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


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21 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?

 

If I were a tanker, I'd be most worried about throwing a track. They're meant to adjust the tension as they kneel, but losing a track as you back out of a firing position would be rather terminal

 

9 hours 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. 

 

I'm picturing a Big Hydraulic Turny Thing™ between the end of the bar and the hull, probably with a dog clutch or similar to lock it in position when you're driving. Dunno what has been used previously, but that looks like a elegant solution to me

 

3 hours ago, Xoon said:

Use nitrogen? 

 

They already do, any gas is going to do thermodynamic things as the temperature changes

 

 

8 hours 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 aerosolizes hot hydraulic oil, making a fuel-air bomb. Perfecting a system such as this could keep a large team of engineers safely away from the eastern front gainfully employed for years.

 

FTFY

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9 hours ago, Alzoc said:

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.

Yes (no for the last idea).

I will try to develop about this point tomorrow or latter, for people who don’t the job with tank

9 hours ago, Alzoc said:

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

Countries like RoK are mountainous countries so in some case, it can help. But I would be very surprised if they don’t have an MBT indirect fire support doctrine. We lost it in France with Leclerc MBT. 

9 hours ago, Alzoc said:

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.

No. 

They are working like MBT so it’s of no use. 

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Adjustable suspension are only used :

- to adapt you cross country capability (low position for road, high position for off road) ;

- to sight in mountainous area (but, it’s very, very rare.) ;

- to provide indirect fire support. 

 

You will never use the lower position (park height) in combat, even when concealed. 

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If retrofitting HPS to an vehicle currently fitted with torsion bar suspension (Abrams etc.), then you have the possibility of using the now void space to improve under-belly protection, without requiring a belly plate, which has the added benefit of restoring ground clearance. 

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A USMC M1A1 fitted with Trophy:

 

BKznzYm.jpg

 

as seen on @Damian twitter account.

 

Also here: http://www.candp.marines.mil/Programs/Focus-Area-4-Modernization-Technology/Part-3-Ground-Combat-Tactical-Vehicles/M1A1-Vehicle-Protection-System/

 

The M1A1 Trophy TD phase is complete. The USMC project is partially funded to procure (48) of (56) systems as a special mission kit for four tank companies.”

 

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On 7/12/2018 at 11:22 AM, Xoon said:

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?


 

Suspension travel is the total vertical distance that the roadwheel can move in the vertical direction; that is why it is a metric to measure suspension performance independent of the suspension type. It would make more sense to differentiate between bump and rebound values, but unfortunately I haven't found these separated values for tanks with hydropneumatic suspensions like the Challenger 1 and Challenger 2.

 

Yes, you can make hydropneumatic suspensions with more travel than currently achieved on tanks like the Leopard 2 and M1 Abrams (and that is actually easier than making a better torsion bar suspension), but these systems always have issues. The MBT-70 had 600 mm total suspension travel (but the design was unreliable), the 1980s German design (that was never adopted due to the 250 kg weight of each suspension element) provided even 650 mm travel. In case of tanks like the Challenger 2 and Leclerc, the total wheel travel is limited to 450 mm. The in-arm suspension offered for the M1 Abrams has a total travel of 21 inches (533 mm), the earlier hydropneumatic suspension of the T95 medium tank had a travel of 19 inches (482 mm).

 

I don't know anything about the performance data of the Japanese and South Korean HSUs, but the Arjun's suspension is slightly better than the Leopard 2's in terms of suspension travel (535 mm vs 526 mm. Then again the Arjun's suspension is claimed to be extremely unreliable...

 

On 7/12/2018 at 11:22 AM, Xoon said:

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

 

No, I am saying that one has to make a trade-off. If a hydropneumatic suspension would be the perfect solution, every tank since the 1950s (the T95 and the Leopard 1 prototype of work group "B" had HSUs) would have been fitted with such as a system. It is not possible, to make a hydropneumatic suspension that performs better than a current torsion bar design, while being lighter and equally/more reliable.

 

  • You can make a lighter and reliable hydropneumatic suspension, but this won't offer more performance than a torsion bar suspension (which was done on the Challenger tanks, the Leclerc and the hybrid systems adopted on K1 Type 88 and the Type 90 tanks) 
  • You can make a HSU with greater suspension travel and low weight, but this system will then be less reliable than a torsion bar suspension (see MBT-70, XM803 and Arjun)
  • You can make a reliable hydropneumatic suspension with greater travel, but this will then be heavier than a torsion bar suspension (like the rejected West-German design of the 1980s)

 

On 7/12/2018 at 11:22 AM, Xoon said:

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. 

 

It would be possible, but increases the complexity of the system.

 

On 7/12/2018 at 11:22 AM, Xoon said:

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

 

You answered your own question; faster wear, higher localized pressure, etc. The Merkava's springs seem to be rather heavy in order to be sturdy and reliable enough.

 

On 7/12/2018 at 11:47 AM, Mighty_Zuk said:

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. 

 

That depends on the exact implementation. While torsion bars are indeed an additional hazard in case of a mine strike, the in-arm suspension offered for the M1 Abrams and the hydrogas systems used on the Challenger tanks and the Leclerc are not optimized for increasing underbelly protection. These systems make use of external elements, that are bolted ontop of pre-cut holes on the hull sides, thus they still require a ballistic hole (a detonation of an IED or mine will simply tear the connection apart, this also happened on a VBCI in Mali).

 

For future AFVs designed with mine protection in mind, hydropneumatic suspensions (ideally with a fully decoupled running gear) are the way to go.

 

On 7/12/2018 at 12:22 PM, Collimatrix said:

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.

 

That is indeed true, Hilmes for example mentioned that the Leopard 2's torsion bar system was only possible due to advancements in metalurgy; but I think that these types of high-grade steel alloys had more possible applications in industry and therefore were an expected evolution in the 1950s-1990s. Hydropneumatic suspensions capable of dealing with a 50-70 ton vehicle were however not very practical outside of military vehicles, as simpler HSUs didn't necessarily suffer from the same issues (although early hydropneumatic systems in civilian cars were often leaky).

 

 

7 hours ago, 2805662 said:

A USMC M1A1 fitted with Trophy:

 

BKznzYm.jpg

 

Note that it also got these "weight simulators" on the turret front. I've never read about the USMC also planning to upgrade their tanks with the new armor package within the next decade, so maybe these are just counterweights for Trophy and have nothing to do with simulating the increased weight of a new armor package?

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1 hour ago, SH_MM said:

 

Suspension travel is the total vertical distance that the roadwheel can move in the vertical direction; that is why it is a metric to measure suspension performance independent of the suspension type. It would make more sense to differentiate between bump and rebound values, but unfortunately I haven't found these separated values for tanks with hydropneumatic suspensions like the Challenger 1 and Challenger 2.

 

Yes, you can make hydropneumatic suspensions with more travel than currently achieved on tanks like the Leopard 2 and M1 Abrams (and that is actually easier than making a better torsion bar suspension), but these systems always have issues. The MBT-70 had 600 mm total suspension travel (but the design was unreliable), the 1980s German design (that was never adopted due to the 250 kg weight of each suspension element) provided even 650 mm travel. In case of tanks like the Challenger 2 and Leclerc, the total wheel travel is limited to 450 mm. The in-arm suspension offered for the M1 Abrams has a total travel of 21 inches (533 mm), the earlier hydropneumatic suspension of the T95 medium tank had a travel of 19 inches (482 mm).

 

I don't know anything about the performance data of the Japanese and South Korean HSUs, but the Arjun's suspension is slightly better than the Leopard 2's in terms of suspension travel (535 mm vs 526 mm. Then again the Arjun's suspension is claimed to be extremely unreliable...

As far as I am aware, you simply use a longer swing arm if you want longer travel. However, considering that you can't have 1000 mm of travel because of obvious reasons, you need better dampening, which is where the actual performance of the suspension comes in.  The reason why the Challenger II has less travel is because it does not need it. The better dampening compensates for it. 

Think about how the recoil mechanism of a gun works. 

 

 

Quote

No, I am saying that one has to make a trade-off. If a hydropneumatic suspension would be the perfect solution, every tank since the 1950s (the T95 and the Leopard 1 prototype of work group "B" had HSUs) would have been fitted with such as a system. It is not possible, to make a hydropneumatic suspension that performs better than a current torsion bar design, while being lighter and equally/more reliable.

 

  • You can make a lighter and reliable hydropneumatic suspension, but this won't over more performance than a torsion bar suspension (which was done on the Challenger tanks, the Leclerc and the hybrid systems adopted on K1 Type 88 and the Type 90 tanks) 
  • You can make a HSU with greater suspension travel and low weight, but this system will then be less reliable than a torsion bar suspension (see MBT-70, XM803 and Arjun)
  • You can make a reliable hydropneumatic suspension with greater travel, but this will then be heavier than a torsion bar suspension (like the rejected West-German design of the 1980s)

Thanks for explaining!

 

 

Quote

It would be possible, but increases the complexity of the system.

How? 
As long as you can adjust the pressure of the hydraulic line, it should not really add anything to the system. 

AFV manufactures keep advertising their "open architecture high speed networked" AFVs. 

This means that all the subsystems are networked together.  No additional wiring needed between the FCS and main computer, and no extra needed wiring between the main computer and suspension control unit. 

If not, I would honestly fire the engineer in charge of these systems for incompetency.  Or straight out reject the AFV as a costumer. 

The rest is just code:


def suspension_temperature_compensation(temp_value, adjust_value):

   """ Program for adjusting the suspension after the ambient temperature.  """

   sus_adjust = temp_value * adjust_value
   return sus_adjust

 

suspension_temperature_compensation(80, 0.1)

 

By inputting the value 80, meaning 30 degrees C ( -50 C becomes 50, and 30 C becomes 30, 50 + 30 = 80), and the adjustment value, which would be the expansion ratio of the gas compered to the temperature.

I set it to a arbitrary 0.1, which would make the function output 8, as in 8 mm increase in the suspension height.  This would then be feed into a the controller of the suspension, which would adjust accordingly. 
Actually, the entire code above would probably be integrated into the ride height programming. 
This was coded in Python, for those who want to know the syntax. 

This is not really complex. Digital programming does not really break down faster because of more complexity.

 

Or you can use a virtual PID regulator. It would be better. 

 

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3 hours ago, SH_MM said:

Note that it also got these "weight simulators" on the turret front. I've never read about the USMC also planning to upgrade their tanks with the new armor package within the next decade, so maybe these are just counterweights for Trophy and have nothing to do with simulating the increased weight of a new armor package?

 

Doubtful. Those simulators have four welded plates per turret "cheek", which is consistent with the simulators added to the Trophy-less M1A2 SEP v3 preproduction units:

 

H4F1WcL.png

 

Looks like USMC is looking to add NGAP/NEA to its M1A1FEPs.

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12 hours ago, 2805662 said:

A USMC M1A1 fitted with Trophy:

 

BKznzYm.jpg

 

as seen on @Damian twitter account.

 

Also here: http://www.candp.marines.mil/Programs/Focus-Area-4-Modernization-Technology/Part-3-Ground-Combat-Tactical-Vehicles/M1A1-Vehicle-Protection-System/

 

The M1A1 Trophy TD phase is complete. The USMC project is partially funded to procure (48) of (56) systems as a special mission kit for four tank companies.”

 

If we look at the M257 smoke granade launchers, then it really is USMC tank

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9 hours ago, SH_MM said:

 

That depends on the exact implementation. While torsion bars are indeed an additional hazard in case of a mine strike, the in-arm suspension offered for the M1 Abrams and the hydrogas systems used on the Challenger tanks and the Leclerc are not optimized for increasing underbelly protection. These systems make use of external elements, that are bolted ontop of pre-cut holes on the hull sides, thus they still require a ballistic hole (a detonation of an IED or mine will simply tear the connection apart, this also happened on a VBCI in Mali).

 

For future AFVs designed with mine protection in mind, hydropneumatic suspensions (ideally with a fully decoupled running gear) are the way to go.

 

On challenger the hole for the mounting stub doesn't go all the way through the hull, and there's a fairly substantial block of steel filling it when the suspension is fitted (also a noticeable bump on the inside). It's not as if you're losing volume from a composite block, I'd be surprised if it made a difference to the base hull side armour

 

7 hours ago, Xoon said:

As far as I am aware, you simply use a longer swing arm if you want longer travel. However, considering that you can't have 1000 mm of travel because of obvious reasons, you need better dampening, which is where the actual performance of the suspension comes in.  The reason why the Challenger II has less travel is because it does not need it. The better dampening compensates for it. 

Think about how the recoil mechanism of a gun works. 

 

A longer swingarm will increase the moment, and so the force on the piston (and add a bit of weight). That'll need either a higher pressure system (adding weight, more chance of leaks and more faff servicing), or a bigger piston (adding weight).

 

7 hours ago, Xoon said:

How? 
As long as you can adjust the pressure of the hydraulic line, it should not really add anything to the system. 

AFV manufactures keep advertising their "open architecture high speed networked" AFVs. 

This means that all the subsystems are networked together.  No additional wiring needed between the FCS and main computer, and no extra needed wiring between the main computer and suspension control unit. 

If not, I would honestly fire the engineer in charge of these systems for incompetency.  Or straight out reject the AFV as a costumer. 

The rest is just code:


def suspension_temperature_compensation(temp_value, adjust_value):

   """ Program for adjusting the suspension after the ambient temperature.  """

   sus_adjust = temp_value * adjust_value
   return sus_adjust

 

suspension_temperature_compensation(80, 0.1)

 

By inputting the value 80, meaning 30 degrees C ( -50 C becomes 50, and 30 C becomes 30, 50 + 30 = 80), and the adjustment value, which would be the expansion ratio of the gas compered to the temperature.

I set it to a arbitrary 0.1, which would make the function output 8, as in 8 mm increase in the suspension height.  This would then be feed into a the controller of the suspension, which would adjust accordingly. 
Actually, the entire code above would probably be integrated into the ride height programming. 
This was coded in Python, for those who want to know the syntax. 

This is not really complex. Digital programming does not really break down faster because of more complexity.

 

Or you can use a virtual PID regulator. It would be better. 

 

You can't assume every system lets you adjust the pressure on the fly. That'll need a super high pressure hydraulic line plumbed out to every unit, which means you lose the benefits of modularity and no hull penetrations (the designers didn't bother on challenger and the mooted abrams suspension last page). Getting the pixies to do it is the easy bit, turning pixies into high pressure hydraulic oil is hard

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6 hours ago, Renegade334 said:

Doubtful. Those simulators have four welded plates per turret "cheek", which is consistent with the simulators added to the Trophy-less M1A2 SEP v3 preproduction units: 

 

Notice how the hull weight simulators also used to consist of three plates, but on the later US Army tank (with Trophy) only one plate is left (and none is fitted to the USMC's M1A1 tank!). That already tells us that these weight demonstrators are not used solely to simulate additional armor weight, if they simulate armor weight changes at all. The fact that an earlier M1A2 SEP v3 prototype without Trophy is fitted with these weight simulators also doesn't mean that the US engineers didn't add them in expectation of an APS.

 

abrams-tank.jpg

3aohR8t.jpg

 

Also note that the steel plates on the USMC's prototype and the US Army's SEP v3 have different sizes. The M1A2 SEP v3 after mounting Trophy is left with three large steel plates and a smaller one moutned ontop, which covers only about half as much surface area.

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17 hours ago, SH_MM said:

 

That is indeed true, Hilmes for example mentioned that the Leopard 2's torsion bar system was only possible due to advancements in metalurgy; but I think that these types of high-grade steel alloys had more possible applications in industry and therefore were an expected evolution in the 1950s-1990s. Hydropneumatic suspensions capable of dealing with a 50-70 ton vehicle were however not very practical outside of military vehicles, as simpler HSUs didn't necessarily suffer from the same issues (although early hydropneumatic systems in civilian cars were often leaky).

 

 

ESR and VIM/VAR steels are used pretty extensively in tanks.  Aside from torsion bars, they make mighty fine gun tubes and they're a good choice for inner layers of armor because they have less tendency to spall.  They are used outside of military applications, but in predictably expensive and demanding fields like biomedical and aerospace.  The bolts of AR-15 rifles are made of Carpenter 158, which is an electroslag refined steel.  But the use of these steels is confined to applications where performance to weight ratio is paramount.  The process for making them is energy intensive and demanding, and this is reflected in the price.

 

I doubt that any suspension that's competitive on a modern MBT will have much in common with civilian vehicle suspensions.  I think, in general, this is part of what has driven the cost of new military technology so high.  This isn't the 1940s and you can't make a tank engine by gluing five automobile engines together.  Top-of-the-line military hardware has very production commonality with civilian products anymore, and that drives the prices up.

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15 hours ago, Collimatrix said:

 

ESR and VIM/VAR steels are used pretty extensively in tanks.  Aside from torsion bars, they make mighty fine gun tubes and they're a good choice for inner layers of armor because they have less tendency to spall.  They are used outside of military applications, but in predictably expensive and demanding fields like biomedical and aerospace.  The bolts of AR-15 rifles are made of Carpenter 158, which is an electroslag refined steel.  But the use of these steels is confined to applications where performance to weight ratio is paramount.  The process for making them is energy intensive and demanding, and this is reflected in the price.

 

I doubt that any suspension that's competitive on a modern MBT will have much in common with civilian vehicle suspensions.  I think, in general, this is part of what has driven the cost of new military technology so high.  This isn't the 1940s and you can't make a tank engine by gluing five automobile engines together.  Top-of-the-line military hardware has very production commonality with civilian products anymore, and that drives the prices up.

 

Plus the fact that so few items are replaced on a one for one basis, orders for future vehicles keep getting smaller, which drives up the price per vehicle.

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