general canister weapon question

[silverdevil]

hello all. general question. is the burst height of canister weapons based on distance from the ground or barometric pressure? i figure the former. for example bombing a target on a 500 ft mountain peak and i want a 1500 burst height. thanks.

[Notso]

hello all. general question. is the burst height of canister weapons based on distance from the ground or barometric pressure? i figure the former. for example bombing a target on a 500 ft mountain peak and i want a 1500 burst height. thanks.

 

Height above the Target (distance from the ground).

[Vanguard]

Regardless of what it should it, I believe its barometric. I generally use 700 HOF on CBU-97/105- in A-10C, and if I don't increase the height when going into terrain they just smash onto the ground before opening.

[Notso]

Sorry, I should have been more specific.... Cluster munitions have various fuzing options to determine when the release the submunitions. The most common is a simple time setting after release. Once the arming wire is pulled a countdown timer starts (like 2, 4, 6 sec etc) and at the end, the clamshell opens. So mission planning is intensive to release at the correct altitude to get the correct effects. The other way is a proximity fuze in the nose which is a little mini-radar altimeter. At a predetermined height (essentially AGL) its opens the dispenser. To my knowledge there are no barometric fuzes, because if you think about it - it would make it super hard to employ against different targets due to the terrain changes as well as the ability to set the correct altimeter.

 

I can’t say for sure how DCS mechanizes them, but I can’t imagine baro is what they use.

[Vanguard]

I don't disagree that's how it "should" work, which is why I began my sentence that way, but it game, I believe its baro. The fuze is a doppler radar proximity sensor, so yes it "should" be AGL. But when deploying in mountainous terrain, I definitely need to bump the HOF or they run into the ground. Either I'm missing something or it's a bug.

[Notso]

I don't disagree that's how it "should" work, which is why I began my sentence that way, but it game, I believe its baro. The fuze is a doppler radar proximity sensor, so yes it "should" be AGL. But when deploying in mountainous terrain, I definitely need to bump the HOF or they run into the ground. Either I'm missing something or it's a bug.

 

It very well could be a bug, I haven’t played with Cluster bombs in game much. Maybe throw a track file to the mods to see if its messed up.

 

One thing to think about if you are dropping them in mountainous terrain.... if the target is up on a hill and you’re dropping from over a valley - it could be that you are closer in range to the target that you think you are and releasing inside the HOF of the cans even though your altimeter shows you should be high enough. That may explain why they are dudding. Dunno. Next time I get a chance, I’ll play with it to see if I’m getting the same thing.

[Vanguard]

I'll post a track next time I'm up. Last mission the targets were in fairly open terrain, but at about 275ft and at 700 HOF they just hit the turf, at 1000 HOF, they opened about what looked like 200ft off the deck, like maybe 7 seconds of parachute action.

[silverdevil]

my experience that caused my question in first place was i have a FANSONG on a peak elevation of 1590 in the hills / mountains west of Fujairah. using a HT of 1500 may be calulated by the position given to the weapon by the co-ords. either PP or TOO with the lightening. that calc + the HT input?

[Notso]

my experience that caused my question in first place was i have a FANSONG on a peak elevation of 1590 in the hills / mountains west of Fujairah. using a HT of 1500 may be calulated by the position given to the weapon by the co-ords. either PP or TOO with the lightening. that calc + the HT input?

 

There is no position given to the weapon. Until we get WCMD, canisters (CBU-87/97, Mk-20, etc) are dumb bombs. The release point is calculated solely by the jet and you need to mission plan where your release point in space is such that you can meet the HOF numbers. If you release less than that number in HAT (not AGL) then they will dud.

[Northstar98]

I wonder how the Mk-20 works, what's the turbine on the front for? Is it just to provide power/arm the fuse?

[amalahama]

I wonder how the Mk-20 works, what's the turbine on the front for? Is it just to provide power/arm the fuse?

 

 

Oh it is for propelling the bomb forward

[Northstar98]

Oh it is for propelling the bomb forward

 

:lol:

[draconus]

I wonder how the Mk-20 works, what's the turbine on the front for? Is it just to provide power/arm the fuse?

 

On the MK 339 fuze, the airstream driven impeller rotates, which physically allign the firing train, and allows the fuze to detonate at preset time.

[Northstar98]

On the MK 339 fuze, the airstream driven impeller rotates, which physically allign the firing train, and allows the fuze to detonate at preset time.

 

Okay, so in that case the bomb dispenses sub munitions after a set time, in that case I wonder how different times are selected and what it actually does to the fuze?

 

EDIT: I did some digging and it looks like that the Mk 339 has 2 wires, primary and optional. And which wire gets pulled (which can be selected in flight) selects between the 2 times which are preflight selectable.

 

It looks like DCS uses the FMU-140 fuze for the Rockeye, which works like a RADAR altimeter. It again looks the fuzing altitude options are preflight selectable, I'm not sure how many values are available to the fuze (with the Mk 339 it looks like there's just 2). I imagine the pilot can select which value to use, but can't configure what the values actually are in-flight.

Edited March 13, 2020 by Northstar98

[Harker]

I imagine the pilot can select which value to use, but can't configure what the values actually are in-flight.

Correct, to my knowledge. The pilot selects the value that's set on the ground, so that the correct firing solution can be computed by the aircraft's mission computer.

[Notso]

Okay, so in that case the bomb dispenses sub munitions after a set time, in that case I wonder how different times are selected and what it actually does to the fuze?

 

EDIT: I did some digging and it looks like that the Mk 339 has 2 wires, primary and optional. And which wire gets pulled selects between the 2 times which are preflight selectable.

 

It looks like DCS uses the FMU-140 fuze for the Rockeye, which works like a RADAR altimeter. It again looks the fuzing altitude options are preflight selectable, I'm not sure how many values are available to the fuze (with the Mk 339 it looks like there's just 2). I imagine the pilot can select which value to use, but can't configure what the values actually are in-flight.

 

These types of weapons from the late 90s to mid 2000s in DCS is that the Jet is not physically able to talk to the bomb itself to change settings. The pilot sets the bomb settings on the ground - fuze arm times, Fuze delay times, Laser codes in the case of LGBs, etc. Then the settings are matched in the aircraft SMS or weapons page so that the jet can correctly display the release and dud parameters. There are a couple of things the pilot can change what the bomb does in the cockpit such as selecting nose or tail or N/T together. This simply tells the jet which wires to pull and which ones not to.

 

So in the case of cannister weapons, the pilot would set the function time or the HOB/HOF during preflight based on what the mission planned parameters and desired weapons effects are. Setting the HOF on the jet weapon page would not change the bomb at all. The CBU is going to do what its been set to do on the ground.

 

The only time you can change actual bomb settings while in flight is if its a smart weapon that has an umbilical that is attached to the jet that can pass data back and forth.

 

In DCS, obviously we can't preflight the jet and the weapons to set these settings. So the SMS interface is sort of a trick to get the weapons to do what we want. It would be really cool (and very realistic) if you could set all the weapon settings in the mission editor page like you can set the laser code. I would have the ability to set fuze arm times, delay settings, function times, etc. It would require more work during the preflight setup, but that's the way its done.

[Ramsay]

I'll post a track next time I'm up. Last mission the targets were in fairly open terrain, but at about 275ft and at 700 HOF they just hit the turf, at 1000 HOF, they opened about what looked like 200ft off the deck, like maybe 7 seconds of parachute action.

 

How the weapons deploy depend on the type.

 

HoF is with respect to AGL for the CBU-87 and CBU-97

 

• CBU-87 deploys it's bomblets at it's HoF

 

• CBU-97 activates at it's HoF but has a delay of about 1 s (450 ft) before the casing splits and the 10 BLU-108 submunitions (with 4 pucks each) are deployed.

 

Tested using the A-10C, Groom Lake, DCS Open Beta 2.5.6.44266

Edited March 12, 2020 by Ramsay

[Northstar98]

...

Gotcha, cheers Notso! That cleared everything up nicely.

 

And yes I agree, having the preflight set-up available in the mission editor to change laser codes and fuze settings etc would be fantastic. As would a ground crew option.

Edited March 13, 2020 by Northstar98

[silverdevil]

all of this is great read. so question. what is the purpose of designating a target with TGP while already engaged in mission if all of this is seemingly PP rather that TOO. TOO by definition is "you won't know until you get there". i fly A-10C / F-18C / F-16C (latter not some much yet) and use this method all the time and never pre-plan anything. i download user missions and fly them until i survive. changing weapons and moving waypoints, etc.

[MK-82_1_EACH]

It looks like DCS uses the FMU-140 fuze for the Rockeye

 

 

 

Visually in game the MK-20 is using the Mk 339 and not the FMU-140. In either case settings are set on the ground by appropriate personal and not the pilot. Pilot just confirms during pre-flight. Primary/Option usage are determined by Nose/Tail solenoid. I would agree some sortie planning or configuration options would be great.

[Northstar98]

Visually in game the MK-20 is using the Mk 339 and not the FMU-140. In either case settings are set on the ground by appropriate personal and not the pilot. Pilot just confirms during pre-flight. Primary/Option usage are determined by Nose/Tail solenoid. I would agree some sortie planning or configuration options would be great.

 

If you look at page 135 of the Hornet manual it states:

 

For the Early Access release, the Mk-20, CBU-99, and CBU-100 canister weapons default to use FMU-140 fuses. This is a fixed-setting fuse with an arming time of 1.2 seconds after release.

 

When MFUZ is set to VT though, the HT (height) setting is available. Successive presses of the HT pushbutton cycles through the possible Height of Burst (HOB) settings.

 

So while the Mk 339 is visually depicted, it actually seems to be using the FMU-140 as per the manual.

[MK-82_1_EACH]

If you look at page 135 of the Hornet manual it states:

 

For the Early Access release, the Mk-20, CBU-99, and CBU-100 canister weapons default to use FMU-140 fuses. This is a fixed-setting fuse with an arming time of 1.2 seconds after release.

When MFUZ is set to VT though, the HT (height) setting is available. Successive presses of the HT pushbutton cycles through the possible Height of Burst (HOB) settings.

 

So while the Mk 339 is visually depicted, it actually seems to be using the FMU-140 as per the manual.

 

 

Just depends if your are a purist or not. :)

 

From my personal experience

 

FMU-140 options are ground-selectable, with option to override to time based. Dictated by N/T solenoid. Changing the settings HOB in flight are not possible in IRL as there is no communication with the fuze via the aircraft or use the override. As depicted in the game you can change the HOB via HT. This should match what is set on the weapon at loading.

 

This is just something they added to make weapon utilization or dispersion rates selectable via pilot or just a DCS function for playability or fun factor. (Lack of ground crew options)

 

Of course through-out the community you have purist and you have people that just want to blow stuff up. Either case is fine, but personally I would prefer accurate depictions (visual and functions). At the same time with some of the newer weapons, accurate depictions are not possible do to subject matter and 99.9999% percent of the community would not know the differences anyway.

[Northstar98]

Personally I prefer realism, I consider it to be the point of DCS. Of course there are plenty of things that aren't realistic but I'll settle for the mean time.