Boeing to transform this MD-90 jet into X-66A Sustainable Flight Demonstrator to test Transonic Truss-Braced Wing configuration

Boeing to transform this MD-90 jet into X-66A Sustainable Flight Demonstrator to test Transonic Truss-Braced Wing configuration

By Dario Leone
Aug 18 2023
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From MD-90 to X-66A Sustainable Flight Demonstrator

Boeing has ferried an MD-90 airplane to the company’s site in Palmdale where it will be modified to test the Transonic Truss-Braced Wing (TTBW) configuration as part of NASA’s Sustainable Flight Demonstrator project.

NASA and Boeing previously said the aircraft produced through the agency’s Sustainable Flight Demonstrator project has been designated by the US Air Force (USAF) as the X-66A.

NASA and Boeing sought the X-plane designation shortly after the agency announced the Sustainable Flight Demonstrator project award earlier this year. The Air Force confers X-plane status for development programs that set out to create revolutionary experimental aircraft configurations. The designation is for research aircraft. With few exceptions, X-planes are intended to test designs and technologies that can be adopted into other aircraft designs, not serve as prototypes for full production.

As Boeing, NASA and community leaders gathered at the company’s facility on Aug. 17, 2023 to recognize the milestone in development of the experimental X-66A aircraft, Boeing released photos of the jet’s journey from Victorville, Calif., to Palmdale.

Boeing to transform this MD-90 jet into X-66A Sustainable Flight Demonstrator to test Transonic Truss-Braced Wing configuration
Boeing will modify this MD-90 to test the Transonic Truss-Braced Wing configuration as part of NASA’s Sustainable Flight Demonstrator project.

The X-66A Sustainable Flight Demonstrator

The X-66A is NASA’s first experimental plane focused on helping the US achieve its goal of net-zero aviation greenhouse gas emissions. Modification will begin soon and ground and flight testing is expected to begin in 2028.

“This marks an important step in the Sustainable Flight Demonstrator project, advances Boeing’s commitment to sustainability and brings us closer to testing and validating the TTBW design,” said Boeing Chief Technology Officer Todd Citron, in a company news release.

With ultrathin wings braced by struts with larger spans and higher-aspect ratios, the TTBW design and other expected technological advances could lead to reductions in fuel use and emissions by up to 30%. Boeing and NASA have collaborated for more than a decade on the concept through the Subsonic Ultra Green Aircraft Research (SUGAR) Program.

“We at NASA are excited to be working with Boeing on the X-66A Sustainable Flight Demonstrator making critical contributions to accelerate aviation towards its 2050 net-zero greenhouse gas emission goal,” said Ed Waggoner, deputy associate administrator for programs in the NASA Aeronautics Research Mission Directorate.

Boeing to transform this MD-90 jet into X-66A Sustainable Flight Demonstrator to test Transonic Truss-Braced Wing configuration
The MD-90 that will become the X-66A pictured at Boeing’s Palmdale site, where it will be modified to test the Transonic Truss-Braced Wing configuration as part of NASA’s Sustainable Flight Demonstrator project.

NASA X-planes

“Aerospace Valley has a long and distinguished history as the cradle of aerospace innovation, and this unveiling is a continuation of that critical work. Palmdale’s talented workforce and infrastructure make it the perfect location for this important project,” said Congressman Mike Garcia (CA-27).

The Sustainable Flight Demonstrator project seeks to inform a potential new generation of more sustainable single-aisle aircraft – the workhorse of passenger airlines around the world. Boeing will work with NASA to build, test, and fly the X-66A, a full-scale demonstrator aircraft. The X-66A with extra-long, thin wings stabilized by diagonal struts, known as a Transonic Truss-Braced Wing concept.

NASA’s history with the X-plane designation dates to the 1940s, when its predecessor agency, the National Advisory Committee for Aeronautics (NACA) jointly created an experimental aircraft program with the Air Force and the US Navy. The X-66A is the latest in a long line of NASA X-planes. Additionally, NASA’s Armstrong Flight Research Center in Edwards, California, has provided technical expertise and support for several additional X-planes.

According to a NASA press release, NASA and Boeing unveiled the livery at EAA AirVenture Oshkosh on Tuesday, July 25.

Boeing to transform this MD-90 jet into X-66A Sustainable Flight Demonstrator to test Transonic Truss-Braced Wing configuration
A rendering of the Transonic Truss-Braced Wing X-66A aircraft in NASA’s Sustainable Flight Demonstrator livery.

Photo credit: NASA and Boeing


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Dario Leone

Dario Leone

Dario Leone is an aviation, defense and military writer. He is the Founder and Editor of “The Aviation Geek Club” one of the world’s most read military aviation blogs. His writing has appeared in The National Interest and other news media. He has reported from Europe and flown Super Puma and Cougar helicopters with the Swiss Air Force.

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