Trans-Talk

The Cambridge-MIT Institute’s ‘Silent’ Aircraft Initiative (SAI) unveiled a conceptual design for a silent, environmentally friendly passenger plane at a press conference yesterday at the Royal Aeronautical Society in London. The project aims to develop an actual aircraft by 2030. The conceptual design addresses both the engines and the airframe; the airframe accounts for half of the noise from a landing plane. Predicted noise of the SAX-40 (Silent Aircraft Experimental) is 63 dBA outside an airport perimeter, about 25dB quieter than current aircraft.

The design is somewhat reminiscent of the experimental “flying wing” aircraft developed by the U.S. military in the 1950s. The concept calls for a plane about the same size as a Boeing B-767, with an 68-metre wingspan and length of 44 metres.

Key design features:

• An overall shape that integrates body and wings into a “single” flying wing. As a result, both the body and wings provide lift, allowing a slower approach and takeoff, which would reduce noise. The shape also improves fuel efficiency.
• The elimination of the flaps, or hinged rear sections on each wing. These are a major source of airframe noise when a plane is taking off and landing.
• Engines embedded in the aircraft with air intakes on top of the plane rather than underneath each wing. This screens much of the noise from the ground.
• A variable-size jet nozzle that allows slower jet propulsion during takeoff and landing but efficient cruising at higher speeds.
• It uses wingtip stabilizers rather than the common vertical stabilizer and rudder tail assembly.

(Photo: Silent Aircraft Initiative)

Key challenges:

• integrating the propulsion system and airframe; unlike conventional engines hanging below the wings which allow unimpeded air flows into the engine, air traveling into the air intakes on top of the plane will experience friction. That requires a new engine to operate in strongly nonuniform airflows.
• The craft’s unconventional airframe greatly complicates ensuring the structural integrity of such a pressure vessel.

While originally conceived to make a huge reduction in airplane noise, the team’s ultimate design also has the potential to be about 25 percent more fuel-efficient than current aircraft. In a typical flight, the proposed plane, which is designed to carry 215 passengers, is predicted to achieve 124 passenger-miles per (US) gallon. For a down-to-earth comparison, the Toyota Prius hybrid car carrying two passengers achieves 120 passenger-miles per gallon. (Sources: MIT News; SAI project)

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