Questions regarding to the performance of German 20.3cm guns

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cobralion
Junior Member
Posts: 5
Joined: Sun May 26, 2019 6:52 pm

Questions regarding to the performance of German 20.3cm guns

Post by cobralion »

While calculating the performance of SK20.3/C34 based on ADM 213/951, it seemed like there is a mistake of its Cg value.

On ADM 213/951, SK20.3/C34 was suggested to have a Cg value of 675 for Psgr against KC, however, comparing to Ch value of 650 for Psgr against KC, on graph against same thickness of armor, it seemed like there will be a crossing between heil line and grenze line if Cg=675 was true.

According to my calculation based on Awa A IA 100/40 g.Kdos, I personnally believe that 635 should be SK20.3/C34 Psgr's true Cg value against KC.

The rest Ch=650, Bh=2.5, Ch=1.7 works fine for SK20.3/C34 Psgr against KC

I'm also asking help for calculating SK20.3/C34's Spgr Bdz against WH, the C values and B values I found were very chaotic.

For WH from 180mm to 60mm (10mm, 1 result), the corresponding C values are:
750.6
744.0
735.6
730.2
715.5
711.5
693.3
683.7
669.7
654.0
633.0
619.6
605.0

The B values seemed indeed large for thicker WH plates' curves (180mm, 170mm ......), but fell to smaller values for thineer plates' curves, they were so disporportional I don't even think they should be placed here.

By the way, it seemed like UK MKI 38.1cm gun in German assumptions had Ch=680, Bh=3.13, Cg=675, Bg=2.25, for KC plate and Ch=Cg=660, Bh=Bg=3.8 for WH plates.

Any one know where to find Awa A IA 100/40 g.Kdos Heft b, c for German assumptions on foreign guns' performances in pdf?

ADM 213/951
German steel armour piercing projectiles and theory of penetration
https://web.archive.org/web/20200124093 ... chive.html

Awa A IA 100/40 g.Kdos
Unterlagen und Richtlinien zur Bestimmung der Hauptkampfentfernung und der Geschosswahl
Excel
https://www.kbismarck.org/forum/viewtop ... =36&t=3291
cobralion
Junior Member
Posts: 5
Joined: Sun May 26, 2019 6:52 pm

Re: Questions regarding to the performance of German 20.3cm guns

Post by cobralion »

I will post some personnal use of Gercke-Tierberg formula from ADM 213/951 here:

Original state of Gercke-Tierberg formula:
V = C * (D/G)^0.5 * S^0.8 / (sin a)^m
m = 0.5 + Bx
x = (D/G)^0.5 * S^0.8

Conversion to C:
C = V * (G / D)^0.5 * (sin a)^m / S^0.8
For normal attack, a = 90 degree:
C = V * (G / D)^0.5 / S^0.8

In ADM 213/951 for the Tierberg section, we can see although abbreviations were different, it showed same function as Gercke section, the only difference was that for normal attack (90 degree in formula), Tierberg neglected the influence of B (in formula, when angle equals 90 degrees, (sin a)^m = 1) and assumed that under normal attack only C value would show its effect.

Conversion to B:
B = ( log( C/V * sqrt(D/G) * S^0.8, sina) – 0.5) / (sqrt(D/G) * S^0.8)
Bill Jurens
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Joined: Mon Oct 18, 2004 4:21 am
Location: USA

Re: Questions regarding to the performance of German 20.3cm guns

Post by Bill Jurens »

@ Cobralion.

My thanks for posting these equations, but they are not of any practical use unless unless variables and units are specified, or unless one has ADM213/951 at hand, in which case the equations are actually redundant. It's nice to know, for example, that m = 0.5 +Bx, but not very handy unless the user knows exactly what Bx is.

In that regard, could you provide more detail, and perhaps one or two worked examples?

Bill Jurens
Thorsten Wahl
Senior Member
Posts: 790
Joined: Mon Apr 27, 2009 4:17 pm

Re: Questions regarding to the performance of German 20.3cm guns

Post by Thorsten Wahl »

Adm 213... gave only general values from memory.

The individual values used in the performance charts differ slightly from these.

I have reproduced all values.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!
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