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JDAM guidance?


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Hi all,

 

I'm having a hard time getting JDAMS (and L-JDAMS in non-laser guidance) on target reliably on target. I'm using a SPI designation using the TGP, then dropping in CCRP when in range. However, firing near the upper and lower bounds of the engagement range, the reliability of the bombs is really low, with impacts 20 meters or so meters away from the target. Fiddling with impact angle and azimuth doesn't seems to change that. Is there any trick I'm not aware of ? I found out that firing at roughly two third of the range give good results, but this means that ripple fire on multiple targets isn't doable...

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Are you using area or point track in TGP?  I find point track to be more reliable with latest version.  If using area track, you need to point it at the ground where the target is sitting on.

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15 hours ago, Taz1004 said:

Are you using area or point track in TGP?  I find point track to be more reliable with latest version.  If using area track, you need to point it at the ground where the target is sitting on.

Yes, I'm usually using point track. I'm aware of the ground issue with area track, but this isn't the issue here.

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I don't have an answer for you but I have also noticed this. It seems like 2 mile range is the sweet spot for consistently hitting. Most of my recent attempts have been around 9-12,000 ft, and if I drop near the top of the in range cue (generally around 4 miles), my JDAMs don't hit, seemingly by way more than 20 meters.

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JDAM guidance is kinda off for a really long time now, I've been having issues with them since early 2020.

 

You need to nurse them carefully, drop them around mid range, and always drop them high,

at least above 6000ft AGL, I always drop them above 8000. This would give you good accuracy.

 

The bomb guidance needs to be fixed I think, the glide path is very wacky in some cases.

Sometimes the bomb flies right above the target, then take a 90 degree nose dive, and it misses because it corrects too much at terminal.

And its really random, replaying the track a few times, it doesnt even have the same hit/miss results, the bomb is doing different stuff everytime you replay the track. (From my old test, havent tested them after GBU54 came out, but I dont feel like the glide path changed for better.)

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5 hours ago, Taz1004 said:

JDAM was really inaccurate and was fixed in recent patch.  I'm getting about 80%-90% accuracy now whereas it was pretty much a dumb bomb before.

 

80/90% in single drop? 

Because the issue isn't really with single bomb attacks, the launch parameters are tricky to get right but this can be managed. The issue is more that because the launch parameters are quite restrictive, firing multiple JDAMs at multiple targets usually results in a large proportion of misses. Sure, I can drop one JDAM at a time, but at that point I'm better off using good ol' GBU-12s.

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Posted (edited)
49 minutes ago, LetMePickThat said:

 

80/90% in single drop? 

Because the issue isn't really with single bomb attacks, the launch parameters are tricky to get right but this can be managed. The issue is more that because the launch parameters are quite restrictive, firing multiple JDAMs at multiple targets usually results in a large proportion of misses. Sure, I can drop one JDAM at a time, but at that point I'm better off using good ol' GBU-12s.

 

I am talking about rippling 4.

 

There already is a thread about this and as I posted here couple weeks ago, when rippling 4, I sometimes get one miss from time to time.  But otherwise, they're spot on.

 

 


Edited by Taz1004
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Dropping on markpoints I get 100% accuracy unless the target moves between the time I create the markpoint and drop. 

 

16,000~18,000ft, release at 4~5nm. Never fails for me. 

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Posted (edited)

Are you making sure  INS is aligned before taking off? If I remember correctly GPS guided bombs get thier targeting data from the INS in the A-10 if you move before it is done or do a fast alignment it may not be accurate. Also make sure you are dropping from a height that gives the JDAM time to find the target. I find Angels 10 and up works but I shoot for 15 at least  and if that fails get the coordinates with the TGP and create a custom mission way point for the drop.


Edited by TheOtherSider
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12 hours ago, TheOtherSider said:

Are you making sure  INS is aligned before taking off? If I remember correctly GPS guided bombs get thier targeting data from the INS in the A-10 if you move before it is done or do a fast alignment it may not be accurate. Also make sure you are dropping from a height that gives the JDAM time to find the target. I find Angels 10 and up works but I shoot for 15 at least  and if that fails get the coordinates with the TGP and create a custom mission way point for the drop.

 

AFAIK EGI degraded accuracy is not modeled, just alignment time.  As long as you align the EGI long enough to get your systems running, the EGI accuracy is still perfect.  As such, there's no disadvantage to in-flight or fast alignment in terms of EGI accuracy.

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Are we sure degradation isn't modeled? If you fly straight and level for a long period of time and check the stores page all GPS weapons will show alignment degraded. Rock the wings a bit and they come back to ALN RDY.

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It's not modelled, as such. It's more like… “represented” in that you have to do that little wiggle after a while. A lot of systems in DCS work like that: some semblance of the effect is in, but it's just scripted to be there rather than something that is actually generated by some underlying simulated process of accumulation of errors.

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  • 2 weeks later...

Tried several JDAM (54s and 31s) drops after the update yesterday and it seems to be worse now.  All bombs dropped within range, laser on, point track mode, various altitudes, etc., and most still fly over the target, then start tracking too late and miss the target long.  I also noticed a strange behavior where sometimes they will be tracking correctly, then lose track and miss wildly long.


Edited by dporter22
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Are you trying to drop GPS guided bombs or Laser guided ? If you are dropping a GPS guided bomb you have to enter in the target coordinates on the CDU. The GPS guided bombs do not track lasers to the target. Only the GBU 12 is laser guided, The GBU 31 and 38 are GPS guided bombs. at least that is the only thing I can think you are doing wrong? if you are dropping laser guided bombs make sure your laser codes match.

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Dropped GBU-54's last night, and they worked--okay.  Looks like they're going long at first, then they drop vertically over the target.  One with laser on, one with laser off.

 

FWIW, I designated the target with the TGP by making it SPI.  You don't have to enter location on the CDU, just make it SPI.

 

 

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3 hours ago, TheOtherSider said:

Are you trying to drop GPS guided bombs or Laser guided ? If you are dropping a GPS guided bomb you have to enter in the target coordinates on the CDU. The GPS guided bombs do not track lasers to the target. Only the GBU 12 is laser guided, The GBU 31 and 38 are GPS guided bombs. at least that is the only thing I can think you are doing wrong? if you are dropping laser guided bombs make sure your laser codes match.

You generally want to lase the target even when dropping GPS bombs to compensate for the parallax difference between the actual position and the position by the TGP (which will be behind the target, and possibly quite some distance away at low slant angles). It's not to guide the bomb, as such— it's the get the right position to feed to the bomb's guidance before it drops.

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7 hours ago, TheOtherSider said:

Are you trying to drop GPS guided bombs or Laser guided ? If you are dropping a GPS guided bomb you have to enter in the target coordinates on the CDU. The GPS guided bombs do not track lasers to the target. Only the GBU 12 is laser guided, The GBU 31 and 38 are GPS guided bombs. at least that is the only thing I can think you are doing wrong? if you are dropping laser guided bombs make sure your laser codes match.


He said he was running into the issue with the GBU-54. which is (optionally) laser-guided.

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11 hours ago, Tippis said:

You generally want to lase the target even when dropping GPS bombs to compensate for the parallax difference between the actual position and the position by the TGP (which will be behind the target, and possibly quite some distance away at low slant angles). It's not to guide the bomb, as such— it's the get the right position to feed to the bomb's guidance before it drops.

 

Is laser ranging to obtain more accurate coordinates even simulated in DCS? :huh:

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3 hours ago, QuiGon said:

 

Is laser ranging to obtain more accurate coordinates even simulated in DCS? :huh:

It may be a bit received wisdom and voodoo operation, but it's something that has been recommended as good practice since forever. So there's that. 😄

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3 hours ago, QuiGon said:

Is laser ranging to obtain more accurate coordinates even simulated in DCS? :huh:

 

Pretty sure it is, yes. With a solid track (regardless of POINT or AREA) and a good parallax offset, lasing should immediately update both the slant range and the coordinates as displayed in the TGP. Creating markpoints out of these (with and without lasing) should also reflect the difference in coordinates. I'm almost certain I tested this a few years back just to be on the safe side.

 

BTW and slightly off topic, there's a common pitfall and misunderstanding by inexperienced A-10 pilots that lasing a target once will update the target's coordinates. However, that is only true as long as the laser if firing. As soon as the laser goes off, the ranging goes back to TGP LOS intersecting the ground (as given by the digital terrain elevation database) and will immediately ignore any object between the TGP and the ground. Long story short, lasing makes sense when markpoints are created from the TGP, and when weapons are dropped in CCRP with the TGP as SPI Generator just as the pickle button is pressed and the IFFCC calculates the release parameters and feeds them to the weapon (in case of IAMs).

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5 minutes ago, Tippis said:

It may be a bit received wisdom and voodoo operation, but it's something that has been recommended as good practice since forever. So there's that. 😄

 

Yeah, I've read this recommendation for the A-10C (and sometimes other TGP equipped aircraft as well) so many times over the years, but yet I've never been able to confirm that this is actually simulated in DCS. To me the TGP without lasing seems to be absolutely precise in DCS and lasing doesn't seem to change anything in this regard.

I understand how lasing improves the precision IRL, as the pure navigation and terrain data isn't as precise, but in DCS this doesn't seem to be an issue.

 

 

Edit:

 

2 minutes ago, Yurgon said:

 

Pretty sure it is, yes. With a solid track (regardless of POINT or AREA) and a good parallax offset, lasing should immediately update both the slant range and the coordinates as displayed in the TGP. Creating markpoints out of these (with and without lasing) should also reflect the difference in coordinates. I'm almost certain I tested this a few years back just to be on the safe side.

 

Hmm, I remember you talking about your tests. Maybe I should actually test it myself. The thing is just, that the TGP without laser ranging is already so incredible precise in DCS (unrealistically?), that I don't see any marging for improvement that a laser could bring.


Edited by QuiGon

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12 minutes ago, QuiGon said:

The thing is just, that the TGP without laser ranging is already so incredible precise in DCS (unrealistically?), that I don't see any marging for improvement that a laser could bring.

 

I'm not sure at what range a Mk82 type of bomb will kill an MBT in DCS, but it's got to be pretty darn close. A JDAM hitting 10 meters off might not be good enough to score a mission kill. In that regard, I'll take all the precision I can get. 😉

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11 minutes ago, Yurgon said:

 

I'm not sure at what range a Mk82 type of bomb will kill an MBT in DCS, but it's got to be pretty darn close. A JDAM hitting 10 meters off might not be good enough to score a mission kill.

 

Indeed, but as I said, in my experience the TGP in DCS already provides unrealistically(?) precise target coordinates (down to 1m or so), so I don't see any margin to improve by adding laser ranging.


Edited by QuiGon

Intel i7-4790K @ 4x4GHz + 16 GB DDR3 RAM + Nvidia Geforce RTX 2080 (8 GB VRAM) + M.2 SSD + Windows 10 64Bit

 

DCS Panavia Tornado (IDS) really needs to be a thing!

 

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33 minutes ago, QuiGon said:

Yeah, I've read this recommendation for the A-10C (and sometimes other TGP equipped aircraft as well) so many times over the years, but yet I've never been able to confirm that this is actually simulated in DCS. To me the TGP without lasing seems to be absolutely precise in DCS and lasing doesn't seem to change anything in this regard.

I understand how lasing improves the precision IRL, as the pure navigation and terrain data isn't as precise, but in DCS this doesn't seem to be an issue.

It's not that the terrain data isn't precise enough — it's that if you just go by the TGP calculation, it gets the totally accurate terrain data of the wrong point on the terrain. I've certainly seen indications of that being true when launching from absurdly low angles or at anything on a ridge… but to what extent the error is great enough to truly warrant all the chicken-waggling is still unclear.


Edited by Tippis
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