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Collimatrix

Explosive Reactive Armor

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I had originally sent this as a PM, but I'm going to post this here as well for general critique and stuff.

 

Quote

Anyways, the entire point of my inquiry was to get a better sense of the parameters of a molybdenum jet, so that I could hopefully get a better sense of its performance against ERA and NERA compared to traditional copper jets.

Reading a bunch of papers by Manfred Held, it seems that in his experiments the forward portion of the jet is pretty undisturbed after penetrating ERA/NERA. It seems like the forward portion of the jet, due its higher velocity, is able to exceed the reaction speed of the reactive module and clear it before it's disturbed by the moving plates. Maybe I'm interpreting it wrong, but that would imply that there's a velocity threshold, where if the portion of the jet is above a certain velocity (and it's not too far behind the ERA triggering portion of the jet), it'll be little affected by the disturbance effects of the ERA, and has to simply be eroded. Since the high efficiency of ERA is due to its lateral disturbance effects, a jet that can get a higher portion of the jet clear it before it can react would reduce the efficiency of the module.

This is where the knowing the parameters of a molybdenum jet is so important. Particular its velocity distribution. If the increase in velocity of the tip is reflected linearly down the length of the jet, i.e. the entire jet is faster than a copper jet by x amount, then it would be expected that a greater portion of the jet would be able to clear the ERA module. However, if the velocity increase is localized to the tip, then it might even do worse against ERA, as the tip would experience pronounced stretching compared to the other parts of the jet, and would trigger the ERA at an earlier interval respective to the positions of the other parts of the jet, thus enabling it to "catch" a greater portion of the jet.

Of course, everything I just wrote could be nonsense, because in that paper where they demonstrated the effectiveness of a double NERA system, the fastest jet particle to emerge from the armour system was ~6 km/s. The portion of the jet from 6 km/s to 8.25 km/s correlates to a length of about 400mm, which has an ideal hydrodynamic penetration of about 425mm in steel. The LOS thickness of module itself was 99.5mm in steel, and 33mm in unknown material (but I expect it to not be very dense), which is quite far from 425mm of steel. Thus the forward portion of the jet could not have been eroded to that extent just from penetrating the module, which means that the module was somehow able to disturb even the fast forward portions of the jet.

This also makes me wonder if the advantage of the faster jet tip of molybdenum jets could be mediated somewhat by the fact that it would induce NERA modules to have higher plate velocities, if I understand the operating principle of NERA correctly.

 

 

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3 hours ago, SH_MM said:

The ERA package adopted on the M60A1 of the USMC (originally designed for the US Army) is btw. not Blazer, but made in France (it's called something like "ACA" or" AAC").

 

ARA

 

3 hours ago, SH_MM said:

The AMX-30 received a version of the same ERA system to protect against ATGMs.

 

The AMX-30B2 Brenus uses BS-G2 reactive modules,  here is a picture of a scale model of a M60A1 fitted with BS-G2 :

 

1502564828-m60-brenus.jpg1502564844-0006.jpg

 

 

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I moved these posts to this thread from the active protection systems thread because they are more relevant here.  But this is very interesting.

 

@SH_MM, do you happen to recall the name of the West German anti-apfsds ERA developed for the Leopard 1?  This is very interesting, and the first I've heard of such a thing.

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I find it very hard to believe a certain ERA design was alone sufficient to defeat an APFSDS, or more accurately and akin to the presumed intention in MM's words, the most significant part of an existing KE-defeating array.

 

With sufficient weight it is possible of course, but how was this viable on the Leopard 1 tank?

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The idea that someone was fooling with anti-APFSDS ERA some decades before K5 was fielded strikes me as plausible.  After all, the Soviets were fooling around with ERA in labs decades before the Israelis beat everyone to the punch in actually fielding it.  Also, Ogorkiewicz's Technology of Tanks mentions the possibility of heavy ERA arrays effective against KE threats, which I think predates general western knowledge of K5.

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16 hours ago, SH_MM said:

Isn't the BRENUS ERA a version of the ARA? It's made by the same companies... ;)

 

There have certainly been a technological transfert between the SNPE and Kaman but the BS-G2 bricks used on the AMX-30B2 Brenus are thicker than the ARA tiles and in addition, provide protection against armor-piercing projectiles fired from medium-caliber autocannons.

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19 hours ago, Collimatrix said:

I moved these posts to this thread from the active protection systems thread because they are more relevant here.  But this is very interesting.

 

@SH_MM, do you happen to recall the name of the West German anti-apfsds ERA developed for the Leopard 1?  This is very interesting, and the first I've heard of such a thing.

 

It is based on infomation present in the summary "Perforation - Protection: State of the Art" by P.Y. Chanteret and G. Weihrauch of the French-German Research Institute of Saint Louis (ISL), published as part of the European Forum on Ballistics 2001.

Okay, a small correction: The article mentions that first anti-KE ERA was tested in/before 1973 by the ISL, summarized in the document "Untersuchung zur Mindering der Durchschlagleistung von Wuchtgeschossen" from 1973 by G. Weihrauch, H. Müller and B. Wellige. The specific ERA package for the frontal arc of the Leopard 1, providing protection against 105 mm APFSDS, was tested somewhere in the mid-1970s, the final report "Deutsch-Französische Kommission für Angriff und Schutz, Leo-I Beschuss mit reaktivem Frontschutz mit Pfeilgeschossen Kal. 105 mm" from the ISL is dated at 1977. ERA was first used in combat in 1982, with the first fielded anti-KE ERA being Kontakt-5 in 1985... so 1977 is still quite a bit ahead of schedule.

 

1N4ZfxU.png

 

The ISL research program by Germany (not sure if France was involved, no French names and the cited documents all have German names) lasted more than 10 years and lead to multiple "very effective sandwiches" by optimizing various different aspects of reactive armor. The English-language document "Recent Research Work conducted at ISL in the Field of Reactive (Active) Armour" by G. Weihrauch from 1984 supposeldy contains a summary of them. Unfortunately I couldn't find any of the research papers online aside of the general article form the European Forum on Ballistics (it's on NDIA, can't find link ATM).

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