Grumman X-29
This X-plane, 29th of its name, built on the swept-wing innovations of the X-5 but incorporated them into an aircraft 30 years more modern. First flown in 1984, the X-29 has forward-swept wings that seem counterintuitive. As it turns out, the forward sweep and the canards—the little wings in front of the plane’s main wings—reduce drag, speeding transit through the air. Unfortunately, it also made the X-29 inherently unstable—according to DARPA, “the most aerodynamically unstable aircraft ever built.” Whoops! The plane also brought along other breakthroughs, include a new digital flight-control system and carbon fiber wings, which allowed the relatively light plane to be more maneuverable.
