I hope this may help
I hope this may help
Right now for MN; I'm actually in the middle of prototyping a new way of taking into account some of the additional elements of armor and a different set of numbers used in determining penetration. It's still in the works, but if it turns out to work well and match up decently with real-world tests and real-world evidence, it'll make it's way in a future MN release.
Jacob de Marre equation is a convenient way to resolve this very complex penetration issue. But we need to adjust some variables to get approximate results.
The equation is below:
b*Ｋ^1.43*secα^n=Ｖ^1.43*m^0.715/d^1.07
b: the armor thickness, eg. panther upper glacis =85mm
In russian and allied tests it's 85mm while in some recources it's 80mm.
K:the quality of armor ,it depends on both BHN(hardness) and toughness. Toughness is relative to steel ductibility. A good armor is the combination of good haedness and good toughness while these two usually conflict each other. Very high BHN armor is usually brittle when hit by a large caliber/hard projectile so high hardness is NOT always a good thing for armor.
Toughness depends on not only armor itself characters determined in armor's production process, but also the way we use it. For example , T34's 47mm front armor has very high hardness aound 400 BHN(I can't remember exactly.), so T34's armor is brittle, however, this armor is 60 degree sloped, which means the high sloped amor (47mm/60d) stretch ablility is much better than vertical one (47mm/0d). By this means, we improve the toughness of a brittle amor. Of course, the projectile'a caliber can also impact the toughness performence of armor because armor need more stretch ability to cope with larger caliber projectile.
It's easy to understand: when you double the caliber, the hitting area on targert is 4 times as before, but the projectile weight is 8 times bigger(approximately). We called this phenomenon as
scale effect. Therefore, the T34's front amor has both good hardness and good toughness when facing small caliber projectile(40mm,50mm,57mm) but handling german 88mm shell is another story.
α: actual angle between projectile trace and armor normal direction, e.g Panther's upper glacis sloped angle is 55 degree from vertical, but the actual angle is determined by both sloped angle and side way angle.
If we fire a panther glacis from 30 degree side way, that is to say we are in panther's 11 or 1clock. The actual angle α is calculated by this equation.
cosα=cosβ*cosγ
β, sloped angle, 55 degree for panther
γ,side way angle, 30 degree in this story
α=60.2 degree.
Since is trigonometric function is NOT linear, changing 55d to 60.2 d, the 85mm armor can get much much more stopping power than changing it from 20d to 25d.
In WWII, in my opinion, the most effective slope angle is from 50d to 60 d, with these angles, the extra slope efffect is maximized.
n:slope coefficiency It 's a very complex factor. "n" is always bigger than 1, if n<=1, the T34/panther designers=idiots. To be frank, the most complicated issue in sloped armor penetration is the determination of "n". I'll talk about "n" later.
v: projectile residual velocity At 0m, v=muzzle velocity, the residual velocity is important and determined by projectile's weight and aerodynamics shape(ballistic coeffeciency?).
m: projectile mass
d: projectile caliber
The Left side of Jacob de Marre equation is sloped armor's stopping power, the right side is projectile's penetration power. If right side >left side,the armor penetrated.
"n" is relevant to many factors, such as projectile hardness(BHN),shape and T/D.
T/D is the ratio of armor thickness to caliber.
Jacob de Marre equation is of 19 century when sharp tip,solid shell were popular, but in WWII, sharp tip projectile was obsolete. So it's very hard to calculate the "n" of most WWII projectiles.
For steel,sharp tip, solid AP shell:
n=[-0.08*(T/D)^2+0.66*(T/D)+0.52]/0.7
Note that n>=1, when n=1, the armor is vertical. If n<1, the desginers of sloped armor in WWII are idiots because the steel consuming of b(mm)/α(degree)sloped armor is nearly same as b/cosα (mm) vertical armor. Sloped armor designers in WWII are not idiots, so real equivalen thickness must be bigger than b/cosα (mm), furthermore, APCBC,APBC's designers are not idiot either, so real equivalen thickness must be smaller than de Marre result.
The boundary of real equivalent thickness is below:
(b/cosα, de Marre result)
We can estimate the real equivalent thickness by average: (b/cosα+de Marre result)/2.
For example, when 85mm/55d armor hit by a 122mm APBC shell, the boundary is (148mm,179mm),average is 164mm. The caculation error is within 5-10mm! because the real equivalent thickness must be far from the upper limit and lower limit, otherwise the design of both sloped armor and apcbc/apbc are meaningless.
Fortunately, russian 122mm D25T gun's BR471 (AP)projectile is exactly the solid,sharp tip shell, and BR471 is perfectly suitable for de marre equation. You can check the accuracy of de marre equation by inputing 30 degree penetration data.
Last but not least, the thickness is relevant to armor quality. For thiner armors such as from 40 to 152mm, they can be treated to a high BHN level, of course, the process is time/cost consuming ; those thick armors can hardly be treated to high BHN. That's why elephant front armor is consist of two 100mm armor.
So the 152mm+ mumbers on penetration table are misleading us. For example, the allied/german APCR penetration and US 90mmL70 apcbc, german 88mmL71 apcbc,etc.
For a specific projectile, everything else being equal, the penetration is directly proportional to V^1.43. This can explain the kwk43 is overmodelled.
In WWII, the most successful sloped design is 50-60 degree, 80-120mm thick.Those sloped armor designs have two advantages:
1) the extra sloped effect. (n>1)
2) can use thiner armor with high quality
In RO, we can adjust "k" for different armors and "n" for different projectiles by checking the WWII combat and test reports.
For example, by checking histotical performance, we determine the StugIII's front armor quality, k=2400( just an assumption), 800m away , StugIII's 11 clock. a T34-85 fire a APBC shell and hit the front armor.
Computer will input the APBC' shell's residual velocity, mass, caliber and calculate the penetration power=P, on the other hand, input armor thickness, actual angle, k, and n to calculate the stopping power=S, if P>S, armor penetrated.
BTW, russian never used apcbc shell in WWII, and every T34-85 in 1944 had 4 APCR shells. So the shell types in RO is not enough. And most shells are supersonic, so tanks get hit at first, then gamers hear the sound. isn't it?
I think Amizaur tried to bring this more in line with his last version of AB, and I know he wanted to continue refining it for the next version, but I think he's moved on from RO ![[TW]Wilsonam](/data/avatars/s/0/10.jpg?1568638684){kind=avatar}
