Weight distribution on different tanks.

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Stugbit
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Weight distribution on different tanks.

Post by Stugbit » 14 Nov 2018 23:37

Guys, I would like to see the weight distribution difference between some tanks of the Ostfront:

Soviet BT, T-34 and KV tanks,

German Pz II, III and IV tanks.

(in different versions, if possible)

Would any of you have this information to share here with us? It`s a math I guess.

Best Regards.

critical mass
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Re: Weight distribution on different tanks.

Post by critical mass » 15 Nov 2018 14:18

What kind of weight distribution are You referring to?

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Stugbit
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Re: Weight distribution on different tanks.

Post by Stugbit » 15 Nov 2018 16:36

critical mass wrote:
15 Nov 2018 14:18
What kind of weight distribution are You referring to?
I`m referring to the weight on tracks width. For instance, they say that the T-34 tank would have much better mobility on the snow than the Pz III because it had wider tracks. I would like to make a comparison between those tanks. There`s actually a calculation that could be made to reach the real number.

critical mass
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Re: Weight distribution on different tanks.

Post by critical mass » 15 Nov 2018 18:33

That´s netto or nominal ground pressure.

However, ground pressure is a poor proxy for cross country mobility because it ignores variances in pressure along the length of the track. Such a procedure is ok vs hard surfaces where the transfer mechanics are rigid and sinkage is a non factor but on softer ground, where the vehicle sinks in local stresses caused by the pressure rise of the roadwheels make for significant deviations from the hard surface interaction mechanics. The tracks themselves are flexible -along with the soil, which is partially depressable and therefore one is confronted with a mechanic which does not represent a rigid transfer medium anymore.
Rowland worked out the principles. Some of his research papers can be found in the internet. He and later Ogorkiewicz note that a high number of small road wheels will be benefitial in soft soil interaction (f.e. Churchill, Mathilda, IS) but create more rolling resistence than large diameter road wheels (some designs got around this with a large number of large roadwheels using interlocked or overlapping layouts with excellent results).

For the MMP to calculate You need
W= weight of vehicle in KN
n= number of roadwheels per side
b= track width in m
p= pitch of track links, in m
d= diameter of roadhweels, in m

MMP= .63W/((n x b x c) (p x d)^.5)
where c is the ratio of actual plan area of a track link to the product of p and b
he gives the following data:

PzIIIJ: 220KN/m^2
PANTHER: 150KN/m^2
SHERMAN VVSS: 282KN/m^2
SHERMAN HVSS: 205KN/m^2
Churchill Mk IV: 177-217 KN/m^2 (depending on sinkage)
BT-5: 175KN/m^2
BT-7: 240 KN/m^2
T-34/76: 174KN/m^2
CROMWELL MK IV: 352KN/m^2
CROMWELL MK VII: 300 KN/m^2
TIGER Ausf. B: 184KN/m^2
ELEFANT: 370KN/m^2
E100: 250KN/m^2
MAUS: 470KN/m^2 (hardly readable in my copy)

If one uses MMP as a proxy of soft soil interaction, the thesis of improved cross country mobility of BT-5 and T34/76 vs Pz-III can be readily confirmed.


The MMP of some AFV by Ogorkiewicz are only slightly different from those of Rowland above:

COVENANTER: 370KN/m^2
MATHILDA II: 252KN/m^2
CROMWELL IV: 368KN/m^2
CENTURION V: 275KN/m^2
TIGER Ausf. B: 190KN/m^2
PANTHER: 157KN/m^2
T54: 242KN/m^2
LEOPARD 1: 223KN/m^2

Ogorkiewicz, R.M., Technology of Tanks Part I (Coulsdon 1991), pp.346-348.

hope it helps,
cm
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Stugbit
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Re: Weight distribution on different tanks.

Post by Stugbit » 15 Nov 2018 23:06

This is amazing! Thank you very much for this information, Critical Mass!

admiralTANK
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Re: Weight distribution on different tanks.

Post by admiralTANK » 15 Jul 2021 06:38

I want to use the equation myself but when trying to find the Sherman's Kn/m^2 I got a vastly different number on orders of magnitude larger. I do not understand "c" as shown in the MMP equation below. I believe that is the problem.
critical mass wrote:
15 Nov 2018 18:33
For the MMP to calculate You need
W= weight of vehicle in KN
n= number of roadwheels per side
b= track width in m
p= pitch of track links, in m
d= diameter of roadhweels, in m

MMP= .63W/((n x b x c) (p x d)^.5)
where c is the ratio of actual plan area of a track link to the product of p and b
If the "actual plan area" is the area that is useful on the track I have no way of finding this out and making a "ratio" with the prpduct of length and width (p x b). I tried bruting through without a ratio. That is all I could find without c existing elsewhere.

admiralTANK
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Re: Weight distribution on different tanks.

Post by admiralTANK » 15 Jul 2021 06:46

critical mass wrote:
15 Nov 2018 18:33
For the MMP to calculate You need
W= weight of vehicle in KN
n= number of roadwheels per side
b= track width in m
p= pitch of track links, in m
d= diameter of roadwheels, in m

MMP= .63W/((n x b x c) (p x d)^.5)
where c is the ratio of actual plan area of a track link to the product of p and b
Could someone explain "c?" I don't understand what the actual plan area of the track is and how to get it or the ratio.

Peasant
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Re: Weight distribution on different tanks.

Post by Peasant » 15 Jul 2021 14:43

admiralTANK wrote:
15 Jul 2021 06:46
Could someone explain "c?" I don't understand what the actual plan area of the track is and how to get it or the ratio.
It's a constant specific to a given design of tracks. For most cases, it should be slightly less than 1. I would use 0,9.

critical mass
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Re: Weight distribution on different tanks.

Post by critical mass » 25 Aug 2021 13:01

image "c" as a coverage facor, showing how much of the pitch x tracklength footprint area of a tracklink is actually in contact with soil and presents an interface.

Stiltzkin
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Re: Weight distribution on different tanks.

Post by Stiltzkin » 31 Aug 2021 13:07

Could someone explain "c?" :
https://www.slideshare.net/wolfhag/trac ... d-pressure
Here are Rowlands original words.

Note that these are soil insensitive calculations and do not have track-terramechanics interaction, but still prove useful for a general overview. You would need something like a NTVPM predictive model (Wong, Bekker), in which the results can vary of course. It also depends on whether they are dry or combat weights.
13-Table6-1.png

The index of efficiency as Pmax/Pmean is also of interest (notice the differential between tyres and tracks), e.g.:

Mark V: 1.46/1.63 (@0.25 sinkage)
Churchill (Mk.IV): 2.36/2.54 (@0.14)
Cromwell IV/VII 3.4/3.15
Panzer III: 2.4-2.7
Panzer IV G: 2.1
Panther (Ausf.D): 1.72
Tiger I (E): 1.98-2.01
Tiger II: 1.7
Elefant: 3.5
BT-5/7: 2.35/3.0
T-34/76: 2.5-3.0 (1943)
Sherman (HVSS/VVSS): 2.82
Sherman VC: 3.07
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