Boeing this summer will stop developing NASA’s X-66 truss-braced-wing demonstrator aircraft and shift its focus specifically toward developing thin-wing technology that had been central to X-66’s design.
“By this summer, we will complete near-term X-66 demonstrator milestones – specifically the process of removing the wings – and then put the MD-90 activities on pause to focus on the thin-wing technology, which could have more direct benefit on future generations of commercial aircraft,” Boeing said on 25 April.
“As a result of this focus, some team members will move to Commercial Airplanes to support our development and certification efforts,” Boeing adds.
Boeing Commercial Airplanes is busy working to bring three long-delayed aircraft through certification: the 737 Max 7, 737 Max 10 and 777-9.
Several media outlets broke news on 24 April of Boeing’s development pull back.
The $1.15 billion X-66 was to be a heavily modified MD-90 equipped with long, slender wings supported by trusses – a complex design, but one engineers say would generate less drag, improving fuel efficiency.
Boeing in January 2023 won the NASA contract to develop the aircraft under the agency’s Sustainable Flight Demonstrator programme, with first flight intended in 2028.
“Development work is inherently dynamic,” Boeing says. “We can deliver value sooner by focusing on thin-wing design, which is applicable to multiple configurations and allows us to establish a sustainable and enduring capability to develop a pipeline of new-wing technologies.”
Boeing executives had previously said the truss-braced architecture might be suited for its next passenger aircraft, but the company never committed to the design. Some analysts always doubted Boeing would actually use truss-braced wings for its next production aircraft, citing complexity and risk.
Boeing now calls thin wings X-66’s “most-promising design feature”.
NASA confirms Boeing’s shift, saying the company now envisions having a “ground-based testbed to demonstrate the potential for long, thin wing technology”.
“NASA and Boeing are currently evaluating an updated approach to the agency’s Sustainable Flight Demonstrator project that would focus on demonstrating thin-wing technology with broad applications for multiple aircraft configurations,” NASA says. “The Boeing proposal identifies the thin-wing concept as having broad applications for potential incorporation into aircraft with and without truss braces.”
NATA notes that X-66’s design involved a “more-complex” structure of trusses.
The partners had already started modifying the MD-90 at a site in Palmdale, California.
Boeing has been studying truss-braced wings for decades. Named for the trusses that are required to support them, such wings are longer and thinner than traditional wings, which reduces drag, improving fuel efficiency by up to 25%, according to NASA and Boeing.
Drawbacks include the complexity and weight of the trusses and related support structure. Long wings are also more prone to the dangerous condition of flutter.
In awarding Boeing the contract to build the jet in 2023, NASA said it would contribute $425 million, with Boeing and its commercial partners kicking in another $725 million, for a total project cost of $1.15 billion. The aircraft was to have wings measuring 52m (170ft) – about 17m longer than a 737’s.
