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Wednesday, May 19, 2010

Two Airplanes That Would Use 70% Less Fuel

15 May 2010

An MIT-led team has designed an airplane that is estimated to use 70% less fuel than current planes while also reducing noise and emission of NOx. The design was one of two that the team, led by faculty from the Department of Aeronautics and Astronautics, presented to NASA last month as part of a $2.1 million research contract to develop environmental and performance concepts that will help guide the agency’s aeronautics research over the next 25 years.

The D “double bubble” series design concept is based on a modified “tube-and-wing” structure that has a very wide fuselage to provide extra lift. The aircraft would be used for domestic flights to carry 180 passengers in a coach cabin roomier than that of a Boeing 737-800.

The H “hybrid wing body” series would replace the 777 class aircraft now used for international flights. The design features a triangular-shaped hybrid wing body aircraft that blends a wider fuselage with the wings for improved aerodyanmics. The large center body creates a forward lift that eliminates the need for a tail to balance the aircraft. The plane is designed to carry 350 passengers.
MIT was the only university to lead one of the six US teams that won contracts from NASA in October 2008. Four teams—led by MIT, Boeing, GE Aviation and Northrop Grumman, respectively—studied concepts for subsonic commercial planes, while teams led by Boeing and Lockheed-Martin studied concepts for supersonic commercial aircraft. MIT team members include Aurora Flight Sciences Corporation and Pratt & Whitney.

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

The engineers conceived of the D series by reconfiguring the conventional tube-and-wing structure. Instead of using a single fuselage cylinder, they used two partial 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 fuselage.

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 fuselage. 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.

According to Mark Drela, the Terry L. Kohler Professor of Fluid Dynamics and lead designer of the D series, the design mitigates some of the drawbacks of the BLI technique by traveling about 10% slower than a 737. To further reduce the drag and amount of fuel that the plane burns, the D series features longer, skinnier wings and a smaller tail.

Not only does the D series meet NASA’s long-term fuel burn, emissions reduction and runway length objectives, but it could also offer large benefits in the near future because the MIT team designed two versions: a higher technology version with 70% fuel-burn reduction, and a version that could be built with conventional aluminum and current jet technology that would burn 50% less fuel and might be more attractive as a lower risk, near-term alternative.

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

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