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Bronezhilet

No, Nozh doesn't work as advertised

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So, if you're reading this I assume you know what Nozh is and how it's supposed to work. Just a quick tl;dr to refresh your minds: Nozh is supposed to work by cutting a penetrator with the use of multiple shaped charges, like this: 

158297_original.jpg

 

 

The thing is that it cannot work as advertised, for a plethora of reasons. Most of these reasons have to do with the formation of a shaped charge jet.

 

So lets go.

 

The thing I realised when looking at Nozh is that I usually assume that shaped charges are initiated correctly. That is to say, on the centre axis exactly in line with the 'point' of the liner and a bit behind the liner to get a uniform shock front going. This is not the case with Nozh. Both the 'primary' charge (the one being actually hit by the penetrator) and the secondary charges are initiated badly, but the primary moreso than the secondaries. The problem with this is that shaped charges are ridiculously sensitive to position of the initiation point. And I do mean ridiculously sensitive. A drifting jet will already be formed with an initiation point that is less than 0.01 CD off-center. And the further off-center it is, the higher the drift.

454a22bdd4.jpg

 

09b79eacd9.jpg

(Both pictures from "The influence of asymmetries in shaped charge performance", by Ayisit)

 

It gets even worse when you ramp up the eccentric initiation even further:

c10c3cb9d7.png

b5071c7390.jpg

(Both pictures from "Studies of Shaped Charges with Built-In Asymmetries. Part 11: Modelling" by Brown et al.)

 

As you can see there is quite the amount of drift present (and it's drifting away from an incoming penetrator). But this is still a shaped charge that is otherwise completely intact. So we'll look at damaged shaped charges as well. And oh boy.

 

So since the ERA is getting hit with a penetrator the ERA casing will get deformed and most likely damage nearby liner charges. Not only that, the detonating liner charges will most likely damage the liner charges next to it too. So lets see what happens when the explosive filler in a shaped charge is damaged:

cd8654e95d.png

0104d78679.jpg

(Pictures from "Effect of Fragment Impact on Shaped Charge Functioning" by Chanteret)

 

Not that exciting, it has the same effect as off-center initiation; the jet drifts.

 

But what happens when the explosive *and* liner are damaged?

901aaec4e0.png

1d1f01e5e8.jpg

(Pictures from "Effect of Fragment Impact on Shaped Charge Functioning" by Chanteret)

 

That a significantly worse jet, there's no coherent tip and there isn't really a slug being formed either. That's pretty bad. The most important part of the Nozh ERA (the tip) is basically non-existant. But it gets even worse when you introduce actually moving projectiles instead of just static damage:

0e2c409a78.jpg

(Pictures from "Effect of Fragment Impact on Shaped Charge Functioning" by Chanteret)

 

There's basically no jet and there's no coherent slug being formed. Effectively, this charge is close to useless. But lets look at a couple more results:

7e7290b41c.jpg

4426dc03c9.png

(Pictures from "Effect of Fragment Impact on Shaped Charge Functioning" by Chanteret)

 

This is what Chanteret himself has to say:

Quote

 

It appears that for the impacts that are located close to the liner region, the impacted charges have lost more than 70% of their penetration power as compared to the undamaged charge performance. For the firings where penetration depth was found to be larger than 40% of the nominal performance, it can be seen that they correspond to fragment trajectories which either do not cross the liner (negative or low x/L values) or which just touch the basis of the liner (large x/L).

 

 

So a proper shaped charge can have a penetration loss of more than 70%. This is significant considering these are proper HEAT charges, not EFPs like the ones used in Nozh. I'll get back to that later.

 

But all these things directly affect the shaped charge, what if we introduce obstructions in the liner cavity? In theory that means that a proper HEAT jet can't be formed, and in practice...:

 

02e546247b.jpg

 

50842c9bf5.png

(Pictures from "Investigation of Several Possibilities to Disturb the Jetting Process of 40 mm / 60° Charges" by Voumard et al.)

 

...it's exactly what happens.

 

 

Sadly I haven't been able to find a study which combined all these defects, but I guess we already know the results of those tests: "No jet, only dust".

 

 

Now apply all these things to an EFP (which the liner charges in Nozh are). They are hemispherical liners, which, unless you know what you're doing, have lower penetration than conical liners. They're also slower so they'll intercept the penetrator at a later point than conical liners. And they're drifting away from the penetrator because of off-center initiation. And they're most likely damaged liners so the jet formed will inherently be worse. And the jet formation will probably be obstructed, so the jet can't even form properly in the first place. And the formed jet has to penetrate a thick 'flyer' plate, so the tip velocity will be even lower. And then a slow, eroded and strongly perturbed copper jet will intercept a wolfram penetrator. Now, how was that supposed to cut a penetrator again?

 

 

 

...yeah I realise this became more of a rant about how ridiculously sensitive shaped charges themselves are and less about how bad Nozh is. And I didn't even talk about everything that influences the formation of a jet. What about grain size? What about cavities in the explosive filler? What about an explosive filler detached from the liner? What about a liner with an asymetric thickness? What about an explosive filler detached from the casing?

All of these things have a negative effect on the jet formation. As we already know HEAT warheads in rockets are worse than in ATGMs (afaik due to a cheaper manufacturing process), there is no way that the liner charges in Nozh are of high quality.

 

 

Nozh is bad.

 

 

You also know its bad when you look at this picture from a patent:

i5.gif

 

Now tell me, what's wrong with that drawing?

 

 

So why does Nozh 'work'?

 

Well, it's a relatively giant amount of explosives with a thick flyer plate. Soooo.... it's basically 'Heavy ERA'. REALLY REALLY HEAVY ERA.

 

 

Nozh just gets one giant fucking "...what?" from me.

 

 

 

....discuss away gentlemen, because I think @Collimatrix and I are the only ones that claim that Nozh doesn't fucking work.

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Could the idea have promise if you integrated it with a radar, and pre-detonated the charges before the penetrator got to them? And threw money at the shaped charge manufacturing quality control, of course

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6 minutes ago, Xlucine said:

Could the idea have promise if you integrated it with a radar, and pre-detonated the charges before the penetrator got to them? And threw money at the shaped charge manufacturing quality control, of course

I don't think so. Most of the problem stay.

 

You need to protect the shaped charges from low caliber fire, which means a protective plate. That plate will also protect the penetrator against the jets. But even with a protective plate the shaped charges are still very fragile. I really am not kidding about that:

af3d4b6668.jpg

 

So a hit from lets say a 40mm HE shell might knock the filler loose from the casing, which decreases the effectiveness of the shaped charge. Maybe not by much, but it will decrease it. It might also shift the initiate, which will also decrease effectiveness. So in the end you'll have a whole bunch of tiny degradations which can end up having a bigger effect on the effectiveness of the charge than you at first assumed.

 

But to properly do damage to a long rod penetrator in the first place, you need an angular shaped charge, not a circular*. Angular shaped charges offer more bang for your buck than circular shaped charges, but they're longer. Which is another problem. Shaped charges take up a fair amount of room to work properly. You can already see that in Nozh, which went el cheapo on the charges. The suckers are THICK. A proper linear charge would be even thicker. Which also means more explosives. You'll end up driving around with a thick (a few cm or so) explosive layer on your vehicle. And we don't even know the effectiveness of small shaped charges versus a long rod penetrator. Will it just yaw the penetrator? Will it cut the penetrator in pieces? Will that actually decrease penetration by enough, since we know segmented penetrators are a thing?

 

Yes, it will be more effective than Nozh, but the question is why? If you have radar, why not use it do initiate normal ERA? Normal ERA will be lighter and less explode-y than this. Probably more effective as well.

 

With a working penetrator cutting ERA you'd basically be this guy:

ssGlNjW.jpg

 

 

 

* You can make effective circular charges but it's tricky and expensive to do so.

 

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6 hours ago, SH_MM said:

 

i5.gif

 

Seems like 15 is a "fuze cable" located in the center of the module?

 

 

5 hours ago, LoooSeR said:

Yes, it is a special fuze cable to detonate all charges in one ERA module.

 

 

What about this?  If Nozh is initiated differently than other ERA, i.e. before it gets penetrated?

 

I would be curious to know exactly how this works.  Piezoelectric with explosive bridgewire detonators?  Also, I am curious why it's so prone to chain detonation.

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Since I'm not detecting a radar as part of the Nozh set, how exactly is it meant to work against shaped charges? Shaped charges detonate at a standoff distance, at which the Nozh is claimed, in the patent drawing, to be able to identify and fire off against the just formed jet before it impacts the plate. Doesn't seem like the man who wrote the patent even knew how the system itself was meant to work.

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16 minutes ago, Mighty_Zuk said:

Since I'm not detecting a radar as part of the Nozh set, how exactly is it meant to work against shaped charges? Shaped charges detonate at a standoff distance, at which the Nozh is claimed, in the patent drawing, to be able to identify and fire off against the just formed jet before it impacts the plate. Doesn't seem like the man who wrote the patent even knew how the system itself was meant to work.

 

The shaped charges in Nozh are buried deep under the... flyer plate, or cover plate thingie on top of it.  Conceivably you could have some sort of piezoelectric layer on top that sends a signal that triggers the shaped charges underneath.

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2 hours ago, Mighty_Zuk said:

Since I'm not detecting a radar as part of the Nozh set, how exactly is it meant to work against shaped charges? Shaped charges detonate at a standoff distance, at which the Nozh is claimed, in the patent drawing, to be able to identify and fire off against the just formed jet before it impacts the plate. Doesn't seem like the man who wrote the patent even knew how the system itself was meant to work.

Bingo, we have a winner!

 

2 hours ago, Collimatrix said:

The shaped charges in Nozh are buried deep under the... flyer plate, or cover plate thingie on top of it.  Conceivably you could have some sort of piezoelectric layer on top that sends a signal that triggers the shaped charges underneath.

But wouldn't basically any decently sized hit set Nozh off? I doubt the impact of a HEAT stand-off has more impact energy than whatever 30-40mm shell hitting it.

 

Don't get me wrong, autocannons setting off massed shaped charges would be absolutely hilarious.

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5 hours ago, LoooSeR said:

No, it is not. 

 

So... they just drew a fuse wire in the patent that doesn't actually exist in real Nozh tiles and/or the fuse wire doesn't do anything useful?

 

I am really getting the impression that Nozh is some sort of bizarre, ERA-based scam.

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1 hour ago, Collimatrix said:

 

So... they just drew a fuse wire in the patent that doesn't actually exist in real Nozh tiles and/or the fuse wire doesn't do anything useful?

 

I am really getting the impression that Nozh is some sort of bizarre, ERA-based scam.

Fuse wire or detonation cord is there to ensure that all indivial HEAT "knifes" will explode.

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On 2.10.2017 at 5:09 PM, Collimatrix said:

So... they just drew a fuse wire in the patent that doesn't actually exist in real Nozh tiles and/or the fuse wire doesn't do anything useful?

 

Once a linear shaped charge is penetrated by a projecitle, the fuse wire sets off all other LSCs. This is why I think there always be some LCS fused at ideal standoff distance:

j0T3Z7K.png

(i.e. red = not enough standoff, orange = too much standoff distance, green = ideal standoff distance).

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31 minutes ago, SH_MM said:

 

Once a linear shaped charge is penetrated by a projecitle, the fuse wire sets off all other LSCs. This is why I think there always be some LCS fused at ideal standoff distance:

j0T3Z7K.png

(i.e. red = not enough standoff, orange = too much standoff distance, green = ideal standoff distance).

The thing is that that illustration is literally impossible if a fuse wire sets the others off. The orange ones having a longer jet means that they were set off earlier than the red ones, which is physically impossible if the whole chain is initiated by the penetrator hitting the red ones. Disregarding the shaped charge getting fucked, the shaped charge getting hit by the penetrator always has the longest jet.

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https://zen.yandex.ru/media/id/5a53a86848c85ef3503c96cf/dinamicheskaia-zascita-noj-tanka-bm-bulat-5a53ab5e00b3dd9078274161?

scale_600

 

scale_600

The number 15 is showing the detonation cord/charge used to fuze all linear shaped charges. It is also visible in the cut-through Nozh module above.

 

scale_600

 

High-speed x-ray of a Nozh module interacting with a shaped charge jet.

 

 

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26 minutes ago, SH_MM said:

L8nDxj.gif

 

From a youtube video.

 

PS: Hitting the frontal section of the ERA tile = lower efficiency...

That's why they have multiple layers of it on the sides. So that even if you hit the frontal section of one, you won't do it on the second one. And on the turret they have 3 layers.

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3 hours ago, Mighty_Zuk said:

That's why they have multiple layers of it on the sides. So that even if you hit the frontal section of one, you won't do it on the second one. And on the turret they have 3 layers.

You confuse Nozh with Duplet. Duplet have 2 layers.

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3 hours ago, SH_MM said:

L8nDxj.gif

 

From a youtube video.

 

PS: Hitting the frontal section of the ERA tile = lower efficiency...

IIRC we covered this in ERA thread. And some other aspects of how Nozh work.

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3 hours ago, SH_MM said:

L8nDxj.gif

 

From a youtube video.

 

PS: Hitting the frontal section of the ERA tile = lower efficiency...

 

 

I do not think that this video is accurate.

 

For starters, I was under the impression that the nozh linear shaped charges live underneath a thick steel cover plate.  The linear shaped charges cutting up and projecting this plate is, as I understood it, the primary mechanism of nozh, not direct interaction of the linear shaped charges and the threat.

 

But more significantly, I don't think that shaped charge liners have enough momentum to carry away fragments of long rod penetrator the way this video shows.  120mm APFSDS rods are on the order of 5 kg and impacting at on the order of 1,500 M/S.  Each linear shaped charge is maybe 40mm across, and only about 25mm of the length of the linear jet is going to impact the LRP because the LRPs are only about 25mm in diameter.  The copper liner of each linear shaped charge is maybe 5mm thick.

 

So, per that video, we have five 25x40x5mm patches of copper impacting the front 2/3 of a 120mm LRP.  So that's about 225 grams of copper smacking about 3300 grams of tungsten.  And in the video the linear shaped charges are just batting that LRP aside like it's nothing, so the vector sum of the momentum of the LRP and the linear shaped charge has to be dominated by the momentum of the linear shaped charge.  But that LRP is moving forward at north of mach 4, and the portion of the LRP being hit by the linear shaped charge has an order of magnitude more mass!  Do you see where I am going with this?  The tips of conical shaped charge jets can move an order of magnitude faster than LRPs, but the average liner velocity is much less impressive.  Furthermore, a linear charge like this with a hemispherical liner cross-section isn't going to go anything like that fast.

 

There just isn't enough momentum for nozh to possibly work the way this video shows, unless of course the enemy helpfully shoots at Oplot BMs with aluminum darts that move slowly.

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18 hours ago, Collimatrix said:

 

 

I do not think that this video is accurate.

 

For starters, I was under the impression that the nozh linear shaped charges live underneath a thick steel cover plate.  The linear shaped charges cutting up and projecting this plate is, as I understood it, the primary mechanism of nozh, not direct interaction of the linear shaped charges and the threat.

 

But more significantly, I don't think that shaped charge liners have enough momentum to carry away fragments of long rod penetrator the way this video shows.  120mm APFSDS rods are on the order of 5 kg and impacting at on the order of 1,500 M/S.  Each linear shaped charge is maybe 40mm across, and only about 25mm of the length of the linear jet is going to impact the LRP because the LRPs are only about 25mm in diameter.  The copper liner of each linear shaped charge is maybe 5mm thick.

 

So, per that video, we have five 25x40x5mm patches of copper impacting the front 2/3 of a 120mm LRP.  So that's about 225 grams of copper smacking about 3300 grams of tungsten.  And in the video the linear shaped charges are just batting that LRP aside like it's nothing, so the vector sum of the momentum of the LRP and the linear shaped charge has to be dominated by the momentum of the linear shaped charge.  But that LRP is moving forward at north of mach 4, and the portion of the LRP being hit by the linear shaped charge has an order of magnitude more mass!  Do you see where I am going with this?  The tips of conical shaped charge jets can move an order of magnitude faster than LRPs, but the average liner velocity is much less impressive.  Furthermore, a linear charge like this with a hemispherical liner cross-section isn't going to go anything like that fast.

 

There just isn't enough momentum for nozh to possibly work the way this video shows, unless of course the enemy helpfully shoots at Oplot BMs with aluminum darts that move slowly.

Whether or not it actually pushes the rod (and consider the fact that the jet's velocity is several times higher than that of the rod), it cutting the rod is quite significant in itself. 

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On 27.09.2017 at 7:58 PM, Bronezhilet said:

So, if you're reading this I assume you know what Nozh is and how it's supposed to work. Just a quick tl;dr to refresh your minds: Nozh is supposed to work by cutting a penetrator with the use of multiple shaped charges, like this: 

 

 

So why does Nozh 'work'?

 

 

Nozh just gets one giant fucking "...what?" from me.

@Collimatrix

 

It's really simple - Knive is not czech EFA. It''s work on difrent principles.

 

http://dziennikzbrojny.pl/artykuly/art,5,23,8552,wojska-ladowe,wyposazenie,ukrainski-pancerz-reaktywny-noz-czesc-ii-noz-i-duplet

 

Effectivnes of the Knive ERA is based on foced fregmentation the thick frontplate of ERA casette. No magic there, no mysterious factors - only one or two linear SC in Knive module have optimum stand-off to damage (not even "cut") penetrator BUT - those linear SC will formed about 7 to 14 heavy mettal elements who where hit from under APFSDS. And thats the point - tip of rod placed IN armour, after tip - heavy damage by SC penetrator and after that - strike form "bottom" by sevral formed metal elements from thic k(at least 15mm) ERA  frontplate.

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On 9-1-2018 at 11:23 PM, SH_MM said:

scale_600

 

High-speed x-ray of a Nozh module interacting with a shaped charge jet.

 

 

What I don't like about this picture is that they only show one side of the armour, so you can't really determine when this photograph was taken. For all we know the jet has penetrated 50 cm of armour behind the module already. Or maybe it hasnt exited the back of the module. We simply don't know.

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22 hours ago, Bronezhilet said:

Why would you try to propel a plate with something that is designed to cut?

 

I mean, if the goal is to propel a plate at the highest velocity possible, just... make a normal ERA sandwich?

 

 

Again - nope :-)

 

The goal is to damage penetrator and brake it for as many parts as it's possible - that's the goal for ERA armour. 

 

Single heavy plate, or two or even 3 plates (Relikt) moving whit opposide direction and whit diffrent speed are one solution - very good known on west and able to overcome. I mean western long-rods whit jacked penetrators are higly resistant for flying one or two heavy plates. Of course not immune. What worse - special tip in penetrator is able to dismont ERA tiles whithout ignite it. What even worse - there are present segmented and jacked rods rods (DM53, DM63) able to evercome ERA in sevral ways. Bad news for calssic ER whit flying plates. 

And now we have Knive ERA when you have sevral DIFFRENT factors which are damaging long rods - firs is linear SC -one or two of them will have optimum stand-off and will be able to heavy damage Long-rod or even cut it in one place. Second factors are forced fragmantation of external ERA casette - sevral heavy fragments will hit penetrator after it will be damage by one or two linear SC and what even worse -after it tip will be in armour. So long-rod just MUST be broken in one or even sevral places. Bad news for long-rods...

 

 

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58 minutes ago, Militarysta said:

 

Again - nope :-)

 

The goal is to damage penetrator and brake it for as many parts as it's possible - that's the goal for ERA armour. 

 

Single heavy plate, or two or even 3 plates (Relikt) moving whit opposide direction and whit diffrent speed are one solution - very good known on west and able to overcome. I mean western long-rods whit jacked penetrators are higly resistant for flying one or two heavy plates. Of course not immune. What worse - special tip in penetrator is able to dismont ERA tiles whithout ignite it. What even worse - there are present segmented and jacked rods rods (DM53, DM63) able to evercome ERA in sevral ways. Bad news for calssic ER whot flying plates. 

And now we have Knive ERA when you have sevral DIFFRENT factors which are damaging long rods - firs is linear SC -one or two of them will have optimum stand-off and will be able to heavy damage Long-rod or even cut it in one plates. Second factors are forced fragmantation of external ERA casette - sevral heavy fragments will hit penetrator after it will be damage by one or two linear SC and what even worse -after it tip will be in armour. So long-rod just MUST be broken in one or even sevral places. Bad news for long-rods...

 

 

I have a few problems with this.

 

I was going to write a wall of text, but there's not that much data do go with so I might as well keep it short. One of the problems is that hemispherical liners are badly optimised for cutting, compared to conical liners. They severely lack jet tip velocity (for a 40 mm charge a hemispherical liner has about half the jet tip velocity of a conical liner) and most of the mass is in the wrong bit of the jet. Yes, a hemispherical liner is more effective at converting liner material into a jet (52% efficiency vs 28% for a conical liner), but that doesn't matter if all that mass is concentrated in a slow moving slug. Speaking of slow moving slugs, we don't (at least I don't) know if a copper jet is even capable of properly penetrating wolfram while flying at 5 km/s. The hydrodynamic velocity of wolfram vs steel is around 3 km/s, I have no idea what it is for copper vs steel. But I do know that in case of hydrodynamic penetration your efficiency will still be shit (67%). And I don't even know if a proper jet can be formed because there's a big steel plate in the way.

My prediction of a small hemispherical shaped charge versus a wolfram penetrator is that fuck-all will happen. Even that Mango round which is said to be from a Nozh test doesn't show any damage from shaped charges. It's either broken/shattered, or not. And with a ~575 mm long rod you'd at least suspect some damage due to shaped charges. But I'm not seeing any.

 

The effectiveness of a fragmented flyer plate is a little trickier to determine, since we have no idea how fast the plates are moving. Gurney equations can't be (easily) used because of the varying explosive layer thickness and the fact that the explosive isn't connected to the steel plate. All we know is that it's significantly lower than the theoretical max due to this. In any case, if you want to have a segmented flyer plate, why not make it like that in the first place? I'd recon you can make it significantly more effective at whatever it does compare to the current situation.

 

Anyway, Nozh is one of the other things I want to thoroughly test once I get my computing workstation.

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