The Real Story on ERA

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dwightlooi 10/15/2007 9:13:31 PM

Why is it that no Western force uses ERA? The Israelis did until they built Merkava. It seems to me that there are some serious drawbacks to its use in terms of weight, cost, maintenance and operating with friendly infantry. It must be that the Russians are behind in maeterials science or that their "quart in a pint pot" design philosophy prevents them from having integral armor that can stop both Western LRP and HEAT. If Kontakt-5 and Kaktus are all that is it that the Western design teams are incompetent or do they know something the Russians don't? Or is it, as I believe to be true that the Russians have no choice but to put ERA on their tanks to have any chance of survival on the modern battlefield?

Western MBT designers prefer ceramic laminate armor like the Chobam and Dorchester types which offers more balanced protection against kinetic and chemical energy threats. In general, ERA offers HEAT protection at a relatively light weight but offers either no protection (light ERA) or marginal protection (heavy ERA) against long rod penetrators. Western laminate armors offer very good protection against both threat types. In fact, part of the mechanism for Chobam type armor is the properties of ceramic layers when compressed by a heat charge. The jet out disrupting the HEAT jet very much like ERAs except there is no need to blow of an entire panel and the material also contributes to stopping long rod penetrators.

Basically, the argument is this. You can get good protection against chemical energy threats with ERA with very modest weight gains. You need to put on weight to protect against Kinetic Energy threats - period. However, when you put on the heavy armor it takes to stop long rods and you are using the western ceramic laminate armor types, these are also very effective against HEAT threats and hence the tanks are very well protected without the need for messy ERA tilings.

For instance, the Abrams's base armor itself has been very good at stopping RPG attacks. In fact, despite what some people may think, there has been zero loss of crew due to RPG penetration. In fact, with over 600 rpg hits on M1s since 2003, only 2 ever penetrated to the crew compartment. These were in general "lucky hits" at a seam space between composite armor. There have been instances an M1 took over 20 RPG hits, but the crew was unhurt.

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earlm You seem to be an expert 10/15/2007 9:44:39 PM

How does the armor stop LRP? Is it anything like naval armor where mass, hardness and elasticity are the factors or is it different? My question is, are the materials stopping the projectile in an anlogy with naval armor, British or Japanese way with armor that is hard but also elastic or is it the US way where the goal is to break the projectile? Can an LRP be stopped by mass and elasticity or does it have to be broken?

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dwightlooi 10/16/2007 12:19:42 AM

A common mischaracterization of armor effectiveness is the assigning of a rolled homogeneous steel armor (RHA) thickness equivalent for HEAT and KE threats. Well this works to some extent in describing an armor package's effectiveness against HEAT (CE) warheads, effectiveness against KE threats cannot be responsibly described this way.

Back in WWII, it was realized that the performance of high velocity AT slugs is very much dependent of the face hardness of the target's armor plating. If the slug deforms are shatters on impact, it won't penetrate much if at all. If it doesn't it goes a long way. In otherwords, the initial strike means everything and armor thickness is really secondary. You cannot really describe a penetrator's performance in terms of how many mm of RHA it'll penetrate because two penetrator can penetrate through the same "thickness" of RHA, but have completely different performance against say Chobam or whatever. This is in a similar vein to the fact that you cannot describe a bullet's armor piercing capability in terms of how many inches of butter it can penetrate. Two bullet can go through the same depth of butter, but one may shatter on contact with pot pan aluminum another will hold together and go through a tungsten-carbide plate. Similarly, a tank's armor performance against KE threats cannot be described as a thickness equivalent to RHA simply because it is NOT RHA!

In general, you want to shatter the long rod on impact. If you can do that you go a long way to improving your survivability. Also, not all long rods are created equal. The ones the Russians sold to the Syrians in the 70s broke all the time against relatively primitive Israeli armor of the period, whereas American ones used in Desert Storm (M829A1) cut through T-72s like butter. The current M1 Abrams armor package incorporate such articles as Depleted Uranium strike faces over laminated ceramic matrix armor. The Leopard 2A6 and Merkava IV uses rather bulky applique armor over the base armor with (according to reports) sharply raked plates internally. The purpose amongst other things, is to increase the likelihood of the long rods breaking on impact or while traversing through the applique package. The bulky but mostly hollow applique approach also acts as spaced armor which protects against HEAT and HESH rounds very much like an armor skirt does -- against these 20 inches of air is almost as good as 20 inches of steel!

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YelliChink 10/16/2007 12:41:17 AM

link

They do use ERA to protect sides and weak points, especially after the reported RPG-7V penetration, but they are not as sophisticated as new Israeli ERA and Russian ones. Although the newest Russian or Chinese 125mm penetrator may be able to punch through Chobham, chances are Western Armies are not gearing up to fight Russians, Chinese or Indians on land. So, enough is enough, until there is need, there will be no investment in low-priority items.

Besides, active defense systems seem to be very promising. Why bother wasting money on something so 20th century?

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Bluewings12 10/16/2007 1:15:25 PM

I note few errors :

""In general, ERA offers HEAT protection at a relatively light weight but offers either no protection (light ERA) or marginal protection (heavy ERA) against long rod penetrators.""

Absolutly wrong regarding the heavy ERA . Let me give you an exemple to show you what a good ERA can do ;-)
Let 's take a T-80UM 's front turret , the main armor is a mix of steel , nickel (around 350BHN) and a lightweight fiberglass called Steltexolite . It gives the naked front turret an RHA armor estimate of 490mm versus kinetics rods and 520mm versus HEAT (chape charges) .
Now , add some Kontakt-5 and the RHA estimates jump to 660mm versus kinetics rods and 1120mm versus HEAT .
That is an increase of 34% vs penetrators and 115% vs HEAT . This is far to be marginal !

""In fact, part of the mechanism for Chobam type armor is the properties of ceramic layers when compressed by a heat charge (what do you mean ?) The jet out disrupting the HEAT jet very much like ERAs""

What ? What "jet out" ? It seems to me that you are confusing things here .

""You cannot really describe a penetrator's performance in terms of how many mm of RHA it'll penetrate""

Of course you can , you just need to do the maths .

""a tank's armor performance against KE threats cannot be described as a thickness equivalent to RHA simply because it is NOT RHA!""

As I said , you just need to do the maths to get the RHA rating . Exemple :
Calculus to know the RHA rating of various layering :

"Test of AP shots on various aluminum?steel combinations has revealed that if the less dense layer is on top, the array offers as much as 15% more resistance than the other way around. Tests on APFSDS seem to show this same effect.
Test on ceramic with backing plates show resistance changes with the backing material. The Ceramic/Aluminum, offering much less resistance than the same Ceramic mounted on RHA. In addition, the same ceramic mounted on tungsten plate offers more resistance still. In the case of aluminum, this is less dense than the ceramic and thus it fits into the above model. The case of the Tungsten backing is of note due to the possibility that this might be a key to dU armor effectiveness.
Tungsten offers a TE of 1.44 compared to RHA. But when the ceramic was mounted on Tungsten, the resistance of the ceramic increased by 33% over the resistance offered by the Tungsten plate. Looking at it numerically the 1 part ceramic + 2 parts RHA offered 88% of RHA, making the ceramic only 0.75. The 1 part Ceramic +1 part Tungsten target was 1.16 times RHA. But it should have offered 97% resistance making the combination 11% better."

As long as you know what an armor is made of , you can calculate its RHA rating because we know the properties of the materials involved .
Exemple of a very strong ceramic RHA :
Resistance of UO2-100/RHA @ 1.5 k/ms = 1.8 (basic RHA=1) , so about twice the resistance .
It is why we can say that the front turret of the Abrams SEP has a RHA of 960mm vs penetrators and 1520mm vs HEAT even if its armor is a mix of materials .

To go back on ERA , it is now easy to understand that the material employed to build the moving plates is of the utmost importance .
It has to resist the explosion underneath and be strong enough to cut through the rod while giving a maximal shock wave .
Some materials are better than others ...
I can tell you that the actual testings in Russia are of course leading to a new level of protection vs both penetrators and shape charges . The latest T-80s and T-90s are far lighter than an Abrams , a Chally or a Merkava but their protection levels is almost as good if not on the par .

Cheers .

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dwightlooi 10/16/2007 8:43:38 PM

Absolutly wrong regarding the heavy ERA . Let me give you an exemple to show you what a good ERA can do ;-)

Let 's take a T-80UM 's front turret , the main armor is a mix of steel
, nickel (around 350BHN) and a lightweight fiberglass called
Steltexolite . It gives the naked front turret an RHA armor estimate of
490mm versus kinetics rods and 520mm versus HEAT (chape charges)
.

Now , add some Kontakt-5 and the RHA estimates jump to 660mm versus kinetics rods and 1120mm versus HEAT .

That is an increase of 34% vs penetrators and 115% vs HEAT . This is far to be marginal !

It doesn't work that way because the "heavy" ERA's effectiveness is hugely dependent of whether the long rod breaks when confronted by the shearing action of the ERA plates. They don't always break. In fact, even against earlier long rods like the M892A1, Konkakt-5 does not reliably or usually break the rods, they sometimes do at certain strike angles when the rods strike certain areas on the ERA brick (not all). Basically, the "heavy" ERA is on the threshold of sometimes being able to compromise the long rods. Against, redesigned penetrators however, they are frequently not even on the threshold of being able to do so. When the rods stay intact and uncompromised, the heavy ERA's effect on them is very much like "light ERA" which is that they don't have much of an effect if at all.

""You cannot really describe a penetrator's performance in terms of how many mm of RHA it'll penetrate""

Of course you can , you just need to do the maths .

As I said , you just need to do the maths to get the RHA rating . Exemple :

Calculus to know the RHA rating of various layering :

No you can't. And this is because, as I have said before, a lot of the armor's effectiveness against long rods depends on whether the penetrator shatters on impact or is compromised in some other way. If you what to put things in terms of RHA, one particular armor package can have an RHA rating of say 220mm vs one particular type of penetrator that doesn't shatter hitting it, and a 5000mm rating against another penetrator which it does shatter on impact. The same goes for penetrators, against one kind of armor which it doesn't break on it may be good for say 650mm whereas on one which fractures it it may only be good for 50mm. In other words, you can rate a penetrator against say Chobam armor, Steel Armor, Aluminum Armor, whatever armor. But you cannot rate one in terms of one type of armor and expect it to collate in a meaningful way to the rod's penetration potential on another kind of armor.

Think of it this way. Let's say you measure the penetration potential of glass rods and steel rods shot into cork wood. Even if both rods go the same distance in cork, it means nothing because when shot into cork wood with a thin plexiglass sheet over it the glass rod will likely shatter and not penetrate at all, while the steel rod won't and having gone through the thin skin will drive through the cork like butter. Hence, trying to measure either an armor plate's rating or a penetrator's rating in terms of how much cork it will penetrate is highly misleading. The reason is that the armor plate being rated are not made of CORK and the penetrators won't be penetrating CORK!

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Herald1234 In one sense. 10/16/2007 9:02:20 PM

It makes more sense to get out of game simulation BS terms and stick to the REAL WORLD physics.

For example I would take as a standard measure how much work per square centimeter strike asrea was accomplished against an armor package and determine a penetration ratio against that armor package based on the a standardized mass' SMASH against the armor package face at a standard angle. I would also calculate expected vector deviation from strike based on SHOVE introduced by either ERA or induced yaw resistance designed in the armor package itself to the primary momentum vector. Sum it all up and express it as a numeric offense/defense ratio.

That should eliminate the confusion and the BS factor since it would in effect be a single replicable ENERGY measurement.

Its why you see me write about SMASH a lot.

Herald

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earlm SMASH formula 10/16/2007 11:48:46 PM

How does the formula account for broken/dulled penetrators? It seems to me that trying to quantify the thing is a waste. Either this penetrator penetrates this pakage or it doesn't. Besides, with the M8 penetrator you mention all the formulas are a waste of time, the tank just gets SMASHED.

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andyf 10/19/2007 5:50:50 PM

I think I understand what herald is proposing,

momentum/penetrator frontal area /time ?

say 10 kg penetrator at 1000m/s 1 cm diameter

would give an load in 1000th of a second of 10000kg/m

you could apply that figure to the armour material <sharpy?> strength figures

as the underlying thickness of armour would support the top layers

armour thickness would multiply this-, maybe thickness squared?

is that what you mean?

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Herald1234 10/19/2007 6:37:06 PM

I think I understand what herald is proposing,

momentum/penetrator frontal area /time ?

say 10 kg penetrator at 1000m/s 1 cm diameter

would give an load in 1000th of a second of 10000kg/m

you could apply that figure to the armour material <sharpy?> strength figures

as the underlying thickness of armour would support the top layers

armour thickness would multiply this-, maybe thickness squared?

is that what you mean?

Yep.

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