Carbon fiber?

One of my life's highlights was attending a meeting of a group of guys who were teaching each other how to make glider parts out of carbon fiber.  The finished sailplane would have a 12 meter wingspan (39 ft.) and yet weigh less than 300 pounds (136 kg.)  They were passing around some of the smaller completed parts and they were absurdly light—it was as if gravity had been suspended.  Of course, the reason for the gathering was to exchange building tips because carbon fiber is insanely fussy to work with.  The key to superlight parts is to lay up the fabric with just enough epoxy to wet every fiber—but not one drop more.  Add in the regular problems of proper cure time and temperature, regulating the humidity, accurately mixing the epoxy, etc. and it became quite clear that fabricating the carbon-fiber parts for that 300# sailplane would be a LOT harder than it looked.  As I held an aileron hinge that weighed about as much as a postage stamp, I decided that I would wait a couple of generations before I flew in any airplane made of this exotic wonder-material.

Well, folks, it turns out that Airbus' new super-jumbo is having problems with its carbon-fiber parts.  Goodness knows it's hard enough to build such a plane out of aluminum—and all you have to do is call up the metal guys and they ship over material that has worked magnificently since the days of the DC-3.  So substituting carbon fiber turns time-tested engineering into a crap shoot.  Yes, we know quite a lot about fabricating parts of carbon fiber—but do we know enough to make jumbo-jets out of the stuff?  But the weight savings and the resulting fuel savings are just too large a temptation to pass up.  I mean, I REALLY want folks to solve these tricky fabrication problems because of the fuel savings but are we really ready to test our theories on transportation devices that will kill 400+ passengers at a crack if they fail?

(BTW, this isn't just an A380 question because Boeing's new 747-8 is also heavily into carbon—of course, if Boeing really has solved the fabrication problems, 747-8 will just destroy the A380 in the market.  Because 747-8 is also late and over budget, we don't hear any gloating from Boeing...yet.)

Weight Loss for Superjumbos
The A380 and the Aviation Engineering Dilemma
By Dinah Deckstein and Gerald Traufetter   03/21/2012

To reduce fuel consumption, Airbus used extremely lightweight materials in its flagship A380. Now cracks have appeared in the wings, and repairs will cost the company hundreds of millions of euros. The problem highlights the engineering dilemma caused by the industry drive for fuel efficiency.

The short, wiry engineer scribbles the names of complicated components onto a pad of paper. He cheerfully explains how they work. The warm spring wind of southern France is blowing through the window. But the floral Advent arrangement on the sideboard behind him is gathering dust. The engineer, a Scotsman, has been so busy since Christmas that he hasn't had time to clean up the conference room.

In the middle of the winter vacation period, his technicians alerted him that they had found cracks in the wing of an aircraft -- not just any aircraft, but the A380 superjumbo, European aircraft maker Airbus's flagship model. At that moment Tom Williams, the executive vice president of programs at Toulouse-based Airbus, realized that his vacation was over.

Since then, he has been pushing his engineers to figure out how the cracks could have developed and how they can be rectified. But the real question is: Whose fault is it? "Ultimately, I'm responsible for this," says Williams, 59, as he twists his cufflinks, which feature an engraved horse's head.

His boss Tom Enders was furious. "We screwed that up," the future CEO of Airbus parent EADS said at the Singapore Airshow in February. But it would be easy to assign most of the blame for the wing debacle to Tom Williams. More than 10 years ago, the Scotsman took over a team of 900 people tasked with developing the innovative wings for the world's largest passenger plane. Now Williams has become the victim of a development that makes the construction of airplanes, especially such large ones, a hard-to-predict economic adventure, as airlines are demanding that aircraft manufacturers produce increasingly fuel-efficient planes. This creates a dilemma for engineers, especially with the A380, because they were also expected to design the giant new Airbus to be even bigger than the Boeing 747 jumbo jet.

The laws of physics also apply to experts in aerodynamics, engine engineers and materials scientists at Airbus. When an aircraft becomes bigger and heavier, the size of the turbines and wings also increase, which in turn increases weight and fuel consumption. On the other hand, the European megaliner was also required to be 20 percent more efficient than the competing Boeing 747. This was almost impossible to achieve, given that the giant plane was already substantially overweight before it even left the factory.

As a result, Williams and his creative engineers were told to subject the A380 to a radical diet. They used innovative composite material and extremely lightweight aluminum alloys, even for important parts of the wings. But now the results of this effort to economize are coming home to roost, as hairline cracks, some as long as a centimeter, are forming in the connecting elements between the inner frame and the outer skin of the wings.

From his office, Williams can see the buildings in Toulouse where the final assembly of the A380 takes place. At the site, known as Station 45, heavy hydraulic legs lift the wing, which is almost 40 meters (131 feet) long, and bring it into position against a two-meter seam on the fuselage. The plane being assembled on this morning is numbered MSN089. But before the wings are attached to the aircraft, engineer Paul McKenzie stops the hydraulic system. McKenzie is responsible for production and is feeling a little uneasy at the moment, because his workers are installing parts with a built-in material defect. "All the wings that we are now delivering will have to be repaired later on," says McKenzie.

The gaunt British engineer sticks his head into a porthole on the underside of the wing and shines a flashlight inside. A cross strut becomes visible in the light beam, one of the 60 ribs that support the aerodynamic shape of each wing. "These are precisely the ones that are causing all this trouble," says McKenzie.

The ribs are made of innovative composite materials containing carbon fibers. "The corresponding brackets are the real problem," McKenzie explains. They connect the cross strut with the outer skin of the wing and are made of an especially lightweight aluminum alloy, which has the unfortunate drawback that it is subject to cracking in this particular location. By using these high-tech materials, the Airbus engineers were able to reduce the weight of the aircraft by a few hundred kilograms, which is considerable. They did not see the use of the materials as a risk. "We've used this alloy in many other aircraft in the past," says A380 designer Williams.