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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.

There is a document on DTIC from 1987, where the probability of fuel fires after armor penetration was being investigated on the M2 Bradley, M113 and M1A1 Abrams tank (with diesel fuel, JP-08 was introduced in the Army later). The document is a technical report from the Ballistic Research Laboratory written by Antony E. Finnerty.

 

It is noted that the automatic fire suppression system (AFSS) of the M1A1 is not capable of supressing engine fires.

 

Depending on hit location and how much fuel is left inside the fuel tanks, the probability of incinerating the diesel stored in the Abrams with the first hit by a shaped charge is between 10% and 50%; the probabiltiy of a fire in the frontal fuel tanks was only 15% at 8°C ambient temperature and 25% at 24°C ambient temperature. These values are based on Soviet 125 mm HEAT rounds and might not be valid for more modern, larger calibre, HEAT warheads with tandem charges.

 

The probability of a fuel fire after penetration by a 125 mm APFSDS projectile is between 50% and 60% (at 8°C and 24°C ambient temperature respectively). Again this represents Soviet technology from the 1980s and might not be valid for modern APFSDS rounds.

 

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?

The efficiency is determined by using a sample shaped charge against steel armor as reference (reference penetration is Pref), then using the same type of sample charge against the fuel tank (to determine the penetration into fuel Pfuel). The efficiency then is calculated using these factors.

 

If the fuel tank includes 25 mm front and 20 mm back plates of steel, and this is included in Pfuel, the efficiency will be exaggerated depending on the reference penetration of the sample charge. Let's say (just for this argument) that the reference shaped charge penetrates 180 mm, but it can be stopped by 25 mm steel + 680 mm of fuel + 20 mm steel. Then 680 mm of fuel provides as much protection as 135 mm steel. Now if somebody forgets the fact that there is a 25 mm coverplate and a 20 mm back plate, the efficiency of fuel will be exaggerated by 33%.

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The efficiency is determined by using a sample shaped charge against steel armor as reference (reference penetration is Pref), then using the same type of sample charge against the fuel tank (to determine the penetration into fuel Pfuel). The efficiency then is calculated using these factors.

 

If the fuel tank includes 25 mm front and 20 mm back plates of steel, and this is included in Pfuel, the efficiency will be exaggerated depending on the reference penetration of the sample charge. Let's say (just for this argument) that the reference shaped charge penetrates 180 mm, but it can be stopped by 25 mm steel + 680 mm of fuel + 20 mm steel. Then 680 mm of fuel provides as much protection as 135 mm steel. Now if somebody forgets the fact that there is a 25 mm coverplate and a 20 mm back plate, the efficiency of fuel will be exaggerated by 33%.

 

That explains how included steel could exaggerate the thickness efficiency of diesel, but not how it could exaggerate the mass efficiency, which was your original objection:

 

 

 

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.

 

 

 

 

There is a document on DTIC from 1987, where the probability of fuel fires after armor penetration was being investigated on the M2 Bradley, M113 and M1A1 Abrams tank (with diesel fuel, JP-08 was introduced in the Army later). The document is a technical report from the Ballistic Research Laboratory written by Antony E. Finnerty.

 

It is noted that the automatic fire suppression system (AFSS) of the M1A1 is not capable of supressing engine fires.

 

 

 

Linky?

 

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There is a document on DTIC from 1987, where the probability of fuel fires after armor penetration was being investigated on the M2 Bradley, M113 and M1A1 Abrams tank (with diesel fuel, JP-08 was introduced in the Army later). The document is a technical report from the Ballistic Research Laboratory written by Antony E. Finnerty.

 

Making such a statement without linking is considered a permabannble offense on this forum.

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TbhGq66.png

My problem with this image is it does not take into account any side armor.

Take a Leopard 2 for example. It may not have armor cavities directly over its bustle, but the armor over the crew compartment still provides cover for its ready rack from a sizable frontal angle.

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I forgot the link :wacko:

Here is it.

As for the mass efficiency and the thickness efficiency; in the original discussion on TankNet the ME was calculated from the TE. You just need to take into account the areal density for this.

Ramlaen, on the Leclerc, Leopard 2 and similar designed tanks, the side skirts are meant to cover only the crew compartment (i.e. driver's place + turret ring section) along the 30° arc. The ammo would need to be stored behind the turret ring. While it is possible to extend the skirt armor, this would lead to an increase in weight or a decrease in frontal arc protection for the crew compartment (compare Leopard 2 and Leclerc with ~150 mm thick skirts to M1 Abrams with ~70 mm skirts). Each tank design is a trade-off between benefits and disadvantages.

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Ramlaen, on the Leclerc, Leopard 2 and similar designed tanks, the side skirts are meant to cover only the crew compartment (i.e. driver's place + turret ring section) along the 30° arc. The ammo would need to be stored behind the turret ring. While it is possible to extend the skirt armor, this would lead to an increase in weight or a decrease in frontal arc protection for the crew compartment (compare Leopard 2 and Leclerc with ~150 mm thick skirts to M1 Abrams with ~70 mm skirts). Each tank design is a trade-off between benefits and disadvantages.

What? I wasn't talking about hulls. The Leopard 2's bustle ammo rack is protected from frontal angles by the crew compartment armor.

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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.

The May 1951 version of TM 9-729 for the M24 Chaffee notes that "The use of any fluids (water, antifreeze compound, or ammudamp) in ammunition box cans has been discontinued. All ammudamp cans will be completely drained of ammudamp fluid." So it seems that the US discontinued wet stowage even in tanks already using it not long after WW2.

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The May 1951 version of TM 9-729 for the M24 Chaffee notes that "The use of any fluids (water, antifreeze compound, or ammudamp) in ammunition box cans has been discontinued. All ammudamp cans will be completely drained of ammudamp fluid." So it seems that the US discontinued wet stowage even in tanks already using it not long after WW2.

That is quite interesting.  Didn't know that.

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It is noted that the automatic fire suppression system (AFSS) of the M1A1 is not capable of supressing engine fires.
Ah that is correct. But that's because the engine bay doesn't have an AFSS.

 

As for the AFSS in the crew compartment:

987492d222.png

Which follows on to this:

8871ef0c2e.png      c31bc4cec3.png

tl;dr:

- Where there's an AFSS the chance of a sustained fire is zero.

- Sustained fires can only happen in locations where there is no AFSS and where there the fuel is actually in a form in which it can form a sustained fire.

 

And with that in mind the only place where sustained fires can happen are the REFC, LEFC and EHY. All of which are in the engine bay.

 

Furthermore, all this is based on calculated probabilities, with the actual calculation not mentioned in the paper:

c78564384b.png

 

Also, only steel/aluminium armours were considered in the paper, for as far as I can see. While currently we obviously have NERA and ERA which will result in different terminal ballistics.

 

Reading further on in the paper, there is some data that's outright wrong, based on actual tests I've attended. But for (hopefully) obvious reasons I can't discuss the tests nor the results of the tests. And the more I read this paper, the more I'm raising my eyebrows. Here are a few quotes:

Considerable personal judgment was required
Only one useful model of sustained fuel fires caused by munition attacks has emerged. This is the Dehn Model.
Unfortunately, at this time we cannot use the mathematical form of the Dehn Model. We simply do not know the correct values of the parameters and variables which go into the model.
(!!!)
At this point In time, we do not have sufficient data to implement even the simplified form of the Dehn Model.
(!!)
It is also necessary to use personal judgment as to the applicability of much of the data

 

...these aren't things I want to read in a report.

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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.

 

 

I missed this when I first went through it, but this old canard is beloved of the Military Reform crowd (when they were busy bashing on supposed survivability shortcomings of the M1) and is just as wrong now as it was in the 1980s.

 

flash point is not a general indicator of flammability.  It refers to something very specific; it is the lowest temperature at which fumes of a liquid will ignite if exposed to an ignition source.  JP-8 has a lower flash point than some diesel fuel, but because JP-8 has much more precisely formulated than diesel fuel is.  The flash point of commercially available diesel fuel is a wide range that straddles the flash point of JP-8.  JP-8 and diesel just aren't that different; they're very slightly different average molecular weights of hydrocarbon, and JP-8 has a number of additives which mainly improve shelf life.  Look at a destructive distillation diagram for petroleum cracking; jet fuel is based on C10 to C16 while diesel is C14 to C20.  They're just not that different.

Moreover, flash point is not generally indicative of flammability.  It is a component of flammability, but it refers to a specific circumstance under which ignition can occur; namely when there are fumes present and the fumes are exposed to an ignition source.

 

And the fumes are exposed to oxygen.

 

The fact that diesel fuel usually ends up burning when military vehicles are hit does not prove that the fuel was the source of the fire.  There's plenty of other shit on a tank that burns, like lubricants, hydraulic fluid (which was enough of a fire hazard that it was re-formulated after the great 1973 Arab-Israeli rematch), and of course the ammo.

 

I don't see how you jump from the idea that anything that can penetrate an MBT will automatically vaporize and ignite JP-8, especially when the availability of oxygen is in question.

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From Otvaga:

 

cixhM0iHW6I.jpg

 

rVwdWP1h7lY.jpg

 

Looks like the MBT-80 designs were better protected than the XM1, at least when it comes to protection against APFSDS ammunition. The XM1 has better protection against HEAT ammunition, but that doesn't really matter. The MBT-80 had much better turret armor than the XM1, so it was much less likely to be destroyed in hull down configuration (11 to 28% chance on the MBT-80, 17 to 58% (!) chance on the XM1).

 

f.jpg

 

5pq3om.jpg

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2 hours ago, SH_MM said:

From Otvaga:

 

cixhM0iHW6I.jpg

 

rVwdWP1h7lY.jpg

 

Looks like the MBT-80 designs were better protected than the XM1, at least when it comes to protection against APFSDS ammunition. The XM1 has better protection against HEAT ammunition, but that doesn't really matter. The MBT-80 had much better turret armor than the XM1, so it was much less likely to be destroyed in hull down configuration (11 to 28% chance on the MBT-80, 17 to 58% (!) chance on the XM1).

 

f.jpg

 

5pq3om.jpg

 

Could the reason the XM1 proved more resilient to CE when fully exposed be because off the front mounted fuel tanks and composite side skirt?

Or could it be because the XM1 had almost all it's ammunition in the turret, while the MBT-80 had all of the propellant in the hull, assuming the layout is similar to the Challenger 1?

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MBT-80 had that stupid hull design with the giant cutout in the glacis for the driver:

 

LUbrT7I.jpg

 

 

As for the MBT-80 having better turret armor than the XM1, I don't think that means a lot.  This is the XM1:

 

9wVzzD7.jpg

 

As you can see, the armor package installed on the XM1 doesn't particularly resemble the armor package of the production M1.  It might not even have composites at all.  Likewise, neither MBT-80 turret was representative of a production tank.  The one with the big, sloped slabs near the front of the turret is simply an FV4211 turret with additional weights attached to it to simulate the mass and moment of inertia of the final armor package.  The other one in the picture above is simply a test rig.

 

So when a test document or archival document or whatever (where did you get those numbers, @SH_MM ?) comes forward saying that the XM1 has inferior HEAT protection to the MBT-80, it's not really clear what they're comparing.  Are they comparing the calculated protection of the prototype turrets against each other?  That would just be silly in the case of the MBT-80, neither test turret actually had composite armor installed.  Are they comparing the calculated protection of the production turrets against each other?  That would be more interesting, but how close was the MBT-80 to production at the time the statements were made?  As I recall, fairly late in the MBT-80 program they were still screwing around with concepts like asymmetrical gun mounts.  And what production M1 turret were they comparing to the MBT-80?

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12 hours ago, Collimatrix said:

As for the MBT-80 having better turret armor than the XM1, I don't think that means a lot.  This is the XM1:

 

9wVzzD7.jpg

 

As you can see, the armor package installed on the XM1 doesn't particularly resemble the armor package of the production M1.  It might not even have composites at all. 

 

Except for the original validation prototypes, all manufactured XM1 prototypes either featured Burlington ("Chobham") armor or weight simulators representing Chobham armor. The armor technology was given to the United States by the UK in 1973. The photo you posted shows an XM1 validation prototype from Chrysler with Chobham armor, which was made after Chrysler completed a redesign of their tank to adopt the new type of armor in 1974.

 

In 1976, after both designs from Chrysler and General Motors were trialed (including ballistic tests), the tanks were redesigned for the FSED (full scale engineering development) stage. The photo below shows a model of the Chrysler FSED prototype, which is pretty much identical (except for a few minor modifications) to the initial production M1 Abrams tank.

 

bCIJJ1u.png

 

12 hours ago, Collimatrix said:

Likewise, neither MBT-80 turret was representative of a production tank.  The one with the big, sloped slabs near the front of the turret is simply an FV4211 turret with additional weights attached to it to simulate the mass and moment of inertia of the final armor package.  The other one in the picture above is simply a test rig.

 

So when a test document or archival document or whatever (where did you get those numbers, @SH_MM ?) comes forward saying that the XM1 has inferior HEAT protection to the MBT-80, it's not really clear what they're comparing.  Are they comparing the calculated protection of the prototype turrets against each other?  That would just be silly in the case of the MBT-80, neither test turret actually had composite armor installed.  Are they comparing the calculated protection of the production turrets against each other?  That would be more interesting, but how close was the MBT-80 to production at the time the statements were made?  As I recall, fairly late in the MBT-80 program they were still screwing around with concepts like asymmetrical gun mounts.  And what production M1 turret were they comparing to the MBT-80?

 

The two excerpts posted earlier are taken from a 1978 report (WO 194/2767) from the British military (afaik FVRDE). Obviously the MBT-80 tanks were pure paper designs, given that there are no prototypes/testrigs (known to the public), which have been fitted with a V16 engine or a gas turbine. However I don't see a reason to assume that the British report used the old 1974 design of the XM1 Abrams (rather than the improved design from 1976) as reference. I also don't see much reason to dispute the credibility of the report, given that the XM1 is fitted with a type of Chobham armor and the UK had started researching Chobham armor two decades before this report.

 

There wasn't a MBT-80 production design, the program was canceled before it lead to any results. However the XM1 FSED prototype from Chrysler is the same design that went into LRIP and final production, aside of fixing a few errors and improving reliability.

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Here is something for this topic:

 

A Greek blog entry on their testing of the Challenger 2E, Leclerc, Leopard 2 Improved, M1A2 Abrams, T-80U and T-84 tanks. The scores from the evaluation are the following:

  1. Leopard 2 Improved - 78.3
  2. M1A2 Abrams - 72.95
  3. Leclerc - 71.92
  4. Challenger 2E - 69.89
  5. Т-80U - 59.2
  6. Т-84 - 56.3

The google translate output is quite interessting, if correct. Supposedly the Challenger 2E was found to be worse armored (!) than the M1A2 Abrams and Leopard 2 Improved despite being heavier. So much about mighty "Chobham Mk. 2 Dorchester" being the best armor. Even the ten tons lighter Leclerc tank had nearly the same level of protection as the Challenger 2E. The use of the EuroPowerPack in the Challenger 2E is believed by the blog author to not have enhanced the mobility, because there have been issues with power delivery and despite switching the powerpack, nothing else was changed to properly optimize the tank for the different engine (?).

The T-80U had issues with the semi-automatic transmission and general reliability, including the weapon systems (guided missiles) and FCS.The T-84 has a weird internal layout and bad controlls, essentially requiring the driver to have "three hands" to work with the steering wheel and operate his other controls. Operating the T-84 was so tiring, that the Greek crew had to be replaced by the Ukranian crew in some tests. Leclerc, Leopard 2 and M1 Abrams had no issues with driving up and down a 60% slope, the other tanks however had some problems.

 

Btw: the Italian C1 Ariete and the Israeli Merkava III tanks were considered, but the manufacturing companies/officials didn't want them to participate in a competition (maybe because they were afraid of these relatively new vehicles underperforming and causing big political backlash).

 

20170514_185634.jpg

 

20170514_185259+-+Copy.jpg

Note that the Leclerc is fitted with additional armor.

20170514_185326.jpg

The Challenger 2E lost most of it's track's pads when trying to climb a wall. Does anybody know if the Challenger 2E used the same tracks (by Cook Defence) as the British Army model? Did the greater powerpack cause these issues?

 

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2 hours ago, SH_MM said:

Here is something for this topic:

 

A Greek blog entry on their testing of the Challenger 2E, Leclerc, Leopard 2 Improved, M1A2 Abrams, T-80U and T-84 tanks. The scores from the evaluation are the following:

  1. Leopard 2 Improved - 78.3
  2. M1A2 Abrams - 72.95
  3. Leclerc - 71.92
  4. Challenger 2E - 69.89
  5. Т-80U - 59.2
  6. Т-84 - 56.3

The google translate output is quite interessting, if correct. Supposedly the Challenger 2E was found to be worse armored (!) than the M1A2 Abrams and Leopard 2 Improved despite being heavier. So much about mighty "Chobham Mk. 2 Dorchester" being the best armor. Even the ten tons lighter Leclerc tank had nearly the same level of protection as the Challenger 2E.

 

I find it hard to believe the Leclerc was deemed better armored than a significantly heavier Challenger 2, especially when both were very modern at the time.

Maybe they meant it was better protected, as opposed to better armored? No need to mention that protection and armor are not the same thing.

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machine translating the conclusion section

 

Quote
Final assessment of tanks
 
The tanks participating in the competition were as follows:
Compared with other Leopard-2A5S front of the most well preserved and was the only one at the top of the tower which is listed in the manufacturer had thought seriously. The ideal result of firing tests showed that it was quite reliable and convenient and ergonomic for the crew.
M1A2 Abrams reservation was the second best. The Americans offered the Greeks a tank without a "Depleted Uranium" reserves (DU reserves are still prohibited). The tank was superb enough and was a special ergonomic for the crew. The car was reliable and there was only one major disadvantage on the tests - it was a gas turbine engine that thawed the fuel.
Leclerc- was that a few years earlier by the French, the United Arab Emirates proposed variant slightly differed, double impression: ideal for building and driveline (ie, German firms, RENK- and MTU-'s, the latest generation of diesel engine and speed transmission, so Called Europack), an excellent hydro-pneumatic suspension and weight of participants The best ratio of A-power. All of this made it particularly fast and flexible, and with all of this it was distinguished by the low fuel prices. In terms of armor, Leo-2A5S and M1A2 have always been distinguished in comparison with the previous two tanks, but it was probably very high at the level of its weight. The tower, with a completely automated charger, offered innovative innovation to the customers, but in practice the automated performance did not justify the expectations and was constantly crippled and spoiled. On the other hand, the tank was not distinguished by the crew's ergonomics (mainly due to the lack of existing space), for the same reason was the use of weapons, such as pulverizing machine guns. In the precision of the hand, well, but not the best.
Challenger-2E was a negative surprise. Despite the fact that the version presented in the competition was equipped with a similar type of Europack-type military equipment, it was often spoiled when switching to high speeds, which was responsible for the transmission of the motorway from the machine. The 1200-horsepower engine with the Challenger-2 engine was replaced by a 1500 horsepower engine and did not have a proper study of the kinetic circuit and adjusted to the engine that caused frequent outflow from the car. It was also a disadvantage of his annexed armor. The car was distinguished with a relatively weak armor compared to Leo-2A5S and M1A2, while Leclerc even 10 tons was almost never behind British tanks.
The car was not very precise, it was the only one that was equipped with a 120 millimeter stroke and was used in three parts (shells, sparkle and insulating capsules), while Ukrainians and Russians used both guns and rifles, Doing this with automatic charging). However, the car had a positive side: he served in the army with long military experience and was the only one who had a toilet in the tower and traditional British tea makers.
Russian Т-80У Soviet tankmsheneblobis School was a classic representative. Its main problem was the semiconductor speed of the prototype at the moment, which was often out of order. The machine showed low results in accuracy, as well as the crew's ergonomics. In addition, the two systems, which the manufacturer claims, compared with Western counterparts, the electrical-optical flaw system and a 6-kilometer laser-guided tank missile, was unreliable in practice and did not show any possible results.
Ukrainian Т-84- on the whole characterized by Russian tanks, but another significant disadvantage, he ortaktiani diesel engine, which predictably burn oil, and mechanical gear box was equipped with Russian car unlike the steering wheel instead of a lever ruled. That is why the Greeks were saying jokingly "I need three hands for him to manage" (to turn the driver-mechanic into a curve, let alone the third hand). It is also worth mentioning that the car was causing the crew of the crew - the Greek crew was replaced by Ukrainian crew due to fatigue in checking stock.
In January 1999, the General Staff of the Greek Army presented the results of the competition, according to the scores the following places were distributed:

         Leopard-2A5S - 78.3
         M1A2 Abrams - 72.95
         Leclerc - 71,92
         Challenger-2E - 69,89
         Т-80У - 59,2
         Т-84 - 56,3

 

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13 hours ago, SH_MM said:

The use of the EuroPowerPack in the Challenger 2E is believed by the blog author to not have enhanced the mobility, because there have been issues with power delivery and despite switching the powerpack, nothing else was changed to properly optimize the tank for the different engine (?).

 

 

I can definitely buy this part.  Technology of Tanks describes a little bit of the engine tweaking and optimization that went into the Leo 2.  Despite having a better power to weight ratio than the late-model Leo 1, the early Leo 2 had worse acceleration until modifications to allow better engine RPM increase were made.

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21 minutes ago, Volkswagen said:

When I open that blog post, it's in georgian. Am I the only one who has it so?

 

Oh, that is Georgian? I didn't pay too much attention to this and assumed it was Greek. My mistake resulted from using Chrome (Chrome has a built-in translator, which I use for most languages other than English).

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      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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