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CIWS dispersion and addition of MK149 shell


nighthawk2174
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This is a supplemental thread at the request of 9L. I want to make the case that the dispersion for the CIWS system on ships is exceptionally high. Documentation indicates it should be less than 1 milliradian yet in game it uses the same 22+ seen on the airborne guns. This is a difference of over 2200%. In addition to this there is the MK141 shell that these guns use that is not used in game. This shell (as far as I can tell) is apds shell with a red tracer. That seems to have a significantly reduced drag shape over the standard M56 shells in game.

 

copied from my reddit post on the subject of dispersion:

Quote
CIWS

 

As of right now American CIWS uses the exact same dispersion values as the aircraft guns. Here though is truly the case that makes the least sense for the current DCS values. These values are catastrophically high for a system where:

 

x5r18Qi.png

-Note the changes that were recommended were made to US CIWS so the 2mill values here are before the introduction of additional bracing.

 

66CkfTt.png

0.97 for the Mk 149 and 0.56 milliradians for the Mk244 respectively

 

There can be no doubt by just watching any video with CRAM (the exact same gun as CIWS on modern US ships) that the dispersion is wrong and needs to be reduced drastically to be accurate…

 

 


Edited by nighthawk2174
APDS shell without tracer or HE filler.
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With the release of the SC soon just wanted to bump this

htS5Pbo.png

X6x3hPa.jpg

GKKargB.jpg

As you can see not just the dispersion but the kinematic performance of the MK149 round is signifigantly higher, at sea level it doesn't even go subsonic until its traveled ~4km.

 

Some stats:

MK-149 APDS

V0 = 1160m/s

Dispersion = ~.7-.9mills

Round mass = ~74.1g for tungsten and ~73.3g for DU (assuming solid slug as per diagram)

Explosives = not sure, at first I thought there was but i'm not so sure anymore.

Caliber = 12mm (subcaliber shell)

Drag = No data but should be quite good the shell slows down much slower than the PGU

Tracer = None


Edited by nighthawk2174
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Currently it uses the same rounds as all the other vulcuns minus F16 PGU. Which is a much slower shell with a much higher dispersion than what it should have.

 

And considering more than 1mill of dispersion is considered unsatisfactory well...

jgTJNp7.jpg (note this was a paper about how to improve the CIWS's dispersion and the method they came up with was ultimantly adapted)

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Oh I thought you were talking about the WW2 gun accuracy for a second there, unfortunately I'm afraid this is too much out of my expertise at the moment to have anything worthwhile to say.

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+999

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+1 would love for these systems to have their correct rounds (namely the Mk149 an later the Mk244) APDS projectiles (both untraced).

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Modules I own: F-14A/B, F/A-18C, Supercarrier, F-16CM, AJS-37, F-5E-3, MiG-21bis, Ka-50, A-10C (+ A-10C II), UH-1H, Mi-8MTV2, P-47D, P-51D, FC3, MiG-15bis, Yak-52, CA, C-101, Hawk

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  • nighthawk2174 changed the title to CIWS dispersion and addition of MK149 shell
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  • 1 month later...
On 3/13/2020 at 5:11 AM, nighthawk2174 said:

This is a supplemental thread at the request of 9L. I want to make the case that the dispersion for the CIWS system on ships is exceptionally high. Documentation indicates it should be less than 1 milliradian yet in game it uses the same 22+ seen on the airborne guns. This is a difference of over 2200%. In addition to this there is the MK141 shell that these guns use that is not used in game. This shell (as far as I can tell) is apds shell with a red tracer. That seems to have a significantly reduced drag shape over the standard M56 shells in game.

 

copied from my reddit post on the subject of dispersion:

 

Speaking about dispersion we must specify what measurement unit of dispersion is used:
D100%
D80%
D50%
R100%
R80%
R50%
vertical/horisontal median or
standard deviation.

It's like a values - the same value but in different currencies (but fortunately  the exchange rate is constant)

So, stating about 1 mil "dispersion" what currency, sorry, unit did you mean?

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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Posted (edited)

@Yo-Yo, the document fragment above already gives you some numbers, the dispersion having been measured at between 0.9mrad to 2mrad, and specifically stating 2mrad = 4m at 2000m.  While the CEP error percentage isn't offered, it's probably not quite as big of a deal as these numbers (but obviously it is a factor because it determines the density of rounds in a given volume).  I think the document is needed to determine the conclusion of the matter (ie. what IS the dispersion?) - and also some interesting information about the rounds used in Phalanx is given above, specifically time-to-distance.

 

@nighthawk2174, is there a link to the rest of the document?  I think at this point the best move is to provide Yo-Yo with as much relevant information as there is.


Edited by GGTharos
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33 minutes ago, Yo-Yo said:

Speaking about dispersion we must specify what measurement unit of dispersion is used:
D100%
D80%
D50%
R100%
R80%
R50%
vertical/horisontal median or
standard deviation.

It's like a values - the same value but in different currencies (but fortunately  the exchange rate is constant)

So, stating about 1 mil "dispersion" what currency, sorry, unit did you mean?

@Yo-Yo @GGTharos For the study initially referenced the values referenced are for a circular area representing the total 100% circle:

image.png

Normal modes of vibration of the PHALANX gun : Peterschmidt, John C. : Free Download, Borrow, and Streaming : Internet Archive

image.png

image.png

Correlation of bullet dispersion and transverse barrel tip displacement on a firing PHALANX gun system : Cela, David : Free Download, Borrow, and Streaming : Internet Archive

It was noticed, according the document linked below, that when better measuring equipment came online that the dispersion for the system was higher than expected.  While each barrel fired individually was averaging near the 1milliradian dispersion total.  When in full use (especially with longer bursts) these values would rise up towards 2mills which was considered unacceptable.  Essentially the document was a study looking to reduce the then current measured range of average 100% dispersion values from the .9-2milliradian range down to the desired sub 1milliradian.  Keep in mind when Phalanx first came out it looked like the below sample lacking the additional bracing structure seen nowadays.  In addition to this new barrels were given to the system starting on the block 1B further reducing dispersion.  These barrels were not part of the study above so the values seen in the study would be further reduced with the addition of these barrels.
Phalanx_CIWS_-_ID_061001-N-4207M-023.jpg

Now ofc something else to consider is the MK 244 round which entered service in 2004.   Which from the documents shown above reduces dispersion by a further 40% over the MK 149.  Which considering the time period of most of the aircraft being added to DCS right now may be worth adding. 

shell("M61_20_MK149", _("MK-149 APDS"), {
  model_name     = "tracer_bullet_red",
  v0             = 1160.0,
  Dv0            = 0.0060, --https://forums.eagle.ru/showthread.php?t=266214
  Da0            = 0.00008, --Block 1B with reduced dispersion barrles factored in
  Da1            = 0.00008,
  mass           = 0.0741, --Tungsten penetrator is 74.1g
  round_mass     = 0.253,
  cartridge_mass = 0,			
  explosive      = 0.0,
  life_time      = 16.0,
  caliber        = 12.75, --Is SubCalliber Shell; Diamater of 12.75mm
  s              = 0.0,
  j              = 0.0,
  l              = 0.0,
  charTime       = 0,
  cx             = {0.12,0.7,0.80,0.22,1.9}, --just a copy paste of PGU drag values will be different
  k1             = 2.0e-08,
  tracer_on      = 0,
  tracer_off     = 0,
  scale_tracer   = 0, 
  name           = "MK149 APDS",
  cartridge      = 0,
});

These are the stats I was able to gather on the MK-149 round, although the MK244 round should ED choose to add it (which I think they should) would have different values.

 

of note also:

image.png

image.png

Something to note for the aircraft guns as the values currently being used are the worst possible values allowable for a gun to pass.  Hopefully you'll consider this in relation to the airborne Vulcans.

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You just misinterpreted the definition from the articles. If you read the whole material you can find the direct statement what unit is used at the page 4: 1.4 mrad at one standard deviation according to "Notes from Hughes Missile Systems Company, Pomona, California, 23 October 1992." 
Returning to the manufacturer's data for aircraft gun and calculating standard deviation from D80% we get 2.2 mrad at one standard deviation, so the addition of restraint framework enhanced dispersion only by 50% that is far away from 2200%...

Page 4.png
One of the tests result  the second article was based on is shown at the second picture in your post, and this pattern is in full accordance with the ~ 1 mil (at std deviation, as it was stated). The 50% difference between the manufacturers data and the test results for a single specimen can be explained for example that the manufacturer provides the worst or the most probable result for a several specimens in batch production.

Dispersion Phalanx.png

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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We can add this reduced dispersion for the navy variants, yes. If some reliable sources exist for this new barrel we can take a look.

 

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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I unfortunately haven't found any good sources for the OGB's yet only that they were longer, made thicker, and had a redesigned end brace holding the barrels together.  But considering that the biggest contributor to the dispersion for the gun according to the above sources is the deformation of the barrels due to rotational forces this makes sense.  The above document lists a 40% reduction over the MK149 and I see no reason to doubt that.  As these rounds were designed to work with the new barrels and are listed as being incompatible with the older barrels. 

 

Additionally if you guys do add the MK244 shell something I've had worries about that I'm hopping you can also make note of is both the max range and the reaction time of the system.  I unfortunately don't have access to the lua files anymore but this was something that I changed was both the system reaction time and max range.  CIWS while in combat can be set to an automatic targeting mode not requiring any human input allowing rapid engagements the moment targets came in range, iirc there is a significant delay in DCS.  Not only this but the system is meant to be trying to hit targets at the limits of its range with a controlled burst.  Currently the system will only begin the engagement process once a target hits this Rmax and then with the delay it allows the target to get much closer.  

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Posted (edited)

Here's a 2017 Army PDF giving stats for Mk.244. The round is stated to fire 1,950 grain/126 gram projectile at 3,610 fps/1,100m/s

 

There's also this 1975 DOD Appropriations hearing, Phalanx is stated to fire a 1100 grain projectile. I'm not sure how accurate that is, as this is an early version with the DU rounds not tungsten, but should be interesting.

 

Dimensional sketch

WNUS_Phalanx_Mark-149_sketch_pic.jpg

 

An older 2002 Mk149 brochure giving a bit more info, including penetration


Edited by Mandolin
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