X-59 Readied For Structural Testing

Credit: Lockheed Martin

SAN DIEGO—Lockheed Martin is poised to start structural tests of the X-59 Low Boom Supersonic Demonstrator at its Fort Worth facility as part of final preparations for flight tests later this year in Palmdale, California.

The aircraft, which is designed to evaluate the public acceptability of low-boom supersonic flight over land, completed assembly last year in Lockheed Martin’s Skunk Works and was shipped to Texas for structural tests in late December. 

The work was moved to Texas due to the current unavailability of a sufficiently large area at the California site to accommodate structural tests of the X-59, which is almost 100 ft. long with the extended nose section attached.

Following the evaluation, the X-59 is expected to return to Palmdale in March for installation of its General Electric F414 engine. After completion of extensive engine and fuel system ground tests, the aircraft is due to make its first flight in late summer, says Peter Coen, NASA’s Low-Boom Flight Demonstration mission integration manager.

The structural tests in Texas will calibrate strain gauges and sensors that form part of the flight test instrumentation. “It’s pretty much a standard static load test and it is meant to make sure we have the system set right,” says Coen, who adds that a follow-on set of ground vibration tests will be conducted in Palmdale. 

Speaking to Aerospace DAILY on the sidelines of the AIAA SciTech Forum in San Diego, California, Coen says the X-59 will start full envelope expansion tests when the aircraft is transferred from Palmdale to NASA Armstrong Flight Research Center at Edwards AFB. “It will go pretty quickly to supersonic speed and we will take the opportunity if it presents itself to make some initial [sound] measurements,” he says.

Envelope expansion marks the first of three main flight test phases planned for the X-59, which is designed to re-shape the supersonic shock wave pattern to substantially reduce the sonic boom to more of a sonic “thump” when it reaches the ground. The second phase, starting in 2023, will consist of acoustic validation flights with measurements of the pressure taken in-flight at mid-field distances and on the ground.

Rendering of the X-59. Credit: Lockheed Martin

“We will look at the signature for various flight conditions and make sure they match our signature predictions,” Coen says. “The near-field pressure measurements will be calibrated against computational fluid dynamics predictions while the ground results will be measured as pressure but calculated as loudness.” Coen says the target is to lower the classic “double thump” of a sonic boom to 75 perceived decibels or less in supersonic cruise at Mach 1.4. 

“Part of the reason we are doing the acoustic validation so thoroughly is so when we get to community testing, which is phase three, we want to have a range or matrix of levels that will be appropriate to establish a dose-response relationship,” he says, referring to the over-flight test program planned for 2024-2026. During this period NASA will use the X-59 to gather data on public acceptance of the low-boom technology by flying over select U.S. cities and asking residents to share their response to the sound the aircraft produces.

Data from the flights will be used to inform an International Civil Aviation Organization Committee on Aviation Environmental Protection meeting, which is scheduled in 2025 to establish a standard for an allowable loudness level created by a sonic boom. 

Guy Norris

Guy is a Senior Editor for Aviation Week, covering technology and propulsion. He is based in Colorado Springs.