Airborne Awesomosity

Going Tailless

When Northrop began development of the X-4 Bantam, tailless aircraft weren’t new. However, the US had no experience with them and was hoping to find a solution to shock stall as we pushed towards breaking the sound barrier.

In June of 1946, Northrop was contracted to build two X-4s. The aircraft were to have swept wings, no tailplane, and a top speed of just over Mach 0.9. The thinking in the 1940s was that the shock stall issues experienced on the tailplane could be eliminated by eliminating the tailplane altogether. Since Northrop already had experience with elevon — combine aileron and elevator — controls with the N-9M, XB-35, and YB-49, they were the natural choice.

Work started in 1946, but Northrop wouldn’t turn the aircraft over to NACA until 1950 after they had completed their contractor flight program. The first aircraft was soon grounded due to reliability issues leading Walt Williams, the head of the NACA Muroc Flight Test Unit, to call the aircraft a “lemon”. It was used for spare parts for the second aircraft.

What NACA found was the same thing the Germans found with the Me 163 Komet: at transonic speeds, the aircraft would begin oscillating in pitch and it would get worse as speed increased. Additionally, the aircraft had a tendency to “hunt” in all three axes. Project engineers found that increasing the thickness of the trailing edge of the elevons would help with these stability issues. The installed balsa wood strips between the two halves of the elevons and raised the onset of porpoising from Mach 0.88 to Mach 0.92.

The X-4 was used to test several other issues related to high speed flight and the possibilites of the tailless design until 1953. In the end, it was found the configuration showed promise, but until better control systems could be developed, it was not practical.

It wouldn’t be until the late 1990s when another tailless X-Plane, the X-36, and McDonnel-Douglas’ Bird of Prey would be studied by NASA.

[Image Credit: NASA]

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