JDAM accuracy changed?

Am I doing something wrong, or have JDAMs become less accurate in recent updates? I think I’m doing the same procedure of making my TGP SPI and pointing it at the ground at my target. It seems like I used to be able to nail small stationary trucks, but the other day I was dropping on FARP tents and missed so wide the tent was undamaged. I know the CEP on a gbu 38 isn’t zero, and maybe these errors are realistic but it definitely feels like a change from prior and I want to see if anyone else feels this way.

Parallax error against the DTSAS surface? Try again with laser active TGP SPI. You can see the coordinate-elevation readout on the TGP during release and compare it to the F6 view right before impact. They should be quiet close.

I’ve tried laser on when holding TMS, laser on when releasing, not much different. Oddly what has seemed to make a difference is putting the TGP in Point mode, even when not bracketing a target. In a quick test it seemed more accurate than Area, but I can’t tell why, but that was with only 4 drops (two point, two area) so could be just luck.

Just be careful of angle slant, if the laser point / spi is in the middle of the tent or tank etc.

The A-10 database cannot see the tent, sometimes it will mark the ground through the tent from the slant angle.

I always put the laser on then spi right at the base of the target or wheel of the truck etc.

Same when you create mark points for multi JDAM drop.

Are you in POINT or AREA? You should be in POINT when you slave all and lase to get the most accurate, otherwise you're just pushing very generic 100x100m DTED target (probably, just a guess based on what I've seen) elevation data into the weapon. That's enough to throw off the DMPI.

I do it the same way learning off this old video by Excessive Headspace

He uses area and puts the laser on the wheels for a better position / slant accuracy.

Not sure if it's the absolute correct way to do it or just a DCS thingy.

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Testing accuracy is best down by eliminating sources of error. Instead of generating target location by TGP or other sensor look up the coordinates of a test target (eg F7 vehicle coordinates) and make one (or four to test coordinate resolution) waypoints at the target and drop on waypoint.

Waypoint N42 05.909 E042 37.757 256'

Target N42 05.900 E42 37.750 77m

TLE .009' N, 0.007' E +3' or 19m slant

Weapon time of flight >60sec

Weapons at impact

1 N42 05.900 E042 37.750 80m

2 '' visually about 2/3rds vehicle length to N

3 '' visually in #2's crater

4 '' visually 1.5 vehicle length NNW of previous

Trial 2 with coordinates override to match F7 readout

1 Didn't record L/L

2 N42 05.900 E042 37.733 82m visually 1/2 vehicle length 7 o'clock from #1

3 '' visually center of #1 crater

4 N42 05.833 E042 37.750 visually fringe of combined crater at 12-1 o'clock

Estimate typically repeatability dispersion 5m with one near 10m. TGP notably when pointing at matching coordinates at numbers was not on target but did match impact points. Noted that resolution of DM.M style coordinates was 1 arc second (step 0.0166666...'). A second of longitude being ~13m and of latitude ~31m.

Trial3

WP N42 05.909 E042 37.757 256

TGP INR N42 05.909 E042 37.760 252

TGP INR L N42 05.909 E042 37.756 258

TGP AREA N42 05.909 E042 37.757 255

TGP AREA L N42 05.909 E042 37.756 260

TGP POINT N42 05.909 E042 37.757 255

TGP POINT L N42 05.909 E042 37.756 260

Release four at TGP AREA L (POINT didn't want to track the vehicle) and impacts:

#1 .900/.750 78m visually with 1/6th vehicle length slightly short of second tire near side vehicle

#2 '' visually 1/2 vehicle length north of #1

#3 '' visually within #2's crater slightly longer few m

#4 '' visually within 1/5th vehicle length SE of vehicle center

Conclusions:

1. JDAM has some natural dispersion on the order of 75% within 10m.

2. TGP generated coordinates have a systematic shift relative to GUI coordinates

3. Navigation accuracy may be degraded by location within LAR at release

Conclusions:

1. JDAM has some natural dispersion on the order of 75% within 10m.

2. TGP generated coordinates have a systematic shift relative to GUI coordinates

3. Navigation accuracy may be degraded by location within LAR at release

Great post, very helpful. That’s probably about what I’ve been seeing with a few misses outside that 10m range. I guess that sums up that even with perfect target data I won’t be able to reliably splash small targets with JDAMs

Our squadron doctrine forbids dropping JDAMs unless there is a 10-digit grid reference via either a created markpoint or mission point and the only allowed guidance is via STEERPOINT as SPI in the HUD. Generally speaking, we only employ JDAM against a pre-determined target or else under the direction of a FAC(A) who gives a 10-digit grid in a Nine Line.

the only allowed guidance is via STEERPOINT as SPI in the HUD.

Same here. Only allowed to drop onto a pre planned waypoint or a in mission generated waypoint

Understanding is improved by more scientific thinking about the situation. If one bomb is dropped and it lands some place relative to aimpoint it is not certain if it an accuracy or precision issue. Instead drop as many bombs as possible at one time on the exact same targeting coordinates. If bombs are precise then all bombs will hit the same spot even if that spot is inaccurate.

Before worrying that you have some systematic error, consider that the miss from an individual bomb may due to non-systematic (random) error.