Bomb Fuzes options in the rearming panel

[graveyard4DCS]

Since the bomb fuzes are now available in DCS World, do you think it's necessary to invest time in researching information and creating a guide to their operation and use?

[kotor633]

Well, actually I expect such a documentation from the manufacturer, i.e. ED...

[graveyard4DCS]

I eventually started writing a guide on this topic. You'll find the first part here. All other parts are on my personal page, don't hesitate to check it.

Bombs fuzes - Introduction

In 2024, the release of the fuzes options in the rearming panel in DCS World brought a new level of realism and complexity to this very unique flight simulator. Understanding what’s the role of a fuze, how it works and what the different settings are, is necessary in order to use this feature correctly, i.e. to maximize damages to the target and avoid duds or self-damages.

This article is a short introduction to the essentials terms that have to be known and to what an " aerial bomb" is comprised of.

1.1 - References

• Articles:

  • Understanding the FMU-139 and Its Employment Options;

• Documents:

  • NAVAIR 11-1F-2 - Description and Characteristics - Airborne Bomb and Rocket Fuze Manual;

  • Safe arming times for Mk-81, Mk-82, Mk-83, Mk-84 and M117 Low Drag Bombs;

  • Increasing the Reliability of General Purpose Bomb Fuzing in Precision Strike Warfare;

  • Explosive Weapons Effects by GICHD;

  • USAF JDAM Tactical Manual on Wikileaks;

1.2 - 1.3Definitions

• Fuse: cord or tube for the transmission of flame or explosion usually consisting of cord or rope with gunpowder or high explosive spun into it.

• Fuze: a physical system designed to respond to one or more prescribed conditions, such as elapsed time, pressure, or command, and initiate a train of fire or detonation in a munition. Safety and arming are primary roles performed by a fuze to preclude ignition of the munition before the desired position or time. The spelling FUZE is used to denote a sophisticated ignition device incorporating mechanical and/or electronic components for example a proximity fuze for an artillery shell, magnetic/acoustic fuze on a sea mine, spring-loaded grenade fuze, pencil detonator or anti-handling device as opposed to a simple “burning fuse”.

• Main charge: the explosive charge which is provided to accomplish the end result in the munition; e.g., bursting a casing to produce blast and fragmentation. These explosives, because of their relative insensitivity, ordinarily require initiation by a booster explosive.

• Armed: a fuze is considered armed when any firing stimulus can produce fuze function.

• Function: a fuze “functions” when it produces an output capable of initiating a train of fire or detonation in an associated munition.

• Arming delay or arm time: the time elapsed from launch to arming.

• Dud: a munition which has failed to function, although functioning was intended.

• Early burst: a weapon detonating after completion of the arming delay but before hitting the intended target.

• Premature function: a fuze function before completion of the arming delay.

• Safe separation distance: the minimum distance between the delivery system (or launcher) and the launched munition beyond which the hazards to the delivery system and its personnel resulting from the functioning of the munition are acceptable.

• Safety and arming device: a device that prevents fuze arming until an acceptable set of conditions has been achieved and subsequently effects arming and allows functioning.

• Explosive train: the detonation or deflagration train (i.e., transfer mechanism), beginning with the first explosive element (e.g., primer, detonator) and terminating in the main charge (e.g., munition functional mechanism, high explosive, pyrotechnic compound).

1.3 - Bomb description

Bomb bodies are made up of multiple parts.

We can distinguish in particular:

• the nose plug (1): it has a role in terms of mid-course ballistics and target penetration. In particular, the MXU-735 is a round shaped solid nose plug that is designed to provide better penetration of hard targets, without the likelihood of nose plug shearing during oblique impact.

• the arming wire(s) (13): they are a physical link between the aircraft’s pylon and the bomb. When the bomb falls away from the aircraft, the wires that have been selected in the cockpit (nose, tail or both) are pulled away from the parts to which they have been linked to on the bomb (e.g. the nose fuze, or the battery for a PWY-II), thus authorizing the functioning of the mechanism. If the arming wire has not been selected, the bomb is dropped with its wire still attached and the associated mechanism won’t function. For example, during a jettison, the bombs are dropped with their wire and are therefore inert. Physically speaking, the wires can in some cases be “crossed” on the bomb’s body, meaning that selecting the “nose” option in the cockpit will actually enable the “tail” fuze on the bomb. In any case, the crew has to know the effects of the cockpit settings, rather than the actual wiring diagrams on the bombs.

• the inner tubes (23): they are used to link the fuzes with the aircraft in FFCS (or “Navy”) mode (detailed later).

• the coating: navy bombs have a gray thermal protective coating that makes them IM or “Insensitive Munitions”, for safety on board of ships (in case of fire for example). Training munitions are painted blue. Munitions containing live explosive have a yellow stripe.

• fuzes (11 + 26): they will be detailed below.

As you can already see, the fuzes are just a one element among many others of an aerial bomb. They will be detailed in the following articles.

Edited November 10, 2024 by graveyard4DCS

[graveyard4DCS]

Application to the Case of the F/A-18C in DCS World

5.1 - FMU-139:

• Description

The FMU-139 (series) electronic bomb fuze is an electronic impact or impact-delay fuze. It is used in Mk 80 series general-purpose bombs, including laser-guided bombs. The arming times can be in-flight selectable, and the functioning delay must be set during weapon assembly.

• Theoretical use

The U.S. Navy’s F/A-18 fuzing system can be divided into two major subsystems, which are the aircraft and the weapon. The FA-18 aircraft subsystems that affect weapon release and reliability include: aircraft software, AWW-4 Fuze Function Control Set (FFCS), aircraft wiring, connections, decoders, and bomb racks. The weapon subsystems include: a MK-122 safety arming switch with M70 bomb cable assembly or a FZU-48 bomb fuze initiator with a coil power cable, a FMU-139 electro-mechanical fuze, a bomb tail section, and MK-3 arming wire. The fuzing system is identical when used in “dumb” free-fall bombs and “smart” LGBs or JDAMs because they are all based on legacy MK-80 series bomb bodies.

The FMU-139 does not contain its own internal source of electrical power but relies on an externally produced supply of direct current (DC) provided by either the aircraft at release or a ram-air turbine generator mounted in the warhead’s charging well. The fuze will function differently depending on the electrical power provided.

The current U.S. Navy FMU-139 electro-mechanical bomb fuze within the bomb fuzing system receives power from either the aircraft Fuze Function and Control Set (FFCS) by a pulse through the MK-122 arming switch and M70 cable assembly or continuously from a FZU-48 air turbine. The fuze does not receive power until the bomb is separated from the aircraft for both bomb fuzing configurations. Only Navy aircraft have an FFCS and so this mode is sometimes referred to as “Navy mode.” The Air Force were first to utilize the air turbine to power their fuzes and not until 2001 have Navy aircraft used the air turbine mode so this mode is sometimes referred to as “Air Force mode.”

When looking more closely at the FMU-139’s faceplate, we can notice on the upper part the “LOW DRAG ARM TIME” settings. In order to use the “Navy mod”, the screw has to be placed on the X setting. When using the “Air Force mode”, the low drag arming delay has to be set to the desired value. In this configuration, the setup is selected on the ground, and cannot be modified in flight. The “Navy mode” brings an extra flexibility, because the arming delay can be selected in-flight, while it’s locked on a single value in “Air Force mode”.

In “Navy mode”, the crew must select two different settings: the arming time (ARM: either 5.5S or 10S) and the explosion delay (EFUZ: OFF, INST or DLY1). Once this is done, the plane’s FFCS will send a specific electrical current to the bomb that will understand the required configuration.

In “Air Force mode”, the EFUZ setting is replaced by an MFUZ setting, that will only let the pilot decide whether the bomb will be armed (TAIL) or not (OFF). Selecting the ARM setting to either 6”, 7”, 10”, 14” or 20” has no effect on the actual arming delay, since it has been set up on the ground, but it will enable correct DUD cues on the HUD (when trying to drop the bombs too low for example).

Regarding the explosion delay, it is set up on the ground by the screw on the lower part of the faceplate. Four values are selectable: INST, 10 ms, 25 ms or 60 ms. As described above, these settings cannot be modified anymore in flight, unless in “Navy mode” where it’s possible to force an INST setting even if a longer delay has been selected on the faceplate.

As indicated on the FMU-139’s faceplate, the same fuze can be used for high drag bombs. The fuze has a built-in accelerometer, and if after bomb release a strong deceleration is sensed, the HIGH DRAG settings will be automatically applied. If this event is not detected, the LOW DRAG settings apply. We can notice that in HIGH DRAG configuration, four arming delays are selectable: 2.0”, 2.6”, 4” and 5”. The 2.0” option is marked in red and requires a manual push on the “interlock” button to confirm that the selection is intentional. But it has to be understood that this delay is very short and poses great risks for the shooter, and its use is actually forbidden.

You’ll find below a flow chart summarizing all the possible configurations for the FMU-139.

• Current situation in DCS World:

Current DCS fuzing options do not offer the possibility to use the X setting on the FMU-139. It means that the FMU-139 is always used in “Air Force mode”, and that only the MFUZ option should appear in the STORE pages, both with dumb bombs, LGBs and JDAMs.

In reality, the current model does is not following this logic, and the options on the STORE page are always the same, whatever the actual fuze choice:

• Mk-8X - Low Drag & High Drag

  • MFUZ/OFF-NOSE-TAIL-N/T

  • or MFUZ/OFF-NOSE

  • or MFUZ/OFF-TAIL

  • or EFUZ / OFF-INST-DLY1-DLY2

  • or a combination of both EFUZ and MFUZ when selecting a mechanical fuze and an electronic fuze on the same body (a situation that never happens).

• GBU-1x / 2x - General purpose: EFUZ / OFF-INST-DLY1-DLY2

• JDAM - General purpose: EFUZ / OFF-(VT1)-INST

Note: for cluster bombs, the settings are: MFUZ/OFF-PRI-OPT (Mk 339 - PRI = PRIMARY = first time setting, OPT = OPTION = second time setting.) or MFUZ/OFF-VT1-VT2 (FMU-140).

Therefore, as of 2024, it is clear that the parameters in the STORE pages in DCS World are not correct. They tend to mix several concepts, and do not take into account the programmable side of some fuzes.

For example, the correct stores format options for JDAM are described in the table below. This is what the developers should try to reproduce to go to the end of their development process.

Read the original article for more details about FMU-143, FMU-152, DSU-33, M904, M905, Mk 339 Mod 1 and FMU-140.

A kneeboard page summarizing recommended fuze settings for the F/A-18C in DCS World is also available.

Edited November 10, 2024 by graveyard4DCS

[Nealius]

On 9/17/2024 at 10:14 PM, graveyard4DCS said:

the coating: navy bombs have a gray thermal protective coating that makes them IM or “Insensitive Munitions”, for safety on board of ships (in case of fire for example). Training munitions are painted blue. Munitions containing live explosive have a yellow stripe.

Very pedantic correction, but the thermal coating isn't exclusively gray. Before the "gray era," that started some time around OIF/OEF, the bombs were still painted green, but had the same thermal coating. The primary indicator of thermal coating is double or triple yellow stripes (IIRC three stripes is a specific explosive filler?) vs. single yellow stripe for bombs without thermal protection. I had a long writeup about this with a lot of research put into it, but ED in all its genius moved it away from the sim research section to the wishlist dungeon where no one can find it.

Edited November 1, 2024 by Nealius

[graveyard4DCS]

For those interested, I published additional data regarding FZU-39 used in BLU-87/103 and BLU-97/105.

I also created a kneeboard page with all recommended settings for the F-16C in DCS world, on the same model as the one I made for the F/A-18C (see my previous posts) . 

 

Edited November 8, 2024 by graveyard4DCS

[graveyard4DCS]

I eventually took the time to regroup all the various articles already published on my personal page and publish them as a single pdf file.
I also createded kneeboards that summarize recommended operational settings for the F/A-18C and the F-16C in DCS World. The kneeboards are better understood after reading the more comprehensive guide obviously, that's why the full guide is included with the kneeboards.
Enjoy your reading!

[Thallios]

Can you elaborate additionally on the laser codes. Do I understand it correctly that the laser codes can now only be set on the ground and not in the cockpit of the F-18 anymore?

[graveyard4DCS]

Yes, you have understood correctly.

It is similar to what's done for real. Laser code on the Paveway family bombs are set manually by turning screws on the bomb's head kit.

In the cockpit, you still have to select the laser codes that you are using for lasing and LST.