NASA's X-59 begins US overland sonic boom tests

Crewed experimental planes compete with advancing drone technology

The X-59, with its elongated snout and rear-set cockpit, is built to reshape the shockwave produced when an aircraft breaks the sound barrier, flattening what is normally heard as a loud boom into a more muted bump. NASA program manager Peter Coen, who has worked at the agency for 43 years, said the X-59 should sound “like a car door being closed across the street” when passing Mach 1 — roughly 660 mph at airline cruising altitude. “We want to figure out what level of boom is acceptable to people on a regular basis,” Coen said.

The sonic-boom problem is what kept supersonic commercial flight away from land. Concorde was restricted to flights over the sea because of the shockwave created by a jet breaking the sound barrier, and barred from lucrative routes across the US. NASA’s X-59 program aims to determine whether reshaping the shockwave can change that.

The aircraft first flew in 2025 and is now conducting community overflight tests. Lockheed Martin assembled the plane for NASA from parts cannibalized from existing military jets: the cockpit and ejector seat from a T-38 training aircraft, the landing gear from an F-16 fighter, and the engine from an F-18. Because the pilot sits so far back in the fuselage, a camera feeds a screen in front of the pilot to provide forward vision, relying on instantaneous computer processing.

Coen traced the X-59’s lineage through NASA’s experimental aircraft program, which began with the Bell X-1 in 1947, when test pilot Chuck Yeager flew through the sound barrier. Engineers knew a .50 caliber bullet traveled faster than sound, so the original aircraft was shaped like a bullet with wings attached. Twenty years later the X-15 rocket plane — a cylinder with tiny wings dropped from a B-52 bomber — flew at 6.7 times the speed of sound, or 4,520 mph, reaching the edge of space and paving the way for heat-resistant materials later used on the Space Shuttle.

“Our approach is to pick small goals we aim to prove with flight data and we construct an airframe for that one task,” Coen said. The philosophy, he said, is to “minimise goals” because “the more goals you have the more expensive it gets.” For the X-59, the single goal is suppressing sonic booms within budget.

The broader question is whether crewed experimental aircraft remain the right approach. Drone technology has advanced rapidly, including in Ukraine’s war against Russia. NASA considered an unmanned X-59 but concluded that removing the pilot would have added the cost and complication of certifying a robot jet to fly fast over urban areas. The X-59 also needed to be large enough to resemble an airliner punching through the sound barrier, which in turn made space for a cockpit.

NASA has prior experience with drone X-planes. The X-48, a scaled-down model of an airliner that blends wing and fuselage to create a single lifting body, flew in 2007. Its 20-foot wingspan kept the program within budget.

“It’s likely that future X-planes will be uncrewed,” Coen said, “unless the technology we’re researching relates to piloting or if crewing it is more cost-effective.”

Guy Gratton, professor of Aircraft Test and Evaluation at Cranfield University, pushed back against the assumption that crewed test planes have become obsolete. “There’s a belief in certain quarters that drones can do everything. In Ukraine they’ve done amazing things with drones, but if you want to carry people you can’t take short-cuts,” Gratton said. “You lose a huge amount without pilots, you miss lessons a pilot would identify, plus it can take four times as many people on the ground to test a drone.”

The United Kingdom has its own history of crewed technology demonstrators. The Experimental Aircraft Programme flew from Lancashire in 1986 and tested systems later used in the Typhoon fighter, with Chris Yeo in the cockpit. “They all research some facet of flight, and demonstrate the design is working correctly,” Yeo said. “A lot of people say they can do something, but you only know it works when the design has been tested and certified.”

Forty years on, BAE Systems is preparing a new UK technology demonstrator that Tony Godbold, who runs the project, called “the X-plane of our generation.” The initiative brings together 100 UK suppliers including Rolls-Royce and will borrow engines from the existing Typhoon, with a planned first flight in 2028. It is intended to test ideas that might feed into the Global Combat Air Programme (GCAP), a joint UK-Italy-Japan fighter scheduled to fly in the 2030s.

“This proves we are serious in this space,” Godbold said of the demonstrator’s political significance.

About 14 of the UK’s qualified fast jet test pilots have already tried the new plane on flight simulators. “You can model a lot on computers and simulators, but the experience of test pilots is when stuff gets real, we only really learn things when we get their feedback,” Godbold said.