

A Tiger Bites Its Tail



On Sep 21, 1956 Grumman test pilot Tom Attridge shot himself down in a graphic demonstration of two objects occupying the wrong place at the same timeone being a Grumman F11F-1 Tiger [138260], the other a gaggle of its own bullets..



It happened on the second run of test-firing four 20mm cannon at Mach 1.0 speeds. At 20,000' Attridge entered a shallow dive of 20°, accelerating in afterburner, and at 13,000' pulled the trigger for a four-second burst, then another to empty the belts. During the firing run the F11F continued its descent, and upon arriving at 7,000', the armor-glass windshield was struck, but not penetrated, by an object..



Attridge throttled back to slow down and prevent cave-in of the windshield, flying back to Grumman's Long Island field at 230 mph. He radioed that a gash in the outboard side of the right engine's intake lip was the only apparent sign of damage other than for the glass, but that 78 percent was maximum available power without engine roughness occurring..



Two miles from base, at 1,200' with flaps and wheels down, it became evident from the sink rate that the runway could not be gained on 78 percent power. Attridge applied power and said "the engine sounded like it was tearing up." It then lost power completely. He pulled up the gear and settled into trees less than a mile short of the runway, traveling 300 feet and losing a right wing and stabilizer in the process. Fire broke out, but, despite injuries, Attridge managed to exit the plane and get away safely, to be picked up by Grumman's rescue helicopter.



Examination of the F11F established there were three hitsin the windshield, the right engine intake, and the nose cone. The engine's inlet guide vanes were struck, and a battered 20mm projectile was found in the first compressor stage..



How did this happen? The combination of conditions reponsible for the event was (1) the decay in projectile velocity and trajectory drop; (2) the approximate 0.5-G descent of the F11F, due in part to its nose pitching down from firing low-mounted guns; (3) alignment of the boresight line of 0° to the line of flight. With that 0.5-G dive, Attridge had flown below the trajectory of his bullets and, 11 seconds later, flew through them as their flight paths met..

