Effective armor

[Gryphon]

Hello there,

Does anyone know how to calculate effective armor? eg. 80mm@55 degrees is how much mm@0 degrees?

i've been trying but my math skills have gone lost Hey, that's what u get after a long holiday

Thanks alot in advance

Gryphon

[John D Salt]

Originally posted by Gryphon:

Hello there,

Does anyone know how to calculate effective armor? eg. 80mm@55 degrees is how much mm@0 degrees?

i've been trying but my math skills have gone lost Hey, that's what u get after a long holiday

Gryphon

Maths won't help all that much. You can mess around with cosines if you like, and indeed that's a pretty good way to do things for HEAT rounds and modern long-rod penetrators. For WW2 vintage AP (yes, yes, and APC, APCBC, APHE, APCR, APCNR and APDS) rounds you will probably do better to use the table I include here(text formatting permitting), which is what was used by the US and UK at the time:

slope multiplier

10º 1.01

15º 1.03

20º 1.08

25º 1.15

30º 1.25

35º 1.37

40º 1.52

45º 1.69

50º 1.89

55º 2.13

60º 2.5

This is adapted from PRO document WO 185/118, "DDG/FV(D) Armour plate experiments". The values are read from an American armour basis curve, which it was suggested be adopted as an agreed standard as it did not differ greatly from that previously used in Britain.

I hope it's obvious enough how to use the table. To find, say, the equivalent of 45mm of armour sloped at 60 degrees (as on the glacis of a T-34) multiply the plate thickness by the multiplier for 60 degrees -- so, 45 x 2.5 = 113mm.

This adheres to the WW2 Anglo-American convention of citing the angle from the vertical, not the WW2 German and modern NATO convention of angle from the horizontal.

Notice that the benefits of slope get better than a plain cosine rule would indicate as slope increases; using a cosine rule, the T-34 glacis would be worth only 90mm.

The document I took the figures from also contains the following cautions about using armour basis curves:

"It is considered, however, that the facts are too complex to be represented even approximately by any single armour basis curve, and, as illustrated in figures I to V, the armour basis curve varies widely according to the type of projectile and plate attacked."

"...in the case of the 6pdr the armour basis curve is wrong by 7% and in the case of the 2pdr wrong by 28%."

The "too complex" facts include armour and projectile quality and hardness, the effects of piercing caps, and a whole bunch of stuff that I believe CM:BO probably deals with rather better than was possible even for research establishments during WW2.

All the best,

John.

[Gryphon]

Thanks for the info, guess my math ain't that bad afterall

Regards,

Gryphon

[Dschugaschwili]

The effective armor depends on the projectile type and the armor slope.

For hollow charge ammo (Bazooka, Panzerfaust, 'c' ammo from guns, etc.) the cosine rule is (apparently) used to determine effective armor thickness.

For 'normal' ammo ('a' ammo from guns, probably also 'h' ammo) the cosine rule is quite accurate to about 40°, after that the effective armor is more than predicted by this formula.

For 'special' ammo ('t' ammo from guns) sloped armor is even worse. Generally 't' ammo has better penetration than 'a' ammo from the same gun against slopes up to about 60°, and less against greater angles.

Dschugaschwili

[wbs]

What is the "cosine rule" to which y'all are referring?

[Mattias]

That would be the one that tells you the "actual" thickness of a sloped armour

100mm @ 30 degrees for example:

100 / sin 30 = 200

Thus the thickness of 100 mm armour angled at 30 degrees is 200 mm "as the AP flies".

M.

[wbs]

Okay, Thanks Mattias.

[DaveN]

I think armor quality also comes into play here...so with that added to the equation a T-34 has 1mm..