DOUBLE BUBBLE: One aircraft proposed by a group led by the Massachusetts Institute of Technology (M.I.T.), including researchers from Pratt & Whitney and Aurora Flight Sciences, resembles a bulbous, flat-topped baguette capable of carrying 180 passengers. A cross section of the fuselage, which is two merged cylinders, looks like fused soap bubbles--earning it the nickname the "double bubble." Image: © NASA
It took 24 years for humankind to advance from the first powered flight in 1903 to Charles Lindbergh's famous crossing of the Atlantic (and even less time for the U.S. space program to go from launching the first American astronaut into suborbital space to landing men on the moon). NASA officials are now hoping 25 years into the future is enough time for the nation's aerospace engineers to come up with more ecofriendly airplanes.
The agency's main initiative in this arena, N+3, calls for ideas that look ahead three generations into the future of aircraft design—from 2030 to 2035. NASA also has a similar program, N+2, which focuses more specifically on making airplanes more environmentally friendly in the nearer future, from 2020 to 2025. Through N+3, the aerospace agency is funding research into "green" planes that would use 70 percent less fuel than today's airliners while generating at least 75 percent less nitrous oxide (a greenhouse gas) as well as less noise pollution. These future aircraft are also expected to require less real estate and air space for takeoffs and landings, which could help alleviate air congestion and flight delays. (The N+2 initiative has a somewhat more modest fuel consumption target, a 50 percent reduction, but also shoots for a 75 percent cut in nitrous oxide.)
A number of aircraft-makers and aerospace engineers are bidding to become part of N+3. NASA has already awarded $12.4 million in contracts to Boeing, GE Aviation, Lockheed Martin and Northrop Grumman as well as the Massachusetts Institute of Technology (M.I.T.) to support their research and design efforts. NASA expects to hand out the next round of grants in April 2011.
Fuel consumption is a major environmental concern, not to mention a financial one for airlines, typically consuming roughly one third of their budgets, according to the Air Transport Association trade group. The Federal Aviation Administration (FAA) estimates that by 2030, the U.S. fleet of commercial aircraft will consume more than 110 billion liters of fuel, up from about 68 billion liters this year, and nearly 160 million people will be flying on U.S. planes compared with the current 70.7 million, according to the agency. For this reason the FAA in June announced its own $125 million Continuous Lower Energy, Emissions and Noise (CLEEN) program to promote environmentally friendlier flight by modifying existing designs, as opposed to NASA's strategy to solicit designs for entirely new aircraft.
Commercial aircraft are a small but significant contributor to greenhouse gases in the environment because of the amount of jet fuel they burn—they account for about 2 percent of yearly carbon dioxide emissions, according to Green Aviation International Association, an eco-flight trade group based in the U.K. Airplanes generate 670 million tons of carbon dioxide each year, twice the figure from 1990. That number is projected to double by 2025, the group says.
Environmental concerns played a major role in the decision by U.K. officials earlier this year to cancel plans to add a third runway at London's Heathrow Airport, the world’s busiest international airfield.
Rethinking commercial airplanes
Aircraft-makers have been conservative about changes they make to the basic design of their planes over the past several decades because major redesigns are an expensive gamble. Designing and building a new model from the rivets up is a $10-billion proposition, says Mark Drela, professor of fluid dynamics in the M.I.T. Department of Aeronautics and Astronautics, and a leader of the university's N+3 team. "You literally bet the company on almost every new plane," he adds. Drela's estimate may be conservative, given the notorious cost overruns in the airline industry.
As a result, the configuration of the typical passenger jet has not kept pace with the more dramatic advances in engine design since the 1950s. "We are still flying aircraft whose basic template is 50-plus years old—a long tube with wings projecting outwards, engine attached to them," says Andrew Pozniak, managing director of Green Aviation, who supports NASA's initiative but questions whether any of the new designs ever will be commercially viable.
The idea behind N+3 is to rethink the possibilities. One vehicle proposed by Drela's group, which included researchers from Pratt & Whitney and Aurora Flight Sciences resembles a bulbous, flat-topped baguette capable of carrying 180 passengers. A cross section of the fuselage, which is two merged cylinders, looks like fused soap bubbles—earning it the nickname the "double bubble." Conspicuously absent are engines hanging from the wings—they are mounted instead between twin tail struts, where they provide more efficient thrust—and the wings themselves are longer, thinner and more delicate-looking than those on modern jetliners like the Boeing 737 that the "double bubble" is intended to replace. M.I.T. also submitted a design for a larger plane for international travel capable of ferrying 350 passengers.