Boeing and NASA are to pause development of the X-66 flight demonstrator in order to focus their research on the evolution of long, thin-wing technology.
In a statement on April 25, 2025, NASA announced that the pair were “evaluating an updated approach” to the agency’s Sustainable Flight Demonstrator project.
The X-66 design incorporated extra-long, thin wings stabilized by diagonal struts, known as a Transonic Truss-Braced Wing concept, and there were high hopes that its development could lead to more efficient and sustainable aircraft.
However, it appears that Boeing and NASA now wish to put their energies specifically into the development of long, thin wing technology which could be used across multiple aircraft configurations.
“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,” NASA said.
Under the existing plan, a McDonnell Douglas MD-90 was being modified in Palmdale to test the Transonic Truss-Braced Wing with flight testing expected to commence in 2027/28.
NASA said that Boeing’s new proposal is based on “knowledge gained through research conducted under the Sustainable Flight Demonstrator project so far”.
“The Boeing proposal identifies the thin-wing concept as having broad applications for potential incorporation into aircraft with and without truss braces. NASA and Boeing are discussing potential options for advancing these sustainable flight technologies,” said NASA.
NASA issued the Sustainable Flight Demonstrator award to Boeing in 2023, with a goal of informing future generations about more sustainable commercial airliners.
Boeing and NASA have 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.
“NASA’s ultimate goal for this sustainable aircraft research is to achieve substantial improvements for next-generation airliner efficiency, lower costs for travelers, reduced fuel costs and consumption, and increase U.S. aviation’s technological leadership,” the space agency stated.
