In this 1950 view of the left side of the NACA High-Speed Flight Research Station's X-4 research air…

NACA test pilot Joe Walker (on left) is seen discussing tests points to be flown on the X-4 aircraft…

NACA High-Speed Flight Research Station's X-4 research aircraft, the low swept wing and horizontal t…

NACA High-Speed Flight Research Station's X-4 research aircraft, the horizontal tailless design is q…

NACA High-Speed Flight Research Station X-4 research aircraft is seen in this 1950s in-flight photog…

NACA High-Speed Flight Research Station X-4 research aircraft is seen in this 1950s in-flight close-…

X-4's design allowed it to be broken in two, aft of the engines, for servicing and instrumentation w…