The Flying Prius

The future of aviation that engineers dreamed about 70 years ago didn’t look much like the present. But it did look a lot like the future of aviation they’re still dreaming of today.

Back in 1938, for instance, Popular Mechanics magazine ran a cover story on “The Flying Wing of the Future,” an amazing machine in which the fuselage was almost indistinguishable from the wide V of the wings. In May of this year, NASA presented the latest thinking from Boeing, General Electric, Northrop Grumman, and MIT about the “down to earth” shape of planes to come in the next 20 to 30 years, with companion studies by Boeing and Lockheed Martin about supersonic transport. Sure enough, one of the MIT proposals is for the Hybrid Wing Body H-Series, an enormous flying wing, and NASA actually has been test-flying a model of something similar, the X-48B, since 2006. At first glance they look like they’re straight out of 1938.
But the operative phrase here is “at first glance.” Basic principles of lift and propulsion are immutable, so certain design features keep coming back. What’s really new is just about everything else that’s likely to go into making the next generation—indeed, the next several generations—of planes: the composites for the bodies; the engines that propel them; the computers that steer them; and, most important, the new economic, environmental, and political imperatives of the 21st century. Manufacturers really have little choice but to produce quieter, safer, more fuel-efficient, and greener machines than ever before—if only they can figure out how.

As almost 1,400 exhibitors gather at the Farnborough Air Show in Britain this week, the usual razzle-dazzle of military hardware, the thunderous fly-overs, and the glitzy presentations of airline luxury won’t be able to obscure the enormous challenges that loom on the horizon. The skies already are saturated with planes and passengers, but traffic is expected to double or even triple by 2050. The stunning disruptions caused by a single volcano in Iceland last spring showed just how delicately balanced, and vulnerable, the whole system has become. Meanwhile, the cost of aviation fuel has quadrupled since the mid-1990s and if, as many predict, the global oil supply continues to grow tighter, those prices could go through the stratosphere.
“In the future, environmental concern will be a really huge issue,” says Jaiwon Shin, head of aeronautics research at NASA. “We are seeing that in other industries. I think aviation will not be an exception.” Add the traditionally low profit margins on which the airline industry operates, and “the trend is fairly predictable,” Shin says. “It’s got to be fuel-efficient and environmentally friendly, so any concept that meets these two criteria will win out.” The recent studies commissioned by NASA are for planes that burn 70 percent less fuel than today and fly 71 decibels quieter than a 737. “NASA’s goal,” says spokeswoman Beth Dickey, “is to bring these technologies to a point where they are ready for prime time. Then it is up to the industry to put them on their airplanes.”

What’s new about such projects is not the expression of concern about the environment but the sense of urgency about addressing it. For years, airlines and airplane manufacturers tended to treat climate change as if it were largely a public-relations problem. Their carbon footprint in the sky, after all, was only about 2 to 3 percent of the global total. International air traffic wasn’t even mentioned in the 1997 Kyoto Protocol on the environment. But according to the most recent studies, aviation’s share of greenhouse gases could increase dramatically to about three times current levels by midcentury, with technical improvements being offset by the expected increase in traffic in and among developing countries. In the meantime, the European Union, with some of the most crowded skies in the world already, is trying to force airlines to join its existing carbon-trading scheme. And carbon isn’t the only problem. High-altitude nitrogen-oxide emissions from commercial jets may be destabilizing the ozone layer, while on the ground people are ever less patient with deafening noise around airports. “People will not be as tolerant as we were 30 years ago when 707s were flying like jet fighters overhead,” says Shin.

It’s tempting to think that some truly radical new approach can change all this for the better. “I think we will come to the point in the next 30 to 40 years where we will say, now we have to make a break and go for rather radical designs, which is maybe a completely different design of an aircraft—a completely different type of engine, a completely different type of fuel,” says a European Commission source who asked not to be cited by name because he was not authorized to speak publicly on the issue. “At a certain stage that break will come, don’t ask me when.”

The European Commission sponsored a much-talked-about “Out of the Box” study looking at the future of aviation in 2006, a brainstorm exercise that entertained such whimsical notions as the invisible airplane and a flying boat. This week the commission will call for a raft of new proposals that will actually get funding for further research. That’s the crucial step in any of these efforts to turn designer dreams into soaring realities. Under consideration are nuclear engines, plasma jets, biofuels, and green fuels along with innovative configurations of the fuselage and engines. Some funding targets will have pilots, and some could be computer-controlled from takeoff to landing. But even when the research is well funded, such concepts are mostly geared toward that moment when, or if, the possibilities of somewhat more conventional approaches really have been exhausted. That’s not likely until the middle of the century at the earliest.
The NASA program, meanwhile, is looking toward what it hopes are more-feasible projects for planes that could be in the air two or three decades from now. One that has created a lot of buzz in aviation blogs is being called “the double bubble,” a design proposal that might just as easily be dubbed “the double-wide in the sky”: two tubular fuselages crunched together side by side and held aloft by what seem like impossibly thin wings.

More interesting still is one of the designs that Boeing came up with for NASA: the Subsonic Ultra Green Aircraft Research, or SUGAR Volt. This plane looks a little like a World War II glider with long tapered wings held in place by trusses. But like a Prius or other hybrid cars, you don’t really get an idea how revolutionary it might be until you look under the hood.

The engines that drive modern commercial planes have undergone a quiet revolution—or a massive evolution, if you will—over the last 30 to 40 years. Old jets combined air and kerosene in an explosive mix that blasted out the back to provide rocketlike thrust. They were powerful, loud, and sucked up fuel like nobody’s business. Some jet fighters still do this. But the engines of today’s commercial airliners combine the hot air from a jet at their core with cooler air pushed around it by fans and compressors. The system allows them to be much quieter and more fuel-efficient than earlier engines, and a great deal of R&D these days is focused on making turbines better still by increasing the amount of cold air in the mix—the bypass ratio, as it’s called—to give extra thrust with minimal extra noise and fuel consumption. Common bypass ratios today are about 5 to 1, some are greater than 10, and researchers are shooting for 20 or more. There is also growing interest in what are called “open rotors,” which look like updated versions of propeller engines, but with more blades.

Boeing’s SUGAR Volt proposes to use a hybrid propulsion system that, in broad outlines, really is reminiscent of a Prius: the cool-air fans and compressors would be powered part of the time by electric motors that would be charged by the combustion engine.

Some green aviation projects, meanwhile, are developing independently of aerospace giants and big government programs. One of the most intriguing is the spindly SolarImpulse, funded by Omega watches and other corporate sponsors. It may bear a striking resemblance to those rubber-band airplanes you flew in the backyard as a kid, but with its wings soaking up solar energy it proved in Switzerland earlier this month that it can run both day and night on nothing but the power of the sun. Its builders aim to fly it around the world in 2013.

Many industry experts remain skeptical about the possibilities for truly revolutionary change. Jean-Marc Thomas, a senior vice president of EADS, the European Aeronautic Defence and Space Company, gently mocks the computer-generated pictures firms provide as “dream images” of a distant future. “The more outlandish a plane looks, the more it gives the impression that it’s terribly modern,” says Thomas. “But things don’t really work that way in the aerospace industry.” Aircraft that are going to carry millions of passengers have to be extremely safe and reliable, which militates against their being extreme in most other ways.
As Thomas points out, the enormous-but-conventional-looking Airbus 380 now in service is the only airliner aloft that uses fewer than three liters of kerosene per passenger per 100 kilometers—mainly because it carries up to 800 people at a time. By comparison, in 1985 the average commercial aircraft consumed about 8 liters per passenger per 100 kilometers. Critics have talked about supersize aircraft as if they’re the Hummers of the sky. But the arithmetic for green aviation is different than it is for cars. Thus the International Air Transport Association says many “modern aircraft” already have gotten to the point where they get 3.5 liters per 100 kilometers per passenger, while one person driving alone in an actual 2010 Prius will burn up 3.8 liters to travel the same distance.

Even proposals for a new generation of supersonic airliners are being presented in a greener context these days. The concepts that Lockheed Martin and Boeing submitted to NASA this year would actually be a little slower than the French-British Concorde, which flew from the 1970s until a disastrous crash brought its service to an end in 2000. The new planes would cruise at about 1.6 to 1.8 times the speed of sound, roughly twice as fast as conventional airliners. The Concorde flew at Mach 2. The new ones would carry about three times as many passengers as the Concorde and their design would radically reduce the explosive-sounding boom made crossing the sound barrier from “a crack to a rumble,” says NASA’s Peter Coen, who is overseeing the project. So the planes would be “greener” than the Concorde, but not as friendly to the environment as subsonic aircraft. They’d be high-end time savers, not fuel savers.

“Supersonic airplanes tend to drive a wedge between naysayers and supporters, because we are really talking about opening up whole new markets,” says Shin. “And our perspective is that in order for supersonic markets even to start there is a huge 800-pound gorilla right in the middle of the room, and that is sonic-boom regulation.” Whether a crack or a rumble, the noise is illegal over the continental United States right now. For the moment, neither politics nor economics are favorable to such projects.

So when it comes to outlandish-looking—but practical—planes, the levelheaded seers of the aviation world keep coming back to the subsonic flying-wing designs being developed in both Europe and the United States. These would most likely be enormous craft capable of carrying as many as 1,000 passengers. The lift characteristics of the fuselage would give them savings of about 40 percent on fuel right away, says Shin. Their advanced engines, with bypass ratios two or three times as high as current jets, would be mounted above the fuselage rather than below the wing, lowering dramatically the amount of noise heard on the ground.
According to Fay Collier, who has overseen NASA’s 80 test flights of the X-48B scale model prototype, most of the problems of low-speed control and the structural issues are on their way to being resolved. If manufacturers and airline companies are receptive, commercial aircraft built along these lines could be rolling out of the factory in 15 to 20 years, conceivably even sooner, if the public wants them. Will passengers be comfortable flying inside such a big enclosed space? Could “virtual windows” supplant real ones? Shin thinks customers will get used to such things. Will airports be ready to accommodate the huge change in shape and the multiple points from which passengers would board and disembark? Many terminals already have adapted to the Airbus 380, which had some of the same issues.

Flying wings—truly the jolly green giants of the sky—may not be ready for prime time in NASA terms, but they’re getting close.

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