Cutaway model of a BLU-77/B APAM (Anti Personel Anti Material) clusterbomb. 717 of these clusterbombs are packed in a CBU-59 Mk.7 Mod.3 dispenser. The complete bomb (container + clusterbombs) is called the “CBU-59 Rockeye II”. It was developed in the 1970’s as a replacement for the Rockeye.
The BLU77/B has an intersting design feature; if it hits a hard target (a tank or armoured vehicel for instance) the shaped charge is activated, if a soft target (sand, earth, mud, water, snow) is hit, the BLU-77/B will bound up approximately 1,5 meters up into the air before exploding. It also has a secondary incendiary effect. One hundred and eighty-six Rockeye II clusterbombs were deployed during the first gulf war.
The BLU-77/B exists of a drawns steel slightly tapered body, embossed on the inside to improve fragmantation. The red copper shaped charge cone with an electricaly ignited detonator (S) crimped to it’s base is placed in the body. Into a rim in the base of the cluster bomb body a base plate is crimped with a long triangular pin over which the white nylon tail is placed. On top of the body the Fuze FMU-88/B is placed on the cluster bomb body by means of a roundgoing crimp. The fuze body acts as a mortar pipe / launching pad if the fuze is activated on a soft underground.
Functioning of Fuze FMU-88/B:
When packed in the CBU-59 Mk.7 Mod.3 dispenser container, the bomblets are packed in such a way that the safety lock (A) (transport safety) on the fuze is kept pushed in inward position by the tail of the BLU-77/B above it. This prevents the fuze from arming while in the CBU container. Upon release from the CBU the flutter arming vane lock (B) pops up, enabeling the flutter vane (C) to start vibrating. In the lock two angled plates are placed in line with the flutter vane which press the airstream along the sides of the flutter vane, enshuring that the direction and amount of airstream is optimal. The flutter vane is connected to a small shaft (D) that transmits the vibrating movement to the other side of the fuze where it ends in a disc (E) to which an unbalanced spring loaded click hook (F) is mounted. A leaf spring (G) connected to this disc tries to return the disc in the neutral position. The click hook (F) hooks into a click wheel (H) which has a pin on the backside that hooks into an indentation in the arming rotor (J). While the flutter vane vibrates, the click hook pushes the click wheell around clockwise –tooth by tooth- rotating the arming rotor from safe into the armed position -90 degrees rotation-. A small edge on the rotor is painted bright orange; a small hole in the fuze body enables to look into the fuze i.w.o the rotor. When armed, the bright orange edge can be seen through the hole.
The arming rotor has two stab detonators (K,L) placed beside one another in the rotor. A small hole drilled over the length of the stab detonator connects both stab detonators, however a small pyrotechnic delay train is placed between the two stab detonators (M). The first stab detonator (K) is placed under the triangular firing pin (N) of the nose spike (O) –which is activated when hitting a hard target- . Below this stab detonator a piezo-electric cell (P) is placed which starts delivering current when placed under pressure. This current is transmitted to the electric detonator (S) below the shaped charge cone, igniting the shaped charge. This type of ignition can only take place when the two rivets (Q) in the nose spike are broken off by impact on a hard surface, pushing the nose spike violently into the firing pin (N) below the nose spike (O).
The second stab detonator (L) is actuated by the all-ways fuze (R), placed below the second stab detonator. This exists of a firing pin with a conical indentation below which a steel ball is placed. The firing pin is kept away from the stab detonator by a light spring. If –upon impact- the shear rivets (Q)of the nose spike are not sheared off because the BLU-77/B falls into soft underground, the ball with the firing pin (R) is swept forward, igniting the stab detonator (L). The flame of this detonator travels in two directions; left into the rotor channel into the pyrotechnic delay (M), right into the channel (V) leading to the “bounding powder charge” (U). As the cover of the fuze acts as the mortar tube or launching pad the clusterbomb is thrown up into the air. The pyrotechnic delay (M) is now burned up and will ignite the first stab detonator (K), exploding the BLU-77/B in mid air, enshuring an even and optimal distribution of the fragments.
In fact, this whole “soft-hard target discrimination” system can be brought back to the smart use of two shear rivets (Q).
Data for the BLU-77/B :
Length : 224 mm (8,8 inch)
Diameter : ø40,4 mm (1,59 inch)
Weight : 0,46 kg (1,02 Lb)
Weight explosive charge : 57 grams (0,125 Lb) RDX
Penetration : not known ( I expect somewhere around 175 mm)
Regards, DJH
The BLU77/B has an intersting design feature; if it hits a hard target (a tank or armoured vehicel for instance) the shaped charge is activated, if a soft target (sand, earth, mud, water, snow) is hit, the BLU-77/B will bound up approximately 1,5 meters up into the air before exploding. It also has a secondary incendiary effect. One hundred and eighty-six Rockeye II clusterbombs were deployed during the first gulf war.
The BLU-77/B exists of a drawns steel slightly tapered body, embossed on the inside to improve fragmantation. The red copper shaped charge cone with an electricaly ignited detonator (S) crimped to it’s base is placed in the body. Into a rim in the base of the cluster bomb body a base plate is crimped with a long triangular pin over which the white nylon tail is placed. On top of the body the Fuze FMU-88/B is placed on the cluster bomb body by means of a roundgoing crimp. The fuze body acts as a mortar pipe / launching pad if the fuze is activated on a soft underground.
Functioning of Fuze FMU-88/B:
When packed in the CBU-59 Mk.7 Mod.3 dispenser container, the bomblets are packed in such a way that the safety lock (A) (transport safety) on the fuze is kept pushed in inward position by the tail of the BLU-77/B above it. This prevents the fuze from arming while in the CBU container. Upon release from the CBU the flutter arming vane lock (B) pops up, enabeling the flutter vane (C) to start vibrating. In the lock two angled plates are placed in line with the flutter vane which press the airstream along the sides of the flutter vane, enshuring that the direction and amount of airstream is optimal. The flutter vane is connected to a small shaft (D) that transmits the vibrating movement to the other side of the fuze where it ends in a disc (E) to which an unbalanced spring loaded click hook (F) is mounted. A leaf spring (G) connected to this disc tries to return the disc in the neutral position. The click hook (F) hooks into a click wheel (H) which has a pin on the backside that hooks into an indentation in the arming rotor (J). While the flutter vane vibrates, the click hook pushes the click wheell around clockwise –tooth by tooth- rotating the arming rotor from safe into the armed position -90 degrees rotation-. A small edge on the rotor is painted bright orange; a small hole in the fuze body enables to look into the fuze i.w.o the rotor. When armed, the bright orange edge can be seen through the hole.
The arming rotor has two stab detonators (K,L) placed beside one another in the rotor. A small hole drilled over the length of the stab detonator connects both stab detonators, however a small pyrotechnic delay train is placed between the two stab detonators (M). The first stab detonator (K) is placed under the triangular firing pin (N) of the nose spike (O) –which is activated when hitting a hard target- . Below this stab detonator a piezo-electric cell (P) is placed which starts delivering current when placed under pressure. This current is transmitted to the electric detonator (S) below the shaped charge cone, igniting the shaped charge. This type of ignition can only take place when the two rivets (Q) in the nose spike are broken off by impact on a hard surface, pushing the nose spike violently into the firing pin (N) below the nose spike (O).
The second stab detonator (L) is actuated by the all-ways fuze (R), placed below the second stab detonator. This exists of a firing pin with a conical indentation below which a steel ball is placed. The firing pin is kept away from the stab detonator by a light spring. If –upon impact- the shear rivets (Q)of the nose spike are not sheared off because the BLU-77/B falls into soft underground, the ball with the firing pin (R) is swept forward, igniting the stab detonator (L). The flame of this detonator travels in two directions; left into the rotor channel into the pyrotechnic delay (M), right into the channel (V) leading to the “bounding powder charge” (U). As the cover of the fuze acts as the mortar tube or launching pad the clusterbomb is thrown up into the air. The pyrotechnic delay (M) is now burned up and will ignite the first stab detonator (K), exploding the BLU-77/B in mid air, enshuring an even and optimal distribution of the fragments.
In fact, this whole “soft-hard target discrimination” system can be brought back to the smart use of two shear rivets (Q).
Data for the BLU-77/B :
Length : 224 mm (8,8 inch)
Diameter : ø40,4 mm (1,59 inch)
Weight : 0,46 kg (1,02 Lb)
Weight explosive charge : 57 grams (0,125 Lb) RDX
Penetration : not known ( I expect somewhere around 175 mm)
Regards, DJH
Attachments
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01- cutaway model of a BLU-77B.JPG -
02- BLU-77B complete in parts.JPG -
03- Fuze FMU-88B complete.JPG -
04- Fuze FMU-88B top view.JPG -
05- Fuze FMU-88B bottom view.JPG -
06- Fuze FMU-88B flutter vane and flutter vane lock.JPG -
07- Fuze FMU-88B safe.JPG -
08- Fuze FMU-88B armed.JPG -
09- BLU-77B piezo electric fuzing detail.JPG -
10- BLU-77B all ways fuze detail.JPG
