Boeing X-66A Sustainable Flight Demonstrator

The Boeing X-66 is an experimental airliner that was under development by Boeing. It was part of the X-plane series created in collaboration with NASA and the Sustainable Flight Demonstrator program. It used an extra-long and thin wing design stabilized by diagonal bracing struts, which is known as a Transonic Truss-Braced Wing. The aircraft configuration was based on research studies referred to as "Subsonic Ultra-Green Aircraft Reach (SUGAR)" which extensively studied truss-bracing and hybrid electric technologies.

Summary from Wikipedia, photo via Wikimedia Commons, licensed under CC BY-SA.