reported CBU-105 not correcting with heavy winds

[Falconeer]

So, i fly on a MP server tonight and noticed that my CBU 105 were hitting nowhere near the aiming spot. I tried manual tracking a target with the TGP and used the LSS function. The F-16 was cold started and fully aligned and the bombs themselves were fully aligned. Out of 4 bombs dropped, al 4 of them missed.

Could reproduce it in ME (so no alignment issue)

I have the MP track aswell, but it's 50Mb in size if needed

F16-CBU105.trk

Edited February 14, 2023 by Falconeer

[NineLine]

Thanks for the report, I will look soon. In the meantime if you can recreate a short mission with the same parameters it would be better. I will try and check out your track though.

[NineLine]

I took the winds from the track and set up a quick test, I adjusted burst to 1000 feet, dropped in pairs (this was recommended to me from an SME) and set the spread to 500 feet between the two 105s and I was able to hit the group of vehicles quite well. I did not see an issue. If you can set a mission more on what you are seeing I can take another look. 

[Falconeer]

Hello Nineline, some more info from what i have seen last night.

If you take a the outside view of the bomb falling towards the target, you can see it's already not going straight to the target but off to the side. When the bomb gets closer you can see it even beter that it's not going straight to the target. 

I also have a feeling the canister opens too late, causing the bomblets to overshoot the target, even if i get the correct range using the laser from the tgp.

I'll try to set up a mission and a new track tonight and see if it behaves different.

Dropping singles and pairs should not matter for accuracy, it only will give you more bomblets over the target area. Dropping pairs with spacing only creates a larger footprint.

[Moonshine]

the current inaccuracy of the TGP might not help with it. same as other GPS guided weapons (like the GBU38) dont hit within their parameters, i dont believe its the weapons fault but more the TGPs lack of accuracy. post for reference: 

TGP CZ issue (results in shifting Coordinates everytime CZ is pressed) ->  https://forum.dcs.world/topic/315078-cz-function-issues/#comment-5132696

JDAM inaccuracy (most likely due to the inaccurate coordinates received from the TGP, making bombs miss beyond their 5m CEP) ->  https://forum.dcs.world/topic/317925-jdam-still-inaccurate-beyond-the-5m-cep/#comment-5144779

 

 

 

[Falconeer]

25 minutes ago, Moonshine said:

the current inaccuracy of the TGP might not help with it. same as other GPS guided weapons (like the GBU38) dont hit within their parameters, i dont believe its the weapons fault but more the TGPs lack of accuracy. post for reference: 

TGP CZ issue (results in shifting Coordinates everytime CZ is pressed) ->  https://forum.dcs.world/topic/315078-cz-function-issues/#comment-5132696

JDAM inaccuracy (most likely due to the inaccurate coordinates received from the TGP, making bombs miss beyond their 5m CEP) ->  https://forum.dcs.world/topic/317925-jdam-still-inaccurate-beyond-the-5m-cep/#comment-5144779

 

 

 

That actually might be the same cause here. I did use CZ after i set the altitude from my steerpoint to ground level and slave the TGP to that point 

[Moonshine]

i think so too. while it is harder to detect on cluster bombs since their bomblet-footprint is so large and somewhat random that it is hard to tell if it did hit the correct spot or fell short (or otherwise missed). even more so if 2 bombs are dropped like @NineLine did in his test

 

Edited February 15, 2023 by Moonshine

[Sinclair_76]

Within DCS The AGM-154A compensate for bomblet wind drift and the CBU-105 doesn't. 

 

Edited February 15, 2023 by Sinclair_76
new post

[Moonshine]

18 minutes ago, Sinclair_76 said:

Within DCS The AGM-154A compensate for bomblet wind drift and the CBU-105 doesn't. 

interesting approach to a WCMD (wind corrected munitions dispenser) if thats the case

 

Edited February 15, 2023 by Moonshine

[Sinclair_76]

Correction, I did some testing about a year ago ...

and the AGM-154A compensated nicely for wind dropping submunition wel on the upward side to compensate for drift.

 

Now the JSOW doesn't seem to compensate anymore. The105 remain unadjusted and fails miserably in a strong breeze. Due to the shorter drift time compared to the -105, the -103 submunition scatter less and actually do some damage. But the drift is still there

Test-xwind-AGM-154A.trk Test-xwind-CBU-103.trk Test-xwind-CBU-105.trk

Edited February 15, 2023 by Sinclair_76
correction

[NineLine]

7 hours ago, Moonshine said:

the current inaccuracy of the TGP might not help with it. same as other GPS guided weapons (like the GBU38) dont hit within their parameters, i dont believe its the weapons fault but more the TGPs lack of accuracy. post for reference: 

TGP CZ issue (results in shifting Coordinates everytime CZ is pressed) ->  https://forum.dcs.world/topic/315078-cz-function-issues/#comment-5132696

JDAM inaccuracy (most likely due to the inaccurate coordinates received from the TGP, making bombs miss beyond their 5m CEP) ->  https://forum.dcs.world/topic/317925-jdam-still-inaccurate-beyond-the-5m-cep/#comment-5144779

 

 

 

That makes more sense, and I see those issues are reported. 

[Sinclair_76]

8 hours ago, Moonshine said:

the current inaccuracy of the TGP might not help with it. same as other GPS guided weapons (like the GBU38) dont hit within their parameters, i dont believe its the weapons fault but more the TGPs lack of accuracy. post for reference: 

TGP CZ issue (results in shifting Coordinates everytime CZ is pressed) ->  https://forum.dcs.world/topic/315078-cz-function-issues/#comment-5132696

JDAM inaccuracy (most likely due to the inaccurate coordinates received from the TGP, making bombs miss beyond their 5m CEP) ->  https://forum.dcs.world/topic/317925-jdam-still-inaccurate-beyond-the-5m-cep/#comment-5144779

 

 

 

With the tracks I submitted I specifically did not use the TGP to update the weapons with TMS up. I used preplanned coordinates so the error would be isolated to the weapon itself. Besides the TGP error, as I've seen it is causing weapons to fall short, no lateral errors reported. So the lateral error you see in the submitted tracks is due to lack of correcting for wind. 

 

Edited February 15, 2023 by Sinclair_76

[Moonshine]

Sinclair is right. WCMD are not actually correcting for wind. Did the same thing, not using the TGP to designate the target point, rather just used pre planned ones out of the ME. Add some wind and the bomblets go everywhere but not on target. @NineLine i think we have more than just the TGP inaccuracy issue at hand here. Currently the cbu-105 behave like the cbu-97, not correcting for wind

Edited February 15, 2023 by Moonshine

[Falconeer]

Here are some more tracks.

First is again a mission with strong winds. 2 bombs dropped on 2 different targets, which were designated with the TGP. Both bombs miss and pay speccial attention to the second bomb. It doesn't even lands near the intended target! Also watch the bombs fly to the target, they don't fall straight to the target they move slightly sideways.

Second test is without TGP, no targets marked with the radar to set a SPI, the coordinates are entered in the UFC (see the name of the files without the word TGP in it) again same mission with same wind condition. 2 bombs dropped, both missed. Again the bombs fly in a slight sideways angle to the target, you can also see clearly with the second drop, the bomb drift to the left side of the intended target. When the canister from the second bomb opens, the bomblets immediately start drifting to the right and miss their target

Added another track, this time designating the target in visual mode. 2 bombs dropped, both miss their target and again flying slighty sideways to the target. When the canister from mthe second bomb opens, the bomblets immediately start drifting to the right and miss their target, i think this is due to the wind direction?

F16TGPCBU105.miz F16tgpCBU105miss.trk F16CBU105miss.trk F16TGPCBU105.miz

F16HUDCBU105.trk

Edited February 15, 2023 by Falconeer
More tracks added

[void68]

Missed this thread, so I did a lot of CBU-105 testing in vain.

However I use just preplanned, no TGP correction needed, just from the Mission Editor into flight. I just put the WP plain into the target group's center. Zero winds, full hit. 60kts wind, some logic lets the CBU fly a certain lead into the wind, it ejects the BLUs not over the target like before but windward like it should. The poles drift and explode like they should but not where they should. The higher the wind and the BA the stronger the drift. With BA1200 and ca 15° windspeed I had to move the WP around 300ft windward.

So from my observation: There is indeed some calculation in the WCMDs but it's wrong - like it was in the CBU-95 before. Perhaps same cause?

iooinoin.trk

[Lord Vader]

Hi @void68

60kts knots wind on ground level is classified as "Violent Storm" on the Beaufort Scale. I honestly don't think these are adequate speeds to use WCMDs or any IDMs that rely on wind calculation. 

Remember that there is also a weapon limitation factor, there's certainly a calculation to be made between burst altitude and position. If the wind is beyond reasonable limitations, the bomblets will deploy on altitude regardless, they are not guided anymore.

[void68]

Hello Lord Vader,

 

sure, still with 14kts it's 300'+ deviation and that's just 4Bft mid breeze. I guess with 1Bft and BA2500 calculated wind correction will be still way off target (time for another test)

With insane 60kts I would understand that it's out of the limitation if the BLUs drift in a somewhat chaotic manner. But... they hit the ground always at the same spot, so there is calculation. And that calculation is wrong.

Like playing darts, you aim for the bullseye and all your darts hit exactly the same 1cm² 5cm off to the right. All the time. So the shooter is excellent at aiming, he just has to correct his aiming offset.

It was the same with CBU-97, always off the same distance / direction.

Edited February 17, 2023 by void68

[Falconeer]

2 hours ago, Lord Vader said:

Hi @void68

60kts knots wind on ground level is classified as "Violent Storm" on the Beaufort Scale. I honestly don't think these are adequate speeds to use WCMDs or any IDMs that rely on wind calculation. 

Remember that there is also a weapon limitation factor, there's certainly a calculation to be made between burst altitude and position. If the wind is beyond reasonable limitations, the bomblets will deploy on altitude regardless, they are not guided anymore.

If you try my mission and lower the crosswind to like say 30-ish knots, the bombs still won't hit the target

[Moonshine]

first track:

i did it with 25kts crosswind, BA 1500ft. still way off. and 25kts is labelled as "strong breeze". should not be a problem for that bomb. bomblets drift way south of the target, with the most northern bomblet still not on target.

interestingly; following the bombs flight path, she glides straight to the steerpoint, then going nose down for the final phase and only then trying to adjust for wind (large flight path correction in the final phase of flight). is that as it should be or should the bomb correct its flight path way earlier, reducing the need of significant last second adjustments?

as of now it looks like she cant reach the desired offset point before reaching the defined BA, resulting in a miss

Second Track:

yes, lowering BA does help (set it to 1000ft), still only 1-2 bomblets actually fall withing the target point. youd have to set it so low you wont get any spread anymore, so why bring a cluster bomb in the first place.

CBU-105_25kts_xwind.trk CBU-105_25kts_xwind_BA1000.trk

Edited February 17, 2023 by Moonshine

[Lord Vader]

Hello again.

Thanks for your tracks @Falconeer, really helped rule out TGP influence.

I am going forward with an internal report on this.
There could be the case that it needs tweaking. We will compare with our data and if there's a discrepancy we will correct.

Thank you all for your patience. 

[VarZat]

Thank you Vader!