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CBU-99


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The Raven 1 campaign asks you to set VT to 1200 ft. I did it and the accuracy was spot on. Try using this value and see if it helps.

 

I've found that VT makes a difference with CCIP bombing but it varies with target elevation. To get a good hit on the Nevada Map I had to set VT to 2200. 1500 seemed to do OK on the coast of Iran; I didn't try 1200 there but it sounds reasonable. CCRP always missed long with CBU-99s no matter what.

 

Either something is busted or there is something about CBU-99 employment that we are missing.

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From the tests I did some time ago, the bombs were bursting about 1.2 seconds after reaching 1500 ft AGL for some reason, instead of immediately after reaching that height. Therefore, depending on their vertical velocity at the time, you may find them bursting between, say, 900 and 1450 ft. Which, of course, is not really helping this matter.

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That's possibly a misunderstanding about the fuze. There is an arming timer of about 1.2s but that's before the proximity device is enabled for immediate action.

 

I know 1.2 seconds (after release) is also the second option (in-flight selectable), that also works in the F/A-18C (by MFUZ = PRI, IIRC). There might be a mistake here on ED's part? Maybe this would actually warrant a bug report.

 

There is also the backup 500 ft (IIRC) for VT fuzing (if the bomb never senses it crossed the (ground-)selected HOB, it will burst at 500 ft anyway), that I think is not modelled right now in DCS.

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I mispoke.

 

FMU-140A on the front of the CBU-99 has arming times of 1(.2?), 2, 4, 6, 8, 10 seconds and HOF of 3, 5, 7, 9, 12, 15, 18, 22, 26, 30 hundreds of feet HOF as set on the face plate. The option wire is a 1.2s secondary dispensing mode which bypasses the primary requirements for burst (decreasing altitude, primary arm time, HOF).

 

In the proximity mode, if the pre-selected altitude is reached before the fuze has had time to arm, or the dispenser is released below the pre-selected altitude, the fuze will have the potential to function any time after arming. If the fuze has not functioned by the time it reaches an altitude of 300 ±25feet, it will function at that time
It seems the minimum time to arm in either primary or secondary mode is 1.2s (if we consider the "1 second" option for primary is actually 1.2). I don't think DCS ever uses the secondary method which could be verified if it is at all possible to get a release-1.2s-dispense at 30,000'.

 

The phrase "has the potential to any time after" is interesting. Makes one wonder in practice if the arming time is up and the bomb is <HOF what are the chances to dispense between that height and 300'. Is it common? Is it rare?

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I mispoke.

 

FMU-140A on the front of the CBU-99 has arming times of 1(.2?), 2, 4, 6, 8, 10 seconds and HOF of 3, 5, 7, 9, 12, 15, 18, 22, 26, 30 hundreds of feet HOF as set on the face plate. The option wire is a 1.2s secondary dispensing mode which bypasses the primary requirements for burst (decreasing altitude, primary arm time, HOF).

 

It seems the minimum time to arm in either primary or secondary mode is 1.2s (if we consider the "1 second" option for primary is actually 1.2). I don't think DCS ever uses the secondary method which could be verified if it is at all possible to get a release-1.2s-dispense at 30,000'.

 

The phrase "has the potential to any time after" is interesting. Makes one wonder in practice if the arming time is up and the bomb is <HOF what are the chances to dispense between that height and 300'. Is it common? Is it rare?

 

The 1.2 s option is modelled. It’s called PRI on the DDI. There should be a secondary 4.0s mode when the FMU-140 is not installed. The MK339 fuze has only the 1.2 pri and 4.0 option modes. Strangely the 3D model has the mk339 fuze, while we have prox fuze settings. There’s a proper 3D model for the prox fuze in the DCS model viewer.

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Mk 339 can be adjusted for 1.2-100s for both primary and optional delays but they come from the factory with 1.2, 4.0 by default. If the Navy changes them before use I don't know. It's sort of weird to say "when FMU-140 not installed." Either Mk 339 is installed or FMU-140 is. It's a substitute, not an addon. In any case certainly none of the CBUs on the Hornet use the Mark 339 so no need to worry ourselves with it.

 

I'm a little surprised that pulling both wires on the FMU-140 is called "PRI" (since that's really pulling the PRImary and OPTion wires) but "VT" should certainly correspond to radar proximity function. I guess F-18 avionics likes to call the non-VT mode PRI. The 1.2s "dumb" option mode works just fine. No issues there.

 

Yeah, as far as I can tell both Mk 20 and CBU-99 weapons are pre-set for HOF 1500' and then wait until 1500' and then 1.2s after that they burst. I can also say that the FMU-140 function which won't burst until the dispenser is coming back down after a loft isn't modeled either. If you loft a RET from 500' it will burst when climbing.

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  • 1 month later...
Mk 339 can be adjusted for 1.2-100s for both primary and optional delays but they come from the factory with 1.2, 4.0 by default. If the Navy changes them before use I don't know. It's sort of weird to say "when FMU-140 not installed." Either Mk 339 is installed or FMU-140 is. It's a substitute, not an addon. In any case certainly none of the CBUs on the Hornet use the Mark 339 so no need to worry ourselves with it.

 

I'm a little surprised that pulling both wires on the FMU-140 is called "PRI" (since that's really pulling the PRImary and OPTion wires) but "VT" should certainly correspond to radar proximity function. I guess F-18 avionics likes to call the non-VT mode PRI. The 1.2s "dumb" option mode works just fine. No issues there.

 

Yeah, as far as I can tell both Mk 20 and CBU-99 weapons are pre-set for HOF 1500' and then wait until 1500' and then 1.2s after that they burst. I can also say that the FMU-140 function which won't burst until the dispenser is coming back down after a loft isn't modeled either. If you loft a RET from 500' it will burst when climbing.

 

Ok, given what you've said can we simply stick to 1500 feet setting to be effective against tanks at all elevations/terrains? or is there a bug in the software that we need to compensate for?

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