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Why airplanes often cause so much noise

The noise emitted by airplanes sounds as if it is coming from the engine, but it is basically airflow over the plane's wings, flaps and landing gear, according to University of Florida researchers.

india Updated: Dec 19, 2005 13:46 IST

The noise emitted by airplanes sounds as if it is coming from the engine, but it is basically airflow over the plane's wings, flaps and landing gear, according to University of Florida researchers.

Engineers hoping to reduce the racket have just completed construction of a wind tunnel that simulates flight conditions and is enabling researchers to figure out exactly why airplanes often cause so much noise. "(Most noise) is caused by the unsteady flow over various components wing flaps and slats, horizontal and vertical tails, the landing gear (and) the edges and tips of various control surfaces.

Various components on the airplane are bluff, like the landing gear, and produce significant unsteady flow in (their) wake that produce audible sound," Discovery News quoted project's leader, Lou Cattafesta. He explained that the phenomenon is comparable to a hand stuck outside the window of a fast-moving car. If the hand is tilted, the lift and drag due to the wind fluctuates. This resulting unsteady airflow that produces audible noise.

Yet another source of airplane noise is turbulence, such as small vortices in the air flow, that interact with parts of the plane to create aerodynamic noise. "The main issue at cruise is reduction of cabin noise for passenger comfort. Here, the turbulent flow over the fuselage makes a broadband, random noise in the cabin," Cattafesta said.

Mehdi Khorrami, an aerospace technologist in the Computational AeroSciences Branch of NASA Langley Research Center, said, "An important NASA goal in the field of aeronautics is to mitigate the environmental impact of civil aviation, including the reduction of the radiated noise by low flying aircraft during landing and take-off." “The footprint of objectionable aircraft noise is confined within airport boundaries thereby allowing more flights and longer operating hours economic benefits," he added.

First Published: Dec 19, 2005 13:46 IST