Washington, Jul 3: NASA is set to publicly demonstrate and test a flight manoeuvre that allows jets to travel faster than sound without generating the characteristic sonic boom. Supersonic flight over land was banned in the US because they generated characteristic loud sonic booms, that could sometimes damage buildings. Using a repurposed fighter jet F/A-18, NASA showed that a diving manoeuvre can be used to generate quiet sonic thumps over a specific area.
An initial test of the research methodology using the F/A-18 was conducted in 2011 with the help of the US military community that lives on base at Edwards Air Force Base in California. Researchers want to take the show on the road and try the same thing over a community that is not used to sonic booms regularly sounding on any given day the way the Edwards community is.
Using the F/A-18 and its ability to aim quiet sonic thumps at a specific area, teams from Armstrong, Langley Research Center in Virginia, and Johnson Space Center in Texas plan to conduct a series of data-gathering flights over Galveston, Texas, in November this year. The Gulf Coast city was chosen because it was next to the Gulf of Mexico, which enables the F/A-18 to keep its louder sonic booms (near the dive point) out to sea, while throwing the quieter sonic thumps (far forward of the dive point) at Galveston. At least 500 resident volunteers will be solicited to provide input to a secure web site about what they have heard, if anything, and what they felt about the sound. At the same time, audio sensors strategically placed around the city will provide researchers a measure of scientific ground truth about how loud the noise really was.
"We'll never know exactly what everyone heard. We won't have a noise monitor on their shoulder inside their home. But we'd like to at least have an estimate of the range of noise levels that they actually heard," said Alexandra Loubeau, NASA's team lead for sonic boom community response research at Langley. NASA recently awarded Lockheed Martin Aeronautics Company a USD 247.5 million contract to build a faster-than-sound X-plane - official designated X-59 "QueSST" - that will demonstrate quiet supersonic technologies in straight and level flight over a large area.
Part of the Low-Boom Flight Demonstration mission, the X-59 is shaped so that supersonic shockwaves do not coalesce together to create the characteristic sonic booms, which prompted the government to ban supersonic flight over land years ago. "With the X-59 you're still going to have multiple shockwaves because of the wings on the aircraft that create lift and the volume of the plane. But the airplane's shape is carefully tailored such that those shockwaves do not combine," said Ed Haering, an aerospace engineer at NASA Armstrong Flight Research Center.
"Instead of getting a loud boom-boom, you're going to get at least two quiet thump-thump sounds, if you even hear them at all," Haering said. NASA intends to fly the X-59 over several towns or cities and gather data from residents on the ground about their perception of the sound the supersonic aircraft generates.