Commercial aircraft are big, heavy, and noisy as they fly through the air, but a lot of that noise when they come in for landing is generated by the airframe rather than the engines. NASA decided to try and make aircraft quieter using new technology, and the end result is up to a 70 percent reduction in airframe noise.
As NASA explains, the most complaints the Federal Aviation Administration (FAA) receives from the public is about aircraft noise. NASA’s Langley Research Center in Virginia started investigating the situation and identified three key areas where noise reduction could be achieved: the landing gear, cavities, and wing flaps.
When an aircraft makes a runway approach for landing, its landing gear is down. This creates two noise problems. The first is the additional noise produced by the landing gear itself as air rushes into and around it. The second is the open cavity left by the landing gear when it is down. Air rushing into this cavity produces a lot of additional noise.
NASA significantly reduced the noise created by the landing gear by making the fairing porous along the front. So rather than air being deflected and forced around the gear, it can travel through the porous frame. As for the cavity noise, it was discovered that chevrons at the front of the cavity, sound-absorbing foam at the back, and a net stretched across the opening altered airflow and reduced the noise generated considerably.
In order to reduce wing flap noise, NASA replaced a standard wing flap with a new flexible flap. It’s a seamless flap with no gaps between the flap and the main body. This not only increases efficiency, but also reduces noise.
The different technologies were tested as part of a series of Acoustic Research Measurement (ARM) flights carried out in May at NASA’s Armstrong Flight Research Center in California. A modified Gulfstream III research aircraft flew at 350 feet above a 185-sensor microphone array in order to gauge noise. The end result was an airframe noise reduction of more than 70 percent.
This will be great news for the ears of anyone who lives near to an airport and suffers daily with aircraft landing and taking off every few minutes. It’s also encouraging that none of this tech looks too difficult to install on existing aircraft. Combine it with NASA’s folding wings and you’ve got quieter flying which is also much more efficient.