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Help me understand tank suspension

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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
Adding link

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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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      Let's say you're developing a tank with a unique (AKA non-historical) gun for one of our competitions here on SH. It would be nice to have an idea of the size of the gun, its shells, and what their performance both in terms of shell weight and velocity but also penetration, wouldn't it? Well, fortunately there is a way to do this with reasonably accurate results using your solid modeling software and some free to use browser tools.

      First, you want to have a general idea of the size and performance of your gun. For this example, I decided I wanted an optimized, high velocity 85mm caliber gun with a case about as big as the 7.5cm KwK 42 (as it happened, I ended up with a case that had significantly greater volume, but that fact is unimportant for this example). The cartridge I decided on has a 130mm wide rim and a 640mm long case, of course in 85mm caliber. My first step was to model this case in SolidWorks:


       
      You will also need to model your projectile, in this case a tungsten-carbide cored APCR round:


       
      Next, we need a bit of freeware: A Powley computer. Originally developed by DuPont engineers for small arms ammunition, the Powley computer is an accurate enough tool to use for much larger tank rounds as well! When you click the link, you'll be greeted with this screen:
       

       
      You'll note the dimensions are in inches and this thing called "grains" (abbreviated "gn"). The grain is an archaic Imperial mass unit equal to 1/7000th of a pound which is still used in the small arms field, today. Another quirk of small arms has the case capacity - a volume measurement - listed in grains as well. This is in fact grains of water (gn H2O), or the weight of water that will fill the case to the top. To find this, simply multiply the volume in cubic centimeters by 15.43 - which is also the exchange rate between the metric gram and grains mass.
       
      Finding the volume of the case is easy with a solid modeling program; simply model the interior as a solid and find the volume of that solid:


       
      Filling in my Powley inputs gives me this:
       

       
      Note that I typically use the diameter of the projectile across the driving bands for "Bullet Diameter", but it really makes very little difference.
       
      So far, though, we haven't actually produced any results. That's because our gun is well outside the bounds of DuPont production IMR powders, hence the output "Much slower than (IMR) 4831" in the lower left. So, we need to override the computer by checking the box next to the blue "Pressure" function, and typing in a pressure value in CUP that is reflective of tank guns of whatever era we are trying to represent. My tank gun is trying to represent something from about the late 1940s/early 1950s, so I'm going to use 45500 CUP EDIT: USE 41000 CUP for APCBC and 42800 CUP FOR APCR (or better yet, do your own calibration!):
       

       
      This gives me an estimated muzzle velocity of 3,964 ft/s for my L/50 barrel. Not bad! Note the outputs on the left, which tell you a bunch of fun facts about your round but aren't terribly relevant to what we're doing here today. Next, we need to put this gun's performance in terms of penetration. The way I like to do this is through comparative analysis.
       
      The first thing we need is to know to find penetration the ballistic performance of our round. We can estimate this using JBM's ballistic calculator and a few rules of thumb. When opening the calculator, the first thing you'll see is this:
       

       
      We care about basically none of these settings except BC, velocity, and maximum range. Caliber, projectile weight, chronograph distance, etc are all pretty irrelevant to us. Keep the environmental settings (temperature, pressure, etc.) set to their defaults. First, change the ballistic coefficient type from G1 to G7 using the dropdown menu. Then, change the muzzle velocity from 3000 to whatever the muzzle velocity was that was calculated by the Powley computer. Finally, set the maximum range to your desired distance - in my case 2,000 yards.

      For my round, I now have inputs that look like this:
       


      We also need to get some idea of how fast our projectile loses velocity, something we can't know for certain without actually building a real gun and test firing it - or at least without some really sophisticated simulations. However, projectiles with the same shape tend to fly the same way, and that's something we can exploit here. To figure this out, we need a graph showing us the performance of a real-life gun. Fortunately, there is a handy one for an IRL gun similar to what I'm designing, the 90mm M3 from World War II, and its M304 HVAP-T, which is broadly similar in construction and shape to my 85mm APCR projectile:
       

       
      Based on this chart, we see that the M304 should drop from its 3,350 ft/s muzzle velocity to about 2,500 ft/s at 2,000 yards. Doing a little trial and error with JBM tells me that this means the M304 has a G7 ballistic coefficient of about 1.13.
       
      Now, our projectile will not have the same ballistic coefficient, due to it being a different size and mass. But, we can figure out what its ballistic coefficient would be by finding its sectional density and comparing that to the sectional density of M304. To find sectional density, take the projectile's weight in grains and divide it by the square of the projectile's diameter in inches, times 7000. So for M304, we get:
       

       


      And for my 85mm, we get:


       

       
      This means that the ballistic coefficient for an identical-shape projectile with our size and weight will be about 1.019/1.330 - or 76.6% as much - as that of the 90mm M304. That means a BC of 0.866 G7 should be approximately correct for my 85mm APCR round. Let's plug that in:


       
      And then scroll down to the bottom to click "calculate", which gives us a big ol' chart that goes out to 2,000 yards:
       

       
      O-Kay! Now we have some data. It looks like at 2,000 yards, my projectile holds about 2,800 ft/s striking velocity. It's important to note here that what we really care about isn't the striking velocity of the projectile per se, but the velocity and energy of the projectile's core. The core is what's actually doing a lot of work to the armor, so for now let's stop thinking in terms of the whole projectile, and take a look at these two cores, that of the M304 90mm HVAP, and that of my 85mm APCR round. The core of the 90mm M304 is an approximately 8 pound lump of tungsten-carbide that is about 45mm in width. My penetrator is also 8 pounds, but it's longer and thinner in proportion - just 40mm wide, rather than 45mm. This means my penetrator will penetrate more armor at a given striking velocity, and we can estimate how much more by taking the specific energy of the rounds and comparing them. That is, the energy in Joules of the penetrator alone, divided by the penetrator's diameter squared:
       

       


      So the specific energy at 2,000 yards is about 826J/mm^2. Now, we need to find out at what impact velocity the M304 penetrator produces this same specific energy. Do do that, we go backwards, using the figures for M304:
       

       

       
      Therefore, the equivalent impact velocity for my 85mm APCR round at 2,000 yards is 3,150 ft/s for the M304. That means, in theory, that the M304 would have to impact a target at 3,150 ft/s to produce equivalent penetration of RHA to my 85mm APCR striking at just 2,800 ft/s.

      Now, we head back to that chart:


       
      On the left side of the graph, we put our cursor on the line that corresponds to approximately 3,150 ft/s velocity, and follow it over until it hits the curved line that corresponds with the angle of plate we care about - arbitrarily, let's pick 20 degrees. Then, we follow that point straight down until it hits the x-axis:


       
      Therefore, we estimate that at 2,000 yards, my 85mm has just over 10 inches of RHA penetration - not bad at all for a lowly APCR round!
    • By LostCosmonaut
      Backstory (skip if you don't like alternate history junk)
       
      The year is 2239. It has been roughly 210 years since the world was engulfed in nuclear war. Following the war, the United States splintered into hundreds of small statelets. While much knowledge was retained in some form (mostly through books and other printed media), the loss of population and destruction of industrial capability set back society immensely.
       
      Though the Pacific Northwest was less badly hit than other areas, the destruction of Seattle and Portland, coupled with the rupturing of the Cascadia Subduction Zone in 2043, caused society to regress to a mid-19th century technology level. However, in the early 2100s, the Cascade Republic formed, centered near Tacoma. The new nation grew rapidly, expanding to encompass most of Washington and Oregon by 2239. The Cascade Republic now extends from the Klamath River in the south to the Fraser River in the north, and from the Pacific roughly to central Idaho. Over time, the standard of living and industrial development improved (initially through salvaging of surviving equipment, by the late 2100s through new development); the population has grown to about 4.5 million (comparable to 1950 levels), and technology is at about a 1940 level. Automobiles are common, aircraft are less common, but not rare by any means. Computers are nonexistent aside from a few experimental devices; while scientists and engineers are aware of the principles behind microchips and other advanced electronics, the facilities to produce such components simply do not exist. Low rate production of early transistors recently restarted.
       
      The current armored force of the Cascade Republic consists of three armored brigades. They are presently equipped with domestically produced light tanks, dating to the 2190s. Weighing roughly 12 tons and armed with a 40mm gun, they represented the apex of the Cascade Republic's industrial capabilities at the time. And when they were built, they were sufficient for duties such as pacifying survivalist enclaves in remote areas. However, since that time, the geopolitical situation has complicated significantly. There are two main opponents the Cascade Republic's military could expect to face in the near future.
       
      The first is California. The state of California was hit particularly hard by the nuclear exchange. However, in 2160, several small polities in the southern part of the state near the ruins of Los Angeles unified. Adopting an ideology not unfamiliar to North Korea, the new state declared itself the successor to the legacy of California, and set about forcibly annexing the rest of the state. It took them less than 50 years to unite the rest of California, and spread into parts of Arizona and northern Mexico. While California's expansion stopped at the Klamath River for now, this is only due to poor supply lines and the desire to engage easier targets. (California's northward advanced did provide the final impetus for the last statelets in south Oregon to unify with the Cascade Republic voluntarily).
       
      California is heavily industrialized, possessing significant air, naval, and armored capabilities. Their technology level is comparable to the Cascade Republic's, but their superior industrial capabilities and population mean that they can produce larger vehicles in greater quantity than other countries. Intelligence shows they have vehicles weighing up to 50 tons with 3 inches of armor, though most of their tanks are much lighter.

      The expected frontlines for an engagement with the Californian military would be the coastal regions in southern Oregon. Advancing up the coastal roads would allow California to capture the most populated and industrialized regions of the Cascade Republic if they advanced far enough north. Fortunately, the terrain near the border is very difficult and favors the defender;


      (near the Californian border)


      The other opponent is Deseret, a Mormon theocratic state centered in Utah, and encompassing much of Nevada, western Colorado, and southern Idaho. Recently, tension has arisen with the Cascade Republic over two main issues. The first is the poorly defined border in Eastern Oregon / Northern Nevada; the old state boundary is virtually meaningless, and though the area is sparsely populated, it does represent a significant land area, with grazing and water resources. The more recent flashpoint is the Cascade Republic's recent annexation of Arco and the area to the east. Deseret historically regarded Idaho as being within its sphere of influence, and maintained several puppet states in the area (the largest being centered in Idaho Falls). They regard the annexation of a signficant (in terms of land area, not population) portion of Idaho as a major intrusion into their rightful territory. That the Cascade Republic has repaired the rail line leading to the old Naval Reactors Facility, and set up a significant military base there only makes the situation worse.
       
      Deseret's military is light and heavily focused on mobile operations. Though they are less heavily mechanized than the Cascade Republic's forces, operating mostly armored cars and cavalry, they still represent a significant threat  to supply and communication lines in the open terrain of eastern Oregon / southern Idaho.


      (a butte in the disputed region of Idaho, near Arco)
       
      Requirements
       
      As the head of a design team in the Cascade Republic military, you have been requested to design a new tank according to one of two specifications (or both if you so desire):
       
      Medium / Heavy Tank Weight: No more than 45 tons Width: No more than 10.8 feet (3.25 meters) Upper glacis / frontal turret armor of at least 3 in (76mm) LoS thickness Side armor at least 1in (25mm) thick (i.e. resistant to HMG fire) Power/weight ratio of at least 10 hp / ton No more than 6 crew members Primary armament capable of utilizing both anti-armor and high explosive rounds Light tank Weight: No more than 25 tons Width: No more than 10.8 feet Upper glacis / frontal turret armor of at least 1 in thickness Side armor of at least 3/8 in (10mm) thickness Power/weight ratio of at least 12 hp / ton No more than 6 crew members Primary armament capable of utilizing both anti-armor and high explosive rounds  
      Other relevant information:
      Any tank should be designed to operate against either of the Cascade Republic's likely opponents (California or Deseret) The primary heavy machine gun is the M2, the primary medium machine gun is the M240. Use of one or both of these as coaxial and/or secondary armament is encouraged. The secret archives of the Cascade Republic are available for your use. Sadly, there are no running prewar armored vehicles, the best are some rusted hulks that have long been stripped of usable equipment. (Lima Tank Plant ate a 500 kt ground burst) Both HEAT and APFSDS rounds are in testing. APCR is the primary anti-armor round of the Cascade Republic. Either diesel or gasoline engines are acceptable, the Cascade Republic is friendly with oil producing regions in Canada (OOC: Engines are at about a late 1940s/early 50s tech level) The adaptability of the tank to other variants (such as SPAA, SPG, recovery vehicle, etc.) is preferred but not the primary metric that will be used to decide on a design. Ease of maintenance in the field is highly important. Any designs produced will be compared against the M4 Sherman and M3 Stuart (for medium/heavy and light tank), as these blueprints are readily available, and these tanks are well within the Cascade Republic's manufacturing capabilities.  
       
       
       
       
    • By Walter_Sobchak
      Since we don't have a thread for British and Commonwealth tanks of WWII, I thought I would start one.  
       
      Check out this manufacturers instructional video on the Crusader.
       
       
    • By Walter_Sobchak
      Since Xlucine suggested it in the general AFV thread, here is a new version of the old Tank ID thread that used to exist at the WoT forums, back before the great exodus to SH.
       
      The rules are simple.  Post a picture of some sort of AFV and everyone has to try to name what it is.  Try to avoid posting a new picture until the previous picture is identified.  Generally, the person who was first to correctly ID the picture in question gets to post the next picture, unless they want to pass.  If a picture is not ID'd in a day or two, the person that posted it should say what it is and bask in their own sense of superiority.   They should then post a new picture for the sake of keeping the thread moving.  Please, no fictional tanks, paper napkin drawings that never made it to prototype or pictures where the vehicle in question is obscured or particularly hard to see.  Also, if posting a picture of an unusual variant of a relatively common vehicle, be sure to note that you are looking for the specific variant name, not just the general family of vehicles it belongs to (for example, if I post a picture of a Panzer IV with the hydrostat drive, I would say in the post something like "What makes this Panzer IV unusual?" since everyone can ID a Panzer IV)
       
      It is perfectly ok to shame those that make spectacularly wrong guesses.  That's just how we roll around here.  
       
      I'll start 
       

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