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Entac Missile Penetration


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#1 Nikolas93TS

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Posted 21 June 2017 - 0823 AM

I am analysing penetration power of early first generation ATGMs. For example, the vast majority of sources quote penetration of ENTAC as 600-620mm steel, which is obviously too much for the 130mm warhead of the era.

 

I am guessing that number comes from figures for the mild steel since few times I saw HEAT rounds requirement from the 1950s and 1960s having both mild and RHA steel listed. For example, 152mm M409 HEAT was requested to penetrate 500mm of mild steel and 425mm of steel armour. When static tests were performed (no rotation and stand-off distance) between 575mm and 600mm of mild steel were penetrated (490mm to 510mm steel armour equivalent assuming 0.85 coefficient from the requirement) while 10-inch stand-off requirement at all spin-rates was 470mm mild steel (400mm steel armour). The actual test gave 547mm as highest mild steel penetration at 90 RPM, and 425mm to 454mm mild steel at 105 RPM.

 

Is there any rule of thumb to convert mild steel thickness to RHA equivalent, in particular, when hit by HEAT? Because similar high penetrations are encountered for other missiles as well, like SS.11, Vigilant etc.



#2 Nikolas93TS

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Posted 21 June 2017 - 0830 AM

There is also a case of early TOW being reported as 600mm, but actual penetration is closer to 430mm. ENTAC being at ~400mm sound more in line with contemporary missiles.



#3 GARGEAN

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Posted 22 June 2017 - 0108 AM

How much forward your research goes? I am interested in HOT missile, which have obviously too high number for it in most sources.

#4 Nikolas93TS

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Posted 22 June 2017 - 0732 AM

Anything from Cold War, really. 

 

65870_65572425_entac.jpg

Here is an ENTAC warhead, looks like the very basic copper liner.



#5 bojan

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Posted 22 June 2017 - 1531 PM

Rule of thumb -if it does not have wave-shaper it will not much over 400-450mm, no matter diameter. Initial TOW lacks it, and so does SS-10/11, Entac etc. Hence all should be about 400mm give it or take it.


Edited by bojan, 22 June 2017 - 1531 PM.


#6 TTK Ciar

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Posted 22 June 2017 - 1827 PM

"Journal of Battlefield Technology" Vol 1-1 published this penetration chart for non-precision HEAT:

http://www.ciar.org/....google.com.txt

Otherwise, the rule of thumb for relative resistance to hypervelocity penetration of different steels is the ratio of the square roots of their Brinell hardness ratings.

So to compare mild steel (170BHN) against RHA (varies, but call it 350BHN):
sqrt(170)/sqrt(350) = 0.7 mild steel thickness efficiency relative to RHA.

This isn't a great rule of thumb, but it's at least simple. The devil is in the details, and there are thousands of published studies about those details.

#7 bojan

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Posted 22 June 2017 - 1920 PM

While non-precision HEAT in theory will penetrate about 4 CD it goes up the some caliber that is about 100-110mm. After that penetration will be less in CDs, even if it will grow in mm of RHA up the some point. Something to do with jet fracturing in the process of being made due the too much mass of liner not being shaped efficiently w/o wave shaper.

IIRC, for 600mm penetration you would need about 200mm diameter shaped charge vs 150mm theoretical if you take 4CDs as a rule.

 

Once you add wave shaper you can go up the 4.5CD with non-precision charges and up the 140-150mm effective diameter where penetration in CDs starts dropping again.

 

And this is only the beginning, there is a factor if copper was rolled or stamped, if it was rolled was it rolled both sides or just one, was it rolled only clockwise (or counterclockwise) vs rolled in both directions, was it annealed or not etc, etc, Most of this was not known until '70s.


Edited by bojan, 22 June 2017 - 1927 PM.


#8 Nikolas93TS

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Posted 25 June 2017 - 1057 AM

How much forward your research goes? I am interested in HOT missile, which have obviously too high number for it in most sources.

 

I found this cut of the 130mm warhead, but details are not very clear.

 

93c3b1003edc88adc1dbcc448a674c18.jpg

 

It has "flow-formed electrolytic copper liner" and claimed penetration of 800mm, while F2 model 152mm warhead is claimed as 1200mm, but I was not able to find a cut. F3 is a tandem with the same 1200mm claimed penetration.


Edited by Nikolas93TS, 28 June 2017 - 1328 PM.


#9 Nikolas93TS

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Posted 25 June 2017 - 1103 AM

Also, many thanks, to TTK Ciar and Bojan, very helpful. 



#10 Nikolas93TS

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Posted 25 June 2017 - 1129 AM

sAtEajf.jpg

 

I tried to improve it slightly.



#11 bojan

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Posted 25 June 2017 - 1944 PM

Looks like it has wave shaper. For late 1970s tech, with wave shaper 800mm might be doable, but not with this little standoff - about 3 CDs. At that standoff it is about 5.3-5.4 CDs, or about 700mm.



#12 Nikolas93TS

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Posted 28 June 2017 - 1323 PM

Yeah, adding a probe to increase standoff is what they did with F2 model, together with increased warhead diameter.

 

hot2-2-b.jpg

 

And it claimed to penetrate anything from 900mm to 1100-1200mm, depending on the source. Former is no doubt feasible (even if warhead was left unaltered), later would require 7.2-7.8 CDs penetration. 


Edited by Nikolas93TS, 28 June 2017 - 1342 PM.


#13 TOW-2

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Posted 03 July 2017 - 0106 AM

Something very relevant to this came up, I think Bojan and I were talking a bit about the MGM51 Shillelagh vs. 1st generation TOW and how damn close they were in penetration values.  MGM51 was like 400mm, and TOW-1 was ~430.  It struck me odd that they would have such similar penetration values.

 

(And I apologize, Bojan, if it wasn't you with whom I was discussing this.)



#14 Nikolas93TS

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Posted 03 July 2017 - 0447 AM

I tend to consider them even closer in penetration performance.

During the Anti-tank CM-CCM conference on December 18, 1968 in Redstone Arsenal, Alabama, it was stated that the Shillelagh warhead is capable and has demonstrated an ability to penetrate 17 inches of armor (430mm) at 0° obliquity. The House Armed Services Committee (HASC) on September 25, 1969 also pointed out that the range, accuracy, and lethality of the TOW and Shillelagh were virtually identical, but that TOW was twice as expensive. According to declassified CIA study, the BGM-71A had an ability to penetrate 430mm (16.9 inches) of RHA, which sounds in line with above mentioned reports.

I think often quoted figure of missile penetrating 18.25 inches of mild steel (equivalent to 15.5 inches of RHA, or 394mm) seems to come from comparative test performed in June 1967 for XM131 Hornet anti-tank missile warhead study. However, actual penetration value should be very likely slightly higher as one of the test criteria was standoff distance of 17 inches.

Edited by Nikolas93TS, 03 July 2017 - 0449 AM.


#15 GARGEAN

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Posted 03 July 2017 - 0453 AM

I tend to consider them even closer in penetration performance.

During the Anti-tank CM-CCM conference on December 18, 1968 in Redstone Arsenal, Alabama, it was stated that the Shillelagh warhead is capable and has demonstrated an ability to penetrate 17 inches of armor (430mm) at 0° obliquity. The House Armed Services Committee (HASC) on September 25, 1969 also pointed out that the range, accuracy, and lethality of the TOW and Shillelagh were virtually identical, but that TOW was twice as expensive. According to declassified CIA study, the BGM-71A had an ability to penetrate 430mm (16.9 inches) of RHA, which sounds in line with above mentioned reports.

I think often quoted figure of missile penetrating 18.25 inches of mild steel (equivalent to 15.5 inches of RHA, or 394mm) seems to come from comparative test performed in June 1967 for XM131 Hornet anti-tank missile warhead study. However, actual penetration value should be very likely slightly higher as one of the test criteria was standoff distance of 17 inches.

Wow. Why TOW would be such expensive when compared with Shillelagh? Simpler guidance, not so harsh weight and dimensional requirements...
And did they considered huge deadzone of Shillelagh as drawback in that study?

#16 Nikolas93TS

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Posted 03 July 2017 - 0724 AM

I doubt.

 

They were initially envisaged for two different roles: TOW for infantry (HAW) role and Shillelagh for combat vehicle weapon system (CVWS) role. Already in 1962, it was proposed that whatever design was more successful, and could be adapted for both roles, it should be pursued alone. However in August 1962, MICOM advised that conclusive evidence of the feasibility of using TOW in the CVWS role (due to the issue of pulling wire from a closed breech tube) would not be available before December 1962, whereas the decision regarding the system(s) to be developed for the CVWS and HAW roles was scheduled for mid-October or earlier.

 

Although the TOW and Shillelagh very likely could be developed in a version which would be usable in both the HAW and CVWS applications, the selection of either one to fulfill both roles would mean the acceptance of less than the best system for one role or the other. This stemmed from the fact that the Shillelagh and TOW had specific limitations which were intrinsic to their respective concepts. The consequences of Shillelagh limitations were more pronounced in the HAW application and the consequences of the TOW limitations were more pronounced in the CVWS application. Moreover, there was some doubt that the economic and logistic advantages would offset the performance penalties inherent in such a system. For these and other reasons, Balistic Reserch Laboratory favored the development of both systems, and this was corrobated by Hudges Aircraft study too. Seven years later, however, the TOW/Shillelagh competition again surfaced and very nearly caused the cancellation of the TOW program.

 

In the fall of 1969, MICOM learned that higher headquarters were again giving consideration to replacing the TOW with the Shillelagh system. The Department of the Army first reduced the budget for 1970 because of delays (although by that point the system was maturing and reaching requested set requirements). Then the above mentioned House Armed Services Committee cancelled the entire program from the FY 1970 budget on 25 September 1969. The committee suggested that the guidance and control elements of the Shillelagh could be repackaged so that Shillelagh could replace the more expensive TOW in its ground role. DDRE also concluded that this adaptation might present potential cost savings to the Government.

 

Secretary of the Army wrote to Congress and argued that, in full production, the cost of TOW would be about equal to the Shillelagh and that converting the latter to the ground role would be expensive in terms of time and money. Given the urgency of HAW requirement, and expected three to four-year delay if Shillelagh was to be converted, Congress eventually restored the TOW program in November 1969, although one of the congressmen defined the TOW a "billion-dollar boo-boo" and a "wasteful duplication" of the Shillelagh missile which was already in production. Congress opposition versus Army support for TOW continued into 1970, extending debate into what missile should be used in helicopter role, being eventually subdued in 1971 when TOW proved to be a cheaper solution and excellent weapon in service.


Edited by Nikolas93TS, 03 July 2017 - 0727 AM.


#17 GARGEAN

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Posted 03 July 2017 - 0749 AM

And what's with famous reliability problems of Shillelagh? Was TOW suffering comparable ones in its early days or they was again not looked at in studies?

#18 TOW-2

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Posted 05 July 2017 - 1910 PM

I think the MGM51's issues came not from the basic design and sighting of the missile itself.  This is just pure speculation on my part but if I may, had the MGM51 been used in a tripod mount on a light vehicle (Jeep, 3/4-ton truck) or on the ground, it likely would have fared in performance more or less the same as TOW-1.  Perhaps it would have done as well as a helicopter mounted weapon like the SS-11 Nord or (again) TOW-1.

 

However, the missile and its guidance/sight systems were subjected to constant shock from firing the huge 152mm gun in the M551 Sheridan and probably ill treatment due to the operational conditions on the ground in Vietnam.

 

Had the MGM51 been a stopgap between light systems like LAWs and recoil-less rifles and "heavy" ATGMs like TOW-1, rather than being fired from a tank gun, maybe it would've fared better?

Pure speculating on my behalf.



#19 JohnAbrams21

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Posted 05 July 2017 - 2137 PM

However, the missile and its guidance/sight systems were subjected to constant shock from firing the huge 152mm gun in the M551 Sheridan and probably ill treatment due to the operational conditions on the ground in Vietnam.


I thought the Shilleagah was never used/tested in the Vietnam war? I've never seen any sources or references to its usage there.

#20 TOW-2

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Posted 06 July 2017 - 0736 AM

 

However, the missile and its guidance/sight systems were subjected to constant shock from firing the huge 152mm gun in the M551 Sheridan and probably ill treatment due to the operational conditions on the ground in Vietnam.


I thought the Shilleagah was never used/tested in the Vietnam war? I've never seen any sources or references to its usage there.

 

 

I had one of those coffee-table books that talked about it (in fact I probably still have it).  I will see if I can find the exact info and quote it back here.






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