Cutaway model of a tail Fuze M113, as used in US 500 LB G.P. and S.A.P. bombs
Functioning of the fuze:
Upon release from the bomb rack, a pin is withdrawn from the rotor vane, allowing it to rotate in the airstream. After 18 to 21 revolutions the threaded stem is unthreaded from the inertia plunger (rotor vane has risen 0.75 inch), and the fuze is to be considered armed. The inertia plunger is fixated from rotating by a small radial pin that falls in a longitudal slot on the outside of the inertia plunger (not visible in this cutaway model). After a few more rotations the rotor vane unthreads from the cap of the fuze body and falls out of the fuze.
The inertia plunger houses a brass spring-loaded firing pin, held in backward position by two balls. Upon impact the inertia plunger moves forward into a wider part of the fuze body (compressing it’s spring), allowing the two balls to move outward and release the spring loaded firing pin into the firing cap (red). This ignites the pyrotechnic delay which –on its turn- ignites the detonator in the base of the fuze, exploding the bomb.
A delay of 4 to 5 seconds is used for sea targets (M16 delay detonator), a delay of 8 to 15 seconds is used for land targets (M16 A1 delay detonator)
It must be noted that the fuze will function on an impact angle of 3 degrees.
Partly unscrewed rotor vanes are never to be screwed back in (counter clockwise) as one may push the inertia plunger forward instead of engaging its thread again, exploding the bomb.
The difference between fuzes M112, M113 and M114 can be found in the length of the complete fuze:
M112(A1): 9,6 inch, and used for 100 LB GP and 250 LB GP bombs
M113(A1): 12,6 inch, and used for 500 LB GP, and 500 LB SAP
M114(A1): 16,6 inch, and used for 1000, 1100 and 2000 Lb GP and 1000 and 2000 LB SAP
Regards, DJH
Functioning of the fuze:
Upon release from the bomb rack, a pin is withdrawn from the rotor vane, allowing it to rotate in the airstream. After 18 to 21 revolutions the threaded stem is unthreaded from the inertia plunger (rotor vane has risen 0.75 inch), and the fuze is to be considered armed. The inertia plunger is fixated from rotating by a small radial pin that falls in a longitudal slot on the outside of the inertia plunger (not visible in this cutaway model). After a few more rotations the rotor vane unthreads from the cap of the fuze body and falls out of the fuze.
The inertia plunger houses a brass spring-loaded firing pin, held in backward position by two balls. Upon impact the inertia plunger moves forward into a wider part of the fuze body (compressing it’s spring), allowing the two balls to move outward and release the spring loaded firing pin into the firing cap (red). This ignites the pyrotechnic delay which –on its turn- ignites the detonator in the base of the fuze, exploding the bomb.
A delay of 4 to 5 seconds is used for sea targets (M16 delay detonator), a delay of 8 to 15 seconds is used for land targets (M16 A1 delay detonator)
It must be noted that the fuze will function on an impact angle of 3 degrees.
Partly unscrewed rotor vanes are never to be screwed back in (counter clockwise) as one may push the inertia plunger forward instead of engaging its thread again, exploding the bomb.
The difference between fuzes M112, M113 and M114 can be found in the length of the complete fuze:
M112(A1): 9,6 inch, and used for 100 LB GP and 250 LB GP bombs
M113(A1): 12,6 inch, and used for 500 LB GP, and 500 LB SAP
M114(A1): 16,6 inch, and used for 1000, 1100 and 2000 Lb GP and 1000 and 2000 LB SAP
Regards, DJH
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