By Stephanie Dwilson | 2025-06-09

NASA just convinced a supersonic jet it was flying -- without ever leaving the ground.

In a key milestone toward its first real flight, the X-59 "quiet" supersonic aircraft completed a high-stakes ground simulation in May.

The "aluminum bird" simulations tested if the craft's hardware and software would work together seamlessly while in flight.

Researchers found a few small problems that needed correcting, said Yohan Lin, the X-59's lead avionics engineer at NASA's Armstrong Flight Research Center in Edwards, California.

The simulation involves turning on most of the X-59's systems -- with the engine off -- while it is connected to a ground computer that sends signals simulating real-life changes like altitude and speed.

The pilot then "flies" the aircraft to see how it responds.

'Trick it into flying'

David Nils Larson, a research test pilot at the Armstrong Flight Research Center, explained more about the simulation in a NASA video.

"The aluminum bird uses our actual airplane, where we trick it into thinking it's flying," Larson said. "We're gonna actually be able to check the real airplane systems, the real hydraulics, see how it moves, put it in different flight conditions and trick it into flying."

Lin said the results were exactly what they hoped for.

"We thought we might find a few things during the tests that would prompt us to go back and tweak them to work better, especially with some of the software, and that's what we wound up experiencing," Lin said. "So, these tests were very helpful."

These types of simulations are typically called "iron bird" tests because they use a special mockup of the craft. But engineers are calling the X-59's an aluminum bird test because it used the X-59 craft itself.

"Most airplanes have a purpose-built, ground-testing aircraft called an iron bird," Larson said. "We ended up deciding we're just gonna use our own airplane to do these tests. Our airplane's made of aluminum; hence, aluminum bird."

Lin said this type of test was an ideal choice for the X-59.

"It's a perfect example of the old tried and true adage in aviation that says, 'Test what you fly. Fly what you test,''' Lin said.

Quieter sonic boom

Lockheed Martin Skunk Works is developing this unique craft in collaboration with NASA's Quesst Mission. The goal is to achieve a sonic boom that is only about as loud as a car door closing.

Lockheed will use the X-59 to collect community response to the quieter sonic boom. This information can help regulators create a supersonic noise standard that ultimately lifts the current ban on commercial supersonic travel over land.

The X-59 is not a prototype craft that will eventually carry passengers. Its sole purpose is to serve as an experimental craft to test residents' response to the quieter sonic boom.

When it is finally tested in the skies, the X-59 will be flown by a single pilot at Mach 1.4 (925 mph) at 55,000 feet.

Still, before the X-59 can achieve its first true test flight in the skies, a few more milestones need to be achieved, including a series of taxi tests in Palmdale, California.