Fly-through testbed to help build quieter aircraft

Research coming from a new a 3-dimensional aircraft noise measurement facility might some day make living at the end of a runway or very close to an airport more palatable.

The US Air Force Research Laboratory today said it has started the construction of a 3-dimensional measurement facility at White Sands Missile Range in New Mexico that will be used to test the noise levels of military and civilian aircraft. Ultimately the information gleaned from such a testbed will be used by manufacturers to design and build quieter aircraft. This facility, the Aeroacoustic Research Complex, will let aircraft fly through the array, collecting fully 3D acoustic data.

The facility is being developed in two phases: The first phase includes two 300ft tall towers separated by 800 ft and will focus on noise from helicopters and unmanned aircraft. The second phase will add two 1,200ft tall towers separated by 2,000ft and will focus on large and high performance fixed wing aircraft, according to the Air Force.

The facility will allow more accurate characterization of in-flight noise directivity by providing synchronized 3-dimensional magnitude and spectral acoustical signatures from more than 50 microphones. Aircraft noise has been traditionally measured with either a few ground-based microphones or a linear ground array of microphones. These techniques capture one-dimensional and/or two-dimensional characteristics of aircraft flight noise, the Air Force stated. Noise propagates in every direction and you can't do the kind of (data collection) we want to do with a 2D system, the Air Force stated.

Scheduled to begin testing possibly as early as September, the complex will initially only be able to evaluate small aircraft, such as helicopters, light fixed wing, and unmanned aircraft but ultimately the facility will be large enough to test most cargo or commercial aircraft, the Air Force said. The benefits of quieter aircraft aren't limited to the battlefield; many airbases and airfields around the world are located near civilian populations. Encroachment of civilian communities and developments can result in noise complaints and limit training opportunities. Reducing the noise emitted by military aircraft will allow US military aircraft to operate and train near civilian populations while minimizing complaints, the Air Force stated.

Aircraft noise, in particular sonic booms are why NASA and the Japan Aerospace Exploration Agency (JAXA) recently partnered up to jointly research sonic booms. NASA said sonic boom modeling is one of the key technologies needed to let a next generation supersonic aircraft quiet enough that it can fly supersonically over land without significant disturbance to the people or damage to property under such noise.

The sonic boom work will include a look at what JAXA has done with its "Silent Supersonic Technology Demonstration Program" that is researching key technologies to realize a silent supersonic transport. JAXA's program looks at all manner of flight technologies - such as aircraft body and wing composition as well as wing design to reduce sonic booms. Because of sonic boom intensity, the Federal Aviation Administration prohibits supersonic flight over land, except in special military flight corridors.NASA has a long history of supersonic flight and sonic boom testing. Last year it noted that researchers had spent some 200,000 processor-hours on the Columbia supercomputer, screening various new control concepts for a tailless supersonic aircraft. Exploration of non-conventional controls today may someday translate to better fuel economy, increased flight range, and sonic boom reduction.

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