The Northrop SX-4 Bantam, later re-designated the X-4, was designed to explore the flight characteristics of swept wing semi-tailless aircraft at transonic speeds (about Mach .85). The X-4 was a small airplane, measuring only 23.25 feet in length with a wingspan of 26.75 feet. It had no horizontal tail surfaces, depending instead on combined elevator and aileron control surfaces (called elevons) for control in pitch and roll attitudes. The aircraft also had split inboard flaps, which doubled as speed brakes.
The museum acquired the number one X-4, tail number 46-676 in 2001. It was painted a very light gray. During flight testing, it was discovered that the aircraft was very hard to see due its size and how it blended in with the system. The restoration included adding the red strips that Northrop added to improve tracking the aircraft and hence overall safety during testing.
No speed records, no altitude records, but the X-4 did leave its mark in aviation history. The X-4 fulfilled its mission in that its primary mission involved proving a negative – swept-wing semi-tailless design were not suitable for speeds near Mach 1 (although the F7U Cutlass proved to be something of a counterexample). It was not until the development of computer fly-by-wire systems that such designs would be practical. Perhaps the F-117A is the best example of successful swept-wing semi-tailless aircraft.
Northrop X-4 (SN: 46-676) is on display at the AFFT Museum at Edwards AFB.
Span: 26 ft. 10 in.
Length: 23 ft. 3 in.
Height: 14 ft. 10 in.
Weight: 7,550 lbs. maximum
Armament: None Engines: Two Westinghouse XJ-30 turbojet engines of 1,600 lbs. thrust each
Crew: One Maximum speed: 640 mph
Cruising speed: 480 mph
Maximum endurance: 44 minutes
Service ceiling: 44,000 ft.