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HerrTom

Vehicle protection from artillery shells

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Thanks for the discussion everyone! Good to learn new things!

6 hours ago, c3k said:

Fantastic!

Obviously, the armor thickness/hardness/angle you're using in the models are going to be important. If you include that information in your final results, well, hmm, I'm not sure if I'd have any other wishes. ;) 

Great stuff...especially the analysis of how the incoming artillery angle and offset at time of detonation makes such a critical difference in airburst effectiveness against armor. (Don't have the nose of the shell pointing at the target when the shell goes "boom"; better to have the target perpendicular to the shell's line of flight.)

Angle is all there - I calculate the normals of all the polygon faces in the model to get the "angle of attack" of the fragments.  Thickness is the one that's currently 10mm all around for the BTR (which I think is fairly accurate specifically for the BTR).

 

1 hour ago, Sgt.Squarehead said:

Just a thought, but wouldn't an average of armour thickness over broad areas suffice, I'm presuming this model does not take into account the variable mass of the fragments? This would add 'fuzz' to the numbers which might actually be advantageous for gaming?

Oh, I definitely take into account the variable mass of the fragments!  That was one of my hardest-fought victories! :D   To shed some light on it - I use a couple of arrays of random numbers to figure out if there was a hit, and what the mass of the fragment was.  Programmatically:

%%%% Figure out vertices that received a hit %%%%
% Roll a random number to check for hits
roll = rand(length(V),1);
% Ignore any rolls for angles of attack greater than 90 degrees!
roll(abs(incAngle) > pi/2) = 1;
% The probabilty of a hit is the density of fragments at the vertex scaled by the area of the vertex
probHit = fragDensTgt .* areaVert;

%%%% Now we want the mass of each fragment that hit %%%%
% Convert the "number of fragments of greater mass" to a list of fragment numbers and their mass
listN        = cumsum((NOverall));
% Roll a number from 1 to N_frags to figure out what fragment number would hit each vertex (V)
massRoll    = rand(length(V),1) .* max(listN);
% Interpolate against the frag mass (mx,listN) list to figure out what the mass of the fragment was
%     This is "fuzzed" in that I didn't pull an integer, and instead interpolated the fragment number
%    I also extrapolate to prevent it from failing if it rolls a zero (which actually happened!)
fragMassTgt    = interp1(listN,mx,massRoll,'linear','extrap');

1 hour ago, Armorgunner said:

What kind of hardnes of the armour are you using? From the 350 Bmp's Sweden bought in the the late, first half of the 90's. I know they had a high brinell hardness of 350-400 IIRC. Which is quite high. Makes the armour strong, but brittle. As a comparison, the Swedish PBV 302 had a brinell hardness of 250-270 IIRC. I know that soviet used high brinell hardness steel on their Apc/ifv's at the time of BMP/BTR/MT-LB.

That's good to know.  I made the assumption of face-hardened steel, rather than high hardness steel or mild steel.  I can't specifically set the hardness of the steel since the THOR equations for penetration take a set of coefficients that are curve fit to a specific steel.  I'm limited to "high strength" "mild" and "face hardened" in addition to other metals like magnesium or aluminium.

1 hour ago, Armorgunner said:

And I can add to that. That the armor on the BMP resisted the .50 AP bullets of the time, even in the side. We (Sweden)  belived that the .50 should be able to penetrate the side armor. At weakspots it did of Course. But the armor was tougher than expected against smallarms, and HMG. But brittle when the limitation was met.

The BMPs do have much better armor than the BTRs do though.  If I remember correctly the sides are protected by fuel tanks as well as the armor plating, all acting kind of like spaced armor.  That's another pair of things I don't take into account with this model.  To do spaced armor I'd probably have to do some raytracing or something which is a lot more complexity that I don't want to get myself into.  After all, I'm not a programmer! B)  I might be able to generate a special set of coefficients to use from a curve fit of various spaced armor geometries...

 

It's worth mentioning at this point that the model as it stands is far from being real-time enough to use, for example, in black sea.  It could be significantly sped up if a lot of the tables I generated were simply presaved and read in when needed, but it's still pretty slow.  Some of the slowness comes from poor programming on my part, I'm sure, as well as making the plots and things.  But it still takes 2.99 seconds to run - too slow even if a CS person could probably speed it up 10x.

But never fear!  I do intend on simplifying or building a schematic algorithm that would easily work real-time.  We'll lose a lot of specifically simulated detail in the armor facet angles and all these other goodies, but I think we'll all be happy if we can get a reasonable result and still be able to play a game!  My plan is to devolve everything into relatively small look up tables and interpolate along the surfaces - including turning a vehicle into a few numbers describing its resistance at certain angles.  If I can make it so that we only have to look up a few things at once I'll be happy!

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HerrTom 

Now when you bring it up. I dont remember if it was facehardened, and it only was the "face" outerside that was of this hardnes. I'm sorry. The T-72M1's that Sweden bought from Germany, after the fall of the Wall.  Had facehardened steel, with much higher brinell on the surface. So if no other here have some more info? I don't know.

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I only remember the technology's fascinated voices, about the difference in the armor of our vehicles. And that they were so fascinated about the high brinelll figure in the Russian BMP. But maybe Haiduk or some other can give us more info, if its facehardened. Or have the high brinellscale right through.

Edited by Armorgunner

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HerrTom,

Found you the plate thickness breakdown for a BTR-80 over on the incredible Tankograd, whose appearance change is so extraordinary I wasn't sure I was on the right site.. The relevant portions of the armor thickness diagram are conveniently color coded. Would've provided data for a more advanced BTR, but this is as high as it goes. The material is "high hardness steel," which fits, I believe, the high Brinell numbers we've seen on Russian AFV steel going back to at least the T-34/76.  The Tankograd writeup for the BMP-2 mentions a specific type of armor steel, BT-70Sh. Bold mine.

https://thesovietarmourblog.blogspot.com/2016/05/bmp-2.html

(Fair Use)

Though the steel hull appears to be outwardly identical to the hull of the BMP-1, the BMP-2 uses a more advanced Cr-Ni-Mo steel alloy designated BT-70Sh, which is used for the new turret as well. BT-70Sh is almost exactly equivalent to the ATI 500-MIL steel used for the tests described in the aforementioned paper, as you can see for yourself in this patent mentioning the hardness of BT-70Sh (link). BT-70Sh steel has a hardness of 534 BHN when processed to the type of thin plates used on the vehicle (it becomes exponentially more difficult to treat steel to extreme levels of hardness past a certain thickness using available thermomechanical techniques at the time, and thinner plates are typically much easier to process).

(Fair Use)

PROTECTION

The BTR-80's hull is constructed from welded high hardness steel. The armour profile is resistant to most small arms fire and artillery shell splinters all around the vehicle. The roof of the vehicle is resistant to small arms fire. The windscreen is made of polycarbonate. It can only resist raindrops. The frontal profile is fully resistant to .50 caliber M2 AP bullets from at least 200m, if not closer. Generally speaking, the BTR-80 only viable as a "battle taxi".

Here is a more detailed breakdown of the armour configuration:

 
Blog.png


Upper plate: 10mm RHA @ 45° = 14mm RHA
Bow deck: N/A
Lower plate: 9mm RHA @ 45° = 12.7mm RHA
Cheeks: 9mm RHA @ 45° = 12.7mm RHA

Blast shields: 6mm RHA @ 45° = 8.4mm RHA

Upper sides: ~10mm RHA
Side hatch upper half: ~10mm RHA
Side hatch lower half: 9mm RHA
Lower sides: 9mm RHA
Lower sides (gap): 9mm RHA

Rear: 7mm RHA

Hull roof: 7mm RHA
Hull belly: 7mm RHA

Turret (all around): 7mm RHA @ 45° = 10mm RHA
Turret roof: 7mm RHA
 
Image and Data Credit: Tankograd 2014-2017 BTR-80
 
 

 

On a separate note, I'm rather surprised the rather modest 82 mm mortar HE projectile is capable of wreaking such havoc on the BTR from the side. Wouldn't have thought it could pretty much sieve the vehicle from that far away.


Regards,

John Kettler

Edited by John Kettler

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The 82mm isn't quite the armor-shredder it may have appeared.  If you land VERY close it can do some damage.

2Ige5GA.png

This is an airburst at 5 meters, 30 degrees in to aim the frags more or less directly at the BTR.  247 fragments hit the BTR, and 16 penetrated in this case.  One of those may have jammed the turret, and a couple may have wounded passengers, though most missed vital areas of the vehicle.  This is the best case scenario you can get for this shell, too.  Spray is aimed right at the side armor, and the side armor is normal to the burst, making it very vulnerable.

9kJ9Diq.png

Compare that to the ground burst, shell coming in at 30 degrees still, just hitting the ground.  Here we have 8 penetrations from 330 hits!  The armor is sloped from this angle and prevents many penetrations from occurring.  Of those 8 penetrations, a number were also on the wheels, which likely would be relatively fine.

7aUn2Sv.png

Where the 82 mm shell really shines is if it scores a direct hit on the BTR.  Then it receives 1,500 hits with over 200 penetrations.

 

Good to know my 10mm estimate was not far from the truth here!  I've been choosing the BTR as my target for this whole thread since it's relatively easy to analyse because of its relative homogeneity.  Thanks for the info John!

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2 hours ago, HerrTom said:

247 fragments hit the BTR, and 16 penetrated in this case.

That, IMHO, is why travelling opened up in a combat zone is a really bad idea!  ;)

Edited by Sgt.Squarehead

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This is more work than I put in across three different game issues combined, so I really hope someone in BF has taken note. On the plus side, in two of those cases there were changes made reasonably quickly that improved things.

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Still plugging away at this.  Found an interesting tidbit while researching tinkering around with war simulations in MATLAB.

http://www.dupuyinstitute.org/pdf/v1n6.pdf

Pages 26-29 talk about tank loss rates from artillery fire in WWII.  Through 7 cases studied, they found that an average of 12.8 percent (!) of tank losses were due to artillery fire.  It's an interesting and short read.

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5 hours ago, HerrTom said:

Still plugging away at this.  Found an interesting tidbit while researching tinkering around with war simulations in MATLAB.

http://www.dupuyinstitute.org/pdf/v1n6.pdf

Pages 26-29 talk about tank loss rates from artillery fire in WWII.  Through 7 cases studied, they found that an average of 12.8 percent (!) of tank losses were due to artillery fire.  It's an interesting and short read.

Thanks for the link. Indeed, interesting. 

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HerrTom,

Read it and found it useful, within limits, in that the level of aggregation is so high as to make it difficult to draw more than the broadest of conclusions. Also, the observer OLE (Own Location Error) is enormous relative to now, which would have considerably degraded the ability to accurately attack armor directly. Consequently, all we can do is pull, if known, the ammo expenditures for FA on the day or days in which AFVs were engaged, then look at rounds per kill and such. David Isby, writing in his Weapons and Tactics of the Soviet Army, Fully Revised Edition said, in the Artillery section something of the order of 5000 rounds were required (forget per whom, but imagine this was WW II data) to secure a direct hit on a tank. Naturally, this doesn't take into account that set of US artillery live fire tests at Soviet norms vs US tanks and APCs, for by those standards, this was practically precision fire, as opposed to conducting FFE based on a 100 yard bracket, which was typical of the period. Of course, the objectives were considerably different, and the target array in the case of the Army's test was immobile throughout. If you haven't read it, may I commend to your attention the article in that same journal on recomputing the OLIs (Operational Lethality Indexes) for the Germans in Italy? Good stuff, with some valuable insights.

Regards,

John Kettler

Edited by John Kettler

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Posted (edited)

Some more examples of tanks, hit by HE ammunition. In this case - hit in the hull top in the place of driver hatch. There is no information what exactly ammunition types hit these tanks.

34158148_2493130054046279_10379364769495

34278658_2493130184046266_43442527372113

34183731_2493130114046273_86331453860866

Edited by Haiduk

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59 minutes ago, DougPhresh said:

I think this will be especially relevant in CMSF2 as arty might be the only way for the Syrians to dent certain coalition assets.

yeah don't count on that if you play as NATO- this ain't CMBS.  :D 

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Posted (edited)

T-72B3 near Debaltsevo after 152 mm of 2A65 Giatsynt-B hit.

This is fantastic "lucky shot" - artillery spotter of 25th motorized infantry battalion told about this. Two enemy tanks approached to UKR positions on 1200 m, UKR troopers have only RPG-26 and one AT-4C Fagot with 5 missiles. All missiles failed because exhausted term of use. Spotter called battery of 55th artillery brigade on this tank, other two spotterts were preparing to make corrections, when ajustment shell of main howitzer will hit ground. Spotter heard shot of the howitzer in 10 km and explosion and... silence in the radio network. He asked: "why you don't transmit adjustments?" They answered: "No need - the turret is out"

Enemy considerd the tank was hit with ATGM, becase they seen several launches.

id6290-08.jpg

 

Edited by Haiduk

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16 hours ago, Haiduk said:

All missiles failed because exhausted term of use.

This is the bit that was most interesting.  Is built-in obsolescence now normal for weapons systems/  Rather scary if one has to check "expiration dates" on ones weapons systems like they are groceries.

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1 hour ago, Erwin said:

This is the bit that was most interesting.  Is built-in obsolescence now normal for weapons systems/  Rather scary if one has to check "expiration dates" on ones weapons systems like they are groceries.

A 50-year-old (most likely horribly stored) missile has my permission to fail anytime it wants :P 

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1 hour ago, Erwin said:

This is the bit that was most interesting.  Is built-in obsolescence now normal for weapons systems/  Rather scary if one has to check "expiration dates" on ones weapons systems like they are groceries.

The trouble primarily is that the rocket propellant degrades, which could make it not launch or injure the operator. The explosives too, but I think it's to a lesser extent.

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In most cases such missiles either don't want to launch itself, or fly on weird trejectories. Soldiers told, average number of Fagot missiles fails is 30% - those guys were not lucky, probably because of old missiles were long time on open position on the frost and high humidity.

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All of the above responses make perfect sense.  FAGOT 4C was introduced in 1970.  RPG-26 started service in 1980's.  But surely not ALL of the missiles were from initial years.   

The Stinger was supposed to be unusable in a decade or less due to battery failure - but the Taliban figured out how to use a car battery to enable it to fire again.  

Am wondering about the built in obsolescence issue.  Old fridges used to last for decades, now new ones break down in under 10 years etc.

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