Experimental Supersonic Aircraft XB-1
Boom Ultrasound
According to US company Boom Supersonic, when the experimental XB-1 aircraft broke a sound wall three times during its first supersonic flight on January 28th, it did not generate an acoustic boom from the ground.
“This confirms what we’ve long believed in. Supersonic travel is affordable and gentle on board and on the ground,” he said. Blake ShawlFounder and CEO of Boom Supersonic; press release.
As the aircraft pushes through the atmosphere at high speed, the ambient air pressure changes, creating sound waves. And when supersonic flight exceeds the speed of sound (Mach 1, or about 1224 km/h), these sound waves combine to form a shock wave away from the flight path. This sonic boom can move far enough to reach the ground. There, it produces very loud noises, rattles the buildings and breaks the glass.
The land’s so destructive boom helped to contribute to the retirement of the legendary commercial airliner Concorde in 2003, driving many countries to ban commercial supersonic aircraft. Since then, aerospace engineers have been trying to develop designs for aircraft that could become supersonic without a boom.
In this case, the XB-1 utilized a physical phenomenon called the Mach cutoff. Sound travels more slowly at higher altitudes, so aircraft that violate the sound wall at those heights will generate booms that cannot reach the ground. As the boom moves down, the shock wave is pushed up as the sound speed increases.
The trick is that the ideal altitude and speed of a supersonic aircraft depends on the atmospheric conditions, as temperature and wind also affect the speed of sound. “The real challenge is to get a very accurate atmospheric prediction of temperature and wind. It’s very easy from there to calculate the flight speed of the actual Mach cutoff.” Bernd Liebhardt At the German Aerospace Center in Germany.
Boom Supersonic says the latest final test flight of the XB-1 on February 10 also reached supersonic speeds without a boom. Now, the company uses what it learns from its test flights to help future commercial airliners called Overture achieve the same feat. Supersonic land flights are up to 50% faster than today’s commercial airlines. This could reduce travel time from New York to Los Angeles by 90 minutes.
Flying at supersonic speeds during shorter land routes can also burn less fuel than flying at “aerodynamic worst speeds” (just underneath the sound barrier). However, he warned that taking advantage of Mach’s cutoff is probably like a niche use case for “ultrasonic business jet users.” That would reduce the economic rewards of commercial airline services.
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