Examination of the F11F showed it had been hit by at least three 20-millimeter rounds—one in the windshield, one in the right intake lip, and one in the nose cone
The F11F Tiger, redesignated F-11 in 1962, began as a 1952 Grumman project to improve the company’s F9F-6/7 Cougar. In its final form, however, it looked very different from its predecessor. Developed as a lightweight fighter, the prototype F11F first flew in July 1954 and had thin swept wings, spoilers instead of ailerons, and an area-rule fuselage that gave it a coke-bottle shape and allowed it to break Mach 1. During F11F-1 test flights, one of the strangest moments in aviation occurred when a Grumman test pilot reportedly “shot himself down” with his own bullets.
As JP Santiago notes in an engaging article on his website, Tails Through Time, part of the Tiger’s flight test program involved determining the safe operating range for its four 20-millimeter Colt cannons, which were mounted beneath and behind the air intakes. Because the Tiger was designed to be as lightweight as possible to achieve top performance with its Wright J65 Javelin engine—a license-built version of the British Sapphire—the spent casings and links were ejected overboard instead of being carried aboard. During cannon testing, it quickly became clear that airflow around the aircraft caused the spent casings and links to cling to the fuselage, leaving dents and scratches. At one point, the test aircraft even needed an armored leading edge on the horizontal stabilizer because the links, in particular, caused substantial damage.
The fix was to modify the ejection system and its chutes so the shells were forcefully expelled through longer chutes that extended into the airflow and clear of the turbulent air along the Tiger’s sides. A more complex internal system routed the links into a special compartment just ahead of the cannon ammunition boxes, since the links caused more surface damage than the spent casings.
On September 21, 1956, Grumman test pilot Tom Attridge took aircraft BuNo 138620 from the company airfield at Calverton, Long Island, to perform high-speed cannon firing trials. It was the 41st flight of that F11F-1 Tiger and Attridge’s second test flight that day. According to Robert Munro in Aero Album (Spring 1968, Volume One), the test began at 22,000 feet, with the aircraft accelerating in afterburner at a 20-degree angle past Mach 1. At 13,000 feet, he would fire a four-second burst from the cannons, pause three seconds to let them cool, then fire again, finishing at 7,000 feet when the ammunition was exhausted.
Attridge flew the assigned profile, and after firing the ammunition, he was suddenly hit by the shattering of the forward armored windscreen, apparently from some kind of object. He immediately reduced power and pulled up to slow the aircraft and keep the windscreen from collapsing. At 13,000 feet and 200 KIAS, he turned back toward Calverton. The only damage he could identify was a gouge on the right intake lip, and the engine began running rough whenever he increased power above 78%.
Two miles from the end of the Calverton runway, with the gear down and flaps extended at 1,200 feet, Attridge realized that 78 percent power was not enough to hold his glide path and the descent rate was increasing. He pushed the throttle to full, but the engine, as he put it, “sounded as if it was tearing up,” and he immediately lost power. Three-quarters of a mile short of the runway, the Tiger dropped into the trees and slid another 300 feet before stopping. Although the aircraft caught fire, Attridge got out quickly without injury, and the Grumman crash crew and rescue helicopter arrived in under three minutes. Eleven minutes after landing, the company helicopter took him to a local hospital for evaluation.
Inspection of the aircraft showed that it had been struck by at least three 20-millimeter rounds: one in the windshield, one in the right intake lip, and one in the nose cone. Projectile fragments were also found in the engine’s first compressor stage, along with damage to the fan blades, leading engineers to suspect that the round hitting the intake may have ricocheted into the engine. Investigators concluded that Attridge had, in effect, shot himself down. During the first cannon burst, he was in a 0.5G supersonic descent and had actually passed below the path of the rounds. Eleven seconds later, as he began pulling out of the dive, he flew into the stream of projectiles from that burst.
A later examination also revealed that Attridge had flown the same test profile earlier that day, and what was initially thought to be a large dent from an ejected casing on the vertical fin was actually a projectile strike. In other words, on the first flight of the day, he had apparently grazed himself and narrowly avoided shooting himself down.
Photo by U.S. Navy
