Bombing Table wrong mils for Direct

[MBot]

Despite the fix in the latest patch, the mils for Direct in the Bombing Table are wrong.

Following screenshot was taken in active pause. Bombing Tables was populated with the actual flight paramteres at this instance. Bomb impact is 20 mils off the value provided by the Bombing Table.

[MBot]

Question to HB: Is the sight depression in the Bombing Table AOA corrected? An AOA of -1.2° (as per bottom bar) would almost perfectly match a 20 mils error.

[HB_Painter]

Hey did you make sure to click outside of an input field to let the calculation do its thing? The AOA is not doing anything in the Bombing table

Also please provide a track.

Edited June 10, 2024 by HB_Painter

[MBot]

24 minutes ago, HB_Painter said:

Hey did you make sure to click outside of an input field to let the calculation do its thing? The AOA is not doing anything in the Bombing table

Also please provide a track.

Yes I have updated the Bombing Table to calculate things. A track wont help much, since this will not record what I do in the bombing table.

To reproduce: Make a random dive at the ground. At a random time press active pause. Note your actual flight parameters (info bar) and insert numbers into Bomb Table. Enter mils value from Bomb Table into sight. Drop bomb. Compare actual impact point to pipper location.

If the bombing table is providing mils values measured from flight vector (as the initial vector of the dropped bomb), then the pipper will always be off by the amount of AOA you currently have (and this is pretty significant). Mils from a bombing table always have to be corrected for AOA (which is weight dependant), since any discrepancy between the fuselage reference line and your flight vector will likewise move your pipper. Heavier -> more AOA -> higher pipper than intended.

Edited June 10, 2024 by MBot

[HB_Painter]

Please don't use the parameters from the bar but rather the ones that the plane shows you in the cockpit just to make sure there is no conversion problems there, as for example the AOA is not translated to the planes AOA. In my tests it worked as accurate as it can get with direct bombing but I can test that again. I only need a screenshot of your I/O from the bombing calc and than I can see in a track where the problem might be

Edited June 10, 2024 by HB_Painter

[MBot]

The data in the bar should be the most accurate available in regards to altitude and true air speed, as they represent the true in game state which will be starting point for the actual bomb ballistic trajectory. To which aicraft reference line the PTH value in the bar is measured is questionable indeed. But on the other hand, there is no way to read the plane's ADI with such precision either. You would probable have to make a script to output the actual aircraft flight path to get a high precision dive angle. But in any case it is not too relevant for the issue at hand, because +/- 1° deviation in dive angle will not make a hugh difference in mils (certainly not 20 mils).

Please clarify whether the sight depression value in the Bomb Table is calculated in relation to the FRL or the flight path. If it is displayed in relation to flight path, then AOA correction would have to be applied for the mils.

[Zabuzard]

(The AOA reported by the game is significantly different to the AOA shown on your gauge, as the gauge displays AOA units, not degrees. The conversion is complex and not linear.)

[IronMike]

1 hour ago, MBot said:

The data in the bar should be the most accurate available in regards to altitude and true air speed, as they represent the true in game state which will be starting point for the actual bomb ballistic trajectory.

 

Not really. The DCS calculation for non-standard pressures is ideal, which is not the case for the device itself. And for dynamic pressure (so for IAS and Mach) DCS uses a formula for incompressible flow. This is why it is important you go by the values in the cockpit. You can observe the same in the Tomcat, the DCS altitude in F2 is off, which isn't a bug as some think.

The other thing to keep in mind, is that the bomb calc uses TAS, which is the peskily hidden gauge to the left of your front console armament panel. Usually it won't be much off, but if you want to be on the money with your speed, that's the gauge to go by.

To answer your question for the depression value, it is best I leave that to @JNelson to explain, but I would not be aware that you have to compensate for AOA, but again, I would have to ask, so take it with a grain of salt. All I can say is that I don't compensate for AOA.

The easiest to test btw is with laydown mode. You just define alt and speed, and you can pick a fairly low one, and then you set the distance simply such that you get a desired (not too high) depression value. Fly level, fly at speed, pickle on pipper over target. You can use the AFCS ALT Hold for it, too.

I'll test a bit later, but I did several bomb runs in the past week with laydown and it was always pretty much bang on the money.

[MBot]

23 minutes ago, IronMike said:

Not really. The DCS calculation for non-standard pressures is ideal, which is not the case for the device itself. And for dynamic pressure (so for IAS and Mach) DCS uses a formula for incompressible flow. This is why it is important you go by the values in the cockpit. You can observe the same in the Tomcat, the DCS altitude in F2 is off, which isn't a bug as some think.

The other thing to keep in mind, is that the bomb calc uses TAS, which is the peskily hidden gauge to the left of your front console armament panel. Usually it won't be much off, but if you want to be on the money with your speed, that's the gauge to go by.

Thanks, but are you aware though that the bar can be changed to display "True Speed" (TS)? Which is what I did. The altitute in the bar is your geometric altitude in the game world (Y coordinate in DCS's coordinate system), which is the relevant value for the ballistic calculation. If you go by the cockpit gauge this might introduce altimeter lag or other differences. I chose the bar exactly because I want the true values.

I will provide a track this evening to statisfy that requirement.

Edited June 10, 2024 by MBot

[stonewall197922]

Sorry for interruption. But is there any mils table for AG Guns and rockets? 

[MBot]

As requested, here is a track:Direct_Mils.trk

Airspeed: 540 kts on TAS gauge, 539 kts on info bar

Altitude: 1820 ft on altimeter, 1839 ft on info bar

Dive angle: 18°-ish on ADI, 18° on info bar

The bomb table gives 86 mils:

Actual impact at 60 mils. 26 mils error.

Everything clear now?

[MBot]

As a side note, Time of Flight in the Bomb Table is also completely off. It gives 22.4 seconds, while measured bomb TOF was 6 seconds.

[Longiron]

You didn't enter target altitude 

[MBot]

It is zero (wasteland at edge of map with no elevation).

[Zabuzard]

As requested, here is a track:Direct_Mils.trk
Airspeed: 540 kts on TAS gauge, 539 kts on info bar

Altitude: 1820 ft on altimeter, 1839 ft on info bar
Dive angle: 18°-ish on ADI, 18° on info bar

The bomb table gives 86 mils:

Actual impact at 60 mils. 26 mils error.

Everything clear now?

Perfect, thanks for the track. We will look into whats going on there abd callback :)

[Stickler]

I would like to add my own observations here.

Reference the following release:

Disregarding that the calculated bomb range and TOF are completely off (that's not the concern of this post), note that the calculated required sight depression is 85 mils. This calculation is confirmed by my own bombing calculator (which uses in-game bomb cx values determined from testing) when inputting the same parameters (plus/minus 1 mil).

Observe also that the "correct" depression required (see the crater near the reticle) is 69 mils.

Release CAS was 425.

At release, my G per the F2 view was 0.8, versus a nominal G of 0.68 for a 47° dive angle. As per the correction chart below, this approx. 0.1 G error introduces a sight depression error of approximately 2 mils. For simplicity's sake, I'll ignore it.

At the time of release, the aircraft's gross weight was 47717 lbs as per the mission editor (I set unlimited fuel to make sure).

As per the below chart, the aircraft's AOA should have been 17,8 mils (rounded 18 mils).

To compensate for this AOA, the actual sight setting would have had to be 85 + 18 mils = 103 mils, thus even further from the actually required sight setting.

This makes me believe that the simulated F-4E's AOA diverges significantly from the real F-4 at given parameters. Note that if you were to subtract 18 mils from 85 mils, you would approximately get the really required 69 mils, but this is a coincidence based on other tests with different release parameters.

It is entirely possible that I'm completely misunderstanding how the above calculations should work, so if anyone spots a flaw in my logic please help me out.

[MBot]

Nice effort. One thing to consider is also where the various lines are referenced in the aircraft. In The F-5E for example, the Fuselage Reference Line (from where AOA is measured) is 35 mils above the Zero Sight Line (from where the pipper is depressed, i.e. "0 mils"). So you always had to calculate mils depression from flight path + mils AOA - 35 mils. I don't know how how the reference lines in the F-4E are related to each other.

[Stickler]

Based on further testing, the in-game AoA is approximately 39 mils LESS than the AoA of the real aircraft as taken from the above chart under identical conditions. This is true in the speed range of 400-500 KCAS. With lower speeds, the difference decreases. The difference is most pronounced (around 41 mils) with high gross weights and least pronounced (around 37 mils) with low gross weights. Dive angle seems to have a negligible effect on the difference.

Thus, for a one-size-fits-all, easy to apply fix, subtract 40 mils from the AoA obtained from the above chart, then add the result to the sight depression obtained from the bombing calculator to obtain the actual required depression. This is provided you keep your release KCAS in the "usual" range of 400-500 KCAS.

Based on the attachments, the ZSL and FRL seem coincide in the F-4E.

Edited June 15, 2024 by Stickler

[Stickler]

Another aspect to add here:

The bombing calculator does not at this time seem to take into account the different drag of submunitions compared to their canister.

Witness the CBU-87. A calculated release solution for DIRECT bombing - if taking AoA into account as above - will be highly accurate with an airburst altitude of 300 ft, but the submunitions will fall short of the calculated sight setting with an airburst altitude of 3000 ft.

Without being able to categorically prove this, I believe this is the case because at 3000 ft to go, a wrong drag coefficient will have a much larger impact on calculations than with only 300 ft worth of "wrong" drag.