CMBB to CMAK, why did pen values change?

[ww2steel]

I am putting gun performance values into my calculator/ graphs. While entering CMAK data that was sent to me I noticed that the guns (German, for example) differ slightly - by maybe a few mm - from CMBB to CMAK. Is this because they were facing Western armor instead of Soviet??? I have spent some time looking through old posts, because I'm sure this has been covered, but haven't managed to find anything.

Grille, 0°, HE, all dates: (one of many examples)

CMBB:

37 36 33 29

CMAK:

31 31 30 26

Does this mean that Soviet armor is somehow more vulnerable to this HE ammo? Did Battlefront change their evaluation of all of the guns? What's up?

Thanks for the help!

Mike

[John Kettler]

ww2steel,

Western armor was mostly RHA (Rolled Homogeneous Armor), which is fairly soft and yielding. In the West, it is the baseline armor against which armor penetration tests are run. Russian armor, though, has different ballistic characteristics, being made of high hardness steel. As such, under HE attack, it may be experiencing brittle failure the more yielding RHA resists better. This is an HE case only. What is happening with the AP numbers, if anything?

Regards,

John Kettler

[Sgt Joch]

I remember there was an ancient thread where this was discussed as well as BFCs rationale. I believe it was due to updated research and differing ammo types used on the western front.

I you search the posts by "battlefront" in the 2003-2004 CMAK archives, you may find your answer.

[ww2steel]

I have searched all under Madmatt, Moon, Battlefront, and Battlefront.com. The long lists kept screwing up around page 9 for some reason each time I tried. I will try to contact Charles directly.

JK: (same format as before: 0°, at game pub. ranges)

2cm L/55, AP shot, CMBB 31 23 13 3

2cm L/55, AP shot, CMAK 36 24 12 2

(at the other end of the spectrum)

8.8cm L/56, APCBC , CMBB 154 142 129 105

8.8cm L/56, APCBC , CMAK 170 157 142 116

So, in these few cases at least, HE is better on the East Front, where the harder armor protects better against AP? AP does better against western RHP, which is made to protect more against attack from a howitzer perhaps? This makes sense, but I'd love to back it up with info from Battlefront.

Mike

[flamingknives]

IIRC, the armour tables are vs. a typical opponent. So something like an M4 for CMAK, and a T34 for CMBB.

Hardened armour is more effective vs AP projectiles, but more brittle and subject to shatter when hit hard with a large projectile or HE.

[Battlefront.com]

Hi Mike,

Very interesting project you're working on. I'll do what I can to help you out.

The main problem with showing the data visually is that there are a lot of equations going on under the hood of CM that don't translate well into predictable numbers. Or at least not cleanly all the time. More than likely the effects are very sensitive to things like distance and approach angle. In situation x you get result Y, out a further 10m or off by 1/2 of a degree you get result z. And of course probability comes into play quite heavily, with constricted randomness as well. There are also vehicle, or side, specific factors that come into play. For example, a shot trap, weak point, or poor quality shells of a specific type.

What this means is that the best your documentation can do is show what is the most likely result between a matchup rather than offering a wide range of results based on the myriad of variables that can't possibly be simulated outside of CM.

As has been pointed out, the results in the armor penetration charts are against "typical plate" of the opposing side. Generally this is good enough since the same type of plate is usually used by an entire nation's worth of vehicles. The problem is this isn't always the case. The Soviets, for example, had their own domestic vehicles as well as US and British Lend Lease. Soviet vehicles were up against German, Hungarian, Italian, and French equipment. That's a pretty varied bunch of stuff!

In general face hardened armor is better at defeating armor piercing shells. It's hardness hopefully bridges the "shatter gap" and causes the incoming AP rounds to literally shatter on the super hard hardened outer surface. The problem with hardening is that the rest of the armor is softer. When an AP round "overmatches" the resistance of the face hardening, the result is often catastrophic failure of a large section of the armor plate.

The problem for users of face hardened armor, such as the US, is that the Germans had weapons with extremely high kinetic energy and mass. Worse still, they were going against armor that was really not all that thick. This meant that the German rounds could often defeat the hardening and then slice right through the remaining armor. There are many pictures out there of extremely large amounts of damage to the plate from hits.

Cast armor is similar in that it offers very good rounded surfaces, however when hit too hard it just shatters. On top of that, casting is a very difficult process and therefore there was a practical limitation on the size of the pieces, such as the turret on a Matilida.

Spaced and bolted/welded on armor offer different types of resistance. Spaced works best against HEAT type projectiles because they prematurely detonate the round and cause the gases to dissipate instead of concentrate because the path of least resistance is inbetween the armor plates, not directed through the inner surface. Standup distance, therefore, is messed up.

Bolted/welded add on armor does nothing for standoff distance, but metallurgically it doesn't offer as much protection as a single piece of armor of the same thickness. The rule of thumb is that 200% (2x) thickness add on armor offers 50% (1.5x) more resistance. Yet the vehicle suffers the penalty of having "dead weight" on its chassis.

Armor quality was sometimes quite poor, especially for the Soviets and for late war German tanks. This effectively lowers the resistance compared to higher quality plate of the same thickness and hardening style. Same with certain ammo. The US 76mm AP rounds, found in the Hellcat for instance, were overhardened and therefore suffered the same sort of fate that face hardened armor suffers from. If the armor offers good resistance then the round tended to shatter instead of penetrate.

All kinds of stuff like this in the game

I don't know if this helps, but at least now you know some of the areas that aren't easy to cover.

Steve

[cinacchi]

Hi Steve,

I read with great interest what you wrote about the equations governing the game. Since I'm a Physics student, I was curious to know if in the code (i.e. ballistic) do you use differential equations (in the "original" form with derivative e/or differentials) or just theyr solutions form (non differential equations, coming aout from differential equations, like the first law of kinematics in the form x = x(0) + V(0)t + 1/2(a t^2), that coume out from its differential form).

When you wrote "there are a lot of equations going on under the hood of CM that don't translate well into predictable numbers" I was thinking just to differential equations...

[ww2steel]

Hi Steve, thanks for your response.

I already have calculators for slope and obliquity, taking into account published quality figures. I take into account the published stats for the different ammo (but not things like shatter gap).

I will include what you said about appliqué armor next. Just to get this accurate for CM- let me ask a little more to make sure I reflect it correctly please.

Let's take the PzIIC, Elefant and PzIIIL for instance.

The Elefant I know is a simple bolt on 100+100 over the majority of the front hull. If I interpret this correctly, this only equals 150mm plate in CM, correct?

The PzIIC is 15+20 or actually 15+10=25mm. (Which does actually mean that the 30mm PzIIF is better.)

Then the PzIIIL, since it is standoff on the front, would that still equal 50+20, 50+(10)=60mm?

Simply the equation in CM is (Base armor thickness) + .5(Appliqué thickness)= (apparent thickness) Correct?

Can you tell me what standoff armor does to HEAT in the CM engine?

Oh, also, can you clarify the Tiger's reinforced turret front and the Panther's front upper hull notes and how CM uses it.

Trying not to be greedy here. (Tell me EVERYTHING!)

I really appreciate it, just a couple of little tidbits like these give me a lot of programming time to play with! I did see Charles' graphs years ago, always wanted to do some similar, so here they are!

Thanks,

Mike

[Bannon DC]

Good to see Steve slumming in the CMX1 forums. WWII must be on his mind. :D

[Lanzfeld]

Mike,

you have a message.

[undead reindeer cavalry]

Mike,

you may find the following explanation by Charles about CM's armor penetration calculations interesting:

A kind soul on the Internet directed me to a publication from the National Technical Information Service. The publication was a research paper written by British scientists shortly after World War II that detailed their understanding of then-current armor penetration systems. The mathematics were complicated, but they worked - and of course a computer has no trouble crunching numbers like these. So little trouble, in fact, that it drew very pretty color pictures detailing probabilities for armor kills at various ranges and angles.

here is one such picture:

look familiar?

i don't know what the referred paper is, so i can't direct you to it. perhaps someone else knows it.

[undead reindeer cavalry]

see this thread:

http://www.battlefront.com/community/archive/index.php/t-24792.html

[ww2steel]

Very interesting data and equations. I would love to know more about this Livingsto/ Bird equation and how the CM peeps converted it to a penetration percentage as shown by Charles' graphs (above). I might be able to estimate these percentages based upon the above graph, but I suspect I may be very far off. (Well, far enough off to be unacceptable to the CM community.)

Mike

[ww2steel]

I looked on Gamespot under the CM screens (apparently where the above screen is located). Do any of you know where the other screens of this type are? If I remember correctly there were a couple of them.

BTW, how the heck do I edit my posts??? I'm signed in but none of the buttons (on my screen at least) allow me to edit my previous posts. (frustrating)

Thanks,

Mike

[undead reindeer cavalry]

sorry, don't know about locations for other graphs.

you understood that the main algorithms are based on the British paper, right?

otherwise:

overmatch factor = thickness of armor / diameter of shell.

overmatching occurs if the factor is less than 1. then, the effective thickness of armor is:

(armor thickness)(1+(slope multiplier-1)(overmatch factor))

slope multiplier varies per type of ammo and armor, but one standard is:

angle   multiplier

10   1.01

15   1.03

20   1.07

25   1.15

30   1.25

35   1.37

40   1.52

45   1.69

50   1.89

55   2.13

60   2.5

an example:

75mm against 45mm@60

overmatch = 45 / 75 = 0.6 = overmatch!

due to overmatch the effective resistance of armor is reduced to (45mm)(1+(2.5-1)(0.6)) = 85.5mm

[Redwolf]

I hacked the Livingstom/Bird stuff into Common Lisp code at the time and played with it a little.

The major pieces of uncertainty are:

1) to decide on the values of those variables that are shell specific.

2) computing the slowdown by air resistance. The problem here is that objects passing through the sound barrier (up or down) behave extremely erratic and the total slowdown during the transition period can be much more than you would get out of a formula just using standard fluid resistance mechanics.

I am not aware of any formula that would get you a better model of a projectile falling before speed of sound.

[ww2steel]

Thanks guys,

I understand these features (hadn't though of supersonic transition ballistics, nor do I have any idea how to simulate them). In short, I am trying to redo CM's ballistics for my graphs, but have little data to do it with. Right now I am redoing everything use equations for each ammo type and the published angles. I take into account the armor types, guessing at how BF put them into the game (like high and low hardness RHP, high and low hardness cast, etc), applique armor, armor quality, armor slope and obliquity.

One more question- does anyone know if CM1 takes into account things like the cylindrical turret of a Tiger (which should give a 'curved' effect), or does it treat everything like a KV-2 style square box with a square turret?

Mike