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 startling and even shatter glass.
Sonic booms are part of the reason supersonic passenger planes fail to fly today, and are one of the factors limiting the success of Concorde, which last flew in 2003. Supersonic aircraft were limited to subsonic speeds when flying over land or near coastlines. and current international regulations still limit the speed of land commercial transport to below Mach 1, or the speed of sound, to prevent disturbance from sonic booms in populated areas.
Now NASA is trying to change these regulations by turning the explosion into a “thump,” paving the way for a new generation of quieter supersonic aircraft. The agency is doing this through a program called Quesst, which centers around a new aircraft called the X-59 that is the result of decades of research and debuted Friday.
distant thunder
The X-59 is the latest in a series of experimental aircraft that includes the X-1, the first manned aircraft to break the speed of sound in 1947, and the X-15, which still holds the record for the fastest ever. Manned flight at Mach 6.7 in 1967.
The new vehicle was designed and built by prime contractor Lockheed Martin Skunk Works in Palmdale, California, under a $247.5 million NASA contract. Following completion of the factory rollout, the X-59 will now undergo integrated system tests, engine start-ups and taxi tests in preparation for its first flight. It is preparing to take off for the first time later this year, ahead of its first silent supersonic flight.
“We went from an ambitious concept to reality in just a few years. NASA’s X-59 will help change the way we travel and bring us closer together much faster,” NASA deputy administrator Pam Melroy said in a statement.
“It will be significantly quieter than Concorde or any other supersonic aircraft that exist today,” Craig Nickol, senior advisor at NASA Headquarters, told CNN in 2022. “It is extremely long and thin: It is almost 100 feet long, but its wingspan is only 29 feet. The nose is a distinguishing feature of this aircraft: it is about a third of the length.”
Its elegant shape plays an important role in making the aircraft much quieter during supersonic travel.
So how does a sonic boom happen? When an aircraft moves at subsonic speeds, the sound waves it normally creates can travel in all directions; However, at supersonic speeds, the aircraft will leave its own sound behind and the sound waves will compress and combine into a single shock wave, starting from the nose and ending at the tail.
When this highly compressed shock wave encounters the human ear, it produces a loud boom; This does not occur as a result of the aircraft breaking the sound barrier, but rather is a continuous effect that can be heard by anyone in a cone-shaped area below the aircraft. as long as it exceeds the speed of sound.
The shape of the X-59 is designed to prevent shock waves from coming together. Instead, they spread with the help of strategically placed aerodynamic surfaces. The single engine is located at the top of the aircraft rather than at 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 Concorde’s 105 decibels.
“What this means is that this plane could sound like distant thunder on the horizon, or it could sound like someone closing a car door around the corner,” Nickol says. “People may not even hear the explosion at all, and if they do they certainly won’t be surprised because the sound will be low and wide and not as loud.”
Changing the regulations
The expectation is that the X-59 will fly at 1.4 times the speed of sound, or 925 mph. Before that, the Quesst team will conduct several flight tests at Lockheed Martin Skunk Works before transferring the aircraft to NASA’s Armstrong Flight Research Center in Edwards, California, which will serve as its base of operations.
The most important part of the program will begin in late 2024, when a series of test flights will be conducted in more than half a dozen locations across the U.S., selected to offer a diverse mix of geographic and atmospheric conditions: “This will be fun.” It’s part of the project because we’ll be interacting with the public and we’re going to create some citizen science,” Nickol said.
The plan is reminiscent of an experiment the Federal Aviation Administration (FAA) conducted in 1964, in which supersonic fighter jets flew repeatedly over Oklahoma City to test the impact of sonic booms on the public.
Things didn’t go well, with up to 20 percent of people objecting to the explosions and 4 percent filing complaints and damage claims. “Of course we don’t want to repeat this, so first we will test this aircraft in a limited range and measure all the booms,” says Nickol. “We will only go into communities when we are satisfied with the performance, and we will still carefully control the level of sonic booms.”
After X-59 flies over selected areas, NASA will contact communities on the ground to gauge their reactions to the noise. The aim is to confirm the theory that a blast of 75 decibels would be acceptable.
The data collected this way will then be submitted to the US Federal Aviation Administration and international regulators.
New generation
NASA believes a change in regulations would open up the skies for a new generation of supersonic aircraft that would be allowed to fly over currently disallowed routes from New York to Los Angeles, cutting flight time roughly in half.
But we don’t know what these planes will look like and who will produce them because the X-59 is not a prototype, just a technology demonstration.
“The design of any future low-boom commercial aircraft for supersonic flight will certainly differ from this, but some design elements are directly transferable,” Nickol said, pointing to the extended nose, some flight control systems, and flight control systems. The X-59’s unique eExternal Vision System provides high-resolution displays that show the pilot what lies ahead, in the absence of a true forward-facing window due to the aircraft’s aerodynamic nose.
Several companies, including Hermeus, Boom, and Spike, are currently developing supersonic passenger planes and plan to have them flying in a decade or less. But it is doubtful that any of them will benefit from the findings of the Quesst program that will inform the next generation of supersonic aircraft.
Nickol believes such aircraft, with the ability to fly anywhere, will democratize supersonic travel and make a big difference to Concorde’s luxury status: “If you look back 100 years, you see the emergence of many advanced mobility technologies, including railways and airplanes, leading to world-class experiences.” “But as technology advanced and costs came down, they became generally available.”
“One of the long-term goals is to make this form of high-speed travel available as a widespread application, and there is no reason why this cannot happen.”
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