Quieter aircraft

NASA and aerospace industry partners are flight testing new technologies to see if they can make aircraft quieter.

Scalloped edges on engine exteriors and toboggan-like fittings on landing gear are some of the high tech ideas being tested to reduce aircraft noise.

Experts at NASA's Langley Research Center in Hampton, VA, and industry team researchers developed the advanced noise reduction concepts and used wind tunnels and computer simulations to initially test them out.

With the initial conceptual testing completed, the team is now assessing the ideas and actual hardware at a test flight facility in Glasgow, MT on a specially equipped 777 passenger jet provided by Boeing.

A three-week test flight program will validate the ideas, including two improved chevron designs on the engine and a cover that fits on the landing gear. Chevrons are scalloped or serrated edges already used on some newer jet engines. One improved chevron design includes asymmetrical scallops around the engine.

"The new design tailors the chevrons to take into account the air flow and acoustic differences that occur when the engine is installed on the aircraft," said Charlotte Whitfield, NASA's Quiet Aircraft Technology manager of airframe system noise reduction.

Laboratory tests show the advanced chevron shape will reduce noise as much as four decibels during take-off and when flying at cruise altitude. Results of the flight tests may lead to changes in aircraft configurations, future aeroplane engine and landing gear designs.

Goodrich Corporation's Aerostructures Division, Chula Vista, CA, and Goodrich Corporation's Landing Gear Division in Cleveland, OH designed and built a toboggan-like shaped cover for the 777's main landing gear.

The cover streamlines the gear and makes it less noisy. NASA and Goodrich tested this concept in a wind tunnel on a 26% scale model of the 777 landing gear. NASA research indicated when landing, air rushing past conventional landing gear is almost as loud as engine noise. The covered gear concept could reduce landing noise by another three decibels.

When testing is completed, Boeing will deliver the new technology equipped 777 to All Nippon Airways (ANA), in Tokyo. The aircraft will join the ANA passenger fleet and provide additional noise data based on regular operations.