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

The X-59’s 25th flight took place on 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. As with all 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.

This came 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 tool the X-59 team uses to monitor 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 – match simulations closely.

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

The X-59 has also not experienced any unexpected phenomena, 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 flying and landing safely while demonstrating stability. Since then, it has been able to reach 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 in previous ones, and the test has shown the X-59’s components responding 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, 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.