Aircraft wings have gotten steadily longer and thinner over the past 70 years, but there is a limit. Beyond a certain aspect ratio, a conventional cantilever wing, attached only at the fuselage, cannot support itself. The solution may be a truss: a diagonal strut connecting the fuselage to the underside of the wing, sharing the load and allowing wings to be far lighter and more aerodynamic than anything flying today.
NASA has now taken one of these “truss-braced wing” designs and pushed it to destruction, gathering the first experimental data on how a representative composite version of the structure actually fails.
The 15-Foot Wing
The test article, called SWEET-15 (Structural Wing Experiment Evaluating Truss-bracing), is a 4.57-meter (15-foot) subscale wing built at 18.6% of the span and chord of a full-scale design. It was manufactured at NASA Langley using the ISAAC robot, one of only three such machines in the world when it was acquired in 2014, which can lay carbon-fiber tows along curved paths rather than straight lines. This “tow-steering” technique allows engineers to place material exactly where loads demand it, saving weight everywhere else.
According to a 2025 technical paper by NASA researcher Brian H. Mason and colleagues, published at the AIAA SciTech conference, tow-steering alone reduced the upper cover panel weight by 6.4% compared with a straight-fiber design.
The wing was then shipped to NASA Armstrong’s Flight Loads Laboratory in California, where engineers spent months bending it incrementally with hydraulic actuators while a fiber-optic sensing system (FOSS) recorded thousands of strain measurements along the structure.
127% of Design Load
The wing withstood its design limit load, the maximum force it would ever be expected to encounter in flight, without any sign of trouble. The test team then kept pushing, well beyond the safety margin. The wing finally failed at 127% of the design limit load.
The failure occurred near the trailing edge and in the upper wing skin. For engineers, knowing exactly where and how a novel structure fails is almost as valuable as knowing where it succeeds. The data will feed back into computer models, which accurately predicted the behavior, the first time a representative composite truss-braced wing has been validated against a real test-to-destruction.
Why It Matters
The Transonic Truss-Braced Wing (TTBW) concept, which NASA has been developing since the late 2000s, aims for an 8-10% fuel burn reduction from the wing alone, and up to 30% when combined with improved engines and materials. The X-66A demonstrator, a heavily modified MD-90 with 51.8-meter (170-foot) truss-braced wings, was selected by NASA for the Sustainable Flight Demonstrator program in 2023, though Boeing indefinitely paused the program in April 2025.
The SWEET-15 data remains directly applicable regardless of the X-66’s fate. The structural validation of the joints connecting the wing to its main strut and jury strut, the critical load paths that make the truss-braced concept work, provides certification-level evidence that the design can meet safety requirements.
The data also supports the broader U.S. Aviation Climate Action Plan goal of net-zero greenhouse gas emissions by 2050. If truss-braced wings enter service on next-generation single-aisle aircraft in the 2030s, they could cut fuel consumption by millions of metric tons per year across the global fleet.
Sources
1. S. Mann, “NASA Pushes New Wing Design to Find Structural Limits,” NASA Armstrong Flight Research Center, July 17, 2026. https://www.nasa.gov/centers-and-facilities/armstrong/nasa-pushes-new-wing-design-to-find-structural-limits/
2. B.H. Mason, E.K. Anderson, A.M. Cardona, C.V. Jutte, & R.A. Larson, “Structural Sizing of a Tow-Steered Truss-Braced Wing Box Test Article (SWEET-15),” AIAA SciTech 2025. NASA/TM-20240014171.