NASA and Boeing are to begin a major flight test programme to demonstrate the effectiveness of new noise-reduction technologies for commercial airliners.
If the tests are a success the systems could become standard on Boeing’s next-generation 787 Dreamliner aircraft, making it significantly quieter during take-off and landing than current designs.
The two aerospace giants are investigating ways to reduce noise caused by engines and landing gear, as well as limiting the level of sound experienced by people inside the aircraft’s cabin.
The Quiet Technology Demonstrator 2 (QTD2) project involves adapting an All Nippon Airlines Boeing 777 to assess the impact of the various changes during actual service. The test airliner features a chevron nozzle — an engine nozzle with scalloped or serrated edges.
These are asymmetrical, and are tailored to take into account the acoustic characteristics experienced by a wing-mounted engine. A chevron nozzle using a shape memory alloy is also being tested.
Experiments in NASA’s laboratory indicated that the design could reduce noise by 4dB during takeoff and when flying at cruise altitude.
The engine also features a single piece inlet, which reduces internal noise levels for passengers sitting in front of the propulsion unit.
In addition, NASA and project partner Goodrich Aerostructures have created a toboggan-shaped cover for the landing gear, which should reduce noise by an extra 3dB. Part of QTD2 involves the development of new noise measurement technologies.
‘We have designed a 600-microphone acoustic camera,’ said Charlotte Whitfield, NASA’s Quiet Aircraft Technology manager for airframe system noise reduction.
‘This is placed on the ground and examines the origins of noise so we can then look at engineering solutions. We can separate noise data from each engine, and even isolate the noise caused by the wing flaps and slats.’
NASA has set a goal of creating an aircraft demonstrator that reduces noise by 10dB compared to 1997 levels by 2007.
The ultimate aim of the Quiet Aircraft Technology project is to contain engine noise within the boundaries of airports, reducing it by 50 per cent in 10 years and by 75 per cent in 25 years compared to 1997.
As well as benefiting those living within earshot of runways, reduced noise would help the social acceptability of development of new, smaller airports that would be more convenient for users than having to transport people and freight from a small number of large hubs.
This is a key element of Boeing’s commercial strategy and underpins the business case for the 787 programme.
The first Quiet Technology Demonstrator programme produced noise-reduction technologies that are now being generally used on the Boeing 777 series of aircraft.