KwK 43 L/71 tank gun

[Mobius]

Thanks Mobius. 

 

I don't remember this bit when you were hammering thru the redo of the programs -- did you play with Nathan's original slope effects algorithm.  Or; Better yet did you pin down where it was in the original code.  Seems like I plodded thru his code at one point but missed where the program details slopes effects.

 

Best Regards

Jeff

392090[/snapback]

My focus was on getting something to tell me the penetration of deck and vertical ship armor at various ranges. But I did incorporate his M79APCLC for the deck armor tables.

For the test I mentioned I used the US WWII B class armor and the Horizontal impact to find this. Using 15cm or the 8" shell and choosing "other". Then input shell size as 3.465" and input weight. The total weight has to be slighty more than the body weight or the program thinks there is no AP cap.

 

I've mostly used that section just to check the NAAB results match his program.

Edited November 14, 2006 by Mobius

[Gille]

Thanks very much for posting that Jeff, I don't understand it yet but its given me a lot to think about.

 

One question - in the final graph where you put slope multiplier on the vertical axis, is that slope multiplier calculated as:

 

limit velocity at X degrees obliquity/limit velocity at zero obliquity

 

or as:

 

effective armor thickness at X degrees obliquity/armor thickness at zero obliquity?

 

 

By effective armor thickness at X degree obliquity I mean the equivalent thickness at zero obliquity that would resist impacts as well as the plate sloped at X degrees from vertical.

 

If the graph is the former (ratio of limit velocities) then would the graph have a different shape if it were the ratio of effective thicknesses? How does a change in limit velocity relate to a change in effective thickness?

 

My untutored understanding is that penetration is related to kinetic energy so wouldnt an increase in impact velocity produce a squared increase in penetration capability? That is, if the limit velocity for a particular plate against a certain projectile was say 700m/s, then if the limit velocity of the same projectile against another plate of identical manufacture was say 800m/s, would it imply that the second plate was about:

 

(800/700)^2 = 1.306 times as thick as the first plate?

 

The reason I ask is that I am interested in the armoured warfare side of ballistics rather than naval ballistics and I'm more familiar with penetration capability in terms of mm at various ranges and slope multiplying armor thicknesses than limit velocities.

Edited November 16, 2006 by Gille

[jwduquette1]

Thanks very much for posting that Jeff, I don't understand it yet but its given me a lot to think about.

 

One question - in the final graph where you put slope multiplier on the vertical axis, is that slope multiplier calculated as:

 

limit velocity at X degrees obliquity/limit velocity at zero obliquity

 

or as:

 

effective armor thickness at X degrees obliquity/armor thickness at zero obliquity?

By effective armor thickness at X degree obliquity I mean the equivalent thickness at zero obliquity that would resist impacts as well as the plate sloped at X degrees from vertical.

 

If the graph is the former (ratio of limit velocities) then would the graph have a different shape if it were the ratio of effective thicknesses?  How does a change in limit velocity relate to a change in effective thickness?

 

My untutored understanding is that penetration is related to kinetic energy so wouldnt an increase in impact velocity produce a squared increase in penetration capability?  That is, if the limit velocity for a particular plate against a certain projectile was say 700m/s, then if the limit velocity of the same projectile against another plate of identical manufacture was say 800m/s, would it imply that the second plate was about:

 

(800/700)^2 = 1.306 times as thick as the first plate?

 

The reason I ask is that I am interested in the armoured warfare side of ballistics rather than naval ballistics and I'm more familiar with penetration capability in terms of mm at various ranges and slope multiplying armor thicknesses than limit velocities.

393186[/snapback]

 

Hi Gille:

 

Makes no difference if we are talking about Naval Armor penetration of Army Armor penetration. It's all just armor steel -- RHA or FHA. As you go back further and further in time you realize that most of the empirical relationships for armor penetration of full caliber projectiles have their roots in various Navies and their ballistic testing of armor & projectiles.

 

Wargamers typically like to think in terms of mm's of armor at some particular range. However ballistic testing is typically conducted in terms of either a limit velocity; or a limit obliquity for a specific velocity. Both Armies testing their tank armor and Navies testing their ship armor typically did things in terms of Limit velocities -- not range and mm's of armor. The limit velocities were than converted to ranges and thicknesses. The latter is perhaps simpler in some respects to get a handle on. Sort of like a "limit thickness" rather than a limit velocity. But again, it makes no real difference how you wish to look at it. Limit Velocity for a specific projectile is simply being translated into a range. You know -- projectile drag – how much remaining velocity does a projectile have at such and such a range.

 

The second graph you were asking about -- and as I indicated in the example calculation in my previous post -- represents a ratio of limit velocities, not "limit thickness". It is limit velocity at the Obliquity of interest divided by the limit velocity of the same projectile at zero degrees. But you can get to “limit thickness†using the same figure as the slope effect ratio is pretty much the same – depending on how you look at the problem.

 

For example: The projectile I had been considering was a 25kg 122mm AP round. This just happened to be what was plugged into my spreadsheet at the time. So I started farting around with it to generate the various graphs I posted above. I’ll stick with it, as that’s what all my other graphs are based upon.

 

The limit velocity of this projectile using the 1931 USN EQ, at obliquity =0-degrees, and t/d = 1.5 works out to be: 2197-fps. (We can make this into a “limit thickness†for a specific range by seeing what range for this projectile correspond to a remaining velocity of 2197-fps – but this is going off track). Now the same projectile using t/d=1.5 and an obliquity = 50-degrees has a limit velocity of 4442-fps. Slope effect is therefore about 2 based upon limit velocities – 4442/2197 = 2. This corresponds to what I have shown in that second graph.

 

What to do for slope effect based upon “limit thickness� Lets hold constant the 0-degrees obliquity, t/d=1.5, and limit velocity of 2197-fps. Limit thickness = 1.5 x 122mm = 183mm (7.2-inches).

 

We than need to back-calculate what equivalent plate thickness is required at 50-degrees that will result in the same limit velocity of 2197-fps. Pretty simple exercise – the results predicted by the 1931 USN Equation is about 3.58-inches (90.9mm) @ 50-degrees. The slope effect based upon “limit thickness†is therefore:

 

183/90.9 = 2

 

But what are the t/d values?

Well for the 0-degree calculation we already know that the t/d is 183mm/122mm = 1.5

However the t/d at 50-degrees is 90.9mm/122mm = 0.75

 

Let’s do it another way. Lets start from 50-degrees and t/d=1.5. Plate thickness is 1.5 x 122 = 183mm (7.2â€). The limit velocity for 183mm at 50-degrees is 4442-fps. Now how much armor at 0-degree obliquity results in the same limit velocity? Turns out to be about 15.33-inches (389.4mm). Slope effect based upon this approach to finding comparable “limit thickness†is than:

 

Slope Effect = 389.4/183 = 2.13

What are the t/d values?

For the 50-degree calculation we already know that the t/d is 183mm/122mm = 1.5

However the t/d at 0-degrees is 389.4mm/122mm = 3.19.

 

I mean this is pretty subtle and perhaps splitting hairs, but it always made more sense to me to directly compare limit velocities at the same t/d ratio rather than working with “limit thicknessâ€. But you get to the same ballpark regardless off which route you like taking.

 

Best Regards

JD

Edited November 16, 2006 by jwduquette1

[jwduquette1]

My focus was on getting something to tell me the penetration of deck and vertical ship armor at various ranges.    But I did incorporate his M79APCLC for the deck armor tables. 

For the test I mentioned I used the US WWII B class armor and the Horizontal impact to find this.   Using 15cm or the 8" shell and choosing "other".  Then input shell size as 3.465" and input weight.  The total weight has to be slighty more than the body weight or the program thinks there is no AP cap.

 

I've mostly used that section just to check the NAAB results match his program.

392091[/snapback]

 

Thnx. My interest was in recreating penetration values for M79 AP vs. RHA using your version of M79APCLC rather than plodding thru Okun's old DOS based thingie again. That's why I was interested in weather you tweaked his slope effects or not. Moreover, compare his output for M79 AP to actual ballistic trial data I have for M79 AP at various slopes to determine the contrast in slope effects. This -- as I recall -- was what I had asked Okun about sometime ago as the actual slope effects of the projectile didn’t match well with his predicted slope effects. Or that’s the way I remember it -- like I say this was a couple years ago, so I could be remembering this wrong.

Edited November 16, 2006 by jwduquette1

[jwduquette1]

My focus was on getting something to tell me the penetration of deck and vertical ship armor at various ranges.    But I did incorporate his M79APCLC for the deck armor tables. 

For the test I mentioned I used the US WWII B class armor and the Horizontal impact to find this. Using 15cm or the 8" shell and choosing "other".  Then input shell size as 3.465" and input weight.  The total weight has to be slighty more than the body weight or the program thinks there is no AP cap.

 

I've mostly used that section just to check the NAAB results match his program.

392091[/snapback]

 

 

Hey Steve:

 

Ok – I ran through the numbers again, and this is what I came up with. The first figure is actual ballistic test data generated at the BRL using 2.5†RHA armor at varying hardness levels and varying obliquity. The data points are from actual test results. Everything in terms of Complete Through Penetration criteria – Naval Ballistic Limit – BL(N). On the other hand, the solid lines represent predicted penetration from a post-WWII BRL empirically based equation. Note that the BRL Empirical is keyed to what the Army perceived to be optimal plate hardness values. These were the hardness levels that RHA armor of the period were produced at for 2.5-inch thick plate. Moreover, Army specifications of the period were for 2.5-inch thick RHA plates to be produced at hardness levels between about 240 to 270BHN.

 

 

The next figure represents the same BRL test data for spec armor hardness levels as well as the BRL Equation Predicted values – again BL(N). The yellow curve is the Naval Limit velocity BL(N) as predicted by N.Okun’s DOS program “M79APCLCâ€. As you can see there is a fair bit of contrast in slope effects between Okun’s predicted, the BRL predicted values, and the actual BRL test results.

 

 

Regards

JD

[Mobius]

Jeff, I used the program for 3" APC and get something different

 

Deg-------NBL

0°..........1531

30..........1635

40..........1760

45..........1916

50..........2288

60..........3854

Edited November 18, 2006 by Mobius

[jwduquette1]

Jeff, I used the program for 3" APC and get something different

 

Deg-------NBL

0°..........1531

30..........1635

40..........1760

45..........1916

50..........2288

60..........3854

394073[/snapback]

 

Hey Steve:

 

I didn’t look at 3" M62 APC with this analysis -- just 3" M79 AP. As I recall from some of Lorrin's in-depths, APC was supposed to be less efficient than AP in RHA shoots. APCs' function was to overcome FHA -- the penetration cap was supposed to keep the nose from breaking or shattering on cemented armor. I reckon that's why the US Army sort of lost interest in APC after WWII and started going with APBC -- ala 90mm T33. Moreover tanks were typically being armored with RHA or cast armor by the tail end of WWII and post-WWII.

 

I also have a fair amount of BRL testing data for M62 APC -- lemme have a look at this and post some of the ballistic test data tomorrow. However I don't think Okun's M79 program distinguishes between capped and uncapped projectile perforation. Or maybe I am using a very old version of M79?

 

Best Regards

Jeff

Edited November 18, 2006 by jwduquette1

[jwduquette1]

Jeff, I used the program for 3" APC and get something different

 

Deg-------NBL

0°..........1531

30..........1635

40..........1760

45..........1916

50..........2288

60..........3854

394073[/snapback]

 

Sorry couple more questions -- trying to back-calc your results from NAaB1.0 rather than using M79APCLC. What did you use for input parameters.

 

Projectile Weight of M79 AP is 15-lbs

Projectile Weight of M62 APC (including cap) is 15.4-lbs

I think the Navies 3" Mk29 APC was lighter than M79 and M62 -- but I would need to double check this.

 

Deck Armor Screen -- did you use Avg. US WWII era Class-B; or STS?

Projectile Screen -- did you use Avg-post-1935 A.C.D. APC Shot; or did you use 3" Mk 29-1 APC?

[Mobius]

Sorry couple more questions -- trying to back-calc your results from NAaB1.0 rather than using M79APCLC.  What did you use for input parameters.

 

Projectile Weight of M79 AP is 15-lbs

Projectile Weight of M62 APC (including cap) is 15.4-lbs

I think the Navies 3" Mk29 APC was lighter than M79 and M62 -- but I would need to double check this.

 

Deck Armor Screen -- did you use Avg. US WWII era Class-B; or STS?

Projectile Screen -- did you use Avg-post-1935 A.C.D. APC Shot; or did you use 3" Mk 29-1 APC?

394092[/snapback]

I just used the default shell weight which I is 12.8lbs. Class B WW2 armor.

I think the different APCs seem to work about the same. It seems to be just mass size and velocity are taken in account in M79APCLC and not so much the cap factors which I think pertain more to facehard.

[jwduquette1]

I just used the default shell weight which I is 12.8lbs.  Class B WW2 armor.

I think the different APCs seem to work about the same.  It seems to be just mass size and velocity are taken in account in M79APCLC and not so much the cap factors which I think pertain more to facehard.

394195[/snapback]

 

Hey Steve:

 

12.8-lbs is about the weight of 3" Mk 29-1 APC. I actually have one of these things sitting on my shelf. This would presumably explain at least some, if not all of the contrast between yours and my calcs. Moreover M79 AP is over two pounds heavier and M79 is uncapped. It therefore makes sense that M29-1 is penetrating less armor than M79.

 

3" Mk 29-1 is actually even different from 3" M62 APC. M62 being heavier -- 15.4-lbs. The penetrator on Mk29-1 is much shorter -- more compact I guess than M62. But it wasn't as efficient as M62.

 

I ran the numbers in NAaB1.0 using two other possible projectile input screens (see attached image). These seemed -- at least from their descriptions -- to be better analogs for 3" M79 AP. Although curiously the results were identical for the resultant Naval Ballistic Limits. The upper most screen capture seemed like the most appropriate comparison to 3" M79 -- i.e. 3" A/N uncapped Steel AP Shell (1890 - 1945). But as I say I also tried 3" Avg post-1935 APC Shot and got the same results. Both had BL(N) = 1510-fps for 2.5" Class-B @ 30-deg. Pretty much the same thing that M79APCLC cranks out (see the graphs in my above post).

 

 

I also tried additional runs in NAaB1.0 at 45 and 60-deg with similar results to what I show in the graph from my previous post.

 

2.5†Class-B at 45-deg BL(N) = 1770-fps

2.5†Class-B at 60-deg BL(N) = 3560-fps

 

Again – no contrast in limit velocity between the choices of either “3" Avg post-1935 APC Shot†or “3" A/N uncapped Steel AP Shell (1890 - 1945)â€. But the latter would be what I would intuitively guess to be the right model for 3†M79 AP.

 

I did run your choice of projectile -- 3" Mk 29 APC -- and got basically the same results as you did. This could suggest a couple things about the original program code and how it is dealing with slope effects. However, without having a handle on how the original slope effects are being computed in either FACEHARD or M79APCLC, it's tough to say for sure what’s going on. All one can do is compare output to real testing data and speculate as to what Okun was thinking.

 

Best Regards

Jeff

[Mobius]

The one thing I don't understand in Okun's stuff is how his quality, elogation and other factors compare to BNH factors.

If Class B WW2 is the standard what factors can one give more modern armor?