Jet planes may be the sound of freedom, but patriotic sentiment doesn’t make aircraft any less loud for those who live and work around airports.
Now, new NASA technologies recently flight-tested at Armstrong Flight Research Center in California have shown a remarkable 70-percent reduction or more in airframe noise during landing.
Airframe noise is produced not by powerful jet engines but by non-propulsive parts of the plane — largely, the landing gear and wing flaps.
“The No. 1 public complaint the Federal Aviation Administration receives is about aircraft noise,” said Mehdi Khorrami, an aerospace scientist at NASA Langley Research Center in Hampton.
Khorrami is the principal investigator for the Acoustic Research Measurement (ARM) project. Langley was heavily involved in developing, testing and analyzing the new ARM technologies.
What most people don’t realize is that most of what they’re hearing when a plane lands is produced by the airframe, not the engine, he said.
This wasn’t the case in the ’60s and ’70s, when propulsion noise was much worse. Then the industry worked hard to get that noise down, making significant gains in high-bypass engine technologies.
Now, advances in airframe noise technologies can “substantially” improve the quality of life even further for communities within earshot of airports, he said.
ARM project manager Kevin Weinert called the technologies “definitely momentous,” both for the public and the aircraft industry. Weinert is at NASA Armstrong in Southern California.
“While there are obvious potential economic gains for the industry,” Weinert said in a statement, “this benefits the people who live near major airports and have to deal with the noise of aircraft coming in to land.”
Three technologies were tested in a series of flights conducted 350 feet above a dry lake bed at Edwards Air Force Base, adjacent to NASA Armstrong. The test flights concluded in May, and NASA announced the results last week.
Two technologies involve the landing gear and the noises made when air moves past the landing gear upon approach to a runway, and when it gets pulled into the airframe cavity after the gear is deployed.
Langley engineers addressed the first issue by devising porous fairings with tiny, strategically placed holes that allow air to flow through while also deflecting some of it around the landing gear. Fairings are structures placed over gaps in an aircraft to smooth out the shape and reduce drag.
And what NASA’s precision computer simulations came up with, the agency said, is “the ideal (fairing) design for maximum noise reduction without increasing aerodynamic drag.”
Engineers addressed the second issue by placing a series of chevrons, or a sawtooth pattern element, near the front of the cavity, and a sound-absorbing foam at the trailing wall, Khorrami said.
They also stretched a net across the cavity opening to displace the airflow.
For the third technology, addressing wing flaps, engineers used an experimental, flexible, seamless design that eliminates the gaps between the flap and the main wing.
“It’s almost like a morphing wing,” said Khorrami, and virtually eliminates flap noise.
The flexible flap was part of NASA’s earlier Adaptive Compliant Trailing Edge project, and built by FlexSys Inc. of Ann Arbor, Mich.
Khorrami said NASA is working with industry manufacturers to convey the benefits of the new technologies in hopes they’ll be incorporated into next-generation aircraft.
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