Long Bombs in Manual Bomb Delivery

[MBot]

I am pretty certain now that bombs fall too wide with delivery parameters by the T.O. 1F-5E-34-1-1-1980 Weapons Delivery Manual. Since this is a broad subject with many variables, I invite anyone interested to document and supply additional data to this topic.

 

Here is one specific first example.

 

This is our intended delivery profile:

 

 

We are looking at a 30°, 7000 ft AGL, 520 KTAS Mk-82 delivery which will require a sight depression from flight path of 176 MILS. Next lets look at the AOA correction:

 

 

Aircraft weight at drop is 16'900 lb with only the CL station loaded.

 

A + B - 35 = 28 + 8 - 35 = +1 ZSL AOA Correction (C not needed with retracted auto flaps).

 

A sight depression of 176 + 1 = 177 MILS should therefore indicate impact point at 30° dive, 7000 ft and 520 KTAS.

 

Now lets look at the drop:

 

 

Drop at 7167 ft MSL. Target elevation is 148 ft. Release is therefore at 7019 ft, very close to the intended 7000 ft. Flight path is 29° instead of 30°. A shallow delivery should result in a slightly shorter bomb.

 

 

TAS is 519 kts, very close to the intended 520 knots. A slow delivery should result in a slightly shorter bomb.

 

 

Sight picture at release. The pipper is set to 168 MILS (the value was just for testing and has no further meaning).

 

 

Bomb impact position. From this we can determine at what MILS setting the bomb hit at the point of release:

 

 

The pipper was set at 168 MILS. Calculated impact point was 177 MILS. The bomb was going to impact at a point that corresponds to 154 MILS.

 

The expected correct sight setting for this delivery was 177 MILS, while a setting of 154 MILS would have predicted the impact that actually happened. We can therefore conclude that the usage of the weapons delivery parameters from the real manual results in a long bomb.

Edited August 7, 2016 by MBot
More labels added to last picture.

[IvanK]

Nice Job ... but as in the other posts I believe the real issue is Altimeter lag :)

[autogyro]

Nice Job ... but as in the other posts I believe the real issue is Altimeter lag :)

 

This is "corrected" for altimeter lag as it had taken true altitude via the stats at the bottom of the screenshot, he hasn't used the altimeter inside the aircraft.

 

All the values check out to me and thus I agree that the manual sight tables are not producing consistent impacts with the module.

[IvanK]

Mbot I know you discussed this in the other thread. AOA(FRL) from the chart you come up with is 36mils. In your Screen grab it shows AOA of 0.9deg or 16mils. Assuming the AOA displayed on the screen bar is FRL referenced than the diff between the chart AOA and what you achieve is 20mils only 6mils diff to the angular bomb error you show in your graphic of 14mils.

 

So if my mental gymnastics and lines in space are right then if your Game and all other parameters are correct using planned numbers with pipper on (assuming game bomb range is the same a chart bomb range) AOA is 16mils less than the Chart AOA it would mean that if using Chart AOA figures (38mils .... just talking about FRL referenced AOA)) then bombs would go over the top.... since the error would result in a weapons release point closer to the target, pipper on.

 

So it follows to get bombs on target would require the actual in game release point to be further away therefore to have pipper on would require less depression ... by about 16mils in this case.

Edited August 7, 2016 by IvanK

[MBot]

Here is an example with different conditions.

 

Intended profile:

 

 

15° dive at 1500 ft and 480 KTAS. Depression from flight path 109 MILS. Next AOA correction:

 

 

Wight 17'000 lb with CL stores. A + B - 35 = 28 + 8 - 35 = +1

 

Sight setting: 109 + 1 = 110 MILS

 

 

Drop at 1627 ft MSL, target elevation 148 ft, 1479 ft AGL. Dive 15°. Pulling some slight Gs, which would result in a bomb shorter than intended.

 

 

Speed 482 KTAS looking good.

 

 

Sight picture at release. Sight is set to 100 MILS, which again is just for reference and has no particular meaning (calculations above show that 110 MILS should predict bomb impact point).

 

 

Here we have the impact.

 

 

And this is the actual impact as it happened at 80 MILS versus the predicted impact point at 110 MILS. The bomb went 30 MILS long.

Edited August 7, 2016 by MBot

[MBot]

More data, this time with the Snakeye.

 

 

Selected profile.

 

 

Weight: 17'000 lb, CL store

AoA correction: 29 + 8 - 35 = +2

Sight setting 134 + 2 = 136 MILS

 

 

 

Delivery on parameters.

 

 

 

 

Calculated impact 136 MILS versus actual impact 120 MILS. Bomb 16 MILS long.

[MBot]

From the data collected so far, let's see if we can already draw a conclusion. Let's note first that variations in release speed/altitude/dive angle/load factor, as well as time delay between release and taking the screenshot, probably account for a single digit MILS error in the observed differences between calculated and observed bomb impact points. Yet I think the 3 examples above show that bombs land roughly 20 MILS longs, or rather that the pipper displays 20 MILS short.

 

As IvanK already mentioned above, let's have a closer look with applying AOA corrections from game data rather than chart data:

 

Profile 15°/7000ft/520KTAS:

Calculated MILS (chart AOA correction) = 176 + 1 = 177

Calculated MILS (game AOA correction) = 176 + (0.9 * 17.5 - 35) = 157

Observed MILS (impact point) = 154

 

Profile 15°/1500ft/480KTAS:

Calculated MILS (chart AOA correction) = 109 + 1 = 110

Calculated MILS (game AOA correction) = 109 + (1.2 * 17.5 - 35) = 95

Observed MILS (impact point) = 80

 

Profile 0°/300ft/480KTAS/Snakeye:

Calculated MILS (chart AOA correction) = 134 + 2 = 136

Calculated MILS (game AOA correction) = 134 + (1.1 * 17.5 - 35) = 118

Observed MILS (impact point) = 120

 

 

As we can see, calculating the AOA correction from actual game data rather than from chart data produce a better, in some cases even very accurate, bomb impact prediction. The game bomb ballistics therefore seem to match the chart data. The problem seems that observed game AOA is lower than the calculated chart AOA, which in turn puts the pipper about 20 MILS too low.

 

If the AOA in game would be larger by 20 MILS, the nose would be 20 MILS higher and the pipper would raise by a corresponding 20 MILS in reference to the ground (while the set depression setting remains untouched). The bomb impact point on the ground would remain the same, as it is depended on flight path which is unchanged. The calculated bomb impact point with chart AOA correction, the calculated impact point with game AOA correction and the observed impact point would then coincide.

[diditopgun]

Thanks a lot for all your tests Mbot ! I hope devs will listen and find the issue. But they are rather silent currently...

[IvanK]

Great Work Mbot slowly getting to the bottom of this.

 

I agree using measured in game AOA rather than the dash 34 chart is the way to go. Also need to add the huge Altimeter lag we have in game. For me I now go out and fly the planned pass in game and note both actual AOA and Altimeter lag (thanks for the idea). I use the recorded in game AOA for the calculation and then apply the noted Altimeter lag to the altimeter for the actual release.

 

For the devs I guess they could play with AOA in the FM (I doubt they will) or publish a DCS AOA chart..... or we users could if we all got together produce our own measured AOA chart.

 

The Devs have indicated they will look at the altimeter lag issue.

[diditopgun]

Hi !

 

I haven't flown the F-5 since august. Any news on this side or nothing has changed ?