GBU-38's inaccurate or is it me?

Hi folks, I've found that my GBU-38's aren't hitting as close as I would like and I'm not sure if it is me or the accuracy of the bombs themselves and I was wondering if you guys could help me out. No matter how hard I try while in mission the bombs seem to hit no closer than 15+ meters ish away from where I target, often leaving my target undamaged, but when I did the precision guided training, I don't believe I had any problems hitting the target.

I do the exact procedure listed in: http://simhq.com/forum/ubbthreads.php/topics/3171145/all/How_to_use_weapons_Picture_gui

1. Turn on latch on laser

2. Find target in TGP

3. Lase target

4. Make target SPI whilst lasing

5. Turn off laser

6. release GBU-38 from 10000+ feet

7. bam miss

Am I expecting too much from these GBU-38s? or am I doing something wrong?

I attached a quick track of me trying them out on two separate targets in an instant action mission. Thanks!

gbu-38 missing2.trk

The GBU-38 is a JDAM, meaning it's not laser guided. The laser may help in getting distance and such exact, but it's not used by the GBU-38. Do you by any chance not fly steady when you drop it? Did you select the GBU-38 before making the target SPI?

Whilst I can't think of anything very wrong of the top of my head in that guide, small things such as instructing people to turn on a laser for a GPS guided weapon that does not track or even register a laser does lead me to say that it might not be the best guide in the world. Try the training mission.

The GBU-38 is part of the JDAM family—it's a GPS guided weapon. The bomb will try to guide in on your SPI the moment you release it, so you'll need to put your SPI on the target you intend to bomb before you pickle. You also do not need to lase to guide the bomb in, although you might want to quickly lase before you drop to get an accurate SPI slant range measurement.

You dont need to be at +10000 feet altitude when relasing gbu´s, it works also lower altitudes such as 5000 feet for example...

By watching your track i can say that you were kind a low with your airspeed, you were climbing on high angle and little too offset with your target on the relase moment. So i think these caused the bomb to miss.

The GBU-38 is part of the JDAM family—it's a GPS guided weapon. The bomb will try to guide in on your SPI the moment you release it, so you'll need to put your SPI on the target you intend to bomb before you pickle. You also do not need to lase to guide the bomb in, although you might want to quickly lase before you drop to get an accurate SPI slant range measurement.

I understand, and thats what I did before I marked SPI, I will clarify my lase release in the OP.

You dont need to be at +10000 feet altitude when relasing gbu´s, it works also lower altitudes such as 5000 feet for example...

 

By watching your track i can say that you were kind a low with your airspeed, you were climbing on high angle and little too offset with your target on the relase moment. So i think these caused the bomb to miss.

The 10000+ is giving the bomb plenty of time to correct itself, I will try to flatten out / speed up and perfect that. Thankyou.

You have to make target SPI with pressing TMS long forward. If you had done it correctly, lower left corner of the HUD wouldn't read STPT (red arrow). It would read TGP

You were missing, because your Steerpoint was SPI, not your TGP aiming point.

This is original picture from SimHQ article (I hope it's OK to link it here). Have a look at lower left corner of the HUD.

Thanks alot! No wonder It was hitting in between the trucks every time.

Whilst I can't think of anything very wrong of the top of my head in that guide, small things such as instructing people to turn on a laser for a GPS guided weapon that does not track or even register a laser does lead me to say that it might not be the best guide in the world. Try the training mission.

You should read up on that.

What are the coordinates the JDAM gets programmed to hit?

Without lasing, the Terrain Elevation database would assume you're aiming at a spot on the ground. These coordinates would then be programmed into the JDAM prior to release.

In order to make sure that the target itself gets indeed targeted, it should be lased before making it SPI. This way, with the exact distance available to the Fire Control Computer, the bomb will be programmed to hit the target's coordinates.

That's why the guide as used by the OP does indeed make a whole lot of sense even though the JDAM itself couldn't care less about lasing.

Edit: There's some clarification on the next page. The above example is not entirely invalid, but it's usually not necessary to lase the target if the TGP remains SPI generator all the way to weapon release.

Would you care to read my entire post that you quoted, or does taking convenient parts out of context to misrepresent what I actually wrote suit you better?

1. Turn on latch on laser

2. Find target in TGP

3. Lase target

4. Make target SPI whilst lasing

5. Turn off laser

The GBU-38 is a JDAM, meaning it's not laser guided. The laser may help in getting distance and such exact, but it's not used by the GBU-38. Do you by any chance not fly steady when you drop it? Did you select the GBU-38 before making the target SPI?

 

Whilst I can't think of anything very wrong of the top of my head in that guide, small things such as instructing people to turn on a laser for a GPS guided weapon that does not track or even register a laser does lead me to say that it might not be the best guide in the world. Try the training mission.

Would you care to read my entire post that you quoted, or does taking convenient parts out of context to misrepresent what I actually wrote suit you better?

I did read your entire post. I was just under the impression that you hadn't read the OP's post in its entirety and were actually saying something that, both in and out of context, would lead others to believe there was something wrong with the guide the OP was following - which is not the case, the guide is fine and makes perfect sense. That's what I wanted to specifically point out, and also explain why the guide makes sense.

But if you would prefer to make this a debate about misquoting others, let's continue via PM.

I did read your entire post. I was just under the impression that you hadn't read the OP's post in its entirety and were actually saying something that, both in and out of context, would lead others to believe there was something wrong with the guide the OP was following - which is not the case, the guide is fine and makes perfect sense. That's what I wanted to specifically point out, and also explain why the guide makes sense.

 

But if you would prefer to make this a debate about misquoting others, let's continue via PM.

Agree with Yurgon.

You should read up on that.

What are the coordinates the JDAM gets programmed to hit?

 

Without lasing, the Terrain Elevation database would assume you're aiming at a spot on the ground. These coordinates would then be programmed into the JDAM prior to release.

 

In order to make sure that the target itself gets indeed targeted, it should be lased before making it SPI. This way, with the exact distance available to the Fire Control Computer, the bomb will be programmed to hit the target's coordinates.

 

That's why the guide as used by the OP does indeed make a whole lot of sense even though the JDAM itself couldn't care less about lasing.

And that whole concept comes from a fundamental misunderstanding of how the SPI/SPI generating SOI work.

If you are using the TGP to generate a SPI on which to drop a JDAM, there is no reason whatsoever to employ the LASER. It can make some sense if you're creating a mark point from a TGP generated SPI at a low angle and high slant range from which you will later generate a SPI for a JDAM, but in such a situation it's likely that you'd be beyond the effective range off the LASER anyway, and simply being aware of how the SPI works and adjusting the aim point would be more effective.

By the time you're at a range from which the A-10 is able to release a JDAM on target, the slant angle will be such that any error caused by looking though the target with a TGP generated SPI will be nonexistent.

That does imply that the SPI is generated only a relatively short time before the actual drop?

(Edit: As in about before turning onto the attack heading)

That does imply that the SPI is generated only a relatively short time before the actual drop?

As far as I know, the SPI is being generated continually. The surface coordinates under your TGP crosshairs will be the SPI, assuming of course that you've set you TGP as SOI. So it's a good thing to get into the habit of checking your TGP just before you pickle, to make sure your crosshairs are still over the target.

EDIT: Should also add that you probably need to generate a SPI through the TGP with TMS Up Long too. I don't think generating a SPI through the TAD or HUD and then making your TGP the SOI will do the trick, but I could be mistaken.

And that whole concept comes from a fundamental misunderstanding of how the SPI/SPI generating SOI work.

 

If you are using the TGP to generate a SPI on which to drop a JDAM, there is no reason whatsoever to employ the LASER. It can make some sense if you're creating a mark point from a TGP generated SPI at a low angle and high slant range from which you will later generate a SPI for a JDAM, but in such a situation it's likely that you'd be beyond the effective range off the LASER anyway, and simply being aware of how the SPI works and adjusting the aim point would be more effective.

I'm not sure I'm following you here, so let me try to clarify.

When generating a SPI with the TGP without lasing, is the SPI's fatual position on the object in the TGP or is it placed on the ground (based on the DTSAS digital elevation database) in regards to TGP LOS?

It's my understanding that in such a case the SPI coordinates reflect the position on the ground as if no object was present. Is this correct?

It may well be the case that we're talking centimeters in deviation here. I'm just trying to figure out whether I'm entirely wrong and what exactly the fundamental misunderstanding is.

By the time you're at a range from which the A-10 is able to release a JDAM on target, the slant angle will be such that any error caused by looking though the target with a TGP generated SPI will be nonexistent.

Well even if it's just a foot or half a foot or half of that, I'll take all the precision I can get.

But we were talking about generating the SPI, not about releasing the weapon. Both don't necessarily happen within a short time frame. Therefore, if the SPI coordinates were bad when I set the SPI, they will be bad when I release the weapon, or won't they?

That does imply that the SPI is generated only a relatively short time before the actual drop?

(Edit: As in about before turning onto the attack heading)

Huh, that's a much shorter way to put it. :)

As far as I know, the SPI is being generated continually. The surface coordinates under your TGP crosshairs will be the SPI, assuming of course that you've set you TGP as SOI. So it's a good thing to get into the habit of checking your TGP just before you pickle, to make sure your crosshairs are still over the target.

Now that's an interesting point. Would indeed be very interesting if someone could elaborate.

No, just no. A laser isn't some magic GPS.

Afaik Yurgon is right on this, the TGP uses elevation data, therefore lasing the target gives you higher accuracy in terms of target coordinates. But still, the GBU 38 is not that accurate. I can launch from steady flight with target perfectly aligned and SPI right on target, the Bomb still misses by ~2m, which is enough for a MBT to survive the attack. Everything else still gets busted w/o big problems, but if this behaviour is correct and I don't do something wrong it is not suited as an antitank weapon

As far as I know, the SPI is being generated continually. The surface coordinates under your TGP crosshairs will be the SPI, assuming of course that you've set you TGP as SOI. So it's a good thing to get into the habit of checking your TGP just before you pickle, to make sure your crosshairs are still over the target.

 

Now that's an interesting point. Would indeed be very interesting if someone could elaborate.

Okay, simple enough, I just tested it in a mission and NoCarrier is correct.

The manual is also pretty clear about it in the section "SPI Sensor Designators":

Targeting Pod (TGP). Like the Maverick, when the TGP is SOI and the "set sensor as SPI" function is selected, the line of sight point at ground intersection marks the SPI with a TMS Forward Long. This will be the same coordinates and elevation displayed in the TGP display. As the TGP crosshairs are slewed, the SPI will move along with it. To un-assign the SPI from the TGP, you may either use the "reset SPI to steerpoint" function or assign the SPI to another sensor.

That means that with the TGP as SPI generator, the SPI will always be where the TGP is pointing at at that time (or, more precisely, the ground at TGP LOS according to the digital elevation database).

Therefore Eddie is correct in that there's normally no need to lase the target when setting the SPI if the TGP is SPI generator by the time of JDAM release and the TGP crosshairs are over the target at that time and the slant angle at that time is high enough that the target coordinates are actually on the intended target.

Fascinating. With this sim, I really learn something new every day.

No, just no. A laser isn't some magic GPS.

Uh... no one ever said it was (at least in this thread)? :confused:

ED has added failures the the game. In early versions this never happened. Slaving the SPI to target does'nt all ways help. When using mark points you dont slave your SPI

ED has added failures the the game. In early versions this never happened. Slaving the SPI to target does'nt all ways help. When using mark points you dont slave your SPI

What's wrong with it? Just tested it, works fine.

You must make sure SPI is set to steerpoint (TMS Aft Long) and double check HUD for SPI generator = STPT. Headspace didn't mention that in the video, maybe it was obvious to him. But other than that, it works like a charm. :)

And this is also an example where lasing a target before setting a markpoint on it would seem to make a lot of sense.

I thought TMS-forward long designated SPI?

Afaik Yurgon is right on this, the TGP uses elevation data, therefore lasing the target gives you higher accuracy in terms of target coordinates. But still, the GBU 38 is not that accurate. I can launch from steady flight with target perfectly aligned and SPI right on target, the Bomb still misses by ~2m, which is enough for a MBT to survive the attack. Everything else still gets busted w/o big problems, but if this behaviour is correct and I don't do something wrong it is not suited as an antitank weapon

This.

JDAMs are not ideally suited to targets that require precision down to a few meters. They are quite effective, however, for buildings, bridges, and other static targets for which the GPS precision provided is sufficient. For tank plinking, as described in the flight manual, you're better served by laser guided bombs like the GBU-12/10.

As Eddie indicated earlier, slant range errors are only noticeable when the target is far away. As you approach the target, the effect becomes negligible. I recommend you check out ExcessiveHeadspace's video

JDAM's are not the most accurate weapons in the world, not guaranteed to hit. I would only bother with them in bad weather or when you need a more stand-offish PGM than a Paveway.....but you need lots of speed and altitude for that.

I don't recall any of my pilots lasing JDAMS in other than 54's. I would also add depending on your angle of attack you can get spillover from the laser due to beam divergence. Not sure if the game simulates that though.