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Operatsiya_Ivy

[BUG REPORT] 20mm HE Ammunition

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Well laid out case - but I agree not necessarily a bug. I would guess that the reason the Hispano comes off better in game than in your comparison is that the developers did not think that comparing total energy was the right approach. It has the largest KE by some distance, so perhaps that is weighted more.  If you were to perform identical tests with AP ammunition, where it is all KE, you could probably calculate the KE/CE ratio used by the HE shells.

 

Question on the test - it is a little ambiguous how many tests you did: there are 9 different gun/plane combinations, did you do 100 tests to destruction for each combination? (That is a lot - well done).

 

On other thing stands out when combining the effect of gun and damage - for any gun, the Yak took fewer hits to lose it's wing to HE than the Spitfire or 109. So people who think the Yak is too robust should aim at the wings!  

 

 

Edited by unreasonable
edit - whoops, KE obviously, not PE

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Energy amounts are useful for "physical accounting" but it is momentum and pressure which break things. Rounds' total E gives some insight but doesn't explain what is actually happening or what should happen.

 

The shot's speed may affect explosive effects as well - the shock wave could be modulated by the round's original vector and shell shape. Explosives differ in more ways than the energy content per gram (like detonation velocity). Then we have fragmentation with multitude of variables...

Edited by Ehret
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Thank you for building on top of my results and actually comparing them with something. 

6 hours ago, Operation_Ivy said:

Formula:

 

Kinetic energy: Joules = 0.5*mass*velocity^2

+

Chemical energy: Joules = explosive filling*explosive energy of the explosive

 

I propose that you do the following test. Compare the HE shells vs inner HE shells. That is, repeat the test bank, but replacing the impact HE damage, for a round with 0 explosive charge. This way you "should" be able to estimate how much of the damage is coming from the kinectic energy and how much is coming from the explosive charge.

 

cheers!

 

 

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Test results show how the Shvak is just as good as the Minenegeschoss and Hispano about twice as good as the others.

There is no reason to justify this and with regards to evidence totally implausible.

It is absolutley mind boggling to me how people still defend status quo with all types of explanations.

It is so obvious yet there seems to be no limit to the amount of argument construction in order to defend status quo.

If it looks like fish and smells like fish we probably just haven’t found the horns and hoofs... 😂

 

I think you did a very good job OperationIvy thanks for the testing.

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3 hours ago, =EXPEND=SchwarzeDreizehn said:

Test results show how the Shvak is just as good as the Minenegeschoss and Hispano about twice as good as the others.

There is no reason to justify this and with regards to evidence totally implausible.

It is absolutley mind boggling to me how people still defend status quo with all types of explanations.

 

There is something off but you are making a mistake by reducing everything to a single (total E) number. For an example the brisance of explosive does matter too and higher (like PETN has) is not always better because it can inhibit effective fragmentation.

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No I am exactly not doing that. Forget all the complex models that everyone muses about there being in the game or not.

Simply look at the result of the test. The result is

Minengeschoss = Shvak = 0.5 x Hispano.

It is off by a big margin. No way to support that

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At the risk of telling complete nonsens (read: correct me if I'm wrong):

Assuming a direct hit, I would expect all kinetic energy from a shell to be absorbed by the plane that got hit.

However, the explosive energy would be distributed evenly in 3 dimensions.

As the shells don't have no delayed fuze (?), this would theoretically mean that at least (depending on the hit point, could be more) half of the explosive energy would not "hit" the plane, but would be wasted into free space.

 

In numbers, the destructive energy compared here, as listed in post 1...

 

Minengeschoss = 138847

ShVAK = 39920

Hispano = 98461

 

...would change to...

 

Minengeschoss = 84514 (-39%)

ShVAK = 34158 (-14%)

Hispano = 74399 (-24%)

 

This would still fail to support the test results, but at least point into their direction compared to where we're coming from.

 

Cheers!

Mike

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Hello Ivy,
maybe it is possible to get some data for this special topic.
It is possible to order some Reports from the Bundesarchiv:
https://www.bundesarchiv.de/DE/Navigation/Home/home.html
The files are:
RL 39/27
Die Detonation eines 2 cm M - Geschosses.- Bericht 5/42 (Bearbeiter: Struth, Burkhardt und Turetschek)
1942
RL 39/664
Zur Beschussfestigkeit von Metallflugzeugen gegen Minenmunition
ca. 1943
RL 39/841
Die Detonation eines 2 cm M-Geschosses. - Forschungsbericht Nr. 1601 (Bearbeiter: Struth, Burkhardt und Turetschek)
1942

I have given the intel about this source the devs months ago, so it is possible that they will use this in the future.

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The bigger fragments have higher inertia so they can travel longer/deeper into target's structure. The M-shell is (almost) purely explosive - the damage is by pressure wave, mainly. It's strong but could dissipate quickly but what exactly would happen? The game  is supposed to model HE by multitude of small fragments. It could be they decelerate too quickly or their quantity is still insufficient.

 

Historically Hispano 20mm and MG151/20 were equally matched, overall. The former had better ballistic but was heavier. The latter had faster cycling rate and high HE content would make up for lighter projectiles.

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That's roughly what I'm suspecting as well.

And if it's mainly a blast wave effect caused by the thin-walled Minengeschoß, then we have to remember that blast waves are getting reflected by surfaces like plane's metal skin, so the effect would even be smaller.

 

Not trying to conclude anything, just saying.

 

Cheers!

Mike

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I am currently preparing part 2 which i will edit to a later date. I don't have much time in the coming days but let me just hop in here real quick.

 

The Hispano cannon ingame file says it got 47 fragments. The Minengeschoss only 30. I suspected that this might be one reason for the big damage difference. I gave the Hispano the number and attributes of the Minengeschoss Fragments. A short test showed no big difference in performance (Avg=2,3 Sdv=0.82 against a F-4 wing). So far i failed to "nerf" the Hispano to a Minengeschoss even when i swapped out 90% of the values.

Edited by Operation_Ivy
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48 minutes ago, SAS_Storebror said:

At the risk of telling complete nonsens (read: correct me if I'm wrong):

Assuming a direct hit, I would expect all kinetic energy from a shell to be absorbed by the plane that got hit.

However, the explosive energy would be distributed evenly in 3 dimensions.

As the shells don't have no delayed fuze (?), this would theoretically mean that at least (depending on the hit point, could be more) half of the explosive energy would not "hit" the plane, but would be wasted into free space.

 

 

Being pedantic, I think that the kinetic energy of the whole shell gets transfered to the various parts of the shell after it explodes: it will only transfer to the target plane to the extent that the shell's components - including the gases that the HE filling has transformed into -  impact the target plane and stop moving.

 

So the KE transfer would also only be partial too. 

6 minutes ago, Operation_Ivy said:

I am currently preparing part 2 which i will edit to a later date. I don't have much time in the coming days but let me just hop in here real quick.

 

The Hispano cannon ingame file says it got 47 fragments. The Minengeschoss only 30. I suspected that this might be one reason for the big damage difference. I gave the Hispano the number and attributes of the Minengeschoss Fragments. A short test showed no big difference in performance (Avg=2,3 Sdv=0.82 against a F-4 wing). So far i failed to "nerf" the Hispano to a Minengeschoss even when i swapped out 90% of the values.

 

If you can edit the file variables, why not change all of the MG151/20 to the Hispano's values, and vice versa. ;)  (Ie see if there are any hidden variables).

 

 

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Specific energy of explosive transformation for A-IX-2 is 6350 - 6480 kJ/kg

Not 1750 as in "test source data"

Edited by Brano
units

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19 minutes ago, Brano said:

Specific energy of explosive transformation for A-IX-2 is 6350 - 6480 kJ/kg

Not 1750 as in "test source data"

 

If you give me a source i will gladly change it. Especially because it would deliver more realistic results. It would still deliver the smallest amount of energy 

 

"soviet cannon" by Christian koll states it with 1750 though.

Edited by Operation_Ivy

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Thanks for doing the tests Operation_Ivy! :good:

 

I agree with your conclusions that when it comes to de-winging an airplane, HE/Mingeschoss hits should in general have a higher lethality than AP:

 

As an engineer who has worked with aircraft structures, I would be more concerned with a hit in the wing from a HE/Mingeschoss round than an AP: Sure, if the AP hits a “single point of failure” part of the structure like a wing spar cap or the wing-fuselage connection then sure the wing goes off. But those are small isolated parts not very likely to be hit. Most of the structure of a wing provides so-called alternative load paths meaning you will for a hit anywhere else certainly lose some of the structural strength but in most cases the wing won’t fail. That is not the case with the HE/Mingeschoss rounds which as opposed to the AP punching a nice 20 mm hole will blow out wing panels, control surfaces, bellcranks, jam control rods etc. So in general, a HE/Mingeschoss round should score a higher hit point when hitting structure. At least this is certainly true with the smaller volumes encountered in a fighter size targets wing or empennage. So while a larger structure like a bomber fuselage may be able to vent the pressure enough to avoid failing, the tighter confines of a fighter wing means a HE/mingeschoss round hit is as a rule much more bad news than an AP hit.

 

However, as we know this is not the state of affairs in the current DM modelling where a Hispano hit in the wing seems to count for more than a MG151 hit. Since the DM seems to work with hitboxes and points, one way around this would be to introduce a simple factor of how much damage the calculated sum of the kinetic plus chemical energy does depending on where they hit. Instead of always calculating with the sum which IMHO would turn the tables and instead make the HE/Mingeschoss rounds more effective than they should, a factor could be applied if the round hits structure or engine, armour or other parts more susceptible to AP. So, as an example: say the total kinetic and chemical energy of a round was E_tot= E_kin+E_chem, then if the round hits structure, the hit scores E_tot= E_kin*F1+E_chem*F2 and if it hits engine, E_tot= E_kin*F2+E_chem*F1, where F1<<F2.

 

An even simpler approach would be to retain the “score” points we have today and use the factors F1 and F2 depending on which round hits where: An AP hit in wing is factored with F1 while and HE/Mingeschoss with F2 und so weiter……

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Nice post 👍

 

We could also work in seeing how much the KE has an effect in this. We could compare with AP rounds modified to have the same velocity and weight as the HE ones, or having the HE ones have 0 explosive filler. Most probably this is a big player in the performance differences. However looks like it had some part in overall effectivenes IRL, seeing how the Hispano and MG 151/20 were similar apparently despite the bigger explosive load in the German round. Or maybe the physical relation between explosive power and destructiveness has a constant that makes the differences less important (for example twice the explosive weight only makes it 50% more destructive or something like that). 

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Yes, I think the ideas you outline are also good ways to tune the DM. I mean I think we all are just trying to make a god thing even better because I'm really impressed by the IL-2 DM and I think the developers have done a great job but that does not mean that some things can't be made even better and while an AP hitting the engine block or back armour should score high, an AP punching a hole through a wing in a high deflection pass should score pretty low. I think the method you proposed is probably also an option or to keep the development effort down do like unreasonable proposed earlier: Set the damage points for MG151 hits in wing structure equal to that of Hispanos or vice versa. While I would prefer the other options, doing that would at least be a step in the right direction. :)

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The Hispano 20mm round used in the test was the HE, not an AP...

It should generate bigger fragments and some incendiary effect thus probability hitting something important is higher than just a plain AP.

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I think it have huge difference if you are shooting 151/20 from targets direct 6, or some other angle, deflection. 151/20 is especially weak when shooting from direct 6. Or VVS planes have too durable tailsection. I would like to see a test about that. I cant do it thou. Even the wngs can take more hits from direct six than deflection shots.

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On 6/10/2018 at 2:59 PM, VesseL said:

I think it have huge difference if you are shooting 151/20 from targets direct 6, or some other angle, deflection. 151/20 is especially weak when shooting from direct 6. Or VVS planes have too durable tailsection. I would like to see a test about that. I cant do it thou. Even the wngs can take more hits from direct six than deflection shots.

 

Yaks have fuselages based on truss like structures instead of more modern semi-monocoque. This may explain resilience to HE hits. The Lagg, La5s and Mig3 seem to have s-monocoq, thought.

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On 6/10/2018 at 7:59 PM, VesseL said:

I think it have huge difference if you are shooting 151/20 from targets direct 6, or some other angle, deflection. 151/20 is especially weak when shooting from direct 6. Or VVS planes have too durable tailsection. I would like to see a test about that. I cant do it thou. Even the wngs can take more hits from direct six than deflection shots.

 

I had noticed that too - HE hits on planes from the rear quarter often appear to hit the trailing edge of wing or tail and explode without any visible damage, while a hit square onto the wing or tail has a good chance of taking a piece off.  That does not mean that they have done no damage: perhaps just not enough to trigger the holy decal or loss of pieces.

 

On the one hand I wonder if the trajectory of the fragments takes into account their inertia as part of the shell - apart from the base plate and nose unit, the splinters from an HE shell will all travel sideways and forwards creating a hollow conical damage zone, not a sphere.

 

On the other hand, even if the splinters are moving forwards, when an HE shell is set off at the trailing edge only a very small proportion of fragments are going to hit the wing: the vast majority will go above or below. Obviously the further into the wing the shell travels before exploding the larger the area of the target that can be hit.  But the angle at which an HE shell hits should make a great difference to the damage, just as it should for AP.  

 

My hypothesis is that AP "likes" low deflection shots so that the shells can pass through the structure until they hit something important, and do not like high deflection shots where they will usually just make a neat hole.  In contrast, HE shells should "like" a high deflection shot so that all the fragments have a chance of hitting something. 

 

(Leaving the German mine shells out of the equation.)

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Maybe it is modeled the way that HE ammo from direct 6 will often bounce off from the wings ( or planes) skin and explode in the air and not inside the plane. Some bullets would do that irl too im sure, but it should be about the same with all ( HE ) ammo.

 

Thanks Operation_Ivy and Pupo and all!

Edited by VesseL
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I updated the OP with another Test.

 

On 6/8/2018 at 2:54 PM, unreasonable said:

If you can edit the file variables, why not change all of the MG151/20 to the Hispano's values, and vice versa. ;)  (Ie see if there are any hidden variables).

 

I tested it and there are no hidden variables

 

On 6/8/2018 at 3:10 PM, Brano said:

Specific energy of explosive transformation for A-IX-2 is 6350 - 6480 kJ/kg

Not 1750 as in "test source data"

 

I updated the explosive energy of A-IX-2. However, calculating it with its RE factor of 1.54, it resulted in it having only 5390 kg kilo joules. Thanks @JaffaCake for pointing out that mistake

 

On 6/10/2018 at 2:59 PM, VesseL said:

I think it have huge difference if you are shooting 151/20 from targets direct 6, or some other angle, deflection. 151/20 is especially weak when shooting from direct 6. Or VVS planes have too durable tailsection. I would like to see a test about that. I cant do it thou. Even the wngs can take more hits from direct six than deflection shots.

 

The tests weren't conducted from dead 6. The shots were taking from 6 at an angle of roughly 25-30%. In the future i am going to conduct a test on the tail section.

 

10 hours ago, unreasonable said:

On the one hand I wonder if the trajectory of the fragments takes into account their inertia as part of the shell - apart from the base plate and nose unit, the splinters from an HE shell will all travel sideways and forwards creating a hollow conical damage zone, not a sphere.

 

On the other hand, even if the splinters are moving forwards, when an HE shell is set off at the trailing edge only a very small proportion of fragments are going to hit the wing: the vast majority will go above or below. Obviously the further into the wing the shell travels before exploding the larger the area of the target that can be hit.  But the angle at which an HE shell hits should make a great difference to the damage, just as it should for AP.  

 

I doubt that it is modeled to such an degree. It would also apply to all HE shells and, if modeled correctly, would actually speak in favor of the Minengeschoss.

 

1 hour ago, VesseL said:

Maybe it is modeled the way that HE ammo from direct 6 will often bounce off from the wings ( or planes) skin and explode in the air and not inside the plane. Some bullets would do that irl too im sure, but it should be about the same with all ( HE ) ammo.

 

Thanks Operation_Ivy and Pupo and all!

 

As far as i understand the in game files correctly, the ShVAK and Minengeschoss cannot ricochet off the target. 

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On 6/12/2018 at 5:19 PM, Operation_Ivy said:

I updated the explosive energy of A-IX-2. However, calculating it with its RE factor of 1.54, it resulted in it having only 5390 kg kilo joules. Thanks @JaffaCake for pointing out that mistake

 

I disagree. You cant use coefficient/factor,of which we dont know how it was calculated, to simply decrease empiricly measured
explosive energy of a mixture. What is your reference for TNT equivalent? TNT  can have large range of energy released
during explosion (from ~2500 up to ~6000 kJ/kg) depending on many factors. I have seen studies with ~4200 kJ/kg but also with
values of ~5800 kJ/kg as TNT equivalent.
I have posted my source of empirically measured explosive energy of different mixtures used by Russian military. For your formula any TNT
equivalent coefficient is irrelevant. So if you want to have a comparable results,use empiricaly measured values.
For M-geschoss
PETN was never used in its pure form as explosive.It is too sensitive and a small amount of mechanical shock could set it off.
For more representative evaluation,you should use 2 different 20mm M-geschoss

 

1. for MG.FF cannon,that would represent older ammo of 1941/mid 1942 
This ammo used so called Pentrit A explosive mixture consisting of 80% PETN and 20% aluminium grit
5700-5800 kJ/kg seems plausible for pure PETN. We need specifically measured value for the mixture Pentrit A.

 

2. for MG151/20 representing ammo from mid 1942 onwards
Fullung 25 aka HA41 mixture (mentioned in march 1942 edition of aircraft ammo manual) consisting of 80% Hexogen and 20% of aluminium powder

= almost identical composition to russian A-IX-2 6400 kJ/kg...but would be better if someone has got specificaly measured value for it.

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13 minutes ago, Brano said:

 

I disagree. You cant use coefficient/factor,of which we dont know how it was calculated, to simply decrease empiricly measured
explosive energy of a mixture. What is your reference for TNT equivalent? TNT  can have large range of energy released
during explosion (from ~2500 up to ~6000 kJ/kg) depending on many factors. I have seen studies with ~4200 kJ/kg but also with
values of ~5800 kJ/kg as TNT equivalent. 

.....

 

 

 

Explosive energy does not translate directly into damage. Which is why RE, or "TNT-equivalent" is a commonly used measurement of how destructive the explosive is. RE is used to calculate precise charge sizes for demolition work with non TNT explosives (rather than directly using the explosive energy of the material) https://en.wikipedia.org/wiki/TNT_equivalent#Relative_effectiveness_factor.

 

While both can be used, RE provides a more accurate estimate of the expected destructiveness of the charge. Even with variances in RE equivalents.

 

PS. your point regarding the PETN mixture may force the use of original CE anyway, as I doubt RE would be available for the mixture used.

Edited by JaffaCake

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13 minutes ago, Brano said:

I have posted my source of empirically measured explosive energy of different mixtures used by Russian military. For your formula any TNT
equivalent coefficient is irrelevant. So if you want to have a comparable results,use empiricaly measured values.

 

I told you that i am not able to make use of your table without any further notes because i am not able to read russian. That's why i asked your for english sources. 

 

The RE factor is even used in the in game files. 0.02=Minengeschoss, 0.0026=ShVAK 20mm HE and 0.0113 for Hispano 20mm HE. Obviously this is just an artificial number for the game, however it is supposed to imitate the actual values.

 

15 minutes ago, Brano said:

For M-geschoss
PETN was never used in its pure form as explosive.It is too sensitive and a small amount of mechanical shock could set it off.
For more representative evaluation,you should use 2 different 20mm M-geschoss

 

1. for MG.FF cannon,that would represent older ammo of 1941/mid 1942 
This ammo used so called Pentrit A explosive mixture consisting of 80% PETN and 20% aluminium grit
5700-5800 kJ/kg seems plausible for pure PETN. We need specifically measured value for the mixture Pentrit A.

 

2. for MG151/20 representing ammo from mid 1942 onwards
Fullung 25 aka HA41 mixture (mentioned in march 1942 edition of aircraft ammo manual) consisting of 80% Hexogen and 20% of aluminium powder

= almost identical composition to russian A-IX-2 6400 kJ/kg...but would be better if someone has got specificaly measured value for it.

 

I am aware of this but due to lack of historical sources i went with PETN. Like i said in the OP, it would be great if someone could deliver actual sources to make the calculations more accurate.

 

In the end this discussion is tedious without having a big impact on the bigger picture overall. If someone provides good and comprehensible sources, i am happy to change the explosive energy. However it won't explain the real issue at hand.

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Hi Ivy,

It was not my aim to upset you or make the discussion tedious. Neither your test nor bug report is of any special interest to me...or as native english speakers use to say "I have no horse in this race".

 I just expressed my oppinion on input data and explosive mixture types. You must admit that setting value of A-IX-2 at level of badly mixed medieval black powder is a good trigger to step into discussion.

 So carry on and dont be discouraged by my useless rant 😉

 

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No worries, sorry if i came across in an upset way. I appreciate every input. What i wanted to say is that in the bigger picture, this discussion isn't changing anything. 

 

Again, if i am provided with comprehensible sources i am gladly to edit my post. In the end getting more accurate is a very good thing. 

Edited by Operation_Ivy

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1 hour ago, Operation_Ivy said:

I am considering this post a report to the devs

You should. If you dont they will do nothing. 

There are a lot of test there and I made a long time before a video when the problem was even worse. I consider it acceptable after the change regarding to the power of the ammo but your test is a detailed analysis about mostly everything can be tested so will be precious information and the most complete report they can have from comunity. 

 

The only thing I am missing here is the disperssion of the armament on the game and the efective range. A small diference on muzzle velocity on the Svak compared to Mg151 seems to have a big effect in long distance shots. And with no disperssion at all is quite frustraring to get headshoted from +700m with ease on this game. Would be nice to test and to get facts comparing this situation on the game with a real comparation about effective ranges etc. 

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