NASA's mission to create a supersonic aircraft that doesn't rattle windows and vibrate teeth is one step closer to reality as the experimental X-59 aircraft dubbed the "Son of Concorde" may soon be ready for its first test flights.

The X-59 is the centerpiece of NASA's Quiet Supersonic Technology or "Quesst" project to reinvigorate civilian use of aircraft that break the sound barrier, and this week NASA said the Skunk Works team at Lockheed Martin, who are building the craft, have wheeled it out to the flight line to begin ground checks before an estimated nine months of safety flight tests.

Once the first phase of the X-59's development ends it'll be handed over to NASA to prove it can fly over land at mach speeds without leaving a community-disturbing sonic boom in its wake. Instead, NASA hopes the X-59's unique design will create a "sonic thump" that's just about as loud as a car door being slammed from 20 feet away - quieter than a bouncing basketball, the sound of two hands clapping, or nearby thunder.

The X-59 will hopefully accomplish its quiet supersonic flight (with a max speed of mach 1.4, 925 mph or 1,488 kph) through its unique design, which NASA says prevents shockwaves created by flying faster than sound.

"The X-59 is shaped in a way that prevents the shockwaves from coming together, resulting in a gentle sonic thump," NASA said [PDF]. "Normally, these shockwaves merge and generate disruptive sonic booms heard on the ground for miles on either side of the aircraft's flight path."

It could be quietly flying over you as early as 2025.

Flight of the Son of Concorde

Once fully assembled and ready for flight, the single-seat X-59 [PDF] will be just shy of 100 feet (30.5m) long, with a hard-swept wingspan of just 29.5 feet (9m) and a height of just 14 feet (4.25 meters). It will be able to cruise at 55,000 feet and, as mentioned above, has a cruising speed of mach 1.4.

That's a bit smaller, lower, and slower than the famous (or infamous, depending on where you lived) Concorde supersonic jet that was used for passenger flights between 1976 and 2003. The 100-passenger craft cruised at 60,000 feet and a speed of mach 2 - around 1,350 miles per hour (2,173 kph). 

Those speeds allowed the Concorde to make some incredibly speedy flights, shuttling from New York to London in just under three hours.

While considerably higher than the cruising altitude of today's subsonic commercial jets, between 33,000 and 42,000 feet, the Concorde still left incredible noise in its wake, leading to the US government banning non-military supersonic flights over land in 1973.

"It's a rule that many people today aren't aware of, yet it's at the heart of what our Quesst mission with its quiet supersonic X-59 airplane is all about," said Peter Coen, Quesst mission integration manager at NASA.

When flights over select US cities get underway, NASA will be polling locals on the ground to get their response to the sound left in the X-59's wake.

By 2027, NASA hopes to have data from the X-59 experiment over to regulators "for their use in considering new sound-based rules regarding quiet supersonic flight over land," the space agency said. If it's successful, NASA said it hopes US and international regulators will undo, or at least modify, the 1973 ban. That, of course, would require a whole new generation of aircraft to be created too.

Lockheed hadn't responded to questions about the aircraft or when its first test flights may occur at the time of publication.

NASA wasn't specific about whether the X-59 and future supersonic aircraft would be as fuel-hungry as the Concorde, which consumed approximately 5,638 gallons, or 25,629 liters, of fuel per hour of flight - but the space agency did tell us: "Because the Quesst mission is focused on the sonic boom challenge, the X-59 is not intended to be used as a tool to conduct research into other challenges of supersonic flight such as landing and takeoff noise, emissions and fuel burn. These challenges are being explored in other NASA research.

"Thanks to projects like NASA's Commercial Supersonic Technology (CST), the agency continues to be a leader in exploring technology to make supersonic flight more sustainable and environmentally friendly. NASA is also directly addressing climate and ozone impacts of future supersonic aircraft." ®

https://www.theregister.com//2023/07/07/nasa_quiet_supersonic_jet/