can not reproduce JDAMs hitting short or long - what's the ideal spot for ground targets with the crosshair?

[LePaul]

I've used BogeyDope's tutorials over on YouTube to learn how to mark and drop the JDAM bombs via the TGP.

Using a tank as an example, I would put the cross hair at the very base of the tank tread and the 500 pound JDAM would score a direct hit.

Lately, I am hitting short of the target.  Using the zoom and the VR zoom to verify, I am just touching the base of the vehicle.

If I put the crosshair on the tank itself, the bomb will overfly the target.

I am (correctly) using the range slider on the right side of the HUD and drop from 15K or so, depending on cloud cover.

Has anything changed in the recent releases that changed how JDAMs hit?  I'm also finding it hard to find the target via the TGP at times, whether in TV or the IR modes.

Thanks!  I appreciate your help!

 

[razo+r]

Did you fire the laser prior to release?

[LePaul]

That's interesting.  I definitely have it locked up for way longer than that and encounter the issue mentioned.

I locked the target up in VIS mode and move the TGP and zoom in on the target.  I'll do some more testing.

 

[VarZat]

My technique was always to aim at the ground that the vehicle is sitting on. Works for me

[Falconeer]

On 10/30/2023 at 5:36 PM, LePaul said:

That's interesting.  I definitely have it locked up for way longer than that and encounter the issue mentioned.

I locked the target up in VIS mode and move the TGP and zoom in on the target.  I'll do some more testing.

 

Having a Point or Area track is not enough, you need to manually "lase" the target using 1st stage trigger, for 3 seconds before release and as mentioned above, aim for the wheels/tracks

Edited November 1, 2023 by Falconeer

[TobiasA]

JDAM have a very poor precision from 25k altitude. They can be handy in a pop-up attack but rarely ever hit anything smaller than a barn from high altitude. 

It is the sum of all errors. Ownship error, TGP error, ranging error... They never hit from altitude. Even if you lase.

[Hobel]

 Not one track has been posted yet.  

What does too short or long mean? In that context.

   3 meters 30 or 300 meters?  

[Hobel]

I have tested it and the precision without laser is still more than sufficient for soft targets.

so what's the problem here?

unfortunately not comprehensible without a track

[TobiasA]

vor 2 Stunden schrieb Hobel:

I have tested it and the precision without laser is still more than sufficient for soft targets.

so what's the problem here?

unfortunately not comprehensible without a track

You are right, for soft targets. Any slightly armored vehicle will survive.

Usually, JDAMs will land anywhere in a 10m radius when dropped from 25000ft, but it is very rare to score within 3m. I stopped using them quite a while ago... 

Might be able to get a track, I'll try.

[Hobel]

vor 24 Minuten schrieb TobiasA:

You are right, for soft targets. Any slightly armored vehicle will survive.

 

vor 24 Minuten schrieb TobiasA:

You are right, for soft targets. Any slightly armored vehicle will survive.

Usually, JDAMs will land anywhere in a 10m radius when dropped from 25000ft, but it is very rare to score within 3m. I stopped using them quite a while ago... 

Might be able to get a track, I'll try.

 

Track?

I could also destroy apc without problems from 25,000 feet and more cep was around  5m

 

Edited November 3, 2023 by Hobel

[TobiasA]

vor 22 Minuten schrieb Hobel:

 

 

Track?

I could also destroy apc without problems from 25,000 feet and more cep was around  5m

 

 

Gimme a second

It is the same mission that I used for my previous tests (january if I am remembering it correctly), with the results being slightly better but still off. We talked about this back then, then the changelog came with that entry, I tried, it was different but still too far off to be useful, but as it was regarded as fixed, nobody talked about it and I was so fed up with JDAM that I stopped using them and didn't even bother.
APC's work most of the time, but still the precision is far less than 3m. A T-55 has a length of 9m. I'd say this is about 10m CEP. It works for trucks, most of the time.
If you consider it to be correct, then the JDAM should not be "advertised" with a 3m CEP because the system error on the whole thing is far larger than that. It's great for trucks and houses or your average insurgent, but the total system precision isn't suitable for vehicles.
You can mark this as "correct as is" or see it as a bug.
They have a natural tendency to go long, as the point in space is above ground, and if you miss it with the CEP in the "long" part of it (too high), you land several meters long. And it also depends on where you lase, and your luck, and also on if you drop uphill or downhill. Don't ever drop downhill.
If you want to kill vehicles, forget JDAMs and use LJDAMs (not gonna happen on the 16 in DCS) or LGB.

F-16_JDAM_2_9.trk

[TobiasA]

Plus, it is not the impact angle (that seems to not affect the JIZ either way), it is the total system error.
Picture from this track, pickled later, lased, impact angle 90°:

I leave it up to you to decide if this is a bug or not, but the CEP is not 3m. Also, most shots should land near the center, but if they miss, they will miss by about the same distance. At least in my tests. Most of them will hit, but about one or two in four will miss.

F-16_JDAM_2_9_Part2.trk

[Hobel]

Thanks, the post is already much richer in detail.    I will test the whole thing again in more detail and take your points into account.  

 

But what I see from your post seems to be the old bug that is back?  

  I have not been able to observe this yet, will test when I get home.  

Edited November 3, 2023 by Hobel

[itn]

@TobiasA what are your expected results here? Maybe there is a misunderstanding of CEP? Circular Error Probable (CEP) is a statistical measure, defined as the radius of a circle within which 50% of the impacts should land.

8 drops is not much statistics-wise but you did get four direct hits out of eight JDAMs, with the other four being maybe 7-9m out.

I took the miz and tried it. Two runs, one without laser and with. Designated a bit lower than you, at the tank tracks/side. On both runs I got pretty much exact same results each: Two direct hits, two close misses, one of the close misses ended up killing a tank. So in two runs 6/8 tanks killed.

For actual CEP calculations I think you need to do quite a bit more drops. You can do this with for example some creative usage of target range scripts, Unlimited Weapons, Active Pause, Joystick Gremlin and Excel...

Most definitely this is not the old bug with the really inaccurate JDAMs.

[Sinclair_76]

I was one of the original (for lack of a better word) complainers of the lack of precision of the GBU-38. I also suggested and referenced the CEP of the GBU-38 being 5m. 

First of all the CEP:
 

54 minutes ago, itn said:

Circular Error Probable (CEP) is a statistical measure, defined as the radius of a circle within which 50% of the impacts should land.

This means that a miss of 10 meters is as likely as a direct hit. 

That is still pretty huge. The first iterations of the JDAM (at least just prior 2003) weren't even considered precision but near precision weapons. They are not as precise as LGB's which have a CEP of 1.1m. With the lack of splash damage in DCS I wouldn't consider GPS/INS guided munition suitable for hard targets, the -108 being the exception .

In the complaint/bug finding in the beginning of this year I tested it on soft skin vehicles (BTR-80's) and 4 out of 4 survived. Just now did a similar test with 3x BTR-80's and none survived (3x K-kill) with pretty much 2 of 3 direct hits. To further develop the test I used T-55 in stead of BTR's and now 2 out of 3 were K-kills (tested it 3x with the same results). 

All in all the GBU-38 seems to work as advertised. I did use the 3 second lase before designating (TMS up) to get a precise coordinate hand-off. 


Test-GBU38.mizTest-TOO-GBU-38.trkTest-TOO-GBU-38-t55.trk

Edited November 3, 2023 by Sinclair_76
adjusted feet to m.

[Hobel]

So without lasers I was able to destroy 10 out of 10 BMP2s
 

as far as i can see, the laser probably makes no difference


Note:the Targeds were not the vehicles, only serve as scale

Edited November 3, 2023 by Hobel

[TobiasA]

I am unsure if this is a bug. Honestly... If you want a CEP of 3m, or precision like the LGB with 1.1m (the optics and its drives and stabilization needed for that on a platform moving with half the speed of sound is INSANE) you need to be perfect with everything. You need to compensate incredibly weird things like the speed of light, computing delays and other stuff.

And yes, i had a wrong picture of the CEP and I was under the impression that the majority of hits land inside of 3m (Gauss distribution).

Thanks for pointing that out. 

Bottom line: Don't use JDAMS for vehicles. 

[Hobel]

vor 5 Stunden schrieb TobiasA:

I am unsure if this is a bug. Honestly... If you want a CEP of 3m, or precision like the LGB with 1.1m (the optics and its drives and stabilization needed for that on a platform moving with half the speed of sound is INSANE) you need to be perfect with everything. You need to compensate incredibly weird things like the speed of light, computing delays and other stuff.

And yes, i had a wrong picture of the CEP and I was under the impression that the majority of hits land inside of 3m (Gauss distribution).

Thanks for pointing that out. 

Bottom line: Don't use JDAMS for vehicles. 

I just posted a video where 10 out of 10 vehicles were destroyed.   The weapon works well and reliably against the type of target in dcs, very much so.

[jubuttib]

On 10/30/2023 at 6:24 PM, razo+r said:

Did you fire the laser prior to release?

Slightly different, but related: It says in the patch note that "... or AGR required", do I need to do something specific with the A-G radar to get the improved accuracy, or just have it turned on?

[razo+r]

33 minutes ago, jubuttib said:

Slightly different, but related: It says in the patch note that "... or AGR required", do I need to do something specific with the A-G radar to get the improved accuracy, or just have it turned on?

AGR is only available in certain modes like STRAFE, CCIP, DTOS, EOVIS, HUD MARK, - FIX, - ACAL. 

[Sinclair_76]

On 11/5/2023 at 1:49 AM, jubuttib said:

Slightly different, but related: It says in the patch note that "... or AGR required", do I need to do something specific with the A-G radar to get the improved accuracy, or just have it turned on?

The way I interpret this is that a AG radar handoff is already as accurate as it can get. Makes sense because unlike the laser it's constantly ranging already. 

[TobiasA]

I am pretty sure that laser ranging is more accurate than radar ranging.