A team from the Massachusetts Institute of Technology's Dept. of Aeronautics and Astronautics has come up with an advanced airframe configuration and propulsion system for NASA that could lead to a fleet of more energy efficient airplanes around 2035.
The MIT concept is for subsonic (slower than the speed of sound) commercial planes. 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 MIT team developed 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 777 class aircraft now used for international flights.
The engineers conceived of the D series by reconfiguring the 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.
The MIT team designed two versions of the D Series: a higher technology version with 70% fuel-burn reduction, and a second model that could be built with conventional aluminum and current jet technology. It would burn 50% less fuel and might be more attractive as a lower risk, near-term alternative.
The MIT team designed a triangular-shaped hybrid wing body aircraft for the H Series that blends a wider fuselage with the wings for improved aerodyamics. The large center body creates a forward lift that eliminates the need for a tail to balance the aircraft.The large structure also allows engineers to explore different propulsion architectures for the plane, such as a distributed system of multiple smaller engines. Although the H series meets NASA’s emissions-reduction and runway-length goals, the researchers said they will continue to improve the design to meet more of NASA’s objectives.
More info is available at the MIT site: http://web.mit.edu/press/2010/green-airplanes.html