NASA X-59 Ground Test Hits Flight Control, Hydraulic Issues

COLORADO SPRINGS—NASA says it is still too soon to know if a recently discovered series of subsystem issues with the X-59 low-boom supersonic demonstrator may jeopardize agency plans to begin flight tests later this year.

NASA says the problems, which were uncovered during system checkout tests at Lockheed Martin’s Skunk Works facility in Palmdale, California, were made “across a number of subsystems, including issues related to the flight control computer and hydraulic system. These issues are currently being resolved before the team proceeds with further testing.”

Developed by Lockheed for NASA’s Quiet Supersonic Technology program, the almost 100-ft.-long X-59 originally was due to fly in 2021 but has been delayed by workforce hiring issues, the COVID-19 pandemic and technical challenges related to wiring and final systems integration. The current schedule calls for first flight by year’s end with a transition to the nearby NASA Armstrong Flight Research Center at Edwards AFB for follow-on envelope expansion.

The specially configured X-59 has been designed to collect community response data on the public acceptability of reduced sonic booms. The data will be used by U.S. and international authorities to determine whether a boom standard can be set that will enable lifting of the prohibition on civil supersonic flight over land, which has been in place since the 1970s.

However, to achieve low-intensity booms at the X-59’s design speed of Mach 1.4, the aircraft is configured with a sharply swept delta wing and extended cantilevered nose section that makes up more than one-third of the vehicle’s length. Specifically designed with stiffness for high-speed testing, rather than strength for payload capability, the long, slender shape therefore poses significant aeroelastic challenges.

First reported by Flightglobal, issues were encountered during structural coupling tests at Palmdale. The tests are designed to evaluate the interaction between the airframe and the flight control system, and to ensure freedom from any aeroelastic and aeroservoelastic instabilities. Testing also uncovered unexpected issues with the flight control computers.

NASA adds that “the project team is currently working to ensure that reliability and airworthiness is as robust as it can be prior to the X-59’s first flight.”