HE vs Armor

[Doug Beman]

JonS, firing airbursts requires proximity fuzes, which I believe were in very short supply for the Germans this late in the war.

The Tiger did not fire AA shells, but the HE/anti-personnel version of the shells they DID fire probably were quite similar to those used by the AA version of the 88. Why mess with a good thing? If it can whack a bomber, it's good enough for killin' Amis.

DjB

[Neutral Party]

Fascinating discussion about HE blast and schrapnel effects.

Can I ask the experts some dumb questions - I know little about artillery but a bit about physics.

What is it that triggers the detonation of a HE shell fired from a tank - Is it impact with the ground?

If so then isn't the shell stationary - I don't get Bulletheads point about the centroid of the blast remaining on the shells initial trajectory. An airburst would be different of course.

88mm vs. 75mm - The 88mm would be about 60% bigger in simple volume terms but what size are the cavities inside these shells that contain the HE - are the casings the same thickness ?

The other thing is - can someone explain in simple terms what you mean about the cone as opposed to dome shape for the HE blast. Thanks

Joe

[Guest scurlock]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Richard III:

Sorta vagely relevant to this topic: did the KV-II have an AP round available for it? Or did it do its work solely with HE?<HR></BLOCKQUOTE>

The KVII did have a concrete busting shell; however, Word never got down to the crews to use them as anti-tank shells.

[Doug Beman]

Joe asked some questions:

"What is it that triggers the detonation of a HE shell fired from a tank - Is it impact with the ground?"

I b'lieve so.

"If so then isn't the shell stationary - I don't get Bulletheads point about the centroid of the blast remaining on the shells initial trajectory. An airburst would be different of course."

But the individual pieces of said shell will have an awful lot of momentum, and will want to continue moving in the same direction (BonusQuestion: which law of motion is this?)

"88mm vs. 75mm - The 88mm would be about 60% bigger in simple volume terms but what size are the cavities inside these shells that contain the HE - are the casings the same thickness ?"

The 88 shell had more propellant, so had less capacity for HE oomph. Also, the higher stresses on the shell probably required a thicker casing, further reducing how much bang you cuold pack in.

"The other thing is - can someone explain in simple terms what you mean about the cone as opposed to dome shape for the HE blast. Thanks"

Here's my answer: Imagine a HE shell whomping into the ground. In the split-second before detonation, it will dig itself a little pit in the ground. When the charge goes off, it will be directed by the walls of the pit into a more-straigh-up path, as opposed to spreading out horizontally. For the blast to spread out in a perfect dome, the shell will have to explode IMMEDIATELY upon contact with the ground; common HE was not fuzed sensitively (is that even a word?) enough.

DjB

[Guest scurlock]

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

I'm just puzzled as to why an 88mm HE shell is so devastating compared to the 75mm. Neither is very big as shells go (both would be classed as light arty), and to me there doesn't seem to be enough difference in size between them to account for the very different combat results.

-Bullethead<HR></BLOCKQUOTE>

Trick question: what's the difference in weight between a 155mm HE round and a 203mm HE round?

Answer the 203mm weighs twice as much at about 200lbs.

I don't know the exact weight of each round but the 88 would weigh significanty more than the 75.

------------------

Eric Scurlock

"He who gets there the fastest with the mostest wins."

[Neutral Party]

Thanks Doug

So the first point depends on the angle of attack relative to the ground. This determines the component of momentum that is parallel to the ground and may be retained following detonation - the component perpendicular to the ground being effectively lost.

This implies that the effect will be more important for a low trajectory tank shell rather than high trajectory arty

Was there less HE in the 88 than in the 75 ?

Thicker casing = more schrapnel but less HE means schrapnel has less KE and is less penetrating right?

OK I get the cone thing - impact crater funneling

Joe

[billcarey]

<BLOCKQUOTE>quote:</font><HR>But the individual pieces of said shell will have an awful lot of momentum, and will want to continue moving in the same direction (BonusQuestion: which law of motion is this?)

<HR></BLOCKQUOTE>

Well, that would be the conservation of momentum (which is really just conservation of mass and energy) Newton's first: Objects in motion will stay in motion (barring outside forces acting on them - like armor or the ground...)

- Bill

[Guest JonS]

LONG post on HE rounds coming up. Not for the faint hearted …

Arty HE rounds are usually fused PD (Point Detonating). There is in effect a little trigger on the nose of the projectile that causes the HE charge inside to explode. The time interval between the fuse being triggered and the detonation of the round is very short - ie the round doesn't burrow very far.

In case any of you don’t know, an artillery projectile looks externally very similar to a rifle bullet – it has a long axis, a cone shaped nose, and a flat base. When the HE filling goes off it expands the shell until the casing fractures into small pieces.

Since the round is longer that it is wide, most of the fragments come out at roughly right angles to the long axis of the projectile – which is of course also at right angles to the direction of flight.

If the round impacted the ground vertically it would produce an even, circular distribution of fragments around the impact point. However, they don’t do that, and a significant proportion of the fragments, and force is directed into the ground or up into air (too high to harm anything).

The normal shape of the beaten zone for an artillery round is a rounded ‘V’ shape, with the point of impact near the base of the ‘V’. If you imagine this page as the impact zone, and each ‘V’ as a round landing, then the line of flight for all these shells is from the bottom of the page to the top. That’s right – it produces two forward extensions at angles to the line of flight. I don’t have my notes here going over the reasons why, so you’ll have to trust me on it

As the angle of impact steepens up toward vertical then the forward projections become less and less pronounced, and the overall shape approaches circular. This is one of the reasons mortars are so effective – they have a very high trajectory, and come down very steeply, so produce a more even beaten zone.

The reason indirect, airburst HE is so effective is that when they go off at optimum height (20-40m up) there is nothing to get in the way of the fragments and they come down in a more or less even circle. Also, because the fragments come down like rain, you need something with OverHead Protection (OHP) to stop them. (Note – this isn’t necessarily a plug for inclusion in CM. Battlefield use of radar fused proximity was rare, and the clocks in variable time fuses were rather imprecise)

Doug said:

<BLOCKQUOTE>quote:</font><HR>firing airbursts requires proximity fuzes, which I believe were in very short supply for the Germans this late in the war<HR></BLOCKQUOTE>

Actually, I don’t think the Germans ever develop prox fuses during the war. These rely on a little radar in the fuse to note when something is close, and use that info to start the detonation sequence. Variable Time fuses have a little count-down timer in them, and detonate when the timer reaches zero. By changing the length of the count down, and knowing the muzzle velocity of the round, you can get an AA round to conveniently detonate at B17 height. If the barrel is depressed and pointed toward some infantry wandering around, then using the same technique will allow you to detonate the round over their heads Since these 88s were AA guns (I’m not talking about the 88 in a Tiger, or the PaK 43s, but the big ones with shields in Reisburg), Then I would expect that they would have a supply of VT fuses on hand. Maybe – would depend on their orders and the supply situation also I suppose…

Regarding the AA HE round being perfect for anti-personnel use: Well, I’m not so sure. The optimum size for indirect HE fragments is about the size of your thumbnail (or a little bigger if you chew your nails too much…). I don’t know what the optimum size for AA fragments is, but I’d be surprised if it was the same.

Phew, that’s my long post for today …

Regards

Jon

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Ubique

[Lee]

I think that point being made about these blast cones

was that if a tank fires an HE shell at you it will

have a fairly shallow arc and thus have lots of forward

momentum in a direction fairly parallel to the ground.

And even though the impact with the ground will soak

up some of that momentum there will still be a good bit

left when the fuze detonates the shell, thus biasing the

blast radius of the shrapnel towards the direction

the shell was travelling in when it detonated.

This would result in a cone shaped pattern to the shrapnel (though

probably not a terribly pronounced cone). So the most

dangerous place to be when the shell hits is in front

of where it struck the ground.

Of course, the degree to which this effect would manifest

itself would vary with the impact angle (i.e., firing down

from a cliff at someone would greatly reduce the cone

effect as it relates to shrapnel traveling parallel to

the ground). Although I doubt even CM takes this into

account.

[Doug Beman]

So I got some stuff right. Good enough for me.

JonS, that was a most excellent post (dude, that was like totally killer!) that does a very good job of explaining why tank-fired HE seems to be such a poor infantry killer. If only the designers of the CC series had asked you that question, the game would have been MUCH different (as it is, it seems they assumed that a HE shell will always create a circular blast pattern, making tank HE extremely effective, nah?)

DjB

[Bullethead]

Steve said:

<BLOCKQUOTE>quote:</font><HR>Well, I will run the comparision between the 75 and 88 by Charles and see what he has to say.<HR></BLOCKQUOTE>

Thanks! But remember, if it needs fixing and will delay shipment, please save it for a patch

<BLOCKQUOTE>quote:</font><HR>As for taking out 4 men, WIA/KIA, I still say it is VERY possible.<HR></BLOCKQUOTE>

A big enough shell could certainly do this. My basic question is two-fold: 1) was the 88mm really big enough, and 2) if it was, then why is the 75mm so much worse, given that both are very nearly the same size? Conversely, if the 75mm isn't big enough, then why is the only marginally bigger 88mm so much more effective?

<BLOCKQUOTE>quote:</font><HR>And yes, the 88 HE round was designed for maximum shrap effect as that is what flak is all about. If an 88 HE round can take out a B-17 with a near miss while it is going 100+ MPH at several thousand meters distance, it certainly can take out a HT that is going 10mph at 300m.<HR></BLOCKQUOTE>

I don't altogether agree with this.

First, the Tiger I's 88 wasn't the flak gun and it didn't fire the same ammunition, at least from what I can tell. I believe the Tiger I's ammo was specifically designed for ground use.

Second, there's a world of difference in target hardness between an armored vehicle and an aircraft. The plane's vital systems (except for the pilot) are only protected by an aluminum skin a few thousandths of an inch thick. Engines, weapons, control lines, fuel lines, hydraulic lines, oil lines, oxygen lines, all are very vulnerable.

Now, the reason all this is nagging me is because of certain parameters of shell design. First off, as shell diameter increases, the thickness of its walls also has to increase or they won't be strong enough to withstand the shock of firing. So it turns out that larger shells actually have a lower percent of explosive per total volume than do smaller shells. So where the difference between shell diameters is small, such as the 15% difference between the 75 and 88, most if not all of the theoretical advantages of having the larger shell wash out.

Second, it's my understanding that fragment initial velocity from the shellburst is primarily a function of the type of explosive used. Thus, for shells of similar design (minimum wall thickness for their diameter), all fragments have more or less the same initial velocity from the shellburst, regardless of the diameter of the shell. All bigger size does for you is a) increase surface area and thus number of fragments, increase the size of individual fragments (both thickness and area) so they go further, and c) increase damage from blast and flash. But these effects occur gradually and, as noted above, cancel each other out to some extent. Thus, it takes a significant difference in shell size to really notice much difference in effect. Note: I could be wrong on all this, but this is what I've heard.

So, as to how all this applies to the 75mm vs. 88mm question.....

The shells are very nearly the same size in all dimensions, so the 88 isn't going to produce very many more fragments than the 75. The only way it could do so is if each fragment was much smaller than those of the 75, which would make them LESS effective vs. an AFV. Small fragments, however, work wonders on aircraft so, if you are correct in saying the Tiger I shot flak shells, then I could see it making smaller fragments, being very good against infantry, but being very poor against halftracks.

Assuming, however, that both shells make fragments about the same size, then there shouldn't really be much difference in effect between the two. First off, both shells will make very nearly the same number of fragments, and all fragments will be approximately the same mass. Second, both sets of fragments will be moving at about the same velocity. Thus, fragments from either shell will hit the halftrack with very nearly the same energy and thus will have equal chances of penetrating. And because the number of fragments are nearly the same, the total amount of damage done should be very nearly the same.

This sort of thing is why arty is defined in broad classes such as light, medium, heavy, and super heavy. Within each class, there isn't really much to choose from between 2 calibers of nearly the same size, and the biggest light shell is essentially just as effective as the smallest medium shell.

So anyway, maybe it IS realistic for a Tiger to always kill a halftrack and many of its occupants. But if so, it seems to me the 75 should do nearly as good a job.

Thanks for wading through this.

-Bullethead

[Bullethead]

Sarge said:

<BLOCKQUOTE>quote:</font><HR>its so obvious maybe thats why no one has mentioned it: the diff between 75 & 88?

one word "velocity"<HR></BLOCKQUOTE>

Well, higher velocity is actually counterproductive for HE rounds. After impact, it takes a certain amount of time for the fuse to work and set off the main explosive charge. In this time, the faster shell moves further, burying itself further in the ground before it explodes, which decreases the effectiveness of both blast and shrapnel.

So, another reason why the 75's HE shouldn't be so much worse than the 88's

-Bullethead

[Major Tom]

Here's a freakish example of an unsuspecting AA gun. You might think it wierd and impossible for a vehicle such as the Tiger having a weapon with AA capability or firing AA rounds (even though it doesn't). The Japanese Battleship class Yamato had the capability to fire its 18" guns as AA defense. It wasn't too good in shooting down anything, but, the FlaK bursts must have been a sight!

[Doug Beman]

BH, if there's really not much increase in HE effect from 75 to 88, what sort of increase was there from 57 or 60 to 75? I'm asking because I've always read that one of the most pronounced benefits of the Brits replacing 57mm-gunned (and the Germans their 60mm) tanks with 75mm-gun was markedly greater anti-personnel ability.

This is probably one of those horrid "diminishing returns" relationships. Sounds like my social life...the more I try the worse it gets.

DjB

[Guest JonS]

Maj, The Brits had something similar with their 6" guns IIRC.

Current warships' 5" guns have a ROF of ~45 rpm, and are expected, I believe, to take on attacking aircraft and even missiles! Any squids out there able to confirm or deny (references a local joke about the Pentagon)

BTW, I didn't say that the Tiger *couldn't* fire AA rounds, just that IU'd be surprised if it did.

Regards

Jon

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Ubique

[Bullethead]

Doug said:

<BLOCKQUOTE>quote:</font><HR>BH, if there's really not much increase in HE effect from 75 to 88, what sort of increase was there from 57 or 60 to 75?<HR></BLOCKQUOTE>

This brings up another shell design constraint . As you increase designed muzzle velocity, you have to increase shell wall thickness or the shell breaks up in the barrel. Thus, higher velocity shells have less room inside for explosive than slower shells of the same caliber.

The 6pdr/57mm was designed as a high-velocity ATG. For its caliber, then, the shell wall had to be pretty thick. OTOH, the short 75s used in the Sherman and some Brit tanks were designed for lower velocities, so they had more explosive inside for their diameter than say the 75 HE of the Panther. Thus, not only was the 57mm a smaller shell, it didn't have much explosive for its size.

This sort of thing is probably why the 76mm Shermans' HE shell was considered inferior to the 75, and why the Panther's HE wasn't as good as the StuG's. I didn't mention it in the StuG 75 vs. Tiger I 88 wall o' text because both those guns were designed for roughly similar velocities.

-Bullethead

[Bullethead]

JonS said:

<BLOCKQUOTE>quote:</font><HR>Actually, I don’t think the Germans ever develop prox fuses during the war. These rely on a little radar in the fuse to note when something is close, and use that info to start the detonation sequence. Variable Time fuses have a little count-down timer in them, and detonate when the timer reaches zero.<HR></BLOCKQUOTE>

Ah, another trans-oceanic difference in terminology. Over here, we call the radar "prox fuse" a "variable time fuse" (VT) and the clock timer kind a "mechanical time fuse" or just "time fuse." This is because you set the latter kind for a fixed amount of time, but the radar type goes off at a variable time from firing, depending on when its sensor triggers.

-Bullethead

[Guest Big Time Software]

Bullethead,

Physics ain't my thing, so I can't really comment. However, physics and ballistics IS Charles' thing So I trust that whatever lead him to make the factors what they are have solid scientific foundation. I think he explained some of this stuff in earlier posts if you want to go hunting for it.

As for the gun in the Tiger 1 it was nearly identical to the one used in the Flak 36. Beyond that I know little about the differences. The gun used in the King Tiger and the Pak43 was purpose built for AT duty.

Charles did make a quick comment on your test. It is very hard to do these sorts of tests because the TacAI sometimes switches to AP and targets a vehicle specifically when using Area Fire against a hard target in the immediate area. So there is a very good chance (although without seeing your test I don't know if it is true) that the Tiger happened to switch over to AP and simply shot up the vehicle directly.

In any case, Charles is pretty confident that there isn't anything screwy with the data or how it is being used. However, we have our eye on it just in case

Steve

[Lee]

I'm curious to see what Charles has to say about

the effectiveness of different HE shells and how they

are modeled in CM. Should be interesting.

[Neutral Party]

Steve.

He was area firing at his own half-track. TacAI won't switch to AP and direct fire for that - will it?

Joe

[Sarge]

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

What has velocity to do with HE effectiveness? I believe the 75 mounted on a Panther has a higher velocity than the 88 on a Tiger I.<HR></BLOCKQUOTE>

very true and no argument....i thought the discussion was about 75's fired from arty (extreme low velocity) vs the 88. not a HV round from the PzV 75L70!

but then when you talk 88's there are also several (!) versions of it, AT-FlaK-AFV etc etc

but i am far from an expert-

[Bullethead]

Steve said:

<BLOCKQUOTE>quote:</font><HR>So there is a very good chance (although without seeing your test I don't know if it is true) that the Tiger happened to switch over to AP and simply shot up the vehicle directly.<HR></BLOCKQUOTE>

It would do this even against a German halftrack? When I gave the target, it wouldn't fix on the HT itself because it was a friendly unit I suppose, so I had to area fire right next to it.

-Bullethead

[dalem]

Doug-

Everything I've read about the 57mm/6pdr states these facts about its HE capability:

The British didn't worry about HE for their smaller ATGs (2pdr, 6pdr) and so they either a) didn't develop an HE round at all for them

or

developed around with "mediocre" HE performance.

Read that as "the 6pdr/57mm is not the weapon of choice against troops in any period".

Then again, maybe there's a point of 'diminishing returns' under which you can't get enough HE oomph in a shell smaller than 75mm - I've never studied the effectiveness of, say, the German 50mm or Soviet 45mm guns using HE. Were they effective or were the coax and hull MGs more relevant for antipersonnel work?

-dale

[Guest Big Time Software]

Good point about the friendly unit thing. OK, rule that out as the TacAI will never target a friendly unit.

Steve

[CrapGame]

Whew.... here we go with this topic:

Doug Beman - the 88mm shell having more propellant than the 75mm shell is irrelevant to the HE ooomph capacity of the warhead as the propellant is stored in the piece of shell that remains in the barrel of the gun when it fires, not inside the cavity of the warhead. No internal area of the warhead is consumed by the propellant. As the 88mm shell has roughly 60% more internal volume than a 75mm shell one can extrapolate a little less than 60% (not the full 60% due to thicker walls of the shell) more HE is sitting in the cavity of the 88mm than in the cavity of the 75mm. Note this relationship is similar to the one between the 203mm and the 155mm shells discussed by scurlock.

Bullethead - the 75mm and the 88mm shells are not "very nearly the same size". The diameter might be only 13mm difference, but the length and volumes of the shells must be different as well, which will cause a geometric difference is he capacity. I don't have the exact comparisons, but I am sure someone like Fionn or Steve does have this info somewhere and can settle this question for us.

You said:

"Now, the reason all this is nagging me is because of certain parameters of shell design. First off, as shell diameter increases, the thickness of its walls also has to increase or they won't be strong enough to withstand the shock of firing."

This is true, but the walls do not have to be that much thicker as the shell size increases. Thus, despite thicker shell walls, the internal volume of the 88mm is still much larger.

You said: "So it turns out that larger shells actually have a lower percent of explosive per total volume than do smaller shells." - True, but to an insignificant extent.

You said: "So where the difference between shell diameters is small, such as the 15% difference between the 75 and 88, most if not all of the theoretical advantages of having the larger shell wash out." - Definitely not true. You are combining several partial truths to make a bigger generalization that is less than true.

You said: "So, as to how all this applies to the 75mm vs. 88mm question.....

The shells are very nearly the same size in all dimensions," - Can someone verify this? The volume difference is 60% per scurlock.

"...so the 88 isn't going to produce very many more fragments than the 75." - definitely Not True. If the Volume of the 88mm is 60% larger than the 75mm, then there must be a mathematical relationship to the surface area as well.

"The only way it could do so is if each fragment was much smaller than those of the 75, which would make them LESS effective vs. an AFV." - Here you are ignoring your previous statement that the walls of the larger 88mm shell must be thicker than that of the 75mm. If this is held to be true, then pieces of shrapnel that are identical is shell surface area would be larger from the 88mm as they have more mass due to the thicker wall dimension. The greater mass = greater kinetic energy imposed on enemy target = more damage to enemy than smaller sized fragment moving at identical speed.

You said: "Assuming, however, that both shells make fragments about the same size, then there shouldn't really be much difference in effect between the two." - Definitely Not True as pointed out above.

"First off, both shells will make very nearly the same number of fragments, and all fragments will be approximately the same mass." - This is impossible as the shell cases are not nearly similarly sized, and the fragments of the 88mm should have greater mass due to the thicker shell walls you have already pointed out.

You said: "Second, both sets of fragments will be moving at about the same velocity." - This is true if the explosive used in the shells is identical.

You said: "Thus, fragments from either shell will hit the halftrack with very nearly the same energy..." - not true due to differences in fragment mass pointed out above

"...and thus will have equal chances of penetrating. And because the number of fragments are nearly the same," - again, not true due to the 88mm shell being substantially larger

"...the total amount of damage done should be very nearly the same." - WHEW!!!! As you know, this is completely false. Many partial truths and generalizations can no be lumped together and presented as fact. If someone has the details ( and I know there are numerous cannon cockers lurking here ), please post them for us. I apologize for any abruptness, but there were so many inconsistancies and bad logic that I had to reply.

CrapGame out...