CBU-99 Zero damage unless scoring a full target hit

[Kah0tika]

EDIT:

After further testing here are my conclusions:

• Adjusting burst height to 1500ft slightly improve the GBU99's effectiveness (still very underwhelming). Best results were achieved on static vehicle in CCRP mode with an attack angle of 30° or more. UFC settings: 4 bombs in pairs with 50ft intervals. CCIP give extremely random and unreliable results.
• The damage model/system of some vehicle seem to be involved as well and has been highlighted. In this case the BMP3 seems to be unrealistically resistant to GBU99s submunitions and 20mm rounds (and possibly rockets). Still testing with other light armoured vehicles. In fact some tanks are more vulnerable than light armoured vehicles.
• Finally the dispersion effect doesn't reflect the actual sub munition spreading resulting in a visual discrepancy between the visual effect and the actual impact.

 

 

CBU99_Bug.trk

Edited 1 hour ago by Kah0tika
Edit after further testing

[BIGNEWY]

Hi,

you are using the default airburst altitude of 300 ft, which is insufficient for proper dispersion with the FMU-140 fuze. You should use at least 1,500 ft airburst for armour penetration to be successful. Hope that helps  

 

[Spartan111sqn]

2 hours ago, BIGNEWY said:

Hi,

you are using the default airburst altitude of 300 ft, which is insufficient for proper dispersion with the FMU-140 fuze. You should use at least 1,500 ft airburst for armour penetration to be successful. Hope that helps  

 

Thanks, maybe a doc or white paper indicating some parameters for some weapons is needed, in some cases we are a bit lost on it.

[Kah0tika]

Thank you for the answer.
I should have mentioned in my edit that I did have better results with a 1500ft airburst and above.
Yet it's still extremely difficult to damage light armoured vehicles with it.
Usually it take one precise direct hit and seems in inflict no damages to other nearby vehicles and objects.
In CCIP on moving targets I can visually see the area of impact being clearly on top of the vehicles but doesn't do much more than a cloud of dust.
I'll test a little more and come back with additional results.

[Renko]

On 11/4/2025 at 9:51 AM, BIGNEWY said:

Hi,

you are using the default airburst altitude of 300 ft, which is insufficient for proper dispersion with the FMU-140 fuze. You should use at least 1,500 ft airburst for armour penetration to be successful. Hope that helps  

 

I think the issue comes from the explosions effects discrepancy

I noticed this a while ago

and today during test to report it i noticed something.
Even if i changed the Airburst Height at which the submunitions released, the effect remained the same. The visual effect of it i mean.

If you slow down the replay you can see the submunitions diferent dispersions, but the visual effect will mislead the user.
I think it will worth to update the visuals to match the dispersion. That will help the user to see what the settings and how he deployed it really does.
null

[Dragon1-1]

19 hours ago, Kah0tika said:

Usually it take one precise direct hit and seems in inflict no damages to other nearby vehicles and objects.

This is realistic, the submunition has a HEAT warhead about the size of a hand grenade. If it doesn't land directly on top of an armored vehicle, it won't do a whole lot, and it doesn't even fragment all that much. The visuals are fake because actually showing 247 distinct bomblets and corresponding explosion effects per bomb (meaning a 4-bomb ripple has almost 1000 of the buggers, and a fully loaded four ship of Hornets will dispense close to 8000) would likely bog down the sim.

[SloppyDog]

Damage effects of CBU-99s with FMU-140 are hit or miss...literally.

I've been testing them for some time, and the best results I have are with CBU-99 with Mk 339 at low altitude.

For FMU-140, as per ED's instructions on September 7th changelog, for DCS 2.9.20.15010, under the Weapons section it reads:

• Mk-20/CBU-99. Improved bombsight accuracy. Please note that using FMU-140 in low-altitude horizontal flight bombing runs will lead to poor accuracy - in these cases Mk 339 fuze must be used. FMU-140 should provide acceptable accuracy in dive bombing runs and, in specific conditions, in horizontal flight bombing runs (function altitude set to ca. 1/3 of release altitude and specific airspeed at release, e.g. function altitude - 3 kft, release altitude - 10 kft, TAS - 580 kts)
•  
• Mk-20/CBU-99. Fixed Mk 339 fuze function delay being counted down after arming instead of after release

In my testing, FMU-140 works best by flying level,dropping  at 10,000 feet, with an airburst of 3,000 feet AGL, using AUTO mode.
This way the bomblets have enough time to arm and spread. The spreadsheet below gives you an idea of various profiles for dropping these cluster munitions. (If you are asking yourself why would I spend too much time doing this and testing, the answer is: I'm a stubborn nerd).

So, the end game is that you must allow time for the bombs to separate from the aircraft, open and, most important, arm. 

However, the bomblets do cause damage only when they directly hit the targets. Funnily enough, the result is that -99s are most effective against armored than against light targets. I blame that on the lack of a proper fragmentation model, but ED said they are working on it. From the July 23rd changelog:

• Weapons. Work in progress fixes for the following bombs explosive mass: M117, Mk-80 series, and WWII AN-M GP series. This also applies to Guided Bomb Units (GBU) that use the Mk-80 series of warheads. This is connected to the changes for SAMP bombs that we did in the previous patch and will be evaluated and finalized in future patches. Most rocket warhead families (at least Hydra/Zuni/FFAR, S-5/8/13/25, and SNEB-68) are already set up with parameters that match our available sources. Actual effect on targets is subject to change along with implementation of the fragmentation model. (We missed mentioning this in June 18’s update).

Try to hit the same targets with Mark 82s, and better yet, Mark 84s. You don't need to hit light targets directly, they'll catch fire from the frag effect.

P.S.: I forgot to mention that the -99s are falling short, either in AUTO or CCIP mode.

 

 

 

 

 

  

 

CBU-99 Height of Function.xlsx

Edited yesterday at 08:14 PM by SloppyDog

[Kah0tika]

6 hours ago, Dragon1-1 said:

This is realistic, the submunition has a HEAT warhead about the size of a hand grenade. If it doesn't land directly on top of an armored vehicle, it won't do a whole lot, and it doesn't even fragment all that much. The visuals are fake because actually showing 247 distinct bomblets and corresponding explosion effects per bomb (meaning a 4-bomb ripple has almost 1000 of the buggers, and a fully loaded four ship of Hornets will dispense close to 8000) would likely bog down the sim.

Interesting.
I initially thought the bomblets were not powerful enough to do any damages so I decreased the burst height to 300 in order to have a more concentrated effect but actually had worse results.
So if it works as intended it seems these bombs are quite under powered.
 

6 hours ago, SloppyDog said:

However, the bomblets do cause damage only when they directly hit the targets. Funnily enough, the result is that -99s are most effective against armored than against light targets. I blame that on the lack of a proper fragmentation model, but ED said they are working on it. From the July 23rd changelog

That might indeed be part of the problem.
I think there might be a hit detection system/damage model  issue on some vehicles.
When I go for a gun run sometimes it destroys or realistically damages some BMPs. But sometimes I can send 200 rounds on the side of the target with zero effect. In this case it's the BMP3 which seems to be stronger than a tank.
I've notice the same issues with rockets.

Something is definitely wrong. And I suspect it's the same issue that is affecting the GBU99s.

Here's a youtube clip that illustrate the issue.

In the Debrief windows we can see it registered 153 direct hits...but zero damages.
Now I wouldn't expect a BMP to survive a 20mm canon direct hit on the side and on the top.
Even a tank would take substantial damages with repeated hits in the back or on the top.

 

 

Hit_detection_test.trk

Edited 17 hours ago by Kah0tika
added content and precisions

[Kah0tika]

7 hours ago, Renko said:

I think the issue comes from the explosions effects discrepancy

I noticed this a while ago

and today during test to report it i noticed something.
Even if i changed the Airburst Height at which the submunitions released, the effect remained the same. The visual effect of it i mean.

If you slow down the replay you can see the submunitions diferent dispersions, but the visual effect will mislead the user.
I think it will worth to update the visuals to match the dispersion. That will help the user to see what the settings and how he deployed it really does.
null

 

 

Nice catch!
Hope this get fixed too. 

[Dragon1-1]

2 hours ago, Kah0tika said:

When I go for a gun run sometimes it destroys or realistically damage the BMPs and sometimes I can send 200 rounds impacting directly the side of the target with zero effect. So perhaps the issue is not only the bomb but also the hit detection system.

Worth remembering, the damage model for ground units in DCS isn't that great. In particular, IRL the top armor of almost all pre-2010s armored vehicles is paper thin. They're basically protected against small arms fire, maybe .50 if it's a particularly thick skinned vehicle, but not much else. Depending on the angle, the A-10 could punch through most tanks of its day with 30mm AP, as long as it hit the top armor. DCS doesn't model any of that, I'm not sure if there's any difference at all between where you hit, but even if there is some accounting for direction, the armor model is simplified, making top armor way too strong. I suspect that's in play here, realistically putting 20mm rounds in the side of a BMP probably shouldn't work, but they should go through the top no problem.

[Kah0tika]

2 minutes ago, Dragon1-1 said:

Worth remembering, the damage model for ground units in DCS isn't that great. In particular, IRL the top armor of almost all pre-2010s armored vehicles is paper thin. They're basically protected against small arms fire, maybe .50 if it's a particularly thick skinned vehicle, but not much else. Depending on the angle, the A-10 could punch through most tanks of its day with 30mm AP, as long as it hit the top armor. DCS doesn't model any of that, I'm not sure if there's any difference at all between where you hit, but even if there is some accounting for direction, the armor model is simplified, making top armor way too strong. I suspect that's in play here, realistically putting 20mm rounds in the side of a BMP probably shouldn't work, but they should go through the top no problem.

I might be wrong but I think it would definitely go through the side, the top and the rear of a BMP. Only the front might resist a little better to a single impact but not much more.
They are designed to survive 12.7 not 20mm canon.
Furthermore coming at a 35-45° angle almost guaranties some hits on the top just like in the YouTube vid.

I definitely hope the damage models could be improve to reflect the reality and reward real tactics.

[Dragon1-1]

10 minutes ago, Kah0tika said:

Furthermore coming at a 35-45° angle almost guaranties some hits on the top just like in the YouTube vid.

Hits, yes, but not penetrations. The angle means the round has more armor to go through and is more likely to bounce. That is modeled in DCS. As mentioned, DCS does not account the roof is just some 15mm of aluminum alloy. In fact, I don't know if there's more than a single armor value for the BMP-3. It might be surviving things it shouldn't due to simplified modeling.

Also note, a single 20mm AP going through the infantry compartment won't cause the BMP-3 to explode into a fireball (though anyone sitting inside will have a bad time). In DCS, it won't take off all its hitpoints. That stuff is simplified to the point of inadequacy, strafing with 20mm in particular gets hit hard (30mm usually kills light armor reliably).

[Kah0tika]

With AP rounds the crew would get killed by shrapnel as you mentioned. The engine and other mechanical parts would get damages. They could implement a simplified"crew kill" that would prevent the BMP to shoot back once hit.
With SAPHEI rounds it would eventually catch fire. It would just take more rounds to go through.

I hope this damage system gets improved as it would solve the GBU99s, guns and rockets issues at the same time and make it far more realistic.

Edited 16 hours ago by Kah0tika

[Dragon1-1]

Wags mentioned it in the interview, they'd like to look into it at some point, but it's way down on the list of priorities. ED knows it's a big issue with ground units.

Worth noting, there's a chance that it'll still cause some randomness. For instance, if the rounds gut the troop compartment, but spare the forward part where the crew are sitting, the BMP would still shoot back. It might even remain drivable. With spall liners everywhere, an AP round might just punch a hole. SAPHEI rounds aren't particularly common on aircraft, it's usually regular a mix of AP and HEI. The former punches a hole, the latter detonates on impact.