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Old 09-19-2014, 06:51 PM
Pursuivant Pursuivant is offline
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Harping further on damage model flaws to fuel tanks.

I was finally able to get information about how self-sealing fuel tanks worked in WW2.

Basically, they were multiple layers of rubber and/or leather, that self-sealed by allowing raw rubber to flow into the hole to seal it. Also, they were all soft-sided so that they wouldn't rupture as a bullet passed through them.

Patent application for one form of self-sealing fuel tank here:

http://www.google.com/patents/US2401627.pdf

Contemporary article on the Ju-88 which explains the self-sealing fuel tanks in detail:

http://www.flightglobal.com/pdfarchi...0-%203429.html
http://www.flightglobal.com/pdfarchi...0-%203430.html

Note that the Ju-88 was equipped with fuel dumping capability for its fuselage tank, although the fuel tanks don't appear to have been blanketed with engine gasses as a fire-protection measure.

Advertisement for self-sealing fuel and oil-tanks, which claims that they will not ignite even when hit by tracer, incendiary or ball ammo.

http://www.flightglobal.com/pdfarchi...0-%202064.html

This video is extremely helpful:


Notice that the U.S. self-sealing fuel tanks used in the B-24 bomber (and presumably all other U.S. types) INSTANTLY self-seal against .50 BMG shots fired at close range. They do not rupture due to fluid pressure when the bullet exits the tank. They also self-seal against multiple hits with no apparent loss of integrity.

U.S. Navy reports indicate that self-sealing tanks used on U.S. planes instantly sealed against 0.50 caliber bullets, and occasionally against 20mm shells.

Summary: Single small caliber bullets or shrapnel hits should not be able to start fuel leaks in planes with self-sealing tanks. Single 0.50 caliber bullets should also not be able to start fuel leaks in such planes unless they are also explosive. Even 20 mm shells might not cause a fuel leak (assuming they fail to explode)!

Multiple bullets hitting very close together, or an explosion, are required to get self-sealing tanks to leak.

This means that slow-to-stop fuel and oil tank leaks in the game are bad Damage Modeling. It also means that it should be even harder to set planes on fire.
Last edited by Pursuivant; 09-19-2014 at 08:53 PM.
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Old 09-19-2014, 08:25 PM
Pursuivant Pursuivant is offline
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Another period video showing exactly how rifle caliber MG fire works against both unsealed and sealed fuel tanks.


Both guns appear to be .30 caliber MG, firing from about 20 yards with a mixture of tracer and ball.

Notice that against the unsealed tank, the initial burst of bullets DON'T cause a fire, nor does the fuel in the tank ignite. Instead, several seconds after the bullets hit, once sufficient fuel has spilled, the incendiary or tracer bullets ignite the spilled fuel. The fuel in the tank itself only starts to ignite several seconds after that, once the heat from the spilled fuel fire has had a chance to volatilize the contents and make gasoline vapor spill out of the tank to mix with air.

In the second part of the video, you have a self-sealing tank filled 3/4 full of AvGas. Multiple 0.30 bullets which penetrate and exit the otherwise rigid tank fail to produce serious fuel spills and do not ignite the tank.

I count 8 entrance holes and 6 exit holes in the tank, with some obvious tumbling by a few of the bullets.

Notice that almost no fuel has spilled, since the tank stops leakage almost instantly.

This video is circa 1940, so represents equipment that would be installed on Western Allied planes by late 1940 to 1941.

As a side note, some planes (e.g., the LaGG series) vented exhaust gasses into the fuel tanks to prevent fuel vapor and air from mixing. This is now standard on most planes, but many WW2 planes didn't have this technology. In part, this was because the hydrocarbons in the fuel exhaust interacted badly with the rubber material that made up the fuel cell.
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