Boeing to put NASA X-66 X-Plane on hold

Artist’s concept of the X-66 aircraft. Boeing and NASA have already collaborated on wind tunnel tests, computational fluid dynamics modeling, and structural design and analysis aimed at exploring how best to approach fuel-efficient, sustainable designs. Source | NASA

The X-66 Sustainable Flight Demonstrator (SFD), an X-Plane project with a high-mounted truss-braced thin wing launched in January 2023, is being put on the back burner. Boeing’s (Arlington, Va., U.S.) April 24 announcement that it is making moves to pause the NASA-led (Washington, D.C., U.S.) project has been followed by a report by the agency that both partners are “currently evaluating an updated approach ... that would focus on demonstrating thin-wing technology with broad applications for multiple aircraft configurations.”

To become NASA’s largest X-Plane, the demonstrator was specifically focused on helping the U.S. achieve net-zero aviation emissions by 2050, informing future single-aisles with a new wing rendering — extra-long, thin wings stabilized by diagonal struts known as the transonic truss-braced wing (TTBW) concept. Boeing was working with NASA to build, test and fly a full-scale version, with wing assembly supported by Boeing company Aurora Flight Sciences (Bridgeport, W.Va., U.S.). Though materials were never /confirm/ied, both Boeing and Aurora have extensive composites expertise that could potentially inform the future wing design.

According to an Aviation Week article, the X-66 was previously expected to fly in 2028. Now, Boeing has proposed work on the X-66 “would pause for later consideration based on thin-wing testbed results and further truss-braced configuration studies.” Under this proposal, all aspects of the X-66 flight demonstrator’s design, as well as hardware acquired or modified for it, would be retained while the long, thin-wing technology is being investigated with more focus. NASA and Boeing would also continue to collaborate on research into the transonic truss-braced wing concept.

Aviation Week reports that from Boeing’s perspective, this move is part of a “pragmatic program revision,” one that simultaneously seeks to redirect resources to certify the delayed 737 MAX and 777-9 while avoiding “premature commitment to a thin-wing configuration that may not work out in the long term.”

In summary: While the X-66 program is in limbo, the thin-win seems to live on.

“We have learned a lot in the past few years partnering with NASA on the X-66 program that will influence the future generations of airplane design,” a Boeing spokesperson tells CW. “That learning has shown us the value of thin-wings and associated technology. Going forward, we will focus efforts on maturing the technology to support thin-wing design. What we learn with this approach can be applied across multiple products, including potential truss-braced wing configurations and beyond.”

There are still concerns that the program pause will be detrimental to the ambitious X-Plan project in the long-term. This is reinforced by the termination of the NASA X-57 experimental electric aircraft in 2023, followed by the agency’s X-59 supersonic demonstrator that is years behind schedule. But it is clear that there is still a lot to be determined. For the moment, Boeing’s X-66 facility in Palmdale, California, is set to wind down over the next few months.