[REPORTED] JDAM LAR not accounting for target elevation.

Chris935 · August 16, 2022

Issue:

The JDAM LAR works as expected on targets at low elevations, if you release when the system says it's in range, it hits the target. When the target elevation is higher this isn't the case and the bomb will often fall short, assuming the same aircraft altitude in both cases. The LAR calculation does not appear to be accounting for the elevation of the target. It appears the calculation is using the aircraft altitude above sea level where it should be using height above target.

Test:

The attached track has two targets at low elevation near sea level and two targets at high elevation, around 18K on top of Mt. Elbrus. The aircraft altitude is 25.8K throughout (per Dos Gringos I did the whole damn mission on altitude hold). Speed is 0.86-0.88 throughout.

Each elevation has a GBU-38 and a GBU-32 dropped on it. These are set up as waypoints in the mission editor, and converted to TGT points in the jet using DESG and TOO. All pickle presses are made as the LAR percentage comes up through 20.

Results:

For given speed and altitude of the aircraft, the LAR symbology gives indications of "20" at the same slant range regardless of the aircraft height above target. In the attached track it's 13 miles for a GBU-38 and 9 miles for a GBU-32. With a height above target of 25K, these slant ranges are sufficient for the bombs to reach their targets. When the height above target is only 7K, the bombs fall short as you might expect.

Not shown in the track, it's also possible to get LAR in range indications while below the target. I've attached an image of the LAR coming up through 98 as I'm 5 miles away and 6K feet below the target. The target is in the top right of the HUD. Altitude above sea level is 12.7K, so the 5 miles makes sense if you incorrectly assume a target elevation of 0.

Chris

AV8B JDAM LAR ALTITUDE ISSUE.trk

Tacview-20220816-025611-DCS.zip.acmi

Edited August 18, 2022 by Chris935
Added Image