w.i.p. F-16 Pre-setting JDAM Accuracy (Steerpoint) in free server after april Patch

[dinnfish]

Hi dcs team..,

I've been playing on the Freeserver (Caucasus, Syria) map, flying the F-16 with "hot start". I typically use the JDAM 500-pound bombs to target ground locations, obtaining coordinates from the MAP (F10) feature and then deploying the JDAMs without a targeting pod (TGP).

However, since the recent patch, I've noticed that the JDAMs are no longer hitting their targets accurately. It seems like there's an issue with targeting precision after the update. Have you encountered this problem before, and do you know if there's a solution?

 

Here is situation 

1) I normally used hot start/ but tested with cold start. 

2) the jdam shot always near the target but, not work, almost have same distance. 

I posted in reddit and people said "It could be the way you are starting the plane."

And I also saw mini update about align, 

But for hot start, could you make it all good without extra process?

 

[Furiz]

We will need short track replicating the issue,

JDAM is not so accurate, it wont miss by a mile but it can miss its target,

using it with TGP Laser Ranging will increase its accuracy, also in VIS mode with AGR (air to ground ranging).

[dinnfish]

Hi.

 

I replicating in training JDAM, It does work at all. 

It can miss, but all jdam were away from actual target. 

 

Here is comments what I got from reddit and discord

 

null

monkeythebee

•3d ago

 

I also have noticed this on the free server the other day that even entering dead accurate coordinates and altitude of the target, the way point is still off from the target that even CBU105 isn’t enough to take the target out.

Could be combo of CEP and new INS bug. Marverick air boresight is also completely borked with new INS implementation.

 

 

 

Alen — 2024.04.21. 오후 4:54

Yes i ve encountered the same problem even with the jf17s glide jdams, its normal for jdams to miss by a few meters in pp mode so it might stay like that. I suggest you to use tgp with jdams as it will spare u the coordinate entering time on the ground

Lesson 24 - JDAM Employment.miz_24042024_11-11.trk win7.mds

[RyanR]

Is the steerpoint at ground level?

I've had no trouble with JDAM's, if I first point the TGP at the steerpoint. Usually, there are multiple targets at a steerpoint. Slew the TGP at each, and let the JDAM's go.

-Ryan

 

[jubuttib]

2 hours ago, RyanR said:

Is the steerpoint at ground level?

I've had no trouble with JDAM's, if I first point the TGP at the steerpoint. Usually, there are multiple targets at a steerpoint. Slew the TGP at each, and let the JDAM's go.

-Ryan

 

This. By default the steerpoints don't really sit on the ground neatly.

[Sinclair_76]

So I've tested this.

Mission setup 2 targets and my player aircraft. One steerpoint over first target. Double checked altitude. 

I did a full NAV line up with the aircraft on a platform, not in a bunker, using GPS according new procedures.
All systems display a high accuracy in the DED.
Made sure the GBU-38 did a full lineup (READY MSG)

Once airborne the TGP slaved roughly 50 meters to the west. The GBU-38 falls roughly on that, 50m west of target, position.

Update the tgt with an TMS up results in the 'normal' 5m CEP. And subsequent tgt kill.

An air start resulted in a different issue. It seems like the target altitude is incorrect / too high. Before tgt the tgp is aiming too high and straight above the error seems almost 0.

Funky stuff. I've some more testing to do so no replay just yet. But it's like 2 steps forward 3 steps back with the F-16.

Edited April 30 by Sinclair_76

[Furiz]

15 minutes ago, Sinclair_76 said:

So I've tested this.

Mission setup 2 targets and my player aircraft. One steerpoint over first target. Double checked altitude. 

I did a full NAV line up with the aircraft on a platform, not in a bunker, using GPS according new procedures.
All systems display a high accuracy in the DED.
Made sure the GBU-38 did a full lineup (READY MSG)

Once airborne the TGP slaved roughly 50 meters to the west. GUB-38 fll roughly on that 50m west of target position.

 

An air start resulted in a different issue. It seems like the target altitude is incorrect / too high. Before tgt the tgp is aiming too high and straight above the error seems almost 0.

Funky stuff. I've some more testing to do so no replay just yet. But it's like 2 steps forward 3 steps back with the F-16.

Please post a track of that test. After you end mission you will see a screen where you can save the track. Name it and post it here.

[Sinclair_76]

3 minutes ago, Furiz said:

Please post a track of that test. After you end mission you will see a screen where you can save the track. Name it and post it here.

 

19 minutes ago, Sinclair_76 said:

I've some more testing to do so no replay just yet. But it's like 2 steps forward 3 steps back with the F-16.

I will. And I know how. But as far as I can tell preplanned JDAM targets are inaccurate.

Edited April 30 by Sinclair_76

[Sinclair_76]

The new navigation alignment for the F-16 is not accurate enough for pre planned GBU-38 delivery.

 

Did a full INS alignment in open air according new procedures.

Aligned GBU-38 on the ground.

Verified target coordinates and corrected longitude (top coordinate on kneeboard). You can verify with miz file

Once airborne delivered a GBU-38 on preplanned target. Target not destroyed. Although this trackfile is only on run I did many, none hit the target.

Than proceeded for a TOO delivery. 1st TOO GBU-38 was fault on my side. 2nd TOO was a hit. You can crosscheck coordinates with kneeboard (lower coordinate).

 

This means that in this configuration the F-16 can't deliver GBU-38 through bomb on coordinates CAS procedure. Or deliver a GBU-38 in a near peer environment with a low level toss. Personally I find it strange that the GBU-38 itself has a 5m CEP. But that F-16 is not capable of exploiting that degree of precision because it's INS/GPS isn't as accurate.

TEST - NAV FULL ALIGN PP GBU38 delivery.trk Test - NAV-TGP.miz

Edited May 1 by Sinclair_76

[Lord Vader]

Hi all.

After the last INS refactoring, the GPS coordinate logic for all IDMs needs to be reviewed by the users, especially in older missions.

Now, weapons like the JDAM, JSOW or WCMD will get the GPS coordinates and the INS drift from the MMC. This means that pure coordinates given to the weapon without a designation (via TPOD, FCR, etc) may introduce and undesired drift (up to 30m in the worse case scenario), adding to the weapon CEP itself (5m).

So, as a rule of thumb, all targets sent to IDM weapons should be designated by one of the aircraft sensors for accuracy.

In the future, some details may be changed, for example the ability for the weapon to have its own guidance. But, for now, this is working as intended.

[Moonshine]

How is there INS drift in an era where GPS weapons are used (unless you specifically turn it off in the jet)? And how would anyone use GPS weapons if GPS isnt existing yet? Thats the only time INS drift should affect bomb accuracy 

Edited May 2 by Moonshine

[Hofftari]

10 hours ago, Lord Vader said:

Hi all.

After the last INS refactoring, the GPS coordinate logic for all IDMs needs to be reviewed by the users, especially in older missions.

Now, weapons like the JDAM, JSOW or WCMD will get the GPS coordinates and the INS drift from the MMC. This means that pure coordinates given to the weapon without a designation (via TPOD, FCR, etc) may introduce and undesired drift (up to 30m in the worse case scenario), adding to the weapon CEP itself (5m).

So, as a rule of thumb, all targets sent to IDM weapons should be designated by one of the aircraft sensors for accuracy.

In the future, some details may be changed, for example the ability for the weapon to have its own guidance. But, for now, this is working as intended.

I'm sorry, but how is this "working as intended"? The JDAMs are basically broken on the F-16 now. Is this really how the F-16 should work with GPS weapons?

[Corrigan]

Why would there be INS drift at any meaningful level in a GPS environment? @Lord Vader 

If I know for a fact that my target is at coordinate x from pre-planning, and I tell the bomb to go to x, why would anything other than the bomb's own GPS position error matter? Like, even if the plane has some degraded sense of where it is, after weapons release the bomb should navigate towards x independently of where it thought it was while mounted on the plane. 

[Tholozor]

The JDAM's onboard INS still receives its initial position from the ownship's INS, they don't fly purely off GPS (generally speaking the JDAM should receive periodic INS updates while powered on). If ownship INS is drifted, JDAM's INS will be drifted by the same amount until the GPS Receiver Module correction starts kicking in. The GPS receiver is deactivated while mounted on the aircraft due to poor visibility/masking of the satellites, and turned on post-release. The receiver module takes some time before the first fix is applied, and this takes about 25~30 seconds.

[Hobel]

vor 2 Stunden schrieb Tholozor:

The JDAM's onboard INS still receives its initial position from the ownship's INS, they don't fly purely off GPS (generally speaking the JDAM should receive periodic INS updates while powered on). If ownship INS is drifted, JDAM's INS will be drifted by the same amount until the GPS Receiver Module correction starts kicking in. The GPS receiver is deactivated while mounted on the aircraft due to poor visibility/masking of the satellites, and turned on post-release. The receiver module takes some time before the first fix is applied, and this takes about 25~30 seconds.

So, even if the F-16's GPS is off and the INS has drifted by several hundred meters, the bomb should have no problem finding the target again at the actual coordinates if there is sufficient approach time

In this example, after the artificial drift that I add and then look at the wrong target, you can see the coordinates displayed in the TGP
41-50-529
41-47-884
and this is the exact position of the actual target in the center from the X, yet the bomb flies to the left target
Should the bomb still fly to the target in the center when it receives fresh data from the GPS?

 

 

[Moonshine]

Okay, understood, bomb gets INS from the jet, GPS only after drop.

now why would the bomb get degraded INS data if my jet has a perfect alignment due to having GPS and therefore no INS drift?

and why does my TGP look exactly at the right coordinates due to having that perfect alignment but the bomb still misses beyond 5m CEP if it does get the same data as my jet?

if that really is as it should be - then please start adding fragmentation damage and proper splash damage as currently you need a near direct hit to destroy even soft targets. Even a miss by 70 feet does not cause something like tracking radar to die. (just had that happen yesterday)

Edited May 3 by Moonshine

[Tholozor]

The Period Transfer Alignment Message (PTAM) sends aircraft latitude, longitude, altitude, and velocities to the JDAM, and the Reset Transfer Alignment Message (RTAM) sends corrections to generate new PTAM information. The PTAM info is wholly dependent on ownship's INS accuracy and GPS solution.

The JDAM's onboard program should also be expecting the aircraft's alignment quality to meet specific criteria of positional/velocity errors to fall within a pre-determined CEP of a GPS-aided solution (this should also be determining the JDAM's transfer alignment status on the SMS). If the aircraft is not using GPS, it cannot calculate the aircraft's CEP, leaving the weapon unable to utilize the PTAM info, as it will end up less accurate than what the JDAM is expecting. Since this data is unsatisfactory in providing proper positional/acceleration/time data, the JDAM's alignment should continue to degrade.

Edited May 3 by Tholozor

[Sinclair_76]

7 hours ago, Tholozor said:

The JDAM's onboard INS still receives its initial position from the ownship's INS, they don't fly purely off GPS (generally speaking the JDAM should receive periodic INS updates while powered on). If ownship INS is drifted, JDAM's INS will be drifted by the same amount until the GPS Receiver Module correction starts kicking in. The GPS receiver is deactivated while mounted on the aircraft due to poor visibility/masking of the satellites, and turned on post-release. The receiver module takes some time before the first fix is applied, and this takes about 25~30 seconds.

The JDAM GPS kicks get it's first fix +/-10 sec after release. It then takes some time for the Kalman filter to wash out the launcher location error to get to the 5m CEP. Best open source I could find is F-16.net (see link below). The link is slightly dated, the Kalman filter has been improved to further reduce the 13m CEP to 5m CEP (2016 SAR document below).

 

21 hours ago, Lord Vader said:

Now, weapons like the JDAM, JSOW or WCMD will get the GPS coordinates and the INS drift from the MMC. This means that pure coordinates given to the weapon without a designation (via TPOD, FCR, etc) may introduce and undesired drift (up to 30m in the worse case scenario), adding to the weapon CEP itself (5m).

Sure the F-16 INS/GPS might develop a 30m error (which is a lot, the aircraft I used to work with had a position confidence of 15m) but the JDAM does not take the full error to the ground if employed correctly. To suggest that the F-16 error of 30m translates in a 30m (error)+5m (CEP) is just incorrect (see sources below and explanation above). In IAMS targeting TLE and CEP are considered, not the launcher location error.

The JDAM is adverse weather and BOC (bomb on coordinate) capable. Especially with BOC the pilot only fat fingers in the coordinates and releases in optimum parameters. Hence that during CAS the only action required for correlation is the readback of the programmed coordinate in the system. In case of the F-16 you readback what you entered in the DED, not what you wrote down. To fiddle around with TGP to update the coordinates would invalidate that procedure (Aircrew will not modify coordinates once read back is complete). 

Sources:
https://www.f-16.net/f-16_armament_article9.html
https://apps.dtic.mil/sti/tr/pdf/AD1019464.pdf
 ATP 3.3.2.1 (NATO UNCLASS) / 3.9.1 BOC / 3.32 BOC and IAMS / 5.4.15.a BOC Correlation / H.5.g Correlation 

and 
Tholozor

 

Edited May 3 by Sinclair_76

[Lord Vader]

Hello again.

Thank you all for your points of view. 

This has been reviewed by the team several times to deliver the best possible depiction of the INS, GPS and IDM behaviour.
I can assure you we're trying to make these as realistic as possible, according to available public documentation.

First of all, 30 meters is the maximum drift value possible. If you have a factor of 10 INS alignment quality you probably will never see that much drift.

The IDMs are indeed primarily guided by INS, blending GPS data, not the other way around. The GPS guidance algorithm is only used to make corrections after about 30 seconds after release. If the target location is closer, reducing that period of time, it completely relies on internal INS and the only source for it is, of course, the aircraft's MMC. However, if the target is more than 30 seconds away, the GPS data can be used, but only to self correct the bombs own errors, especially with a long TOF.

Again, like I said above, this ability to perform its own correction after those 30 seconds TOF is something that will be refined in the future. 

[Hofftari]

An excerpt from the source that @Sinclair_76 posted:

 

Quote

Once released, the JDAM falls free of the aircraft and attempts to acquire a GPS signal. To improve the chances of GPS acquisition, JDAMs are usually released from high altitude. It can take as much as 10 seconds or more for acquisition to happen. The bomb's 3-axis INS and GPS guidance systems will take over and guide the bomb to its target regardless of weather. There are two modes of operation: either GPS-assisted guidance, resulting in a 13m CEP (Circular Error Probable), or INS-only guidance, resulting in 30m CEP. INS-only is used when the GPS-signal is unavailable, for example when GPS jammers are used by the enemy. The important fact is that the Guidance Control Unit (GCU) provides accurate guidance in both modes, so even when GPS is unavailable the JDAM is still accurate.

Where does the 30 second activation come into play here @Lord Vader?

[Lord Vader]

Where is that source quoted from? The F-16.net link contains an interesting article but it's not an official document.
Running through the mentioned sources on that article doesn't refer to official documents. Just brochures, reports and even broken links.

I've never seen any official reference of 10 seconds GPS activation, btw.
We can't rely on unsubstantiated information, sorry. 

[VGlusica]

One of the few things that I can speak to intelligently is this particular issue.   @Lord Vader I must ask, where are you getting the 13m CEP, as this is not published anywhere?  If you are you are referencing error stacking, this could be an INS issue, but GPS system architecture is particularly designed to eliminate this problem.  I will not go further into the subject as this forum is not an appropriate venue.  Suffice it to say that if you label what is being put forward here as conjecture, because there is no reference provided you must then provide reference documenting accuracy of your statement.  If such reference cannot be provided, then we must all agree to adhere and abide by those things which can be directly verified. F-16.net can be quite a good reference, put together by individuals with high degree of familiarity with the aircraft and its systems.  Dismissing it out of hand might be somewhat presumptuous.  My second question here is, do you (and I mean plural you here) have access to "official" documents, because frankly you should not.  So, your statements also must be viewed as conjecture.  Modeling based on conjecture is also unrealistic.  One thing that I think we can all agree on, is open source published and generally accepted notion that current class of JDAM's operate with 5m CEP, so make it easy on yourselves and us and just model that.  With 5m CEP 50% of shots should land within 5m of the target.  Fortunately, or unfortunately, that is all we have to go on here.

Now, If I am to give you the benefit of the doubt, which I don't want to, but will for the sake of this exercise, and we assume that you are correct in you conjectures and CEP with GPS is 13m, once again half of the shots should land within the 13m radius circle centered on the aimpoint.  Under the currently accepted theory of CEP calculation this means that that some number of shots will be closer than 13m to the aim point and some further away.  What we are seeing in the sim right now, at least in my experience, I dropped about forty (40) shots, is every single one was more than 13m from the target point.  To the best of my ability, due to sim limitations, I tried to figure out what the dispersion was, and it seems that no matter what one does or what the environmental factors might be the CEP for these weapons is 13+m.  What is even stranger, is that the weapons seem to be avoiding the target point.  What I mean here is that if the inaccuracy presented here is due to random target point shift due to system error, then within a certain subset of shots the introduced errors should cancel out, this never happens as the weapons always miss the aimpoint.

I do not want to be overly harsh here, but it seems to me that there is something rotten in the state of Denmark and all the conjecture in the world will not fix it, especially if we are closed to any form of outside facts.

[Sinclair_76]

13 hours ago, VGlusica said:

I must ask, where are you getting the 13m CEP, as this is not published anywhere? 

The 13m CEP comes from the F-16.net site. It was one the earlier established CEP prior operation Allied Force. Later finetuning of the Kalman filter resulted in a 5m CEP. 

@Lord Vader

It doesn't matter how you spin it, NATO documents provided (ATP 3.3.2.1 (NATO UNCLASS) 3.32 BOC and IAMS), clearly state that the only factors that determine the outcome of a JDAM release are the CEP and TLE. Nothing references to the launching platform or their location error. I stand by that with a functioning gps on the F-16 the JDAM CEP is 5m and that a location confidence of 30m or ,10m ,for that matter, don't influence the accuracy of a JDAM.

The only reason I provided the F-16.net info is to fill in the gaps, not be used as a red herring.

 

Edited May 4 by Sinclair_76

[VGlusica]

33 minutes ago, Sinclair_76 said:

The 13m CEP comes from the F-16.net site. It was one the earlier established CEP prior operation Allied Force. Later finetuning of the Kalman filter resulted in a 5m CEP. 

@Lord Vader

It doesn't matter how you spin it, NATO documents provided, clearly state that the only factors that determine the outcome of a JDAM release are the CEP and TLE. Nothing references to the launching platform or their location error. I stand by that with a functioning gps on the F-16 the JDAM CEP is 5m and that a 30m or ,10m ,for that matter, don't influence the accuracy of a JDAM.

The only reason I provided the F-16.net info is to fill in the gaps, not be used as a red herring.

 

 

That makes sense, thank you. I was curious where it came from since it does not seem to be the operative factor currently. 

[Lord Vader]

18 hours ago, VGlusica said:

@Lord Vader I must ask, where are you getting the 13m CEP, as this is not published anywhere? 

There must be some mistake here, I never said anything about a 13m CEP, someone else did.

Like I said above, and I think I was quite clear in my explanations, this is just a matter of refining how the bomb self corrects, considering all the limitations, including those 30 seconds of GPS acquisition that some of you seem to be ignoring.

Once more, we are using publicly available unclassified documents to simulate this, and no, we cannot use websites without official sources. We also cannot use interpretations to base our simulations, we need to be accurate. Just because a document doesn't mention or omits a certain condition or limitation, it doesn't mean it isn't there. 

Of course, we encourage anyone to help us improve the simulation. Thank you for your care.