NASA’s Acoustic Research Measurement (ARM) flights tested technology to address airframe noise produced by non-propulsive aircraft parts during landing, achieving more than 70% reduction in airframe noise.

“The No. 1 public complaint the Federal Aviation Administration (FAA) receives is about aircraft noise,” says Mehdi Khorrami, an aerospace scientist at NASA’s Langley Research Center in Virginia, and principal investigator for ARM. “NASA’s goal here was to reduce aircraft noise substantially in order to improve the quality of life for communities near airports. We are very confident that with the tested technologies we can substantially reduce total aircraft noise, and that could really make a lot of flights much quieter.”

Landing gear deploying from the main body of an aircraft typically leave a large cavity where airflow can get pulled in and create noise. Applying a series of chevrons near the front of the cavity with a sound-absorbing foam at the trailing wall and a net stretched across the opening of the main landing gear cavity altered airflow and reduced noise from the interactions between air, cavity walls, and edges. Porous front fairings allow some air to flow through while deflecting some airflow around the landing gear. Porous concepts for landing gear fairings have been studied before, but NASA computer simulations advanced the design.

NASA tested several experimental designs on various airframe components of a Gulfstream III research aircraft at its Armstrong Flight Research Center at Edwards Air Force Base in California, including landing gear fairings and cavity treatments designed and developed at Langley.

To reduce wing flap noise, researchers used an experimental, flexible flap from the adaptive compliant trailing edge (ACTE) wing flap, which was previously flight-tested to study aerodynamic efficiency. Conventional wing flaps typically feature gaps between the flap and main body of the wing, but the ACTE flap, built by FlexSys Inc. of Ann Arbor, Michigan, eliminates those gaps with a seamless design.

To measure the noise, the aircraft flew at an altitude of 350ft over a 185-sensor microphone array deployed on the Rogers Dry Lake at Edwards Air Force Base.

“Airframe noise reduction produced by NASA technology is definitely momentous, and the best part is that it directly benefits the public,” ARM Project Manager Kevin Weinert says. “While there are obvious potential economic gains for the industry, this benefits the people who live near major airports and have to deal with the noise of aircraft coming in to land. This could greatly reduce the noise impact on these communities.”

FlexSys Inc.