The NACA High-Speed Flight Research Station X-4 research aircraft is seen in this 1950s in-flight close-up photograph.
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The NACA High-Speed Flight Research Station X-4 research aircraft is seen in this 1950s in-flight close-up photograph. The two large “X”s seen connected by a line painted on the aircraft were used as an aid in optical tracking. The X-4 Bantam, a single-place, low swept-wing, semi-tailless aircraft, was designed and built by Northrop Aircraft, Inc. It had no horizontal tail surfaces and its mission was to obtain in-flight data on the stability and control of semi-tailless aircraft at high subsonic speeds.1957NASA Photo / NACA/NASA› X-4 Project Description