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ATLANTA — If you’ve heard a sonic boom recently, you probably remember it. The loud explosion-like explosion – caused by an aircraft flying faster than the speed of sound – can be spectacular, and can even cause windows to crack.
Sonic booms are part of the reason there are no supersonic passenger planes flying today, and one of the factors limiting the success of Concorde, which last flew in 2003.
Now, NASA is changing the regulations by turning the boom into a “shock,” paving the way for a new generation of quieter supersonic aircraft. The agency is doing this through a program called Quesst, which is the result of decades of research and centers around a new aircraft called the X-59, which debuted on Friday.
Far away thunder
The X-59 is the latest in a line of experimental aircraft that includes the X-1, which in 1947 became the first manned aircraft to exceed the speed of sound, and the Mach.
The new vehicle was designed and built by prime contractor Lockheed Martin Skunk Works in Palmdale, California, under a $247.5 million contract with NASA. With the factory rollout complete, the X-59 will now undergo integrated systems testing, engine commissioning, and taxi testing in preparation for its maiden flight. It is scheduled to take off for the first time later this year, ahead of the first quiet hypersonic flight.
“NASA’s X-59 will help change the way we travel, bringing us closer together in much less time,” Pam Milroy, NASA’s deputy administrator, said in a statement.
“It will be significantly quieter than the Concorde or any other supersonic aircraft out there today,” Craig Nicol, a senior advisor at NASA Headquarters, told CNN in 2022. “It is very long and thin: about 100 feet long, but its wingspan is “only about 29 feet,” he added. “The nose is a distinctive feature of this plane: it is about a third of the length.”
The sleek shape plays a major role in making the plane quieter when traveling at supersonic speeds.
But how does a sonic boom happen? When an aircraft travels at subsonic speeds, the sound waves it normally generates can travel in all directions; However, at supersonic speeds, the aircraft will leave its sound behind and the sound waves will be compressed and combined into a single shock wave originating at the nose and ending at the tail.
When this high-pressure shock wave meets the human ear, it creates a loud bang, which does not happen when the plane breaks the sound barrier, but rather a continuous impact that can be heard by anyone in the cone-shaped area below the plane, provided that it exceeds the speed of sound.
NASA’s X-59 will help change the way we travel, bringing us closer together in much less time.
– Pam Milroy, NASA
The shape of the X-59 is designed to prevent shock waves from merging together. Instead, they spread out with the help of strategically placed aerodynamic surfaces. The single engine is also located at the top of the plane rather than the bottom, to maintain a smooth lower profile that prevents shock waves from reaching the ground.
As a result, NASA believes the X-59 will produce only 75 decibels of sound when traveling at supersonic speeds, compared to 105 decibels on the Concorde.
“What that means is that the sound of this aircraft might sound like distant thunder on the horizon, or like someone closing a car door around the corner,” Nicholl says.
Changing regulations
The X-59 is expected to fly at 1.4 times the speed of sound, or 925 miles per hour.
The critical part of the program will begin later in 2024, when a series of test flights will be conducted over six residential communities across the United States, chosen to offer a diverse mix of geographic and weather conditions.
Once the X-59 flies over the designated areas, NASA will collaborate with communities on the ground to measure their response to the noise.
The data collected in this way will then be submitted to the US Federal Aviation Administration and international regulators.
New generation
NASA believes the change in regulations would open the skies to a new generation of supersonic aircraft, allowing them to fly over routes that are not permitted now, such as New York to Los Angeles, and cutting flight time by almost half.
However, we don’t know what those planes will look like and who will build them, because the X-59 is not a prototype but just a demonstration of the technology.
“Any future design of a low-altitude commercial aircraft for supersonic flight will certainly be different from this, although some design elements can be translated directly,” Nicholl said, pointing to the extended nose and some of the flight control systems. The X-59’s unique external vision system provides the pilot with high-definition displays showing what is in front of him, in the absence of an actual forward-facing window due to the plane’s streamlined nose.
Several companies are currently developing supersonic passenger aircraft and plan to fly them within a decade or less, including Hermeus, Boom, and Spike. However, it is doubtful that any of them will be able to benefit from the results of the Quesst program, which will likely benefit the next generation of supersonic aircraft.
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