cannot produce and mssing track file CBU99 not accurate at all

[SUHANG]

I believe this is not the first time someone report this problem. After the update of the fuse, the CBU99 plus the MK20 Cluster bombs, are not accurate under CCIP mode and auto mode. The touching ground point always around the target point of the CCIP cross center, rather than direct hit on the target.

This problem occurs under the VT mode, not the PRI mode.  The PRI mode anyway is a dispense immediate mode, so I guess no one requires it to dispense right over the target. PRI mode shall be used to dispense on a wide area for a very low flight over of the target, pe my understanding. It is used for the light armed vehicle or personnel. But for tanks, we shall use VT mode right? of course the dispense hight or time determines the explosion coverage and the density of the bullets, but the problem not is the whole explosion area is far from the targets. 

The CBU99 can set the dispense hight, while MK20 can only send the seconds after drop for dispense. And actually I don't know what is the difference in the game. Is that suit to certain target or not? when shall I use the bomb which can set the dispense hight and when shall be the second?

By the way the CBUs, like CBU97 and especially CBU105, for A10C and F16 are more accurate and deadly. It can cover a wide area and destroy several tanks at one time. Why the CBU99 in FA18 are so useless. not accurate and can destroy nothing. Just like the Cluster bomb for Su25

Edited January 20 by SUHANG

[bfr]

The Mk20/CBU99 cluster munitions available on the Hornet have always been absolutely rubbish against proper armour, even if you get them on target. TBH I can't even remember the last time I tried using them because they're so incredibly limited in capability against all but the softest of targets. So in that sense, I wouldn't even bother trying to take a tank out with one as they just don't work. I assume they should work to some degree (i.e. be able to seriously damage/cripple an armoured vehicle even if they might not fully penetrate the hull like the skeet-based ones can) but I suspect the damage modelling in-game just isn't up to the job.

 

As you say, the CBU97/105 cluster weapons available on other platforms are a completely different story and can be incredibly effective.

[GrEaSeLiTeNiN]

Would the splash damage script help in this case? I’ve used it though I have not tested it with the CBU but the destruction I’ve seen it create in other munitions is quite widespread if not a little over done.

[Muchocracker]

21 hours ago, SUHANG said:

I believe this is not the first time someone report this problem. After the update of the fuse, the CBU99 plus the MK20 Cluster bombs, are not accurate under CCIP mode and auto mode. The touching ground point always around the target point of the CCIP cross center, rather than direct hit on the target.

This problem occurs under the VT mode, not the PRI mode.  The PRI mode anyway is a dispense immediate mode, so I guess no one requires it to dispense right over the target. PRI mode shall be used to dispense on a wide area for a very low flight over of the target, pe my understanding. It is used for the light armed vehicle or personnel. But for tanks, we shall use VT mode right? of course the dispense hight or time determines the explosion coverage and the density of the bullets, but the problem not is the whole explosion area is far from the targets. 

The CBU99 can set the dispense hight, while MK20 can only send the seconds after drop for dispense. And actually I don't know what is the difference in the game. Is that suit to certain target or not? when shall I use the bomb which can set the dispense hight and when shall be the second?

I think you misunderstand how these fuses work 

-The Mk-339 is a mechanical time clock fuse that functions based on time from release. PRI and OPT are just 2 different timing sets that can be chosen. 
-The FMU-140 is a radar altimeter proximity fuse with a secondary time of function. VT1 is rad alt, VT2 is time function. 

Your problem is not with the accuracy, your problem is with their spread. Which you can change by editing the fuse settings to either burst lower (VT1) or by setting a longer function/release them lower. 
 

22 hours ago, SUHANG said:

By the way the CBUs, like CBU97 and especially CBU105, for A10C and F16 are more accurate and deadly. It can cover a wide area and destroy several tanks at one time. Why the CBU99 in FA18 are so useless. not accurate and can destroy nothing. Just like the Cluster bomb for Su25

Not comaprable weapons in the slightest. The 97 and 105 are sensor fused weapons with heat seeking submunitions, of course they're going to be more effective. The 99 and rockeye are not designed for killing heavy armor. 

[Ginsu80]

I’d like to second this. I created a new mission file with the intention to pattern the HOF altitudes against soft trucks spaced 50ft apart. Delivering the CBU-99 with the FMU fuze set at various HOF altitudes I was having trouble getting the bomblets into a 200’x200’ grid of 25 trucks. I tried both CCIP deliveries and auto, level and dives up to 30 degrees, and even did the old ains/gps trick with no change. The 1500’ HOF seemed to be the most accurate, with the extreme 3000’ HOF never coming close. It seems the ballistic calculation for the bomb fall or something is off. Mission was an air start 10nm run in with zero wind. Afghanistan map.

[AndrewDCS2005]

MK20 Rockeye works for me, similar as it worked before.

Conditions: Caucasus, no wind, 20 degrees C, 750mm Hg, targets at near-zero ASL.

Weapon/fuzing: Rockeye MK20, Mk339 mod 1 fuze, 2s PRI delay.

Platform/config: F/A-18C, CCIP, QTY=2, INT=100ft (releasing two MK20s at once, separated by 100ft to cover more area with more dense hits)

Results: 5 targets hit/5 kills on first run, 3 hit/1 kill on the second run.

 

In general its not very easy to achieve accuracy with MK20 with MK339 clock fuzing - release altitude, speed, dive angle (ie velocity vector and its length) all matter a lot, which makes sense from physics/geometry perspective. I found most useful the combo of 3-4kft release alt, 300+kt speed, 30-40 degrees dive. Subjectively the first hits in the spread are always a bit short of CCIP pipper on release, but not way off as it was broken last year (where it fell short by > 1 mile).

FA18-CBU-MK20-CCIP.trk

Edited March 15 by AndrewDCS2005

[AndrewDCS2005]

CBU99 seems to indeed fall short.

Conditions: Caucasus, no wind, 20 degrees C, 750mm Hg, targets at near-zero ASL.

Weapon/fuzing: CBU99, Mk339 mod 1 fuze, 2s PRI delay.

Platform/config: F/A-18C, CCIP, QTY=2, INT=100ft

Results: 0 targets hit/0 kills on first run, 1 hit/1 kill on the second run.

 

There are actually two problems with CBU99

1 - it falls short

2- its spread pattern is much smaller than MK20 despite being exactly the same weapon, in the same SUU-75/A/B dispensers, with the same load of 247 MK 118 MOD 0 HEAT bomblets. And it does not really work as a cluster bomb weapon, and only direct hits on individual target will work. To kill a group of spread units CBU99 is much less effective. MK20 in the same dispenser with the same Mk339 fuze and the same config, released in the same conditions, covers more area. I am not reporting this as a separate issue as there's zero chance of it being fixed (its been like this since forever and no one ever raised this).

FA18-CBU99-CCIP.trk

[jojyrocks]

Cluster bomb issue with CBU 99 using FM140 and Mk82 snakeye bomb CCRP usage totally inaccurate on FF and RET. CCRP is useless with both cluster and dumb bombs.

F-18 FM140 Cluster bomb bug.trk F-18 MK82 Snakeye CCRP test bug.trk

[AndrewDCS2005]

@jojyrocks the track for MK82 lasts one second, there's nothing to see.

[AndrewDCS2005]

Just tested CCRP with MK82 LD, HD, RET - for each with two bombs released, all direct hits, no issues.

Edited March 15 by AndrewDCS2005

[SloppyDog]

On 1/20/2025 at 6:10 AM, SUHANG said:

This problem occurs under the VT mode, not the PRI mode.  The PRI mode anyway is a dispense immediate mode, so I guess no one requires it to dispense right over the target. PRI mode shall be used to dispense on a wide area for a very low flight over of the target, pe my understanding.

This is correct. I'm having a lot of success releasing Mk20s at low level. Be it on the F-15E, the F/A-18C and even in the F-4 (in laydown mode), they work very well at their default settings.  Below I present a spreadsheet showing the predicted height over target of the ARMED bomblets over the target. The detail is that we must consider not only the time for the canister open after release, but also the time it takes the bomblets to be armed.

 

On 1/20/2025 at 6:10 AM, SUHANG said:

 It is used for the light armed vehicle or personnel. But for tanks, we shall use VT mode right? of course the dispense hight or time determines the explosion coverage and the density of the bullets, but the problem not is the whole explosion area is far from the targets. 

Again, I'm having a lot of success with the immediate release mode at default settings, which are Time of Function (meaning, time for the canister to open) of 1.28 seconds, plus the CBU-99 time delay of 1.1 seconds. Trucks, APCs are easily destroyed, moreover if you send multiple CBUs over  the area (pairs, trios or in fours). Tanks require a direct hit, but in this low level, immediate release, they are either destroyed or damaged. Check the attached track for a test using the F-15E releasing CBUs in trios. 

 

On 1/20/2025 at 6:10 AM, SUHANG said:

The CBU99 can set the dispense hight, while MK20 can only send the seconds after drop for dispense. And actually I don't know what is the difference in the game. Is that suit to certain target or not? when shall I use the bomb which can set the dispense hight and when shall be the second?

This is where things get complicated and interesting. Mk20 only allow for the use of the Mk 339 Mod 1 time fuze. CBU-99s on the other hand allow for the use of the time fuze but also the use of the radar fuze, proximity fuze, or variable time (VT) fuze that is the FMU-140. 

In theory, the use of the FMU-140 allows for the opening of the CBU-99 at a certain programmed height, independent of time. 

So, the difference is: with a Mark 20 with the default fuzing of PRI at 1.2 seconds, it does not matter if the aircraft is at 500 feet or at 10,000 feet. At 1.2 seconds after pickle, the canister will open and will spread the bomblets over the area. At 500 ft, they will be more concentrated and hit the targets. At 10,000 feet they will spread out and will be all over the place, falling long and being drifted by the wind.

However, with a CBU-99 set to open at a height of 300 feet, if the aircraft drops it at 500 feet, the canister will open at 300 feet and the bomblets will be very concentrated in the area. The same occurs for an aircraft at 10,000 feet: releasing from this altitude, the canister will open at 300 feet AGL and the bomblets will be concentrated at the area. 

Success, right?

No. Unfortunately not. 

A very important and often overlooked thing is the ARM Delay setting. 

The ARM Delay exists to ensure that the releasing aircraft is not damaged by its own bombs or bomblets after dropping the canisters. 

Let's refer to the spreadsheet below: 

1) At line 4 of the spreadsheet, we have a CBU-99 with the Mk 339 Mod 1 time fuze.

2) In column A we have the aircraft altitude above the ground (AGL).

3) Next to it we have the Primary (PRI) time fuzing setting of 1.28 seconds.

4) At column D we have that the canister will open 26.36 feet below the aircraft.

5) At column F it shown that the canister is opened at 473.64 feet over the target. That would be a great spread, right? Not exactly, because we must take in consideration the ARM delay setting. For the Mk 339 fuze, the arm delay is fixed at 1.1 seconds.

6) So, moving to the right in the spreadsheet, we see in column I that the time for the bomblets to be released AND armed is of 2.39 seconds after release. It corresponds to a height 91.89 feet below the aircraft after launch, as seen in column K.

7) What this means is that the bomblets will be armed over the target at a height of 408.11 feet AGL, as seen in column M. The end result is that it is good enough to destroy targets, but we must have in mind that the bomblets were not ready to explode at 500 feet, but roughly at 100 feet below, due to the Time of Function (time to open the canisters) and Arm Delay (time to arm the bomblets after the canister was opened.

If you follow the same steps, but for the OPT setting of 4 seconds of Time Of Function, we can see on column N of the line 4 that the bomblets will be armed only at 79.93 feet. At this height many may hit the target, but not destroy it.

A worst case is on line 5, using an OPT setting of 8 seconds. In column N, we get a height for armed bomblets of -835.09 feet. It means that the bomblets won't have any time to arm before hitting the target, if released from 500 feet AGL. 

The other lines show various results for different altitudes and fuze settings. 

Let's see line 11, dropping a CBU-99 at 10,000 feet, with a PRI fuze setting of 23 seconds and an OPT fuze setting of 24 seconds. In column M we can check that for the PRI setting, we have bomblets armed at 648.75 feet, which will give a good spread over target. However, if we use the OPT setting, only 1 second later, the result in the N column is of -143.05 feet, meaning that if the canister is opened only 01 second later, there won't be enough time for the bomblets to arm. All you will get is a dud over target.

This happens due to the acceleration of gravity, that makes speed grows linearly, and causes displacement (distance) to grow quadraticaly over time. It means that for every second passed, the time required to cover 100 feet, for example, will diminish dramatically. 

Moving on to the FMU-140, at line 17 we see that for a canister dropped from 500 feet, with a time function of 300 feet over target. Considering an ARM time delay of 1.2 seconds, we get that, at column L, a height of armed bomblets over target of only 140 feet. Again, in my opinion, not ideal.

If we look at line 19, dropping a CBU-99 from 1,000 feet with a 700 feet height of function, we get that the height where the bomblets will be armed over the target is 510.11 feet AGL. Which, for me, is a good result.

So, let's get back to our example of dropping a CBU-99 from 10,000 feet with a height of function at 300 feet. The results for this example can be seen on line 28. In the column L we see that the height where the bomblets will be armed of the target is of -671.22 feet. Again, you would get a dud due to not giving enough time for the bomblets to arm.

So, for releasing a CBU-99 from 10,000 feet, the best height of functions should be 1,500 and 1,800 feet as seen on lines 31 and 32. These settings will give the height where the bomblets will be armed in column L, at 589.36 and 905.16 feet AGL respectively.

Of course, there are other factors to take in consideration, as spread of the bomblets when the opening over the area, type of targets and enemy air defenses.

All in all, the best way to use CBUs is to either fast and low or in a dive, releasing from a low altitude as well.

Anyway, I hope I helped to clarify your questions. And I sincerely apologize if I made it more complicated.

Notes about the spreadsheet: it is in Brazil's notation, so the decimals and thousands are inverted. In the U.S. for instance, decimals are expressed with a dot and thousands with a comma. For us, it is inverted. Also, I did not consider drag or other factors, only plain old high school physics.

Attached files: 
Excel spreadsheet - CBU 99 Height of Function.xlxs

Image - CBU Height of Function.png

TacView File -  Tacview-DCS-F-15E - CBU-99 Test.zip.acmi - Shows the success of using CBU-99 at low altitude.

TacView File - Tacview-DCS-F-18 - CBU-99 Test.zip.acmi - Shows a dud with the improper use of the wrong setting for the CBU-99. Height setting at 300 feet. 

Track file - F-15E - CBU 99 - 1500 ft.trk - Track file containing two successfull atacks with the F-15E at low level. 

Mission File - CBU-99 Test.miz - Mission file used to make the tests.

 

 

 

 

 

 

 

 

 

CBU-99 Height of Function.xlsx F-15E - CBU 99 - 1500 ft.trk CBU-99 Test.miz

Tacview-DCS-F-18 - CBU-99 Test.zip.acmi Tacview-DCS-F-15E - CBU-99 Test.zip.acmi

Edited March 16 by SloppyDog

[SloppyDog]

I deleted my last post.

Turn out that I wasn't using the latest DCS version. My bad.

Anyway, I've tested the CBU-99 again. With Mk 339 they are very effective.

With FMU-140...well, they are somewhat effective. The fuze works fine, they open the bomb at the set altitude.  The thing is, that is bothering other users as seen in other threads is the fact that they do fall short. By a lot. The best results I got was at 5,000 fett AGL with a opening height of about 1,500 - 1,800 feet. 

The tracks files attached show different attack profiles at different altitudes, with similar results.

 

F-18 - CBU 99 - FMU 140 - CCRP - Fall Short 02.trk F-18 - CBU 99 - FMU 140 - CCRP - Fall Short.trk