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Issues with GBU-38


xoxen

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Hi,

I´m flying the Hog since 2013 and believe I´m not a beginner anymore. I´m fine in dropping JDAM´s like the GBU-38. But actually I have issues with it, as I always slightly miss the target, even though the TGP is directly pointing at it. Some friends figured out the same behavior. Even if I´m lasing the target and make it the SPI with laser on I have no success. For soft target this is not of a problem but e. g. a tank only get´s damaged.

Am I missing something new? Any help is very much appreciated.

Thanks,

Xoxen

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Even if I´m lasing the target and make it the SPI with laser on I have no success.

 

Lasing for a jdam wont do anything. Try creating your SPI beneath your target, on the ground.

 

Edit: Just tried it myself on a mission with clear weather. 4 out 5 gbu38's miss their target by 2-3 meters.


Edited by kylekatarn720
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Like the others are saying. Use pod , in point mode, to define SPI(Sensor point of interest). That provides coordinates that the JDAM will guide itself to. Place HUD in CCRP mode, and fly to release point. When HUD shows MAN REL, release the weapon(s). The weapons are self guided, but cannot be adjusted inflight. So no moving targets.

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Thanks for the answers. I'm not using the laser to point the JDAM into the target but to get an even more accurate SPI. But it's like Kylekatarn mentions, 2-3m off the target. So it seems it's not just me. For me it seems like a bug. I was able to get direct hits before.

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Are 2 to 3 meter off the target RL accuracy of JADAMS?

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Are 2 to 3 meter off the target RL accuracy of JADAMS?

 

No :)

 

It's even more.

 

They average at about a 30ft CEP.

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That would make sense. Just found a source which mentions 9.6m accuracy. Maybe it was too deadly accurate before?! So I start thinking away from a bug.

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Same with me, never thought about this so far ;)

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There is a lot of things that affect RL munition. For example the type of ground (sand, concrete, etc.) The fuze setting; a few milliseconds of bomb penetrating soft sand is enough to change the shrapnel pattern and consequently the area damage. Tail or nose fuze, is it an air burst and so on.

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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You need to enter wind and temperature data into the LASTE on the CDU. There is a very specific way to do this. It's important to use the spreadsheet on Google docs to convert wind from the briefing format into CDU format. I have it down pretty good and I can get everything entered on the ground before alignment is complete. I believe you must do this every time, and it will significantly improve bomb rocket and gun accuracy.

 

about 20 minutes and will explain everything. The spreadsheet you need is in the video description.
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HI XOXEN,

 

Im curious as to your standoff when you generate your target coordinates?

 

The people on here are not wrong about CEP or circular error of probability and the ERROR paper says it has.

 

My angle on this is the "angle" your grabbing the coordinates from. If your 5nm's away and your crosshairs are right in the middle of a tank the targeting pod does not know that the tank is there. What it does know if everything is properly aligned is the elevation of planet earth. So the laser is actually detecting the ground BEHIND the target. I suspect that is where the bomb is actually falling.

 

In a threat environment I grab the grid from the base or bottom of the target. In this instance, the tracks of the vehicle.

 

IRL at all possible an aircraft would fly right over the target and only then produce the target coordinates to get the best coordinate possible. thats because like the bomb the aircraft induces its own errors. Grab the grid from right over the tgt. The bomb will go there. Movie quote. "60% of the time, it works all the time"

63

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My angle on this is the "angle" your grabbing the coordinates from. If your 5nm's away and your crosshairs are right in the middle of a tank the targeting pod does not know that the tank is there. What it does know if everything is properly aligned is the elevation of planet earth. So the laser is actually detecting the ground BEHIND the target. I suspect that is where the bomb is actually falling.

Well, in real life the laser obviously would not detect anything behind the target at all. With lasers on this approach should work just fine.

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You need to enter wind and temperature data into the LASTE on the CDU. There is a very specific way to do this. It's important to use the spreadsheet on Google docs to convert wind from the briefing format into CDU format. I have it down pretty good and I can get everything entered on the ground before alignment is complete. I believe you must do this every time, and it will significantly improve bomb rocket and gun accuracy.

 

about 20 minutes and will explain everything. The spreadsheet you need is in the video description.

Eh IMHO no.

 

Entering wind into the CDU wouldn't really matter too much for guided munition, since it's well guided. For dumb bombs maybe, but I never used it. The CDU will already record the wind date while flying.

Main reason fro me not using it is the fact that Eddie from 476th has on numerous occasions stated that it's simply not necessary. IIRCC one of his points are that we as simmers tends to believe that dumb bombs will give us same accuracy as guided bombs if we enter wind into the CDU. If were that accurate then guided munition wouldn't be used at all I guess.

The second reason again IIRCC is that our (mine too) lineup on target and delivery is simply not good enough.

 

Can I proof it. No I am not that good, but reading through all the stuff Eddie posted over the years I have no reason to doubt him.

 

Cheers

Hans

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Kang,

 

The laser assists the aircraft in pointing at the ground to generate the grid.

 

If your pointing your TGP at the top of a tank or better yet a high rise building from a offset slant angle the location you are looking at is not a grid. The system doesnt understand the elevation of the building or the turret.

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Hi,

when I do like Hawg mentions I can see the TGP directly pointing on the target when overflying it. But I know what he is talking about and already had issues like this.

 

Wind is at least something I could enter into the CDU to see if it has an effect. But the last MP mission where I failed was without any wind. So I actually use the GBU-12 instead even though I need to overfly the target.

 

My main concern is that it worked for years and now I´m failing.

 

Xoxen

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Kang,

 

The laser assists the aircraft in pointing at the ground to generate the grid.

 

If your pointing your TGP at the top of a tank or better yet a high rise building from a offset slant angle the location you are looking at is not a grid. The system doesnt understand the elevation of the building or the turret.

Thanks for clarifying that. That's an issue about how the on-board computer handles the results of the laser ranging then, as in the range to the top of the building is interpreted to be something else.

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Well said Kang.

 

Its a very well known issue to those that study this for a living. And even the pros make mistakes.

 

On an educational note and not to get off topic. What you are now mentioning is the increased errors pilots, jtacs, planners and ground force commanders have to take into effect.

 

If your dropping on a beach where the elevation is close to 0 youll have a really close hit with JDAM.

 

BUT! The bomb has its own errors right.

 

And! Most of todays aircraft generate a CAT2 or maybe a CAT1 grid. Cat 1 is an error of 0-6 meters. Cat 2 is 6-12 meters if I remember correctly etc.

 

So now the error increases when you add up all these factors. This is all using MSL. BUT! There is error in MSL because as the moon dances around our planet the "sea level" goes up and down. ERROR!

 

Some people use HAE or Height above elipsoid. Cause the sea goes up and down and the planet isnt really round. MOre like chewed up bubble gum HAE attempts to create 1 line with a shared elevation. Problem is if the JTAC doesnt have that system, or the predator, the A-10, the Aussie super hornet. You get the picture. Everyone has to be on the same page.

 

Thus we know we can chuck a bomb in the ballpark and I am really happy to see with the AV-8B I think the GBU-54. Chuck it on GPS coordinates and at the end of its ballistic flight it is further refined to its target via a laser IF one is available. Best of both worlds in one.

 

Let me tell you. It really is long and painful when a B-1 flies over the tgt to get his best grid then reposition to finally attack the target. They dont show you that in hollywood.

 

XOXEN. I dont understand your last post about using the GBU12 and still having to fly over the tgt?

 

63

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Hawg, you are right, if the laser has free sight I also can go in a turn. JTAC or Buddy lasing would be the option.

Xoxen

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Eh IMHO no.

 

Entering wind into the CDU wouldn't really matter too much for guided munition, since it's well guided. For dumb bombs maybe, but I never used it. The CDU will already record the wind date while flying.

Main reason fro me not using it is the fact that Eddie from 476th has on numerous occasions stated that it's simply not necessary. IIRCC one of his points are that we as simmers tends to believe that dumb bombs will give us same accuracy as guided bombs if we enter wind into the CDU. If were that accurate then guided munition wouldn't be used at all I guess.

The second reason again IIRCC is that our (mine too) lineup on target and delivery is simply not good enough.

 

Can I proof it. No I am not that good, but reading through all the stuff Eddie posted over the years I have no reason to doubt him.

 

Cheers

Hans

There's no reason to enter the LASTE data for guided bombs, but I can say for sure it aids in accuracy of dumb bombs if it's windy. Bunyap did a video demonstrating this a while ago.

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This is all using MSL. BUT! There is error in MSL because as the moon dances around our planet the "sea level" goes up and down. ERROR!

 

Maybe I'm misunderstanding your point, but isn't the "M" in "MSL" there exactly to eliminate this error? Sea level changes with ebb and tide (said up and down caused by moon's gravitational pull), but MSL doesn't. According to Wikipedia, it can change greatly over geological time scales, which I believe are not much of a factor during CAS engagements. ;)

 

Other than that, great post, thanks a lot! :thumbup:

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Yurgon,

 

Im not gonna lie. Now you have me thinking.

 

I believe you are correct. MSL is a standard. My understanding is as you create this imaginary line around the world and create an "average". Error is induced because some areas sea level rises higher in some areas then others. So 0 elevation in some places would not be "true" and again induce error? I could be wrong here and Im really glad where this discussion is going.

 

If that MSL was in fact accurate wouldnt aircraft then no longer have to pull their best grids by flying over the target?

 

63

My CAS (Close air support) JTAC Channel:  RIFLE - YouTube  

RIFLE's Discord:  https://discord.gg/cmDCrr4Z2g  

Publications

JTAC Bible (see/know chapter #5) https://fas.org/irp/doddir/dod/jp3_09_3.pdf

J-FIRE pocket guide (Don't do battle without it!)  BK2 (fas.org)

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My understanding is as you create this imaginary line around the world and create an "average". Error is induced because some areas sea level rises higher in some areas then others. So 0 elevation in some places would not be "true" and again induce error? I could be wrong here and Im really glad where this discussion is going.

 

Oh my. I always thought MSL is pretty much a global definition, but after reading some more on Wikipedia from the above link, it seems MSL is indeed a lot more localized and is defined locally (as in: country-wide) by long term measurements at some fixed reference point.

 

So if the actual MSL values can be different from country to country, that should indeed cause errors in calculation. Unless, of course, the aircraft in question uses the same (local) MSL value that's also true for the target. Sooo... is this only a problem for intercontinental attacks (B-52, B-1, B-2)?

 

Man, that really is an interesting topic! :thumbup:

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