Cutaway model of a Chemical timefuze No.37 . This tailfuze with ant removal device is the replacement for the chemical tailfuze No.17.
http://www.bocn.co.uk/vbforum/threads/96453-Tail-fuze-No-17
The Chemical tailfuze No.17 was an extremely safe fuze, it was completely unarmed during transport, was partly armed after release and only fully armed during impact. The No.17 could be taken out of the bomb if not used, and even when the Aceton ampoule broke for some reason during transport it still was safe.
The Fuze No.17 was designed in peacetime when crew safety and avoiding accidents was of primary concern. It was however an expensive fuze to produce, and due to the many parts and the fact that it protruded into the bomb tail, it led to many duds (fuzes bend upon impact).
It soon occured that the losses of bomber command due to flak and enemy fighters surpassed the number of accidents by far, even when using a much simpeler fuze without safety features. This was to be a fuze of much simpeler design, easier and much cheaper to produce; the No.37.
Description and functioning of the fuze No.37:
The fuze is fully made of brass. The fuze housing consists of an upper and lower part. The lower part houses the aceton ampoule, the firing pin, and anti withdrawal mechanism,. The upper part houses the arming fork.
A slotted countersunk head screw is screwed into the back of the firing pin. The countersunk head of the screw is placed in a celluloid disc that has a countersunk hole that fits the screw’s head. The firing pin is spring loaded and is only prevented from moving down into the firing cap by the celluloid disc. Above the celluloid disc with the countersunk head screw another celluloid disc is placed, as well as a brass ring. This brass ring can be replaced with more celluloid discs.
The firing pin is placed in a firing pin housing that is spring loaded itself. The lower part of the firing pin housing has a chamfered edge, as well as the lower inside part of the lower fuze housing. A locking ring is screwed over the base of the lower fuze housing, keeping twelve steel ball locked up in the V-groove formed by the two chamfered edges . these balls keep the firing pin housing in locked position.
The locking ring’s thread has the same pitch as the fuze in the booster housing.
Below the fuze the No.43 Mk.1 detonator is placed in the booster charge. As the detonator is used with a time fuze it has no delay element.
Upon release of the bomb, the propeller in the tail -connected with propeller fork to arming fork- starts to twist the arming fork inward, pressing the rubber seal inward, breaking the aceton ampoule. The aceton is soaked up by the cottom wool and starts to dissolve the celluloid discs. Depending upon the number of discs this will take 0,5 hours (just the disc with the screw) up to 144 hours (5 discs). The time may deviate in winter or summer due to the ambient temperature. As soon as the disc with the countersunk hole is dissolved far enough, i t will release the screw, allowing the firing pin to move in to the firing cap, exploding the detonator, the booster and the bomb.
If an attempt is made to unscrew the fuze from the bomb, the locking ring is also unscrewed from the lower fuze housing, shifting the outer half of the V-groove upward, allowing the balls to move outward, releasing the spring loaded firing pin housing to move down into the firing cap, detonating the bomb.
Therefore, as soon as the fuze is placed in the bomb, it cannot be unscrewed anymore.
Regards, DJH
http://www.bocn.co.uk/vbforum/threads/96453-Tail-fuze-No-17
The Chemical tailfuze No.17 was an extremely safe fuze, it was completely unarmed during transport, was partly armed after release and only fully armed during impact. The No.17 could be taken out of the bomb if not used, and even when the Aceton ampoule broke for some reason during transport it still was safe.
The Fuze No.17 was designed in peacetime when crew safety and avoiding accidents was of primary concern. It was however an expensive fuze to produce, and due to the many parts and the fact that it protruded into the bomb tail, it led to many duds (fuzes bend upon impact).
It soon occured that the losses of bomber command due to flak and enemy fighters surpassed the number of accidents by far, even when using a much simpeler fuze without safety features. This was to be a fuze of much simpeler design, easier and much cheaper to produce; the No.37.
Description and functioning of the fuze No.37:
The fuze is fully made of brass. The fuze housing consists of an upper and lower part. The lower part houses the aceton ampoule, the firing pin, and anti withdrawal mechanism,. The upper part houses the arming fork.
A slotted countersunk head screw is screwed into the back of the firing pin. The countersunk head of the screw is placed in a celluloid disc that has a countersunk hole that fits the screw’s head. The firing pin is spring loaded and is only prevented from moving down into the firing cap by the celluloid disc. Above the celluloid disc with the countersunk head screw another celluloid disc is placed, as well as a brass ring. This brass ring can be replaced with more celluloid discs.
The firing pin is placed in a firing pin housing that is spring loaded itself. The lower part of the firing pin housing has a chamfered edge, as well as the lower inside part of the lower fuze housing. A locking ring is screwed over the base of the lower fuze housing, keeping twelve steel ball locked up in the V-groove formed by the two chamfered edges . these balls keep the firing pin housing in locked position.
The locking ring’s thread has the same pitch as the fuze in the booster housing.
Below the fuze the No.43 Mk.1 detonator is placed in the booster charge. As the detonator is used with a time fuze it has no delay element.
Upon release of the bomb, the propeller in the tail -connected with propeller fork to arming fork- starts to twist the arming fork inward, pressing the rubber seal inward, breaking the aceton ampoule. The aceton is soaked up by the cottom wool and starts to dissolve the celluloid discs. Depending upon the number of discs this will take 0,5 hours (just the disc with the screw) up to 144 hours (5 discs). The time may deviate in winter or summer due to the ambient temperature. As soon as the disc with the countersunk hole is dissolved far enough, i t will release the screw, allowing the firing pin to move in to the firing cap, exploding the detonator, the booster and the bomb.
If an attempt is made to unscrew the fuze from the bomb, the locking ring is also unscrewed from the lower fuze housing, shifting the outer half of the V-groove upward, allowing the balls to move outward, releasing the spring loaded firing pin housing to move down into the firing cap, detonating the bomb.
Therefore, as soon as the fuze is placed in the bomb, it cannot be unscrewed anymore.
Regards, DJH
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