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StuG III Thread (and also other German vehicles I guess)


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Collimatrix, your post is based on the assumption that the propellant consists of the same components at the perfect mixture, only with one single different ingredient. If you can provide the exact compositon of the propellants used in said ammunition, I won't have an issue with your claims and agree with them.

 

However from the data available to me - and that is unfortunately neither the composition of German nor Soviet propellants, show that there is a much greater room for modifications. Some British propellants were composed of more six or more different materials, not just two or three. This means that the impact of replacing a fraction of one component with another might be a different than expected.

 

They could have dozens of ingredients, but it doesn't matter.  The vast majority of the propellant by mass is the energetic material, and there are only three energetic materials used in large-caliber gun propellant.  All the other ingredients are ancillary ingredients that do not significant contribute to the energy of the propellant.  These are ingredients like triacetin, a plasticizer, graphite, which prevents static buildup, tin, which reduces bore fouling, and titanium dioxide, which helps slow down bore erosion.  Again, the percent of propellant that is anything other than energetic material is minuscule.  Sometimes you'll see recipes that seem to call for more than 10% of non-energetic materials, but don't be fooled.  One is usually a solvent that is cured out (often in a vacuum).  The dry powder that is actually burned in the gun will have 5% or less of anything that isn't the energetic material.

 

So, to a very close approximation, the energy density of the powder will be the weighted average of the energetic components.  You'll get some slight divergence from that approximation due to oxygen balance, but IIRC the effect is fairly small for these propellants.

 

 

In the Cordite propellants, both raising and decreasing the amount of nitrocellulose could improve peformance - at least this is the case when comparing Cordite formula B with the original Cordite Mk. 1 and the Codrite formula C. At least the British propellants using nitroguanidine still had a small amount of nitrocellulose in the composition.

 

Sorry if I wasn't clear.  You would never have a propellant that's just nitroguanidine.  It would always contain some nitrocellulose.  Most nitroguanidine-containing propellants are called "triple base propellants," indicating that they are a mix of nitroglycerin, nitrocellulose and nitroguanidine.

 

The performance improvements are not necessarily a result of tweaking the proportions of energetic materials.  Look up a materials specs sheet; the energetic materials have very similar energy densities.  There is slight synergy from improved oxygen balance from blending the propellants, but again, this is slight.  

 

 

All that said, I'd like to point to the drawing I previously posted. It is from the official data sheet from WW2. As you can see it says in regards to the propellant charge: "Ladung zu etwa 2,6 kg Digl. R. P. - G 1". The "Digl" means that the propellant consists of Diglykol (diethylene glycol dinitrate) and nitrocellulose, together with centralite and sometimes potassium sluphate. It does not contain any nitroguanidine. The "R.P." describes the shape of the propellant (tube propellant). In so far your criticism of the German propellant is not appropriate in this context.

 

 

Then it's a single-base propellant that's practically identical to any other that anyone else was using at the time.  Centralite is a burn rate modifier, Diglykol is a solvent and potassium sulfate is a flash reducer.  There would be at most a few percent by weight of these ingredients in the final product.

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SH_MM; I think you missed the bit where all the tests were against a vertical plate.

And the bit where the calculated performance of PaK 40 (assuming PzGr 39 to be as fair as possible) matched perfectly with the test data with F-34 ammo as the training data.

There really isn't much secret sauce to this stuff, at least not to the point that the Germans would be getting massively different results from their projos compared to their Soviet counterparts.

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Another interesting tidbit gleaned by running various penetration figures through DeMarre:

 

The D25-T and 12.8cm PaK 44 figues are actually pretty close by either metric, with the PaK getting 208mm at 500m/0' when estimated from the D25-T's figures (157mm under Soviet Methodology). This increases only a little with the German methodology, to 219mm for the same conditions (D25-T gets 165mm if the reverse approach is used).

 

So it seems that both approaches begin to draw together once really big, energetic rounds start getting tested. More than that, it seems that the PaK 44 really does live up to its reputation, given the rather patchy and limited information I've been able to find on it.

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The performance specs I've seen for the PAK 44 are all over the place. Sometimes it's only a little more powerful than the D25-T, and sometimes it rivals the M58. I don't recall if there was ever a definitive answer on it.

I can't find much in the way of original test results either (lots of unsourced figures), so my methodology was simply to use those for D25-T as the normalisation/training data. Considering that the results come quite close to the stuff I can find, my feeling is that PaK 44 probably was capable of 200mm of penetration at the muzzle using AP.

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Another tidbit gleaned from comparing penetration and armour values: the vast majority of tanks had, at best, a qualified immunity to the vast majority of weapons over the frontal arc at combat ranges. The big exceptions here are the British, Japanese and Italians - who couldn't into armour.

It's also very apparent just how well put-together the T-34 armour package was, as it was pretty much the only medium of the war to get large amounts of immunity all around.

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Even when PAK 40s show up?

Depends which set of figures you feel are closer to the truth.

The Soviet tests seem to show that PaK 40 was marginal beyond 800m against the turret, and struggled with the hull front at any distance.

The German tests have the T-34 turret as butter at any distance, and the hull front gets ganked within 800m.

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Meanwhile; M4, Pz III, Pz IV and Panther get decent protection for the hull front and turret front at the expense of the sides being vulnerable to everything. And when I mean everything, I mean that 36mm pieces can end you if they get a side shot in.

T-34 was really unusual in being pretty tough from all aspects, and I'm sure more would have been made of this fact if the western allies had faced a significant number in combat.

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What tests are these? The ones I have show the hull to be vulnerable at 1000 meters, 800 if the track links are hit.

Just plugging the Soviet test data (from your site) into simulation.

Just over 100mm of penetration against a flat plate at 100m would intuitively struggle when faced with a 45mm plate sloped back 60'.

That the real world results were very different actually seems to indicate that the Soviet testing methodology underestimated gun performance.

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Since I'm mining this particular seam: I got thinking about what it would take to recreate T-34s relative immunity in a mid-war tank design (to enter service in 1943). This means (once you've laughed at the idea of a medium tank with 80mm of well-sloped plate on all sides) coming up with a vehicle that can resist shorter 75mm and 76mm guns from the sides and bigger stuff (long 75s, 76s, 85s, 88s and so on) from the front.

 

The detailed approach would then be to make the hull front and turret front immune to all but the most nasty stuff (about 150mm effective), have the turret sides immune to shorter 75/76mm guns beyond 500m (about 90mm effective) and the hull sides immune to shorter 75/76mm guns from beyond 800m (about 75mm effective) to prevent long-range ambushes. You would prioritise turret protection because that's where a lot of your hits are happening.

 

The end result, once you make a few assumptions and keep in line with current trends in tank development, is something like:

  • 100-120mm at the turret front (sloped back as much as possible - probably in the region of 30')
  • 75-90mm on the hull front (sloped back around 60')
  • 75-90mm on the turret side (sloped very little to preserve volume)
  • 75mm on the hull side (no slope)
  • 30-40mm everywhere else

Add in a suitably powerful gun from the current generation available to you, and what you end up with is T-44, M-26 and Centurion. Which is obvious in one way, as everyone was gathering data from the same overall set. But still interesting in that the conditions of mid-WWII seem to have produced an ideal template for a tank design to which all the winning powers then conformed. It is as if there was a (remarkably well-specified) medium tank-shaped hole out there in the world that the designers of the various nation simply filled in using the parts available to them.

 

TL;DR - tank designers from the winning nations were able to use the data available to them by the middle of the war to come up with rational specifications for a tank and then design something to fit.

 

Edit: because it's a slow day, I quickly ran through a design for a T-34 in 1943 (ie: same general armour layout but bigger). The result weights 42-odd tonnes.

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Since I'm mining this particular seam: I got thinking about what it would take to recreate T-34s relative immunity in a mid-war tank design (to enter service in 1943). This means (once you've laughed at the idea of a medium tank with 80mm of well-sloped plate on all sides) coming up with a vehicle that can resist shorter 75mm and 76mm guns from the sides and bigger stuff (long 75s, 76s, 85s, 88s and so on) from the front.

 

The detailed approach would then be to make the hull front and turret front immune to all but the most nasty stuff (about 150mm effective), have the turret sides immune to shorter 75/76mm guns beyond 500m (about 90mm effective) and the hull sides immune to shorter 75/76mm guns from beyond 800m (about 75mm effective) to prevent long-range ambushes. You would prioritise turret protection because that's where a lot of your hits are happening.

 

The end result, once you make a few assumptions and keep in line with current trends in tank development, is something like:

  • 100-120mm at the turret front (sloped back as much as possible - probably in the region of 30')
  • 75-90mm on the hull front (sloped back around 60')
  • 75-90mm on the turret side (sloped very little to preserve volume)
  • 75mm on the hull side (no slope)
  • 30-40mm everywhere else

Add in a suitably powerful gun from the current generation available to you, and what you end up with is T-44, M-26 and Centurion. Which is obvious in one way, as everyone was gathering data from the same overall set. But still interesting in that the conditions of mid-WWII seem to have produced an ideal template for a tank design to which all the winning powers then conformed. It is as if there was a (remarkably well-specified) medium tank-shaped hole out there in the world that the designers of the various nation simply filled in using the parts available to them.

 

TL;DR - tank designers from the winning nations were able to use the data available to them by the middle of the war to come up with rational specifications for a tank and then design something to fit.

 

Edit: because it's a slow day, I quickly ran through a design for a T-34 in 1943 (ie: same general armour layout but bigger). The result weights 42-odd tonnes.

So basically something like this?:

s8yWVK4.png

L97yh3K.png

 

Just a rough sketch, not a complete design. 

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What is the turret ring diameter? Also, what engine are you going to stuff in there?

Turret ring diameter would be around 1800mm, plus minus for each nation to accommodate each gun, like the 75mm L70 or 88mm L56 for the germans, 85mm for the Russians and 76mm gun for the US and British. 

Or maybe something for more bang if needed.

 

And engine:

Russia: Model V2-34 V12 diesel engine.

British: Meteor engine.

For the Germans and US, the engine compartment would have to be modified. 

 

Proportions are not up to scale, as the drawing are more made to show the concept. If ammunition should be stored next to the driver, below the turret platform or around/behind the crew is up for debate. Same goes for if the tank should use torsion bar, horstman or HVSS suspension.

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So, a couple of things:

1. I see that you share my love for low crew compartments and bustle ammunition stowage. Unfortunately, it seems that designers were less enlightened back then and had inexplicable issues with the driver lying directly on the hull floor and/or the crew grabbing ammunition from an armoured box located on the most likely part of the vehicle to get hit. As a general rule of thumb, then, I tend to assume that my WWII-era hulls should be 1.5m high and my ammunition stowage should be in the hull.

2. You've mentioned that your proportions are only approximate here. Even so, you should keep in mind that the engine compartment is going to be at least 2m long unless a transverse mounting scheme us used.

3. The general armour scheme and turret ring diameter is very much in the range for my 'ideal' 1943-data design. From there the weight will be determined by a bunch of factors, not least of which is how ruthless your designers are in saving space. It is very interesting to me that the three tanks I mentioned above range from 32 to 51 tonnes while having very comparable armour packages.

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  • 100-120mm at the turret front (sloped back as much as possible - probably in the region of 30')
  • 75-90mm on the hull front (sloped back around 60')
  • 75-90mm on the turret side (sloped very little to preserve volume)
  • 75mm on the hull side (no slope)
  • 30-40mm everywhere else

Add in a suitably powerful gun from the current generation ...The result weights 42-odd tonnes.

 

pixFS7v.jpg

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pixFS7v.jpg

I knew you'd get a kick out of that :)

My simulated design actually used an un-rationalised armour scheme: 80mm all around the hull and 100mm on the turret, all sloped as much as possible (mentioned at the beginning). So IS-2 is actually more like an updated T-34 (in terms of relative armour protection) plus a few years worth of experience and data.

The 'optimal' 1943 medium armour package is, again, almost an exact match for T-44.

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So, a couple of things:

1. I see that you share my love for low crew compartments and bustle ammunition stowage. Unfortunately, it seems that designers were less enlightened back then and had inexplicable issues with the driver lying directly on the hull floor and/or the crew grabbing ammunition from an armoured box located on the most likely part of the vehicle to get hit. As a general rule of thumb, then, I tend to assume that my WWII-era hulls should be 1.5m high and my ammunition stowage should be in the hull.

2. You've mentioned that your proportions are only approximate here. Even so, you should keep in mind that the engine compartment is going to be at least 2m long unless a transverse mounting scheme us used.

3. The general armour scheme and turret ring diameter is very much in the range for my 'ideal' 1943-data design. From there the weight will be determined by a bunch of factors, not least of which is how ruthless your designers are in saving space. It is very interesting to me that the three tanks I mentioned above range from 32 to 51 tonnes while having very comparable armour packages.

1. Yes, I always want my designs to be as volumetrically efficient as possible, which means minimizing to height as much as possible, without impacting crew ergonomics.  But 1,5m seems a tad bit tall. Considering a sitting driver usually is about 1m tall, then add about 80mm for hull roof and belly, which lands at 1,1m, and then add the suspension which would be 0 with horstman and about 100mm with torsion bar I assume. So about 1,2m. The engines used at the time seem to be about 1m tall, except for the German engines which are really tall and short for some reason. So, 1,3-1,4m max I would say. 

 

2. Yes, the engine is transversely mounted. The reason is simply because you decrees the size of the engine compartment by 20-30%. Well, except for the Germans, because their engines are too short.

 

3. Yeah, they all do. However they came too late, and ended up being under armored when they were accepted into service. Well, except the T-54. The Centurion is quite a bad tank armor to weight wise for me. 

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Time marches on, of course. What would have been fantastic for WW II ended up looking a bit mediocre once the Soviets made yet another leap in design and produced T-54/55 (seriously, an armoured clash in 1950/51 would have ended horribly for the Brits and Americans).

Then again, both Centurion and Pershing proved to have substantial upgrade potential. So at least some of the puffiness was worth it.

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Time marches on, of course. What would have been fantastic for WW II ended up looking a bit mediocre once the Soviets made yet another leap in design and produced T-54/55 (seriously, an armoured clash in 1950/51 would have ended horribly for the Brits and Americans).

Then again, both Centurion and Pershing proved to have substantial upgrade potential. So at least some of the puffiness was worth it.

You have a tank that's bigger and heavier than the IS-3 in the Centurion, it better have some upgrade potential or it would be a most inefficient design

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