But when Airbus designed the new A350 a few years later, it dropped Glare because carbon-fiber composites were less expensive and easier to produce, Mr. Champion said.
Industry officials predict the role of composites will continue expanding as engineers learn better how to produce and use them. For example, when Boeing built the first Dreamliner model, the 787-8, designers included big safety margins on many components and later found they withstood stresses “significantly higher than could ever be experienced in even extreme cases,” said Mike Sinnett, Boeing’s vice president of engineering.
For the second version now in development, the 787-9, “we found ways to design to the required conservatism but not to over-compensate,” Mr. Sinnett said. The tweaks aim to improve efficiency without compromising safety.
Despite increasing applications of advanced materials, expansion of their use will be halting. Mitsubishi Aircraft Corp. had planned to make the wings of its new MRJ small jetliner from composites, but in 2009 switched to aluminum, saying it would offer better fuel economy and be less expensive to produce.
And when Airbus and Boeing launched new versions of their popular single-aisle models about two years ago, they largely stuck with the decades-old metals to control costs. As Airbus looks to a successor model that could be built in a decade, “we are competing composites against alloys,” said Mr. Champion.
While that process will take years, engine advances will continue because components are constantly replaced. By introducing more heat-resistant materials, designers can keep squeezing efficiency from existing models. And, notes Mr. Parker at Rolls-Royce, “there are still a couple of hundred degrees for the scientists to go at.”
By DANIEL MICHAELS
Posted on June 17, 2013
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