World of Tanks

[Tamas]

I've had one of the funniest episode in WoT yet.  I was in a T-50, and along with Leopard we're scouting deep into the territory.  Along the way we encounter a pair of enemy T-50s.  A long 60 kph dogfight ensues, where me and my wingman are chasing the enemy and his wingman all over the map, to much comic effect.  Eventually I get both T-50s and neither of us take much damage from their fire.  Unfortunately, near the end of the chase, me and the Leopard crash into each other while trying to finish off the second T-50, and take half our health off each other. 

[DGuller]

I finally got Panther.  I have to say, that long 7.5 cm gun is quickly becoming long in the tooth.  I almost feel like I had that gun back when I was playing with Loltraktor.  Having a top gun with the damage of 135 is a little on the weak side at Tier 7.

[Berkut]

SO use the 88 instead.

I think it is a very good decision point.

You can use the long 75, which has pretty mediocre damage for T7, but ridiculous penetration for Tier 7, or you can use the 88 which has decent pen for T7, and good damage.

[Habbaku]

The L100 fires astoundingly quickly, slices through anything and is one of the most accurate weapons in the game.  The 88 has nothing on it.

[DGuller]

Come to think of it, the very high penetration value can increase damage beyond specified.  I think there is a substantial damage bonus if you can penetrate more than twice the armor width.

[Berkut]

Come to think of it, the very high penetration value can increase damage beyond specified.  I think there is a substantial damage bonus if you can penetrate more than twice the armor width.

you are thinking of armor over-penetration, which is based on the shell diameter being more than twice the armor thickness, so no help with the L100 there.

[DGuller]

I think I am.    

WTF does shell diameter and armor thickness have to do with each other, though?    I would think that penetration being twice that would make sense, since such a round could go through more of the stuff inside the tank.  The diameter thing makes no sense at all, though.  You may as well give damage bonus for firing a shot from a tank with upgraded tracks, but basic engine.

[Berkut]

I think I am.    

WTF does shell diameter and armor thickness have to do with each other, though?    I would think that penetration being twice that would make sense, since such a round could go through more of the stuff inside the tank.  The diameter thing makes no sense at all, though.  You may as well give damage bonus for firing a shot from a tank with upgraded tracks, but basic engine.

It is actually based on real world shot physics, not something they just made up.

During WW2 (I am going from memory here) it was noticed during testing that sometimes when large caliber rounds strcuk armor that was half their diameter or less, they would not just penetrate easily, but would actually cause the armor to fail catostrophically, like crack wide open for example. Something to do with overstressing the armor plate, as opposed to just punching a hole.

[DGuller]

  Interesting.  I still don't see why it has to be a discrete effect, and not just a gradual increase in over-penetration as the ratio of shell diameter to armor thickness increases.  I always assumed that the factor of 2 was there because then you can go through both sides.

[Berkut]

But it is a discrete effect. It has to do with the ability of the metal to actually bend and deform as the projectile's energy transfers into the armor plate. This is a function of kinetic energy of course, but it is also a matter of how much area the energy is being applied to the metal compared to the thickness of the metal itself - as the metal of the surface of the armor plate is pushed inwards, it eventually encounters enough resistance from the metal behind it that it starts to get pushed outward, which is why there is often a circular "bulge", like a crater rim, around holes punched in armor. As the shell continues to penetrate, eventually this is overcomes and the armor "petals" which creates the hole as the projectile punches through.

There is some kind of relationship between the actual diameter of the shell and the thickness of the armor plate that causes the armor to lose its ability to resist the shock wave as the shell diameter exceeds twice the armor thickness. I barely understand this, although I used to "get" it a lot more. So I am probably fucking this all up, but it does end up making sense at some point.

Now you are going to make me go look this up again, damnit...

[Berkut]

BTW, the term we are looking for is actually "overmatch".

If you read much on the physics of armor penetration, the "T/D" ratio is a pretty key variable, and that is the ratio of the projectiles diameter to the armor's thickness. So apparently it really does matter...

[Berkut]

Interesting paragraph that does a decent job of explaining armor overmatch and the importance of the T/D ratio in WW2 combat:

Behind the decision to retain the the 88 mm KwK 36 L/56 as the main gun of the Tiger I, instead of the Rheinmetall 75 mm KwK 42 L/70, was the fact that at that time armor penetration was mainly a function of thickness to diameter (T/d) ratio. During World War II, the Armor Piercing (AP) round relied on its own weight (and a 88 mm KwK 36 L/56 gun APCBC shell weighed 10.2 Kilograms, as opposed by an 75 mm KwK 42 L/70 gun APCBC shell, which weighed 6.8 Kilograms) to penetrate the enemy's armor. Theoretically, the higher the muzzle velocity, the more penetration any kind of AP round would have, all other variables remaining constant. In real World War Two tank combat, however, other important variables intervened, such as the thickness to diameter (T/d) coefficient, which means that the bigger the diameter of any given round relative to the thickness of the armor it is going to strike, the better the probability of achieving a penetration. Furthermore, if the diameter of the armor piercing round overmatches the thickness of the armor plate, the protection given by the inclination of the armor plate diminishes proportionally to the increase in the overmatch of the armor piercing round diameter or, in other words, to the increase in this T/d overmatch. So, when a Tiger hit a T-34, the 88 mm diameter of the Tiger's round overmatched the 45 mm glacis plate of the T-34 by so much that it made no difference that the Russian tank's glacis was inclined at an angle of 60 degrees from vertical.

[DGuller]

Well, I learn something every day.

[DGuller]

Wait, I wasn't imagining things.  Turns out there are two different kinds of overmatches, one depending on caliber, and one depending on the actual penetration statistics.

Shell Normalization

When a shell hits armor, and if it does not bounce/ricochet, it will dig in and try to penetrate at a 90 degree angle. Typically, it only increases the angle of attack by about 10 degrees.
Overmatch -- Shell Size

In WOT, overmatch is currently modeled so that when the caliber of the weapon is 3 times greater than the thickness of the armor, than overmatch (no chance to ricochet) occurs.
Overmatch -- Penetration

Wot adds an additional version over overmatch based upon when the shell's penetration is more than 2 times greater than the thickness of the armor. When this occurs, shell normalization is increased by an undisclosed amount.

[DGuller]

So, no bonus to damage, just bonus reduction to ricochet chances on top of what is already afforded by the higher penetration stat.