Precision-Guided Munitions - GBU-38 won’t drop

When following the instructors guidance to drop the GBU-12 and GBU-38’s, everything goes according to plan throughout the mission, except the GUB-38’s won’t release.

Target is designated as instructed (I tried Point and Area mode), the HUD is in CCRP, Master arm is still engaged, I line up the aircraft on the bomb drop line and after the target enters the dynamic drop zone I hold the pickle button for about 1 second, but the GBU-38’s will not come off their stations.

A friend of mine has exactly the same issue.

Track file here: https://1drv.ms/u/s!AjB8XCqYiep2fJGQ71877YIODDg?e=UH9N4B

The GBU-12 and GBU-38 have different CCRP procedures. With the GBU-12 you need to keep the pickle button pressed until the bomb drop line passes the release line, while with the GBU-38 you need to wait with pressing the pickle button until the inner circle line is located somewhere between the two triangles.

Hi Highwayman-Ed

 

I could see in the track it did not release, but when I took control I double checked TMS long had set the target, and then a long press on weapon release and the GBU-38 was away.

 

Seems ok to me, let me know if you still have issues.

 

thank you

I'm not able to watch the track atm, but your observation just confirms what I suspected: Wrong pressing of the pickle button as I described above.

I could not see the track either.

But another problem could be, that INS has not been aligned fully / correctly. Does the GBU-38 shows "RDY" in DSMS?

At the time I had the problems, my failure has been that I have been taxiing while INS was still aligning. As a result INS failed to align properly and the GBU-38 therefore have never become "RDY" to drop.

Anyhow - just a guess..

I have found that the GBU-38 will lose its alignment in flight - it seems to be worse if you fly the aircraft smoothly. I routinely manoeuvre the Hog fairly determinedly during the last 3 or 4. Miles to release. If you do this with DSM selected on the MPCD, you can see the not ready indication extinguish.

I'm not able to watch the track atm, but your observation just confirms what I suspected: Wrong pressing of the pickle button as I described above.

I can confirm that I did not hold the pickle button whilst waiting for the bomb to drop as it entered the dynamic launch zone, the pickle button was pressed for about 1 second on the first pass when the indicator was well within the max range mark.

Hi Highwayman-Ed

 

I could see in the track it did not release, but when I took control I double checked TMS long had set the target, and then a long press on weapon release and the GBU-38 was away.

 

Seems ok to me, let me know if you still have issues.

 

thank you

Thanks for checking, I’ll try it again, but I re-designated the target over and over with a TMS forward long with each pass and had not joy.

During the track the procedure was as follows; Move cross hairs, tms up short to switch between point and area, tms up long to designate and pickled for ~ 1 second inside the dynamic launch zone marks. No bomb drop.

I could not see the track either.

 

But another problem could be, that INS has not been aligned fully / correctly. Does the GBU-38 shows "RDY" in DSMS?

 

At the time I had the problems, my failure has been that I have been taxiing while INS was still aligning. As a result INS failed to align properly and the GBU-38 therefore have never become "RDY" to drop.

 

Anyhow - just a guess..

I don’t recall, but being as the training mission is an air start, I would assume that the INS is aligned correctly. I’ll check.

OK, just flew the mission again and was very slow and deliberate with each step and the bomb did indeed separate. I did, however, notice that I had to hold TMS Up Long several times before the target was properly designated. Watching the previous track back again I noticed that although I was holding the TMS Up Long on each of the passes over the target I made, the Lightening Pod designator never switched to "POINT". maybe it was sloppy flying on my part, maybe the TGP was too far off the gimbal limits...

Thanks for the support as always Bignewy.

OK, just flew the mission again and was very slow and deliberate with each step and the bomb did indeed separate. I did, however, notice that I had to hold TMS Up Long several times before the target was properly designated. Watching the previous track back again I noticed that although I was holding the TMS Up Long on each of the passes over the target I made, the Lightening Pod designator never switched to "POINT". maybe it was sloppy flying on my part, maybe the TGP was too far off the gimbal limits...

 

Thanks for the support as always Bignewy.

Uhm, there seem to be some missconceptions on your side about several functions that you are mentioning there. I will try to clear them up:

1) TMS UP LONG is not directly related to dropping GBUs. You can drop them just fine without ever pressing TMS UP LONG. What TMS UP LONG does is, it will change your SPI to the current SOI. You can see your current SPI source in the lower left corner of your HUD. By default it should say STP, which means that your Steerpoint (your currently selected waypoint or markpoint) is designated as the SPI and the GBU-38 will use that as the target.

Now, if you want to use the TGP to designate a target for the GBU-38, then you need TMS UP LONG while the TGP is SOI, in order to designate your TGP as the source of your SPI (the HUD should now display TGP in it's lower left corner, as the TGP is now your SPI source). When you do that the GBU-38 will then guide on wherever the TGP is looking at at the moment of release. It's important to understand, that you only need to press TMS UP LONG once to make your TGP the SPI source and can then do as many bomb runs on as many TGP designated targets as you wish without ever having to press TMS UP LONG again, as the TGP will stay your SPI source forever, unless you manually change that again. So you don't have to press TMS UP LONG for every bomb run as you did say.

Important notice: If the terms SPI and SOI don't tell you anything or you're getting confused by them, then this is probably the source of all your problems with weapon delivery in the A-10C, as it is absolutly necessary to understand the SOI/SPI concept of the A-10C, so I would highly recommend to read up on it if that's the case.

2) You mentioned POINT track wasn't working. First of, you can switch between POINT and AREA track by pressing TMS UP SHORT while the TGP is SOI. Now, the important thing about this is, that POINT track is absolutly not necessary to do any kind of weapons delivery. Neither your weapons computer nor the weapon itself care about whether you use POINT or AREA track! POINT and AREA track only matter to the pilot itself and his ability to keep the TGP on the target. If you're are attacking a stationary object or vehicle you can very well use AREA track, as the TGP will try to focus on a specific position. POINT track is helpful ifr you want to focus on a moving vehicle, which the TGP can then track by itself if in POINT mode, but using AREA mode and slewing the TGP manually to keep it centered on the moving vehicle works also. The weapon just cares where the TGP is pointing at, not in which mode it's doing that.

I hope that helps a bit with understanding the A-10C a bit better :)

I have found that the GBU-38 will lose its alignment in flight - it seems to be worse if you fly the aircraft smoothly. I routinely manoeuvre the Hog fairly determinedly during the last 3 or 4. Miles to release. If you do this with DSM selected on the MPCD, you can see the not ready indication extinguish.

That's odd. I have never ever noticed such behaviour. I usally fly very smoothly and in a straight line when approaching my targets and my JDAMs never loose their alignment :huh:

Uhm, there seem to be some missconceptions on your side about several functions that you are mentioning there. I will try to clear them up:

 

1) TMS UP LONG is not directly related to dropping GBUs. You can drop them just fine without ever pressing TMS UP LONG. What TMS UP LONG does is, it will change your SPI to the current SOI. You can see your current SPI source in the lower left corner of your HUD. By default it should say STP, which means that your Steerpoint (your currently selected waypoint or markpoint) is designated as the SPI and the GBU-38 will use that as the target.

Now, if you want to use the TGP to designate a target for the GBU-38, then you need TMS UP LONG while the TGP is SOI, in order to designate your TGP as the source of your SPI (the HUD should now display TGP in it's lower left corner, as the TGP is now your SPI source). When you do that the GBU-38 will then guide on wherever the TGP is looking at at the moment of release. It's important to understand, that you only need to press TMS UP LONG once to make your TGP the SPI source and can then do as many bomb runs on as many TGP designated targets as you wish without ever having to press TMS UP LONG again, as the TGP will stay your SPI source forever, unless you manually change that again. So you don't have to press TMS UP LONG for every bomb run as you did say.

 

Important notice: If the terms SPI and SOI don't tell you anything or you're getting confused by them, then this is probably the source of all your problems with weapon delivery in the A-10C, as it is absolutly necessary to understand the SOI/SPI concept of the A-10C, so I would highly recommend to read up on it if that's the case.

 

2) You mentioned POINT track wasn't working. First of, you can switch between POINT and AREA track by pressing TMS UP SHORT while the TGP is SOI. Now, the important thing about this is, that POINT track is absolutly not necessary to do any kind of weapons delivery. Neither your weapons computer nor the weapon itself care about whether you use POINT or AREA track! POINT and AREA track only matter to the pilot itself and his ability to keep the TGP on the target. If you're are attacking a stationary object or vehicle you can very well use AREA track, as the TGP will try to focus on a specific position. POINT track is helpful ifr you want to focus on a moving vehicle, which the TGP can then track by itself if in POINT mode, but using AREA mode and slewing the TGP manually to keep it centered on the moving vehicle works also. The weapon just cares where the TGP is pointing at, not in which mode it's doing that.

 

I hope that helps a bit with understanding the A-10C a bit better :)

Nope, perfectly aware what SOI and SPI are and how they relate to the various sensors and weapons. I'll admit that it has been several years since I've flown the A-10C, but I logged a lot of hours in it as an original beta backer of the aircraft. A friend of mine recently showed an interest in flying the aircraft and I directed him to the training missions. He had issues with that mission, so I coached him through what should be done, and after not coming up with anything that he did or didn't do, I decided to fly the mission myself and experienced exactly the same issue, hence the post.

Not sure if like I said it was sloppy flying on my part with relation to the JDAM's, but I could not get the bombs off the rails on the 3 passes I made over the target in the original track.

The mention of "POINT" in the resolution post is it to my knowledge is the ONLY thing that was different about the SOI, the SPI and the aircraft configuration, and that time the weapon came off the rail.

I have found that the GBU-38 will lose its alignment in flight - it seems to be worse if you fly the aircraft smoothly.

Haven't played A 10 in a while,but i do remember coming across this issue a few times.

If my memory serves me correctly i used to get aln rdy on the hud and GBU-38 could not be released.

Was able to fixed it every time by rocking the wings (aln rdy changes to rdy and you are good to go).

I watched the track but was unable to determine the source of the problem. Everything looked fine.

That's on the latest OpenBeta 2.5.5.39384.

Just before the launch window was about to close, I took control and was able to release the GBU-38 just fine. Prior to that, I had flown the entire mission on my own and also didn't find anything wrong with it.

-----

Regarding the alignment issues with the GBU-38 and GBU-31 in straight and level flight, that is indeed a feature of the simulation, and was also observable in the track; early on the GBU-38 showed ALN RDY and after selecting the GBU-38 weapon profile, they stayed in ALN RDY and were shown white in the DSMS until OP had flown a turn of 90 or more degrees. Only then did they switch to RDY and a green DSMS indication.

AFAIK, JDAMs have an Inertial Measurement Unit IMU at the core of their INS. And like any INS, it degrades over time. In order to update the weapon's "knowledge" of true north, it may be necessary to rock the wings or even fly a turn of something like 90° or more; this will initiate the so called "transfer alignment" where the weapon checks its own true north measurement against that of the aircraft and updates itself accordingly.

Some 2 or 3 minutes of straight and level flight might be enough to get the GBU from ALN to ALN RDY, which requires a new transfer alignment or the weapon can not be released.

Edit:

I did, however, notice that I had to hold TMS Up Long several times before the target was properly designated. Watching the previous track back again I noticed that although I was holding the TMS Up Long on each of the passes over the target I made, the Lightening Pod designator never switched to "POINT".

Try TMS Up Short. ;)

TMS Up Long is "Make SPI" or "Set SPI Generator" or "Set SPI Source" (whichever way you prefer to think of it) and won't switch between POINT and AREA tracking.

Regarding the alignment issues with the GBU-38 and GBU-31 in straight and level flight, that is indeed a feature of the simulation, and was also observable in the track; early on the GBU-38 showed ALN RDY and after selecting the GBU-38 weapon profile, they stayed in ALN RDY and were shown white in the DSMS until OP had flown a turn of 90 or more degrees. Only then did they switch to RDY and a green DSMS indication.

 

AFAIK, JDAMs have an Inertial Measurement Unit IMU at the core of their INS. And like any INS, it degrades over time. In order to update the weapon's "knowledge" of true north, it may be necessary to rock the wings or even fly a turn of something like 90° or more; this will initiate the so called "transfer alignment" where the weapon checks its own true north measurement against that of the aircraft and updates itself accordingly.

 

Some 2 or 3 minutes of straight and level flight might be enough to get the GBU from ALN to ALN RDY, which requires a new transfer alignment or the weapon can not be released.

Very interesting! I'm flying the A-10C for many years by now and I have not been aware of this transfer alignment stuff at all. That makes me wonder though why I never had any alignment problems with the JDAMs (besides having messed up my own aircraft alignment for some reason), even though I often do approach the target in a straight line all the way from takeoff.

I also don't really understad why a turn is needed for the JDAMs to align their true north properly. Could you explain this a bit more in detail, as I'm very curious about those things? :)

That makes me wonder though why I never had any alignment problems with the JDAMs (besides having messed up my own aircraft alignment for some reason), even though I often do approach the target in a straight line all the way from takeoff.

I just double checked our squad documents; they say it usually takes about 10 minutes for JDAMs to go from RDY to ALN RDY.

Also, when I flew the training mission an hour ago, just rocking the wing sharply switched the JDAM back to RDY.

Gentle turns don't seem to have that much of an impact, but turns of 90° or more should also initiate the transfer alignment.

Next time you fly such a mission, it would be cool if you could check the DSMS and take a mental note if the JDAMs ever go from RDY to ALN RDY.

I also don't really understad why a turn is needed for the JDAMs to align their true north properly. Could you explain this a bit more in detail, as I'm very curious about those things? :)

Damn. I thought I could get away with my partial knowledge. :D

I'm not 100% sure on this. But as I understand it, flying a turn means the gyros in the weapon's IMU will register the heading change, and that somehow initiates the transfer alignment.

However, if the aircraft has a "proper" alignment at all times using its own INS and GPS, it's a good question why the IAMs aren't updated once every couple of seconds. I guess that's for one of the real A-10C wizards to answer. :smartass:

I just double checked our squad documents; they say it usually takes about 10 minutes for JDAMs to go from RDY to ALN RDY.

 

Also, when I flew the training mission an hour ago, just rocking the wing sharply switched the JDAM back to RDY.

 

Gentle turns don't seem to have that much of an impact, but turns of 90° or more should also initiate the transfer alignment.

 

Next time you fly such a mission, it would be cool if you could check the DSMS and take a mental note if the JDAMs ever go from RDY to ALN RDY.

Hmm, yeah, I will definitely pay close attention to the DSMS next time I fly with JDAMs, because I'm really curious about this now (and why it hasn't bothered me in all those years :huh:).

Damn. I thought I could get away with my partial knowledge.

 

I'm not 100% sure on this. But as I understand it, flying a turn means the gyros in the weapon's IMU will register the heading change, and that somehow initiates the transfer alignment.

 

However, if the aircraft has a "proper" alignment at all times using its own INS and GPS, it's a good question why the IAMs aren't updated once every couple of seconds. I guess that's for one of the real A-10C wizards to answer.

Alright, fair enough :D

There may be an issue with TGP.

I have one training mission where i practice releasing 4 mavericks in a single pass(on 4 different targets-tanks) and two GBU-38 on two bunkers,in a second pass using markpoints.

I mark the targets(bunkers and tanks) some 10 miles(approximation)away using Point track in a first pass,attack the tanks,and than,in a second pass i attack the bunkers.Never had any issues.

After some update(cant remember which;2 month ago or so),i have noticed that maverick is not aligned perfectly with the targets that i have marked,but it does menage to lock it(when targeting tanks).

GBU-38 misses bunkers by about 10-20 meters.

Only way to hit the bunkers is to fly directly over them and than mark them.

Also,when both GBU-38 are in the air,on TGP i used to have TTI(time to impact) on the first bomb,and after scoring a hit,TTI for the second bomb was shown.

After said update there was no second TTI on the TGP(IIRC).

I am mentioning this because i am aware that there are some issues with using GBU-38 in A-10C as of late.

Maybe there is an issue with TGP/GBU-38 interaction.

Hmm, I have never ever seen a TTI on the TGP in the past 6-7 years that I fly the Warthog now. :huh:

As for unprecise target designation: That apparently can happen when designating targets (creating markpoints) from far away and I guess it's realistic as the angle of the TGP will be rather flat, which makes it difficult to determine the exact position where the LOS of the TGP intersects with the terrain surface. In theory you should be able to use the laser to get a more precise designation, but, at least in DCS, the laser doesn't work at longer distances as it is restricted to about 8-9nm of distance.

Hmm, I have never ever seen a TTI on the TGP in the past 6-7 years that I fly the Warthog now. :huh:

 

As for unprecise target designation: That apparently can happen when designating targets (creating markpoints) from far away and I guess it's realistic as the angle of the TGP will be rather flat, which makes it difficult to determine the exact position where the LOS of the TGP intersects with the terrain surface. In theory you should be able to use the laser to get a more precise designation, but, at least in DCS, the laser doesn't work at longer distances as it is restricted to about 8-9nm of distance.

I know what you mean.That is why i have mentioned Point track.

It shouldn't be an issue with the Point track(with Area-definitely would be),and as i have mentioned,it wasn't.

It is my routine practice mission(muscle memory practice) and I have never had any issues with it;until that update.

TTI is on the bottom right corner of the TGP display after release.I seldomly attack single target in one pass with JADAMs,and i do remember it distinctly.

I know what you mean.That is why i have mentioned Point track.

It shouldn't be an issue with the Point track(with Area-definitely would be),and as i have mentioned,it wasn't.

Sounds like you should start a new thread; this seems to be off-topic here. Maybe a mod could be so kind to move this part of the discussion.

As for point and area track, how do you figure there's a difference in the LOS ground intersection?

To the very best of my knowledge, that's not the case, the TGP will calculate the exact same coordinates for the center of the seeker LOS ground intersection regardless of POINT or AREA tracking modes (unless, as QuiGon said, the laser is used in order to get the actual slant range. But again, it doesn't matter whether POINT or AREA track is used while lasing).

Sounds like you should start a new thread; this seems to be off-topic here. Maybe a mod could be so kind to move this part of the discussion.

 

As for point and area track, how do you figure there's a difference in the LOS ground intersection?

 

To the very best of my knowledge, that's not the case, the TGP will calculate the exact same coordinates for the center of the seeker LOS ground intersection regardless of POINT or AREA tracking modes (unless, as QuiGon said, the laser is used in order to get the actual slant range. But again, it doesn't matter whether POINT or AREA track is used while lasing).

I am talking about in game behavior,and not strict realism.In layman's terms,AREA tracks the point on the ground,and Point tracks object itself.

When you aim very close to the object that you wish to target,Point track jumps on it and locks it by itself(game behavior).

Like I have said I have had no issues with markpoints before certain update.

What is so hard to understand?

I can not control how others will interpret my post,and with what will they take issue.

My first post on this thread was aimed at addressing GBU problems,and nothing else,so it wasn't totally off topic.

I am mentioning this because I am aware that there are some issues with using GBU-38 in A-10C as of late.

Maybe there is an issue with TGP/GBU-38 interaction.

On the other hand you are,and now,so am I.Or should I have not replied to you?It is common decency after all(off topic or not).

I have no problem if my posts are deleted(if you still believe i am totally off topic),and I have no intention to clog the threads with new topics.

I am talking about in game behavior,and not strict realism.In layman's terms,AREA tracks the point on the ground,and Point tracks object itself.

Point track mode simply makes the TGP follow any shape or object that has a sufficient contrast, and is thus suited to track moving objects. To the best of my knowledge, that is literally the only difference between these two modes. In point track mode, the TGP still doesn't know where the object is located. You could be tracking a helicopter, and if you set a markpoint and then slew the TGP onto it, it'll be waaaay off from the helicopter, because the markpoint is where TGP LOS intersects the ground (and the ground itself is "known" because of the digital terrain elevation database).

If you think the game handles it differently, go ahead and prove me wrong.

And regarding off topic: your question is off topic. It doesn't even have to do with GBU-38 in the slightest. It's usually considered common courtesy to start a new thread for unrelated questions.