The Airplane - Jay Spenser [132]
The Dreamliner doesn’t look all that different from other jets. This low-wing monoplane has two pylon-mounted engines, one on each swept wing, which is the configuration of well over 90 percent of the jetliners that come off the assembly lines these days.
Aerodynamic optimization has pushed us to increasingly similar designs over the decades. This process in many ways mirrors natural selection, as one can see by comparing the shark and the porpoise. Although they are taxonomically entirely different, hydrodynamic optimization has caused them to evolve similar forms.
Even so, the 787 Dreamliner will not be hard to pick out on a crowded airport flight line. A distinctive nose profile and unusual cockpit window framing together make it easy to spot if one knows what to look for. Not so readily apparent are this airplane’s technological innovations, which occur in four areas: airframe, engines, aerodynamics, and systems.
The 787 is the first jetliner to be made primarily of lightweight composites instead of aluminum. Virtually 100 percent of its skin is made of carbon-fiber-reinforced plastic, as is much of its internal structure. Composites are stronger and lighter than aluminum and, unlike metals, they do not fatigue or corrode. Composites are also considerably less sensitive to damage, which is one reason why military helicopters have used composite blades for decades. Even after a lifetime of hard use, a composite 787 will still be stronger than a brand-new metal jet the day it rolls out of the factory.
Aerospace manufacturers have decades of experience with composites in structural or load-carrying applications. A good example is the empennage of the 777, Boeing’s previous jetliner before the 787. The 777’s tail surfaces are entirely composite. Whereas composites account for 12 percent of a 777’s empty weight, however, they are 50 percent of the Dreamliner’s empty weight and—composites being so light—much of its total volume.
To build 787 fuselages, Boeing engineers figured out how to manufacture large sections as single pieces. Built in Italy, Japan, and the United States, these light and durable fuselage barrels incorporate internal structure and are pre-stuffed with wires and tubing to speed assembly. Completing a fuselage involves little more than bolting these barrels together, a rapid process that requires 50,000 fewer fasteners than conventional fuselage manufacture.
The Dreamliner’s gracefully curving wings are equally advanced and are in fact the most aerodynamically efficient yet fitted to a commercial jetliner. These all-composite wings represent a dramatic departure from past practice. Greater material strength let designers define a wing that is somewhat longer and narrower than in the past. This higher aspect ratio enhances overall aerodynamic efficiency.
Helping to shape the 787’s wings was the latest in computational fluid dynamics, an aerospace modeling tool that harnesses supercomputers to perform millions of calculations per second according to known fluid-flow and other physical principles. Because computational fluid dynamics has capability and accuracy limits, Boeing engineers also performed extensive wind tunnel testing to validate and fine-tune the wing design.
Composite weight savings also benefited the Dreamliner through a virtuous circle of design. This occurs when an improvement to one design parameter yields benefits in others thanks to a cascading redefinition of what is needed to achieve the airplane design’s stated performance goals. For example, reducing the airframe weight means that less fuel is needed to fly a given distance, which in turn reduces the weight of and internal volume required for fuel, for a further decrease in airplane gross weight. These readjustments in turn dictate a slightly smaller wing, which reduces aerodynamic drag and