NASA’s X-59 experimental aircraft set for new testing phase

The X-59’s 25th flight took place 21 August this year, from NASA’s Armstrong Flight Research Center in Edwards, California. It lasted a total of 72 minutes with the aircraft reaching Mach 1.2 and approximately 49,000 feet. Like all of its test flights so far, the X-59 was accompanied by a chase plane to monitor it. That chase aircraft’s sonic booms masked any noise from the X-59.

Reaching this point comes after years of design and analysis before the aircraft was built. Now, the X-59 team is seeing the predictions they made using computer models, wind tunnel tests and other tools confirmed through flight testing.

“Through our ongoing flight tests with the X-59, we’ve gained invaluable insights into both the aircraft’s performance and the unique challenges of the aircraft design,” said Cathy Bahm, project manager for NASA’s Low Boom Flight Demonstrator project.

“Each test point has validated our models and predictions, and it has strengthened our confidence in the aircraft’s performance. Every flight brings us closer to transitioning to the next phase where we will demonstrate the X-59’s quiet supersonic flight capabilities.”

The X-59 is shaped so that when it flies faster than the speed of sound it will make just a quiet thump instead of a loud sonic boom. That required extensive modelling and design before construction began. Now that the aircraft is undergoing flight testing, one of the tools the X-59 team uses for monitoring progress is a “real-time digital twin,” which compares flight data to simulated predictions.

So far, the X-59’s real-world flight characteristics – how it moves through the air and responds to the forces acting on it – matches simulations closely.

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Some examples of agreement between flight data and the team’s predictions include its flying qualities or controllability, the stability margin or how close the aircraft is to becoming unstable under certain conditions, as well as flight loads or the forces and stresses that try to bend and twist an aircraft when it’s flying.

The X-59 also has not suffered any unexpected phenomenon, such as instability or excessive vibration, in response to aerodynamic forces.

The aircraft has come a long way from its early test flights with simple objectives, like fly and land safely while demonstrating stability. Since then, it was able to work up to its target cruise speed of Mach 1.4 (924 mph) and altitude of 55,000 feet relatively early in its test schedule.

Each flight has built on what was learned during the previous ones, and the test has seen the X-59’s components respond to each challenge. For example, the top-mounted inlet leading to the aircraft’s single GE-F414 engine has performed as expected across a range of manoeuvres and conditions.

“This is the phase we’ve been working toward. Building and flying a brand-new aircraft is an extraordinary accomplishment, but the next phase is where the real research begins,” said Larry Cliatt, acoustic validation technical lead, NASA’s Quesst Mission.

During the upcoming acoustic validation phase of testing, the team will fly the X-59 while using a variety of ground- and air-based tools to measure and characterise its sonic thumps.

“Acoustic validation will put the tools and methods used to design the X-59 to the test – tools that could ultimately become part of the DNA of every future commercial supersonic aircraft,” Cliatt said.

“It will be a complex and demanding flight campaign focused on demonstrating that the X-59 can produce the quiet sonic thump it was designed to achieve.”

The X-59 is the centrepiece of NASA’s Quesst mission to help enable commercial supersonic flight over land.