NASA’s newest X-plane rolled out last week. Though pitched as potentially ushering in an era of supersonic transport its real goal is not commensurate with its cost.
The X-59 Low Boom Demonstrator is the centerpiece of NASA’s Quesst mission, which the Agency says, “seeks to solve one of the major barriers to supersonic flight over land, currently banned in the United States, by making sonic booms quieter.”
Before a live audience at the X-plane’s rollout ceremony last Friday, NASA Deputy Administrator Pam Melroy characterized the X-59 as a “breakthrough” that “really redefines the feasibility of commercial supersonic travel over land.”
But there are serious questions as to whether the aircraft actually represents a breakthrough, how (or if) its design might extrapolate to future supersonic air transport aircraft and what exactly it is supposed to redefine.
The program is a costly one. In 2018, NASA awarded Lockheed Martin a $247.5 million contract to design and build the X-plane which was supposed to have been delivered in 2022. However, the tab for the eight-year Quesst flight test and demonstration program is an attention-grabbing $632 million.
To pin down what American taxpayers are getting the outlay, I spoke with NASA’s low-boom flight demonstrator project manager, Catherine Bahm, via telephone yesterday.
The raison d’etre for building, flying and testing the X-59 – to make sonic booms quieter – has been repeated ad infinitum in the media for the last six years. Once operational, the airplane will make a series of flights over populated areas to gauge public reaction to the diminution in the sonic boom it is expected to produce as it cruises above at Mach 1.5.
If average citizens find the noise to be the mere “gentle bump” NASA claims it will be, the door will presumably again be thrown open to supersonic air transport operations over land. That hasn’t happened routinely since such flight was banned in April 1973, barring the Concorde from jarring the public and property with its sound and shock waves.
NASA has expectations for the reduction in sonic boom sound that X-59 will achieve.
“For Concorde the [sonic boom noise] was about 100 PLDB [Perceived Level Decibels],” Bahm says. “That’s like a ballon popping right behind you or thunder clapping right above your head. Our target [for X-59] is 75 PLDB.”
At that level decibel level – basically a one-quarter reduction in sound though Bahm says the measurement is logarithmic so it may be more than 25% – the boom noise will be akin to distant thunder or a car door closing down the street.
NASA bases the projection on previous testing it has done with an F/A-18 Hornet which it flew over Galveston, Texas. Using a special supersonic dive maneuver (which alters and reduces the noise) the fighter jet’s boom noise was monitored and recorded by mobile microphone units deployed across the ground in the Galveston area.
Until the X-59 proves itself, this remains theoretical. But even if it does meet the 75 PLDB target the Low Boom Demonstrator is not an airliner. How much of its configuration would be translated to a supersonic air transport and how much noise reduction such a future aircraft might achieve in the real world simply isn’t known.
What’s more, an airliner that did adopt a similar planform would be stuck with wing and wing-loading that will require significant power for takeoff, climb, descent and landing. It would be noisy. The X-59 design does nothing to address these subsonic phases of flight which, if history is any guide, the public would almost certainly object to.
Building on the above, we have to acknowledge that there is no company seriously attempting to build a quieter supersonic airliner.
For all the press it has received Boom – the only company to have made limited strides on the path to building and selling a supersonic air transport – does not intend to operate at supersonic speeds over land, bypassing the need for sound reduction.
I raised these points with Ms. Bahm. She told me that for the Low Boom Demonstration and the X-59, NASA is “singularly focused on reducing the sonic boom to a sonic thump.”
In so doing it will provide data to allow the FAA to change the regulation on over land commercial supersonic flight “from a speed limit to a sound limit.” She agreed that future aircraft will face landing and takeoff noise issues.
She did not challenge the reality that any forthcoming supersonic airliner design will likely diverge from the X-59 design and thus may or may not meet its projected sound reduction performance. The above are not research topics for Quesst though she speculates that future NASA projects may look into them.
“Our first step is to be able to provide the data to change that regulation,” she added. Bahm crystallized NASA’s effort well. Its real goal is to change the metric for the FAA regulation from speed to sound. “That’s correct,” she says.
The public is paying $630 million to essentially change one or a few paragraphs in the relevant FAA regs. It is doing so with no real prospect at present of an emerging market for supersonic passenger travel.
In several of the articles I’ve written on Boom and other would-be supersonic aircraft makers, analysts including Richard Aboulafia have observed that there is no evidence (historic or pending) of pent-up demand for supersonic air transport. Airlines and aircraft OEMs are instead focused almost entirely on wringing out ever greater efficiency from their aircraft for economic reasons and emissions-related goals that are logically dubious at best.
It all points to a return on investment that does not justify the X-59 or Quesst. And when you consider NASA’s own history, the ROI looks even worse.
In the early 2000s NASA embarked on its Shaped Sonic Boom Demonstration (SSBD), a two-year program that used a Northrop F-5E fighter with a modified forward fuselage to confirm that the aircraft’s shock wave, and accompanying sonic boom, could be shaped, thereby reducing the noise of the boom in supersonic flight.
Sound familiar?
In cooperation with Northrop Grumman (rather than Lockheed Martin) NASA followed through, making an extensive study of the modified F-5 with over 1,300 recordings gathered by chase aircraft, some flying inside the F-5’s shock wave, others in front, behind, above and below the fighter. Sonic boom data was also gathered by an array of 42 sensors and recording devices on the ground along the flight path of the F-5.
The result was a demonstrated a reduction in the sonic boom by about one-third. Justly proud, NASA commissioned a book on the SSBD.
In our conversation Bahm suggested that the X-59 provided reasonable ROI given that, “Showing that you can design aircraft for quiet supersonic flight is a novel idea, a novel goal… We believe the investment is well worth it to change the future of the aerospace community.”
She also highlighted NASA’s intention to share the Low Boom technology, design, and analysis tools with commercial companies “so that they can leverage those tools to design and build future supersonic commercial aircraft.”
As noted, which companies these would be is not clear. When reminded of SSBD she explained that the Low Boom team is “leveraging the work that that great team performed”. She explained that SSBD experiments were aimed at tailoring the “front end” of the shaped sonic boom whereas the X-59 study will be directly relatable to future commercial supersonic flight without specifically elaborating on how.
It has to be said, the front-end of the shock wave or sonic boom is what we hear on the ground. Bahm says we hear the wave as it crosses the length of airplane but she did not refute the fact that the report people hear comes from the aircraft’s initial bow wave.
While the F-5 used for SSBD is no airliner either, the data it produced could have been used with modern analysis. The aircraft itself could have been dusted off and taken out of the museum it now resides and flown with new instrumentation to perform a demonstration the same as (or at least highly similar to) the X-59 will undertake to gauge public perception.
Such an exercise could likely have been done for a fraction of the Quesst program price.
Initial X-59 flight testing and envelope expansion is expected to begin this summer at NASA’s Armstrong Flight Research Center in Edwards, California. A Phase 2 of the program will see flights over remote test ranges to determine whether the X-plane is actually as quiet in supersonic flight as NASA projects.
Years from now the public demonstration will finally begin. But unless there are other aspects of the program that are classified for military or other purposes, it arguably looks like little more than a jobs program for NASA and a filip for Lockheed Martin.
That’s a pretty thin return on investment.
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