Re: Facing was: Well, too interesting

From: "Oerjan Ohlson" <oerjan.ohlson@telia.com>

> KHR wrote:
> 
> >At least for WWII tanks, the optimum orientation was NOT facing the
enemy
> >directly, but rather, when the diagonal pointed towards the enemy!
 
> But your main point is very good: for many vehicles, DS2's way of 
> determining the angle of attack in the diagram on p.32 isn't very 
> appropriate - and for some models, eg. GZG's DSM-116 Poruzh with its 
> wedge-shaped hull, it can be pretty difficult to apply the p.32
diagram 
> anyway. I'd prefer to use simple 90-degree arcs instead, mainly
because it 
> is simpler to use in play but also because it takes some of the
effects of 
> glancing fire on the forward side armour (which in reality is
effectively 
> part of the frontal armour anyway) into account.

The only set of rules that I know of that attempted to take into account
facing and slope to the nth degree was Tractics, by Guidon Games, which
later became Tactical Studies Rules, and thence TSR.
http://www.theminiaturespage.com/rules/ww2/tractics.html

The chances though were all wrong : the optimum tank-killer was a
quadruple
50 cal MG on a half-track. With 24 shots per turn, the odds were that at
least one would hit a turret ring, vision slot, track pin etc etc
causing
a mobility or firepower kill.

OO is the expert on exterior ballistics : but I've done a little study
on
effective armour thickness of vehicles. The problem is that to say that
"Vehicle X has thickness Y mm at a slope of Z degrees" is a gross
simplification. Depending upon the angle of incidence of the vehicle,
the type
of terrain it's going through, the range and the type of ammunition
being
fired, you can get anything from 100cm at 85 degrees through to 2cm at 0
degrees
(ie episcope etc).

Hit one place, you have to go through metres of armour - hit 2 cm away,
and
you can jam a turret ring with even a rifle bullet. And a rifle bullet
that
hits the open muzzle of a tank gun while the breech is open can KO
anything.

What tank designers do is play the percentages: they skimp on armour in
areas
normally covered by terrain, they skimp on sides, top and rear. Normal
AP
shells that hit the top of tanks do so at extreme angles of incidence,
over
85 degrees. Long-rod penetrators basically don't even do that. If you
divide
the silhouette of a tank into 100 eqaul-sized areas, you may find
something
like 5 having 2 metres+ armour, 5 having 1.5 metres, 85 having 1 metre,
4 having
5cm, and 1 having 2cm.

And even that's a simplification: for example, a relatively slow-moving
round hitting a sloped plate will tend to rotate and penetrate at nearly
normal
incidence, due to drag. The there's shots shattering vs face-hardened
plate,
ballistic caps to prevent this, and then you have long-rod penetrators
which
are best described as fluids hitting a fluid wall, and HEAT rounds which
if
they're exactly right have metres of penetration, but slightly wrong and
it's
at best 20 cm. (No, they're not plasma jets, the copper lining becomes a
slug
that moves at about 5 km/sec, though I'm sure OO can give more details).

I've done some modelling in insanely intricate detail of shells of
various
types hitting tanks. But a reasonable approximation, within cooie 
of the most detailed and complicated simulation, is to just roll a D6 -
take 80% of the tank's notional armour, and add 10% per score, so result
is 90%-150%.
This doesn't work for all vehicles, or all angles, but close enough for
the majority. There's always oddities like the Archer, or even
up-armoured
Pz IIIJs, where half the time the effective armour is about 4 cm, the
other
it's more like 10. Always remember though that crews often weld tracks
etc
on vulnerable points, but that externally-carried gear can catch fire
even
from 20mm. Penetration does not equal KO, you can penetrate without KO,
and KO
without penetration.
2cm.

Have a look at the WRG rules for AP - they took actual combat results,
then
came up with the simplest method that resembled the reality. They seem 
overly simplistic, but the results they give are more accurate than more
complex systems.