As NASA’s X-59 quiet supersonic research aircraft continues a series of flight tests over the California high desert in 2026, its pilot will be flying with a buddy closely looking out for his safety. 

That colleague will be another test pilot in a separate chase aircraft. His job as chase pilot: keep a careful watch on things as he tracks the X-59 through the sky, providing an extra set of eyes to help ensure the flight tests are as safe as possible. 

Having a chase pilot watch to make sure operations are going smoothly is an essential task when an experimental aircraft is exercising its capabilities for the first time. The chase pilot also takes on tasks like monitoring local weather and supplementing communications between the X-59 and air traffic control. 

“All this helps reduce the test pilot’s workload so he can concentrate on the actual test mission,” said Jim “Clue” Less, a NASA research pilot since 2010 and 21-year veteran U.S. Air Force flyer. 

Less served as chase pilot in a NASA F/A-18 research jet when NASA test pilot Nils Larson made the X-59’s first flight on Oct. 28. Going forward, Less and Larson will take turns flying as X-59 test pilot or chase pilot. 

Staying Close

So how close does a chase aircraft fly to the X-59? 

“We fly as close as we need to,” Less said. “But no closer than we need to.” 

The distance depends on where the chase aircraft needs to be to best ensure the success of the test flight. Chase pilots, however, never get so close as to jeopardize safety. 

For example, during the X-59’s first flight the chase aircraft moved to within a wingspan of the experimental aircraft. At that proximity, the airspeed and altitude indicators inside both aircraft could be compared, allowing the X-59 team to calibrate their instruments. 

Generally, the chase aircraft will remain about 500 and 1,000 feet away—or about 5-10 times the length of the X-59 itself—as the two aircraft cruise together. 

“Of course, the chase pilot can move in closer if I need to look over something on the aircraft,” Less said. “We would come in as close as needed, but for the most part the goal is to stay out of the way.” 

Airborne Photo Op

The up-close-and-personal vantage point of the chase aircraft also affords the opportunity to capture photos and video of the test aircraft.  

For the initial X-59 flight, a NASA photographer—fully trained and certified to fly in a high-performance jet—sat in the chase aircraft’s rear seat to record images and transmit high-definition video down to the ground. 

“We really have the best views,” Less said. “The top focus of the test team always is a safe flight and landing. But if we get some great shots in the process, it’s an added bonus.” 

Chase aircraft can also carry sensors that gather data during the flight that would be impossible to obtain from the ground. In a future phase of X-59 flights, the chase aircraft will carry a probe to measure the X-59’s supersonic shock waves and help validate that the airplane is producing a quieter sonic “thump,” rather than a loud sonic boom to people on the ground. 

The instrumentation was successfully tested using a pair of NASA F-15 research jets earlier this year. 

As part of NASA’s Quesst mission, the data could help open the way for commercial faster-than-sound air travel over land. 

Choice of Chase Aircraft

Chase aircraft have served as a staple of civilian and military flight tests for decades, with NASA and its predecessor—the National Advisory Committee for Aeronautics—employing aircraft of all types for the job. 

Today, at NASA’s Armstrong Flight Research Center in Edwards, California, two different types of research aircraft are available to serve as chase for X-59 flights: NASA-operated F/A-18 Hornets and F-15 Eagles. 

While both types are qualified as chase aircraft for the X-59, each has characteristics that make them appropriate for certain tasks. 

The F/A-18 is a little more agile flying at lower speeds. One of NASA’s F/A-18s has a two-seat cockpit, and the optical quality and field of view of its canopy makes it the preferred aircraft for Armstrong’s in-flight photographers. 

At the same time, the F-15 is more capable of keeping pace with the X-59 during supersonic test flights and carries the instrumentation that will measure the X-59’s shock waves. 

“The choice for which chase aircraft we will use for any given X-59 test flight could go either way depending on other mission needs and if any scheduled maintenance requires the airplane to be grounded for a while,” Less said. 

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The airliner you board in the future could look a lot different from today’s, with longer, thinner wings that provide a smoother ride while saving fuel.

Those wings would be a revolutionary design for commercial aircraft, but like any breakthrough technology, they come with their own development challenges – which experts from NASA and Boeing are now working to solve. 

When creating lift, longer, thinner wings can reduce drag, making them efficient. However, they can become very flexible in flight.

Through their Integrated Adaptive Wing Technology Maturation collaboration, NASA and Boeing recently completed wind tunnel tests of a “higher aspect ratio wing model” looking for ways to get the efficiency gains without the potential issues these kinds of wings can experience. 

“When you have a very flexible wing, you’re getting into greater motions,” said Jennifer Pinkerton, a NASA aerospace engineer at NASA Langley Research Center in Hampton, Virginia. “Things like gust loads and maneuver loads can cause even more of an excitation than with a smaller aspect ratio wing. Higher aspect ratio wings also tend to be more fuel efficient, so we’re trying to take advantage of that while simultaneously controlling the aeroelastic response.”  

 

Without the right engineering, long, thin wings could potentially bend or experience a condition known as wing flutter, causing aircraft to vibrate and shake in gusting winds.  

“Flutter is a very violent interaction,” Pinkerton said. “When the flow over a wing interacts with the aircraft structure and the natural frequencies of the wing are excited, wing oscillations are amplified and can grow exponentially, leading to potentially catastrophic failure. Part of the testing we do is to characterize aeroelastic instabilities like flutter for aircraft concepts so that in actual flight, those instabilities can be safely avoided.” 

To help demonstrate and understand this, researchers from NASA and Boeing sought to soften the impacts of wind gusts on the aircraft, lessen the wing loads from aircraft turns and movements, and suppress wing flutter.

Reducing or controlling those factors can have a significant impact on an aircraft’s performance, fuel efficiency, and passenger comfort. 

Testing for this in a controlled environment is impossible with a full-sized commercial airliner, as no wind tunnel could accommodate one.

However, NASA Langley’s Transonic Dynamics Tunnel, which has been contributing to the design of U.S. commercial transports, military aircraft, launch vehicles, and spacecraft for over 60 years, features a test section 16 feet high by 16 feet wide, big enough for large-scale models. 

 To shrink a full-size plane down to scale, NASA and Boeing worked with NextGen Aeronautics, which designed and fabricated a complex model resembling an aircraft divided down the middle, with one 13-foot wing.

Mounted to the wall of the wind tunnel, the model was outfitted with 10 control surfaces – moveable panels – along the wing’s rear edge. Researchers adjusted those control surfaces to control airflow and reduce the forces that were causing the wing to vibrate.

Instruments and sensors mounted inside the model measured the forces acting on the model, as well as the vehicle’s responses.

The model wing represented a leap in sophistication from a smaller one developed during a previous NASA-Boeing collaboration called the Subsonic Ultra Green Aircraft Research (SUGAR).

“The SUGAR model had two active control surfaces,” said Patrick S. Heaney, principal investigator at NASA for the Integrated Adaptive Wing Technology Maturation collaboration. “And now on this particular model we have ten. We’re increasing the complexity as well as expanding what our control objectives are.”  

A first set of tests, conducted in 2024, gave experts baseline readings that they compared to NASA computational simulations, allowing them to refine their models. A second set of tests in 2025 used the additional control surfaces in new configurations.

The most visible benefits of these new capabilities appeared during testing to alleviate the forces from gusting winds, when researchers saw the wing’s shaking greatly reduced.

With testing completed, NASA and Boeing experts are analyzing data and preparing to share their results with the aviation community. Airlines and original equipment manufacturers can learn and benefit from the lessons learned, deciding which to apply to the next generation of aircraft.  

“Initial data analyses have shown that controllers developed by NASA and Boeing and used during the test demonstrated large performance improvements,” Heaney said. “We’re excited to continue analyzing the data and sharing results in the months to come.” 

NASA’s Advanced Air Transport Technology project works to advance aircraft design and technology under the agency’s Advanced Air Vehicles program, which studies, evaluates, and develops technologies and capabilities for new aircraft systems. The project and program fall within NASA’s Aeronautics Research Mission Directorate. 

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