fixed Cannon round dispersion is too high - gun

[Bucic]

The guy has posted an excerpt from the actual maintenance manual.

 

Also, a swiss documentary titled 'Helvetic Tiger' contains a scene from actual fire tests. At least one.

 

 

Quote

 

Members

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Posted September 1, 2020 (edited)

Sorry to bump but was this ever looked into?

 

ED updated the dispersion for the guns on the F18 + F16 a few months back. Will we see any changes to the F5 or is what we have right now accurate?

 

Thanks,

 

EDIT

 

Took a look at the shell_table.lau that was mentioned earlier in this thread.

 

Seems like ED changed the Da0 value of the M61 from 0.0022 to 0.0015.

 

However, the Da0 value of the M39 is still set as 0.0022.

Edited September 1, 2020 by Grisleybear

 

 

Quote

Currently, the F-5's gun spread is about 30-40 mil (equivalent to a 300-400cm diameter group at 100m). According to the Northrup document, 80% of shots should fall in an 8 mil area (equivalent to a 80cm diameter group at 100m).

https://forum.dcs.world/topic/153180-reportedgun-dispersion/page/2/#findComment-3171628

 

About relative differences:
 

Quote

 

 Aries144 Posted August 15, 2017

So, I just looked in the files and found that the M61 Vulcan, GAU-8 Avenger, and M39 guns have 3x - 4x larger dispersion than the other aircraft guns in the game.

The Mig-29/Su-27 gun is 0.0005 while the F-15 and F-5's guns are 0.0022. The Su-25's gun is set to 0.0005 and the A-10's GAU-8 is set to 0.0017. It appears to correspond to mil. 0.0005 would be 5 mil while 0.0022 would be 22 mil, etc.

I'd really like to hear ED or Belsimtek's reasoning for these decisions. Is it a matter of compensating for some imbalance elsewhere? Gameplay? Based on some sources other than manufacturer's data?

 

 

Please re-investigate the issue.

For anyone wanting to investigate on their own, in accordance with a post by @Aries144

Posted December 23, 2017

New information incoming. I just discovered that it is possible to freeze the aircraft using active pause, decelerate time using alt z, and shoot the cannon in slow motion with no movement of the aircraft. This will make the next videos posted here as accurate as if the aircraft were stationary on the ground!

 

 

 

Other references:

@GGTharosmentions M39 here, plus other M39 mentions

https://forum.dcs.world/topic/168522-bug-report-f-15-gun-accuracy-does-not-match-sources

 

https://forum.dcs.world/topic/155394-f-5-gun-dispersion/

 

 

cannon mod

https://www.digitalcombatsimulator.com/en/files/3151874/

 

ED @NineLine@BIGNEWY@USSR_Rik@Mr.Pitt@f-18hornet

SME @Kev2go @Gianlc@VPS_SPIT@GGTharos

U @LazerPotatoe@Ramsay@Sarge55

Edited January 23 by Bucic

[Bucic]

Fixed in yesterday's update. Any airquakers up for confirming?

Edited February 20 by Bucic

[nairb121]

38 minutes ago, Bucic said:

Fixed in yesterday's update. Any airquakers up for confirming?

I've not tried it myself yet, but I have been told that it's much improved. Hopefully I'll get to see for myself tonight (and find out whether it'll make me hit more, or less!)

[Bucic]

19 minutes ago, nairb121 said:

I've not tried it myself yet, but I have been told that it's much improved. Hopefully I'll get to see for myself tonight (and find out whether it'll make me hit more, or less!)

Please post a track, in whatever state.

[nairb121]

9 hours ago, Bucic said:

Please post a track, in whatever state.

Track attached - just a bit of pure guns-only PvP airquake.

There is a definite difference - not as dramatic as I was thinking it'd be, but a good shot is definitely likely to land more hits.

F-5 guns update test.trk

[AeriaGloria]

Per Quaggles, dispersion was 22 mils, or 17.6 for 80% circle. 
 

Now it is 16 mils, or 12.8 mils for 80% circle. About 30% better. 
 

The manual snippet says 8 mils for 80%, which makes the new value seem like a perfect mean between the manual and old DCS dispersion. 
 

However if we find the diameter of the 8x8 mils box, it’s 11.3 mils, which makes the new value pretty close. 

[Bucic]

10 hours ago, AeriaGloria said:

Per Quaggles, dispersion was 22 mils, or 17.6 for 80% circle. 
 

Now it is 16 mils, or 12.8 mils for 80% circle. About 30% better. 
 

The manual snippet says 8 mils for 80%, which makes the new value seem like a perfect mean between the manual and old DCS dispersion. 
 

However if we find the diameter of the 8x8 mils box, it’s 11.3 mils, which makes the new value pretty close. 

Thanks for referring Quaggles! Do you mean one of his charts or lua files contained that "22 mils, or 17.6 for 80% circle" data?

Which manual snippet and location are you referring to in the last line?

[AeriaGloria]

7 hours ago, Bucic said:

Thanks for referring Quaggles! Do you mean one of his charts or lua files contained that "22 mils, or 17.6 for 80% circle" data?

Which manual snippet and location are you referring to in the last line?

Figure 2-19 in the first post of this thread. Quaggles LUA accuracy of the bullets can’t be found under the ‘shells’ file repo under M-39 HE and M-39 AP, the first few lines Da0 and Dv0 gives maximum spread of the bullets in dispersion and velocity

[Curly]

 Just as an FYI, The dispersion doesn’t scale linearly with Da0. Nor does Da0 = 100% dispersion.

 

In short, Da0 and the 80% diameter circle represent two different ways of describing the probability density functions of dispersion. Da0 is not a measure of radial dispersion. Though it is possible to convert Da0 to a measure of radial dispersio.  

 

The 80% diameter of dispersion is = to Da0 * 5.3199.

If we set Da0 to = 0.00495. The diameter of 99.7% circle would be 50 mils, filling the F-5E’s gunsight

 

At the bottom of this post,I’ll further explain the difference between Da0 and measures of dispersion commonly used in the west, like 8 mil 80%, 

 

Before we examine the recent changes to the dispersion 

I would First like to establish that the 8 mil 80% dispersion rating of The F-5E guns, represent the diameter of a circular pattern. 

 

This is made clear in the F-5E Weapons Delivery Manual F-5E-34-1-1 1 Aug 1979 , rev 1980. On page 223 under the boresight section. Where it states the acceptable dispersion pattern for the M39’s on the F-5E is a 8 mil circle which contains 80% of the rounds fired.

 

 

 

 

 

The 80% diameter of dispersion  can be described mathematically as being  = sigma * sqrt(-8*ln(1-.80)).  Where sigma is the standard deviation of the dispersion.

Based on one the devs comments, 

https://forum.dcs.world/topic/207864-closed-m61-dispersion/page/2/#comment-3916757

 

The DCS dispersion parameter, Da0, is equivalent to a median dispersion. This is commonly called Range or Deflection Error Probable in the west. Da0 / REP is also a function of the standard deviation of dispersion, Where Da0 is = 0.6745  sigma. 

 

We can convert the dispersion rating in the F-5E manual,  8 mil 80%, to (Da0) with some simple math.  We just multiply the 80% circle rating, 8 mils by 0.18797 to get Da0. Which would make Da0 = to 1.5038 mils. In the proper format for the game, Da0 should = 0.0015.

Before the update,  Da0 was = 0.0022

This resulted in an 80% diameter of 11.7 Mils. 

The old dispersion was about 46% larger than indicated in the F-5E’s manual. 

 

With the latest change Da0 was reduced by about 27%  to 

Da0 = 0.0016 

The current setting  should result in a  80% dispersion diameter = to 8.5 mils. Which closely matches the data given in the manuals

 

Below we’ll look at an old dev post on dispersion and I’ll explain the difference between Da0 and the type of dispersion ratings  often given like, 8 mil 80%. 

 

Per the dev, Yo-Yo, about 8 times the dispersion variable, Da0, will give you the diameter of the 100% dispersion circle.  

 

https://forum.dcs.world/topic/207864-closed-m61-dispersion/page/2/#comment-3916757

 

The implication is that Da0 is not a measure of radial dispersion. Da0 represents a normally (Gaussian) distributed univariate measure of dispersion which contains 50% of dispersion along the x and y axis separately. In western technical literature, Da0 would be equivalent to what is known as Error Probable, Range Error Probable Or Deflection Error Probable. Da0 / REP are = to 0.6745 * the standard deviation of the dispersion (sigma)  

 

 

 

In most western literature the dispersion is given as either a radius or diameter and a probability, like 80 mils 80%. Circular Error Probable or CEP is another commonly used measure. CEP is the radius of a circle which contains 50% of the impacts. CEP is = 1.17741 * sigma.

 

 

Note that CEP and REP / DA0 do not have the same relationship to the standard deviation of the dispersion ( sigma). 

 

 

This is because CEP and dispersion ratings like the 80% circle are functions of a different probability distribution than Da0 / REP. 

If bullet dispersion is circular normal. Then sigma x and sigma y are equal. We can describe the radial dispersion as a function of sigma.  With the equation

sigma * sqrt(-2 *ln(1-% radius of dispersion)

 

 

For example the 75% circle is given as;

 

The radius of 75% circle is = sigma * sqrt(-2 *ln(1-0.75)

 

Or sigma * 1.6651 is = the radius of the 75% circle of dispersion.

 

CEP aka the 50% radius of dispersion is = sigma * sqrt(-2 *ln(1-0.50)

Since sqrt(-2 *ln(1-0.50) is = 1.17741 then, 

Sigma *  1.17741 is = to the 50% radius of dispersion.

 

Lets compute the 50% radius of dispersion base on the on the F-5E dispersion value Da0.

The most straightforward way to do this is to compute sigma from the DCS dispersion parameter.

Given that; Da0 = 0.0016 = sigma *0.6745

Then sigma is = (0.0016)/0.6745

Sigma = 0.00237 = 2.37213 mils

Since the 50% radius dispersion is =  sigma * 1.17741

The 50 % radius of dispersion, CEP, is 2.79297 mils   

As,  2.37213 *  1.1774 = 2.79297 mils.