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TimoS.

HE Shell on buttoned up Tank

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I just cant help but got that feeling that Subsystem Damage seems to be random sometimes.

Actually I expect that is the case to some degree. The exact same hit in the exact same place isn't always going to produce the same effect. For example say you have one tank that has a communication system close to being on the fritz, not bolted in correctly or simply has already been batted around and then you have another that is just out of the shop and fairly pristine. The first gets hit and the comms craps out, second does not.

I would hope BF has results with variables that could be just chance.

How random is another question.

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SOME variability is good thing. I mean - after AP or HE hit at the tank MG it may become damaged (usually) but it may not. A HE hit close to unbuttoned crewmember gives very good chance of killing him, but he may have some chance to avoid the shrapnel, or - like someone said - he could just momentarily lower his head shouting something to his driver or his gunner, at the very moment the shell struck. He was just lucky. Things like that had happened.

And some randomnes - like when a HE hit at front turret would generally generate damage to things that are located nearly (optics, gunsight, coaxial MG, radio antenna) but SOMETIMES it can generate damage to something less related, like the engine or bow machinegun.

But something like total randomnes or "everything is possible sometimes" so for example an HE hit against the rear hull damaging the front bow MG or HE hit against top turret damaging a track - sorry, I can't imagine that.

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I just cant help but got that feeling that Subsystem Damage seems to be random sometimes.

If you have a PC tower and start banging the outside of the case with a hammer the vibrations will probably break the most fragile piece inside. This may not necessarily be the piece closest to the impact point. Just think of tank damage the same way.

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One 85mm HE shell vs massive 40-50 tons of tank (thick armoured steel) is not comparable to a computer case vs a hammer :). Tank would barely move when hit.

Maybe a 155mm HE shell vs tank would be comparable :).

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If you have a PC tower and start banging the outside of the case with a hammer the vibrations will probably break the most fragile piece inside. This may not necessarily be the piece closest to the impact point. Just think of tank damage the same way.

I dont have Problem with overall Randomness. Reasonable Randomness as you explained. But i remember back in CMBN Times we had similar Results (or some Topic on it. Cant remember what it was about. Sherman or Tiger) where the same happended. Something like Back of the Tank Hit by HE Shell and the Turret Optic was Damaged. Or something like that.

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Oh, now let me see. How about my post earlier today wanting the passengers of half tracks to hunker down more in their rides?

Hey, I did take note of that :)

On topic, I think that Battlefront are at times victims of their own success - the old Combat Mission engine was full of abstractions, but it also clearly looked that way.

The "new" engine works more 1:1, but there are still some abstractions. It's just that it looks like a high fidelity simulation, so when something doesn't work out quite as it would in real life (or as we assume it would work out), then that sticks out and becomes much more noticeable.

Another example is infantry movement. Usually, it works like it should, but then sometimes, when some lone trooper suddenly doubles back, runs 3 metres, then turns again and continues in the right direction, that seems bizarre.

I posted a couple of times on artillery acting strangely, and there are many other things like that which Battlefront hopefully will continue to improve in future games.

See also: uncanny valley.

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One 85mm HE shell vs massive 40-50 tons of tank (thick armoured steel) is not comparable to a computer case vs a hammer :). Tank would barely move when hit.

Maybe a 155mm HE shell vs tank would be comparable :).

Do you mean that 85 HE shouldn't have enough force to shake the more fragile systems loose?

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I don't believe 85mm HE shell would seriously shake a tank weighting 44-55 tons like Panther or Tiger. But it can seriously shake the armored plate it hits (especially thin side ones, such plate would bulge momentarily) and damage anything that is mounted on this plate (like radio) or too close to it. And 85mm "HE" is really a fragmentation shell (doesn't contain too much explosives) IIRC. The 76mm HE was more effective in HE role than 85mm one.

It happened that HE explosions on armor caused damage (and even engine fire - by loosening the fuel lines and varous valves in the engine compartment) but usually it was either heavy bimbardment of 76mm shells, single 122mm shells or arty shell explosions in proximity. Some Tiger tanks which survived bombardment by heavy allied artillery (western front) but they all had to realign their gunsights before they could fight.

As for AP hits - 10kg 85mm AP shell hitting a tank at 700m/s has 7000kg*m/s of momentum. A Tiger tank weighting 56 tons that would absorb such a hit, would get a velocity change (whole tank) of of 7000/56000 = 0,125m/s so 0.45km/h.

Being hit by 85mm AP shell from close range would give a shake like if the Tiger going 0.45km/h hit a reinforced concrete wall or a pillar of a bridge with it's front armor and stopped instantly. It can be felt, but it's definitely not a big shake.

Of course He hit was louder. And being close to the very armored plate that was hit could be not healthy.

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As for AP hits - 10kg 85mm AP shell hitting a tank at 700m/s has 7000kg*m/s of momentum. A Tiger tank weighting 56 tons that would absorb such a hit, would get a velocity change (whole tank) of of 7000/56000 = 0,125m/s so 0.45km/h.

And if that delta-vee occurred in a thousandth of a second (a SWAG of how long a shell takes to detonate), that's a 12G shock (if I've got my 'rithmetic right). Easily enough to discommode a valve-based RT of the period.

...if the Tiger going 0.45km/h hit a reinforced concrete wall or a pillar of a bridge with it's front armor and stopped instantly...

Nothing stops instantly. It all takes time, and that sort of impact takes orders of magnitude more time to happen than the detonation of HE.

He hit was louder...

A function, at least in part, of its shorter duration.

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And if that delta-vee occurred in a thousandth of a second (a SWAG of how long a shell takes to detonate), that's a 12G shock (if I've got my 'rithmetic right). Easily enough to discommode a valve-based RT of the period.

First, I'm talking about AP shell. No detonation (beside 50g of HE filler). Just pure collision.

About the G-shock: And what if the delta-v occured in even shorter time ? Imagine 1/10^6 ? Would that mean the shock would be 12000g ? Such shock should pulverise whole tank, right ?

Not really. Not in 1/1000000s.

IF we managed to transfer the momentum in 1/1000000s (of course it's impossible for such large objects) then it would be really 12.000g but for a VERY SHORT TIME. Sitting in a tank or a car you wouldn't notice any difference between 12000g in 1/100000s and 12g in 1/1000s (well, the sound could be different). Because what really counts is what kind of damage can cause such impulse.

It is said that a limit of serious damage for human head in a car crash is about 50-80g.

It doesn't mean that a human head can withstand 50g - continuously. The above limit is - precisely - 80g for some miliseconds. If the time was twice as long, the g-limit would probably be about halved. And if time was halved, the limit for human head would be probably almost doubled.

Because what realy counts is what kind of damage would this head suffer in such epizode (80g for xx miliseconds). And what causes the damage ? Acceleration does ? No. A force causes damage - by deformation, and deformation in turn requires energy.

If we apply a large force (resulting in large acceleration) but for a very short time, we don't transfer enough energy to cause much damage. From some point up, it doesn't matter what acceleration is generated, if only the energy is below some threeshold that can cause damage. It's because of elasticity - the steel of the tank, the bones of the skull would simply bend or compress and accumulate the energy that was transferred in very very short time, and then release this enegy much slower transferring it to the rest of the tank/rest of the head.

Same for tank. If the "energy of the shake" is below some threeshold, you can transfer it as rapidly as you want and you won't make more damage that maximum possible - you have only X of energy and it can cause only some limited amout of damage.

On the other hand, if you transfer the energy more slowly (by gently pushing the tank) you won't' do any damage at all :).

Nothing stops instantly. It all takes time, and that sort of impact takes orders of magnitude more time to happen than the detonation of HE.

Nothing stops instantly, right. But "instantly" is good enough approximation in this case.

The point is that a shell hitting the armor transfers the momentum in very short time (about 0,3ms). But it transfers it to the part of the plate it hit. This part of the plate transfers it to the rest of the plate, and whole plate transforms it to the rest of the tank. Those plates would bulge, bend a bit, slowing the process of energy transfer.

A tank hitting a reinforced concrete wall with it's thick 10cm armor at speed of 0,5km/h would also stop very quickly - I don't expect the armor to bend much, it won't deform much, the concrete as well. I guess it would be in order of 0.01s before the whole front plate stops, and then it would stop the rest of the tank it's welded to - but again some bending and compression would happen that would slow down the process.

In both cases the energy was transferred quickly to one part of steel (one plate) and then it had to be retransferred to the rest of the tank, which took much more time as the tank is not an ideally rigid body/structure. It's elastic body.

It's fact that the shell/armor interaction was quicker than concrete/armor interaction, generating more g's - but only more g's regarding the very plate that was hit. The process of transferring the momentum to the whole tank is much longer and because of that those two cases are comparable in regard of delta-v. And comparable in that what kind of damage and how much of damage they can cause to tank internals.

I admit that AP hit can cause more hull vibrations (because of the armored plates bulging) and this can cause some more trouble for things like radio or engine valves (things vunerable to vibrations) but the overall "energy" and amplitude of the shake is very similar in both cases. Or at least I think so.

A function, at least in part, of its shorter duration.

Sometimes when duration is very short, it achieves some kind of "optimum" and there won't be much difference in physical results (damage) if you make duration even shorter.

It becomes effectively just "instant" and then only the energy of that "instant" transfer matters. Shorter time, but still same energy - results practically the same.

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The knowledge of the energy is needed for us only when it comes to the process of damaging things (outside or inside of tank). This process requires energy. Then we can think about how much energy would be spend on damaging things and how much would turn into heat harmlessly or into residual kinetic energy of various elements.

But for analysis of the collision between tank's armor plate and the shell (or tank's plate and reinforced concrete wall) and estimation of the resulting "shake" - the momentum is all that we need, kinetic energy is not usefull here at all - from the very reason that it's not retained in collisions but tends to turn (in lesser or greater part) to heat.

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I would have thought that the much greater energy of the shell collision would move the first armour plate much more (and faster) force times distance , which would vibrate the rest of the tank more, and longer. Like how a spring bounces longer from more compression. So youd have harder shaking longer. If you hit the computer downward with a hammer its still likely to break even tho your not really doing it via momentum.

It also seems like you know a lot more about this than me.

Momentum seems like how you'd get to how much that tank shakes on its suspension, rather than internally. Dont really know about this stuff tho.

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Thanks guys. I'll be taking up a collection shorty. I tried the hammer test. My PC is in pieces all over the floor and my cat is swatting dram around the room. Suffice it to say that a hammer on a pc is a bad move if you want to play CM. However I was able to confirm no one was injured so does that mean the HE shell would not have hurt anyone? Maybe I should run the test a bunch more times...this could get expensive, but you guys are good for it right?

Guess I'll have to go work in the yard for a bit for something to do while waiting for the replacement.

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I would have thought that the much greater energy of the shell collision would move the first armour plate much more (and faster) force times distance , which would vibrate the rest of the tank more, and longer.

Like how a spring bounces longer from more compression. So youd have harder shaking longer.

You are partially right, partially not.

The shell-tank collision would move the armor plate faster than tank-wall collision. So more vibrations, you are right here.

But tank-shell collision won't move the armor plate "much more" than tank-wall collision. Because it's depentant on momentum and not on kinetic energy. And momentum is same in both cases. The great kinetic energy of the shell would be dispersed to deformation of the armor and the shell and to great amounts of heat, only part of it would be actually used to propel the armor plate. How big part ? You can calculate it using momentum instead of kinetic energy. In example of tank-wall, almost all kinetic energy would be used to shake the tank, because of slow speed the loses on deformations and heat would be minimal. That's why those situations are comparable in some regards, even though there is great difference in the kinetic energies involved.

I used the tank-wall example because it's most comparable thing I could think of, that is easy to imagine for everyone.

Everyone can imagine what it feels like if a vehicle hits hard wall at a very slow speed of 0,5km/h. It's something we know from our everyday life, people are good in estimating results of collisions at slow speeds.

Not many people can "imagine" results of collisions of objects going 700m/s, because it's not a part of out everyday experience, so we can't imagine how it is like when a 10kg / 700m/s object hits a 56ton vehicle, what it feels like. I can't imagine that too. But I know physics enough to calculate another collision with same (or very similar) reaction of the tank hull, but happening at slow speeds so I can imagine it.

Good example of similar problem would be trying to imagine how it is like being hit by a bullet. It's impossible, you won't know untill you try ;). But knowing the physics, knowing that the efect you think of (how strong the "hit" would feel) is ruled by momentum conservation principle, you can calculate a different collision happening at slower speeds, closer to your everyday experience, that you CAN easily imagine.

For example if you would like how it feels to be hit by a 9mm pistol bullet, of course while wearing a bulletproof jacket - let's calculate:

7.45g * let's say 380m/s = 2,831kg * m/s.

Now we need to increase the mass to decrease the speed, BUT keep it reasonably similar in "feeling". So we WON't use a mass of 74,5kg going at a speed of 0,038m/s (so barely moving) because being "hit" by such object is something very different than being hit by a bullet. You would barely feel that because of the slow speed - even though momentum is the same. Let's think about something that can really "hit" - so maybe speed of a thrown stone, hm let it be 10m/s.

To have identical momentum as 9mm bullet, the stone have to weight 283g. Better would be to imagine a small lead weight, it would be smaller. So imagine you are hit in the chest with 283g lead weight thrown at a speed of 10m/s. This is something you can imagine. So I caan say you, that the feeling would be _similar_ like when being hit by a 9mm pistol bullet while wearing good bulletproof west (with a ceramic plate).

The results of those two collisions would be quite different, if the bullet actually hit your body and dipersed it's great kinetic energy inside your body, doing horrible damage to your internal organs.

A thrown 300g stone don't have the energy required to do such damage. If you had only a simple "kevlar" type jacket and the bullet hit you, it would break you a rib and leave a big and painfull bruise. The 300g*10m/s stone would probably only leave a bruise, and much lighter one. Again, the stone don't have enouh energy to make serious damage, it's not comparable with bullet in this area.

But as long as your body is well protected (good kevlar vest with ceramic/steel plates) and the bullet does damage only to the vest, not your body, the results behind the vest are almost identical. You feel a hard hit. Both hits would be very comparable. It's not identical, I admit. The bullet hit could feel "faster" and bit more "violent" and be louder :)

But still a thrown stone or weight is the best _comparable_ thing we can easily imagine, and in many regards the hit feels really similar.

Now the bulletproof vest that absorbs almost all of the kinetic energy of the bullet, but transfers the momentum - can be compared to the tank armored plate that is hit and deformed - almost pierced - by the shell, and your body (with internal organs) which feels only the "hit in the chest" and "shake" - can be compared to the rest of the tank - with people inside that feel the hit and various things/mechanisms that can be damaged by the shake.

If you hit the computer downward with a hammer its still likely to break even tho your not really doing it via momentum. .

You are always doing it by momentum :). Only using a light hammer or heavy hammer.

Both hammers do different kind of damage, but they use momentum to push/ove things.

Momentum seems like how you'd get to how much that tank shakes on its suspension, rather than internally. Dont really know about this stuff tho.

Momentum is always present in collisions, both slow and fast and ultra fast, for both light and fast objects and slow and heavy objects. And it's always conserved, never "disperses".

Every time you want to calculate how one object would move/behave as a whole after colliding with another object, you use momentum ONLY, forget about kinetic energy.

Kinetinc energy is not retained, it's diffused in collisions - faster the collision, greater part of kinetic energy is dispersed to deformations, heat, light, sound, ect and smaller part is "used" to push things and move them. This is why we use fast projectiles to damage something - those deformations/heat to the target is called a "damage" after all :).

It SEEMS like there is momentum important in slow collisions, and energy important in fast collisions. It's PARTILLY true - as in slow collisions energy doesn't manifest itself (no bang, sparks, holes, or explosion) and in fast collisions energy manifests itself so evidently (a flash, sparks, flames, pierced armor and lot's of damaged things) that we tend to forget about momentum.

But they are always present - both, and are always "working" - both, momentum and kinetic energy. They just do different things. Depending on what kind of effect/result you need to calculate/estimate, you choose momentum or energy in calculations. You want to know how things would move after collision - momentum only.

You want to know how much energy would be released, how much damage can be done, how much heat can be generated in collision, how much steel deformed, how much armor pierced - you use kinetic energy (or energy at all).

Cheers! :)

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I thought we were some how talking about things on the tank breaking from the impact/explosion even when they arent obviously getting hit directly, like the harddrive in the computer tower. The tanks armour shell is part of the tank, the armour shell vibrating more should make things break more, right? Maybe your back would be a little bruised along with your broken rib from the bullet from the shock wave going though?

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Yes, more vibrating of the hull could cause more damage. But my example was to show in what general ballpark the strength of the "hit" would be. Even with more vibrations, I still think it's far from doing any real damage to the tank internals. And I'm talking about AP hits only.

I do not know much stories about something inside the tank (radio, engine) damaged from the "shake" caused by an non-penetrating medium-calibre AP hit !

There are some known examples of ricochet/non-penetrating hits causing damage, but it always has beed damage to elements that were directly hit or attached to the plates that were hit, so deformations of plates caused by hit was directly transferred to those elements. But not by the "shake".

I don't know any story of an engine being damaged by a front armor AP ricochet. It's a way too small shock/shake, as I tried to explain. Maybe an 122mm AP shell hitting a Tiger (and not penetrating) would have a chance to shake it enough to do something... 85mm AP hit - I would give no chance...

As for HE shell hits on tank - I do not have enough knowledge to estimate what kind of "shake" an HE shell would make against a tank. It depends a lot on many variables - quantity of HE, at what range from the armored plate the charge detonates (so what kind of fuse is used), an probably more. I can only base on tanker's memoirs here, and known incidences.

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Thanks a lot! I wasn't doubting what you said, you've obviously taken more phyics/engineering than I, just trying to reconcile new knowledge with old. I was also thinking HE not AP. It makes sense that most of a tank would be too sturdy to be broken my internal shockwaves/vibations. What part might get damaged? Obviously the radio, but what else? rubber tubes coming out would seem to invlove more movement/bending than would happen. What about small thin metal pipes breaking? Optics getting misaligned? delicate firecontol machineworks getting damaged or are they too heavy duty?

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Maybe the shockwaves could bounce off the sides and rear to constructively intefer and break things in unexpected locations?

Good point. This could happen sometimes.

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