For over 70 years, NASA has been engaged in developing quieter aircraft technology, including the development of quieter engine designs, improved aerodynamics, and innovative materials to reduce noise emissions from aircraft.
1. AAPL
During this time, the space agency’s Glenn Research Center has built an array of test facilities to carry out this work, culminating in the Aero-Acoustic Propulsion Laboratory (AAPL), a world-class noise-reduction research facility, which was completed in 1991. NASA’s efforts often involve conducting flight tests and using specialized ground-based noise monitoring systems.
The AAPL is a unique 39-meters diameter and 19-meters-high hemispherical structure beyond an architectural marvel. It reflects years of dedication to quell the cacophony associated to jet propulsion. Amid its fiberglass-clad interior, intricate microphone arrays capture every decibel, offering insights into the tumultuous marriage of hot exhaust gasses and frigid atmosphere that birthed the ear-splitting roars.
2. Jet propulsion
Jet propulsion has been a cornerstone of NASA Glenn’s research since the center’s establishment as a National Advisory Committee for Aeronautics (NACA) laboratory in the early 1940s. The lab’s improvements to the US’ first generations of turbojet engines contributed to making the first jet airliners possible in the mid-1950s, according to the space agency.
Overall, researchers found that the primary source of noise was not the mechanical elements of engines, but the mixing of the cold atmosphere with their narrow, high-speed stream of hot exhaust gases. In response, they tested unique nozzle and ejector designs and worked to balance sound-reducing hardware’s effects on engine performance and weight.
The AAPL continues to play a key role in NASA’s testing efforts helping researchers to compare noise data collected from Learjet 25 flight tests. This work may improve researchers’ ability to predict takeoff noise for future supersonic commercial aircraft. Still, reducing jet noise pollution is a complex and ongoing challenge, as it involves balancing the need for efficient air travel with the desire to minimize its impact on the environment and communities.
3. Quesst mission
The first flight of the Quesst quiet supersonic aircraft will take place out of Lockheed flight facilities in Palmdale, California, somewhere in 2023, according to NASA’s website. The Quesst mission aims at designing and building NASA’s X-59 research aircraft with technology that reduces the loudness of a sonic boom to a gentle thump to people on the ground. The mission is also set to fly the X-59 over select US communities in order to gather data on human responses to the sound generated during supersonic flight and deliver that data set to US and international regulators.
