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What the Hell is the Point of Interleaved Road Wheels?

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I'm sure that all the SH regulars will know this backwards and forwards, so this is more for the benefit of newer people, or people who stumble in via google, or people who want a quick link they can throw out as an answer to anyone who asks the question.

 

So, what's with the goofy-ass road wheel design on German WWII AFVs?

 

Bundesarchiv_Bild_101I-635-3965-28,_Panz

A puzzled and terrified worker struggles to comprehend and assemble the suspension of a tiger I

 

You may have run into a variety of explanations for this running gear design; that it provided a smoother ride, that the design saved rubber, or possibly some other rubbish.  Like the myth that frontal drive sprockets provide more traction (seriously, how in the hell is that supposed to make any sense?), these wrong explanations of the merits of interleaved road wheels seem to rise from some quote taken out of context.

 

The interleaved road wheel running gear may have saved some rubber relative to an alternative design that was particularly wasteful of it.  But interleaved road wheels are not particularly economic in this respect because, and I realize this is a complicated concept to explain so I'll try my best, they have more wheels.  Interleaved road wheels do allow for large wheel diameters, and a larger diameter wheel will spread wear out over a larger circumference.  So interleaved road wheels might allow for the rubber on the wheels to last longer, although their construction would require more in the first place.

 

Interleaved road wheels would not improve ride quality either.  The ride quality of a tank is not a function of the size or number of wheels it possesses, but of how they are sprung.  So, it is possible that in certain competitive trials an interleaved road wheel design outperformed a design that lacked this feature.  I could readily believe, for instance, that the tiger (H) had a better ride quality on rough terrain than the tiger (P), or that the SDKFZ. 251 had a smoother ride than the M3.  However, this would be because the tiger (H) and SDKFZ. 251 have independently sprung road wheels on torsion bars while the tiger (P) and M3 do not.

 

6mBPdJy.jpg

 

Torsion bar layout of the tiger II

 

1TQzN57.jpg

Volute spring suspension of the M3 half track

 

So, what do interleaved road wheels do?

 

They have two principal effects; one is a small benefit, and the other is an enormous detriment.

 

The small benefit of interleaved road wheels is that they spread the weight of the vehicle out more evenly on the track links:

 

6YyoyEf.jpg

 

The weight of a tank is not completely evenly spread out on the contact area of its tracks.  This is because tracks are not rigid.  If they were, they would be mainly ornamental and tanks' engines would just be for show.  More of the weight of a tank is concentrated under the parts of the track that the road wheels are sitting directly on top of.  Additionally, once a tank starts to sink into the soil a bit, larger road wheels work better than smaller ones because the larger ones have more contact area.  But you can only fit so many large diameter road wheels in the space of a tank's hull.

 

LUDTUkU.jpg

Dynamic!

 

 

So, the only way to have lots of road wheels and have big road wheels at the same time is to interleave them.  Simple as that.

 

If you would like an exhaustive look at the development of the semi-empirical MMP equation, read this.

 

The major, crippling downside to interleaved road wheels is that it makes changing the road wheels extremely time consuming.  

 

Oee5Nmw.jpg

A pair of workers perform maintenance on a panther tank, and contemplate the futility of all human achievement

 

Lucas Friedli reprints in his book on big cat maintenance a report from a training unit complaining that replacing the inner road wheels of a tiger tank took ten hours.  That is completely outrageous, and was a contributor to the poor operational availability of the big cats.

 

For this reason, interleaved road wheels have rarely been used after World War Two; only on a few French prototypes and a Swedish APC:

 

QI2pzse.jpg

PBV 302 variant with interleaved road wheels

 

1024px-AMX-50%2C_Tanks_in_the_Mus%C3%A9e

Some bizarre French tank

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I hate to be a pedant, but there is a difference between interleaved wheels such as the suspension on the Tiger I and overlapping wheels such as the Tiger II.  

 

Here is the interleaved roadwheels of the Tiger I.  Notice how the wheels don't just overlap, they actually surround each other on both sides.

 

ttt_tiger_fig1_suspension.jpg

 

 

This is different from the image in the OP which is for a Tiger II.  The Tiger II wheels overlap, but they are not interleaved.

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Sure.  Panther and Tiger I have three layers (originally 4 for the tiger), while the tigger II has only two layers.

 

From a weight distribution standpoint it makes no difference.  It does mean that in the aristocratic tigger the tracks are being twisted, since each road wheel station is hitting the tracks off center.  This means that the tracks don't last as long.

 

It's probably a bit easier to maintain, but if one of your inner wheels goes you're still looking at pulling two others to get at it.  So it's a pretty similar trade-off in the end.

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If you're on a per-deliverable kickback scheme, getting kickbacks for the number of wheels is a pretty decent move.

 

Better still if the road wheels in question wear out quickly and need frequent replacement.  As the ones on panther did.

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To quote from the interview of Robert Forczyk that I recently posted on  my site (gotta work in that self promotion where I can!):

 

Also, it’s easy for people who never had to change a road wheel or a torsion bar to admire the big gun on the Tiger, but ignore the idiocy of the interleaved road wheel design. Yes, it provided a more stable gun platform, but increased the weight and made maintenance that much more difficult.

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Great find legiondude!

 

I'm actually pretty partial to the E-series suspension concept, as it appears to solve or at least ameliorate the big problem with interleaved/overlapping road wheels.

 

Dv3tczO.jpg

 

There are horizontal tubes filled with belleville washers pressing against a piston.  The piston is attached to the swing arm via that rack and pinion toothed mechanism.  This would probably work fine for the E-10 and E-25, but surely I am not the only one who thinks that those teeth would strip right the fuck off if E-50 or E-75 hit a bump.  Especially with late-war German metallurgy.

 

Anyway, to pull a bad road wheel you pull the bogie of two road wheels off.  Even if they're in fully overlapping configuration, you only need to tilt the bogie off diagonally to get it off the hull without disturbing the other road wheels.  This does mean that you have to take the road wheels off as pairs, and with their associated springs, but this is basically the same procedure for changing a road wheel on a tank with Horstmann suspension:

 

gMROQTX.png

 

And you'll see paeons to the centurion raving about how much easier it was to swap out busted centurion suspension units than it was to change out road wheels and torsion bars on the M48.

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Great find legiondude!

 

I'm actually pretty partial to the E-series suspension concept, as it appears to solve or at least ameliorate the big problem with interleaved/overlapping road wheels.

 

Dv3tczO.jpg

 

There are horizontal tubes filled with belleville washers pressing against a piston.  The piston is attached to the swing arm via that rack and pinion toothed mechanism.  This would probably work fine for the E-10 and E-25, but surely I am not the only one who thinks that those teeth would strip right the fuck off if E-50 or E-75 hit a bump.  Especially with late-war German metallurgy.

 

Anyway, to pull a bad road wheel you pull the bogie of two road wheels off.  Even if they're in fully overlapping configuration, you only need to tilt the bogie off diagonally to get it off the hull without disturbing the other road wheels.  This does mean that you have to take the road wheels off as pairs, and with their associated springs, but this is basically the same procedure for changing a road wheel on a tank with Horstmann suspension:

 

gMROQTX.png

 

And you'll see paeons to the centurion raving about how much easier it was to swap out busted centurion suspension units than it was to change out road wheels and torsion bars on the M48.

This might be a bit off topic but:

Does anyone know why the Centurion was regarded as such a great machine?

To me it only seems like a fatter slightly upgraded Panther tank.

 

To get on topic again:

How does the Horstman suspension compare to torsion bar, Hydropeumatic  and other suspensions? (weight and off road capability)

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Centurion had the good luck to be crewed by generally competent crews and sent against enemies who were generally incompetent.  The IDF's prowess at tanking hardly needs reiteration at this point, and the Indian Army's opponents were, shall we say, not well known for their tactical acumen when it comes to armored combat.

 

Also, the sho't kal is a seriously hot-rodded machine that is a hell of a lot better than a 1945 vintage centurion (which I agree is roughly comparable to a panther, except that the centurion actually works).  In addition to the bigger gun and all the extra armor, it has an entirely new (American-made!) engine and transmission.  They also received new fire control, fire extinguishers, turret motors and gun elevation equipment, although I don't know if they had all that stuff in 1973.  They had the American engine and transmission for sure though.  Most nations that operated the centurion after the 1970s upgraded theirs to Israeli spec (e.g. Sweden).

 

Horstmann suspension was OK by WWII standards, but outdated thereafter.  The biggest problem with it is that the road wheels are not independently suspended.  As you can see in the picture above, the pairs of road wheels share a common spring.

 

This has a few small advantages, such as being lighter as well as providing more resistance to vehicle pitching oscillation.  If you look at this commonly referenced German test of tank resistance to pitching, you can see that the vehicles without independent suspension tend to do better.

 

This is undercut by one enormous disadvantage; non-independent suspensions have horrible ride quality at high speeds.  What happens is that the pairs of wheels sharing a spring will both be compressed by obstacles at the same time, effectively doubling the spring constant and making it much more likely that the road wheels bottom out.

 

Granted, centurion and chieftain had such ass power to weight ratios that this was probably not a huge concern.  But still; it was not the way forward.

 

Horstmann does have the advantage of not taking up room inside the hull at all, and being (supposedly) easy to repair.  The prevalence of torsion bars in post-war tank design suggests that these are secondary considerations.  Also, there are ways of getting torsion bars to be less obnoxious, like on the AMX-30 where the third swing arm is reversed so that the turret basket sits between the torsion bars:

 

NitS93s.jpg?1

Picture courtesy of Walter

 

Other than that, it's hard to make generalizations.  A description like "torsion bar suspension" really only tell you what shape the spring suspending the roadwheel swing arms is.  That doesn't really tell you much about the important parameters of suspension performance like spring constants, travel length, unsprung mass, damping coefficients or harmonic period.  It just tells you that the swing arm is attached to a cylindrical piece of steel that it twists.

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Centurion had the good luck to be crewed by generally competent crews and sent against enemies who were generally incompetent.  The IDF's prowess at tanking hardly needs reiteration at this point, and the Indian Army's opponents were, shall we say, not well known for their tactical acumen when it comes to armored combat.

 

Also, the sho't kal is a seriously hot-rodded machine that is a hell of a lot better than a 1945 vintage centurion (which I agree is roughly comparable to a panther, except that the centurion actually works).  In addition to the bigger gun and all the extra armor, it has an entirely new (American-made!) engine and transmission.  They also received new fire control, fire extinguishers, turret motors and gun elevation equipment, although I don't know if they had all that stuff in 1973.  They had the American engine and transmission for sure though.  Most nations that operated the centurion after the 1970s upgraded theirs to Israeli spec (e.g. Sweden).

 

Horstmann suspension was OK by WWII standards, but outdated thereafter.  The biggest problem with it is that the road wheels are not independently suspended.  As you can see in the picture above, the pairs of road wheels share a common spring.

 

This has a few small advantages, such as being lighter as well as providing more resistance to vehicle pitching oscillation.  If you look at this commonly referenced German test of tank resistance to pitching, you can see that the vehicles without independent suspension tend to do better.

 

This is undercut by one enormous disadvantage; non-independent suspensions have horrible ride quality at high speeds.  What happens is that the pairs of wheels sharing a spring will both be compressed by obstacles at the same time, effectively doubling the spring constant and making it much more likely that the road wheels bottom out.

 

Granted, centurion and chieftain had such ass power to weight ratios that this was probably not a huge concern.  But still; it was not the way forward.

 

Horstmann does have the advantage of not taking up room inside the hull at all, and being (supposedly) easy to repair.  The prevalence of torsion bars in post-war tank design suggests that these are secondary considerations.  Also, there are ways of getting torsion bars to be less obnoxious, like on the AMX-30 where the third swing arm is reversed so that the turret basket sits between the torsion bars:

 

NitS93s.jpg?1

Picture courtesy of Walter

 

Other than that, it's hard to make generalizations.  A description like "torsion bar suspension" really only tell you what shape the spring suspending the roadwheel swing arms is.  That doesn't really tell you much about the important parameters of suspension performance like spring constants, travel length, unsprung mass, damping coefficients or harmonic period.  It just tells you that the swing arm is attached to a cylindrical piece of steel that it twists.

Did the British ever design a great, noteworthy tank?

 

From my point of view, the British wasn't the best tank designers.

 

Thanks for the info by the way!

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This might be a bit off topic but:

Does anyone know why the Centurion was regarded as such a great machine?

To me it only seems like a fatter slightly upgraded Panther tank.

 

To get on topic again:

How does the Horstman suspension compare to torsion bar, Hydropeumatic  and other suspensions? (weight and off road capability)

In anything, the Panther is the "fatter" tank.  Really, the two vehicles have little in common.  The Panther is a very conventional German design of the period, other than the use of slopped armor.  Due to the double torsion bar suspension, the front mounted transmission and the bow gunner, the hull of the Panther is quite a bit taller than Centurion and the Panther also has sponsons, whereas the Centurion hull rests entirely between the tracks.  Look at the front glacis plate of the Panther compared to the glacis of the Centurion, the Panther plate is at least twice as big.  Since this is generally the thickest piece of armor on a tank, you can see how keeping it smaller is a good weight saver.  Despite the sponsons on the Panther, it has a surprisingly small turret ring and turret, whereas the Centurion turret was big enough to allow it to be up-gunned twice over its long career.  

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Great find legiondude!

 

I'm actually pretty partial to the E-series suspension concept, as it appears to solve or at least ameliorate the big problem with interleaved/overlapping road wheels.

 

Dv3tczO.jpg

 

There are horizontal tubes filled with belleville washers pressing against a piston.  The piston is attached to the swing arm via that rack and pinion toothed mechanism.  This would probably work fine for the E-10 and E-25, but surely I am not the only one who thinks that those teeth would strip right the fuck off if E-50 or E-75 hit a bump.  Especially with late-war German metallurgy.

 

 

 

 

 

Speaking of metallurgy.. I'd worry more about the Bellevilles failing with a obnoxious "crunch" before the teeth sheared.

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In anything, the Panther is the "fatter" tank.  Really, the two vehicles have little in common.  The Panther is a very conventional German design of the period, other than the use of slopped armor.  Due to the double torsion bar suspension, the front mounted transmission and the bow gunner, the hull of the Panther is quite a bit taller than Centurion and the Panther also has sponsons, whereas the Centurion hull rests entirely between the tracks.  Look at the front glacis plate of the Panther compared to the glacis of the Centurion, the Panther plate is at least twice as big.  Since this is generally the thickest piece of armor on a tank, you can see how keeping it smaller is a good weight saver.  Despite the sponsons on the Panther, it has a surprisingly small turret ring and turret, whereas the Centurion turret was big enough to allow it to be up-gunned twice over its long career.  

When I was saying "fatter" I was referring to the weight of the centurion, at 51 ton. That is 6 ton more than the Panther, for around 20mm thicker UFP and 50mm thicker turret and 5mm thicker lower sides. 

 

Being in general smaller than the Panther, I find the design inefficient, armor wise, compared to the Panther.  Also it is 10kp/h slower than the Panther, I am unsure of why that is. 

 

In general I feel like the Centurion is like a upgraded Panther, a little better armor, same gun performance (later up gunned to the long 88s performance), slower, heavier, smaller and more room for upgrades.

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When I was saying "fatter" I was referring to the weight of the centurion, at 51 ton. That is 6 ton more than the Panther, for around 20mm thicker UFP and 50mm thicker turret and 5mm thicker lower sides. 

 

Being in general smaller than the Panther, I find the design inefficient, armor wise, compared to the Panther.  Also it is 10kp/h slower than the Panther, I am unsure of why that is. 

 

In general I feel like the Centurion is like a upgraded Panther, a little better armor, same gun performance (later up gunned to the long 88s performance), slower, heavier, smaller and more room for upgrades.

 

The panther's nominal top speed is misleading.  The transmission has extra gears that allow it to have an extremely good top speed for a vehicle of its class.  However, at those high gear ratios the panther would have so little torque that it can really only hit those speeds on paved surfaces.  Its off-road performance is much more comparable to its peers.

 

Walter's Forczyk quote touched on this, but about how what is the overall weight increase by having interleaved roadwheels? 

 

Interleaved road wheels would add a significant amount of weight, considering that you're almost doubling the number of swing arms, road wheels and torsion bars.  Suspension accounts for about 10% of the weight of a tank, so total weight gain might be on the order of 5%, as a rough guess.

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Interleaved road wheels would add a significant amount of weight, considering that you're almost doubling the number of swing arms, road wheels and torsion bars.  Suspension accounts for about 10% of the weight of a tank, so total weight gain might be on the order of 5%, as a rough guess.

That's a non-trivial amount. Imagine if Panther weighed ~42 tons instead of ~45, it could have made it a whopping 175 km without failure instead of 150 km!

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When I was saying "fatter" I was referring to the weight of the centurion, at 51 ton. That is 6 ton more than the Panther, for around 20mm thicker UFP and 50mm thicker turret and 5mm thicker lower sides. 

 

Being in general smaller than the Panther, I find the design inefficient, armor wise, compared to the Panther.  Also it is 10kp/h slower than the Panther, I am unsure of why that is. 

 

In general I feel like the Centurion is like a upgraded Panther, a little better armor, same gun performance (later up gunned to the long 88s performance), slower, heavier, smaller and more room for upgrades.

 

I would suspect that the extra weight of the Centurion vs the Panther is due to the Centurion having a heavier and better armored turret and side skirts over the suspension.  Side protection on the Centurion is most likely much better than Panther.  

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The cent's turret is considerably bigger.  Relative to their gigantic hulls the big cats have teeny tiny turrets.  The panther actually has a smaller turret ring than the sherman.  Panther's side protection is better on its sponsons (50mm inclined 30 degrees for Ausf. G vs 51mm at twelve degrees for cent mk X), but worse underneath the sponsons (40mm flat).

 

The cent mk 1 and the panther are roughly comparable in overall mass, armament and protection.  But the cent had a lot more growth potential.  I can't imagine that the panther would have been as amenable to up-gunning as the cent was given its tiny turret ring.  As for up-armoring, forget it.  The design was already much heavier than the final drives could handle.  Furthermore, improving the armor would cost the panther more weight because its glacis plate is gigantic.

 

Upgrading the engine would have been a trick too.  The space within the engine decks on the big cats is not very large.  The Maybach motors they used delivered extremely good horsepower relative to their size, so naturally the designers didn't leave any space for anything with less specific power (and, you know, maybe a little less break-y).  This is why all the proposals to re-engine the king tiger with a diesel and all the E-series napkinwaffe would have required a complete redesign of the engine deck.

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I would suspect that the extra weight of the Centurion vs the Panther is due to the Centurion having a heavier and better armored turret and side skirts over the suspension.  Side protection on the Centurion is most likely much better than Panther.  

:ian:

 

Actually, The Panther has side skirts, 5mm side skirts. And when it comes to hull armor, the Centurion and Panther (Ausf. F) is pretty much identical, the Centurion having very slightly better overall side armor, while the upper sides of the Panther being a 5mm thicker and sloped, making them a little better. So, pretty much identical. 

 

On a second look, they have identical front armor, side armor, and the panther has a little thicker rear armor (45mm compared to 38mm). 

 

But yes, the Centurion obviously has a much more heavily armored turret, having about 30mm thicker sides, cheeks and rear, and between 150-250mm thick turret face. 

 

Mvh

Xoon.

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The cent's turret is considerably bigger.  Relative to their gigantic hulls the big cats have teeny tiny turrets.  The panther actually has a smaller turret ring than the sherman.  Panther's side protection is better on its sponsons (50mm inclined 30 degrees for Ausf. G vs 51mm at twelve degrees for cent mk X), but worse underneath the sponsons (40mm flat).

 

The cent mk 1 and the panther are roughly comparable in overall mass, armament and protection.  But the cent had a lot more growth potential.  I can't imagine that the panther would have been as amenable to up-gunning as the cent was given its tiny turret ring.  As for up-armoring, forget it.  The design was already much heavier than the final drives could handle.  Furthermore, improving the armor would cost the panther more weight because its glacis plate is gigantic.

 

Upgrading the engine would have been a trick too.  The space within the engine decks on the big cats is not very large.  The Maybach motors they used delivered extremely good horsepower relative to their size, so naturally the designers didn't leave any space for anything with less specific power (and, you know, maybe a little less break-y).  This is why all the proposals to re-engine the king tiger with a diesel and all the E-series napkinwaffe would have required a complete redesign of the engine deck.

Yep, Colli hit it on the head with this.  I always thought it a bit odd that the German's went through the trouble of creating the most compact, high power engine of the period (HL-230) and then put it in completely over-sized vehicles.  If they had put that engine in something around 30 tons or so, they could have had a vehicle as fast as the Comet.  

 

Fun Fact: When they put the AVDS/1790 engine and CD850 transmission into the Centurion, they had the mount the powerpack at about a 3 degree angle sloping down toward the rear of the vehicle in order to position the final drives in the correct location.    

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The cent mk 1 and the panther are roughly comparable in overall mass, armament and protection.  But the cent had a lot more growth potential.  I can't imagine that the panther would have been as amenable to up-gunning as the cent was given its tiny turret ring.  As for up-armoring, forget it.  The design was already much heavier than the final drives could handle.  Furthermore, improving the armor would cost the panther more weight because its glacis plate is gigantic.

 

This. There is a significant difference between two equally-sized tanks when one of them is at the end of it's development life already while the other still has plenty of upgrade space. Think pzIV versus sherman.

 

The cent carried on so long because it has lots of spare load capacity on the suspension, a generous turret ring and a big engine bay. The panther didn't carry on much past a few years with the french because changing anything would have required a redesign of the entire vehicle.

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If you're on a per-deliverable kickback scheme, getting kickbacks for the number of wheels is a pretty decent move.

 

I'm actually not 100% clear on why the Germans were so obsessed with this suspension design.  It wasn't just the big cats that they stuck with these silly things, it was every single Sdkfz 251.  That was probably even worse for them, since those were supposed to be mainstay medium transport.

 

If the Germans ditched the stupid suspension and were able to make a few hundred extra tiger IIs in 1944, I can't see how that would make much difference.  If they had ditched the stupid suspension and made a few thousand more Sdfkz 251s in 1939, that might have material impact.

 

Forczyk mentioned in his T-34 vs panther book that there was some loon in the German armor development bureaucracy who was completely obsessed with torsion bars and interleaved road wheels, and would basically reject any design that didn't have them.  This is apparently why the DB panther design gained them later in development.  But it's not clear to me why this guy had so much say in tank design, and why everyone around him didn't point and laugh.

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      Both warheads penetrate approximately 5 cone diameters.

      D.      Cascadian HEDP 90mm rocket
      While not a particularly impressive AT weapon, being of only middling diameter and a single shaped charge, the sheer proliferation of this device has rendered it a major threat to tanks, as well as lighter vehicles. This weapon is available in large numbers in Cascadian infantry squads as “pocket artillery”, and there are reports of captured stocks being used by the Mormonhideen.
      Warhead penetrates approximately 4 cone diameters.

      E.      Deseret 40mm AC/ Cascadian 35mm AC
      These autocannon share broadly similar AP performance, and are considered a likely threat for the foreseeable future, on Deseret armored cars, Cascadian tank destroyers, and likely also future IFVs.

      F.      IEDs

      In light of the known resistance of tanks to standard 10kg anti-tank mines, both the Perfidious Cascadians and the Mormonhideen have taken to burying larger anti-tank A2AD weaponry. The Cascadians have doubled up some mines, and the Mormons have regularly buried AT mines 3, 4, and even 5 deep.

      2.      General guidelines:

      A.      Solicitation outline:
      In light of the differing requirements for the 2 theaters of war in which the new vehicle is expected to operate, proposals in the form of a field-replaceable A-kit/B-kit solution will be accepted.

      B.      Requirements definitions:
      The requirements in each field are given in 3 levels- Threshold, Objective, and Ideal.
      Threshold is the minimum requirement to be met; failure to reach this standard may greatly disadvantage any proposal.

      Objective is the threshold to be aspired to; it reflects the desires of the People’s Auditory Forces Armored Branch, which would prefer to see all of them met. At least 70% must be met, with bonus points for any more beyond that.

      Ideal specifications are the maximum of which the armored forces dare not even dream. Bonus points will be given to any design meeting or exceeding these specifications.

      C.      All proposals must accommodate the average 1.7m high Californian recruit.

      D.      The order of priorities for the DPRC is as follows:

      a.      Vehicle recoverability.

      b.      Continued fightability.

      c.       Crew survival.

      E.      Permissible weights:

      a.      No individual field-level removable or installable component may exceed 5 tons.

      b.      Despite the best efforts of the Agriculture Command, Californian recruits cannot be expected to lift weights in excess of 25 kg at any time.

      c.       Total vehicle weight must remain within MLC 120 all-up for transport.

      F.      Overall dimensions:

      a.      Length- essentially unrestricted.

      b.      Width- 4m transport width.

                                                                    i.     No more than 4 components requiring a crane may be removed to meet this requirement.

                                                                   ii.     Any removed components must be stowable on top of the vehicle.

      c.       Height- The vehicle must not exceed 3.5m in height overall.

      G.     Technology available:

      a.      Armor:
      The following armor materials are in full production and available for use. Use of a non-standard armor material requires permission from a SEA ORG judge.
      Structural materials:

                                                                    i.     RHA/CHA

      Basic steel armor, 250 BHN. The reference for all weapon penetration figures, good impact properties, fully weldable. Available in thicknesses up to 150mm (RHA) or 300mm (CHA).
      Density- 7.8 g/cm^3.

                                                                   ii.     Aluminum 5083

      More expensive to work with than RHA per weight, middling impact properties, low thermal limits. Excellent stiffness.

       Fully weldable. Available in thicknesses up to 100mm.
      Mass efficiency vs RHA of 1 vs CE, 0.9 vs KE.
      Thickness efficiency vs RHA of 0.33 vs CE, 0.3 vs KE.
      Density- 2.7 g/cm^3 (approx. 1/3 of steel).

      For structural integrity, the following guidelines are recommended:

      For light vehicles (less than 40 tons), not less than 25mm RHA/45mm Aluminum base structure

      For heavy vehicles (70 tons and above), not less than 45mm RHA/80mm Aluminum base structure.
      Intermediate values for intermediate vehicles may be chosen as seen fit.
      Non-structural passive materials:

                                                                  iii.     HHA

      Steel, approximately 500 BHN through-hardened. Approximately twice as effective as RHA against KE and HEAT on a per-weight basis. Not weldable, middling shock properties. Available in thicknesses up to 25mm.
      Density- 7.8g/cm^3.

                                                                  iv.     Glass textolite

      Mass efficiency vs RHA of 2.2 vs CE, 1.64 vs KE.

      Thickness efficiency vs RHA of 0.52 vs CE, 0.39 vs KE.
      Density- 1.85 g/cm^3 (approximately ¼ of steel).
      Non-structural.

                                                                   v.     Fused silica

      Mass efficiency vs RHA of 3.5 vs CE, 1 vs KE.

      Thickness efficiency vs RHA of 1 vs CE, 0.28 vs KE.
      Density-2.2g/cm^3 (approximately 1/3.5 of steel).
      Non-structural, requires confinement (being in a metal box) to work.

                                                                  vi.     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-0.82g/cm^3.

                                                                vii.     Assorted stowage/systems

      Mass efficiency vs RHA- 1 vs CE, 0.8 vs KE.

                                                               viii.     Spaced armor

      Requires a face of at least 25mm LOS vs CE, and at least 50mm LOS vs KE.

      Reduces penetration by a factor of 1.1 vs CE or 1.05 vs KE for every 10 cm air gap.
      Spaced armor rules only apply after any standoff surplus to the requirements of a reactive cassette.

      Reactive armor materials:

                                                                  ix.     ERA-light

      A sandwich of 3mm/3mm/3mm steel-explodium-steel.
      Requires mounting brackets of approximately 10-30% cassette weight.

      Must be spaced at least 3 sandwich thicknesses away from any other armor elements to allow full functionality. 81% coverage (edge effects).

                                                                   x.     ERA-heavy

      A sandwich of 15mm steel/3mm explodium/9mm steel.
      Requires mounting brackets of approximately 10-30% cassette weight.
      Must be spaced at least 3 sandwich thicknesses away from any other armor elements to allow full functionality. 81% coverage (edge effects).

                                                                  xi.     NERA-light

      A sandwich of 6mm steel/6mm rubber/ 6mm 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.

                                                                 xii.     NERA-heavy

      A sandwich of 30mm steel/6m rubber/18mm 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.     2A46 equivalent tech- pressure limits, semi-combustible cases, recoil mechanisms and so on are at an equivalent level to that of the USSR in the year 1960.

                                                                   ii.     Limited APFSDS (L:D 15:1)- Spindle sabots or bourelleted sabots, see for example the Soviet BM-20 100mm APFSDS.

                                                                  iii.     Limited tungsten (no more than 100g per shot)

                                                                  iv.     Californian shaped charge technology- 5 CD penetration for high-pressure resistant HEAT, 6 CD for low pressure/ precision formed HEAT.

                                                                   v.     The general issue GPMG for the People’s Auditory Forces is the PKM. The standard HMG is the DShK.

      c.       Mobility

                                                                    i.     Engines tech level:

      1.      MB 838 (830 HP)

      2.      AVDS-1790-5A (908 HP)

      3.      Kharkov 5TD (600 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- limited

      3.      Operational Requirements.

      The requirements are detailed in the appended spreadsheet.

      4.      Submission protocols.

      Submission protocols and methods will be established in a follow-on post, nearer to the relevant time.
       
      Appendix 1- armor calculation
      Appendix 2- operational requirements
       
      Good luck, and may Hubbard guide your way to enlightenment!
    • By Collimatrix
      Shortly after Jeeps_Guns_Tanks started his substantial foray into documenting the development and variants of the M4, I joked on teamspeak with Wargaming's The_Warhawk that the next thing he ought to do was a similar post on the T-72.
       
      Haha.  I joke.  I am funny man.
       
      The production history of the T-72 is enormously complicated.  Tens of thousands were produced; it is probably the fourth most produced tank ever after the T-54/55, T-34 and M4 sherman.
       
      For being such an ubiquitous vehicle, it's frustrating to find information in English-language sources on the T-72.  Part of this is residual bad information from the Cold War era when all NATO had to go on were blurry photos from May Day parades:
       

       
      As with Soviet aircraft, NATO could only assign designations to obviously externally different versions of the vehicle.  However, they were not necessarily aware of internal changes, nor were they aware which changes were post-production modifications and which ones were new factory variants of the vehicle.  The NATO designations do not, therefore, necessarily line up with the Soviet designations.  Between different models of T-72 there are large differences in armor protection and fire control systems.  This is why anyone arguing T-72 vs. X has completely missed the point; you need to specify which variant of T-72.  There are large differences between them!
       
      Another issue, and one which remains contentious to this day, is the relation between the T-64, T-72 and T-80 in the Soviet Army lineup.  This article helps explain the political wrangling which led to the logistically bizarre situation of three very similar tanks being in frontline service simultaneously, but the article is extremely biased as it comes from a high-ranking member of the Ural plant that designed and built the T-72.  Soviet tank experts still disagree on this; read this if you have some popcorn handy.  Talking points from the Kharkov side seem to be that T-64 was a more refined, advanced design and that T-72 was cheap filler, while Ural fans tend to hold that T-64 was an unreliable mechanical prima donna and T-72 a mechanically sound, mass-producible design.
       
      So, if anyone would like to help make sense of this vehicle, feel free to post away.  I am particularly interested in:
       
      -What armor arrays the different T-72 variants use.  Diagrams, dates of introduction, and whether the array is factory-produced or a field upgrade of existing armor are pertinent questions.
       
      -Details of the fire control system.  One of the Kharkov talking points is that for most of the time in service, T-64 had a more advanced fire control system than contemporary T-72 variants.  Is this true?  What were the various fire control systems in the T-64 and T-72, and what were there dates of introduction?  I am particularly curious when Soviet tanks got gun-follows-sight FCS.
       
      -Export variants and variants produced outside the Soviet Union.  How do they stack up?  Exactly what variant(s) of T-72 were the Iraqis using in 1991?

      -WTF is up with the T-72's transmission?  How does it steer and why is its reverse speed so pathetically low?
       
       
    • By Serge
      The Armored Combat Vehicle Puma started as a privat-venture betwen Krauss-Maffei and Diehl in 1983. The two first prototypes were ready first in spring 1986 with a Kuka 20mm two men turret and second in autumn with a Diehl 120mm mortar turret. 
      ACV-Puma was intented as an export armored vehicle of the 16-28 t class. 
       

       
      By 1983 original concept, it was offered with two engine options (400/600hp) to cope with the level of armor protection asked.
      The running gear was a mixt of both Leopard-1 and 2 components :
      - Leo-1 : road wheels, track support rollers, torsion bars and even the driver's seat ;
      - Leo-2 : track adjuster, cooling system components and sproket hub.
      It was possible to run the engine outside of its compartment. 
       
      In 1988, the concept was improved further :
      - the class range reached 38t ;
      - the engines offer was 440 or 750hp strong ;
      - the chassis was now available in two length (5/6 road wheels) and  hight/low profil hull (20cm).

      The ACV-Puma was a contender at the Norwegian IFV programme from 1991 and the Turkish 1987 relaunched TIFV programme.
      Norway chose CV-90 and Turkey, the AIFV.
      (If anyone have information about how it was a serious contender, I'm interested)
      It was also evaluated by the Swiss army in 1991. I don't know if it took part to the Char de grenadiers 2000 programme. 
       

      In 1983´s concept, the difference betwen the low profil hull and the 20cm higher hight profil hull was obtained by a "box shape vertical raised" rear compartment. With the 1988's design, the front slop is now different to achieve a better ballistic protection. 
       
      When considering documentations of this period, it's important to note the mine/IED protection was not a priority like today. 
       
      I'll post soon a scan showing general layout of the troop compartment. It's a Marder/BMP old fashion one with soldiers facing outside. 
       
      Even if it was not a success at exportation, I think ACV-Puma must be known because of both :
      - the outdated combat beliefs of the 80's (still vigourous today) ;
      - and advanced proposal  such as the differential hull length from the drawing board. 
       
      I have a question :
      Does anyone known if a 6 road wheels chassis was ever built ?
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