Explosive decompression

[jimpeel]

I believe that there is only one instance of a self-shootdown. Here are a couple of writeups the self-shootdown Sep 21, 1956 by an F11F-1.

http://www.aerofiles.com/tiger-tail.html

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..

http://www.f-16.net/library/stories/owngoal.html

The Grumann-made F-11 Tiger achieved some notoriety as being the first aircraft in history to "shoot itself down". Two F-11s were experimentally fitted with massive J-79 engines, giving them thrust-to-weight ratios of nearly 1 to 1. Although their increased weight and limited fuel capacity made them unsuitable for carrier duty and impractical as fighters, the two aircraft were nonetheless tested extensively.

On one such test flight, an F-11 was making passes on a gunnery target. The pilot fired a short burst to clear his guns and began a shallow dive at full power. After several seconds, the pilot pilot pulled the aircraft into a shallow climb and simultaneously began a rapid deceleration maneuver. Almost instantly, the F-11 was racked by a series of explosions, forcing the pilot to abandon his stricken aircraft. The accident investigation board concluded that the F-11 had outrun its own cannon fire, only to have the cannon fire catch up with the aircraft when it decelerated!

 

[hksw]

By your premis, a bullet being fired aft from an aircraft that exceeded the speed of the bullet it would merely fall out of the end of the barrel. The bullet has its own velocity relative to the firearm and does not lose any of that velocity due to the motion of the firearm. If the plane was going 900ft/sec and you fired a firearm that had a muzzle velocity of 900ft/sec, the aircraft and the bullet would, for a short time due to bullet decay, be moving apart at 1,800ft/sec.

I have to disagree. To the person (1) on a platform travelling +900 fps, the bullet would seem to be travelling 900 fps (direction not relavant) as that person 1 would have a relative velocity to the platform of 0 fps. To a person (2) standing on the ground stationary, the plaform and person 1 are travelling +900 fps. When the projectile is fired 180° from the line of flight with a known velocity of -900 fps, the resultant velocity as observed by person 2 is 0 fps. The bullet would literally just fall straight down.

If the bullet were shot forward (0°) instead, then the sum velocity would be +1800 fps and eventually degrade to 0 fps due to wind resistance. At some point, the platform, still travelling at a constant +900 fps, will meet up with the bullet.

 

[Bart Noir]

jimpeel, you're right

I didn't actually say I watched the program! I was just commenting on the original post and applied my engineering nit-picking outside my job. Guess I shouldn't do that. Maybe that is why I am divorced. As of today. AAArg, it's lots more fun thinking of guns and jets.

Bart Noir

 

[Ktulu]

DOH! Stupid Physics!

 

[13A]

I was sitting by the door on a flight once where ice formed on the gap between the door and the body of the plane. I pointed it out to the flight attendant and she said it's not uncommon for the doors to leak. I'm sure that seal was leaking more air than a bullet hole would.