correct as is JDAM hitting long

[greenmamba]

Hello Community,

 

I have been testing the JDAM's on the F-16 for the last 5 hours or so and i am wondering if anyone else has the problem with the JDAM's, GBU-38 hitting long when having the TGP crosshairs on the target ?

 

In order to hit spot on or close enough to damage the intended target, i need to place the TGP crosshairs slightly before the target. All this is done in PRE mode. 

Edited June 17, 2021 by greenmamba

[Silvester.E]

Same! 

[TobiasA]

Yes, kind of. It is paired with a tendency of the TGP to drop lock when switching between JDAMs and LGBs which I need to investigate a little more. 

I need a track for this, but I noticed it in a multiplayer mission so I need to recreate it and see what happens. 

[NineLine]

Can you please include a track so we can see what you are doing? Thanks.

[greenmamba]

Will do 

[bradboom]

Doing the same to me, too. Hitting close to target, but no cigar.

[TobiasA]

It seems to happen when you aim high on a vehicle, I guess. Always go for the wheels.

 

Edit: I found my mistake which caused the TGP to drop lock- the GBU-12 were in CCIP mode which then moved the TGP when I switched to them. Correct behaviour.

I can not reproduce the issue of JDAM's falling short or long in PRE, however, the ground units move away after the first unit gets hit and you must aim for the wheels.
Track is attached, breakfast time is over.

If you can reproduce the issue, please post another track since I am not really sure about my results.

Tacview-20210618-091018-DCS-AG_training.zip.acmi F-16_JDAM_miss.trk

Edited June 18, 2021 by TobiasA

[TobiasA]

So I was finally able to reproduce it with a track....
You mean like this:

 

Was the first JDAM out of a Salvo, and it did hit long so it failed to destroy the vehicle.

It then misses by 38ft and before the vehicle moves:

 

LGB's are fine, I rarely miss something with LGB's so it's not me and my TGP.

 

@greenmamba @bradboom Is that your issue as well?

 

@BN or 9L:

Hope that helps, if I'm doing something wrong let me know. Attached the mission as well, it is pretty simple although I should try it with static targets since everybody moves when the first JDAM strikes. It doesn't matter in this track though because it is the first JDAM that fails, the other three are pretty much on spot (if they had not moved, they would have hit).

 

Tacview-20210619-145017-DCS-AG_training.zip.acmi F-16_JDAM_hit_long.trk AG_training.miz

[txmtb]

Been noticing the same issue.

Using steerpoint set in ME they seem to be accurate. Using TGP to create SPI for drop and they seem to go long.
It's acting like the slant is causing the TGP to produce a SPI that is through the LOS of the target to a point on the ground behind it.
Think there was a same issue with the A10 a long time ago.

 

[Dagger52]

Could be nothing could be the answer
There was a issue back in DCS 1.5 where when dropping jdams in the A10 you had to aim on the bottom line of the vehicle because the tpod is not seeing the vehicle as a obstacle and that’s causing the fact the you get the coordinates of the point behind the target


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[Arikaj]

6 minutes ago, Dagger52 said:

Could be nothing could be the answer
There was a issue back in DCS 1.5 where when dropping jdams in the A10 you had to aim on the bottom line of the vehicle because the tpod is not seeing the vehicle as a obstacle and that’s causing the fact the you get the coordinates of the point behind the target


Gesendet von iPhone mit Tapatalk

That's not a bug. In fact you have to aim beneath the vehicle in order to get the exact coordinates

[TobiasA]

Well I looked on top of the BMP in steep angle so how am I supposed to look behind it?

 

TGP image on pickle:

 

That's on his turret, not 38ft behind him so it is not the issue here.

Edited June 20, 2021 by TobiasA
Added picture

[Crptalk]

2 hours ago, TobiasA said:

Well I looked on top of the BMP in steep angle so how am I supposed to look behind it?

 

TGP image on pickle:

 

That's on his turret, not 38ft behind him so it is not the issue here.

 

 

Aim at the ground right below the BMP. I can't believe this is so difficult for some people.

 

Edited June 20, 2021 by Crptalk

[TobiasA]

vor 24 Minuten schrieb Crptalk:

 

Aim at the ground right below the BMP. I can't believe this is so difficult for some people.

 

 

Again, this is the point track jumping on the BMP. 

And it is not 38ft away unless the BMP is 40 ft high. 

And this does never happen with GBU 12.

You didn't even watch the track. 

Edited June 20, 2021 by TobiasA

[Crptalk]

30 minutes ago, TobiasA said:

Again, this is the point track jumping on the BMP. 

And it is not 38ft away unless the BMP is 40 ft high. 

And this does never happen with GBU 12.

You didn't even watch the track. 

 

use area track

aim at ground where i marked

gbu12 is laser guided, it's not trying to fly to coordinates generated while the bomb is still on the plane

correct

[Frederf]

If the bombs are accurate when targeting a steerpoint but missing when using TGP-supplied location then there's nothing wrong with the bomb. The issue is with the location derived by TGP. Comparison to GBU-12 is not valid because laser-guided bombs see the laser spot.

Realize that when you point track an object the TGP doesn't understand where that is in 3D space. Tracking is only a method to establish a line of sight. The line of sight is then used to calculate the intersection of that line with some kind of ground surface.

 

This is easy to check. Look at the TGP coordinates: N 42 07.389 E 42 08.44 38'. Now compare this to the actual position of the BMP. Alternatively program a steerpoint with those coordinates and see where your TGP points (slaved, not optical track) and where JDAM goes.

 

I point track a BRT-80. TGP says 41 50.529 / 41 47.867 / 33'. Actual BTR location is 41 50.528 41 47.858 (10m). This is an error of ~12.5m.

 

However when I enable laser rangefinder suddenly TGP text displays 41 50.529 / 41 47.857 / 38 without any change in point track. Be aware that while you can type in elevation into steerpoint in DED it has no effect.

 

There may be other sources of error too. TGP to passively discover coordinates needs:

• Position of TGP
• Orientation of TGP
• Relative LOS to target
• Surface of LOS intersection

Any of these can be inaccurate. If F-16 has a system altitude error it will do calculation wrong. If F-16 has INS heading error it will do calculation wrong. Probably in DCS the relative orientation is perfect. Surface of intersection is normally a computer model database loaded into the airplane/pod which is a polygon which is not perfect to real terrain.

Edited June 20, 2021 by Frederf

[TobiasA]

vor 7 Stunden schrieb Frederf:

If the bombs are accurate when targeting a steerpoint but missing when using TGP-supplied location then there's nothing wrong with the bomb. The issue is with the location derived by TGP. Comparison to GBU-12 is not valid because laser-guided bombs see the laser spot.

Realize that when you point track an object the TGP doesn't understand where that is in 3D space. Tracking is only a method to establish a line of sight. The line of sight is then used to calculate the intersection of that line with some kind of ground surface.

 

This is easy to check. Look at the TGP coordinates: N 42 07.389 E 42 08.44 38'. Now compare this to the actual position of the BMP. Alternatively program a steerpoint with those coordinates and see where your TGP points (slaved, not optical track) and where JDAM goes.

 

I point track a BRT-80. TGP says 41 50.529 / 41 47.867 / 33'. Actual BTR location is 41 50.528 41 47.858 (10m). This is an error of ~12.5m.

 

However when I enable laser rangefinder suddenly TGP text displays 41 50.529 / 41 47.857 / 38 without any change in point track. Be aware that while you can type in elevation into steerpoint in DED it has no effect.

 

There may be other sources of error too. TGP to passively discover coordinates needs:

• Position of TGP
• Orientation of TGP
• Relative LOS to target
• Surface of LOS intersection

Any of these can be inaccurate. If F-16 has a system altitude error it will do calculation wrong. If F-16 has INS heading error it will do calculation wrong. Probably in DCS the relative orientation is perfect. Surface of intersection is normally a computer model database loaded into the airplane/pod which is a polygon which is not perfect to real terrain.

 

So that means that the issue is that there was no laser rangefinding used? 

That would actually make sense. 

 

What I meant with comparison to the GBU-12: If the TGP would point to the wrong point on the ground due to looking "through the BMP" my LGBs would miss by the same amount because as I circle around the target, I would see the lateral offset effectively lasing the wrong spot if I do not correct manually. 

I will try if lasing the target solves the problem. 

Thanks for the advice and for actually watching the track!

[TobiasA]

vor 21 Stunden schrieb Frederf:

If the bombs are accurate when targeting a steerpoint but missing when using TGP-supplied location then there's nothing wrong with the bomb. The issue is with the location derived by TGP. Comparison to GBU-12 is not valid because laser-guided bombs see the laser spot.

Realize that when you point track an object the TGP doesn't understand where that is in 3D space. Tracking is only a method to establish a line of sight. The line of sight is then used to calculate the intersection of that line with some kind of ground surface.

 

This is easy to check. Look at the TGP coordinates: N 42 07.389 E 42 08.44 38'. Now compare this to the actual position of the BMP. Alternatively program a steerpoint with those coordinates and see where your TGP points (slaved, not optical track) and where JDAM goes.

 

I point track a BRT-80. TGP says 41 50.529 / 41 47.867 / 33'. Actual BTR location is 41 50.528 41 47.858 (10m). This is an error of ~12.5m.

 

However when I enable laser rangefinder suddenly TGP text displays 41 50.529 / 41 47.857 / 38 without any change in point track. Be aware that while you can type in elevation into steerpoint in DED it has no effect.

 

There may be other sources of error too. TGP to passively discover coordinates needs:

• Position of TGP
• Orientation of TGP
• Relative LOS to target
• Surface of LOS intersection

Any of these can be inaccurate. If F-16 has a system altitude error it will do calculation wrong. If F-16 has INS heading error it will do calculation wrong. Probably in DCS the relative orientation is perfect. Surface of intersection is normally a computer model database loaded into the airplane/pod which is a polygon which is not perfect to real terrain.

 

 

Another test, and I lased each target before I dropped, and it resulted in a solid 4 out of 4 hit strike.

I closely watched the impact positions and they were spot-on. Also, I noticed that the TGP in fact updates the position, and until this morning, I did not know that the TGP actually uses the laser as a range finder to update the position. It makes perfect sense. I was already asking myself how the TGP gets the position, so I tried to be as steep as possible when dropping to minimize angular errors. Of course it does not matter on LGB's since you lase either way. A point track on the BMP is perfectly fine, no need to go for the wheels.

 

Would be cool if JDAM's would exist in the manual, however, this is WIP and I understand that the feature comes first and the documentation second.

 

For me, the issue is solved as of now thanks to Frederf, however @greenmamba created the thread and could mark it either as solved or write back if the problem still exists. Thanks!

[BIGNEWY]

Hi all, 

 

yes its always best to aim at the base of the target for best results.

 

thank you

[Furiz]

On 6/20/2021 at 11:19 PM, Frederf said:

If the bombs are accurate when targeting a steerpoint but missing when using TGP-supplied location then there's nothing wrong with the bomb. The issue is with the location derived by TGP. Comparison to GBU-12 is not valid because laser-guided bombs see the laser spot.

Realize that when you point track an object the TGP doesn't understand where that is in 3D space. Tracking is only a method to establish a line of sight. The line of sight is then used to calculate the intersection of that line with some kind of ground surface.

 

This is easy to check. Look at the TGP coordinates: N 42 07.389 E 42 08.44 38'. Now compare this to the actual position of the BMP. Alternatively program a steerpoint with those coordinates and see where your TGP points (slaved, not optical track) and where JDAM goes.

 

I point track a BRT-80. TGP says 41 50.529 / 41 47.867 / 33'. Actual BTR location is 41 50.528 41 47.858 (10m). This is an error of ~12.5m.

 

However when I enable laser rangefinder suddenly TGP text displays 41 50.529 / 41 47.857 / 38 without any change in point track. Be aware that while you can type in elevation into steerpoint in DED it has no effect.

 

There may be other sources of error too. TGP to passively discover coordinates needs:

• Position of TGP
• Orientation of TGP
• Relative LOS to target
• Surface of LOS intersection

Any of these can be inaccurate. If F-16 has a system altitude error it will do calculation wrong. If F-16 has INS heading error it will do calculation wrong. Probably in DCS the relative orientation is perfect. Surface of intersection is normally a computer model database loaded into the airplane/pod which is a polygon which is not perfect to real terrain.

 

Interesting indeed, thnx

 

18 hours ago, TobiasA said:

Would be cool if JDAM's would exist in the manual, however, this is WIP and I understand that the feature comes first and the documentation second.

They do exist in the manual, page 243 in the English F-16 manual. Not chuck's guide etc.

[TobiasA]

vor einer Stunde schrieb Furiz:

Interesting indeed, thnx

 

They do exist in the manual, page 243 in the English F-16 manual. Not chuck's guide etc.

Yes, however I looked in the german one at first. 

I don't have chucks guide for the F-16.