cannot reproduce JDAM Pre Mode not working

[Viper1031]

Multiple times now I have set up JDAMs in Pre mode, triple checked the coordinates, made sure to enter all three sets of numbers. Once airborne and on my way to target, the target reticle will be hundreds of miles off target, doesn't matter which JDAM I use. I thought at first it was pilot error, (and it still could be) but now, I'm thinking it's a bug. Please help.

[rob10]

Without a track it's going to be very difficult to help you.  My first guess (and without a track it's completely a guess) is you're mixing co-ordinate formats

[Viper1031]

5 hours ago, rob10 said:

Without a track it's going to be very difficult to help you.  My first guess (and without a track it's completely a guess) is you're mixing co-ordinate formats

Not sure how to get a track, but I don't *think* I'm mixing formats, I do alt + y twice on the coordinates before I input them. Strange thing is, if I lose a plane, it seems to start working for a bomb or two

[BIGNEWY]

please try in a single player mission, when you exit the mission you can save the track replay in the debrief window.

thank you 

[Viper1031]

15 hours ago, BIGNEWY said:

please try in a single player mission, when you exit the mission you can save the track replay in the debrief window.

thank you 

Will do. Thank you

[Shibiswag]

19 hours ago, Viper1031 said:

Not sure how to get a track, but I don't *think* I'm mixing formats, I do alt + y twice on the coordinates before I input them. Strange thing is, if I lose a plane, it seems to start working for a bomb or two

Nope, same thing is happening to me, I already submitted a track, did coordinates correctly, even used the A-Fix function to make sure the Delta was only within a few feet 1-3ft yet bombs miss by a good 20-30ft.
Every server I go into to ask, and all people confirm that they are all having the same issue with JDAMS using the 16.
All other aircraft such as 15E and 18 work just fine.

[Sinclair_76]

Apparently the JDAM has sub-modes that haven't been correctly modelled and ED is working on it (or considering it WIP at least). It has to do with the navigation inaccuracies recently introduced in the F-16.

The JDAM sub-modes are called absolute and relative. As per "An Analysis of Target Location Error Generated by the Litening Pod as Integrated on the AV-8B Harrier II Pod as Integrated on the AV-8B Harrier II " p.7.

 

The relative mode of the weapon is used when onboard the aircraft sensors are used to generate the target coordinates. In the relative mode, once the JDAM acquires a GPS signal after release from the aircraft, the weapon compares its GPS position to the JDAM INS position (previously aligned to the aircraft). Any difference is assumed to be an aircraft induced position error. The error is then applied as a correction factor (bias) to the coordinates (Figure 1-3). This bias is nearly zero when the weapon is aligned to a tightly coupled aircraft because both weapon and aircraft are using the same navigation source (GPS). However, if the sources are different (loosely coupled aircraft and tightly-coupled weapon) the bias allows the aircraft to designate a position relative to its own location without concern for aircraft INS induced errors [5]. This bias to the target coordinates will be in the same direction and magnitude as the aircraft handoff error. The application of a bias to the weapon did not change the position of the target but instead changed the reference frame to the aircraft-based (relative) reference frame from the earth-based (absolute) reference frame. 

 

In our version of DCS, the relative sub-mode of the GBU works.

 

Regarding a pre-planned target, the target coordinates are considered absolute. In other words there is hardly or no error in the target coordinates as was certainly the case regarding a target of opportunity, where the aircraft position error carries over to the target location. If the same logic was applied when dropping a GBU on an absolute coordinate the bomb would (incorrectly) maintain the bias and miss the target. That is were absolute mode comes in. When a pre-planned (steerpoint) grid/location, without cursor slew, is transferred to the bomb it is considered absolute. In the absolute sub-mode when the GPS of the bomb comes online (28sec) it won't apply the here fore mentioned bias but will try steer to the given grid and hit the target. 

In our version of DCS, the absolute sub-mode of the GBU does not work.

 

To overcome this discrepancy you would have to trick the system in relative sub-mode by applying cursor slew. The most effective way of doing this is slaving TGP to the steerpoint, slew over to the base of the target and TMS up to designate.

 

All in all, I would rather have ED implementing a complete (relative and absolute) solution rather than what we have now but I applaud their commitment to realism. The fact that there are errors to deal with makes the F-16c feel alive and realistic. At the same time I get that the relative sub-mode is fairly easy to program compared to the absolute sub-mode.

 

 

 

Edited May 29, 2024 by Sinclair_76

[Lord Vader]

Hey @Viper1031

Like previous stated by @Sinclair_76, the IDM self guiding capabilities in the current version are limited to the coordinates + drift delivered by the aircraft's MMC. For that matter, regardless of correct GPS coordinates you input, you will always send your own INS drift to the bomb. This is a realistic outcome. In the future, after a period of time, the weapon will be capable of self correcting it (if given the time), and make it more precise.

For the time being, however, you will always need to designate the target using the onboard sensors (TGP, FCR, HUD) to guarantee the desired precision. 

[Viper1031]

9 hours ago, Lord Vader said:

Hey @Viper1031

Like previous stated, by @Sinclair_76, the IDM self guiding capabilities in the current version are limited to the coordinates + drift delivered by the aircraft's MMC. For that matter, regardless of correct GPS coordinates you input, you will always send your own INS drift to the bomb. This is a realistic outcome. In the future, after a period of time, the weapon will be capable of self correcting it (if given the time), and make it more precise.

For the time being, however, you will always need to designated the target using the onboard sensors (TGP, FCR, HUD) to guarantee the desired precision. 

Thank you and @Sinclair_76 for the answer. 

[Strannix]

Hi, If you use an inboard sensors you will have more inaccuracy. That the way it works IRL.

A inboard sensors need his location (aircraft INS/GPS position) to extract grids. So if you have error on your own location + sensor error you will have less precision compare to a pre planned coordinate. There is no more accurate things than a pre planned location.

As @Sinclair_76 mentioned there is two mode on JDAM:
- INS only. You're completely dependant on the aircraft own position and the accuracy of your TGT grids
- INS/GPS. After release (around 10s)if the internal GPS bomb detect an error between the initiale location given by the aircraft, it will take his own location because he is assuming an aircraft error.

So at this time we've got the more accurate mode of the JDAM and it's even more accurate that the thing you have IRL.

A JDAM Circular Error Probability (CEP) is 13m in relative mode and 30m in absolute mode. That mean you will have 50% of impact inside CEP radius. I don't even speak about of Vertical Error (VE) that put more error on the impact of the bomb.

From my test in DCS, 90% or more of the bombs are hitting inside the 13m CEP so it's far more accurate than reality.

The problem in DCS is the ineffectiveness of ammunitions and to compensate that you need to hit less than 5m of target. That why people are complaining about accuracy but it's not the source of the problem.
    

Edited June 6, 2024 by Strannix

[drspankle]

On 5/29/2024 at 3:14 AM, Shibiswag said:

Nope, same thing is happening to me, I already submitted a track, did coordinates correctly, even used the A-Fix function to make sure the Delta was only within a few feet 1-3ft yet bombs miss by a good 20-30ft.
Every server I go into to ask, and all people confirm that they are all having the same issue with JDAMS using the 16.
All other aircraft such as 15E and 18 work just fine.

The CEP is 30m, or 100ft.  That means 50% of the weapons dropped should fall within that radius. So, 30ft is perfectly acceptable accuracy for a GBU38. Realism we wanted, realism we got ...

[Shibiswag]

21 hours ago, drspankle said:

The CEP is 30m, or 100ft.  That means 50% of the weapons dropped should fall within that radius. So, 30ft is perfectly acceptable accuracy for a GBU38. Realism we wanted, realism we got ...

So then why are 100% failing to hit their target when the coordinates are input in a stp in the 16?
Yet the 15E which uses the same ##.##.### format, bombs hit 100% of the time and on direct target.
the 18 as well even though it uses the ##.##.##.## format, still again, hits are 100% of the time.
As well as the A10C1&2
This issue is specifically tied to the F16 in their last INS/GPS update.
Something broke between the functionally of the GPS/INS system in the plane and the coordinates to the weapons.
It's not just JDAMS, it's any guided munition aside from LGB, this includes WCMDS as well as the AGM-158 all weapons when put in via stp fail to hit their targets.
Because if that's the case for the JDAM, this issue would present on all platforms that can carry it.
Also why is it when i use the TGP in the 16 and creating mark points, they hit their target 100% of the time.
Sorry I don't understand your logic.
and it's actually 40ft (13m) according to the USAF.

[Strannix]

As i already mentioned, JDAM are too much accurate in DCS even more in F18, F15 or A10 that's completely unrealistic. The F16 introduce a more realistic way of INS/GPS system who has input error on the aircraft location during flight. a JDAM will use the aircraft location at the release moment and after few seconds use his own GPS to correct his own location during flight path if it detect an error.
In DCS from what i saw, the CEP is around 4m to 7m with F16, so it's quite more accurate than reality but the effect of bombs and ammunitions in general are bull<profanity> and that's why it's uneffective. 

[Shibiswag]

6 hours ago, Strannix said:

As i already mentioned, JDAM are too much accurate in DCS even more in F18, F15 or A10 that's completely unrealistic. The F16 introduce a more realistic way of INS/GPS system who has input error on the aircraft location during flight. a JDAM will use the aircraft location at the release moment and after few seconds use his own GPS to correct his own location during flight path if it detect an error.
In DCS from what i saw, the CEP is around 4m to 7m with F16, so it's quite more accurate than reality but the effect of bombs and ammunitions in general are bull<profanity> and that's why it's uneffective. 

Yes according to the Airforce it's 13m(40FT)
I understand realism but even the accuracy is 80% within that CEP IRL
However, f16 = 100% miss rate for all smart weapons, not just the JDAMS, but I did some plays online with the WMCDS and Brusers both go way past the PPSTP before releasing their bomblets resulting in a miss, though sometimes the bomblets drift over and dmg the target but still not good.
So they need hopefully update it soon and add the two sub modes and tweak it on those or find some way to fix the INS of the 16.
I mean I'm playing the 18 and the 15 so I don't have to worry about the JDAMS/OSM with those.
Heck even went back to flying the good ol hog.

[Sinclair_76]

On 6/5/2024 at 7:22 PM, Strannix said:

Hi, If you use an inboard sensors you will have more inaccuracy. That the way it works IRL.

A inboard sensors need his location (aircraft INS/GPS position) to extract grids. So if you have error on your own location + sensor error you will have less precision compare to a pre planned coordinate. There is no more accurate things than a pre planned location.

As @Sinclair_76 mentioned there is two mode on JDAM:
- INS only. You're completely dependant on the aircraft own position and the accuracy of your TGT grids
- INS/GPS. After release (around 10s)if the internal GPS bomb detect an error between the initiale location given by the aircraft, it will take his own location because he is assuming an aircraft error.

So at this time we've got the more accurate mode of the JDAM and it's even more accurate that the thing you have IRL.

A JDAM Circular Error Probability (CEP) is 13m in relative mode and 30m in absolute mode. That mean you will have 50% of impact inside CEP radius. I don't even speak about of Vertical Error (VE) that put more error on the impact of the bomb.

From my test in DCS, 90% or more of the bombs are hitting inside the 13m CEP so it's far more accurate than reality.

The problem in DCS is the ineffectiveness of ammunitions and to compensate that you need to hit less than 5m of target. That why people are complaining about accuracy but it's not the source of the problem.
    

 

The JDAM CEP is not bound to the sub-mode employed in the GBU. In a GPS denied environment only the INS will provide guidance and the CEP is 30m. If GPS is available the CEP is 5m (Boeing even claims 1.7m)

source for 5m/30m CEP https://www.esd.whs.mil/Portals/54/Documents/FOID/Reading Room/Selected_Acquisition_Reports/FY_2018_SARS/19-F-1098_DOC_46_JDAM_SAR_Dec_2018.pdf
https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104572/joint-direct-attack-munition-gbu-313238/
source for 1.7m CEP https://www.boeing.com/content/dam/boeing/boeingdotcom/defense/weapons-weapons/images/jdam_product_card.pdf
source for 3m (after JDAM PIP) https://www.esd.whs.mil/Portals/54/Documents/FOID/Reading Room/Selected_Acquisition_Reports/FY_2018_SARS/19-F-1098_DOC_46_JDAM_SAR_Dec_2018.pdf (p.15)

 

The 13m CEP (with GPS) was an early figure before actual use data was available and the JDAM PIP. After actual usage the CEP dropped to 4.2m. After the JDAM PIP, CEP drops to 3m.

The PIP probably consisted of the employment of better Kalman Filters or differential GPS/ GBAS.
https://www.ausairpower.net/TE-JDAMPt1.html
https://www.globalsecurity.org/military/systems/munitions/jdam-antijam.htm

Edited June 10, 2024 by Sinclair_76

[Viper1031]

I've unmarked this as solved due to the issue still occurring. I might need to clarify: Most of these answers are for a few meters. I'm talking MILES. I'll put in target coordinates, after cycling to the correct ones on the F-10 map, once airborne I'll set to that steerpoint, and lo and behold, it's showing that steerpoint is tens to hundreds of miles off from where the target actually is. Some times it corrects itself, some times it doesn't.

[Hobel]

vor 7 Minuten schrieb Viper1031:

I've unmarked this as solved due to the issue still occurring. I might need to clarify: Most of these answers are for a few meters. I'm talking MILES. I'll put in target coordinates, after cycling to the correct ones on the F-10 map, once airborne I'll set to that steerpoint, and lo and behold, it's showing that steerpoint is tens to hundreds of miles off from where the target actually is. Some times it corrects itself, some times it doesn't.

Pls upload a track.

[Lord Vader]

On 6/6/2024 at 4:13 PM, Shibiswag said:

So then why are 100% failing to hit their target when the coordinates are input in a stp in the 16?
Yet the 15E which uses the same ##.##.### format, bombs hit 100% of the time and on direct target.
the 18 as well even though it uses the ##.##.##.## format, still again, hits are 100% of the time.
As well as the A10C1&2
This issue is specifically tied to the F16 in their last INS/GPS update.

This will happen as you describe because currently only the DCS: F-16C uses the newest most realistic INS+GPS model we've developed. You answered it yourself. Furthermore, this isn't an "issue", just a more realistic depiction of how these weapons actually work, minus the already mentioned GPS self-correction algorithm still to be implemented in the IDMs. 

On 6/6/2024 at 4:13 PM, Shibiswag said:

Something broke between the functionally of the GPS/INS system in the plane and the coordinates to the weapons.

There's nothing "broken" in this specific area. The weapons will receive coordinates+INS drift from the aircraft's MMC. This is working as intended.

On 6/7/2024 at 12:01 AM, Shibiswag said:

However, f16 = 100% miss rate for all smart weapons, not just the JDAMS, but I did some plays online with the WMCDS and Brusers both go way past the PPSTP before releasing their bomblets resulting in a miss, though sometimes the bomblets drift over and dmg the target but still not good.

If you have only the pure coordinates sent to the weapon, what is delivered to the weapon is that plus INS drift, this will also be what's calculated in other CCRP type release weapons. If you want precision for all modes, including IDM, please designate targets with sensors like TGP, FCR or HUD.

14 hours ago, Viper1031 said:

I've unmarked this as solved due to the issue still occurring. I might need to clarify: Most of these answers are for a few meters. I'm talking MILES. I'll put in target coordinates, after cycling to the correct ones on the F-10 map, once airborne I'll set to that steerpoint, and lo and behold, it's showing that steerpoint is tens to hundreds of miles off from where the target actually is. Some times it corrects itself, some times it doesn't.

We cannot reproduce your issue. If you use the incorrect coordinate format this may happen. As suggested, a track is necessary to analyse your issue.

[Q3ark]

8 hours ago, Viper1031 said:

I've unmarked this as solved due to the issue still occurring. I might need to clarify: Most of these answers are for a few meters. I'm talking MILES. I'll put in target coordinates, after cycling to the correct ones on the F-10 map, once airborne I'll set to that steerpoint, and lo and behold, it's showing that steerpoint is tens to hundreds of miles off from where the target actually is. Some times it corrects itself, some times it doesn't.

They’re going to need a track replay to fault find, it’s impossible to understand what’s happening at a technical level from a written description on the forum.

[Viper1031]

Issue self resolved. Can close thread