Bell X-5
The Bell X-5 is a pretty neat one—it looks mostly normal, perhaps even more than the X-57 Maxwell—but when it’s in the air, things change. The plane was the first aircraft that could change the sweep of its wings mid-flight. In other words, the Bell X-5 is a Transformer, one that changes from a plane that flies fast into one that flies very fast. Designed in the mid-1950s, the X-5 paved the way for future aircraft with wing-sweep designs, like the F-111 and the Grumman F-14 Tomcat. In that way, the Bell X-5 really did what any successful experimental plane ought to: showcase the utility of a new design or technology well enough that it becomes incorporated in future aircraft.
