The New Airplane

There has been much said about how large a carbon footprint a plane ride does. There is also the annoyance of waiting in an airport or on a security line. At least the carbon footprint may be reduced in the future. In what could set the stage for a fundamental shift in commercial aviation, an MIT led team has designed a green airplane that is estimated to use 70 percent less fuel than current planes while also reducing noise and emission of nitrogen oxides.

Plane design has not changed much in decades. Part of the resistance to change is regulatory and fear that something new will not be safe as well as how airports are constructed limits changes without major reconstruction.

MIT was the only university to lead one of the six U.S. teams that won contracts from NASA in October 2008 to develop new concepts in aviation.

Four teams (MIT, Boeing, GE Aviation and Northrop Grumman)studied concepts for subsonic (slower than the speed of sound) commercial planes, while teams led by Boeing and Lockheed-Martin studied concepts for supersonic (faster than the speed of sound) commercial aircraft.

Their objective was to develop concepts for, and evaluate the potential of, quieter subsonic commercial planes that would burn 70 percent less fuel (and carbon dioxide) and emit 75 percent less NOx than today’s commercial planes. NASA also wanted an aircraft that could take off from shorter runways.

Designing an airplane that could meet NASA’s aggressive criteria while accounting for the expected increased air travel by 2035 is no easy task. In comparison, automobiles have undergone extensive design changes over the last half century while aircraft design has basically remained the same over the past 50 years.

The MIT team met NASA’s challenge by developing two designs: the 180 passenger D (double bubble) series to replace the Boeing 737 class aircraft, currently used for domestic flights, and the 350 passenger H (hybrid wing body) series to replace the standard 777 class aircraft now used for international flights.

Instead of using a single fuselage cylinder, they used two cylinders placed side by side to create a wider structure whose cross section resembles two soap bubbles joined together. They also moved the engines from the usual wing mounted locations to the rear of the plane. Unlike the engines on most transport aircraft that take in the high speed, undisturbed air flow, the D series engines take in slower moving air that is present in the wake of the plane.

Known as the Boundary Layer Ingestion (BLI), this technique allows the engines to use less fuel for the same amount of thrust, although the design has several practical drawbacks, such as creating more engine stress and being a bit slower.

To further reduce the drag and amount of fuel that the plane burns, the D series features longer, skinnier wings and a smaller tail. These small changes added up to a more economical model. 

Although the H series uses much of the same technology as the D series a larger design is needed for this plane to carry more passengers over longer distances. The MIT team designed a triangular shaped hybrid winged aircraft that blends a wider fuselage with the wings. The large center body creates a forward lift that eliminates the need for a tail to balance the aircraft.

In contrast a recent Boeing aviation product is the 787-8 Dreamliner which will carry 210 - 250 passengers on routes of 7,650 to 8,200 nautical miles. The 787 would provide airlines with improved fuel efficiency (20% less fuel used). This is an improvement but along less radical redesign and concepts and concentrating on lighter composite materials.

There was an earlier improved aviation design called the Beech Starship in the 1980's. It never became popular and is no longer made. So the future of aviation in terms of new design is far from certain.

For further information: http://web.mit.edu/newsoffice/2010/nplus3-0517.html