GBU-38 Extremely Inaccurate

Hello guys,

This has frustrated me beyond measure. I have spend the best part of this morning testing dropping these bombs and the are way way off the mark.

This all started with me trying to do the multiple drops in one run. I have been doing bomb drops since A10-C beta so I can say I am no noob. The bombs are just way off the mark. I know that the JDAMs are not pinpoint like the gbu-12 but it is not even missing by a few feet.

I have tried with and without using the laser.

I have tried using mark points and the tgp

Process:

TGT as SPI

center TGP on target ( I do this within 5 - 12 miles for minimum drift).

TMS up short (point track, I have also tried without this)

Lase the target (I have also tried without lasing)

TMS up long

Laser off

Mark-point as SPI

center TGP on target ( I do this within 5 - 12 miles for minimum drift).

TMS up short (point track, I have also tried without this)

Lase the target (I have also tried without lasing)

TMS up long

TMS right short

laser off

I have verified that the on the bottom left side of the HUD is showing either TGP or STPT.

I have noticed that the later I pickle the closer the bombs get to the target. I almost have to wait till the release envelop is almost expire to get it as close as a cars length. pressing the pickle right when I get the manual release indicator result in the bomb dropping like a field length off.

I have tired speed of between 200 and 270

altitude of between 5,000 and 12,000

All resulting in failure

I have also tried lasing the target just before I drop the bombs

I have had a hand full of successes but I did nothing I have not done before.

Gone as far is creating markpoints when I am right above the target but the bombs still miss.

I have watched all the video i can find on YouTube and replicated with no luck.

I would grade my success as 5% at best

Is there now a new process that I am not aware of?

Well something is wrong for sure. I can usually get 2 or 3 if them off just by quickly relocating my TGP while the tail is between the 2 launch Q triangles and at most if and when it misses, the edge of the crater is touching the vehicle I intended to strike.

Do you have some crazy winds in your test mission? Shouldn't matter but I'm just trying to see if we can narrow it down to something. Could you post a track of this happening? That would be the most useful way to debug this.

One thing that has apparently changed at some point:

If you're too eager to drop and pickle at or just after the "window" opens, they'll generally land short. Try pickling more in the middle of the window.

GBU-38s are doing a flight path which in certain situations will run itself out of energy. I was at 6000' and tried 200, 230, 260, 300 KIAS and the first two came up short while the last two were much closer.

I did tests at 6000' and 20,000' as well as with F/A-18. With Tacview graphed Mach vs. time for the bombs. The bombs have a strong requirement to hit M.75+-.03 in the mid phase of the flight. After it reaches this Mach it pulls up into a glide of sorts and then down into a terminal maneuver. The problem is for A-10 releasing at 200 KIAS, 6000' this M.75 mid course goal is suicidal energy wise. By the time the bomb has hit this Mach goal the target is very shallow and there's not enough energy to get there.

Go ahead and drop JDAM at LARmax and then open Tacview and graph Mach vs. Time of the weapon. You'll see a consistent M.75 peak value assuming you release slower than that and there's enough altitude for it to get there.

There is an issue with LAR calculation, JDAM guidance or both. From looking at the resulting profile it looks like a fault in JDAM guidance as it is clearly not managing its energy properly and coming up short when it's obvious that if managed differently it could have reached it. I think LAR is probably fine but JDAM is so goofy who can say.

Analyzing targeting is pretty simple. You'll note that the TGP coordinates display will flicker outside of 8nm range when using the laser. Whatever the coordinates display at the moment of release (TGP SPI) is the JDAM target and the difference between point area and lased are small and not the major issue here. Just compare your SPI coordinates to the actual target and if it's within .003' you're as good as it gets.

I will try to upload a new track, the one I have is too big to upload

I think centering TGP on target and using point track is your problem. Use area track and point at the base of target. When you target the middle of object imagine a laser pointing at it. Now imagine tha laser going through that object and hitting ground behind it. Thats where your JDAMs going since it only sees coordinates at ground level, not objects. You want to target ground beneath middle of target.

Bear in mind as well that GBU-38s are not as accurate as GBU-12s.

IIRC, the CEP of a GBU-38 is like 10 meters or so.

It's not an accuracy problem. The bomb when given enough energy to reach the target in DCS is hitting just fine. The targeting is accurate. The pilot is not doing anything wrong. I don't even think the LAR is wrong. The issue is the JDAM isn't flying like a JDAM should and it didn't use to do this.

The mid course guidance logic is flying the bomb out of energy. It's flying a profile like a slide at a water park. It falls off the airplane, points steeply down to M0.75 and then pulls out of its dive to approach the target like a 737 on final into LaGuardia and coming up 100s of meters short because it runs out of knots. Load up any airplane and launch a JDAM at a target ~200 knots from 10,000 at max range and just watch the bomb fall in F6 view. It should be obvious by qualitative observation.

I’ve seen them do this when dropped the instant the “pickle window” opens. Waiting a bit raises the reliability a lot.

But the CEP is factual. They are not perfect.

Indeed guys indeed.

I had some success last night. I find that taking out main battle tanks are particularly difficult but soft targets and buildings were easier. I guess because they allow for higher margin of failure.

cthulhu68's suggestion made a big difference, aiming at the foot of the the target

No one is listening.

I dont doubt what Frederf is saying either. All guided bombs have questionable physics going on. JSOWs seem even worse.

It's not an accuracy problem. The bomb when given enough energy to reach the target in DCS is hitting just fine. The targeting is accurate. The pilot is not doing anything wrong. I don't even think the LAR is wrong. The issue is the JDAM isn't flying like a JDAM should and it didn't use to do this.

 

The mid course guidance logic is flying the bomb out of energy. It's flying a profile like a slide at a water park. It falls off the airplane, points steeply down to M0.75 and then pulls out of its dive to approach the target like a 737 on final into LaGuardia and coming up 100s of meters short because it runs out of knots. Load up any airplane and launch a JDAM at a target ~200 knots from 10,000 at max range and just watch the bomb fall in F6 view. It should be obvious by qualitative observation.

I thought it was just me but I felt like the bomb was doing its damned just to miss, it looked more like a slide than a dive to me. I would watch it glide and when it is almost at the target I would watch it make some "corrections" causing it to fall short.