The X-56A, Multi-Utility Technology Testbed, also known as the MUTT, was a spunky uncrewed aircraft used to test the flexibility of wings and the suppression of flutter, or the phenomenon of airplane wings vibrating in flight. According to the MUTT’s project page, “The project plans to use these to fly the X-56A with a slender, flexible wing with a much higher aspect ratio than currently used on commercial airliners.” The first flight tests of the system happened in 2013 and 2014.
In January 2023, NASA and Boeing announced their plans for developing test aircraft for the Transonic Trussed-Braced Wing design, which could pave the way for passenger aircraft with longer, thinner wings than current jetliners, with the goal of improving fuel efficiency.