To design a greener, fuel-stingy jet, MIT team throws out the traditional look
For decades, passenger airplanes have looked pretty much the same: a long thin tube with wings. Now, a team led by MIT scientists and engineers has proposed an unusual-looking craft as part of an effort to rethink aviation to address everything from climate change to rising fuel costs.
Asked by NASA to design commercial aircraft appropriate for 2035, MIT came up with the D8 “double bubble,’’ with a fuselage shaped like two soap bubbles fused together. The side-by-side cylinders make the plane lighter and allow it to generate lift more efficiently.
“The aircraft that we’re flying in today are tube-wing concepts; there’s a tube we ride in, the wings provide lift, the engines underneath provide thrust, and the tail provides control. That’s a design that came out of aircraft development of World War II,’’ said Jim Hileman, a principal research engineer in the aeronautics and astronautics department at MIT. “This [double-bubble] concept has to go and meet certain goals, to show what we achieved on paper works’’ in real life.
In 2008, NASA awarded $12.4 million to six teams, asking them to design airplanes for the generation to be launched in the 2030s.
Four teams designed passenger airplanes that traveled slower than the speed of sound, striving to meet a slate of ambitious goals, including a 70 percent reduction in fuel consumption, which would cause a dramatic cut in greenhouse gas emissions, a 75 percent cut in nitrogen oxide emissions, and much quieter planes.
Many of the designs shared themes, but each team came up with its own way of making greener, quieter airplanes.
The MIT team, which included industry partners Aurora Flight Sciences Corp. and Pratt & Whitney, proposed the 180-passenger double-bubble jet and a triangular airplane that could carry 350 people and be used for international flights.
A team from GE Aviation proposed a 20-passenger airplane for use at smaller airports, to reduce congestion at larger airports.
A team from Northrop Grumman proposed a plane that looks similar to today’s jets, but with novel materials and technologies.
Boeing Co. developed an airplane with a hybrid propulsion system and with the option of hinged wings that could fold up when parked at airport gates.
“What the study is giving us is a clear path of what we need to put our emphasis on for the future,’’ said Ruben Del Rosario, the principal investigator for NASA’s subsonic fixed-wing project. “When you look at all four of these concepts and when you look at the technology roadmaps they are proposing, even though the vehicles between one team and the other look differently, you can see common areas of needs.’’
The designs and technologies are being evaluated by NASA, and one or two research projects are expected to be awarded grants for further development and testing.
The MIT double-bubble design reached the fuel and emissions reduction requirement and came close to the noise-reduction goal. The plane also could take off from shorter runways than today’s planes. But the jet is designed to fly 10 percent slower than an equivalent plane today; reducing the speed allowed engineers to make other changes to improve performance.
“In the future, when fuel is going to be very, very expensive, we think the small change in speed will be paid for in fuel,’’ said John Hansman, a professor of aeronautics and astronautics at MIT.
The body of the plane is obviously novel, but it has a number of other innovations. Three jet engines are mounted on the back, instead of under the wings. This minimizes the aircraft’s wake, a source of inefficiency. Due in part to the double-bubble configuration, the lighter aircraft, and the slower speed, the wings will be thinner and lighter. The wider body of the plane, which will have two aisles, should allow for speedier boarding and disembarking.
NASA scientists said they were pleased by the novel ideas presented in the first round. All of the submissions represent leaps ahead of today’s planes, but a critical step will come next as the innovative designs, materials, and technologies are tested.
“Many of these things are in the realm of the doable,’’ Del Rosario said. “We need to experiment, to understand, and put something in a wind tunnel.’’
Carolyn Y. Johnson can be reached at cjohnson@globe.com. 
