correct as is A/G Gun range wrong?

[nighthawk2174]

So I found this video:

 

- strafing run at 19:30

 

But if we look at the Hud this is what the reticule look like:

 

VS what we have in game.

 

that's a difference of 2100ft!

 

Additionally when you follow the same parameters as the video the shot the bullets in DCS fall short! by as much as 100ft.

[Flagrum]

Isn't the max range dynamic, depending on, i.e., air speed of the a/c?

[nighthawk2174]

Yes, although I did my best to both match the speed and dive angle of the video aircraft. The one thing I forgot to match was the tempature, but well... considering how cold it looks in the video the denser air should make it so the rounds don't fly as far. Yet in DCS they don't fly as far.

[Reckoner]

Also should we talk of the dispersion of that burst compared to what we have now?

[BIGNEWY]

Also should we talk of the dispersion of that burst compared to what we have now?

 

Dispersion is correct, the team are happy with it. It has been done to death on these forums so lets keep it off topic here so we can keep on topic for the bug report.

 

thanks

[BIGNEWY]

It is difficult to say without knowing what ammo was also used in the video.

 

Based on the numbers we have this is correct as is.

Edited February 3, 2020 by BIGNEWY

[nighthawk2174]

Could be drag, seems just about everything in this game has too much drag. Also i'm sure you could google what ammo Canadian 18's use I can't right now but I doubt it would be impossible to find out. Also I disagree with the [correct as is mark] until we are sure about the ammo type I think this thread should still be marked as [investigating].

[Canada_Moose]

Could be drag, seems just about everything in this game has too much drag. Also i'm sure you could google what ammo Canadian 18's use I can't right now but I doubt it would be impossible to find out. Also I disagree with the [correct as is mark] until we are sure about the ammo type I think this thread should still be marked as [investigating].

 

 

Whilst I understand that the team feels the technical details of the gun dispersion are correct, comparing what you see in the Jetstream strafe runs to what we actually see in sim is like night and day.

 

 

Just my 2 pence worth......

[nighthawk2174]

Agreed even though the major point of this thread is the question of bullet drag dispersion differences can clearly be seen in the video.

[NineLine]

It was marked as correct as is, you need to match up more like what we have in the sim, you can't use vague comparisons of different aircraft (be it variants or types) to invoke change.

[Yo-Yo]

20 mm ballistics was tuned used the sources we had since 2005 and was not retuned, because our experts never saw something strange in it.

Later we got M61 firing tables (FT), checked some points and the results was good.

 

I returned to this ammo for deeper check, as we have very critical reviews on different forums.

Below I will show several points from these tables and compare it to the in-vitro ballistic

calculation similar to the project ballistics.

 

This FT presented two target altitudes - SL and 5000 ft, and the first one will be used.

 

Let's start from the shortest flight time - FT shows that it is 600 ft altitude, -20 deg fligt and 440 KCAS.

Aircraft AoA is taken in account having different columns for several GW.

The tool can set exact aircraft speed, altitude and shell initial angle.

As we want to compare flight time to the certain distance the initial angle will be adjusted within 2-5 mils to get exact impact distance.

 

The slant range for medium 40k lb TW is 1963 ft and the time of flight (ToF) is 0.61s.

This slant range for the DCS the tool gives ToF 0.59 s. So, the drag for high Mach region is caught quite accurate and,

in any case, is not "too high". The initial angle is 2.35 degrees up from -20 degree, because our goal is to determine

ToF at given slant range at given altitude and aircraft speed.

 

The next point will be 1000 ft and 400 KCAS that give 6537 ft of the slant range and 4.08 s ToF.

The tool gives 3.78 s for the same distance that is even a bit faster. Additional elevation is 2.4 deg - the same

as in previous case.

This shot shows the whole supersonic area of the drag curve, and, as one can see for the fine tuning it requires

more drag.

 

Then, the third point will be a longer run: 7000 ft at 400KCAS, 45 deg diving.

It gives 7.48 s for 9866 ft.

Additional elevation was even a bit less (2 deg) and the ToF is 6.77 s. Not very precise but again -

this time indicates that the only small adjustment required is to INCREASE DRAG.

 

Do not forget that the shell flight path was traced through the different combinations of air density and speed of sound values.

And, finally, this FT has simplification: ToF is the same for three different ranges for different GW. We only have to

consider it for the medium GW value.

 

Total table, ToF

FT Tests

0.61 0.59

4.08 3.78

7.48 6.77

 

Just again: the shells flies a bit better than they should regarding the FT, but I do not think it can change something in practice.

This type of discrepancy looks like something is wrong with the initial velocity or with projectile weight, and yes,

I noticed an elephant - the weight was specified 110 g instead of 100 g.

 

As the drag characteristics was used from the well documented shell of similar form the whole set of points got their places at once,

and applying very tiny drag adjustment (mainly subsonic for long range shots) the table was changed to

 

FT Tests

0.61 0.60

4.08 4.10

7.48 7.48

 

And now another one point we have not try yet: 1000 ft, 400 KCAS and -20 deg.

It gives 1.24s for 3295 ft. The tool gives 1.28 s.

 

And another bonus point: 5000 ft, 400 KCAS and 30 degrees. 7.74 s.

The tool gives 7.77s.

 

The overall table for various altitudes, elevations, slant ranges.

FT Tests

0.61 0.60

1.24 1.29

4.08 4.10

7.48 7.48

7.74 7.77

 

This table is plotted vs correspondent slant ranges

 

And, finally, General Dynamics booklet was used with M50 family speed and ToF graphs.

https://www.gd-ots.com/wp-content/uploads/2017/11/20mm-M50-Series.pdf

 

The graphs seem to be quite strange because of irregular grid ticks, and strange velocity curve

behaviour with very fast deceleration after transonic region (must be the opposite behaviour because of flat

and low Cd, and I do not think the shell becomes unstable so early - it can fly stable at least 8s regarding the FT ).

Anyway, it's interesting to compare DCS tool result and this graph.

Surprisingly it matches except the subsonic part I described above.

Edited February 26, 2020 by Yo-Yo

[nighthawk2174]

Well then I guess we'll have to discover why my values have such a different outcome as I am using a drag chart to generate my results, i'll get to it when I got time. Thanks for the response.

 

Side Notes

 

-Shouldn't the SAPHEI round on the F16 be a PGU round an as such have reduced drag over the rest of the rounds and a higher muzzle velocity?

-Any chance of adding the MK141 round as it should have a far higher muzzle velocity and lower drag than the other 20mm rounds. Currently it uses the same round as the F15.

[Yo-Yo]

Added.

Found a better curve from the General Dynamics

[Yo-Yo]

If PGU is standard for F-16 now it's not a problem to make it.

[nighthawk2174]

Yeah as its my current understanding there are no rounds with the SAPHEI designation in the M50 series.

 

Also I found my error, I had set the shell weight to 210g instead of 110g (as it is in the code) of note as you stated it should be 100g as that's what's indicated in various -34's i've looked through.

 

Sorry if this caused you any trouble, its good to look over old code but I hope I didn't delay you from other work for too long.

 

 

Edit, the new rounds for the F16 are marked as PGU-27/28/30 in the code so definitely worth looking into.

Edited February 26, 2020 by nighthawk2174

[BarTzi]

I apologize for bumping this thread, but I thought this was worth a second look now that we got additional types of rounds for the Hornet. 

In DCS, the In-range cue will pop up once you are 0.8 miles from the target (for all rounds, pgu included). This, however, makes this strafing run impossible in the sim:
 

As you can see, the pilot shoots at the water, and gets the in-range cue earlier than we get it in the sim (at around 1.12 nm slant range or slightly more). Since this video is of a deployment in the early 2000's, I was wondering if we should expect any adjustments to the in-range cue depending on the type of round. 

 -> I'm aware that you have to manually select the round type in the stores page. It affects only the position of the piper and not the in-range cue itself.

Edited September 17, 2021 by BarTzi

[nighthawk2174]

8 hours ago, BarTzi said:

I apologize for bumping this thread, but I thought this was worth a second look now that we got additional types of rounds for the Hornet. 

In DCS, the In-range cue will pop up once you are 0.8 miles from the target (for all rounds, pgu included). This, however, makes this strafing run impossible in the sim:
 

As you can see, the pilot shoots at the water, and gets the in-range cue earlier than we get it in the sim (at around 1.12 nm slant range or slightly more). Since this video is of a deployment in the early 2000's, I was wondering if we should expect any adjustments to the in-range cue depending on the type of round. 

 -> I'm aware that you have to manually select the round type in the stores page. It affects only the position of the piper and not the in-range cue itself.

 

It not affecting the in range cue for switching from M50 to PGU is probably inaccurate.  PGU as far better ballistics.  I'd just go ahead and make a new thread.

Edited September 18, 2021 by nighthawk2174