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#21 Loopycrank

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Posted 16 March 2018 - 2053 PM

I am not so sure:

upaC2x8.jpg


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#22 DKTanker

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Posted 16 March 2018 - 2135 PM

105mm APDS


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#23 Loopycrank

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Posted 16 March 2018 - 2150 PM

Really?  Why are the impact tracks so skinny?


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#24 DKTanker

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Posted 16 March 2018 - 2159 PM

Really?  Why are the impact tracks so skinny?

Because the strike was so oblique.  That's a T-62 from the 73 war, the first time I saw a picture of that tank was during a briefing 35 years ago.


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#25 Interlinked

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Posted 16 March 2018 - 2202 PM

The lower the hardness and strength of the plate, the higher the critical ricochet angle will be. Cast armour would be less optimal than rolled high hardness plate, of course. Still, impact no.1 is a clear ricochet and impact no.2 is also a ricochet although the armour failed, so it's a partial ricochet. When impacting at such a high angle, it is not the tip of the rod that penetrates the target but the tail. Ricocheting only occurs for the parts of the rod that contact the armour plate, and the first to contact the plate is always the tip. The rest of the rod follows the tip and slides on the plate to gain vertical acceleration. The sliding of the rod on the surface of the plate creates a shallow crater and the relative slope of the crater is continually reduced as the plate is eroded so the tail of the rod usually slides on a thinner and less angled piece of armour compared to the tip. Softer and weaker plates will be easier to erode by sliding, so easier to defeat. Here's a nice simulation of 3BM48 "Svinets" hitting and defeating the 50mm upper hull plate of the Abrams.

https://youtu.be/ok_Z8fddJ4g

Edited by Interlinked, 16 March 2018 - 2207 PM.

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#26 Interlinked

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Posted 16 March 2018 - 2213 PM

Yes, and a slight hull down position will largely or fully obscure any surface at that angle, or push it well beyond the critical angle for deflection.

For sub-critical sloping, the efficiency falls for a monolithic plate, but the rod passing the plate may be degraded by yaw, such that the ME of the array may be increased by sloping the outside plate.


Yes, that's right. I'm currently doing some research in this direction to find out how the 68 degree slope of the T-64/72/80 armour affects its performance against long rods. I believe the spaced hull armour of the T-72B relies quite heavily on this mechanism to gain a relatively high ME and TE at the same time. If you have relevant information about that, I'd love to hear it.
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#27 KV7

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Posted 17 March 2018 - 0059 AM

IIRC Abrams glacis is 80mm thick.


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#28 KV7

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Posted 17 March 2018 - 0253 AM

 

Yes, and a slight hull down position will largely or fully obscure any surface at that angle, or push it well beyond the critical angle for deflection.

For sub-critical sloping, the efficiency falls for a monolithic plate, but the rod passing the plate may be degraded by yaw, such that the ME of the array may be increased by sloping the outside plate.


Yes, that's right. I'm currently doing some research in this direction to find out how the 68 degree slope of the T-64/72/80 armour affects its performance against long rods. I believe the spaced hull armour of the T-72B relies quite heavily on this mechanism to gain a relatively high ME and TE at the same time. If you have relevant information about that, I'd love to hear it.

 

There is a lengthy discussion of this issue in that huge blogpost about the T-72, I don't remember where it is though.

Edit - here it is (actually it now seems shorter than I remember and lacking some details) : https://thesovietarm...indication.html


Edited by KV7, 17 March 2018 - 0431 AM.

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#29 methos

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Posted 17 March 2018 - 0543 AM

IIRC Abrams glacis is 80mm thick.

 

1.5 inches (38.1 mm) according to US documents.

 

ABUjwK2.jpg

 

Height of the 50 percentile male head is 22.8 cm (228 mm).


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#30 KV7

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Posted 17 March 2018 - 0632 AM

Thanks, I might have got it confused with the angle. But 38 mm @ 80 deg is only 220 mm LOS though, I thought it was much more. Not disagreeing, it just seems surprising.


Edited by KV7, 17 March 2018 - 0632 AM.

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#31 methos

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Posted 17 March 2018 - 0711 AM

The thickness of the highly sloped part of the Leopard 2's glacis is also only 40 mm. More thickness at the line of sight was not necessary, because early APFSDS and HEAT ammunition was really bad against highly sloped steel plates. An Israeli study came to the conclusion, that a steel plate sloped at 75° provides twice as much protection against (1980s) APFSDS ammunition, due to the fact that the penetrator will break and partly bounce off. Therefore a highly sloped steel plate with a thickness of ~220 mm along the line of sight can resist APFSDS ammo with more than 440 mm penetration into steel armor.

 

However more modern APFSDS should suffer from less reduction in penetration power against highly sloped steel plates due to the more modern tip construction. This is one of the reasons why the upper glacis plate of the upgraded Leopard 2 is reinforced with a layer of composite armor.


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#32 KV7

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Posted 17 March 2018 - 0723 AM

I think another potential problem is that even slightly plunging fire is going to be a real problem if you are relying on a high slope to deflect the shot.


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#33 GARGEAN

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Posted 17 March 2018 - 0743 AM

I think another potential problem is that even slightly plunging fire is going to be a real problem if you are relying on a high slope to deflect the shot.

Plus threats different from tank cannon fire, like top-attack EFP... May look at comparison of top protection of M1 compared with T-series. Highly angled steel plate is really compromise decision.
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#34 KV7

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Posted 17 March 2018 - 0755 AM

 

I think another potential problem is that even slightly plunging fire is going to be a real problem if you are relying on a high slope to deflect the shot.

Plus threats different from tank cannon fire, like top-attack EFP... May look at comparison of top protection of M1 compared with T-series. Highly angled steel plate is really compromise decision.

 

Plunging fire from 122mm HE or larger will go through as well I think.
 


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#35 Interlinked

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Posted 17 March 2018 - 0800 AM

Thanks, I might have got it confused with the angle. But 38 mm @ 80 deg is only 220 mm LOS though, I thought it was much more. Not disagreeing, it just seems surprising.


I can't say I'm surprised. The original requirement was for the high angle to defeat HEAT rounds by preventing it from fuzing on the plate. Nothing was mentioned about APFSDS. If I were to guess, they only cared enough about 115mm APFSDS so that there weren't any obvious gaps in the frontal profile and didn't bother about 125mm APFSDS at all.
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#36 GARGEAN

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Posted 17 March 2018 - 0804 AM


 

I think another potential problem is that even slightly plunging fire is going to be a real problem if you are relying on a high slope to deflect the shot.

Plus threats different from tank cannon fire, like top-attack EFP... May look at comparison of top protection of M1 compared with T-series. Highly angled steel plate is really compromise decision.
 
Plunging fire from 122mm HE or larger will go through as well I think.
 
Well, those would wreck most tanks anyway, difference wound be only between FU and FUBAR.
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#37 Interlinked

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Posted 17 March 2018 - 0924 AM

There is a lengthy discussion of this issue in that huge blogpost about the T-72, I don't remember where it is though.

Edit - here it is (actually it now seems shorter than I remember and lacking some details) : https://thesovietarm...indication.html

Yeah I'm trying to streamline the article, add more information and remove some outdated stuff. There's more info now that the article is split into two parts.

Edited by Interlinked, 17 March 2018 - 2235 PM.

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#38 Loopycrank

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Posted 17 March 2018 - 1445 PM

 

Really?  Why are the impact tracks so skinny?

Because the strike was so oblique.  That's a T-62 from the 73 war, the first time I saw a picture of that tank was during a briefing 35 years ago.

 

 

Thank you for explaining this.


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#39 KV7

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Posted 17 March 2018 - 2251 PM

 

 

 

I think another potential problem is that even slightly plunging fire is going to be a real problem if you are relying on a high slope to deflect the shot.

Plus threats different from tank cannon fire, like top-attack EFP... May look at comparison of top protection of M1 compared with T-series. Highly angled steel plate is really compromise decision.
 
Plunging fire from 122mm HE or larger will go through as well I think.
 
Well, those would wreck most tanks anyway, difference wound be only between FU and FUBAR.

 

Do we have good estimates available for penetration of various impact fused HE rounds ?


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#40 GARGEAN

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Posted 18 March 2018 - 0416 AM


 

 

 

I think another potential problem is that even slightly plunging fire is going to be a real problem if you are relying on a high slope to deflect the shot.

Plus threats different from tank cannon fire, like top-attack EFP... May look at comparison of top protection of M1 compared with T-series. Highly angled steel plate is really compromise decision.
 
Plunging fire from 122mm HE or larger will go through as well I think.
 
Well, those would wreck most tanks anyway, difference wound be only between FU and FUBAR.
 
Do we have good estimates available for penetration of various impact fused HE rounds ?
Well, just out of my mind - 122mm could wreck 60mm plate(like IS-2 did with Panther turret side). That's not taking into account weld lines and whole set of outer equipment like sights.
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