X-planes at Edwards: In the center is the Douglas X-3 Stiletto research aircraft. Clockwise from the top: The Bell X-5 variable-sweep wing jet research aircraft; the Navy’s Douglas D-558-II Skyrocket swept-wing aircraft; the Northrop X-4, the Douglas D-558-I Skystreak and the Convair experimental XF-92A Dart. These aircraft were being tested a little before the birth of the Air Force Flight Test Center, June 25, 1951. (Air Force photo)