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11 hours ago, LoooSeR said:

 

 

@LostCosmonaut

Are mechanical assisted loading mechanisms/mechanised ammoracks a thing in this universe?

 

Not really, there's some limited mechanical assitance (i.e. to ram the round forward once you put it in the breech), but getting the ammunition from the rack to the gun is still done by hand.

 

The obvious exception is if you have a self contained autoloader. Won't work for large rounds, but there's historical precedent for autoloading 75mm guns in this timeframe;

6a1af0218cda80dbf3f9ca3193d15c44.jpg

 

This does have the limit that you can't select the ammo type, less capacity, added weight, etc.

 

 

 

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I’ve been meaning to ask this, but how do I calculate propellant mass for my shell? I have a desired velocity I want to achieve, but have no idea how to calculate anything with the data I have. Any suggestions? 

 

Thanks in advance, Lord James. 

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2 hours ago, Lord_James said:

I’ve been meaning to ask this, but how do I calculate propellant mass for my shell? I have a desired velocity I want to achieve, but have no idea how to calculate anything with the data I have. Any suggestions? 

 

Thanks in advance, Lord James. 

A hacky way is to use the available energy density of the propellant in a known gun/cartridge combination and scale accordingly. It won't be completely accurate but you'll get within a few percent.

 

Tank designer also has some propellant energy density stuff that it then does arcane calculations with to estimate a velocity for a given shell diameter/shell weight/tube length combo.

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3 hours ago, Jeeps_Guns_Tanks said:

I wonder if you could put the stats into something like steel panthers and run some tests on the tanks... 

 

I've been using the Tank archives penetration calculator (in DeMarre mode) with the nearest known gun as a reference. However, the results differ wildly across different nations, ie: my 80mm gun gets 116mm penetration on the flat at 500m using the D-5-T, but 135mm using kwk 36. And thats using the 'normalised' comparative data from Wikipedia.

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2 hours ago, Toxn said:

I've been using the Tank archives penetration calculator (in DeMarre mode) with the nearest known gun as a reference. However, the results differ wildly across different nations, ie: my 80mm gun gets 116mm penetration on the flat at 500m using the D-5-T, but 135mm using kwk 36. And thats using the 'normalised' comparative data from Wikipedia.

Well IIRC the PzGr 39 was actually a very good shell against unsloped armor, while the BR-365 was uncapped and had a larger filler cavity, reducing its penetration. Try DeMarre-ing similar shell designs from different guns, say PzGr 39 from the KWK 36 and KWK 40.

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I don't think that I'll be able to deliver a proper entry this time around, but I'll probably try to at least refine my mockup so that I've got something pretty to post that's in the spirit of this competition.  I've also got to wonder if I'm partly to blame for the sudden trend of rear turreted light tanks with starship-esque turrets (with mine itself just being a copy of the Teledyne expeditionary tank). 🤔🤔

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1 hour ago, N-L-M said:

Well IIRC the PzGr 39 was actually a very good shell against unsloped armor, while the BR-365 was uncapped and had a larger filler cavity, reducing its penetration. Try DeMarre-ing similar shell designs from different guns, say PzGr 39 from the KWK 36 and KWK 40.

Shell construction definitely plays a part, yes.

 

My main point here was more to point out that penetration values will differ significantly depending on your assumptions going in, and for us not to put too much emphasis into them beyond giving a general indication of the potential of the gun. I should also really put my money where my mouth is and round my own penetration figures off to reflect this as well...

 

Edit: I should also note that when checking my 80mm design I used all of the following guns as DeMarre references: 76mm F-34, 85mm ZIS-S-53, 75mm M3, 90mm M3, 75mm KwK 40, 88mm KwK 36. Then I did the scientific thing and... took the one that looked better for my submission.

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19 minutes ago, ApplesauceBandit said:

I don't think that I'll be able to deliver a proper entry this time around, but I'll probably try to at least refine my mockup so that I've got something pretty to post that's in the spirit of this competition.  I've also got to wonder if I'm partly to blame for the sudden trend of rear turreted light tanks with starship-esque turrets (with mine itself just being a copy of the Teledyne expeditionary tank). 🤔🤔

I think we're all prone to outbreaks of cleft turret syndrome...

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10 hours ago, Lord_James said:

I’ve been meaning to ask this, but how do I calculate propellant mass for my shell? I have a desired velocity I want to achieve, but have no idea how to calculate anything with the data I have. Any suggestions? 

 

Thanks in advance, Lord James. 

 

You can actually use the Powley computer to do this. Just remember that a grain is 1/7000th of a pound. Override the pressure computer and use 45500 CUP.

 

The mass of propellant is equal to the internal volume (net capacity) of the round times the loading density. When in doubt, use 0.90 for the loading density.

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Driver's hatch is now a thing:
LRPcvrK.png
Turret had to be slightly raised and enlarged to ensure the gun clears the hatch and periscopes at full depression.
For those wondering, yes the driver is mildly supine. I didn't model an IR-capable hatch because I'm lazy and didn't want to make yet another component so I just used the standard periscopes.
This swinging hatch design with the periscopes mounted  is inspired by the Leclerc and Leopard 2. The problem with it is that the resulting access hole is smaller than the hatch dimensions would suggest, as the periscopes must remain within the hull. For early IR, which is much larger than natural-light periscopes, the solution is to have the driver dismount the scope before opening the hatch. The IR periscope needs a rotating mount as there's only one, with a limited FoV.
but maybe that can be handwaved as the head being the same as the daylight periscope and therefore fitting in the same well.
Clearance illustrated:
NgXh5by.png
The commander has some, if limited, vision over the GPS even at full depression, allowing H-K operation. The cupola is fitted with commander's traverse and elevation override, with slew-to-cue.
I'm really liking how this is shaping up.

EDIT: current weight, including hull, turret, gun, extras, final drives (modeled as part of the hull for now) tracks and suspension come out at 30 tons.
To do this some densities were rectally extracted (wheel hubs include ball bearings and quite a bit of air, I approximated it as half empty, likewise most of the volume of the wheels are rubber)
So assuming suspension is 8-10%, tracks 8--10%, armor 50%, and the gun 5-7%, this means I've got around 70%-75% of the weight accounted for. This in turn leads me to a final weight of around 40-42 tons. Good.

The tank now also has a name:
XM-2239 "Norman"
Named for General Stormin' "did you hear he died" Norman Schwarzkopf.

Edited by N-L-M
weights added, tank named
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8 hours ago, Sturgeon said:

 

You can actually use the Powley computer to do this. Just remember that a grain is 1/7000th of a pound. Override the pressure computer and use 45500 CUP.

 

The mass of propellant is equal to the internal volume (net capacity) of the round times the loading density. When in doubt, use 0.90 for the loading density. 

 

I tried putting the values for the US 105mm on the T29 into that a few years ago and it matched exactly with hunnicutt (IIRC), which shows that there is precedent for predicting large calibres with it

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ok, I did the calculator... but have no idea what the hell I'm doing. I got these values: 

 

Spoiler

s88TNVj.png

XtzrMt8.png

 

but I don't know what to do with them, or what many of them mean (I'm going to assume that 30% efficiency is good)? I calculated that I would have 2.97kgs (6.55lbs) of powder, but I would like to know how much penetration I would get from this data. Also, since my gun is a squeeze bore, is there something I need to account for? 

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To get the penetration, the easiest thing to do is probably just use this penetration calculator; http://tankarchives.blogspot.com/p/demarre-calculator.html

 

For the reference, just use a contemporary projectile (Jeep's site has a good page on the 90mm M3; http://www.theshermantank.com/about/sherman-lee-and-variants-gun-data/90mm-m3-gun-information-page/  )

 

30% efficiency is a lot better than I ended up with for my first attempt.

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32 minutes ago, LostCosmonaut said:

To get the penetration, the easiest thing to do is probably just use this penetration calculator; http://tankarchives.blogspot.com/p/demarre-calculator.html

 

For the reference, just use a contemporary projectile (Jeep's site has a good page on the 90mm M3; http://www.theshermantank.com/about/sherman-lee-and-variants-gun-data/90mm-m3-gun-information-page/  )

 

30% efficiency is a lot better than I ended up with for my first attempt.

 

Ehh, I was getting disappointingly small numbers by using the M304 HVAP on Jeep's site, so I went online and looked for the 75/55 Pzgr. 41 data... and now I am pleased :P

 

I used the numbers I got from several sites and now I'm getting penetration values above 200mm :)I've averaged it out to: 

 

all values are for 30o, 0o being vertical 

220mm @ 100m

214mm @ 250m 

200mm @ 500m

157mm @ 1000m 

99mm @ 1500m 

49mm @ 2000m 

 

 

8.67in @ 100y 

8.46in @ 250y 

8.00in @ 500y 

6.53in @ 1000y 

4.49in @ 1500y 

2.51in @ 2000y 

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13 hours ago, Lord_James said:

ok, I did the calculator... but have no idea what the hell I'm doing. I got these values: 

 

  Hide contents

s88TNVj.png

XtzrMt8.png

 

but I don't know what to do with them, or what many of them mean (I'm going to assume that 30% efficiency is good)? I calculated that I would have 2.97kgs (6.55lbs) of powder, but I would like to know how much penetration I would get from this data. Also, since my gun is a squeeze bore, is there something I need to account for? 

 

I wouldn't worry about efficiency. The second one is running pressure that's a wee bit high for the tech level we're talking about. The first is more representative.

 

Otherwise your numbers for the first one look like exactly what I'd expect. One of my earlier rounds was an 85mm with similar capacity, and it produced similar performance (albeit with a somewhat lighter projectile). So yours looks about right.

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      Supplementary Out of Canon Information:
       
       
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      Non-structural passive materials:
                                                                  iii.     HHA
      Steel, approximately 500 BHN through-hardened. Approximately 1.5x as effective as RHA against KE and HEAT on a per-weight basis. Not weldable, middling shock properties. Available in thicknesses up to 1 inch.
      Density- 0.28 lb/in^3
                                                                  iv.     Fuel
      Mass efficiency vs RHA of 1.3 vs CE, 1 vs KE.
      Thickness efficiency vs RHA of 0.14 vs CE, 0.1 vs KE.
      Density-0.03 lb/in^3.
                                                                v.     Assorted stowage/systems
      Mass efficiency vs RHA- 1 vs CE, 0.8 vs KE.
                                                               vi.     Spaced armor
      Requires a face of at least 1 inch LOS vs CE, and at least 0.75 caliber LOS vs fullbore AP KE.
      Reduces penetration by a factor of 1.1 vs CE or 1.05 vs KE for every 4 inchair gap.
      Spaced armor rules only apply after any standoff surplus to the requirements of a reactive cassette.
      Reactive armor materials:
                                                                  vii.     ERA
      A sandwich of 0.125in/0.125in/0.125in steel-explodium-steel.
      Requires mounting brackets of approximately 10-30% cassette weight.
      Must be spaced at least 2 sandwich thicknesses away from any other armor elements to allow full functionality. 81% coverage (edge effects).
                                                                  viii.     NERA
      A sandwich of 0.25in steel/0.25in rubber/0.25in steel.
      Requires mounting brackets of approximately 10-30% cassette weight.
      Must be spaced at least 1 sandwich thickness away from any other armor elements to allow full functionality. 95% coverage.
      The details of how to calculate armor effectiveness will be detailed in Appendix 1.
      b.      Firepower
                                                                    i.     Bofors 57mm (reference weapon) - 85,000 PSI PMax/70,000 PSI Peak Operating Pressure, high quality steel cases, recoil mechanisms and so on are at an equivalent level to that of the USA in the year 1960.
                                                                   ii.     No APFSDS currently in use, experimental weapons only - Spindle sabots or bourelleted sabots, see for example the Soviet BM-20 100mm APFSDS.
                                                                  iii.     Tungsten is available for tooling but not formable into long rod penetrators. It is available for penetrators up to 6 calibers L:D.
                                                                  iv.     Texan shaped charge technology - 4 CD penetration for high-pressure resistant HEAT, 5 CD for low pressure/ precision formed HEAT.
                                                                   v.     The subsidy-approved GPMG for the Lone Free State of Texas has the same form factor as the M240, but with switchable feed direction.. The standard HMG has the same form factor as the Kord, but with switchable feed direction.
      c.       Mobility
                                                                    i.     Engines tech level:
      1.      MB 838 (830 HP)
      2.      AVDS-1790-5A (908 HP)
      3.      Kharkov 5TD (600 HP)
      4.    Detroit Diesel 8V92 (400 HP)
      5.    Detroit Diesel 6V53 (200 HP)
                                                                   ii.     Power density should be based on the above engines. Dimensions are available online, pay attention to cooling of 1 and 3 (water cooled).
                                                                  iii.     Power output broadly scales with volume, as does weight. Trying to extract more power from the same size may come at the cost of reliability (and in the case of the 5TD, it isn’t all that reliable in the first place).
                                                                  iv.     There is nothing inherently wrong with opposed piston or 2-stroke engines if done right.
      d.      Electronics
                                                                    i.     LRFs- unavailable
                                                                   ii.     Thermals-unavailable
                                                                  iii.     I^2- Gen 2 maximum
                                                                  vi.     Texas cannot mass produce microprocessors or integrated circuits
                                                                 vii.    Really early transistors only (e.g., transistor radio)
                                                                viii.    While it is known states exist with more advanced computer technology, the import of such systems are barred by the east coast states who do not approve of their use by militaristic entities.
       
      Armor calculation appendix.
       
      SHEET 1 Armor defeat calculator 4in-54 1200 yd
       
      SHEET 2 Armor defeat calculator 4in-54 2000 yd
       
      SHEET 3 Armor defeat calculator 6in HEAT
       
      Range calculator
       
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