Fly the Eco-Friendly Skies

Growing Pains

And that is the core of the greenhouse-gas problem: growth. The global market forecast from Airbus, Boeing's only major competitor, predicts that the number of passenger aircraft in service will more than double by 2025, from 12,676 at the end of 2005 to 27,307. Based on increased air traffic, the FAA estimates that aircraft greenhouse-gas emissions in the U.S. will increase by 60 percent in that time. (That might not be the worst part. Recent studies have concluded that water vapor from airplane contrails may have three to four times the warming impact of the carbon dioxide in the exhaust.) The extra demand means that just 4,500 of the airplanes currently in operation, about a third, will be retired; the other 8,200 will remain in service or be converted into freighter aircraft. Even biofuel blends, which appear to be at least a decade off, might not be enough to slow the increase in emissions.

Yet since air travel fuels the global economy as surely as it fuels global warming, few are calling for a hard limit on this growth. Thus technology will be asked to make quite a leap over the coming years, lest the skies grow unfriendly.

Middle Ground : Even though the blended-wing body is much more efficient than the typical cigar-and-stick design, no one wants to sit 50 feet from the nearest window.  the Boeing Company

Whatever Happened to the Blended Wing?

At the Future of flight, a museum just down the road from Boeing's hangar in Everett, Washington, I spoke with Jeanne Yu, a director of environmental performance at Boeing, about radical airplane designs that might reduce greenhouse emissions. The classic example is Boeing's X-48B Blended Wing Project, which turns the entire aircraft into a giant wing [see the gallery here]. The design reduces drag and accentuates lift, and a 2006 study from the Partner team at MIT and the University of Cambridge showed how the design would improve fuel efficiency by 23 percent. Yet Boeing has no commercial plans for the blended wing body; it's developing the craft exclusively for military use.

I ask why, and before Yu can answer, another museum visitor, an Englishman who works for Rolls-Royce, one of the manufacturers of the Dreamliner's engine, turns and says, "The biggest problem with blended-wing designs is that no one can see out a window." Yu agrees. The designs place passengers in what seems to be a small amphitheater. Air travelers want to be able to see out windows and have easy access to an exit. "It's part of human instinct," Yu says. "We need to know where we are and see where we are."

She thinks greenhouse-emission reductions will come from design improvements she calls "low-hanging fruit"—retrofitting existing airplanes with lighter landing gear or wing tips, for instance. As for other radical concepts, Boeing engineers "still haven't found anything better than this platform," she says, gesturing toward a Dreamliner nearby. But that doesn't mean they're going to stop looking. "We believe there are answers out there we don't know about."

Dennis Gaffney is a freelance writer based in Albany, New York. This is his first story for Popular Science.