NACA High Speed Flight Station at Edwards AFB South Base. Aircraft are (left to right): D-558-2, D-558-1, X-5, X-1, XF-92A, and X-4. This is an early 1950s color photo of NACA research aircraft in front of the South Base hangar. On the left is the third D-558-2 (NACA 145/Navy 37975). At this time, the aircraft was still in the combined jet and rocket configuration. NACA 145 was used to test a number of wing modifications intended to lessen the pitch up of the aircraft in turns. Next to it is the third D-558-1 (NACA 142/Navy 37972) which provided aerodynamic data at transonic speeds. The rudder is still painted red, to avoid possible control surface flutter problems which might be caused by weight and balance changes from a coat of white paint. To the right is the first X-5 (Air Force 50-1838), which tested an in-flight variable-sweep wing design. This allowed the gathering of transonic data at a wide range of sweep angles. The X-5 did have very poor stall/spin behavior, which made it dangerous to fly. Beside it is the second X-1 (Air Force 46-063), which was flown by the NACA between September 1947 and October 1951. This aircraft had a thicker wing than the first X-1 (46-062), which created considerable drag. The aircraft was later modified to become the X-1E. Behind the rocket-powered X-1 is the single XF-92A built (Air Force 46-682). Although intended to be the prototype of a jet fighter, it became a research aircraft testing delta wings. Its use by the NACA was relatively brief, but the data proved useful in the design of later U.S. delta-wing aircraft. To the forward right is the second X-4 (Air Force 46-677) which tested the concept of a semi-tailless swept-wing aircraft (no horizontal stabilizer). Without horizontal stabilizers, however, the aircraft proved unstable at high transonic speeds.