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mfuze/efuze: what/when/why?


Asset

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I all,

 

 

I am confused about the fuze settings in free fall bombs. The manual does not say a lot about the meaning of the settings and it certainly does not say when to use what.

 

 

Mfuze:

 

You have a choice of nose, tail, and nose+tail. What does that mean? The fuze is basically what causes the explosives within te bomb to explode, right? So I assume there are two fuzes inside a bomb, nose and tail, but which option to use? Do all bombs have two fuzes? A nose fuze makes perfect sense to me, 'cause that's what the bomb will touch the ground with. What is a tail fuze good for? And why not simply always go with nose+tail, just to make double sure the bomb explodes? Unless it is not "nose OR tail" but "nose AND tail"...

 

 

Efuze:

Do all bombs have an efuze? I saw several people dropping bombs without setting the efuze. Will it still explode? If it does, why is there an INST setting? I thought INST means it will explode as soon as it hits the target (in contrast to DLY1/2). I guess DLY means it will not explode right away but a little later. But what do I need that for? Also, what does VT do?

 

 

Thanx, Asset

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i believe mfuz = mechanical fuze and efuz=electrical fuze

 

this is from a pdf i found on the topic...

 

Mechanical Fuzes

All mechanical bomb fuzes are activated by means of an arming wire or lanyard. Pulling the arming wire or lanyard at weapon release frees a vane. Rotation of the vane in the air stream provides mechanical energy to an internal mechanism to arm the fuze or unlock a powered mechanism so that arming can occur. When a fuze is armed, the explosive train is aligned so that the mechanism that determines the mode of fuze functioning is free to operate and the main explosive charge in the weapon can be detonated. The arming time of a fuze can be fixed or variable. In the former case, the arming time is determined at fuze manufacture. In the latter case, the arming time is either pre-flight selected during the weapon build-up operation or aircraft loading sequence, or selected during flight via Serial Data Interface (SDI) from the cockpit. The actual arming time is a function of the delivery tactic employed during weapon delivery. For safe, effective operation, any fuze (mechanical or electrical) must have the following design features:

• It must remain safe in stowage, while it is handled in normal movement, and during loading

and downloading evolutions

• It must remain safe while being carried aboard the aircraft

• It must remain safe until the bomb is released and is well clear of the delivery aircraft (arming delay or safe separation period)

1-3

• Depending upon the type of target, the fuze may be required to delay the detonation of the

bomb after impact for a preset time (functioning delay), which may vary from a few milliseconds to many hours

• It should not detonate the bomb if the bomb is accidentally released or if the bomb is jettisoned in a safe condition from the aircraft

To provide these qualities, a number of design features are used. Most features are common to all types of fuzes.

 

Electrical Fuzes

Electrical fuzes have many characteristics of mechanical fuzes. They differ in fuze initiation. Electrical fuzes can be activated either by means of a lanyard, or by means of electrical energy transferred from aircraft carried equipment to the fuze as the weapon is released from the aircraft. If a fuze is activated by means of a lanyard, its arming time and its function time delay are selected before flight (i.e., at weapon buildup or aircraft loading). With electrical activation, the fuze arming time and functioning characteristics can be determined in-flight to match changing conditions at the target area or conditions at alternate target areas.

If a fuze is electrically activated, the electrical signal can both be a source of energy and contain commands. An electrical pulse from the delivery aircraft charges capacitors in the fuze as the bomb is released from the aircraft. Arming and functioning delays are produced by a series of resistor/capacitor networks in the fuze. The functioning delay is electromechanically initiated, with the necessary circuits closed by means of shock-sensitive switches.

The electric fuze remains safe until it is energized by the electrical charging system carried in the aircraft. Because of the safety interlocks provided in the release equipment, electrical charging can occur only after the bomb is released from the rack or shackle and has begun its separation from the aircraft; however, it is still connected electrically to the aircraft's bomb arming unit. At this time, the fuze receives the energizing charge required for selection of the desired arming and impact times.

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much of what i have on this topic references Airborne Bomb and Rocket Fuze Manual, NAVAIR 11-1F-2

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MFuze: On bombs such as general purpose (unguided) or laser guided, you can always set nose/tail and it will work but you only need to pick one if it only has one fuze. Where it becomes more important is if you have the MK-82AIR. If you pick nose only, it will drop the bomb in the low drag option without the chute coming out. If you pick nose/tail then the arming wire for the chute will be pulled so the bomb comes off high drag.

 

Electronic fuzes are generally in JDAMs so your GBU-31, GBU-32, and GBU-38s. It makes the delay cockpit selectable, so good for a dynamic targeting environment or close air support. For hitting vehicles or small buildings, you want instantaneous set. For larger buildings or bunkers, you want something like 5ms set, and add as a rule of thumb add 10ms for every extra floor you want it to go through before exploding. I don't know what the DLY1/2 correspond to in timing, and don't know what VT does, but I don't think any of this is modeled yet.

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thats awesome info RS... thanks for that.

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MFuze: On bombs such as general purpose (unguided) or laser guided, you can always set nose/tail and it will work but you only need to pick one if it only has one fuze. Where it becomes more important is if you have the MK-82AIR. If you pick nose only, it will drop the bomb in the low drag option without the chute coming out. If you pick nose/tail then the arming wire for the chute will be pulled so the bomb comes off high drag.

 

Electronic fuzes are generally in JDAMs so your GBU-31, GBU-32, and GBU-38s. It makes the delay cockpit selectable, so good for a dynamic targeting environment or close air support. For hitting vehicles or small buildings, you want instantaneous set. For larger buildings or bunkers, you want something like 5ms set, and add as a rule of thumb add 10ms for every extra floor you want it to go through before exploding. I don't know what the DLY1/2 correspond to in timing, and don't know what VT does, but I don't think any of this is modeled yet.

 

VT is modeled for Cluster munition burst height.

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Also with EFUZE you can set a burst height on GP bombs such as the MK-82, allowing for an airburst.

 

 

The GP proximaty fuzes on slicks still have lanyards and are mechanically armed. They don’t require an electrical connection

 

You EFUZEs are going to be for the bombs that can “talk” to the jet and have an electrical connection with pilot selectable options as mentioned above already.


Edited by Rainmaker
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So, MFUZE for dumb bombs, EFUZE for JDAMs?

 

Essentially that is correct. I can't say how well it is modeled in DCS yet though. MK-82, MK-84, GBU-10, GBU-12, GBU-16 are going to all be using FMU-139s for the most part and you should set nose/tail unless using AR variants as mentioned before. GBU-31, GBU-32, and GBU-38s are generally using the FMU-152 electronic fuzes.

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Essentially that is correct. I can't say how well it is modeled in DCS yet though. MK-82, MK-84, GBU-10, GBU-12, GBU-16 are going to all be using FMU-139s for the most part and you should set nose/tail unless using AR variants as mentioned before. GBU-31, GBU-32, and GBU-38s are generally using the FMU-152 electronic fuzes.

 

An EFUZE can and is (or maybe more appropriately was) used with MK series, JDAM or not. The JDAM kit is for guidance, not fusing. A mk-82/3 can be airburst regardless of the guidance or lack thereof. All that matters is the type of fuse when the bomb is selected, and on more advanced fuses what is selected by the pilot. From the AO TRAMAN:

 

The Mk 43 Mod 0 target-detecting device (fig.

1-11) is a proximity nose element that gives airburst

capability for electric-fuzed Mk 80 (series) bombs.

The Mk 43 Mod 0 element is compatible with all

electric tail fuzes and is identified by the dark green

color of the nose cone. A thermal battery powers its

internal circuitry. The thermal battery is initiated by

+300 volts dc or by the striker rod.

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An EFUZE can and is (or maybe more appropriately was) used with MK series, JDAM or not. The JDAM kit is for guidance, not fusing. A mk-82/3 can be airburst regardless of the guidance or lack thereof. All that matters is the type of fuse when the bomb is selected, and on more advanced fuses what is selected by the pilot. From the AO TRAMAN:

 

The Mk 43 Mod 0 target-detecting device (fig.

1-11) is a proximity nose element that gives airburst

capability for electric-fuzed Mk 80 (series) bombs.

The Mk 43 Mod 0 element is compatible with all

electric tail fuzes and is identified by the dark green

color of the nose cone. A thermal battery powers its

internal circuitry. The thermal battery is initiated by

+300 volts dc or by the striker rod.

 

 

You’re confusing electrically armed on release through electrical impulse vs mechanically armed through a lanyard. They are two seperate things. GP purpose bombs are not electrically tied to the aircraft through an umbillical and are armed by pulling lanyards on release. Newer smart weapons kits are tied electrically to the jet. There’s more to it than what you are reading and misunderstanding.

 

Mechanical fuses are armer by pulling a lanyard durig release

Electrical fusing is referring to arming through an electrical connection to the bomb itself

 

He’s not wrong and is correct in what he posted.


Edited by Rainmaker
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An EFUZE can and is (or maybe more appropriately was) used with MK series, JDAM or not. The JDAM kit is for guidance, not fusing. A mk-82/3 can be airburst regardless of the guidance or lack thereof. All that matters is the type of fuse when the bomb is selected, and on more advanced fuses what is selected by the pilot. From the AO TRAMAN:

 

The Mk 43 Mod 0 target-detecting device (fig.

1-11) is a proximity nose element that gives airburst

capability for electric-fuzed Mk 80 (series) bombs.

The Mk 43 Mod 0 element is compatible with all

electric tail fuzes and is identified by the dark green

color of the nose cone. A thermal battery powers its

internal circuitry. The thermal battery is initiated by

+300 volts dc or by the striker rod.

 

I'm talking all from experience with F-15E, not F-18. From F-15E side, even if you put a FMU-152 electronic fuze into a mk82, you still can't change anything from the cockpit. Everything is set on the ground and all you can change in the jet is which arming wires are pulled when released. JDAMs are different because it communicates to the jet via the mil-std-1760 bus so you can change the settings in FMU-152 fuzed bombs. Any other bomb you have to tell the PACs what bomb is on the station, with JDAMS they self-identify in the PACs because it's communicating to the jet. Can F-18s connect to electronic fuzes other than JDAMs?

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Also with EFUZE you can set a burst height on GP bombs such as the MK-82, allowing for an airburst.

DSU-33 at best can be enabled/disabled providing yes-no selection of proximity initiation. The range of proximity triggering is integral to the design and not adjustable. Voltage applied to DSU and fuze are equal. DSU operation is selected by +-195V (cockpit selection of a EFUZ mode other than instantaneous).

 

FMU-139 and -152 can be electrically controlled in GP or JDAM but options are limited. It is possible to employ these fuzes without lanyards.

 

JDAM configurations

[TABLE]Nose|Tail|Arming|MFUZ|EFUZ|AD

-|FMU-139|MK-122||OFF INST DLY1|5.5 10

DSU-33|FMU-139|MK-122||OFF INST VT1|5.5 10

DSU-33 or -|FMU-139|FZU-48|none tail*||6 7 10 14 20**

-|FMU-143|FZU-32|none tail||5.5 12

DSU-33*** or -|FMU-152|MK-122|||Off On|set through JPF page

[/TABLE]*DSU always operates with fuze

**times are informative only, matching face plate configuration, 10s minimum authorized

***DSU always initiates the FMU-152 action since EFUZ ON for JPF applies +-195V

 

JPF on GP bombs is not serial programmable because it is not connected through 1760 interface. In such case functions similar to FMU-139. Options are 5.5 and 10 as per FMU-139 but "10" results in time as set on face plate.

 

FMU-139, FFCS (EFUZ) control. FFCS only applies 0, +300, -300, +195, or -195 volts by cockpit selection. Low drag selection dial should be X. Zero volts is off safe. Positive/negative polarity commands 10/5.5 second arming decision. Voltage magnitude 195/300 commands delay/instantaneous action. If delay action is selected, action time is as set on the fuze face plate. In case of high drag deceleration sensing the arming time is 2.6s and action time is the same as low drag.

 

FMU-139, FZU (MFUZ) control. Mechanical solenoids are selected by the airplane. Arming delay is as set on the face plate 4 6 7 10 14 20s X, X will dud. Action time is as set on the separate high drag portion of the face plate. If high drag deceleration is sensed the arming time is as set on the high drag portion of the face plate (2-5s).

 

The inventory of weapons and their fuzes is set on the weapon insertion panel on the outside of the airplane. Only options which are appropriate for the programmed weapons and fuzes are available in cockpit. For example if you punch in a "0" for the nose fuze on the WIP then it knows there is no nose fuze and will not let you choose any MFUZ or EFUZ option dependent on nose fuze present. If you don't tell it there is a DSU-33 present then it will not allow the "VT" fuze option to be selected.

 

Electronic fuzing will result in appropriate automatic backup mechanical solenoid alteration to match.

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VT is modeled for Cluster munition burst height.

 

VT stands for Variable Time, which is a fancy way to say proximity fused. For most MK80 series this means you would see a plastic dome TDD on the nose with an electronic fuse in the tail. There is a different color TDD for the MK82, 83, and mk84. Theyu look like colored gumdrops stuck on the nose of the bomb. The options were green white and red, but for the life of me i cant remember which went with which. Pain in the ass to walk up on for defusal when they dont go off.

 

You would generally only see VT fuses used for the mk80 series or for almost any dispenser, as most of the precision guided munitions have electronic fuses in the tail that sense impact or negative-space after impact.

 

***addendum***

I almost forgot about the DSU-33 which was a joint Airforce/Navy venture to replace the TDD's, which were Navy exclusive. They perform identical functions for the MK80 series


Edited by 75th ORD EOD Cheesecake
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Time served in Royal Air Force, aircraft weapons (armourer) in our 'mob' nose fusing was only used for air burst, tail fusing for everything else as post impact detonation requires the fuse to be in one piece!. Both nose and tail fuses were mechanical, the tail fuse being armed by rotation of the arming vein in the tail unit, and the nose fuse having it's own rotating mechanism.

 

Post cold war the RAF introduced the Multi Function Bomb Fuse (MFBF) which was electronically programmed either by armourers on the ground or aircrew in mission, and is/was always fitted to the tail fuse pocket.


Edited by crowebar

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Sorry to interrupt the high level discussion with a probably simple question. Why is it when I have Mk82s loaded (the basic gp ones, no retarding), when I select Nose/Tail I get an X through the weapon on my STRS Page. Just selecting Nose doesn’t give me that.

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Sorry to interrupt the high level discussion with a probably simple question. Why is it when I have Mk82s loaded (the basic gp ones, no retarding), when I select Nose/Tail I get an X through the weapon on my STRS Page. Just selecting Nose doesn’t give me that.

 

 

This is making some assumption, but I'm going to assume that the sim is simulating a MK-82 slick with only a nose arming option. In the real jet, you have to enter in specific codes into the computer so it knows what's on the airplane, that step is skipped for us. There again, that's assuming, the devs have chosen to simulate a certain type of bomb. Will it change down the road as things are developed more? Maybe.

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Influence fuze for unitary bombs and cluster dispenser are different hardware.

 

The FMU-140 fuze for the Rockeye dispenser has two operating modes: normal and option. In normal mode it applies the more restrictive of the time and height dial selections on its face plate (exception height <300'). In option mode the dispenser activates a set time after release.

 

The FMU-140 is triggered by physical arming wires and not voltage applied from the FFCS.

 

MK 43 TDD predates FMU-139 use and functions through the FFCS. I'm sure Hornet can use the MK 43 and has at some point in time.

 

Not sure why you'd have an X reaction to a particular MFUZ setting. The WIP is where you tell the jet what fuzes are present and it shouldn't let you pick fuze options that are invalid. USN is tail fuzes in all of the scenarios I know.

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  • 2 years later...

Apparently ED recommend for the DB 82,83,84 to set just “nose” and efuze  to “instantaneous” for most targets.

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Quote

"The manual does not say a lot about the meaning of the settings and it certainly does not say when to use what."

 

As true today as it was when the OP's very reasonable question was asked nearly three years ago.  The manual needs to be much clearer on this, otherwise you just end up with forum speculation.  That is not meant to be a criticism of the many interesting comments above, but delving into the minutiae of, for instance, model numbers of fuses doesn't really help in DCS; the manual should provide, at the very least, a layman's explanation of each fuse type and a table of what should be selected for each weapon, and for instances where there is more than one choice when to use each.

 

The whole DCS fuse thing still remains a mystery to me.  My best guess is that ED have an idea of what should appear on the MFD pages but much of the background implementation is just not there.  With a few exceptions only one set of options will work for a specific weapon anyway and I just set those because Matt Wagner said so on YouTube, without having a clue as to why.  If different options are available IRL that are set on the ground they are not in DCS (yet?) as they would need to be a mission editor option (similar to what is available for rockets).

 

My request for the next YouTube video?  Wags's Wonderful World of Fuzes.  Pt I. Nose, tail or nose/tail: how, why and when.


Edited by Hippo
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So I got on Google and found this:

 

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwit2oulv6XwAhVVuXEKHQ1gAKAQFjAQegQIFRAD&url=https%3A%2F%2Fwww.globalsecurity.org%2Fmilitary%2Flibrary%2Fpolicy%2Fnavy%2Fnrtc%2F14313_ch1.pdf&usg=AOvVaw1bVnWPEQ806gN8bSQ6abbk

 

And, er, it's complicated - but the document does give a good insight into what's going on.


Edited by Hippo
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