GBU-12D/B Paveway 2 and other derivates of the Mk-82 500Lb bomb, USA

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As this posting contains a lot of pictures accompanying the text, pictures and partnumbers are described in the following way:
(P01-2 ) = (Picture 01-partnumber 2 ).
(P01, P04-2 ) = (Picture 01, Picture 04 -partnumber 2 ).

Aircraft bombs are meant to reduce or destroy the enemy’s war potential. Aircraft bombs do this by causing a shock wave, overpressure fragmentation and fire.

After World war 2 it became clear that the aircraft bombs in use were not suitable for the faster jet planes that were developed in the USA. This resulted in the development of the Mk-80 LDGP (Low Drag General Purpose)series aircraft bombs in the 1950s, producing less aerodynamic drag than the round nosed WW2 bombs.
The bomb shape was designed by Ed Heineman of the Douglas aircraft company and is known as the Aero 1A design. The length-diameter ratio is approximately 8:1.
Four bombs were developed in this range, -similar in shape and construction- ; the 250 pound Mk81, the 500 pound Mk-82, the 1000 pound Mk-83 and the 2000 pound Mk-84.
The bomb bodies are made of drawn an forged steel, with a threaded hole in the nose to receive the nose fuze well, which receives the nose fuze or the fuze extender, and a large hole in the base to receive the threaded base flange. The base fuze well is screwed into the base flange.
A ring with a machined V-groove is welded to the aft end of the bomb body to receive the mounting bolts for different types of bomb tails.
In top of the bomb body two thick plates are welded into two cut out holes. In these two plates three threaded holes are placed. The forward and afterward hole are blind threaded holes for the suspension lugs of the bomb.
The middle threaded hole has two holes in the bottom that connect to two question mark shaped thin walled steel pipes, one running from the middle hole of the bomb to the nose fuze well, one running from the middle hole to the tail fuze well. These pipes are meant to connect the forward and/or afterward electric fuzes to the FZU-48/B bomb fuze initiator (air flow generator) or the Mk-122 safety and arming switch by means of an electric cable, a steel pull wire to activate the firing pin activated battery of the FMU-81 /B nose or tail fuze, or an elastic cord to activate the FMU-54/B fuze.

P01:
The bomb described in this posting is the 500 Lb Mk-82 in different versions.
The bomb body has a number of different fillings, with corresponding different type designations;

- The Mk-82 which is normally filled with 89 kgTritonal (80% TNT, 20% powdered aluminium), Minol (appr 40/45% TNT, 40/45% Ammonium nitrate and 10/20% aluminium powder) or Composition H6 (44% RDX, 29,5% TNT, 21% powdered aluminium, 5% parrafin wax and 0,5% Calcium Cloride).

-The BLU-111/B, which is filled with PBXN-109, a plastic bonded less sensitive explosive.

-The BLU-111A/B, which is filled with PBXN-109. The bomb has a thermal protective added coating to prevent it exploding within a certain time frame when in a fuel fire. It is meant for use on aircraft carriers by the navy only.

-The BLU-126/B, a BLU-111 with a smaller charge to prevent collateral damage. The rest of the bomb is filled with an inert filler to obtain the same drop trajectory.

-The BLU-129/B which has a tungsten laden carbon composite bomb body to reduce collateral damage due to blast and fragmentation radius.

-The Mark 62 Quickstrike mine. A naval mine derived from a Mk-82 bomb body.

-The Mk-82 mod.7 is a Mk-82 bomb body made from ductile cast iron that has a high fragmentation and uses a fuze that explodes the bomb at a certain height above the ground. This bomb is to replace clusterbombs in the future.

Mk-82 bomb body data:
Weight : 500 Lbs (241 kg). Thermal coating adds 14 kg (30 Lb) to the bomb body weight.
Explosives weight : 89 kg (192 Lbs) Trinotal , Minol II or H-6.
Diameter : 273mm.
Length : 1535mm.

P02/P03/P04:
In picture 02 the normal Mk-82 LD (Low Drag) bomb is depicted, using a M904E2 nose fuze and/or a M095 tail fuze. It uses the MAU-93B fin set, which has an ATU-35 drive placed in the side of the cone of the tail when the M905 tail fuze is used. A hatch in the side of the tail is used to inspect the fuze and ATU drive flexible cable, either the arming wire of other suitable bomb fuze types running down from the hole in the top of the cone to the fuze.
This configuration of the Mk-82 is the most widely type used.
The nose fuze M094E2 is described in picture 26 & 27, the M905 tail fuze is described in picture 28 & 29.

P05
Depicts the Mk-82 with the BSU-49 retarding tail. The BSU-49 is used mainly by the US air force for low level bombing. With low level bombing the risc of an airplane being hit –and downed- by it’s own bombs fragments is present. To avoid this, the bomb has a retarding ballute (the cross between a balloon and a parachute) which enables the airplane to escape it’s own fragmentation. The forward end of the tail has a steel ring with 8 radial placed hexagon socket set screws to connect the tail to the V-groove at the base of the bomb body.
The tail can also be used as a ‘normal’ bomb tail by not opening the ballute tail upon release, i twill than follow the trajectory of a ‘normal’ mk-82.
In this case, the bomb is fuzed with a M905 base fuze in combination with a ATU-35 drive assembly. A hatch in the side of the tail is used to inspect the fuze and ATU drive flexible cable, either the arming wire of other bomb fuze types running down from the hole in the top of the tail housing to the fuze.

P06
The Mk-82 equiped with a Mk-15 Snakeye tail, called Mk-82 Snakeye. This tail is used mainly by the US navy and Marines for low level bombing. With low level bombing the risc of a plane being hit –and downed- by it’s own bombs fragments is present. To avoid this, the bomb uses four flip out brake petals to reduce the speed of the bomb, enabeling the plane to escape it’s own fragmentation.
The tail consists of a one piece cast and machined aluminium cover with a pipe that fits over the base of the bomb and uses eight Hexagon socket set screw to fixate this cover to the V-groove of the bomb body. the hinges of the petals is are placed in an aluminium profile that is screwd over the far end of the pipe. The four petals are connected by means of a sliding block that enshures all four petals move outward with the same speed, and also act as one side of the shock absorber, which prevents the tail of being ripped apart upon high speed release opening. This shock absorber is a corrugated aluminium pipe which is pushed inward 190 mm with 5 tons of force to absorb the shock.
In closed position the fins are kept inward by a spring loaded release band. The springs opening the tail petals are four leaf springs (one on the inside of each petal) that opens the fins just about 5 cm, enough to catch the airstream for further opening. The band is held in position by a lever, which is held in position by a coter pin. When withdrawn, the fins open and catch the airstream.
The fuze used is the M904E1 nose fuze. No fuze is placed in the base.
In picture 12 a Cosiar A7 can be seen, dropping Mk-82 Snakeye bombs.

P07:
The Fuze FMU-81 /B can also be used in this configuration , but as a nose fuze only. A descripion of this fuze can be found at pictures 37 & 38.

 

[pzgr40]

In P08/P09/P10/P11
A special configuration of the Mk-82 Snakeye is the version with the M346 mod.0 time fuze. This fuze can be set from 1/2 hour to to 33 hours delay with 15 minutes intervals, and uses the “arming assembly bomb fuze Mk5 Mod2” propeller placed in the back of the Mk-15 snakeye tail to arm the fuze. An aluminium pipe with an adapter on both sides is used as a drive shaft between the M346 Mod.0 fuze and the Mk5 Mod.2 arming assembly.
A steel nosepiece is screwed to the nose of the bomb to allow the bomb to dig itself in.
A despription of the Mk346 Mod.0 fuze can be found with Pictures 32,33 & 34.

P13/P14
Here the Mk82 is shown with a Mk-15 Snakeye tail and the 36 inch fuze extender, also called a “Daisy cutter”. This fuze extender enshures the bomb explodes approximately 1 meter above the ground for improved blast and fragmentation. The fuze normally used in the 36 Inch fuze extender is the nose fuze M904 E2. In a discussion on the BOCN It was stated that this combination was most probably not used, but I found a you tube movie of an aircraft carrier based Douglas Skyraider using a Mk-15 snakeye tail and the 36 inch fuze extender.

 

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Introduction GBU-12 D/B (picture 15/16):

Prior to WW2 bombing was done by plotting a course to the target and dive bomb, either bomb from low height for precise bombing. However, due to the increasing effectiveness of anti aircaft guns, this became increasingly dangerous, and if a target is interesting enough to be bombed, it is also interesting enough to be -heavily- defended.
Before WW2 bomb sights were quite rudimantary until the U.S. Nordon bomb sight appeared.
Due to the high losses caused by daylight bombing, the British descided late 1939 to change to night bombing to evade flak and fighters. Bombing was done by plotting a dead reckoning course to the target and/or use landmarks visable at night like rivers and coast lines. This led to very poor bombing accuracy; it was even quite common to have to bomb a specific city, and completely miss it, or bomb another city.
A survey of bombing photographs in August 1941 indicated that fewer than one bomb in ten fell within an eight kilometer radius of the intended target.
The Germans on the other hand were having the same problems; a He111 send out to bomb the London dockyards at night accidentally bombed a residential area. Churchill send bombers to Berlin in revenge. With succes, as Berlin did not yet blackout, and was big enough to score hits, even when missing the town’s centre with eight kilometers.

On the other hand, bombing did not have to be quite precise; as bombing was a new weapon at the start of WW2, it caused great terror on the civillian population, although the British became used to it quite soon and “life went on”.
the British made a study about the effects of German bombing on their city’s like London, Belfast and Coventry. The British professor Lindeman wrote the “de-housing” paper, a study on the expected effectiveness on the bombing of industrial and residential areas.
This resulted in the “thousend bomber attacks” on city’s like Colone, and the firestorm raids on Hamburg and later Dresden. As it was “total war”, no questions were asked if it was politically correct to bomb residential area’s.
The Americans entered the war in a later stadium, preferably bombing industrial targets at daylight to archieve more precission. Still, precission didn’t get much further than “bombs per acre”, especially when bombing from a high altitude.

Late in WW2 bombing precission improved, as tactics and technical means improved. Tactics like the Pathfinder force, where the best -hand picked- bomber crews were send in advance of the bomber force to mark the target, and technical means like Oebo and Gee (crossing radiobeams above the target) and H2S (ground scanning radar).
Technical improvements were also made on bombs themselves, like the American Azon and Razon bombs, steerable bombs with a flare in the tail, that were steered to the target by means of a joystick by the bombadier. The Azon (Azumuth only) had yaw steering only, The Razon (Range and Azimuth only) had Yaw and pitch steering.
The Germans were the first to use television Guidance with the HS-293D glide bomb. The main disadvantage of these bombs was that the launching plane had to maintain a straight and level course during the steering of the bomb to the target, making the plane quite vurnerable to Flak or enemy fighters. Therefore, these steerable bombs were not liked by the bomber crews.

After WW2 studies were made about the tactics and results of bombing and it was descided that indiscriminate bombing of residential areas was quite ineffective and not politically oppertune any more.
During the Vietnam war pilots bombing North Vietnam were subject to severe restrictions as to avoid bombs falling into residential area’s as this was easily exploited in anti US propaganda by the North Vietnamese. Therefore, targets near -for instance- Hanoi and harbours where Russian freighters were moored were off limits.
Still, relatively small and heavily defended targets like bridges were hard to destroy targets. An example of this is the Thanh Hoa Bridge -nicknamed the dragon’s yaw by the North Vietnamese-, an important Nort South supply connection over the Song Ma river. It had been attacked hundereds of times by the USAF with ‘dumb’ bombs -changing the landscape around the bridge into a crater landscape- , without destroying the bridge or even damaging it to an extent that it was out of order for an extended time. It did however cost 11 US airplanes that were lost during these futile attacks, starting in 1965.
It was not until 1972 when F-4 Phantoms, armed with the newest gadget, the laser guided bomb, destroyed the bridge with 2000Lb Mk84 Laser guided Bombs.
Before the Vietnam war, the USAF was not interested in precission guided bombs, as it was thought that the next conflict was going to be nuclear, so the full focus was on the Strategic air command.
In 1964, at the beginning of the Vietnam war one realized that precission weapons for smaller scale conflicts were needed, and the development of the laser guided bomb started when Texas instruments -then a small and unknown company- changed the design for a radar guided bomb into a laser guided bomb within a weekend. It did however take years and a lot of bureacracy from design until service.
After the Vietnam war debacle the US avoided getting into new conflicts, until forced into the first gulf war in 1991, when laser guided bombs and surgical strikes with F-117’s in the heart of Baghdad suddenly were hot TV items. In the weeks following the public was shown an abundance of clips showing the destruction of Iraqui haedquarters, bridges, aircraft shelters and communication centers, showing as well that collatteral damage to civillians was reduced to a minimum.
One should however take into concideration that appr 80% of the bombs used were dumb bombs , used on troop concentrations, tanks and artillery positions in the open desert where the risk of collateral damage was about zero.
Today most bombs used are laser-, either GPS guided, either both. This to make shure the target is hit and destroyed the first time, and one does not have to take the risc of attacking the same target twice with the risc of getting shot out of the sky with the second attempt. Most countries with a weapon industry have their own development on guided bombs in many different shapes and sizes.
According to the US Raytheyon company factsheet, the circular error probable (C.E.P) for 99 dropped Paveway II bombs is 1,1 mtrs (3,6 feet) against 94,5 mtrs. (310 feet) for unguided bombs, dropped under similar conditions. Looking back at the start of this chapter, one will understand the amazing improvement.
In some cases where a single house in a city, or even a single room in a house has to be hit and collateral damage is off limit, the Mk82 bomb body is replaced with a BDU/45 concrete filled 500 Lb practice bomb, which is exactly the same in dimensions and weight as the Mk-82 bomb body. This combination is designated GBU-45 and acts as an air launched wrecking ball, destroying only the part of the building that is hit.

Description of the GBU-12 D/B (P15/P16/P17/P18/P19/P20/P21/P22/P23/P24/P25):
The GBU-12 D/B consists of a Mk-82 Bomb body, a MAU-169 CCG -Computer Control Group- (Picture 19) screwed to the nose , and a MXU-650 tail section (picture 24)mounted to the V-groove at the back of the bomb body.
The GBU-12 D/B can be fuzed with the FMU-139 as a nose or tail fuze -either a FMU-139 in both-, a M905 tail fuze, the FMU-81 in the tail, or the FMU-152 tail fuze.

Steering the bomb to the target is done by illuminating the target with a laser beam (picture 25). The bomb will aim for the end of the beam where the light is relected off the target into the laser seeker at the nose of the bomb. This is called “painting” the target. There are a number of possiele laser sources :
-A footsoldier with a -handheld- laser designator marking the target, mostly a terminal air controller, either a special forces soldier.
-A vehicle mounted laser designator
-A helikopter with a laser designator
-A drone with a laser designator
-Another airplane with an airborne laser designator, aiming only. (Pave knife, Pave spike, LANTIRN)
-An airplane with an airborne laser designator, aiming it’s own bombs.

Early lasers used a single beam to which the bomb aimed itself, but when the quantity of bombs on attacks increased the risc of all dropped bombs aiming at the same laser beam, either going astray as multiple laser beams were available became obvious. Therefore , the paveway II series has a coded laser that has to be set before take off by dialing a number on three selector switches in the side of the CCG body (picture 18). This code is passed to the person serving the laser designator, which uses the same code as the bomb. This enhures only one bomb reacts to the coded laserbeam. It also prevents the laserbeam from being jammed by the enemy.
The bomb is steered to the target by two sets of steering fins. These fins are connected to two crossing yokes , a set of fins per yoke. Each yoke is also connected to two pistons –one on each side of the yoke- which can rotate the the yoke(s) clockwise either counterclockwise, thus rotating a fin set.
The four pistons are placed in cilinders in a machined aluminium cilinder and valve block (picture 19). In the base of this block a 505 Bar air bottle is screwed, serving the steering block with the air to steer the fin sets. Four magnetic served valves are screwed into the side of the cilinder and valve block. By electrically serving these valves, air is allowed to escape, thus letting the pressure drop, allowing the yoke with fins to rotate to the side where the pressure is lower. Electricity is generated by a firing pin ignited battery, initiated by a pull wire upon release of the bomb.
On the nose of the bomb the laser seeker is placed (Picture 20). This consists of a lens which receives the reflection of the laser beam and projects this dot on a disc of photoconductive material, divided in four quadrants (picture 21). The laser light is of a frequency that is not normally found in nature, and the lens filters out any other light as to have as little clutter as possible.
In the drawing (picture 21)the black dot is the centre of the laser beam, the hatched circle is the dispersion of the reflected light. If the reflection of the hatched circle falls in the centre of the disc , the conductivity in all four quadrants is the same, and no steering signal is passed (situation 1). A deviation where the bomb drifts off to the left and slightly undershoots the target (situation 2) will be translated into a combined electronic signal over four quadrants where the conductivity decreases and increases proportional to the deviation, resulting in a combined steering signal that seeks the situation as depicted in situation 1. In situation 3 the deviation is fully in one quadrant , resulting in a single signal.
The four quadrants are orientated in a + position, the fins are placed in a x position compared to the zero orientation of the bomb (suspension lugs of bomb in top).
This means that a signal as in situation 3 will actuate a single fin set (when the bomb is in zero orientation). When the bomb starts rotating and the quadrant orientation changes to X and the fins to + , the signal will be on the edge of two quadrants(in situation 3) , and the steering signal will be a compilation of the rotation of two fin sets. For all angles between + and X this will progress proportionally.
When steering to the target the bomb uses “bang bang” steering; this means the fins deflect fully on receiving a steering signal, not proportionally. This results in the bomb moving towards the target in a sinusoide motion, constantly correcting it’s course.
The Fov (Field of view) of the laser seeker is 30 degrees, this means that the plane dropping the bomb can be of cource 15 degrees to the left or right and the bomb will steer to the centre (although it is preferable to release the bomb as much as possible aligned with the laser beam illuminating the target.
When the bomb is still far away from the target, one can still deviate (take another tank in the column, or another building in a street) within the 30 degrees cone, however when the bomb closes in to the target it is not possible anymore to suddenly change target as this will fall out of the 30 degrees cone of the seeker, so the distance of possible last minute deviation will decrease with the bomb closing in to the target. When following a target that moves with a relatively constant speed (a moving tank for instance) this does not apply, as the steering mechanism continuously adjusts during the flight to the target.
All steering signals are processed by the electronics placed behind the seeker head and passed to the four magneticly operated valves in the cilinder block, actuating the fins, steering the bomb to the illuminated target.
The advantage of a laser guided bomb over a GPS guided bomb is that a laser guided bomb can follow a moving target, a GPS guided bomb can only be used against a stationary target. However a Laser guided bomb is sensitive to cloud cover or smoke on the battlefield, disrupting the laser signal, a GPS guided bomb is not. Therefore, these days the newer types of guided bombs are combined laser guided-GPS, where GPS takes over if the laser signal is disrupted.

The XMU-650 tail fin (picture 24) consists of a machined aluminium castpiece with four sets of wing roots. The forward end has eight radial placed hexagon socket set screws to connect the tail to the V-groove at the base of the bomb body. Four aluminium flip out wings are connected to the wing roots by mean of a shaft. Inside the aluminium cast piece four compression springs are tensioned between a shackle at the wings inner edge and a compression piece for the springs. Two shock absorbers are placed between the forward part of the cast piece and the compression piece. A sheet aluminium housing is screwed to the aft end of the cast piece to form the housing of the folded wings.
The compression piece for the four wings is placed just over the dead point of the shackles on the inner wing tips and just needs a small push with the latch lever to open the wings. This lever is positioned in a latch frame on the side of the cast piece. Upon release of the bomb, the cable connected to the latch release lever pulls it forward , flipping out the four wings.
A safety pin is placed through one of the wings, preventing the wings from accidentally opening during mounting of the fin set to the bomb body. As these fins open with enough force to cause serious injury, this safety pin should allways be in place when working on the fin set.
A small rectangular hole in the side of the sheet aluminium tail housing allows for the ATU-35 drive to be installed. A flexible drive cable is connected to the ATU-35 on one side and the M-905 tail fuze.

GBU-12 D/B (Paveway II series) data:
Bomb body diameter : 273mm
Bomb length : 3330mm
Explosive filling : 89 Kg Tritonal , Minol II or H6
Complete weight : 363 Kg (800 Lb)
Tail: MXU-650
Tailspan Min/Max : 430/1540mm
Computer Control Group : CCG MAU-169
Gliding range : 15km

 

[pzgr40]

P23, “Initiator bomb fuze FZU-48/B”;
The Initiator bomb fuze FZU-48/B is an air turbine driven dynamo. It is placed in the middle pocket between the suspension lugs. Two thin walled steel pipes run down from this pocket to the forward and afterward booster pockets, and are meant for the electric wiring of the electric powered fuzes when used. The turbine housing is closed when inserted in the bomb, and has a steel pull wire to the flip open cap housing the air turbine. When the bomb is ejected the cap is pulled open, the turbine starts rotating in the air stream and current is delivered to the fuze(s).
When electrical served fuzes are not used, the pocket hole is plugged with a plastic cap.
The FZU-48/B is normally used with the FMU-139/B or the FMU-54/B

P26/P27, “Bomb fuze, Nose, M904E2”;
Cutaway model of a M904E2 nose fuze. This is a vane armed, impact activated nose fuze with a variable arming delay. The arming times are 2,4,6,8,10,12,14,16 and 18 seconds, When the arming wire (not shown) is withdrawn from the fuze, the arming vane is free to rotate. Rotation of the arming vane turns the governor drum at a constant speed. Rotation is transmitted through a gear reduction mechanism to the arming stop. The governor drum is transmitted through a gear reduction mechanism to the arming stop. Two driving pins, extending from the arming stop through the striker, turn the striker. The firing pin is keyed to the striker, and is secured to the firing pin guide by the shearpin. As a result, the firing pin and firing pin guide turn with the striker. When the preselected arming time has elapsed and the notch in the striker is aligned with the index stop, the striker spring forces the striker upward against the bottom of the arming stop, and the spring-loaded striker ball enters the space above the firing pin from the side. Simultaneously, a longitudinal slot in the firing pin guide aligns with the rotor release stem. A spring lifts the stem upward through the pin-held stem guide into the slot. This raises the rotor release clear of the rotor, and the rotor pivots to align the detonator with the explosive train. The rotor is then locked in position by the rotor latch. The fuze is now armed.
On impact, the nose is driven into the body against the arming stop. This forces the striker against the striker ball, and the ball against the firing pin which, in turn, strikes the primer of the M9 delay element (picture 30). The primer initiates the remainder of the explosive train.

P28/P29, “Bomb fuze, Tail, impact, short delay, M905”:
Before the fuze is installed in the bomb, the M9 impact delay element (picture 30) is inserted in the fuze. Than the fuze arming delay time is set. The arming times are 4,6,8,12,16 and 20 seconds and can be set by pushing in the spring loaded lock and rotating the afterward part of the fuze housing to the desired arming delay setting.
When the bomb is released from the aircraft, the arming wire is withdrawn from the ATU-35 fuze drive assembly, freeing the arming vane. The airstream rotates the arming vane which turns the flexible drive shaft and the fuze MAU-87D/B governor (P31). The fuze governor rotates the input shaft at a constant speed. The input shaft rotates the internal setting gear through the gear reduction train at approximately 2 rpm. The internal setting gear, inertia plunger, firing pin, and firing pin guide are keyed to rotate as a unit. When a projection on the internal setting gear reaches a stop on the body, the lug on the inertia plunger aligns with the axial lug slot in the body. This frees the inertia plunger and firing pin to move, restrained only by the creep spring. Simultaneously, the shutter release pin groove aligns with the shutter release pin which moves into the groove by spring action. This releases the spring-loaded shutter to align the detonator with the remainder of the explosive train. The spring-loaded shutter lock holds the shutter in place.
Firing Function; Upon bomb impact, the inertia plunger overcomes the creep spring and drives the firing pin forward into the M9 delay element to initiate the firing train.
The lower gearweheel of the internal geartrain has a red and white part on it’s circumference, which can be observed through a small round window in the aft part of the fuze housing. This is the indication if the fuze is armed or safe (red=armed, white = safe).
A “coupler drive assembly governer MAU-87” is placed over the drive shaft of the fuze. This governer regulates the rotating speed of the input drive shaft of the fuze. Functioning of the governor is explaned in the description of picture 31. The governor enshures the maximum rotating speed of the firing pin is 2 rpm.
The M905 fuze, the “coupler drive assembly governer MAU-87” and the ATU-35 drive are normally used as a set.

P32/P33/P34, “bomb fuze , tail, M346 Mod.0.”
Cutaway model of a M346 Mod.0. tail fuze. This fuze is a time fuze, placed in the tail of the Mk-80 series aircraft bombs. The time delay can be set from ½ to 33 hours with a ¼ hour increment by rotating a set screw on the arming shaft beside the drive shaft of the fuze. A small window on the lower fuze body shows the time lapse until detonation.
The fuze consists of an upper and lower housing , riveted together. The upper part is an aluminium cup supporting the set screw and the drive shaft.
In the lower housing the mechanical mechanism is placed. In top the clutch driving segments and retention spring, coupled to the input gear train. When the arming vane rotates with 1200 RPM, the clutch engages. The gearbox rotates the arming shaft. The fuze is now partially armed.
Upon impact, the arming shaft is driven forward through inertia, releasing the anti withdrawal cam, the detonator shutter and the clockwork timer. The anti withdrawal cam springs outward and engages the wall of the adepter booster. The detonator shutter moves the detonator into alignment with the firing pin, and the clockwork starts funtioning.
The fuze is powered by a clockwork spring positioned in the lower large gearwheel.
A small window in the middle of the fuze has a rotating safety cam behind it, painted partially green, the rest with red black hatching over the circumference. If a green colour is seen through the window, the fuze is safe , when observing the red/black hatching, it is armed.
Above the clockwork, a hardened steel plate is placed , to prevent the drilling of holes through the clock to stop it.

P37/P38, “Bomb fuze, impact, short delay, Nose and/or tail, FMU81/B”:
The FMU-81B is a nose and/ or tail short delay impact fuze. It has two opposite thumbwheels on the nose. One thumbwheel is for the arming delay, allowing for 2,4,6,8,10,12,14 and 20 seconds and a “S” which stands for Safe. The other thumbwheel is the impact delay setting, which allows for .00, .01,.02,.005,.10 and .25 seconds. The two thumbwheels are connected to selector switches in the electronics package to provide the arming and firing selections. The electronics package consists of three circular trays of electronics above one another, cast in resign. Below the electronics, the firing pin activated battery can be found. The spring loaded firing pin is connected to a hook and a cable which runs through the pipe in the bomb, protruding from the hole in the middle of the bomb body. It is connected to the pincer solenoid in the middle of the MAU-12 release mechanism. Upon release, a hook is pulled back, allowing the spring loaded firing pin to move into the battery ignition, starting the battery.
Below the battery the detonator rotor housing assembly is placed . This detonator in this rotor is placed out of line with the auxiliary booster charge and has to rotate to get in line with the auxiliary booter. This is done by two opposite expanding bellows (see pic 32 left for example with one), filled with a small black powder charge, which extend in length and rotate the detonator rotor housing. Opposite of the booster, an electric switch is placed that is closed as soon as the hook from the firing pin is retracted, closing the battery circuit.
Regretfully the rotor housing assembly is missing in this cutaway model.

P30, “M9 percussion primer and delay element” ;
In the M904 nose- and M905 tail fuze the M9 percussion primer and delay element is used. This consists of a cilinder shaped aluminium slider with a firing cap and –if required- a built in delay element.
In this slider a groove and an index are machined that allow the cilinder to be placed in the fuze body in only one position, enshuring it cannot be accidentaly placed upside down, backward or not far enough inserted.
Two types of elements are available; delay and non-delay.
The available delays are: 0,01 sec, 0,025 sec, 0,05 sec, 0,1 sec, 0,25 seconds.
These delays allow the bomb to penetrate the target to a required depth before exploding.

P31, “coupler drive assembly governor fuze bomb MAU 87 D/B “,
The coupler drive assembly governor fuze bomb MAU 87 D/B is used with the M905 tail fuze, and can be used with the M346 Mod.0 fuze when used with the MAU-93/B fin set. It is placed over the drive shaft of the fuze and regulates the arming speed. It is connected with the air driven propeller on the side of the bomb tail by means of a flexible cable. Inside the governor four 90 quarters form a ring, held in place by a spring around the circumference of the four quarters of the disc. As long as the rotation speed of the flexible cable is not too high, the spring keeps the quarters pulled inward, allowing for the fuze to arm at the required speed. If however the rotation speed of the flexible cable becomes too high, the centrifugal force will throw the quarters outward, regulating the rotation speed by reducing it. The governer is connected with the ATU-35 drive on the other side.

P35, “Bomb fuze, electronic, nose and/or tail , FMU-139 A/B”;
The fuze contains the fuze electronics and the safety and arming (S&A) components in a
housing which is crimped at both ends.
The upper selector switch has a number of pre-set arming delays which are used by the air force only 4,6,7,10,14 and 20 seconds ; the X is safe (storage) , resulting in a dud if used.
The lower selector switch is both air force and Navy usage and has a number of pre-set arming delay and impact delay time combinations.
The electronics consists of the printed wiring board assemblies, electrical connector assembly, 4 retard sensors, impact switches, and the arming and firing selector switches. The S&A unit is placed behind the electronics and consists of the detonator rotor housing with printed electronics board (picture 36) It is rotated in it’s armed position by a expanding bellow that used a small internal black powder pellet to expand. Below the detonator rotor housing, the main booster is positioned.
The air force uses the FMU-139 A/B in combination with the FZU-48/B, the navy uses it in combination with the Mk122 Mod.0 initiator.

 

[Fusse2004]

Hey DJH !! This is a masterpiece !!! The madness!!! How many hours of work?

 

[pzgr40]

P39/P40, “Bomb fuze, tail, inertial FMU-54A/B”;
The FMU-54 A/B is an inertially armed air-burst or impact-fired, cocked striker tail fuze with a selectable arming delay from 2.5 to 6.0 seconds. The fuze is normally used in conjunction with the Mk 43 Mod 0 target detecting device (TDD) on the nose of the bomb.
When used alone, the fuze has an impact firing capability (mechanical detonator); when used with the TDD, the fuze has an airburst (electrical detonator) with impact backup capability. The fuze is designed for use only in the tail fuze well of bombs equipped with a retardation device (Mk-15 tail or BSU-49/B tail)
Here, the FMU-54A/B used as a stand alone tail fuze will be described.
Upon release from the bomb rack, the cord assembly which runs from the fuze to the middle well in the bomb body will pull the elastic cord. When 5,9 kg of force is applied this will retract the unlock shaft, removing the first rotor safety.
The Mk15 snakeye tail will open, causing decsceleration of the bomb. The timing block is thrown forward towards the G weight, the speed of forward movemnent being controlled by an escapement gearbox. The sensing weight is also thrown forward through desceleration. This only occures with a 0.6 seconds susutained desceleration. When the G weight is in it’s forward position, it allows a retaining ball to move sideways, which allows the sensing weight to move further forward, locking the timing block and the G-weight in it’s forward position. With the timer block locked in forward position, a locking pin for the arming timer is released, allowing the arming timer to run down. With the timer expired the D-pin is retracted, allowing for the rotor to rotate and align the electrical (only in used with the Mk43 mod0 TDD) and firing pin activated detonators.
When expired, te arming timer als rotates a pin that blocks the G-weight of the firing pin assembly from moving forward. Upon impact, the G-weight of the firing pin assembly moves forward, allowing four balls which fixate the spring loaded firing pin in it’s backward position to fall in a recess in the inside of the G-weight, releasing the spring loaded firing pin to move forward into the detonator, igniting the explosive train.

P41:
A nosepiece is avialable for the Mk80 series of bombs. This nosepiece is meant to give the bomb some penetrating capebillities. It is made of mild steel.
A special -hardened- nosepiece is avialable for armour piercing purposes. This however also fills the booster pocket below, which is not the case with the nosecap depicted here.

P42/P43/P44/P45,
The Mau 12 is a dual piston heavy duty ejection rack.
The Mau-12 is used with the F-15, F16, C130 and B-52. It can carry bombs (conventional and nuclear) as well as fuel tanks. It can carry weights up to 5000 Lbs.
The Mau -12 is placed in the pylons under the wing. It can be placed in a single version as wel as a tripple version (TER Tripple Ejection Rack). It is meant to safely fixate the bomb until the moment of release.
The rack consists of two rectangular steel plates between which the ejection mechanism is placed. In the two plates four holes are drilled to connect the MAU-12 to the aircraft pylon by means of four steel pins. (P42-01)
Two sets of release hooks are placed at 14” -355mm- (P42-02) and 30” -762mm- (P42-03)apart. These hooks are made from forged steel. The forward 14” and 30” and the afterward 14” and 30” release hooks are connected to one another by means of steel strips (P42-04), enshuring the forward and afterward sets are simultaniously served. The two release hook sets are connected with lever bars (P42-05). In closed position these bars are just before the dead centre so the release hooks are firmly fixated in closed position.
A solenoid (P43-06) locking mechanism places a rotating bar (P43-07) in the lever bars (always closed system). This can be unlocked by turning the arming switch in the cockpit, serving the solenoid (P43-06) which rotates and thereby retracts the safety bar and also serves set of switches (P43-08), one most probably the light bulb in the cockpit that points out the release mechanism is armed, the other to allow the ejection catridges to be fired.
In the middle of the ejector rack two cartridges are placed in two chambers; the first cartrridge (P43-09) is used to serve a piston (P43-10) that pushes one set of lever bars through the dead centre, rotating the two sets of release hooks, releasing the bomb. The second cartridge (P43-11) simultaniously places two pistons (P44-12) under pressure which move outward (P44-13) , pushing the bomb away from under the wing with 3 meters per second. At the end of the piston stroke a small piston with two radial holes (P44-14) moves outward, bleeding the pressure from the pistons.
Three solenoids (P45-15) are placed at both end and in the middle of the bomb rack, serving a pincer (P45-16) like mechanism. In these “pincers” the rings of the arming wires can be placed. When served, the rings are fixated by these pincers , so the arming wires are retracted from the bomb upon release, arming the bomb. When not served, the bomb is released with it’s arming wires in place (emergency release).
The connection plug (P45-17) is used for electric power and serving of the bomb rack.

Literature / sources of info:

Technical Manuals (TM’s)
-B-2-3-12 U.S. BOMB FUZES, NOSE, M904E1, M904E2, M904E3, AND M904E4
-B-2-3-27 U.S. BOMB FUZE, TAIL, IMPACT, SHORT-DELAY, M905
-B-2-3-54 U.S. BOMB FUZE, IMPACT, SHORT-DELAY, NOSE &OR TAIL, FMU-81B
-B-2-3-53 U.S. BOMB FUZE, TAIL, INERTIAL FMU-54 A/B
-B-2-3-62 U.S. BOMB FUZE, ELECTRONIC, NOSE AND/OR TAIL, FMU-139B, FMU-139A/B, AND FMU--139B/B
-B-2-3-38 U.S. BOMB FUZE, TAIL, MK346 MOD
-138884415-MIL-Handbook-146-Octtalog-Procurement-Standard-PDF pages 157 & 158.
-NAVAIR 11-1F-2, Table 2-4. GENERAL CHARACTERISTICS OF THE M904E2 FUZE CONTINUED (M9 ELEMENT) (internet source)
-GBU-12 Arming wiring examples (internet source)
-Aicraft Bombs, fuzes and associated components, NAVAIR 11-5A-17, chapter 1, fuzes and boosters (internet source).

-Bombs for beginners
http://www.globalsecurity.org/military/systems/munitions/intro-bombs.htm

-Navy aviation:
http://navyaviation.tpub.com/14313/css/Mk-15-And-Mods-Snakeye-Fin-Assembly-34.htm

http://www.globalsecurity.org/military/systems/munitions/mk82.htm
https://en.wikipedia.org/wiki/GBU-12_Paveway_II
http://www.globalsecurity.org/military/systems/munitions/gbu-12.htm
https://www.youtube.com/watch?v=26XYeQK1lm4
https://www.youtube.com/watch?v=V30vSPFLeoE
https://www.youtube.com/watch?v=3_RM19hOMo4
https://www.youtube.com/watch?v=pytjJETpvFc
https://www.youtube.com/watch?v=ntidhsh0ZpE

A big thank you to Erik (BLU-97), Kit, and Joop (MTM-CE) for their support in all the little parts I needed to complete the cutaway models and the documentation needed.

Regards, DJH

 

[Slick]

An amazing treatise. Outdone only by the sectioned items.

 

[HAZORD]

They don't make enough complimentary words to describe these postings DJ! Phenomenal!

Of course the Daisy-Cutter Snakeye is a favorite.

I will post some photos of the JDAM version when I get a chance, unless you have one of those in the works.

 

[pzgr40]

Hi folks, thanks for the kind words .

@ Fusee 2004; Writing the posting (with translation to Dutch for the NVBMB forum) took me about two months, roling it from the collection room to the next room and taking pictures about 3 days, collecting all the loose stuff I needed to make the cutaway models complete (Wiring, fuze parts, CCG) about two years. I produced two of these bombs (as depicted in P01 in 2001. I think I do not have the condition anymore to repeat that kind of heavy work.

@ Slick, thanks

@ Hazord; I like the Snakeye tail with fuze extender very much too, but I like the Paveway version just a littele more. The JDAM and the paveway III version are the only one version still missing. Regretfully these JDAM tails are not available for collectors yet... a matter of patience I think.

 

[blu97]

Hij is weer mooi, Nicely done DJ greetings from czechislovakia

 

[pzgr40]

Dank je Erik, en jij bedankt voor alle hulp!! Hoe is het weer en de pils daar

 

[Bellifortis]

Dear pzgr40,
thank you very much for this beatiful piece of work which I personally consider your Best. You are improving every time. Fantastic. I have a question : In your very good explanation about the functioning of the laser-optic you write, that the field of view of the optic is 30 degrees. The optics-casing is gimbaled at its back and the whole optics-casing can move in a fixed horizontal plane. What is the effective, complete search radius of the optics ? This would have to be added to the field of view of the optic.
With kind regards,
Bellifortis.
P.S.: Do you know the current procurement price of the full Paveway 2 version with laser, GPS and the knifeblade retarder airfoil brakes ?

 

[pzgr40]

Hi Bellifrtes, Thank you.
No the FOV is not descided by the roration of the seeker (or 'birdie' as it's also called), the birdie is forced in one diredtion by the strong airflow through it's ring wing and is only altered if the complete bomb changes course.
I looked up the unit cost : $21,896 , https://en.wikipedia.org/wiki/GBU-12_Paveway_II
Of cource I did not pay that, as mine is a gathering of loose parts, The Mk-82 bomb body was a sand filled -red painted- body from the (long ago discontinued) civil defence, the knifeblade fins have the text "for loading exercise only' on the backside, and the seeker is an inert drill type, meaning that the air bottle was bleeded and had a hole drilled, and the battery fired. Of cource the last two make it a safe item and interesting as a collectable item.

 

[Chris]

DJ as you know we are not aloud to talk about our work. But you my friend I will tell the beer and the weather were great.
Had a terrible trip back 15 hours driving