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Help me understand tank suspension


Jamby
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Sooooo...after doing a site-wide search and perusing Google, I'm surprised not to have found anything about tank suspension, other than a somewhat doubtful thread on the WoT forums. Would my learned colleagues of SH be able to assist me in understanding and identifying the different types of tank suspension? I think I've got leaf-spring more or less mastered, as well as both VVSS and HVSS (thanks, JGT!) but was somewhat embarrassed not to be able to differentiate between the suspension of a Type 97 Chi-Ha and an FV4201 Chieftain.

 

UPDATE: I think I understand tank suspension better now. Thanks, everyone!

Edited by Jamby
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@EnsignExpendable wrote a bit about this some time ago.  Technology of Tanks does have a good summary of the matter, but it's such an expensive book that I recommend going straight to the piracy option and getting the shitty OCR version.  Ogorkiewicz's more recent Tanks: 100 Years of Evolution has a condensed, but far less detailed commentary on the development of tanks suspension.

Here is my heavily editorialized summary of tank suspension:

Tank suspension is what gives the track some "give" while the tank is moving at speed over rough terrain.  The main purpose of tank suspension is to keep the crew from being incapacitated by the tank shaking up and down while the tank is moving off-road.  It has some minor benefits to weapon and sight stabilization, but the technology of weapon and sight stabilization is so advanced at this point that it doesn't really matter today.

The very first tanks had no suspension whatsoever; the entire run of the track was rigidly attached to the tank's hull.  This meant that there was no shock absorption whatsoever when these old tanks went over bumps, but this was basically acceptable because the first tanks were also very slow, and tended to poison their crews with carbon monoxide anyway.

In the interwar period, tank suspension tended towards systems where several road wheels share a common spring element.  In some cases, four road wheels would be attached to a common leaf spring by  series of levers and balances.  More commonly, pairs of road wheels would share a common spring as in the HVSS and VVSS suspension of the Sherman, but also the bizarro longtitudinal torsion bar design in the Ferdinand.

 

The interwar period also saw the first independent suspension systems.  In independent suspension each road wheel acts upon its own spring.  Independent suspensions give a better ride quality for the crew at high speed, but they suffer from greater pitching oscillation (nose of the tank rocking up and down) than the older-style suspension where pairs of road wheels share a common spring, especially at lower speeds.  Independent suspensions are also heavier.  Christie suspension is independent, as are the majority of torsion bar systems (the Soviets screwed around with some non-independent systems, and there was the Ferdinand).  The majority of tank designers switched from the older spring-sharing systems to the newer independent systems, as in the US T20 series of medium tanks where the M4 evolved into the M26 and lost its volute spring suspension for torsion bars.  The British went backwards and switched from the independent Christie suspension of Comet to the spring-sharing Horstmann suspension in Centurion.  This is because the British are bad at tank design, although Centurion was a decent tank once you ripped out the old engine and transmission and put an AVDS and Allison tranny in there.  The British would stay with the Horstmann suspension through Chieftain and until Challenger 1.  Again, Chieftain was generally a bad tank, and the British made the world's best tank in 1916, and have been trailing since then.

 

The majority of publications will categorize tank suspension by what springing medium the swing arms are tensioned by.  This is completely stupid and conveys almost no useful information.  It doesn't tell me anything about the comparative automotive performance of the M60 vs the Pz. 68 to know that one has the swing arms tensioned by long, twisting rods of spring steel while the other tensions the arms with a stack of frisbee-shaped discs of spring steel.  The shape of the piece of steel being bent to absorb energy from the suspension elements is literally the least useful piece of information about the suspension performance.  More useful information would be the limits of the articulation of the swing arm, spring coefficients, swing arm length, damping coefficients, and unsprung mass of the suspension components.  Also useful would be the location of the center of mass of the tank relative to each of the road wheels and swing arms and its moment of inertia about the pitch axis.  But this more specific information is hard to come by.

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Why does Horstmann suspension necessarily denote bad tank design? I think it was arguably quite suitable for the speed that tanks like the Chieftain could reasonably reach, given what I've been reading here:

https://archive.org/stream/Janes_Technology_of_Tanks_01/Janes_Technology_of_Tanks_01_djvu.txt

 

The part I'm referring to is about two thirds of the way down the document - section 13 (I figured out how to link it: http://prntscr.com/iu7i68) - and seems to suggest that the appropriate choice of suspension is largely dependent on the speed you're moving at, from leaf-spring at the lowest speeds to torsion bar at the highest.

 

Unless you were bombing along rough country at particularly high speed (even for a vehicle designed to do that to a degree), would the difference between torsion bar and Horstmann suspension really be appreciable? Are there tankers from both sides of the pond here?

 

 

 

 

 

Edited by Jamby
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Well there's different kinds of suspension that have evolved since WW1 and they offer different tradeoffs (although some have been superseded) such as cost, simplicity/reliability, effectiveness, etc.   but I also think there may be an element of semantics to it (how people define such things, which is where the sources you use and quality of that source) probably applies.  

 

Also there's going to be more issues than just 'speed' to consider in your suspension choice.  For example on page 319 of Jane's:

 

Quote

The advantages of torsion bar suspensions are however accompanied by a number of disadvantages. Thus, while the installation of the torsion bars across the bottom of tank hulls is simple and well-protected, it also increases their height.

 


 

This is undesirable in itself and it can also significantly increase the weight of
tanks, particularly when they are heavily armoured. Damaged torsion bars are also difficult to replace when a hull is distorted by mine blast. Moreover, the fact that torsion bars store a large amount of energy in relation to their weight means that their outside is highly stressed, which makes them vulnerable to surface damage.


Their installation in the hull makes torsion bar suspensions compare unfavourably in some respects with suspensions of the Horstmann type. In the case of the latter the coil springs are outside the hull, mounted together with their associated pairs of wheels and suspension amis on a subframe so that they form a self-contained bogie which can be replaced as a unit in the event of damage. The same applies to the externally mounted suspension of the Israeli Merkava. The latter is however greatly superior to the Horstmann suspension of the British Centurions and Chieftains because the road wheels arc independently sprung, by vertical coil springs, and because they are provided by it with greater vertical travel.

 

 

It would seem tradeoffs and design (complexity, protection, weight, internal space) are drivers over 'good' or 'bad' decisions as how it is implemented (possibly getting back to the 'semantics' again?)   Speed will matter too since that affects comfort/safety/stability of the crew and vehicle vibration and such matters as Collimatrix described (the better a suspension can cancel out the bouncing/shaking of rough terrain, the faster you could in theory go.) but it's still going to be about tradeoffs in the end (including speed.)

 

Also, the suspension itself is just part of a larger system (Wheels for example, which is also discussed in Janes) which can also play a role and probably shouldn't be ignored.

 

Differences in engineering and metallurgy  (especially over time) probably affect things too.

 

Sorry if that isn't answering what you're specifically asking I'm trying to guess at it from your words and where in Janes you're alluding (unless you mean the Damping section?)

 

Edit (again after many):  Maybe this is what you're referring to from 13.4 in Jane's? 

 

https://imgur.com/a/Et56F

 

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4 hours ago, Jamby said:

Why does Horstmann suspension necessarily denote bad tank design? I think it was arguably quite suitable for the speed that tanks like the Chieftain could reasonably reach, given what I've been reading here:

https://archive.org/stream/Janes_Technology_of_Tanks_01/Janes_Technology_of_Tanks_01_djvu.txt

 

The part I'm referring to is about two thirds of the way down the document - section 13 (I'm sorry for not linking the specific screenshot, but I absolutely cannot manage to do it somehow) - and seems to suggest that the appropriate choice of suspension is largely dependent on the speed you're moving at, from leaf-spring at the lowest speeds to torsion bar at the highest.

 

Unless you were bombing along rough country at particularly high speed (even for a vehicle designed to do that to a degree), would the difference between torsion bar and Horstmann suspension really be appreciable? Are there tankers from both sides of the pond here?

 

 

 

 

 

I think its partly an in-joke (the British were about as good at tonk design in WW2 as you would expect given the amount of effort they put into it, which was none) and partly because the Brits have this weird tendency to combine good engineering with contrarian bodging in all their stuff.

 

Going back to a 1920s suspension design for all your tanks just as literally everyone else is embracing torsion bars is... very british.

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3 hours ago, Jamby said:

Why does Horstmann suspension necessarily denote bad tank design? I think it was arguably quite suitable for the speed that tanks like the Chieftain could reasonably reach, given what I've been reading here:

https://archive.org/stream/Janes_Technology_of_Tanks_01/Janes_Technology_of_Tanks_01_djvu.txt

 

The part I'm referring to is about two thirds of the way down the document - section 13 (I'm sorry for not linking the specific screenshot, but I absolutely cannot manage to do it somehow) - and seems to suggest that the appropriate choice of suspension is largely dependent on the speed you're moving at, from leaf-spring at the lowest speeds to torsion bar at the highest.

 

Unless you were bombing along rough country at particularly high speed (even for a vehicle designed to do that to a degree), would the difference between torsion bar and Horstmann suspension really be appreciable? Are there tankers from both sides of the pond here?

 

While it is true that Chieftain had such a low power to weight ratio that putting independent suspension on it wouldn't much improve its mobility, that hardly speaks well of it.  It meant that Chieftain was generally inadequate, both in terms of power to weight and suspension performance.  Centurion, Conqueror and Chieftain are literally the only tanks designed after WWII without independent roadwheel suspension.  It was a specifically British bit of backwardness.  They were behind on hydraulic torque converters in tank transmissions, behind on smoothbore guns and APFSDS ammunition, and behind on fire control systems too.  The track record of British tank design post 1945 is really not very impressive.

On top of that it was contemporaneous with the T-64, which sported a stereo rangefinder, much higher power to weight ratio, composite armor, and a comparable gun while being something like fifteen tonnes lighter than Chieftain.

The design of Chieftain isn't all bad, and there are several individually good ideas on it.  The mantletless turret is a good idea, the reclined driver is a good idea, and the ammunition stowage is probably the safest of any tank of that generation.  But overall?  It's underwhelming.

 

2 hours ago, A_Mysterious_Stranger said:

Well there's different kinds of suspension that have evolved since WW1 and they offer different tradeoffs (although some have been superseded) such as cost, simplicity/reliability, effectiveness, etc.   but I also think there may be an element of semantics to it (how people define such things, which is where the sources you use and quality of that source) probably applies.  

 

Also there's going to be more issues than just 'speed' to consider in your suspension choice.  For example on page 319 of Jane's:

 

 

It would seem tradeoffs and design (complexity, protection, weight, internal space) are drivers over 'good' or 'bad' decisions as how it is implemented (possibly getting back to the 'semantics' again?)   Speed will matter too since that affects comfort/safety/stability of the crew and vehicle vibration and such matters as Collimatrix described (the better a suspension can cancel out the bouncing/shaking of rough terrain, the faster you could in theory go.) but it's still going to be about tradeoffs in the end (including speed.)

 

Also, the suspension itself is just part of a larger system (Wheels for example, which is also discussed in Janes) which can also play a role and probably shouldn't be ignored.

 

Differences in engineering and metallurgy  (especially over time) probably affect things too.

 

Sorry if that isn't answering what you're specifically asking I'm trying to guess at it from your words and where in Janes you're alluding (unless you mean the Damping section?)

 

Edit (again after many):  Maybe this is what you're referring to from 13.4 in Jane's? 

 

https://imgur.com/a/Et56F

 



There are indeed cost issues to consider, but these days those aren't pressing.  The cost of modern tanks is driven by the fancy composite armor and fire control systems so advanced that they are practically magical.

Again, the type of suspension isn't too useful a piece of information.  The M60 and M1 Abrams both have torsion bar suspension, but the M1's suspension articulates through about double the range of motion that the M60's does, and thus has correspondingly better ride when hauling ass offroad.  Leaf spring suspensions could be used for a high-speed tank.  Indeed, the early Daimler Benz VK. 30.01 prototypes were slated to have leaf spring suspension, and they were only later changed to torsion bars because some asshole in the bureaucracy had a fetish for interleaved roadwheels and torsion bars.  Seriously, that's what the Osprey book on the matter says.

Leaf springs would weigh somewhat more than torsion bars for the same performance.  Imagine bending a leaf spring; the atoms of iron in the outer surfaces on the top and bottom of the leaf spring are being stretched apart from each other the most.  This stretching of the metallic bonds between the atoms is how a spring stores energy.  The atoms in the center of the leaf spring are being deflected apart from each other very little, they're nearly deadweight.  The atoms on the sides of the leaf spring aren't doing much either.

A torsion bar is a big cylindrical tube that gets twisted about its long axis.  Therefore, the entire surface of the cylinder minus the ends is contributing to storage of energy.  The center of the torsion bar isn't storing much work, and there has been the odd attempt here and there to use hollow torsion bars to further improve suspension efficiency.  But for the most part, normal torsion bars are satisfactory and offer a good performance to weight ratio relative to other spring types.

Now, there are all sorts of interesting considerations when it comes to servicing the stupid things.  Torsion bar suspensions have a few problems here.

BZLTede.jpg

Torsion bar suspensions are almost always slightly asymmetrical.

E7XpCjQ.png
This is simply because one bar has to sit slightly in front of the other, which means that one roadwheel will end up sitting slightly in front of the other.  That leading wheel will eat more of the shock from bumps, which in turn means that the leading torsion bar will wear out faster than the others.

Actually changing out torsion bars ranges from a pain to a giant pain if the hull is somehow warped, as noted above.  The Israelis noted that the Horstmann suspension on their Centurions was faster to swap out than the torsion bars on their M48s.  This should not be construed as a defense of Horstmann suspension in TYOOL 1973, however.  There were plenty of other suspension systems that were completely external to the hull of the tank that offered independent roadwheel suspension, like the Belleville washer suspension in the Pz 68 and the external coil spring suspension the Israelis ultimately adopted for the Merkava.

Another problem of torsion bar suspensions is that the bars themselves take up space inside the hull, and thus force the turret basket to be a little higher:

88xAInV.png

But there are ways around this; as in the AMX-30:

FKMkxku.jpg

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One thing that have always surprised me is that even on new tank designs we still see torsion bars suspensions (T-14 I'm looking at you) while hydrogas seem to be superior in every single way but cost.

 

I mean that it allow for a smoother ride, doesn't intrude into the hull (most important point from a design perspective), add some metal on the sides where there is usually none, is external so it's not too much of a pain to replace and finally allow you to play with ground clearance and hull pitch (IMO the last part is more of a nice gimmick than something really useful combat).

 

How expensive are hydrogas compared to torsion bar (but as Collimatrix said, suspensions doesn't make up for a lot of the price in a modern MBT)?

Or is there another major downside I overlooked?

 

Same could be said about Israli coil spring suspension (which seem close to hydrogas but are maybe cheaper)

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You can see in some of the pictures in the T-14 thread that the side armor under the top run of the track is ridiculously thick.  Any sort of external suspension would probably have taken up too much room there.  So that is one advantage of torsion bars.

Aside from that, hydropneumatic seems generally superior.  I'm not even sure that it's more expensive.  Some modern torsion bars are made of very fancy and expensive VIM/VAR or electroslag steels.  I suspect (but don't know for sure) that the reason the Leo 2 and Abrams have nearly double the range of motion in their suspensions is that their torsion bars are made of these low-fatigue steels.

 

I don't know why the independent external coil spring suspension wasn't more popular.  It seems like a good and logical design.  The US T49 tank destroyer prototype used it:

iSPvaWq.png

And as you can see, it also had a rear sprocket drive.  But the production M18 Hellcat went with torsion bars and a frontal drive sprocket for reasons I do not ken.

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10 minutes ago, Collimatrix said:

I don't know why the independent external coil spring suspension wasn't more popular.  It seems like a good and logical design.  The US T49 tank destroyer prototype used it:

And as you can see, it also had a rear sprocket drive.  But the production M18 Hellcat went with torsion bars and a frontal drive sprocket for reasons I do not ken.

 

My guess would be steel fatigue, the section of a coil spring being smaller than the one of a torsion bar probably meant that coil spring could endure less cycles.

But metallurgy has come a long way since WWII.

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6 hours ago, A_Mysterious_Stranger said:

(. . .)

 

Sorry if that isn't answering what you're specifically asking I'm trying to guess at it from your words and where in Janes you're alluding (unless you mean the Damping section?)

 

Edit (again after many):  Maybe this is what you're referring to from 13.4 in Jane's? 

 

https://imgur.com/a/Et56F

 

 

This is the bit I meant - I think I finally figured out how to link it:

Screenshot

Edited by Jamby
Fixing broken link
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7 hours ago, Alzoc said:

 

My guess would be steel fatigue, the section of a coil spring being smaller than the one of a torsion bar probably meant that coil spring could endure less cycles.

But metallurgy has come a long way since WWII.

 

I'm no mechanical engineer, but as I understand it coil springs are basically torsion springs that are coiled into a helix.  So torsion bars and coil springs should have similar energy density and fatigue properties.

That said, fatigue in springs is largely dependent on how smooth the surface of the spring is kept.  As I said above, it's the surface of the spring that is storing the most work, so the bonds between the atoms are at their most stretched there.  Any imperfections in the surface of the spring, like little micro-nicks or corrosion tend to spread and accelerate fatigue.

So the fact that a torsion bar is safely tucked into the hull of the tank where it is less likely to develop such imperfections may give them an edge in fatigue life.  So... score another point for torsion bars, I guess.

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48 minutes ago, Collimatrix said:

 

I'm no mechanical engineer, but as I understand it coil springs are basically torsion springs that are coiled into a helix.  So torsion bars and coil springs should have similar energy density and fatigue properties.

 

As you said, both work in flexion.

So for the same energy absorbed, the coil spring will absorb it over a smaller section (in each "floor" of the spring) but at the same time the amplitude of movement on the thread should be smaller.

 

Edit: They work in torsion my bad, I wasn't thinking (and reading) straight. :wacko:

Time to stop for today

 

Since fatigue comes from the propagation of defects in the structure of the material, which makes it stiffer and stiffer (until it fail), I think that the amplitude of the movement should have some importance.

 

On top of that there is also the problem of surface defects, and here it would make sense for springs to be more vulnerable as you said.

 

I think it's a non trivial problem and I'm not a mechanical engineer either so I haven't done this kind of calculation since school (and when I did it was in simple configurations anyway).

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55 minutes ago, EnsignExpendable said:

Foam core or air filled? Air filled tires offer a smoother ride, but are obviously easy to shoot out. Foam core tires are bulletproof, but have the downside of settling if you're parked for too long, so the first few minutes of your ride will be very bumpy.

Are they cheaper than conventional roadwheels? 

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On 3/21/2018 at 4:04 AM, Collimatrix said:

You can see in some of the pictures in the T-14 thread that the side armor under the top run of the track is ridiculously thick.  Any sort of external suspension would probably have taken up too much room there.  So that is one advantage of torsion bars.

Aside from that, hydropneumatic seems generally superior.  I'm not even sure that it's more expensive.  Some modern torsion bars are made of very fancy and expensive VIM/VAR or electroslag steels.  I suspect (but don't know for sure) that the reason the Leo 2 and Abrams have nearly double the range of motion in their suspensions is that their torsion bars are made of these low-fatigue steels.

 

I don't know why the independent external coil spring suspension wasn't more popular.  It seems like a good and logical design.  The US T49 tank destroyer prototype used it:

iSPvaWq.png

And as you can see, it also had a rear sprocket drive.  But the production M18 Hellcat went with torsion bars and a frontal drive sprocket for reasons I do not ken.

Torsion bar, likely because of the increased weight of the M18 (T70) over the T49 & T67, and front drive because of weight (re) distribution, and it allowed the engine and transmission to be easily serviced/replaced as independent units. (the engine and trans will "slide out" on tracks.).

 

 

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On 21/03/2018 at 9:52 AM, Collimatrix said:

 

While it is true that Chieftain had such a low power to weight ratio that putting independent suspension on it wouldn't much improve its mobility, that hardly speaks well of it.  It meant that Chieftain was generally inadequate, both in terms of power to weight and suspension performance.  Centurion, Conqueror and Chieftain are literally the only tanks designed after WWII without independent roadwheel suspension.  It was a specifically British bit of backwardness.  They were behind on hydraulic torque converters in tank transmissions, behind on smoothbore guns and APFSDS ammunition, and behind on fire control systems too.  The track record of British tank design post 1945 is really not very impressive.

On top of that it was contemporaneous with the T-64, which sported a stereo rangefinder, much higher power to weight ratio, composite armor, and a comparable gun while being something like fifteen tonnes lighter than Chieftain.

The design of Chieftain isn't all bad, and there are several individually good ideas on it.  The mantletless turret is a good idea, the reclined driver is a good idea, and the ammunition stowage is probably the safest of any tank of that generation.  But overall?  It's underwhelming.

 



There are indeed cost issues to consider, but these days those aren't pressing.  The cost of modern tanks is driven by the fancy composite armor and fire control systems so advanced that they are practically magical.

Again, the type of suspension isn't too useful a piece of information.  The M60 and M1 Abrams both have torsion bar suspension, but the M1's suspension articulates through about double the range of motion that the M60's does, and thus has correspondingly better ride when hauling ass offroad.  Leaf spring suspensions could be used for a high-speed tank.  Indeed, the early Daimler Benz VK. 30.01 prototypes were slated to have leaf spring suspension, and they were only later changed to torsion bars because some asshole in the bureaucracy had a fetish for interleaved roadwheels and torsion bars.  Seriously, that's what the Osprey book on the matter says.

Leaf springs would weigh somewhat more than torsion bars for the same performance.  Imagine bending a leaf spring; the atoms of iron in the outer surfaces on the top and bottom of the leaf spring are being stretched apart from each other the most.  This stretching of the metallic bonds between the atoms is how a spring stores energy.  The atoms in the center of the leaf spring are being deflected apart from each other very little, they're nearly deadweight.  The atoms on the sides of the leaf spring aren't doing much either.

A torsion bar is a big cylindrical tube that gets twisted about its long axis.  Therefore, the entire surface of the cylinder minus the ends is contributing to storage of energy.  The center of the torsion bar isn't storing much work, and there has been the odd attempt here and there to use hollow torsion bars to further improve suspension efficiency.  But for the most part, normal torsion bars are satisfactory and offer a good performance to weight ratio relative to other spring types.

Now, there are all sorts of interesting considerations when it comes to servicing the stupid things.  Torsion bar suspensions have a few problems here.

BZLTede.jpg

Torsion bar suspensions are almost always slightly asymmetrical.

E7XpCjQ.png
This is simply because one bar has to sit slightly in front of the other, which means that one roadwheel will end up sitting slightly in front of the other.  That leading wheel will eat more of the shock from bumps, which in turn means that the leading torsion bar will wear out faster than the others.

Actually changing out torsion bars ranges from a pain to a giant pain if the hull is somehow warped, as noted above.  The Israelis noted that the Horstmann suspension on their Centurions was faster to swap out than the torsion bars on their M48s.  This should not be construed as a defense of Horstmann suspension in TYOOL 1973, however.  There were plenty of other suspension systems that were completely external to the hull of the tank that offered independent roadwheel suspension, like the Belleville washer suspension in the Pz 68 and the external coil spring suspension the Israelis ultimately adopted for the Merkava.

Another problem of torsion bar suspensions is that the bars themselves take up space inside the hull, and thus force the turret basket to be a little higher:

88xAInV.png

But there are ways around this; as in the AMX-30:

FKMkxku.jpg

Off topic, but how is a mantlet-less turret better?

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23 hours ago, Toxn said:

Off topic, but how is a mantlet-less turret better?

 

For various reasons the edge of an armor array is always a weak point.  There's free edge effect, the fact that the moving elements in NERA/ERA usually don't go all the way to the edge, and the fact that their range of intersection of incoming threats is smallest at one edge.  A mantlet-less turret presents the smallest possible weakened zone in the turret frontal armor from this edge.

 

Most mantlets don't have very much armor.  Look at the picture of the Leclerc's mantlet in the Contemporary Western Tank thread if you want to see the worst example.  Even on tanks with relatively thick, and presumably well constructed mantlets like the Leo 2A5 and up, there will still be a weak point where the edges of the mantlet touch the edges of the hole for the gun.

 

There are two objections to the mantletless design.  The first is that it will make gun replacement harder.  This is only true if the gun tube can't detatch from the gun breech.  On some guns the tube can loosen from the breech and come out forward, and on some it cant.  Obviously, a mantletless turret ought to use one that can.  The second objection is that the trunnions will intrude into the armor package and create a weak point (although this is obviously true of designs with mantlets too).  The solution to that is just make the package a bit thicker on top of where the trunnions are.

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11 minutes ago, Collimatrix said:

 

For various reasons the edge of an armor array is always a weak point.  There's free edge effect, the fact that the moving elements in NERA/ERA usually don't go all the way to the edge, and the fact that their range of intersection of incoming threats is smallest at one edge.  A mantlet-less turret presents the smallest possible weakened zone in the turret frontal armor from this edge.

 

Most mantlets don't have very much armor.  Look at the picture of the Leclerc's mantlet in the Contemporary Western Tank thread if you want to see the worst example.  Even on tanks with relatively thick, and presumably well constructed mantlets like the Leo 2A5 and up, there will still be a weak point where the edges of the mantlet touch the edges of the hole for the gun.

 

There are two objections to the mantletless design.  The first is that it will make gun replacement harder.  This is only true if the gun tube can't detatch from the gun breech.  On some guns the tube can loosen from the breech and come out forward, and on some it cant.  Obviously, a mantletless turret ought to use one that can.  The second objection is that the trunnions will intrude into the armor package and create a weak point (although this is obviously true of designs with mantlets too).  The solution to that is just make the package a bit thicker on top of where the trunnions are.

Thank you!

This makes a lot of sense, but then raises the question of why big mantlets used to be a thing?

Is edge effect just a lot less of an issue than movement in a NERA array?

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      1.      Background.
      As part of the War of 2248 against the Perfidious Cascadians, great deficiencies were discovered in the Heavy tank DF-1. As detailed in report [REDACTED], the DF-1 was quite simply no match for the advanced weaponry developed in secret by the Cascadian entity. Likewise, the DF-1 has fared poorly in the fighting against the heretical Mormonhideen, who have developed many improvised weapons capable of defeating the armor on this vehicle, as detailed in report [REDACTED]. The Extended War on the Eastern Front has stalled for want of sufficient survivable firepower to push back the Mormon menace beyond the Colorado River south of the Vegas Crater.
      The design team responsible for the abject failure that was the DF-1 have been liquidated, which however has not solved the deficiencies of the existing vehicle in service. Therefore, a new vehicle is required, to meet the requirements of the People’s Auditory Forces to keep the dream of our lord and prophet alive.
       
       
      Over the past decade, the following threats have presented themselves:
      A.      The Cascadian M-2239 “Norman” MBT and M-8 light tank
      Despite being approximately the same size, these 2 vehicles seem to share no common components, not even the primary armament! Curiously, it appears that the lone 120mm SPG specimen recovered shares design features with the M-8, despite being made out of steel and not aluminum like the light tank. (based on captured specimens from the battle of Crater Lake, detailed in report [REDACTED]).
      Both tanks are armed with high velocity guns.
      B.      The Cascadian BGM-1A/1B/1C/1D ATGM
      Fitted on a limited number of tank destroyers, several attack helicopters, and (to an extent) man-portable, this missile system is the primary Cascadian anti-armor weapon other than their armored forces. Intelligence suggests that a SACLOS version (BGM-1C) is in LRIP, with rumors of a beam-riding version (BGM-1D) being developed.
      Both warheads penetrate approximately 6 cone diameters.
      C.      Deseret tandem ATR-4 series
      Inspired by the Soviet 60/105mm tandem warhead system from the late 80s, the Mormon nation has manufactured a family of 2”/4” tandem HEAT warheads, launched from expendable short-range tube launchers, dedicated AT RRs, and even used as the payload of the JS-1 MCLOS vehicle/man-portable ATGM.
      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
      Addendum 1 - more armor details
      Good luck, and may Hubbard guide your way to enlightenment!
    • By Monochromelody
      IDF had kept about 100 Tiran-6/T-62s since 1973, and remain service until 1990s. 
       
      I wonder if there's any modification on Tiran-6, like changing the powerpack into 8V71T+XTG-411, adapting steering wheel. 
       
      I also heard that British ROF had produce a batch of 115mm barrel for IDF, while MECAR or NEXTER produced high-performance APFSDS for 115mm gun. Did IDF really use these barrels for original barrel replacement? 
       
      And about protection, did IDF put Blazer ERA on Tiran-6? Or they use more advanced APS like Trophy? 
       
      Thank you. 
    • By Sturgeon
      The LORD was with the men of Deseret. They took possession of the hill country, but they were unable to drive the people from the plains, because they had chariots of steel.
      —The Book of Latter Day Saints, Ch 8, vs. 3:10, circa 25th Century CE
       
      BULLETIN: ALL INDUSTRIAL-MECHANICAL CONCERNS
       
      SOLICITATION FOR ALL-TERRAIN BATTLE TANK
       
      The Provisional Government of the Lone Free State of Texas and The Great Plains issues the following solicitation for a new All-Terrain Battle Tank. The vehicle will be the main line ground combat asset of the Lone Free State Rangers, and the Texas Free State Patrol, and will replace the ageing G-12 Scout Truck, and fill the role of the cancelled G-42 Scout Truck. The All-Terrain Battle Tank (ATBT) will be required to counter the new Californian and Cascadian vehicles and weapons which our intelligence indicates are being used in the western coast of the continent. Please see the attached sheet for a full list of solicitation requirements.
       

       
      Submissions will be accepted in USC only.
       
       
      Supplementary Out of Canon Information:
       
       
      I.     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 judge.
      Structural materials:
                                                                    i.     RHA/CHA
      Basic steel armor, 360 BHN. The reference for all weapon penetration figures, good impact properties, fully weldable. Available in thicknesses up to 4 inches (RHA) 8 inches (CHA). 
      Density- 0.28 lb/in^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 4 inches.
      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- 0.1 lb/in^3 (approx. 1/3 of steel).
      For structural integrity, the following guidelines are recommended:
      For heavy vehicles (30-40 tons), not less than 1 in RHA/1.75 in Aluminum base structure
      For medium-light vehicles (<25 tons), not less than 0.5 in RHA/1 in 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 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
       
    • By Beer
      I haven't found an appropriate thread where to put some interesting rare stuff related to WW2 development, be it industrial one or makeshift field modifications. 
       
      Let's start with two things. The first one is a relatively recently found rarity from Swedish archives - a drawing of ČKD/BMM V8H-Sv tank. The drawing and a letter was found by WoT enthusiasts in Swedish archives in 2014 (the original announcement and the drawing source is here). The drawing is from a message dated 8th September 1941. One of the reasons why this drawing was not known before may be that the Czech archives were partially destroyed by floods in 2002. Anyway it is an export modification of the V-8-H tank accepted into Czechoslovak service as ST vz.39 but never produced due to the cancelation of all orders after Münich 1938 (for the same reason negotiations about licence production in Britain failed). Also later attempt to sell the tank to Romania failed due to BMM being fully busy with Wehrmacht priority orders. The negotiations with Sweden about licence production of V8H-Sv lasted till 1942, at least in May 1942 Swedish commission was present in Prague for negotiations. The tank differed compared to the base ST vz.39 in thicker armor with different front hull shape (armor 60 mm @ 30° on the hull front and also 60 mm on the turret; all sides were 40 mm thick). The tank was heavier (20 tons) and had the LT vz.38 style suspension with probably even larger wheels. The engine was still the same Praga NR V8 (240-250 Hp per source). The armament was unchanged with 47 mm Škoda A11 gun and two vz.37 HMG. The commander's cupola was of the simple small rotating type similar to those used on AH-IV-Sv tankettes. It is known that the Swedes officially asked to arm the tank with 75 mm gun, replace the engine with Volvo V12 and adding third HMG to the back of the turret. In the end the Swedes decided to prefer their own Strv/m42. 

      Source of the drawing
       
      The second is makeshift field modification found on Balkans. It appears Ustasha forces (and possibly some SS anti-partizan units) used several Italian M15/42 medium tanks with turrets from Pz.38(t). There are several photos of such hybrids but little more is known. On one photo it is possible to see Ustasha registration number U.O. 139.

      Few more photos of such hybrid.
       
      It appears that the source of all those photos to be found on the internet is this book, Armoured units of the Axis forces in southeastern Europe in WW2 by Dinko Predoevic. 
       
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