EVERETT — By now, everybody knows that the 787 will be the first commercial airliner made primarily of carbon-fiber composites, a fiberglass-like material that’s been used in military aircraft for decades. Composites are lighter than the aluminum used in the Boeing Co.’s airplanes since the dawn of the Jet Age; that’s one reason why the new plane will be more fuel-efficient than the 767s it’s replacing.
But from an engineering standpoint, that’s far from the only major difference between the 787 and old-school aluminum jets.
Aluminum aircraft are put together like an old-fashioned erector set: Mechanics build up a skeleton of aluminum, steel and titanium stringers and spars, then cover those with sheets of aluminum that are bolted on to build the plane’s air frame before the tube is stuffed full of wiring, fuel lines, insulation and the like.
But with composites, which can be molded like plastic, none of that is required. Boeing’s major suppliers around the globe use huge ovens called autoclaves to bake complete “barrels” — round, hollow sections of an airplane that are ready to be stuffed as soon as they cool.
The result is far fewer parts — and far less labor to assemble them. Boeing calculates that in the front section of the 787 alone, using composites has eliminated the need to bolt 1,500 sheets of aluminum together, which also means drilling between 40,000 and 50,000 fewer holes for the nuts and bolts that would otherwise be holding the plane together.
This is a major reason why Boeing thinks someday it will be able to snap together 787s in three days on the Everett assembly line, compared with the three weeks it has typically taken to build a 777.
There are big differences between the engines and engine coverings of the 787, which won’t be visible to the typical passenger but represent significant engineering achievements:
No-bleed engines: Traditionally, airliners have utilized energy from the engines to run key onboard systems, including the air for the passenger cabin. This is done by “bleeding” off air compressed by the engines, which is then cooled by air conditioners and pumped through ductwork around the plane. This system works, but it also cuts into engine performance because some of the energy that would otherwise push the plane through the air instead pushes air through the plane. The air conditioners themselves also suck up energy.
With the 787, Boeing plans to use power from the engines to instead run electrical generators that will run the air supply system. The company says these are lighter and more efficient than the old systems — after all, they don’t have to cool air super-heated in the engines to a breathable temperature. The generators are also less of a drag on engine performance, Boeing says — by as much as 35 percent.
Interchangeable interface: For decades, each aircraft engine builder has used a different method to connect its engines to the airplanes, and to transfer the power along it. You can think of it in car terms — a Chevrolet Impala has a different drivetrain than a Hyundai Sonata. And — much like you can’t cram a V-8 Chevy engine under the hood of that Hyundai — the different jet engine interfaces have usually meant that once a plane has one type of jet engine under its wings, it’ll always have that type of engine. It’s just too time-consuming and expensive to swap out a Rolls-Royce in favor of a new General Electric.
This complicated the sale and leasing of jets. If Airline A wants to lease a plane from Airline B, but the two didn’t use the same kinds of engines, that usually would sink the deal.
Boeing’s new 787, however, will have a common interface that will work with both the GE GENex engines and Rolls-Royce Trent 1000s that are going to power the Dreamliner. And it may already be paying off: In April, Flight International reported that Chinese airlines that had ordered Dreamliners with GENex engines have backed away from plans to take some of the earliest planes. Instead, they’ll go to Japan’s All Nippon Airways, which uses Rolls-Royce Trents — a much easier swap, given the new interface.
Nacelles: It would take a sharp-eyed airplane geek to spot the difference, but passengers inside the plane should hear a difference thanks to a simple design change to the engines’ air intakes. Tests involving Boeing and Goodrich Corp., which is supplying the parts, found that when air bounces over seams in the inlet, it creates noise. To eliminate that, Goodrich is casting the part as one big circular piece with no seams, and using an automated drill so precise that the heads of the bolts attaching the part will be flush within microns. The result could be as much as a 15-decibel reduction in the engine whine heard in the first-class cabin.
There’s been a lot of talk about how the lighter, stronger hull of the 787 will allow airlines to increase the air pressure inside the cabin, and also increase the humidity. With aluminum hulled-planes, this wasn’t practical: Beefing up the structure so it could handle the increased air pressure inside without bursting would make planes too heavy; increasing the humidity would lead to condensation, which would cause vital metalwork to rust.
The result? Cabin air was a lot like sitting atop an 8,000-foot mountain in the desert, and that dry, thin air is a major cause of complaint among passengers. Tests suggest the higher air pressure and greater humidity will relieve much of that, making flying more comfortable.
But in addition to that, the composite hulls allow Boeing to install larger windows than is typical in aluminum planes now. Boeing also is moving those windows down so window-seat passengers will be able to look out and see the terrain they’re flying over without having to crane their necks. The combination, the company expects, will make flying more fun for passengers.