Aries144

Well done Belsimtek! Thank you!

Yep, sorry. Must have missed that. Been bouncing back and forth between this and other personal things. Not enough time in the day!

Yeah, Jenkins is just plain wrong. 5 mil, as it's used in the US, is 20 feet at 4000 ft. 1 mil is equal to 1m at 1km or 1 ft at 1000ft. Not difficult math. Also, I want to see where the original source got the info for 5 mil, 80%. I'm nearly certain that that's a maintenance figure describing the worst a gun can perform before requiring repair/replacement. This video of a new m61 being tested seems to bear that out. The M61 (used on the F-15, F-14, F-16, F-18, etc) is sourced as shooting 8 mil, 80%. The example in the video is tested the same way as one in service would be tested and shoots much better than 8 mil, 80%, with only 1-5% of rounds outside the 8 mil circle.

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!

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!

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 as accurate as if the aircraft were stationary on the ground!

Now updated with ShadowPlay recordings.

Updated tests with ShadowPlay recordings.

Updated the first post with links to some Shadowplay recordings. I believe this clearly demonstrates that the numbers in the lua do, in fact, directly relate to mil. 0.0008 is 8 mil, 0.0022 is 22 mil, 0.004 is 40 mil, etc. The Da0 value indicates extreme spread. A 50% CEP, based on the Da0 divided by 2, seems to be evident. For a Da0 value of 0.004 (40 mil), approximately 50% of rounds will fall into a 20 mil diameter while the remaining 50% fall between 20 mil and 40 mil. Only a small percentage of rounds fall at the extreme edge of the extreme spread (40 mil).

You're absolutely correct. It's become a colloquialism to refer to "precision" as "accuracy" unfortunately, and I was afraid people wouldn't know what I was referring to. Thanks for the correction.

In real life, this would be a function of Muzzle Velocity and Ballistic Coefficient. I'm not sure how accurate DCS' ballistics modeling is and I'm afraid it's outside the scope of the current discussion.

That's not accurate. Dispersion IS linear. At 2000 ft 8 mil would be a 16ft diameter circle. The 80% isn't being correctly understood either. As guns wear, eventually they lose precision all the way down to a point where they won't stabilize projectile anymore and the projectiles begin to tumble in flight, becoming wildly inaccurate and losing velocity quickly. 8 mil, 80% is a maintenance standard for when a gun is worn out and needs repair/parts replacement. If more than 20% of fired shots fall outside an 8 mil circle, it's time to replace parts in the gun. That's all the 80% part means. A new M61A1 doesn't shoot 8 mil, 80%. The new gun we see in our video evidence certainly performed much better. As shown in the video, the M61 actually shoots a main group smaller than 8 mil with a very low percentage of outlier rounds (1-5%) falling outside of 8 mil. DCS doesn't simulate aged hardware, it takes everything as if it is brand new from the factory, so we should probably throw the 80% out completely. It simplifies things greatly, as we'd need to get into Circular Error probable to accurately calculate how far outside of 8 mil the 20% of shots would land. Besides, I don't think DCS can model an 80% CEP. I think it is hard coded to always do a 50% CEP, with the Da0 value indicating what the maximum extreme spread is allowed to be, which means that with a value of 8 mil, 50% of shots are falling into a dispersion of about 4 mil, with the rest spreading out everywhere between 4 and 8 mil. Guys, please go back and have a look at the first post. It's been updated.

Can we please stay on topic?

Accuracy tests seen here by modifying lua file for different accuracy values and measuring dispersion with the F-5's 40 mil diameter gunsight + actual M61 Vulcan accuracy test video (same accuracy as the M39 200mm cannon on F-5) https://forums.eagle.ru/showthread.php?t=198157

Accuracy tests seen here by modifying lua file for different accuracy values and comparing with the F-5's 40 mil diameter gunsight + actual M61 Vulcan accuracy test video (same accuracy as the M39 200mm cannon on F-5) https://forums.eagle.ru/showthread.php?t=198157

Please check the first post. Essentially, the 80% isn't important to model, as 8 mil, 80% doesn't represent the typical precision of a new gun, but instead the failure point beyond which a gun is considered too worn and requires repair. The linked M61 accuracy test video on the first post illustrates this, as the vast majority of the 100 shot burst seen on target in the video visibly impacts entirely inside the 8 mil circle, with the narrator stating later that only 1-5% of shots were striking outside of that. Even without a more precise, scientific test, it can clearly be understood from my included Da0 = 0.0022 track (the current default) that far more than 20% of shots are exceeding 8 mil. Also: Tracks didn't work. Here's some raw video recorded with ShadowPlay instead. Default accuracy, Da0 = 0.0022 40 mil accuracy, Da0 = 0.004 8 mil accuracy, Da0 = 0.0008

Can you explain to me why this would be? The rounds velocity will be it's own plus that of the launching aircraft. The dispersion angle is still the same... Regardless, this demonstrates the relationship between the lua value and mil. Multiplying the lua value by 10,000 produces an effect conspicuously close to the appropriate mil value, as measured using the F-5's 40 mil gunsight. Modify the lua so that all fired rounds are tracers, go into the game, and see it for yourself.

Just tested again with Da0 value set to 0.0040. It does indeed produce an extreme spread that very nearly touches the insides of the 40 mil sight ring. Only a small percentage of rounds are going that far out. As an imprecise observation, I'd say that 50-60% are falling within 20 mils with the rest spread out between 20 and 40 mils. Pending more precise testing, it's a safe assumption at this point that using 0.0008 would produce very close to the source value of 8 mil.

Edit: Esb77 I see what you're saying, but those figures don't match what I'm seeing in the game. The dispersion is certainly much larger than 2.2 mils. A larger spread being an advantage or not, the fact is that the sources all state 8 mil is the precision of the gun. This is a simulation, so we want it to be as accurate as possible. I just finished recording a track of the F-5 firing a single gun with all rounds being tracers. The aircraft is airborne, loaded with bombs to help stabilize it, and a mountain peak is aligned with the 6 o'clock pip on the gunsight for reference. All shots are fired in a single burst. This is very effective because a given round reaches the height of the sight line so quickly that there isn't much time for the aircraft to yaw from recoil. We also have the mountain peak to use as a reference if we want to be very precise. By measuring only in the horizontal and only as the rounds' reach the sight line to eliminate error from the rounds' drop, it looks as if the Extreme Spread is, in fact, very close to 22 mil. Rounds can be seen going as far out as halfway between the center pip and the outer ring, both left and right. That's very close to 22 mil. I'm going to attempt to get hold of someone with recording software so that they can advance the track footage frame-by-frame and mark the high point of each round's flight through the sight. This, combined with different values entered in the F-5's Da0 entry, and measured against the 40 mil gunsight ring, will give us a very accurate estimate of what the Da0 value means in relation to mil. Next experiment will be to set the Da0 value to 0.0040 and see if the outer-most shots closely reach the outside of the 40 mil ring. If they do, frankly it's so close that further experimentation will just be academic. Whew! That's a lot easier than the previous method I was looking at. I may try another experiment using the A-10C firing from the ground with the recording taken through the gunsight of an F-5, also on the ground, near the A-10C.

Right. 22 mil would be 3-4 times larger. The Russian planes seem to have accuracy of 5-7 mil, if that interpretation of the lua number is correct. Where are you getting 40 times larger from?

Can someone please clarify what this G-limit means in terms of performance in game vs performance in real life? i.e. Does this mean decreased performance vs fighters at close range?

Entirely possible. Typos in code can cause hours of hair pulling frustration! It could make sense too that Belsimtek would simply copy that value for the F-5 without checking it, as sources indicate that the M39 cannons on it have the same dispersion as the M61A1 of the F-15. It doesn't explain the A-10 gun's value though, as that is also too large.

You mean deviation at the muzzle? I know the Operation Flashpoint/Arma games use a similar method for dispersion value.

The F-5's and F-15's guns both use the 0.0022 value. The A-10's gun uses a value of 0.0017. The Mirage is 0.0008 the Harrier's gunpod is 0.0005 the Mig-29/Su-27 is 0.0005 the Su-25 and Su-25T are 0.0005 the Mig-21 is 0.0007 the Ka-50 is 0.0005 for HE and 0.0004 for AP. You can modify the values in the file yourself and see the change in-game, it just won't pass integrity check for multiplayer. The file is called "shell_table.lua" and is located in Eagle Dynamics\DCS World\Scripts\Database\Weapons

The above-linked video shows an m61 cannon fire a burst with a dispersion smaller than 8 mil. The video goes on to state that, at a range of 1000ft, 95-99% of rounds were within the 8 mil bullseye. We can confidently say that 8mil, 80% is a minimum standard. In other words, 8 mil, 80% is what the gun would shoot when it's completely worn out and on the verge of needing parts replacement. The easiest way to handle this is to just go with 8 mil and throw out the 80% entirely. Or, if that isn't precise enough, there exists a formula that can estimate how far outside a given dispersion area rounds in that 20% could be. I've seen it but can't remember where. It isn't very far outside the circle. Maybe 4 mils for the outermost 0.5%. I'll try and dig it up. In the mean time, unless someone can talk to ED and find out the what real-world figure "Da0 0.0022" in the shelltable.lua represents, we're going to have to rig up a test that's going to take a lot of hacking and work. I'm still not convinced that it isn't directly related to mils. Something else that might work is to use the gunsight in the F-5. If it's accurately modeled, it has a diameter of 40 mil. Again, by far the easiest way to handle this would be to have cannon rounds spawn "bullet hole" textures on the spots where they touch our target, similar to what's done in first person shooter games when a player shoots a wall.