Why some HMG break wings & others don't

[Pursuivant]

As part of my damage model bug stomping extravaganza, I've started to look at how various heavy machine guns work in the game.

My first test really made it very clear why the M2 .50 caliber MG seems "underpowered" in the game. The answer: lack of HE bullets in the belting.

By contrast, both the UBT 12.7 & MG131 13 mm MG include some variety of explosive bullet in the mix.

Regardless of weight of fire that hits a particular part, the game's damage modeling seems to need an explosive effect to trigger breaking parts for some planes. The MG 131 and UBT have that explosive effect, the M2 doesn't.

This isn't necessarily unrealistic. The USAAF made a clear decision with its choice of the M2 .50 caliber as its weapon of choice, and standardized beltings of AP, API, Incendiary and Tracer bullets. They were out to hunt fighters, not bombers, and their pilots and gunners were trained to go for engines, fuel tanks and cockpits - not airframes.

Looking at gun camera films by USAAF fighters, I don't see many instances where an enemy plane's wing was blown off as a result of gunfire alone (vs. secondary explosion). Reports of Japanese planes falling apart under .50 caliber fire might just be effects of fuel tank explosions or damaged wings failing under high G turns.

But, were the game to allow customized ammo beltings, with the option of including HE rounds for the M2, then I think that there would be no further complaints about that weapon's combat effectiveness.

Edit: There's also an argument to be made that the UBT and other 12.7mm or 13 mm machine guns (but not MG131) shouldn't have any special ability to break parts that the M2 can't. The USAAF did tests using HE bullets for the M2 and came to the conclusion that API shells carried a greater weight of fire. That is, they were the more combat effective round.

Typical .50 caliber, 12.7mm or 13 mm HE bullets of the era carried a very small explosive charge, but with a disproportionate reduction in bullet mass and effective penetration, so there is very good logic to the USAAF's decision.

The exception to the rule was the German 13 mm Minengeschoss bullet, which carried a much larger mass of explosive in a very thin-walled bullet case. These had a much more powerful explosive effect, but at the expense of much reduced penetration.

While the Allies were aware of minengeschoss ammo, for some reason they never reproduced it, since seems odd since it's an excellent choice for hunting fighters.

[Ice_Eagle]

Every airforce, well almost every airforce used a 'party mix' of ammo. So even the Germans
used a mix of ammo types along with the M-geschoss. Also, of all the guncam footage I've
seen, wings RARELY get blown off. Off that, the ones I do see are BF-109's and FW-190s
losing there wing to 50cal hits. Which can be reproduced in-game. M-geschoss bullets were
designed for critical damage on flight surfaces & engines. As seen on guncam footage of
-17's being attacked. Usual target are ailerons, elevators, rudders, and engines.

[Pursuivant]

Originally Posted by Ice_Eagle

Every airforce, well almost every airforce used a 'party mix' of ammo. So even the Germans used a mix of ammo types along with the M-geschoss.

Granted, although the Luftwaffe didn't get minengeschoss ammo until 1941, and, later in the war they had shortages of that ammo type.

Originally Posted by Ice_Eagle

Also, of all the guncam footage I've seen, wings RARELY get blown off. Off that, the ones I do see are BF-109's and FW-190s
losing there wing to 50cal hits. Which can be reproduced in-game.

I think we're looking at the same gun camera films. We're both in agreement that it's a rare thing for a fighter to lose a wing to .50 cal fire. I disagree that it's possible to reproduce those (rare) effects.

In my extensive damage model tests, I've discovered that it is literally impossible to remove an FW-190's wing using just .50 cal BMG fire. This is due to the lack of explosive bullets in the mix, as I described in my previous post.

On the other hand, it is depressingly easy to remove a Bf-109's wing.

Originally Posted by Ice_Eagle

M-geschoss bullets were designed for critical damage on flight surfaces & engines. As seen on guncam footage of
-17's being attacked. Usual target are ailerons, elevators, rudders, and engines.

Agreed. Sadly, IL2 doesn't model the effects of different sorts of ammo as well as it might, because the game engine doesn't (or can't) recognize different materials used for plane construction at the time.

[Ice_Eagle]

Well its does recognize different parts.. sort of. For example, and engine will
have a damage threshold of 350, the rudder 20, ailerons 100, and so on. But as
far as AI aiming for certain areas of the plane, seems they almost always go
for the engines. At least that's what I observe.

[Pursuivant]

Originally Posted by Ice_Eagle

Well its does recognize different parts.. sort of. For example, and engine will have a damage threshold of 350, the rudder 20, ailerons 100, and so on.

Giving various aircraft parts a "panzer rating" or some sort of "damage resistance" or "penetration threshold" rating is only the beginning of modeling terminal ballistics realistically.

Where I think that IL2's terminal ballistics fall down is that the game doesn't model retained energy correctly, especially when a bullet penetrates a fuel tank or thick armor plate.

For example, on some aircraft (e.g. the Ki-21), it is possible to shoot bullets entirely through a large, completely full fuselage tank, with the bullets retaining enough energy that they can still penetrate the aluminum on the other side of the fuselage and carry on to damage the engine on the other side!

Additionally, the game doesn't do a good job with bullets like HE or M-geschoss which should make a big hole on the airplane's surface, but shouldn't penetrate to do damage to internal parts.

Finally, the game does a terrible job with fragmentation damage, where tiny fragments from 12.7mm bullets can travel dozens of meters and still retain enough energy to penetrate not just a layer of aircraft aluminum, but also an engine block!

Originally Posted by Ice_Eagle

But as far as AI aiming for certain areas of the plane, seems they almost always go for the engines. At least that's what I observe.

When it aims correctly, AI always aims for an aircraft's "center of mass" - which typically means the engine and the cockpit area for a single-engined plane. Fly a P-38 or Bf-110 sometime and you'll notice that your guns and cockpit will get all shot up, but your engines will be unscathed.

The exception is that AI might be programmed to go for engines or fuel tanks on 4-engined bombers. I'll have to check it out.