Boeing has shelved its plans to build and fly the X-66 experimental airplane for NASA’s Sustainable Flight Demonstrator (SFD) project, which sought to introduce new airframe technologies for the next generation of more efficient single-aisle airliners. In a statement, the U.S. space agency said it is working with Boeing to evaluate “an updated approach” to the SFD program that would focus on demonstrating long, thin wings—a key aspect of the transonic truss-braced wing architecture of the X-66.
“Boeing’s proposed focus centers on a ground-based testbed to demonstrate the potential for long, thin-wing technology,” NASA said. “Work on the X-66 flight demonstrator—which currently incorporates a more complex transonic truss-braced wing concept that uses the same thin wing technology as well as aerodynamic, structural braces—would pause for later consideration based on the thin-wing testbed results and further truss-braced configuration studies.”
Boeing announced in January 2023 that it intended to fly a full-scale demonstrator aircraft for the NASA SFD program by 2028. The company planned to use a modified McDonnell Douglas MD-90 with composite truss-braced, high-aspect-ratio wings installed above the fuselage.
Through a Space Act agreement, NASA pledged to spend $425 million on the SFD project, while Boeing and its commercial partners were expected to contribute up to $725 million. It is unclear how much of those financial commitments have already been spent.