Unobtrusive aircraft

A three-week flight-test program recently completed Boeing and its industry partners has confirmed the effectiveness of several significant airplane noise-reduction technologies.

Known as the Quiet Technology Demonstrator 2 (QTD2), the research and development program is a co-operative commercial aircraft industry project among Boeing, the General Electric Company, Goodrich Corporation and NASA. ANA (All Nippon Airways) of Japan provided one of its new 777 airplanes for the flight-test activities.

The flight-test program provided the opportunity for each company to validate key technologies for incorporation into its own current and future products. NASA joined the effort to acquire data to support its advances in propulsion aeroacoustics, landing gear noise, and computational fluid dynamics research.

The 777-300ER with GE90-115B engines, already the quietest airplane in its class, was fitted with eight different noise-reduction engine inlet and exhaust combinations on the right wing, and the baseline production engine on the left wing. Fan and engine-core chevron exhaust configurations achieved as much as a two-decibel improvement -- a significant community noise reduction. Because jet noise is generated by the jet wake -- extending nearly 50 feet behind the engine -- any reduction is considered a significant achievement. In addition, the low-frequency rumble heard in the aft cabin by passengers during cruise was reduced by up to four to six decibels.