IL-2 has to have something modelled drastically different than AH as far as the gunnery/damage model goes. Planes seem to take a LOT more punishment in that game than in AH. That is a good thing though, in my opinion.
As a matter of fact, they do have drastically different models.
Well, the main mechanism of "hit surface - deal damage" might be pretty much the same, but the way the damage is done is reall different.
The DM in FB/AEP is consisted of internal parts and exterior parts - and the "quality" of a round hit differs according to its type, situation, and penetration.
One example - it's a rare case, but in one case, I've hit a La-7 from almost 90d deflection to the wing. I've roped it vertical and came down on it's top with speed. The MK108 shell I fired penetrated the upper surface of the La-7's wing, rammed through the wing, and actually penetrated the underside of the wing. And then, it detonated as it left the underside of the wing!!
The plane received a puncture, but most of the destructive force from detonation was dissipated, and the La-7 had its wings intact. Now, that's some impressive DM when it comes to "variance according to situation"!
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Personally, I was really skeptical about the DM until finally in FB/AEP the 'variance' factor seems to have stabilized and a certain tendency now shows. The chances of structural failures are really low in FB/AEP compared to AH.
In AH, the result of good gunnery immediately piles up as kills achieved. You hit something, and it immediately snaps off. It's because of that people are able to land something like 7~10 kills per sortie - clearly, that's very unlikely in FB/AEP.
In FB/AEP, structural failures are more rare, but the destruction of internal systems depriving the pilot's ability to fly, is more probable. Some damages are progressional, others are immediate. Whatever the case, when it comes to the recently released Aces Expansion Pack, now my opinion is the gunnery/DM portrayed there is the most believable ever portrayed in the history of air combat sim games.
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What makes it even more fun, is other small "candies".. like how a temporary fire may start when a well landed 20mm blast ignites oil running in the engine. When you cut the engine and enter a dive, the airflow actually temporarily puts out the flames.. And then, as the airspeed slows down, the engine catches fire again. Man, that's impressive.
Also, P-38s catch fire with damage, and then voila, the pilot feathers the damaged engine and engages the fire extinguisher system - the flame stops.. man, that's cool.