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I am fully aware that you can put fuel tanks there, my point was that it's a big empty space that is excellent for ammunition storage.

 

I see your point, although I still don't know about a place where "if you get penetrated, your ammo goes up" being an excellent location for that.

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I see your point, although I still don't know about a place where "if you get penetrated, your ammo goes up" being an excellent location for that.

It is as excellent as the Challenger II's ammunition storage. 

 

Space efficient but very deadly for the crew.

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Actually, as a ex-Leo 2A6 crew member and current TNO researcher told me, he thinks it's the biggest flaw of the Leo 2 design. He also went as far as claim that the lower plate isn't actually all that thick. Which, combined with the ammo stowage behind the lower plate makes me raise an eyebrow.

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Actually, as a ex-Leo 2A6 crew member and current TNO researcher told me, he thinks it's the biggest flaw of the Leo 2 design. He also went as far as claim that the lower plate isn't actually all that thick. Which, combined with the ammo stowage behind the lower plate makes me raise an eyebrow.

One thing I have been pondering about lately is:

It is possible to extend the ammunition rack to the whole width of the bustle?

Removing the pumps and old FCS should clear up space. Alternative you could add a auto loader like the Leclercs if you need it for the 130mm gun. 

 

So you can either:

Install a autoloader.

Increase ammunition capacity.

Or move more ammunition to the turret.

 

Would this be too expensive? 

 

The hull rack could be made into a armored wet storage rack, with fuel tanks on the side for added protection. But I have a feeling they would simply leave it as it is for increased ammunition capacity.

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Actually, as a ex-Leo 2A6 crew member and current TNO researcher told me, he thinks it's the biggest flaw of the Leo 2 design. He also went as far as claim that the lower plate isn't actually all that thick. Which, combined with the ammo stowage behind the lower plate makes me raise an eyebrow.

That sounds like a hell of a liability in dealing with IEDs

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That sounds like a hell of a liability in dealing with IEDs

 

It would take a really big or specialized mine.  Those do exist, but the 20-40mm of belly armor most MBTs have makes them a hell of a lot harder to kill with mines than, say, trucks or APCs.  To put it in perspective, most MBTs have about two to three times as much belly armor as a LAV-25 has over the frontal arc.

 

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   IEDs are not really a problem for LFP. Generally only EFP mines can be real danger, but they are usually placed in such way that only side armor is in real danger.

 

   And ALL Western tanks are needlessly big comapred to MUH SOVIET MEDIUM TANKS like T-64. Yes, medium, because i am now fully into "USSR never had MBT from 1960s to 1990s" theory.

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One thing I have been pondering about lately is:

It is possible to extend the ammunition rack to the whole width of the bustle?

Removing the pumps and old FCS should clear up space. Alternative you could add a auto loader like the Leclercs if you need it for the 130mm gun. 

 

So you can either:

Install a autoloader.

Increase ammunition capacity.

Or move more ammunition to the turret.

 

Would this be too expensive? 

 

The hull rack could be made into a armored wet storage rack, with fuel tanks on the side for added protection. But I have a feeling they would simply leave it as it is for increased ammunition capacity.

 

For the record, I'm dubious about the effectiveness of wet ammo stowage.  Sure, wet ammo rack Shermans burned far less frequently than their dry rack counterparts.  Wet rack Shermans also moved the ammo out of the easily-penetrated hull sponsons and onto the hull floor, where they were less likely to get hit in the first place. 

The chemistry just doesn't make much sense.  Gun ammunition and explosives contain both fuel and oxidizer, so pouring water over burning nitrocellulose won't snuff it out like it would a regular fire.  In a few edge cases, if the water gets to the spark very early the heat energy could dissipate into the water quickly enough that the temperature inside the propellant would drop, and the combustion could no longer proceed.  Maybe maybe maybe the water could get into a hole fast enough to waterlog the propellant, which would render it more or less inert, but flame propagation in nitrocellulose-based propellants is scary fast and I would be shocked if water managed to outrun it.  I would think in most cases, however, that the wet ammo stowage just slows down the fire by absorbing some of its energy for a time.  This is not without value, as it could allow precious extra seconds for the crew to GTFO.

 

I recall some study of knocked-out tanks from the Iran-Iraq War, including T-62s and Chieftains, which concluded that the wet ammo stowage on Chieftains did not make them less prone to fire.

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Does anyone have ground clearance figures for the T-72?  I had always heard that it's about two inches less than for Western MBTs.

According to Steven Zaloga, the T-72 has 490 mm ground clearance; this about the same as the M1 Abrams (19 inches/482 mm according to Hunnicutt), but about two inches less than the frontal area of the Leopard 2 (550 mm).

 

Also curious if anyone has figures showing the approximate thickness of the armor in the front hull of the Leo 2.

The upper section of the Leopard 2's hull nose (the one sloped at ~45°) has a line-of-sight thickness of more than 600 milimetres. The distance to the end of the special armor cavity is 600 mm, behind this is a further steel plate; I have commonly seen estimations in the range of 640-660 mm.

This is essentially the same thickness as the armor cavity with backplate on the Abrams (estimated to be 600-700 mm). Also one should note that this is the same thickness as the M1A1 Abrams and Leopard 2A4 turret when attacked from 30° angle.

The composite armor at the lower nose section gets thinner; to some 200-300 mm-ish thickness until it ends. Something like this photo from SteelBeasts shows, but the lower armor cavity slopes back and is no straight.

 

56e83cf99636b_leopard_2a5hullarmor.jpg.5

Overall it appears that the Leopard 2 has essentially the same armor thickness at the hull front as the M1 Abrams. The full thickness of the armor cavity might cover a slightly smaller area, but overall the Leopard 2 seems to have a slightly larger coverage of the front hull with composite armor.,

 

However the Leopard 2 has further armor packages for the hull available, such as IBD's MEXAS-H design (as adopted on Strv 122, Leopardo 2E, Leopard 2HEL, Leopard 2A5DK and Leopard 2A7 QAT), RUAG's SidePro armor aswell as the AMAP armor (as operational with Singapore and Indonesia). This armor packages add at least one foot thickness of composite armor to the tank. When the adoption of this armor package was tested on the M1A2 and Leclerc tanks for Sweden, the Swedish FMV noted a 50-100% increase in protection according to FMV's Richard Lindström.

 

strv_ny-16.jpg

 

In Germany the armor package was originally ordered in 1995 for adoption within the KWS 3 upgrade (whole hull would require an overhaul for KWS 3, as this meant the adoption of a new turret with 140 mm gun), but the order was canceled shortly after. Currently Germany is trying to enhance the Leopard 2A7 design (enhanced tank currently codenamed Leopard 2A7V), which also includes the adoption of the further armor package.

 

Frontal hull vulnerability, at first glance, looks like one area where the Abrams is greatly superior to the Leo 2.  The left side of the Leo 2 hull is filled up with non-compartmentalized ammo and the right side of the Leo 2 hull is filled up with driver.  On the Abrams the driver is centerline, and the right and left are filled with fuel tanks.

 

If you are talking about crew survivability, the frontal fuel tanks of the Abrams might be an advantage. On the other hand, once the fuel tanks are hit and the fuel is incinerated, the tank has be abandoned unless you want to eat fried Abrams tankers.

The fuel tanks of the Abrams are more likely to be incinerated, because of the thinner side armor compared to the Leopard 2. The Leclerc might have the best hull armor design (at least as long as there is no AMAP/MEXAS-H armor), but it's lower front is not protected by composite armor.

 

I always thought it was an odd decision to put the ammo at the front.

 

It is the safest place. All current tanks are optimized for anti-tank warfare, which means the armor of the tank is designed to protect the frontal 60° arc of the vehicle. By placing the ammo directly behind the hull armor, the largest amount of the frontal 60° arc of the the ammo is protected by the tank's thick frontal armor. Moving the ammunition away from the armor, means it is more exposed, as less of it is covered by the tank's frontal armor.

 

One thing I have been pondering about lately is:

It is possible to extend the ammunition rack to the whole width of the bustle?

Removing the pumps and old FCS should clear up space. Alternative you could add a auto loader like the Leclercs if you need it for the 130mm gun. 

 

So you can either:

Install a autoloader.

Increase ammunition capacity.

Or move more ammunition to the turret.

 

Would this be too expensive? 

 

The hull rack could be made into a armored wet storage rack, with fuel tanks on the side for added protection. But I have a feeling they would simply leave it as it is for increased ammunition capacity.

It is possible to extend the ammo rack to the whole width of the bustle; Rheinmetall once proposed to fit a semi-automatic loader at the bustle containing all ammunition. However storing all ammunition in one place is not an ideal design decision, because this means you have to put enough armor at this place to survive anti-tank weapons; otherwise your ammo rack will be hit and the tank is useless. This is why the M1 Abrams' bustle has the same armor protection as the crew compartment.

 

The 130 mm gun will need an autoloader.

 

Rheinmetall claims that their Leopard 2 Revolution tank has a new "decoupled ammunition bunker". I am not sure if this also has a blow-out compartment or is just a fancy new term for ammo rack.

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Now it's Ariete bashing time. The Italian engineers had no knowledge of manufacturing proper tanks (even the OF-40 export tank was largley based on Leopard 1 components; in fact the original hull design was made by German companies), so the Ariete is a bit special.
 
It's turret has extremely thin side armor, some say it's spaced armor, other people claim it's normal steel armor or composite. Judged by the thickness of the ammunition hatch, it's side armor might be 100-150 mm thick.
 

HApousZ.jpg?1


 
Looks kind of like the Leopard 1A3's ammunition hatch. The hull side armor however is more than average, because it extends along the whole hull sides (whereas tanks like the Leopard 2 and Abrams have thin armor at the engine compartment).
 
CjRDH0Y.jpg
 
This might be ~60 mm armor at the engine compartment vs the Leopard 2's 40 mm and Abrams' 38 mm. Btw. did I forget to mention, that the ammunition in the Ariete's turret is stored like in the M48 tank?
 
There are armor upgrades; a PSO package used in Iraq and a frontal turret armor upgrade, which apparently hasn't been purchased yet.

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If you are talking about crew survivability, the frontal fuel tanks of the Abrams might be an advantage. On the other hand, once the fuel tanks are hit and the fuel is incinerated, the tank has be abandoned unless you want to eat fried Abrams tankers.

The fuel tanks of the Abrams are more likely to be incinerated, because of the thinner side armor compared to the Leopard 2. The Leclerc might have the best hull armor design (at least as long as there is no AMAP/MEXAS-H armor), but it's lower front is not protected by composite armor.

 

 

The fuel cells in the Abrams are separated from the crew, so a hit would need to penetrate it, start a leak, and also ignite it.  And then spread inside the tank.  And then prove absolutely impossible for the built-in automatic fire extinguisher to put out for some reason.  A fire on the outside of a tank is simply not that threatening to things on the inside:

 

 

Furthermore, a JP-8 fire can be extinguished (say, by the automatic halon fire suppression system that every Abrams has), unlike an ammunition fire, which categorically cannot be put out once it gets going.

 

And this is essentially kerosene we're talking about, not the easiest stuff in the world to catch on fire:

 

 

 

It is the safest place. All current tanks are optimized for anti-tank warfare, which means the armor of the tank is designed to protect the frontal 60° arc of the vehicle. By placing the ammo directly behind the hull armor, the largest amount of the frontal 60° arc of the the ammo is protected by the tank's thick frontal armor. Moving the ammunition away from the armor, means it is more exposed, as less of it is covered by the tank's frontal armor.

 

 

Except that turret armor is thicker than hull armor.  By that logic, putting the ammunition directly behind the turret cheeks would be the safest possible location.

But the Leo 2's designers must have been very confident in their location of the hull ammo rack, seeing as they didn't bother to isolate it from the crew at all, unlike the designers of the inferior Abrams, who were so terrified of their paper creation being penetrated in the hull rear that they even put blowoff panels and blast doors on the hull ammunition storage:

 

UYLr7Gs.jpg

 

 

 

It is possible to extend the ammo rack to the whole width of the bustle; Rheinmetall once proposed to fit a semi-automatic loader at the bustle containing all ammunition. However storing all ammunition in one place is not an ideal design decision, because this means you have to put enough armor at this place to survive anti-tank weapons; otherwise your ammo rack will be hit and the tank is useless. This is why the M1 Abrams' bustle has the same armor protection as the crew compartment.

 

 

The armor on the turret sides over the ammunition storage of the Abrams might be thicker than the armor over the turret sides of the crew compartment.  Go to 2:32 in this video:

 

You can see that the crew compartment is wider that the ammunition storage.

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It is the safest place. All current tanks are optimized for anti-tank warfare, which means the armor of the tank is designed to protect the frontal 60° arc of the vehicle. By placing the ammo directly behind the hull armor, the largest amount of the frontal 60° arc of the the ammo is protected by the tank's thick frontal armor. Moving the ammunition away from the armor, means it is more exposed, as less of it is covered by the tank's frontal armor.

 

 

I disagree. While true that it is protected by the frontal armor, would it not be also true that a center-placed ammo rack is also protected by the frontal armor? The difference here is that a penetrating shot has more distance to travel until it can hit the ammo, meaning it will have a far lower chance of actually being hit by high speed fragments as it will be saved by modules between it and the armor. However, not the case in the Leopard.

 

That is, if it's taking hits from the front.

 

If it takes hits to the sides or to the belly (IED/mines), then ammo placement doesn't matter because with any design, it would be just as easy to hit. 

 

Tank armor doesn't completely prevent a modern KEP's penetration. It just determines how much range has to be between the tanks until a penetrating shot can be scored. With Russia's new 1-piece ammo and improved 125mm gun, I'm pretty sure a T-14 can penetrate the hull front of a Leopard 2 at decent range. And since we can never actually guarantee a certain place in the tank will be completely impregnable to all threats, it's important to design a fail-safe solution. 

 

This is exactly why I am critical of the T-14's design (crew located at frontal section). Although it was a compromise due to the general design, it's still a flaw.

 

However, for both points I do admit that for any tank, a hull down position is an ideal situation and thus protection features should be focused on the turret. 

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So basically in a conventional layout, this is the most optimal way?:

KqSeze4.png

 

All the ammunition rack have blow out panels and are armored.  The auto loader is a Leclerc style bustle auto loader. The fuel in the sponsons are optional, when the front cant fit more fuel, it is stored in the sponsons. 

Side exhausts to avoid spewing smoke in the face of the infantry.

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Is that a driver-in-turret config, or is the driver buried in the hull along with the fuel?


I don't know about optimal, but that seems pretty good.  Conceivably all the ammo could be located in the hull, and an autoloader could pluck it out and handle it round by round into the breech.  The Swiss NKPZ was going to work like this:

 

zviMXgu.jpg

 

Object 187's glacis design seems like an improvement too:

 

qCYwLWD.jpg

 

Instead of having an extremely sloped glacis that meets the turret ring, it has a somewhat less sloped glacis and a long flat section.  This avoids the weak zone where the turret ring meets the glacis seen on... just about every current MBT, actually.

It would reduce the driver's visibility, but with the wondrous cameras now available this could be less of a problem.

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So basically in a conventional layout, this is the most optimal way?:

KqSeze4.png

 

All the ammunition rack have blow out panels and are armored.  The auto loader is a Leclerc style bustle auto loader. The fuel in the sponsons are optional, when the front cant fit more fuel, it is stored in the sponsons. 

Side exhausts to avoid spewing smoke in the face of the infantry.

 

 

This is cross section of Object 490, so in 1980s designers were looking at such layout.

img003.jpg

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The fuel cells in the Abrams are separated from the crew, so a hit would need to penetrate it, start a leak, and also ignite it.  And then spread inside the tank.  And then prove absolutely impossible for the built-in automatic fire extinguisher to put out for some reason.  A fire on the outside of a tank is simply not that threatening to things on the inside:

 

Furthermore, a JP-8 fire can be extinguished (say, by the automatic halon fire suppression system that every Abrams has), unlike an ammunition fire, which categorically cannot be put out once it gets going.

 

And this is essentially kerosene we're talking about, not the easiest stuff in the world to catch on fire:

Come on, were are talking about something that is capable of penetrating the Abrams' hull armor; so essentially a tank round or some sort of modern anti-tank weaponry (RPG, ATGM, EFP). There shouldn't be much doubt about the JP-8 being incinerated in such a case. Btw. diesel has a higher flash point than JP-8 and is often set on fire during combat.

As for the video of the burning T-80U; there are huge differences to our hypothetical scenario. First of all there are several hundred gallons of fuel in an Abrams (most of which is stored in the front), not just a tiny bit. The fuel tanks are not insulated from the interior, there would be only a small amount of steel and foam between the fire and the crew, while the T-80U has about two feet of composite armor including non-metallic materials (with much lower thermal conductivity than the Abrams' fuel tanks).

 

The automatic fire extinguishers might work in some cases, but they most likely not designed to extingusih the fire of the main fuel tanks. The amount of halon seems to be more limited. I don't know; actually I was talking about the fuel being on fire without the crew compartment being penetrated.

 

Fire_suppression_system_1.jpg

 

 

Except that turret armor is thicker than hull armor.  By that logic, putting the ammunition directly behind the turret cheeks would be the safest possible location.

Yes and no. The turret armor is not thicker, if you take a look along the complete 60° frontal arc. But even if it was, there still is another difference: the turret is more likely being hit (depending on source, up to 75% of all hits occur on the turret). Moving the ammo to a place with lower likelyhood of it being hit, is the first step to make the tank more survivable.

 

Except that turret armor is thicker than hull armor. By that logic, putting the ammunition directly behind the turret cheeks would be the safest possible location.

But the Leo 2's designers must have been very confident in their location of the hull ammo rack, seeing as they didn't bother to isolate it from the crew at all, unlike the designers of the inferior Abrams, who were so terrified of their paper creation being penetrated in the hull rear that they even put blowoff panels and blast doors on the hull ammunition storage:

There is absolutely no need to become huffy and feel insulted. Everything I said is either based on a direct source or can be measured. I have read about and seen (although not in person) many cases of vehicles starting to burn after the fuel tanks were penetrated. This is why I wrote about this previously.

 

I don't think the Leopard 2's hull design is a genius idea and the very optimal design; however I also don't think it is horrible and (a lot) worse than the Abrams hull design. In the end every design decision on an armored vehicle is a trade-off between multiple different factors. While people online are always very eager to praise the Abrams hull design, there is one major issue about it that bogs me: nobody cared about using the same design. The Leopard 2, the Leclerc, the Challengers, the K1, the Type 90, the Ariete, GM's XM1 design, hell even the brand new built-from-blueprint tanks such as the Type 10, K2 Black Panther and Altay have the same "dumb ammo storage" as the Leopard 2.

 

So I cannot believe that it is inherently bad. What is the likelyhood of the frontal armor being penetrated and the ammo being incinerated without the crew dieing? Is there enough time to leave the tank before the ammo completely explodes (after initially being set on fire) for the crew to leave? Maybe these questions play a major role in tank designing; I don't have answers to them, but the people who should have access to such data (the people responsible for designing tanks) choose the dumb Leopard 2's layout.

 

I'd personally love to see the same ammo storage layout, but fitted with blow-off panels and a proper isolated compartment.

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Is that a driver-in-turret config, or is the driver buried in the hull along with the fuel?

I don't know about optimal, but that seems pretty good.  Conceivably all the ammo could be located in the hull, and an autoloader could pluck it out and handle it round by round into the breech.  The Swiss NKPZ was going to work like this:

 

zviMXgu.jpg

 

Object 187's glacis design seems like an improvement too:

 

qCYwLWD.jpg

 

Instead of having an extremely sloped glacis that meets the turret ring, it has a somewhat less sloped glacis and a long flat section.  This avoids the weak zone where the turret ring meets the glacis seen on... just about every current MBT, actually.

It would reduce the driver's visibility, but with the wondrous cameras now available this could be less of a problem.

Yeah, the idea was for the driver to be up front like in the M1, protected by the fuel. 

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I disagree. While true that it is protected by the frontal armor, would it not be also true that a center-placed ammo rack is also protected by the frontal armor? The difference here is that a penetrating shot has more distance to travel until it can hit the ammo, meaning it will have a far lower chance of actually being hit by high speed fragments as it will be saved by modules between it and the armor. However, not the case in the Leopard.

 

That is, if it's taking hits from the front.

 

If it takes hits to the sides or to the belly (IED/mines), then ammo placement doesn't matter because with any design, it would be just as easy to hit. 

 

Tank armor doesn't completely prevent a modern KEP's penetration. It just determines how much range has to be between the tanks until a penetrating shot can be scored. With Russia's new 1-piece ammo and improved 125mm gun, I'm pretty sure a T-14 can penetrate the hull front of a Leopard 2 at decent range. And since we can never actually guarantee a certain place in the tank will be completely impregnable to all threats, it's important to design a fail-safe solution. 

 

This is exactly why I am critical of the T-14's design (crew located at frontal section). Although it was a compromise due to the general design, it's still a flaw.

 

However, for both points I do admit that for any tank, a hull down position is an ideal situation and thus protection features should be focused on the turret. 

 

 

TbhGq66.png

The further away from the front, the more exposed is the ammo. Traveling through more distance won't realistically affect the penetration power of an APFSDS/hollow charge jet or it's fragements. It will be enough to set the ammo on fire.

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Come on, were are talking about something that is capable of penetrating the Abrams' hull armor; so essentially a tank round or some sort of modern anti-tank weaponry (RPG, ATGM, EFP). There shouldn't be much doubt about the JP-8 being incinerated in such a case. Btw. diesel has a higher flash point than JP-8 and is often set on fire during combat.

As for the video of the burning T-80U; there are huge differences to our hypothetical scenario. First of all there are several hundred gallons of fuel in an Abrams (most of which is stored in the front), not just a tiny bit. The fuel tanks are not insulated from the interior, there would be only a small amount of steel and foam between the fire and the crew, while the T-80U has about two feet of composite armor including non-metallic materials (with much lower thermal conductivity than the Abrams' fuel tanks).

 

 

An uncontrolled fire inside the hull, whether it's a big fuel tank or the ammo would require evacuation of the tank.  There's just too much energy in that stuff; the heat in ammo cooking off is frequently enough to de-temper the torsion bars, which is why knocked-out tanks frequently sink into their own suspensions.

 

But to put out a fuel tank fire, one need only deprive it of oxygen.  There only needs to be enough halon to displace the oxygen entering the burning fuel tank to get the fire to go out.  In principle you could even displace the oxygen in the fuel tanks with an inert gas as the fuel is consumed (such systems are standard on fighter aircraft) and render it very hard indeed to ignite.  It's also fairly easy to make the fuel tanks cellular so that only a small portion is threatened at any time.  The cellular divisions could also help disrupt HEAT jets; there have been studies of such cellular fuel tanks that have a mass efficiency of 3 vs RHA against HEAT threats.  Fuel is pretty damned effective armor, and since you're going to be carrying around a bunch of it anyway...

 

AFAIK the Abrams' fuel cells are just big, dumb fuel containers, but upgraded fuel tanks are a part of the M1A3 program.

 

Whereas ammo, once it gets going, effectively cannot be extinguished.  So wherever you end up putting the ammo, it had better be isolated and under blowoff panels.

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But to put out a fuel tank fire, one need only deprive it of oxygen.  There only needs to be enough halon to displace the oxygen entering the burning fuel tank to get the fire to go out.

When you penetrate a fuel tank, there are two holes from which oxygen can enter. One at the interior of the MBT, one at the place where the penetrator originally impacted. I am no expert for halon gases, but it seems somewhat unlikely that it is capable of exiting the tank through the penetration hole and is capable of completely blocking all air of entering. While Halon has a lower density than air, there still is Fick's law... this topic might need further research.

 

It's also fairly easy to make the fuel tanks cellular so that only a small portion is threatened at any time.  The cellular divisions could also help disrupt HEAT jets; there have been studies of such cellular fuel tanks that have a mass efficiency of 3 vs RHA against HEAT threats.  Fuel is pretty damned effective armor, and since you're going to be carrying around a bunch of it anyway...

 

I don't know your source, but a few years ago there was a discussion on the TankNet forums, where somebody claimed that fuel hat a ME of 3 vs HEAT. After he posted a link to a research paper, it became clear that this included the (relatively thick) steel walls of the fuel tanks.

 

According to Israel Tal, fuel was found to be about 1/7 as efficient against HEAT as steel of the same thickness. This matches the expectations of the density law.

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In the "Theoretical Study of a Diesel-Filled Airtight Structure Unit Subjected to Shaped Charge Jet Impact" study done by Zhen-Yu Gao et al, there is no mention of the fuel starting to burn or there being a danger of fire.

 

I don't know your source, but a few years ago there was a discussion on the TankNet forums, where somebody claimed that fuel hat a ME of 3 vs HEAT. After he posted a link to a research paper, it became clear that this included the (relatively thick) steel walls of the fuel tanks.
That doesn't matter all that much. Steel armour perpendicular to the hydrodynamic jet will barely have an effect on the total penetration capabilities. For every 1 cm of penetration in steel, the hydrodynamic jet loses 0.94 cm of length. And if he includes the steel walls in the calculation for relative effectiveness vs RHA and still gets a factor of three, doesn't that mean the fuel is even more effective than calculated, since the steel walls will have a relative effectiveness of ~1?

 

For diesel however it's different because that has a secondary effect where the diesel implodes onto the penetrating hydrodynamic jet, slowing it down and thus decreasing jet velocity. This effect does not happen in solids.

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      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 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 Mighty_Zuk
      Now that we know the Challenger 2's Life Extension Program won't include a new gun, there's news coming in that the Warrior's modernization program is highly likely to be cancelled:
      Axe Hangs Over UK Warrior Upgrade.
       
       
    • 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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