88L71 vs. SHERMAN JUMBO FRONT

[rexford]

Sherman Jumbo front armor is:

Mantlet

3.5" rolled over 3.875" cast

Glacis

1.5" plate over 2.5" glacis at 47°

Assume two plates in contact resist like one plate with 88% effective thickness. 3.875" cast vs. 88 equivalent to 3.62" rolled.

Mantlet resistance => 159mm rolled

Glacis resistance => 179mm @ 0°

88L71 APCBC should be able to penetrate Jumbo glacis at 2000m. Slope effect when 88 hits 100mm at 47° is 2.00 (we used full thickness in T/D ratio to beon conservative side).

We can write short things too.

[Forever Babra]

<BLOCKQUOTE>quote:</font><HR>Glacis

1.5" plate over 2.5" glacis at 47°

Glacis resistance => 179mm @ 0°<HR></BLOCKQUOTE>

Okay, the 179mm I got... But 0°?

[rexford]

Glacis 4" thick but two plates in contact, so use 88% of thickness as effective, for 3.52" rolled single plate equivalent.

T/D ratio of 100/88 (to be conservative) results in 2.00 slope multiplier.

So, 3.52" x 25.4mm per inch x 2.00 slope effect = 179mm at 0° equivalent resistance.

3.52" at 47° has the same penetration resistance as 179mm at 0°.

Slope effect is multiplier that converts sloped armor to equivalent resistance at 0° that can be compared to 0° penetration. If we didn't convert sloped armor to 0° equivalent we would need tables of penetration at every angle for every gun to determine if penetrations occur. By converting to 0° resistance, we only need one penetration table at 0°.

Jumbo Sherman glacis resistance is same as a single 179mm plate at 0° slope. 88L71 penetrates about 175mm 0° plate at around 2000m.

[rexford]

Another way of looking at sloped armor multipliers is that a round that can penetrate 179mm @ 0° on half the hits can also penetrate 3.52" at 47° using the same criteria.

[Dittohead]

But were all jumbo's created equally? Would some of the field mods fair much worse than the official versions? Should there be two different armor versions modeled in the game. Maybe at different costs.

[Jeff Duquette]

Ran through some game tests. 2 x 88mmL71 ATG’s (Crack) vs. 6 Jumbos. Range was between 2000 to 2400 meters. It was very difficult to get hits at this range. Those rounds that did hit were all Ricochets. Each of the guns started with 28AP. Guns were averaging about 1 hit per 8 rnds fired. One 88 finally succeeded in an M-kill at 2000 meters using HE (its AP had run out). 60 rnds fired one M-Kill. ROF for the ATG’s avg’d about 6 to 8 seconds per rnd.

It is interesting to watch the location of round splash. You can click play/pause rapidly and watch the progress of the round. Lay out a grid on your test map with dirt roads. 50 meter grids. I took some notes on splash locations for one turn of firing:

Gun #1

Range to Target was 2366m. Target was stationary through out the turn. No smoke. Weather Clear. ATG didn’t receive any suppressive fire.

1st Rnd at 4seconds into turn…MISS…Short of target by 100 meters (no lateral dispersion)

2nd Rnd at 12sec MISS…over 100m…Left 50m

3rd Rnd at 18sec MISS…over 100m…Left 10m

4th Rnd at 26sec MISS…over 100m…Right 10m

5th Rnd at 34sec MISS…short 100m…Right 50m

6th Rnd at 41sec HIT…ricochet front of turret

7th Rnd at 49sec MISS…over 10m…Right 10m

8th Rnd at 56sec MISS…over 50m…Wide Left 100m

Gun#2

Range to Target was 2374m. Target was stationary through out the turn. No smoke. Weather Clear. ATG didn’t receive any suppressive fire.

1st Rnd at 5seconds into turn…MISS…Short of target by 50 meters …left 10 meters

2nd Rnd at 12sec MISS…short 50m…Left 20m

3rd Rnd at 19sec HIT…Front Turret Richochet

4th Rnd at 26sec MISS…short 50m…Wide Left 150m

5th Rnd at 34sec MISS…short 100m…left 10m

6th Rnd at 42sec HIT… Front Turret Richochet

7th Rnd at 49sec MISS…over 150m…Wide Right 100m

8th Rnd at 56sec MISS…over 100m…Left 50m

Round dispersal is pretty erratic.

[RMC]

JD,

I think that round dispersal is erratic because the engine determines whether or not it hit first. then, if it is a miss it generates a location where it will land in some random fashion within certain constraints. So you don't see any real bracketing going on. But I could be wrong.

BTW, the thread with you name on it seemed to get corrupted. I posted and someone else did but I can't see them. They last post listed on the thread's 2nd page has a different date time stamp than the forum thread listing. hmmmmmmmmmmmm.

[Jeff Duquette]

<BLOCKQUOTE>quote:</font><HR>RMC Said:

I think that round dispersal is erratic because the engine determines whether or not it hit first. then, if it is a miss it generates a location where it will land in some random fashion within certain constraints. So you don't see any real bracketing going on. But I could be wrong.<HR></BLOCKQUOTE>

That’s kind of what I figured. At this level you aren’t really seeing the game engine model gunners “walking” or bracketing their rounds onto their targets. Bracketing (if it is present in the game) is probably a simple “to hit” bonus.

The other thing I noticed is that trajectory tends to be fairly parabolic, rather than somewhat parabolic with a distinct change in curvature as the round drops toward MPI. Difference between firing in a vacuum, or firing in atmosphere. Again I know I am reading to much into the game engine here. The intent of the games tracer element is probably more eye candy than anything else.

Anyway I digress from the intent of this thread. I didn’t see any frontal penetrations of Jumbos armor by 88mmL71 at the ranges I had indicated.

Regarding the range finder thread…I dunno what happened with it. I will attempt to bump it…hey just bumped it and finally saw your response. Agree with your response...just needed a gut check.

One last question RMC (in case you wonder into the forum again soon): Do you have access to dispersion numbers for the Panther 75mmL70 APCBC…lateral…and vertical dispersion of rounds around target MPI relative to range. An example from Rexford for 50mmL60:

@100m: Vertical Dispersion is .03m…Lateral Dispersion is .03m around Mean Point of Impact presumably.

Were penetration values altered in the latest patch? b24? I am still runing b16.

[This message has been edited by Jeff Duquette (edited 01-04-2001).]

[Polar]

Ok... not a narmor penetration expert... so I have a few questions for clarification.

1) The 88 ap rating at 0 degrees... that is assuming that 100% of inertia is delivered on the target, right? The penetration value of the round, unless I am missing something, should decrease as the approach angle increases (reaching 0 at 90 degrees)?

2) Aren't angles measures in 90=dead on contact, and 0 is parallel to the impact surface?

Sorry if these sound silly... but it seems to me that armor penetration conclusions are not as simple as figuring the thickness of armor at angle of contact -vs- armor penetration of round when measured dead-on.

Shaped charges (Panzerfaust, Bazooka) are a different story, but these weren't shape charges that they were firing at each other... were they?

Just wondering... but it seems most of these discussion are over simplified.

Joe

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"I had no shoes and I cried, then I met a man who had no socks." - Fred Mertz

[This message has been edited by Polar (edited 01-04-2001).]

[Mattias]

Polar

The discussion is usually simplified (though usually complex "enough") because the subject, nay science, of armour penetration is incredibly complex when you consider all factors involved. I'd say it is impossible to exactly predict the result of any one test firing for example.

1) True, the armour thickness increases but sloping the armour has a multitude of other effects as well, which further complicates things. One example could be the increasing chance of the projectile ricocheting and thus failing to affect the armour altogether.

2) Depends on where you come from, W.W.II German sources measure from the horizontal (i.e. 0 degrees is horizontal) whereas current American use the vertical. Not sure which is the international standard but at least I was taught to calculate from the horizontal

Finally, like you say, shaped charges are a different story, almost supernatural in complexity when it comes to calculating effect it seems. And no, normally W.W.II tanks engaged each other with, basically, solid AP shots, though shaped/HEAT rounds where used too.

M.

[This message has been edited by Mattias (edited 01-04-2001).]

[Dr. Brian]

<BLOCKQUOTE>quote:</font><HR>Originally posted by rexford:

Jumbo Sherman glacis resistance is same as a single 179mm plate at 0° slope. 88L71 penetrates about 175mm 0° plate at around 2000m.<HR></BLOCKQUOTE>

Okay, not sure what direction you're going. But, if 175mm penetration is less than 179mm of armor, then it should not penetrate at 2000m (give or take the rare occurances).

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Doc

God Bless Chesty Puller, Wherever He Is!

[Guest Big Time Software]

Hello Jeff and RMC:

<BLOCKQUOTE>quote:</font><HR>That’s kind of what I figured. At this level you aren’t really seeing the game engine model gunners “walking” or bracketing their rounds onto their targets. Bracketing (if it is present in the game) is probably a simple “to hit” bonus.<HR></BLOCKQUOTE>

Mostly correct. I am very sure that Charles does model over and under shooting. And yes, bracketing is simulated, but as an increasing chance to hit with each shot.

As RMC described, visual "bracketing" and shellfall patterns are largely eyecandy. There is logic to it, for sure, but it isn't tweaked out for each gun. Obviously, the reasoning here is simple. Only one in a few thousand gamers would even think to LOOK for this stuff, not to mention care if is right or not Since it really is irrelevant to the way the game system works, it would be an unnecessary use of valuable programming time to simulte.

<BLOCKQUOTE>quote:</font><HR>The other thing I noticed is that trajectory tends to be fairly parabolic, rather than somewhat parabolic with a distinct change in curvature as the round drops toward MPI. Difference between firing in a vacuum, or firing in atmosphere. Again I know I am reading to much into the game engine here. The intent of the games tracer element is probably more eye candy than anything else.<HR></BLOCKQUOTE>

Partially correct again. The flight path should be fairly accurate from a physics standpoint, including the effects of gravity and decreasing velocity. At least I know that this is all calculated in the ballistics equations. The question is if this is 100% represented visually. I don't know if it is.

Steve

[Polar]

Mattias,

That is what I though...

That is why I REALLY don't get the arguement here. AFAIK, CMBO doesn't report the actual angle that a shot hit... since (esspecially with a glacis) hitting an inch left or right or up or down can change the impact angle

drastically.

My guess is CMBO doesn't model any tank down to the inch.

I mean, even if the shell impacts at a 30 degree angle to the turret facing, if it hits dead center, then you have a 30 degree calc... if it hit's six inches lower, you have to add the fact that the armor is now curving away from the 30 degree plain... making it a glancing blow.

I think what people miss here is that we are making assumptions that generally have dreastic effect of reality when in reality the effectiveness of any shot, be it 2 kilometrs or 0.2 kilometers, is effected by as little as 6 inches divergance from bullseye.

Pretty silly to argue such things with that much variability.

My guess is there are an adequate number of ricochets... and not too few or too many to warant a fuss.

Joe

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"I had no shoes and I cried, then I met a man who had no socks." - Fred Mertz

[RMC]

Sorry JD, I don't have anything like dispersion data on any guns. I have almost exclusively secondary sources and none of them include anything that detailed.

[rexford]

When penetration is within a few percentage points of armor resistance, from 1/3 to 2/5 of hits might still penetrate, since 50% penetrate when penetration = resistance. 175/179 = 98% ratio, so penetration is still possible.

Penetration data for everyone but Soviets is the armor thickness that can be defeated on half the hits.

We use 0° angle as a right angle hit, with angle of plate measured from vertical. This is what U.S. used during WW II, and Brits too. When they give 30° penetration figures it is for a plate 30° from vertical.

U.S. tests show that angle does not induce ricochets. If 60° penetration is 90mm and 90mm armor at 60° is hit, 50% penetrate and 50% don't. But there is a penetration value where 100% will penetrate 60° slope armor and none will bounce.

88L71 lateral dispersion at 2000m predicts that 50% of shot scatter will be within 0.7m of aim, and 95.5% will be within 2m of aim point. 50m and 100m lateral misses at 2000m with 88L71 seem to require an explanation since they indicate that the gunner is badly overcorrecting.

A 100m lateral miss is 328' left or right, which is longer than a football field. If the 88L71 is aimed at the tank and corrected, it should be closer than 50m from aim point.

[Guest Big Time Software]

Hi Polar,

<BLOCKQUOTE>quote:</font><HR>My guess is CMBO doesn't model any tank down to the inch.<HR></BLOCKQUOTE>

Bingo Yes, this is very much the case. Nobody has a computer beefy enough to handle such exact calculations, so we have to abstract certain aspects of the armor and ballistics treatment. It will be many, many years before we can do things exactly.

<BLOCKQUOTE>quote:</font><HR>I mean, even if the shell impacts at a 30 degree angle to the turret facing, if it hits dead center, then you have a 30 degree calc... if it hit's six inches lower, you have to add the fact that the armor is now curving away from the 30 degree plain... making it a glancing blow.<HR></BLOCKQUOTE>

This is really only an issue for rounded, or multi angled, surfaces. CM does keep this in mind for such surfaces, but not as much as we would like. CM2 will not be fundamentally different, but the proposed rewriting of the game engine (we call it CM II) will be far more advanced. Not mm for mm due to hardware limitations, but much less abstracted all the same.

<BLOCKQUOTE>quote:</font><HR>I think what people miss here is that we are making assumptions that generally have dreastic effect of reality when in reality the effectiveness of any shot, be it 2 kilometrs or 0.2 kilometers, is effected by as little as 6 inches divergance from bullseye.<HR></BLOCKQUOTE>

True. For this we have various random factors built in. This is why you can score a "weak point" hit on certain vehicles in certain circumstances. This simulates, in an abstract way, the shot being 6 inches lower and hitting, say, the underside of the Panther A's mantlet, sending it into the upper deck (penetration) as opposed to skyward (harmless).

Steve

[rexford]

A 100m lateral aim error at 2200m range equates to 2.6° error, or 0.0454 radians or 45.4 mils error.

45.4 mils is a very large aim error. Would it still be on the gun sight?

[rexford]

Our spreadsheet can define projectile shot placement to within a very small area and the placement is then measured out on a model.

If settings are exactly the same on the next shot, the round placement will change due to shot-to-shot dispersion variations.

Measuring on a model gives a better result with regard to hits on odd shapes or potentially damaging ricochets.

[LynnL53]

A good friend who lives in the next town from me, was in a Sherman Jumbo at the end of the war-- his Lieutenant wanted to lead the column and took over his tank-- as it rounded the next curve, an 88 went through the front ( all he said) and killed all of them in the tank- the LT lived lived less than five minutes after changing with SGt. Clark-- I do not know what kind of 88-- or if it was an 88 -- for him every thing was an 88 anyway -- it got through the frontal armor of the Jumbo what ever it was-- do not know the range either. Good but sad story.

[Jeff Duquette]

Tough story Lynn. Thanks for sharing.

This is a Tiger GPS. There are 4 mils between the points on the triangles. A 45 mil deflection error would put the round at about at the edge of the scope…along either the MG or Main Gun range scales. Its on the sight, but not by much.

This is however more for just personal interest. As Steve has indicated the game doesn’t really attempt to model lateral or vertical dispersion in accordance with historical shot pattern testing. Still its fun to tinker with the game and look at various details of the CM model. Its almost as much fun to tinker as it is to play

[rexford]

If CM does not attempt to model actual gun scatter in lateral and vertical directions, maybe this is why CM hit %'s are different than calculated figures using trajectory.

Does CM consider range estimation error?

[Guest Big Time Software]

rexford,

My mistake - I was not aware that the Jumbo used separate plates to make up the 'extra' armor. That should reduce its effective resistance. I'll get this into v1.1.

Charles

[Guest Big Time Software]

Rexford:

<BLOCKQUOTE>quote:</font><HR>If CM does not attempt to model actual gun scatter in lateral and vertical directions, maybe this is why CM hit %'s are different than calculated figures using trajectory.<HR></BLOCKQUOTE>

The debate about the accuracy of CM's chance of hitting is fairly complex and rather lengthy. Substantial physics and ballistic factors are involved in figuring out the chance of hitting, but we do not model every little aspect of gunnery equipment, human interaction with the equipment, and real world performance of each under combat conditions (as opposed to test range and extrapolated test range data).

This is to say... we do not carry everything out to the nth degree for gunnery accuracy. By its very nature, this value is more "fuzzy" beacuse it is influenced by many different, and not easily predictable factors. As I sated above, it is impossible for us to simulate them all. So while it is fairly straight forward (but not at all easy) to accurately simulate things like the effects of AP shot on armor in x and y circumstances, or the basic characteristics of the gun and ballistics in general, the reason why one shot hits and one misses has a lot more to do with multiplicity of finite, variable factors.

When we remake the CM engine, perhaps we will add this degree of shot pattern simulation. For right now, I don't think this is a big issue. Actually, the most significant drawback to the system now is, I suppose, that a "miss" muight land too far away and inflict damage on something that possibly it shouldn't have. But since this is likely a very rare thing, it isn't of great concern for us at the moment.

<BLOCKQUOTE>quote:</font><HR>Does CM consider range estimation error?<HR></BLOCKQUOTE>

Yes, very much so. Each shot taken means a greater chance of the next one hitting its mark. Range estimation errors increase with range and experience plays a huge role. Obviously the inherent capabilities of the gun and the exact circumstances also have a fundamental influence.

Steve

[This message has been edited by Big Time Software (edited 01-06-2001).]

[Spook]

I've been on a lurker level for this topic, but now, Rexford, I was wondering if you care to elaborate on two of your comments:

1) 3.52" at 47° has the same penetration resistance as 179mm at 0°. Or, as put alternately by you, "a round that can penetrate 179mm @ 0° on half the hits can also penetrate 3.52" at 47° using the same criteria."

2) U.S. tests show that angle does not induce ricochets.

I'm a bit curious to the latter one, given the possible factors to richocet as pertains to "impact energy" by shell weight & shape, or by loss of shell velocity over extended ranges.

[rexford]

Really good question, and one that goes beyond normal conclusions. They may be more to it than my previous answer considered.

A 60° angle from vertical does not automatically mean that a certain percentage of hits will ricochet off.

When 75mm APCBC from a Panther hits a 20mm at 70° plate, will most of the rounds bounce off because of the angle?

In penetration tests of U.S. APCBC, 20mm at 70° is equivalent to 50mm at 0° when it is hit by 75mm rounds. A round that can defeat 50mm at 0° angle (vertical plate) on half the hits during tests will penetrate 20mm at 70° at the same velocity and range.

At 2000m the Panther round will be descending onto the target if ground is level, so 20mm at 70° will resist like less than 50mm at vertical, and every Panther hit should penetrate. Will 100% of hits penetrate?

The answer is probably "no", because some projectiles may lose stability in the air for any number of reasons and wobble, which decreases penetration capability. Air turbulence, worn guns that provide little spin to the round, bent guns due to recent hits, etc.

German tests showed that putting spare tracks on 70° angled armor could disrupt the projectile motion enough to make a big dent in the penetration, which is why so many PzKpfw IVH carry spare tracks on the 72°glacis (this area of the pzKpfw IVH is very vulnerable to penetration by the Sherman 75mm).

It is safe to say that most, no, practically all Panther hits on 20mm at 70° from 0m to 2000m will penetrate. Angle alone is not enough to guarantee protection, although I have seen wargames where it was assumed that all hits at 70° or greater would bounce.

TOBRUK had a hit resolution table where 30% or more of the 88mm Flak hits on the Stuart side armor would fail to damage the tank, due to angle and other considerations. U.S. penetration data clearly shows that 70° and 75° slope armor can be penetrated, and naval test data shows the same result for up to 85°.

Penetration data is based on test firing at close range with the velocity that is expected at a given range. They don't put a target at 3500m and fire 88L71 at it.

At 2000m and greater ranges alot of things will occur that don't occur when one tests 2000m penetration using a 100m long firing range and reduced velocity. This is also why penetration data against highly sloped armor does not include descent angle effects, because they conduct the firing at a range where descent angle isn't a factor.

Below 600m range, test firing data should closely match battlefield experience because fewer odd things occur. But consider wind.

If a 30 mph wind is blowing directly at a Tiger I as it shoots, that retards the round and lowers the impact velocity. Cross winds of 25 mph can also help create ammo wobble or hits at angles that don't occur on the short firing range.

In a similar vein, will 37mm APCBC hits on the lower Panther mantlet penetrate the hull top on ricochets as often as 76mm. No.

37mm rounds are long and thin, and bend alot easier than 76mm. When 37mm hits the Panther mantlet bottom and bounces, it is likely to do so after bending the nose and losing flight stability. Husky 76mm rounds are better able to hit and bounce without severe structural or aerodynamic disruption because of size.

Bent noses and funny flight paths due to shape changes decrease the chance that the Panther hull top will be penetrated.

There is an awful lot to armor penetration, but it is not the physics that is the killer, it is the natural phenomena that play games with data based on 100m shooting and is extrapolated to 3000m.

Ricochets off the Panther mantlet bottom fall into the aforementioned category. What % of 76mm hits off the mantlet bottom will penetrate, what percentage will do nothing/ No one knows the answer, but it probably isn't 100% and may not be 0% either.

Some 76mm hits on the mantlet bottom will have sub-par steel and will end up with bent noses. Softer Panther mantlet steel will allow the round to dig in more, so the round loses energy and may not ricochet at all, or will bend or even shatter. There are no tests on this and alot of odd events that can spoil a prediction.

Angle alone will not cause a high percentage of ricochets, if it did we would see alot of 15mm at 80° glacis plates.