GBU 12 can't keep up with moving targets

[Solo_Turk]

there is an issue about flight path I suppose.  we tried this with f16 at high speed. same result. targets are moving at 10 kts.

 

bug gbu 12.trk 18_11_2022_Gorev.miz

[QuiGon]

I don't have any real world experience with dropping GBU-12s at moving targets, but this behaviour doesn't strike me as unrealistic. That's why pilots IRL do lead the target with their laser instead of point the laser right at it. If you do that in DCS as well, you will hit a moving target just fine.

[Ithronwise]

In point track mode targeting pods are able to follow a moving ground target automatically and of course to illuminate it with the laser, otherwise you would have a hard time to hit it with a laser-guided maverick or hellfire. The same technique should work with LGB's. The bomb follows the laser and as long as the target is in range it will be hit.

[Solo_Turk]

53 minutes ago, QuiGon said:

I don't have any real world experience with dropping GBU-12s at moving targets, but this behaviour doesn't strike me as unrealistic. That's why pilots IRL do lead the target with their laser instead of point the laser right at it. If you do that in DCS as well, you will hit a moving target just fine.

just check this. static target with 20 kts wind. it missed

bug gbu 12static.trk

[QuiGon]

51 minutes ago, Ithronwise said:

In point track mode targeting pods are able to follow a moving ground target automatically and of course to illuminate it with the laser, otherwise you would have a hard time to hit it with a laser-guided maverick or hellfire. The same technique should work with LGB's. The bomb follows the laser and as long as the target is in range it will be hit.

Uhm, no. The guidance and physics of an LGB work totally different than that of a guided missile. Especially when we're talking about second generation Paveways like the GBU-12 and their bang-bang guidance. I recommend you to read up on that.

Edited November 21, 2022 by QuiGon

[Ithronwise]

Bang bang guidance doesn't mean that a LGB isn't able to hit a moving target. It is a simplified way to steer the bomb to its target. The only consequence of this is less accuracy.
If the target is moving and the laser keeps tracking the bomb will try to follow the laser point. The bomb doesn't know if the target is moving and so it doesn't play any role for it if the laser is moving because the pilot does some corrections after the drop or it is moving because the tracked target is moving and the laser follows. Of course, if the target is too fast or changes its direction very hard then there is a high chance that the bomb will miss it. 

[Hobel]

I mean there is a report of a F15 that threw a GBU10 at a Mi24 that climbed and flew 100knots fast. that's pretty good.

[Fromthedeep]

2 hours ago, Ithronwise said:

Bang bang guidance doesn't mean that a LGB isn't able to hit a moving target. It is a simplified way to steer the bomb to its target. The only consequence of this is less accuracy.
If the target is moving and the laser keeps tracking the bomb will try to follow the laser point

It will try but it due to the inherent PW2 characteristics (lag, sag and energy loss) it's entirely likely that your bomb will land short if you don't do it properly. The basic employment consideration for PW2 against movers is to get a lead impact point (either manually or modern aircraft may automatically calculate it), lase it continuously and lead the laser spot just in front of the mover to account for the inherent negative characteristics. If you don't do these, your results will be very inconsistent. There's good reason why modern aircraft calculate the lead impact point and automatically utilize lead laser guidance on their own. 

 

The biggest consideration is lag. PW2 is a reactionary weapon, the laser detector is a disk with 4 quadrants and the control section is trying to keep the laser spot center. If it shifts away from the center, the bomb will compensate to recenter it but these can only take effect once the deviation already occurs. Therefore, the corrections are slightly delayed and since the bomb is chasing a constantly moving target (and since normal attack directions are from behind the target, the mover will be moving away from the bomb), in the endgame it's possible that the correction is delayed enough to land short of the target. If you lead the spot ever so slightly, the bomb has a much higher chance of still impacting the target even if the lag would result in a miss.

[BonerCat]

It seems to me like it's no bug, but rather a limitation of the weapon
I can think of a few things to help mitigate the issue, like designating a point on the front section of the vehicle, or giving the bomb more potential and kinetic energy to play with.
I m no expert on these weapons, but knowing how they work this seems to work fine

 

[Ithronwise]

Modern LGB's don't fall ballistic. Their large tail fins are producing some lift what means they are able to glide in a limited way. So, if the moving target isn't too fast and/or the dropping altitude isn't too high the distance the target is moving between bomb release and impact should be within the glide radius. But of course, leading the laser is a practical and used method to maximize the chance of a hit and avoids the bomb from falling short.

[Solo_Turk]

6 hours ago, Solo_Turk said:

just check this. static target with 20 kts wind. it missed

bug gbu 12static.trk 451.79 kB · 0 downloads

what about this one guys. bomb missing static target

[Fromthedeep]

6 hours ago, Ithronwise said:

Modern LGB's don't fall ballistic

No, they fall an even less efficient flight path, they sag below the ballistic trajectory. The only LGBs in DCS that can glide are Paveway 3s, which are completely different weapons. PW2s are at their core 1970s era primitive technology that are cheap and effective but they require operator skill and know how to be effective.

[79Au]

My observations:

- The bomb starts at just 250 knots TAS, which is rather slow. The bomb actually accelerates after the drop. (Which would mean there shouldn't be an energy problem per se if the CCRP math is correct, but I can't tell which mode OP's in or if they're in range) For reference, the default impact velocity of a JDAM is 700fps or 415 knots. I don't have the A-10, but it seems realistic that A-10s are indeed dropping LGBs at around 250-300 kn TAS. But, in my experience (F-18), below ~400 TAS guided munitions begin to struggle maintaining their intended flight path at the terminal stage.  (in DCS of course, don't know about IRL. LGB, JDAM, HARM, SLAM etc., if released manually with too much optimism)

- It looks like the bomb loses the laser spot for a second and drops the nose. (Aims behind intended target) Then it picks it up again and tries to pull up, and that's where the sluggishness appears that I mentioned above. It looks like it's stalling.

- The plane is very low (and slow), maybe that leaves little room for error and the short "hiccup" after drop was enough to make the bomb stall.

- An LGB travelling at a good velocity will impact on an almost straight trajectory. This guy here is dragging it out, much more than the movement of the target justifies. To me it's plausible that the weird trajectory is due to the increase in fin authority as the bomb accelerates. (but it was too late/too slow at release)

Just a couple thoughts, I don't fly the hawg and never dropped LGB's below 500 TAS at that altitude  I've seen a couple reports about LGBs and other weapons missing their allocated impact point (x/y game coordinates), which shouldn't happen in a game, but here it's difficult to rule out velocity/fin authority issues.

Edited November 21, 2022 by 79Au

[Tom Kazansky]

Reading all the tread it could be interesting what happens when the GBU is dropped from the other direction relative to the moving target, i.e. from the front.

The OP shows an aspect angle almost right from behind.

The result should help us getting closer to the culprit of the shown behaviour. (Sorry, that I can't do this myself at the moment.)

[speed-of-heat]

doesn't each course adjustment mean the weapon loses energy?  would you be better dropping it a fixed point and moving the lock to the desired moving target in the last few seconds? 

[Tom Kazansky]

2 minutes ago, speed-of-heat said:

doesn't each course adjustment mean the weapon loses energy?  would you be better dropping it a fixed point and moving the lock to the desired moving target in the last few seconds? 

That would be better, but it would not explain completely what's going on in OP's case.

[speed-of-heat]

2 minutes ago, Tom Kazansky said:

That would be better, but it would not explain completely what's going on in OP's case.

roger that 

[Tom Kazansky]

My thought was: if the GBU dropped from the front still misses, it is not a case of missing ability to glide, but something in the tracking/controlling of the GBU (in DCS). Maybe the rate or magnitude of corrections.

[Solo_Turk]

I've read all comments and retested.please check these tracks. two times I was able to destroy the target, even that time bomb fell behind the target. Mission had same wind as above that I shared. I used to hit 7K a10 shots easly. something has changed for sure.

a10 20K opposite-shot-to-tgt.trk a10 20K perpendicular-shot-to-tgt.trk f18 +400IAS 20K opposite-shot-to-tgt.trk f18 +400IAS 20K perpendicular-shot-to-tgt.trk

Edited November 22, 2022 by Solo_Turk

[Hobel]

vor 4 Stunden schrieb Solo_Turk:

I've read all comments and retested.please check these tracks. two times I was able to destroy the target, even that time bomb fell behind the target. Mission had same wind as above that I shared. I used to hit 7K a10 shots easly. something has changed for sure.

a10 20K opposite-shot-to-tgt.trk 1.35 MB · 2 Downloads a10 20K perpendicular-shot-to-tgt.trk 923.66 kB · 2 Downloads f18 +400IAS 20K opposite-shot-to-tgt.trk 998.39 kB · 2 Downloads f18 +400IAS 20K perpendicular-shot-to-tgt.trk 885.22 kB · 2 Downloads

 

I can't say for sure if it is, but it seems that the bomb flies a slight offset all the time, if it was looking directly as soon as the laser is seen, which shouldn't be a problem, it would hit the target on final flight.

 

offset.zip.acmi

 

So the question is whether this offset is intended and whether these are the limits of GBU12?

 

But the GBU12 has a CEP of 1m in DCS and can pull ~3,2G so where does this  offset come from?

 

Edited November 22, 2022 by Hobel

[=52d= Skip]

On 11/21/2022 at 11:32 AM, Solo_Turk said:

just check this. static target with 20 kts wind. it missed

There is a combination of speed and wind that makes the bomb miss.

If you use the default 11kts for the ground units and have no Groundlevel wind the bomb will hit, even if you tailchase them.

 

 

[Hobel]

vor 30 Minuten schrieb =52d= Skip:

There is a combination of speed and wind that makes the bomb miss.

If you use the default 11kts for the ground units and have no Groundlevel wind the bomb will hit, even if you tailchase them.

 

 

yep, apparently it has something to do with the wind.

a GBU12 has a CEP of 1m at 10knots according to some sources.
in DCS the GBU12 has a CEP of 4-6m at 10knots wind.

this in combination with moving targets = miss

[Solo_Turk]

so what can we say for this topic? is it bug or not

[KlarSnow]

It does not look like a bug, with GBU-12's releasing into the wind or with a crosswind and against a moving target you need to lead the target otherwise it will land short.

A Point track will not do this automatically for you, you have to manually estimate the lead and hold the crosshairs in front of the target.

Here is an example. 10 knot target with a 20 knot wind at altitude, 10 knot wind at the surface.

I estimate a designation/SPI well in front of the target to ensure the bomb has enough energy, and then when lasing estimate 1-2 vehicle lengths is enough, the bomb lands ~1 meter or less from the back of the target which is close enough to destroy it, should have lead it a little bit more for a perfect impact. GBU-12's do not have any capability to pull their own lead and will sag and get curved off course by the wind, you must manually correct for this.

Moving wind.trk

If this is too difficult or complicated, a GBU-54 will pull its own lead and compensate for the winds, it is a much smarter bomb than the GBU-12. A GBU-24 will also do this.

Moving wind 24.trk Moving wind 54.trk

Edited November 23, 2022 by KlarSnow

[Hobel]

vor 1 Stunde schrieb KlarSnow:

It does not look like a bug, with GBU-12's releasing into the wind or with a crosswind and against a moving target you need to lead the target otherwise it will land short.

A Point track will not do this automatically for you, you have to manually estimate the lead and hold the crosshairs in front of the target.

Here is an example. 10 knot target with a 20 knot wind at altitude, 10 knot wind at the surface.

I estimate a designation/SPI well in front of the target to ensure the bomb has enough energy, and then when lasing estimate 1-2 vehicle lengths is enough, the bomb lands ~1 meter or less from the back of the target which is close enough to destroy it, should have lead it a little bit more for a perfect impact. GBU-12's do not have any capability to pull their own lead and will sag and get curved off course by the wind, you must manually correct for this.

Moving wind.trk 1.22 MB · 1 Download

If this is too difficult or complicated, a GBU-54 will pull its own lead and compensate for the winds, it is a much smarter bomb than the GBU-12. A GBU-24 will also do this.

Moving wind 24.trk 1007.13 kB · 1 Download   Moving wind 54.trk 1.6 MB · 0 Downloads

 

Nice thx.

 

But what about the thing that 10knots wind makes for a larger cep in dcs.   Than the sources that give an average cep of 1m.   Are these not correct?