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United States Military Vehicle General: Guns, G*vins, and Gas Turbines

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1 hour ago, David Moyes said:

 

That looks like a different branch of L-3 that is located in Toronto.  From what I can tell from poking around online, it looks like they were researching active suspension systems, which is a bit more sophisticated than the old Teledyne stuff L-3 inherited when they bought the tank engine plant in Muskegon MI.

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1 hour ago, 2805662 said:

Does this require a different mounting plate to the conventional M153 mounted on the SEP v2?

 

From what I can tell it doesn't have the folding mechanism or the 'popped collar' that blocked view from the commanders cupola.

 

Z5O9vVq.jpg

 

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On 7/9/2018 at 7:57 PM, Ramlaen said:

A pair of interesting photographs posted by Damian from @Walter_Sobchak's blog, not (just) because they show an Abrams testing hydropneumatic suspension but because they appear to show the glacis is thicker than it is around the driver's hatch.

 

PlHsWZ7.jpg

OF2QJra.jpg

 

Yes, the photo seems to support that the armor at the hatch might be thinner than the rest of the UFP. But the picture quality is so low...

 

I think these photos currently lead to more questions than they answer:

  • What was the reason to cut a hole into the upper front plate of the M1 Abrams?
  • Was this used to access some components mounted into the (former) fuel tanks? There seems to be an acess hatch or "plug" covering a hole on the left side. If the cut-out wasn't made straight, but rather tampers down (so that a simple "plug" could be used), then it would appear thicker when seen from this persperctive, although this overall seems rather unlikely. 
  • Last but not least the question should bbe asked, wether the greater armor thickness is limited to the fuel tanks or also covers the center section of the glacis (i.e. the section in front of the driver).

 

14 hours ago, Mighty_Zuk said:

I really don't know why HSU (Hydro Pneumatic Suspension) isn't a bigger hit than it is now.

I believe every tank design bureau in the world has at least toyed with the idea.

 

Gun depression is something we mostly hear about in games, but in real life it's still a very important aspect of the tank's firepower. Shame it took until now with the Abrams, and the absence of announced plans for the Merkava and Leopard are worrying.

 

There are three main reasons why hydropneumatic suspensions have been fitted to armored fighting vehicles:

  1. hydropneumatic suspensions double-act as shock absorbers, so they can deliver a smoother ride
  2. unlike torsion bars, the height of the supsension units can often be variable adjusted, thus allowing the make a tank "kneel" in order to keep a lower profile on uneven ground
  3. due to their compact nature, hydropneumatic suspension systems require no penetration of the hull floor

Arguably points 1 and 2 are pretty much irrelevant with modern electronics and fire control systems. Being able to fire accurately on the move is not a result of suspension performance anymore, but rather of gun stabilization and electronics. Specifically the advantage of point 1 can be minimized by simply using more/better shock absorbers.

 

Hydropneumatic suspensions are not automatically better than torsion-bar or even spring-based designs, it always depends on the exact implementation. The Leopard 2 for example has more suspension travel (i.e. it can negate greater variation in terrain height without letting a "shock" hit the chassis) than the Challenger 1 and Challenger 2, despite the latter two having hydrogas suspenions from Horstmann. The Leopard 2's swing arms and torsion bars are optimized for traveling over terrain at fast speeds, which lead to a combined travel (bump + rebound) of 526 mm, while the Challenger 2 has only 450 mm combined suspension travel. 

 

While hydropneumatic suspensions have been around for multiple decades, they tend to have their own issues with reliability, sturdiness and weight efficiency. 

 

In Germany hydropneumatic suspensions were found to be unreliable in the Leopard 1, the Schützenpanzer - Neu (project that lead to the Marder IFV), the MBT-70 and the Leopard 2 (PT 11), thus the all the tracked series production vehicles from the 1960s to the 2010s were made with torsion bar suspensions. A project in the 1980s supposedly solved the reliability issues, but it got extremely heavy (250 kg per module or 3.5 metric tons for a vehicle with seven roadwheel pairs), so the only realistic applications would have been a hybrid system as fielded on the Type 90 tank in Japan (i.e. only use HSUs at the front and rear, but keep torsion bars in the center section).

 

Unlike torsion bars, most/all types of hydropneumatic suspensions are temperature dependent - at low temperatures, the track tension and ground clearance of vehicles can decrease, in hot environments they can increase. During fast travel over rough terrain, the liquid/oil inside the hydropneumatic system and the seals can be damaged by overheating (temperatures of 200°C and above can be reached inside the hydropneumatic suspension when having to absorb lots of shocks under heavy load). High localized pressue can lead to high wear of certain elements. Last but not least HSUs tend to be a lot more complex.

 

These are some of the problems of hydropneumatic suspensions mentioned by Hilmes in his 2007 book. Modern engineering has managed to reduce or completely solve most of the issues, but I think to some extend they will prevail, thus always making torsion bars a more reliable, less complex and cheaper option. The Challenger 2 for example introduced a semi-active track tension adjusting mechanism in order to lower the influences of temperature on the tracks (but ground clearance still might vary). The Puma uses energy-absorbing end stops in the hydrostruts, which are used to spread the thermal energy on a larger surface area and thus preventing overheating. The main reasons speaking for a hydropneumatic suspension are mine protection (no penetration of the hull, specifically in combination with a decoupled running gear) and easier transportability (in case of wheeled vehicles, where HSUs are much more common: lowering the suspension allows air transportability in aircrafts with cargo height restriction).

 

12 hours ago, David Moyes said:

Horstman InArm:
https://horstmangroup.com/horstman-products/horstman-inarm/

Used on Puma and many in-development/prototype AFVs.

 

Actually the Puma uses Horstmann's Hydrostrut system: https://horstmangroup.com/horstman-products/horstman-hydrostrut/

 

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46 minutes ago, Mighty_Zuk said:

Point 2 is not negated at all by electronics. The ability to kneel is very useful when firing from over obstacles, especially in prepared firing positions.

 

Well, modern tanks are more accurate. At common combat ranges - at least those common in Central Europe (where over 50% of all combat is expected to take place at 1,500 m range or less) - it will make a rather small difference wether only the turret or the complete vehicle is visible.

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2 hours ago, Serge said:

Yes. 

And it takes precious time to kneel for a tank. 

Serge your goddamn profile picture is a kneeling tank!

On a serious note, how damaging is it to actually drive about a minute while kneeling?

I understand it may put the whole thing under more stress, but it should be able to take that, right?

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On 6/26/2018 at 11:38 AM, Ramlaen said:

 

I think you are correct, I misinterpreted the press release advocating FY19 funding for the fifth brigade and missed this part.

 

"The FY2018 Appropriations Bill, signed into law last month, provided $348 million to complete the fourth Brigade set of modernized Stryker vehicles."

 

 

https://www.appropriations.senate.gov/imo/media/doc/FY2019 Defense Appropriations Act, Report 115-290.pdf

"Army Stryker Double-V Hull A1.—Following the submission of the fiscal year 2019 President’s budget request, the Chief of Staff of the Army approved an Army Requirements Oversight Counsel [AROC] decision to upgrade and pure fleet all Flat-Bottom Hull [FBH] Stryker combat vehicles to the Double V–Hull A1 variant [DVHA1] in an effort to improve troop survivability and mobility. The fiscal year 2019 President’s budget request includes $21,900,000 to upgrade three FBH Stryker vehicles to DVHA1 variants. Subsequent to the AROC decision, the Army requested a budget based transfer of $149,390,000 to fund additional conversions. With the transfer, the Army can resource 53 DVHA1 conversions totaling $171,290,000. The Committee has also included a congressional adjustment of $94,000,000 for 29 conversions. In addition, the Committee understands that the Army plans to submit a reprogramming request to the congressional defense committees with a request to repurpose fiscal year 2018 congressionally directed funding totaling $285,000,000 for 91 DVHA1 conversions. If the reprogramming action is approved by the congressional defense committees, the Army will have sufficient resources to fund conversions for half the vehicles in a Stryker Brigade Combat Team [SBCT].

The Committee supports the net-zero fiscal year 2019 transfer request and additional funding for DVHA1 conversions, while anticipating the fiscal year 2018 reprogramming request. However, the Committee is concerned with the Army’s ability to maintain this level of effort through resourcing decisions in the Future Years Defense Program profile within future Program Objective Memorandum and budgeting cycles. Therefore, the Secretary of the Army shall report to the congressional defense committees not later than 30 days after the enactment of this act, on the Army’s acquisition strategy to upgrade and pure fleet the remaining FBH SBCTs to DVHA1 variants."

 

If passed that would be $550,290,000 to convert 173 flat bottom Strykers to the A1, which would be the first half of the fifth brigade to be converted.

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17 hours ago, SH_MM said:

There are three main reasons why hydropneumatic suspensions have been fitted to armored fighting vehicles:

  1. hydropneumatic suspensions double-act as shock absorbers, so they can deliver a smoother ride
  2. unlike torsion bars, the height of the supsension units can often be variable adjusted, thus allowing the make a tank "kneel" in order to keep a lower profile on uneven ground
  3. due to their compact nature, hydropneumatic suspension systems require no penetration of the hull floor

Arguably points 1 and 2 are pretty much irrelevant with modern electronics and fire control systems. Being able to fire accurately on the move is not a result of suspension performance anymore, but rather of gun stabilization and electronics. Specifically the advantage of point 1 can be minimized by simply using more/better shock absorbers.

 

Hydropneumatic suspensions are not automatically better than torsion-bar or even spring-based designs, it always depends on the exact implementation. The Leopard 2 for example has more suspension travel (i.e. it can negate greater variation in terrain height without letting a "shock" hit the chassis) than the Challenger 1 and Challenger 2, despite the latter two having hydrogas suspenions from Horstmann. The Leopard 2's swing arms and torsion bars are optimized for traveling over terrain at fast speeds, which lead to a combined travel (bump + rebound) of 526 mm, while the Challenger 2 has only 450 mm combined suspension travel. 

Not sure how comparing the suspension travel of two different suspensions makes sense here?
You could simply make a Hydropneumatic suspension with more travel right?

 

17 hours ago, SH_MM said:

While hydropneumatic suspensions have been around for multiple decades, they tend to have their own issues with reliability, sturdiness and weight efficiency. 

So you are saying that the hydropneumatic suspension is heavier than torsion bar, and that it is lighter is a myth?

 

17 hours ago, SH_MM said:

In Germany hydropneumatic suspensions were found to be unreliable in the Leopard 1, the Schützenpanzer - Neu (project that lead to the Marder IFV), the MBT-70 and the Leopard 2 (PT 11), thus the all the tracked series production vehicles from the 1960s to the 2010s were made with torsion bar suspensions. A project in the 1980s supposedly solved the reliability issues, but it got extremely heavy (250 kg per module or 3.5 metric tons for a vehicle with seven roadwheel pairs), so the only realistic applications would have been a hybrid system as fielded on the Type 90 tank in Japan (i.e. only use HSUs at the front and rear, but keep torsion bars in the center section).

What was the weight of the vehicle?

 

17 hours ago, SH_MM said:

Unlike torsion bars, most/all types of hydropneumatic suspensions are temperature dependent - at low temperatures, the track tension and ground clearance of vehicles can decrease, in hot environments they can increase.

Why not just tell the suspension to adjust to the temperature? The FCS has a temperature sensor last I checked, simply share that with the main computer and tell the suspension to adjust accordingly.  Or take the next step and go for active suspension. 

 

17 hours ago, SH_MM said:

During fast travel over rough terrain, the liquid/oil inside the hydropneumatic system and the seals can be damaged by overheating (temperatures of 200°C and above can be reached inside the hydropneumatic suspension when having to absorb lots of shocks under heavy load). High localized pressue can lead to high wear of certain elements. Last but not least HSUs tend to be a lot more complex.

Won't the springs and their equivalent suffer the same fate? Spring can break under high localized pressure, they also wear out faster this way.  It is just another mechanism of wear. 

 

17 hours ago, SH_MM said:

These are some of the problems of hydropneumatic suspensions mentioned by Hilmes in his 2007 book. Modern engineering has managed to reduce or completely solve most of the issues, but I think to some extend they will prevail, thus always making torsion bars a more reliable, less complex and cheaper option.

Leaf spring suspension is also lighter, less complex and cheaper too, why are we not using it?

The same argument was used in the 1940s against torsion bar. 

 

13 hours ago, Serge said:

Yes. 

And it takes precious time to kneel for a tank. 

Simply begin kneeling before reaching the prepared firing spot?

 

10 hours ago, Mighty_Zuk said:

Serge your goddamn profile picture is a kneeling tank!

On a serious note, how damaging is it to actually drive about a minute while kneeling?

I understand it may put the whole thing under more stress, but it should be able to take that, right?

It should not really make a difference on relatively flat terrain.

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I think the overall advantages of Hydropneumatic and springs outweigh those of other designs.

 

Both hydrogas and springs are external to the hull and thus easier to replace, and provide greater protection against mines/IEDs as they both don't become a hazard (the bars can bend and amplify the effects of the explosion), and they serve as extra material.

 

Springs are obviously better against mines/IEDs but if anyone thinks other parts need more weight in their armor, then a hydrogas is a good alternative even without considering its kneeling capability, which I think is quite useful even in plains.

 

Can someone make a good comparison between the weight of torsion bars and hydrogas? MM had a good argument there with the Type 90 but more specifics would be great.

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Kneeling is not unique to hydropneumatic suspensions, but it is easier to implement.  I recall vaguely that there was a program to make a torsion bar suspension for an APC that could crouch, mainly so it could fit inside transport aircraft more easily.  There was also the crouching suspension proposed for the German E-series bullshit programs to keep engineers off the Ostfront tank destroyers at the end of WWII.  So it's quite possible to make a kneeling torsion bar suspension, but it usually requires some sort of chain winch or other robust mechanical connection to the suspension elements, whereas a kneeling hydropneumatic suspension requires hydraulic connections to the suspension elements, which is much easier.  Also, not all hydropneumatic suspensions kneel.  In fact, I think the majority of them do not.

 

All the comparisons I have seen between hydropneumatic suspension and torsion bars have depended entirely on which system the author was advocating for.

 

In theory torsion bars are cheaper and simpler.  It's just a big rod of steel that twists as the swing arms articulate, right?  Wrong.  To get competitive suspension performance for a modern MBT, the torsion bar has to be made of a high grade of very refined steel.  Processes like VIM/VAR and electroslag refining remove the last small amounts of tramp elements, and drastically improve the fatigue properties of the steel.  But these secondary refining processes are expensive.  Ideally, the torsion bar is pre-stressed too.  Torsion bars are springs, and a big portion of the lifespan of a spring is a function of keeping the surface blemish-free.  The outer surface of a torsion bar is the most stressed part, and any sort of flaws there will quickly propagate and cause a crack and eventually a failure.  So the torsion bar needs to be kept scratch-free and corrosion-free, which adds more weight and bulk, and special handling considerations of spares.  There's a lot that goes into making a good torsion bar.

Hydropneumatic has a lot of big advantages on paper.  All tank suspensions are springs, and their weight is going to be some sort of function of the energy density of the springing medium used to support the swing arms.  A torsion bar uses energy stored in a twisted piece of steel, while hydropneumatic uses the energy stored in temporarily compressed air, translated by hydraulic liquid.  Well, this one is a no-brainer!  Air is way lighter than steel!

But of course it isn't that simple.  The pressure vessel that contains the air and the hydraulic fluid needs to be leak-proof, and it needs to be leak-proof for years under rough field conditions.  Once you make a hydraulic system that's that robust, you start to eat into the theoretical weight advantage vs. the torsion bar.  Also, the air is the springing medium.  Air changes density and pressure as the temperature changes.  That's not a deal-breaker, but the engineers need to at least think about that.

 

Hydropneumatic suspensions make it fairly easy to kneel the tank, but doing this requires some sort of system of hydraulic pumps to move fluid in and out of the suspension units.  This requires a substantial amount of power, and a bunch of additional beefy, high-pressure hydraulic lines.  These things are all fairly beefy and are another potential headache if the engineers responsible for them half-ass their job.

I think for new designs hydropneumatic will prove lighter.  Even if the hydro suspension units themselves aren't that much lighter, the knock-on effects of being able to lower the turret basket by a few inches will be much greater than the difference in the weight of the suspension units themselves.  Tanks are about half armor by weight, so it's generally more effective to make the armor package smaller than it is to make individual components lighter.  But there are other considerations.  Torsion bars take up space in the bottom of the hull, and hydro units take up space on the side of the hull.  Therefore, torsion bars allow the tank to have thicker side hull armor.  Take a look at the T-14 for an example of how extreme this can be made.

 

Hydropneumatic units can have a very high built in damping coefficient for essentially no additional weight, which is not the case with torsion bars, which require auxiliary snubbers and dampers.  However, high damping coefficients effectively increase rolling resistance when the tank is on rolling terrain, so there is some cost to efficiency here.  In theory it shouldn't be too hard to have some sort of variable-geometry orifice inside the hydraulic line that could adjust damping coefficient on the fly, but so far as I know nobody has tried this.

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Torsion bars impose packaging constraints,  They are long and need very stiff mounts.  Hydrodynamic suspensions can distribute components which helps with packaging.  Real value with these in my view is the considerable extra speed on poor terrain that is possible.  By possible I mean accessible.  In other words, crew effectiveness is maintained for longer at higher speeds.

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13 minutes ago, DIADES said:

Torsion bars impose packaging constraints,  They are long and need very stiff mounts.  Hydrodynamic suspensions can distribute components which helps with packaging.  Real value with these in my view is the considerable extra speed on poor terrain that is possible.  By possible I mean accessible.  In other words, crew effectiveness is maintained for longer at higher speeds.

 

Welcome to SH DIADES!


Tank hulls are giant steel boxes.  Torsion bars free rotate inside a hole in the hull on the swing arm end and anchor into the opposite side of the hull (ignoring rare exceptions like the T-64).  Any tank with a hull rigid enough to withstand the rigors of combat is rigid enough to mount torsion bars.

 

Hydropneumatic suspensions need to attach to the hull somewhere, and this is typically done with a small number of bolts that are not particularly spread out.  So I don't think they're particularly lower stress than torsion bars.

 

There's no magical additional cushioning that hydropneumatic suspensions give vs. torsion bars.  They have significant additional built-in dampening, but as I noted above, this has some tradeoffs.

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26 minutes ago, DIADES said:

Real value with these in my view is the considerable extra speed on poor terrain that is possible.  By possible I mean accessible.  In other words, crew effectiveness is maintained for longer at higher speeds.

 

As @SH_MM said, in theory it is possible to make a torsion bar system that have the same or better performance than your average hydropneumatic. But they'll need to be a bit fancier than plain basic torsion bars.

Also when driving in a rough terrain, while dampening is important vertical travel is just as much as it will determine the maximum height of an obstacle the tank can pass without transferring the choc to the hull.

So as Collimatrix said, it really depend on what kind of hydropneumatic or torsion bar your are talking about.

 

Personally I tend to prefer hydropneumatic as they are completely external (so in general easier to replace on the field) and add a bit more material on the tank's side armor (granted it's not much but it's always welcome), but the most important point is that they allow to reduce the overall height of a tank.

 

As for the ability to kneel, I don't think that it is really a critical asset for an MBT.

It can be useful when you want to dig in and wait in defense, but that add a bit of delay when you want to retreat, so it would only be really useful for country that have almost no strategical depth and where the tank cannot really retreat.

The fact that most MBT with adjustable suspension comes from SEA country would tend to support this idea.

 

However I consider it a useful addition for recon AFV which strive to observe without being seen and will in general open fire as a last resort only.

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For clarity - I am talking about contemporary state of the art systems.  These are best described as semi-active and yes, they do offer significantly better VDV that any torsion system.  Nothing wrong with torsion bars - other than that they are purely mechanical and as I stated, they impose particular packaging constraints.

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3 minutes ago, DIADES said:

For clarity - I am talking about contemporary state of the art systems.  These are best described as semi-active and yes, they do offer significantly better VDV that any torsion system.

 

If you're talking about a pure torsion bar system, then I guess.  But no tank with torsion bar suspension has only torsion bars.  They all have auxiliary damping systems, either friction-based or hydraulic.  The advantage of hydropneumatic is that the damping action is built in, and requires no auxiliary system.

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46 minutes ago, Collimatrix said:

Kneeling is not unique to hydropneumatic suspensions, but it is easier to implement.  I recall vaguely that there was a program to make a torsion bar suspension for an APC that could crouch, mainly so it could fit inside transport aircraft more easily.  There was also the crouching suspension proposed for the German E-series bullshit programs to keep engineers off the Ostfront tank destroyers at the end of WWII.  So it's quite possible to make a kneeling torsion bar suspension, but it usually requires some sort of chain winch or other robust mechanical connection to the suspension elements, whereas a kneeling hydropneumatic suspension requires hydraulic connections to the suspension elements, which is much easier.  Also, not all hydropneumatic suspensions kneel.  In fact, I think the majority of them do not.

 

All the comparisons I have seen between hydropneumatic suspension and torsion bars have depended entirely on which system the author was advocating for.

 

In theory torsion bars are cheaper and simpler.  It's just a big rod of steel that twists as the swing arms articulate, right?  Wrong.  To get competitive suspension performance for a modern MBT, the torsion bar has to be made of a high grade of very refined steel.  Processes like VIM/VAR and electroslag refining remove the last small amounts of tramp elements, and drastically improve the fatigue properties of the steel.  But these secondary refining processes are expensive.  Ideally, the torsion bar is pre-stressed too.  Torsion bars are springs, and a big portion of the lifespan of a spring is a function of keeping the surface blemish-free.  The outer surface of a torsion bar is the most stressed part, and any sort of flaws there will quickly propagate and cause a crack and eventually a failure.  So the torsion bar needs to be kept scratch-free and corrosion-free, which adds more weight and bulk, and special handling considerations of spares.  There's a lot that goes into making a good torsion bar.

Hydropneumatic has a lot of big advantages on paper.  All tank suspensions are springs, and their weight is going to be some sort of function of the energy density of the springing medium used to support the swing arms.  A torsion bar uses energy stored in a twisted piece of steel, while hydropneumatic uses the energy stored in temporarily compressed air, translated by hydraulic liquid.  Well, this one is a no-brainer!  Air is way lighter than steel!

But of course it isn't that simple.  The pressure vessel that contains the air and the hydraulic fluid needs to be leak-proof, and it needs to be leak-proof for years under rough field conditions.  Once you make a hydraulic system that's that robust, you start to eat into the theoretical weight advantage vs. the torsion bar.  Also, the air is the springing medium.  Air changes density and pressure as the temperature changes.  That's not a deal-breaker, but the engineers need to at least think about that.

 

Hydropneumatic suspensions make it fairly easy to kneel the tank, but doing this requires some sort of system of hydraulic pumps to move fluid in and out of the suspension units.  This requires a substantial amount of power, and a bunch of additional beefy, high-pressure hydraulic lines.  These things are all fairly beefy and are another potential headache if the engineers responsible for them half-ass their job.

I think for new designs hydropneumatic will prove lighter.  Even if the hydro suspension units themselves aren't that much lighter, the knock-on effects of being able to lower the turret basket by a few inches will be much greater than the difference in the weight of the suspension units themselves.  Tanks are about half armor by weight, so it's generally more effective to make the armor package smaller than it is to make individual components lighter.  But there are other considerations.  Torsion bars take up space in the bottom of the hull, and hydro units take up space on the side of the hull.  Therefore, torsion bars allow the tank to have thicker side hull armor.  Take a look at the T-14 for an example of how extreme this can be made.

 

Hydropneumatic units can have a very high built in damping coefficient for essentially no additional weight, which is not the case with torsion bars, which require auxiliary snubbers and dampers.  However, high damping coefficients effectively increase rolling resistance when the tank is on rolling terrain, so there is some cost to efficiency here.  In theory it shouldn't be too hard to have some sort of variable-geometry orifice inside the hydraulic line that could adjust damping coefficient on the fly, but so far as I know nobody has tried this.

 

Best possible suspension system: hydropneumatic suspension coupled to a hydraulic transmission and hydraulic turret drive. The interior of the tank is a maze of high-pressure lines, and a leak anywhere stops the entire thing from working. Perfecting a system such as this could keep a large team of engineers safely away from the eastern front gainfully employed for years.

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13 minutes ago, Toxn said:

 

Best possible suspension system: hydropneumatic suspension coupled to a hydraulic transmission and hydraulic turret drive. The interior of the tank is a maze of high-pressure lines, and a leak anywhere stops the entire thing from working. Perfecting a system such as this could keep a large team of engineers safely away from the eastern front gainfully employed for years.

Why not add a hydrostatic drive too? For more fun.

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5 hours ago, Collimatrix said:

But of course it isn't that simple.  The pressure vessel that contains the air and the hydraulic fluid needs to be leak-proof, and it needs to be leak-proof for years under rough field conditions.  Once you make a hydraulic system that's that robust, you start to eat into the theoretical weight advantage vs. the torsion bar.  Also, the air is the springing medium.  Air changes density and pressure as the temperature changes.  That's not a deal-breaker, but the engineers need to at least think about that.

Use nitrogen? 

 

Quote

In theory it shouldn't be too hard to have some sort of variable-geometry orifice inside the hydraulic line that could adjust damping coefficient on the fly, but so far as I know nobody has tried this.

Like a valve? 

 

5 hours ago, DIADES said:

-snip-

Welcome to SH!

 

 

Has any tank designer considered moving most of the working elements out of the suspension unit? 
Susp_hydrp.jpg

 

Simply move the accumulator inside the hull, or away. Then you have a simple hydraulic actuator and a swing arm outside the hull, which should not really be much bigger than torsion bar.  
To vary the dampening, add a valve between the accumulator and the hydraulic line. Something like this:

QPw7TSI.png

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      The Leclerc is not geometrically more efficient. It could have been, if it's armor layout wasn't designed so badly. The Leclerc trades a smaller frontal profile for a larger number of weakspots. It uses a bulge-type turret (no idea about the proper English term), because otherwise a low-profile turret would mean reduced gun depression (breech block hits the roof when firing). There is bulge/box on the Leclerc turret roof, which is about one feet tall and located in the centerline of the turret. It is connected to the interior of the tank, as it serves as space for the breech block to travel when the gun is depressed. With this bulge the diffence between the Leopard 2's and Leclerc's roof height is about 20 milimetres.
       

       
      The problem with this bulge is, that it is essentially un-armored (maybe 40-50 mm steel armor); otherwise the Leclerc wouldn't save any weight. While the bulge is hidden from direct head-on attacks, it is exposed when the tank is attacked from an angle. Given that modern APFSDS usually do not riccochet at impact angles larger than 10-15° and most RPGs are able to fuze at such an angle, the Leclerc has a very weakly armored section that can be hit from half to two-thirds of the frontal arc and will always be penetrated.
       

       
      The next issue is the result of the gunner's sight layout. While it is somewhat reminiscent of the Leopard 2's original gunner's sight placement for some people, it is actually designed differently. The Leopard 2's original sight layout has armor in front and behind the gunner's sight, the sight also doesn't extend to the bottom of the turret. On the Leclerc things are very different, the sight is placed in front of the armor and this reduces overall thickness. This problem has been reduced by installing another armor block in front of the guner's sight, but it doesn't cover the entire crew.
       

       
      The biggest issue of the Leclerc is however the gun shield. It's tiny, only 30 mm thick! Compared to that the Leopard 2 had a 420 mm gun shield already in 1979. The French engineers went with having pretty much the largest gun mantlet of all contemporary tanks, but decided to add the thinnest gun shield for protection. They decided to instead go for a thicker armor (steel) block at the gun trunnions.
       

       
      Still the protection of the gun mantlet seems to be sub-par compared to the Leopard 2 (420 mm armor block + 200-250 mm steel for the gun trunion mount on the original tank) and even upgraded Leopard 2 tanks. The Abrams has a comparable weak protected gun mantlet, but it has a much smaller surface. The Challenger 2 seems to have thicker armor at the gun, comparable to the Leopard 2.
       
      Also, the Leclerc has longer (not thicker) turret side armor compared to the Leopard 2 and Challenger 2, because the armor needs to protect the autoloader. On the other tanks, the thick armor at the end of the crew compartment and only thinner, spaced armor/storage boxes protect the rest of the turret. So I'd say:
      Challenger 2: a few weakspots, but no armor upgrades to the main armor Leclerc: a lot of weakspots, but lower weight and a smaller profile when approached directly from the turret front M1 Abrams: upgraded armor with less weakspots, but less efficient design (large turret profile and armor covers whole turret sides) So if you look for a tank that is well protected, has upgraded armor and uses the armor efficiently, the current Leopard 2 should be called best protected tank.
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