Description
In appearance, the VT Fuze Mk 172 is the same as the VT Ring-Type Bomb Fuze T50. The fuze may also be marked as the T2004 for use in Army rockets.
A seal wire through a hole in the arming pin inserted at the factory prevents the vanes from rotating and insures that the arming mechanism is in the proper position. Any turning of the vanes, unless accompanied by set-back, will cause the rotor system to jam, stripping its gears, so that the fuze will be a dud. For this reason, the fuze cannot be pre-armed.
High speed rotation of the vanes is necessary to produce the current to fire the fuze. Therefore, the fuze is actually armed only when in flight on the rocket at speeds in excess of 80 knots. Damaged fuzes may hold the electrical charge in the condenser for quite some time. For this reason, damaged fuzes and duds found on the ground should preferably be handled with care.
Functioning
When the rocket is launched, the arming wire is withdrawn from the vane locking pin, which in turn is forced out by its spring to free the vanes. At the same time, the setback produced by the sudden acceleration forces the hinged inertia weight back against its spring. The hinged inertia weight forces the locking dog from the arming stem gear sector by means of its lever linkage, freeing the gear train. The vanes rotate, driving the electric generator and the gear train. After approximately 100 vane revolutions, the gear sector on the arming stem has rotated 25 degrees clockwise to move clear of the gear train. As the gear sector clears the gear train, the tension spring snaps it 75 degrees clockwise, where it is detained by the stop pin on the hinged inertia weight. Since the arming stem and detonator rotor are integral with the gear sector, they also move 25 degrees by vane rotation and 75 degrees by spring action. The vanes continue to rotate, driving the generator and the gear train, which is disconnected from the arming stem. As acceleration ceases at the end of burning of the motor, the spring forces the hinged inertia weight forward, pulling the stop pin and freeing the gear secor. The tension gear snaps the gear sector 90 degrees clockwise into the armed position, lining up the detonator with the booster lead-in and making electrical connection to the firing circuit. The detonator is locked in position by a spring-loaded detent in the detonator rotor. When the electric detonator is connected to the firing circuit, the firing condenser is charged. After 0.7 to 1.4 seconds, the condenser has stored up sufficient power and the fuze is armed. On approach to a target, the VT element activates the firing circuit, which discharges the condenser through the electric detonator which initiates the explosive train.
Hazardous Components
No information about hazardous components.
See Also
Source(s)
OP 1664, Volume 1 - US Explosive Ordnance (1947)
