LO6 - Fuzes Flashcards
Definition of a fuze
- A fuze is a device designed to function an item of ammunition under pre-determined circumstances.
- A fuze is a device designed to initiate an explosive munition at the correct time or place.
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Abbreviations by position of fuze?
PD - Point Detonating
BD - Base Detonating
PIBD - Point Initiating Base Detonating
Abbreviations by function of fuze?
T, CT, MT, VT, CVT, SQ, DEL, MTSQ, TSQ, PDSQ, MO, ET
T - Time
CT - Combustion Time (May also be PTTF)
MT - Mechanical Time
VT - Variable Time
CVT - Controlled Variable Time
SQ - Super Quick
DEL - Delay
MTSQ - Mechanical Time Super Quick
TSQ - Time Super Quick
PDSQ - Point Detonating Super Quick
MO - Multi Option
ET - Electronic Time
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General requirements and other requirements of fuzes
General
* SAFETY
For storage and transport
Against premature functioning
* RELIABILITY
To high order when required
Other requirements
* Optional delay setting
* Easy time adjustment / setting
* Minimum preparation for use
* Multi role to minimise refuzing
* Standard weight
* Must fit standard cavity size
2 inch Artillery
1.5 inch Mortar
Fuzes are classified according to what three categories?
- Filling
- Position
- Function
Fuzes classified by function have what three types?
- Time
- Impact
- Proximity
Impact Fuzes are divided into which three categories?
- Super Quick(SQ),
- Graze
- Delay
Definition of arming
The process of arming is the unlocking of the devices at the correct time in the correct sequence.
Forces available
- Set-back
- Centrifugal Force
- Spin Decay
- Creep Forward
- Set Forward
- Air or Gas Pressure
- Stored Energy
ACSSCSS
Explanation of forces available
- Set-back - This arises from the reaction of the mechanism to the acceleration forces applied in the gun on firing.
- Centrifugal Force - Any component whose centre of gravity is off the
axis of the fuze tends to be thrown outwards as a tends to be thrown outwards as a result of centrifugal force generated by the angular velocity imparted to the projectiles. - Spin Decay
In the same way that a projectile loses linear velocity, it loses angular velocity.
This decrease in angular velocity can be used to trigger a self–destruction device - Creep Forward
When the acceleration phase ends, components which have been locked tend to ease forward on their seatings.
Springs which have been compressed begin to re- assert themselves.
This gradual unlocking process permits spin forces to act on components susceptible to them. - Set Forward - The relative forward movement of components when a fuze decelerates on impact.
- Air or Gas Pressure
Air or Gas pressure is sometimes used to drive a turbine to generate power for electrically operated fuzes.
Used as an alternative arming method for non spun projectiles such as mortars. - Stored Energy - is usually a spring (mechanical) used to operate clockwork devices or to move shutters.
Common Methods Of Operation of fuses
- A common method of operation is the Four – Stage one/type of:
Unlocking a component by set–back forces.back forces.
Easing it on its seating during creep forward.
Swinging it to an armed position by the application of centrifugal force.
Initiation of the explosive train by set forward on impact.
Principle requirements of fuze
- The principal requirements of fuzes are safety and reliability.
- All fuzes embody mechanical devices which ensure the Fuze:
Functions at the desired moment
Remains safe in handling, before and during loading
Remains bore and muzzle safety immediately after firing
Arms after leaving the muzzle
Broad categories of fuze systems
- Mechanical and Electro/Mechanical –Out of line
- Electronic/Mechanical –Out of line.
- Electronic –In line
Princinple requirements definitions
- Arming
- Material compatibility
- Design safety
- User inspection
- Explosive train
- Mechanical Lock
- Delay arming
Different mechanism in a fuze.
- Holding Devices - A holding device locks other components in a safe position until arming is required; to unlock them when arming is required; and possibly to relock them in the armed position.
- Locking Devices
- Safety Devices
Define Firing Devices. How it is achieved and types
- A firing device is the component which provides the stimuli to initiate the explosive train.
- It may be achieved by either electrical or mechanical.
- Electrical Firing:
Conducting Cap (CC).
Bridge Wire (BW).
Exploding Bridge Wire type (EBW). - Mechanical firing is invariably achieved in modern fuzes by stabbing a detonator with a firing pin.
Other Fuze Components
- Pellets.
- Detonators.
- Magazine or booster.
- Channel.
- Protective Cover/Cap:
Striker Cover.
Safety Cap. - Delay Systems.
Advantages of Electronics
- Lowers costs due to multi role function.
- Versatility in arming.
- Mechanical preparation or initiation.
There are two type of masking devices. What are they?
- Non Delay Arming or Masking Shutters and Slides.
- Delayed Arming Shutter
Time fuzes are set for time before loading by what devices?
- Rotation
- Use of a moving portion of fuze with fuze key
- Fuze setter
- Fuze setting machine
Time fuzes can be divided into three types
- Combustion (T) – Powder Train Time Fuze (PTTF)
- Mechanical (MT)
- Electronic (ET)
3 different types of MT fuzes
- Thiel - British MT Fuzes
A series of wheels and pinions controls the escape of from a main spring which is wound up during manufacture - Junghans - American MT Fuzes
This mechanism is actuated by spring assisted by centrifugal weights - Dixi - Swiss Fuze
This mechanism is driven by centrifugal force acting on driving balls
What is the main design function of the time fuzes?
Time Fuzes are designed to function after a predetermined time whilst in flight
Definition of proximity fuze
Proximity fuzes are automatic time fuzes, with or without PD element, that are designed to function a projectile at the optimum lethal distance from the target, provided that in the case of aircraft targets, the trajectory passes sufficiently close.
Proximity Fuzes are divided into two groups
Variable Time (VT) Timer section arms the fuze electronically after firing. No setting for optimum height.
Controlled Variable Time (CVT) Can be set to activate the Prox function after a set time.
Design consideration of PROX fuze
- Rugged.
- Able to function in all conditions.
- Light weight.
- Economical.
- Able to fit existing projectiles.
- Sensitive and rapid in operation.
- Not easily jammed.
- Not subject to false operation.
- Safe to handle.
- Have good storage characteristics.
Basic sections of Prox fuze
- The Nose
- The Steel Base
- The Sleeve
Basic functioning of prox fuze
- On firing, setback breaks the ampoule or electrolyte which floods the energiser.
- Clock starts (CVT only) and the shutter starts to rotate.
- An electric igniter is short circuited until 3 –5 5 seconds after firing.
- Transmitter radiates radio waves.
- Nearing the target… Doppler effect activatesDoppler effect activates
- FUZE DETONATES.
Define Doppler effect.
- Radio waves are emitted by the fuze, some of the waves are reflected and picked up by the receiver.
- The time taken to return affects the Reflected waves, which interfere with the radiated waves to give a beat known as the Doppler effect.
- As the fuze gets closer to the set target distance the impulses increase to a defined peak value and the fuze functions.
General safety features of prox fuze
- Battery is inert until ampoule is broken.
- Clockwork mechanism prevents signal transmission or functioning until pre-set time.
- Shutter or S & A mechanism keeps explosive train out of line.
- Electric components can be short circuited until safe to arm has operated as intended.
Why are proximity fuzes are commonly stored
nose down?
The battery ampoule activates on setback (rearward), so impact nose-down is less likely to down is less likely to activate the battery.
How are electronic fuze functioned?
- Electronic fuzes are functioned by a current passing through electric leads from some sort of battery.
- Power Sources:
Battery
Turbine generated
Precharged
Electostatic
What results can be expected from a Proximity Fuze when dropped from 1 m or more?
Care should be taken not to strike or drop fuzes or fuzed rounds because a drop in excess of 1m may result in a UXO when fired.
Define MOFA.
A fuze designed to provide a selectable function capability and can include a Proximity function option.
*Proximity
*Superquick
*Delay
*Near Surface Burst
Impact fuze actions
- Superquick (SQ)
- Non Delay
- Graze
- Delay
Explain SQ fuzes
- The mechanism of these fuzes consists of:
A needle supported by a thin metal disc or,A needle supported by a thin metal disc or,
A hammer/striker supported on a shear wire or A hammer/striker supported on a shear wire or coiled spring.
Exposed to a direct blow on impact with the target. - Sensitivity depends on the strength of the disc, shear wire or coiled spring.
Explain Non delay fuzes
- These fuzes differ from the SQ fuzes mainly in being less sensitive.
- The mechanism usually consists of a steel hammer / striker supported on a stout shear pin.
Define graze element fuzes
- The interior mechanism of graze action fuzes is so arranged that when the projectile is checked in flight or receives an appreciable deceleration.
- A moveable part, usually called the graze,inertia pellet or plunger moves forward to carry the detonator on to the needle (or vice versa).
- A creep spring keeps the two apart until this deceleration is experienced.
- As the movement of the plunger or weighted needle gives rise to an ‘air gap’ the fuze detonator is of the flash type.
- Graze fuzes have a small inherent delay.
Define delay fuzes
- These fuzes usually have a masking shutter, interrupter or pyrotechnic composition in-built into the detonating train between the initiator and the fuze magazine so there is a slight delay between the actuation of the initiator and the firing of the magazine.
- This may be achieved by channelling the flash from the initiator around a longer route or slowing it by having to wait for the pyrotechnic composition to burn through before it reaches the next component.
Types of impact fuzes
- Point Detonating Fuzes (PD)
- Point Initiating Base Detonating Fuzes (PIBD).
- Base Detonating Fuzes (BD)
Other functions that can be included in impact fuzes.
- Time and impact
- Proximity and impact
- Self- destruct
Prox fuze dropped
Unpackaged drop –1.5m (e.g. M732A2)1.5m
Packaged drop - 2.0m
Safe lift height –12m
PROX fuze storage.
- Protected from
Dampness
Sunlight
Heat
Drop/ Strike