Supersonic X-59 Completes Cruise Control Engine Speed Test Ahead of First Flight

April 7, 2025

NASA's X-59 supersonic research aircraft sits on a ramp at Lockheed Martin Skunk Works in Palmdale, California, during sunset. The aircraft is powered by a General Electric F414 engine. (Image: Lockheed Martin/Garry Tice)

The team behind NASA’s X-59 supersonic demonstrator completed another critical ground test in March, ensuring the quiet supersonic aircraft will be able to maintain a specific speed during operation. The test, known as engine speed hold, is the latest marker of progress as the X-59 nears first flight this year.

X-59 is an experimental aircraft developed by Lockheed Martin Skunk Works^® as part of the Quiet Supersonic Technology (Quesst) mission of U.S. National Aeronautics and Space Administration (NASA) to quiet loud sonic booms. The goal of the X-59 aircraft, which is expected to make its first flight in 2025, is to help establish an acceptable noise standard for commercial supersonic flights over land, potentially resulting in U.S. and international regulators lifting a five-decade-long ban that was imposed due to loud sonic booms. Thanks to its unique geometry, particularly the elongated nose cone, the X-59 is expected to generate a barely audible thump rather than a boom, reducing noise impacts.

“Engine speed hold is essentially the aircraft’s version of cruise control,” said Paul Dees, X-59 Deputy Propulsion Lead at NASA’s Armstrong Flight Research Center in Edwards, California. “The pilot engages speed hold at their current speed, then can adjust it incrementally up or down as needed.”

The X-59 team had previously conducted a similar test on the engine – but only as an isolated system. The March test verified the speed hold functions properly after integration into the aircraft’s avionics.

“We needed to verify that speed hold worked not just within the engine itself but as part of the entire aircraft system.” Dees explained. “This test confirmed that all components – software, mechanical linkages, and control laws – work together as intended.”

The successful test confirmed the aircraft’s ability to precisely control speed, which will be invaluable during flight. This capability will increase pilot safety, allowing them to focus on other critical aspects of flight operation.

This was the latest engine evaluation milestone completed by NASA for the X-59, after completing its first its first maximum afterburner test at Lockheed Martin’s Skunk Works facility in Palmdale, California in December. An afterburner is a component of some jet engines that generates additional thrust. Running the engine, an F414-GE-100, with afterburner will allow the X-59 to meet its supersonic speed requirements. The test demonstrated the engine’s ability to operate within temperature limits and with adequate airflow for flight. It also showed the engine’s ability to operate in sync with the aircraft’s other subsystems.

“The pilot is going to be very busy during first flight, ensuring the aircraft is stable and controllable,” Dees said. “Having speed hold offload some of that workload makes first flight that much safer.”

The team originally planned to check the speed hold as part of an upcoming series of ground test trials where they will feed the aircraft with a robust set of data to verify functionality under both normal and failure conditions, known as aluminum bird tests. But the team recognized a chance to test sooner.

“It was a target of opportunity,” Dees said. “We realized we were ready to test engine speed hold separately while other systems continued with finalizing their software. If we can learn something earlier, that’s always better.”

With every successful test, the integrated NASA and Lockheed Martin team brings the X-59 closer to first flight, and closer to making aviation history through quiet supersonic technology.

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