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Advanced Conduct of Fire
Terms in this set (145)
What is Ballistics?
The study of everything that happens to the projectile from the point of initial detonation of the round until the projectile comes to a complete stop.
What are the four phases of ballistics?
Internal ballistics, transitional ballistics, external ballistics, and terminal ballistics.
What is internal ballistics?
Initial detonation until shot exit.
What is transitional ballistics?
Just outside the muzzle (blast envelope).
What is external ballistics?
What is terminal ballistics?
Impact on Target?
What is obturation?
Is the means of preventing the escape of propellant gases over or through the case base or the projectile.
How is projectile obturation (forward obturation) achieved?
Using a full-sized, tapered, nitrocellulose cartridge case where the obturator makes a close fit with the bore. The obturator is made of nylon or copper. On firing, the gases are prevented from escaping around the projectile because of the close fit between the bore and the obturator.
How is breech obturation (rear obturation) achieved?
The rubber flange on the case base expands rapidly against the chamber wall to create an air tight seal that prevents propellant gases from escaping into the crew compartment.
What can differences in static tube shape be caused by?
What can cause muzzle displacement?
Thermal bending (caused by uneven heat distribution along the gun tube), and Gravitational Bending (droop).
What two things can influence the direction the round will take on shot exit?
Static Tube Shape, and Muzzle Displacement.
What can both static tube shape and muzzle displacement influence?
the direction the round will take on shot exit.
What is in-bore balloting?
Any transverse motion of a projectile in the gun tube.
What aids in fume extraction?
A bore evacuator
What is a bore evacuator?
A bore evacuator is a device on the gun barrel which helps prevent gases from venting back into the vehicle's fighting compartment when the gun breech is opened to load another round.
What would happen without a bore evacuator? (or when the bore evacuator is not functioning)
Hot gases and other combustible residue would leak into the tank interior, depleting oxygen levels and filling it with noxious fumes resulting in toxicity poisoning and setting the conditions for flare back.
Explain transitional ballistics.
The transition from internal to external ballistics and it describes the period from the instant the projectile leaves the muzzle, until the pressure behind the projectile is equalized and the propellant gases produced cease to have an effect on the projectile.
What is initial yaw?
When the projectile initially leaves the muzzle, the gases are no longer contained by the obturator and rush past the projectile from its base to its Ogive briefly causing a tail wind. This causes the projectile to try and tumble so that the Ogive is facing the gas flow.
As the effects of the gases reduce, the airflow will be reversed and again flow from the Ogive to its base. However, the projectile will have moved slightly offline.
Explain external ballistics.
The external ballistics of conventional guns is defined as the motion of the projectile under the effects of gravity and air resistance.
Explain Spin Stabilization.
Spin stabilization uses the gyroscope principle to stabilize the projectile by spinning it. Spin is achieved by rifling the barrel of the gun. This enables the projectile to be fired more accurately by controlling and minimizing the effects of gravity and air pressure.
Drift is the lateral deviation from the line of trajectory due to the spinning of the projectile and the buildup of air pressure around the projectile nose.
Explain Fin Stabilization.
The term fin stabilization can be equated with an arrow. The fins at the rear of the shaft applies drag, and enables it to fly true to the target. The fin stabilized projectile is spun at approximately 100 revolutions per minute.
Why is the slow spin necessary on fin stabilized rounds?
Because any damage to the fins caused during separation of the sabots would otherwise cause the projectile to be steered offline.
What is the advantage to fin stabilized rounds.
When compared to spin stabilized projectiles, fin stabilized projectiles do not drift, which causes the projectile to tend to stay on the line of trajectory.
Explain cone stabilization.
A cone stabilized round uses a cone shaped projection at the base to induce drag. Thus destabilizing the projectile at slower velocities.
Why use a cone stabilized round?
It reduces the range of the round which limits the safety distance required for tank gunnery training.
What is the purpose of sabot petals?
Sabot petals are used to reduce in-bore balloting and smoothly carry the projectile in the gun tube. Sabot petals must be discarded once free of the gun tube to reduce the drag of the round.
Explain penetration as it pertains to armored targets.
It is the most important consideration. Focusing the largest amount of energy onto the smallest possible area of the target provides the greatest penetration.
How do armor-defeating projectiles achieve penetration?
- Kinetic Energy (KE) attack
- Chemical Energy (CE) attack
Explain Kinetic energy rounds.
A kinetic round punches through the armor of the intended target by concentrating maximum force on a single point. KE is the energy of motion.
What equation is used to calculate Kinetic Energy in joules?
KE = (Mass x Velocity^2) / 2
What are the three stages of Kinetic Energy Penetration?
Setup, Penetration, and Perforation.
Explain the Setup stage of Kinetic Energy Penetration.
This is the initial contact that the penetrator has with the target where a combination of mass and velocity are concentrated at a very small point. It is at this point that the penetrator may posture itself to follow the path of least resistance.
Explain the Penetration stage of Kinetic Energy Penetration.
At this point, the resulting force upon the target commences the penetration of the armor. The speed and effectiveness may be determined by the thickness of the target, its composition and density, other defensive aids, and countermeasures (ERA).
Explain the Perforation stage of Kinetic Energy Penetration.
This is when the penetrator has violated the armor and achieved the desired effects associated with overpressure, intensive heat, and the secondary effects of spalling.
What are chemical energy rounds?
Chemical Energy (CE) round uses chemical reactions in order to cause penetration of a target. The most common forms of CE rounds are explosively formed projectiles (EFP), and HE projectiles (Shaped charges).
Explain a shaped charge.
A conventional shaped charge generally has a conical metal liner that projects a hypervelocity jet of metal able to penetrate to great depths into steel armor. However, in travel over some distance, the jet breaks up along its length into particles that drift out of alignment, greatly diminishing its effectiveness at a distance.
Explain explosively formed projectiles.
An EFP, on the other hand, is an explosive charge with a hollow lined cavity at one end and a detonator at the other. They operate by detonating HE that collapses the (often copper) liner into itself. Some of the collapsing liner goes on to form a constantly stretching jet of material travelling at hypersonic speed. [3000mps+]
How do chemical energy projectiles function?
On detonation of the CE warhead, energy is focused at the apex of the copper shaped cone, which subsequently collapses creating a high velocity shock wave of metal particles that penetrate the target through the process of erosion.
What are the three basic characteristics considered in vehicle design? (When thinking of tanks, obviously...)
Explain Armor Distribution.
A vehicle is more likely to be engaged on the front, within an arc of approximately 1100 mils (62 deg.), than on any other surface. The sides are usually designed to defeat less severe attacks, and the bottom and rear are the least protected
What are the different types of armor?
Sloped Armor, Homogeneous Armor, Spaced Armor, Compound/Composite Armor, Reactive Armor, and Bar Armor.
Explain Sloped Armor.
Sloping the armor allows a greater equivalent of thickness to enemy attack; therefore, significantly less armor is used to provide the same protection. At high angles of attack, it may cause ricochet. For solid shot AP ammunition, this angle is about 1250 mils.
Explain Homogeneous Armor.
Most armored vehicles have their basic structure formed from rolled homogeneous armor. Other types of armor can be added over the rolled homogeneous armor. Rolled homogeneous armor is produced by processing cast steel billets and rolling them into plates of steel.
Explain Spaced Armor.
The armor protection is in the form of plates separated by a gap. With spaced armor, the shock wave generated by a CE round is obstructed from passing through the air gap onto the internal armor.
Explain Compound/Composite armor.
Composite armor consists of layers of different material such as DU, tungsten, RHA, plastics, ceramics or air. Most composite armor is lighter than the all-metal equivalent and occupies a larger volume for the same resistance to penetration. It is possible to design composite armor that is stronger, lighter and less voluminous than traditional armor, but the cost is often prohibitively high, restricting its use to especially vulnerable parts of a vehicle. Its primary purpose is to deter HEAT rounds.
What are the different types of reactive armor?
- Explosive Reactive Armor
- Non-energetic Reactive Armor and Non-explosive Reactive Armor
- Electric Reactive Armor
Explain Explosive Reactive Armor.
ERA = HE sandwiched between two plates. On attack, the explosive detonates, driving the metal plates apart to damage the penetrator. Against a shaped charge, the projected plates disrupt the metallic jet penetrator, providing a greater path-length of material to be penetrated. Against a long rod penetrator, the projected plates serve to deflect and break up the rod.
Explain Non-energetic Reactive Armor and Non-explosive Reactive Armor.
Two metal plates sandwich an inert liner, such as rubber. When struck by a shaped charge's metal jet, some of the impact energy is dissipated into the inert liner layer and the resulting high pressure causes a localized bending or bulging of the plates in the area of the impact. As the plates bulge, the point of jet impact shifts with the plate bulging, increasing the effective thickness of the armor.
Explain Electric Reactive Armor.
Currently in development, this armor is made up of two or more conductive plates separated by space or by an insulating material, creating a high-power capacitor. In operation, a high-voltage power source charges the armor. When an incoming body penetrates the plates, it closes the circuit to discharge the capacitor, transferring a great deal of energy into the penetrator, which may vaporize it or even turn it into plasma, significantly diffusing the attack.
Explain Bar Armor.
A rigid grid of slats around the vehicle at a predetermined distance (11 to 19 inches), on impact will crush or capture the warhead or cause damage to the fusing mechanism to prevent detonation. Should the round strike the bars, the stand-off distance disrupts the formation of the high velocity jet of copper.
Explain the theory of fire.
Links the relationship between the projectile in flight, the influences on the gun, and the sighting system to achieve a target hit at any range.
Explain the principle of elevation.
A projectile fired from a gun at an object in line with the axis of the bore (AOB) will fall short because of the influence of gravity and air resistance. To compensate for this, it is necessary to point the gun above the object to be hit.
When referring to elevation, what are the primary definitions?
Primary definitions deal with the main aspects of elevation. (Horizontal Plane, Axis of the Bore, Line of Sight, Angle of Sight, Tangent Elevation, and Quadrant Elevation)
What is the Horizontal Plane?
An imaginary line drawn through the gun trunnions, parallel to the Earth's surface, but ignoring the curvature of that surface.
What is the Axis of the Bore?
An imaginary line passing through the center of the bore.
What is the line of sight?
An imaginary line passing through the sight and the target.
What is the angle of sight?
The angle of sight (AOS) is the vertical angle formed between the LOS and the HP. When the LOS is above the HP, the angle formed is positive and when the LOS is below the HP, the angle formed is negative. The AOS governs whether more or less elevation is applied to the gun in order to hit the target.
What is Tangent Elevation?
The vertical angle formed between the LOS and the AOB when the gun is laid.
What is Quadrant Elevation?
The angle formed between the AOB and the HP when the gun is laid. It is a combination of TE, plus or minus the AOS.
When referring to elevation, what are the secondary definitions?
The secondary definitions are the aspects of the principles of elevation that require consideration when the gun is fired. (Line of Departure, Jump Angle, Angle of Projection, and Angle of Departure)
What is the line of departure?
The line the projectile takes the instant it leaves the muzzle. This is not necessarily in the exact line of the AOB; it can be above or below it, depending on whether jump is positive or negative.
What is meant by jump angle?
This term refers to the vertical angle between the AOB and the LOD when the gun is fired. It is caused by gun movement upon firing. The angle will vary depending on the gun and type of ammunition being fired.
What is the angle of projection?
This is the vertical angle formed between the LOS and the LOD when the gun is fired. It is a combination of TE and jump.
What is the angle of departure?
This is the angle formed between the HP and the LOD. It is a combination of quadrant elevation and jump.
What is the angle of elevation?
The vertical angle at which the gun is elevated to engage a target.
What factors affect the angle of elevation?
Range to target
Elevation of the target
Why is range to the target an important factor?
The greater the range the longer gravity and air resistance can act upon the projectile.
Why is the elevation to the target an important factor?
If the target is on the same level as the HP, then there is no AOS. However, if the target is above or below the HP, an AOS must be calculated and applied to the elevation factor in order to hit the target.
What is jump?
A measurable factor affecting elevation. In the majority of cases, it can be overcome. When firing directly, it can be accounted for by using a CCF. Jump angle consist of the follow elements:
a. Muzzle Point Angle (MP)
b. Muzzle Crossing Velocity (CV)
c. Center of Gravity Jump at the Muzzle
d. Aerodynamic Jump (AJ)
e. Sabot Discard Jump (SABOT ROUNDS ONLY)
What is Gravitational Bending (droop)?
Droop forms a vertical angle between the AOB at the breech and the AOB at the muzzle. As the barrel heats up during firing, droop will increase.
Explain Meteorological influence.
Meteorological conditions may exert some influence on elevation. Wind may affect the air drag on a projectile and cause a decrease of velocity. An increase in air density will also decrease the velocity of the round. The density of the air is affected largely by the ambient temperature and pressure of the air. On the M1A1, and M1A2 SEP Air temp and Baro are manually entered into the FCS.
Explain how muzzle velocity affects elevation?
A projectile with a low MV requires a larger angle of projection than one with a high MV because gravity and air resistance have a longer time to act on and affect the projectile. (gun wear and charge temperature can affect MV)
What is line?
A ballistic term for azimuth.
Refers to the horizontal angle formed between the AOB and the LOD when the gun is fired. It can be equated to jump in the HP.
Air turbulence moving laterally across the AOB which can force a projectile off its intended line of trajectory.
Explain trunnion tilt. (CANT)
Occurs if the vehicle is on a side slope and one gun trunnion is higher than the other. When this happens and quadrant elevation is applied to the gun, a line error will be introduced. This line error is caused by the gun being elevated obliquely instead of on the vertical plane. Trunnion tilt has a double effect; it not only causes a line error (deflection), but will also affect the amount of quadrant elevation applied in the vertical axis.
What factors affect line?
Ballistic Drift, Throw-off, Crosswind, Trunnion tilt (CANT), and Thermal Bending.
What is error budget?
The influence of the hardware, environmental conditions, and human factors that affect accuracy and consistency.
What is accuracy?
how close the mean point of impact is to the point of aim.
What is consistency?
the ability to strike close to the same point over a number of rounds to create a small shot group.
What are the three major categories of error budget.
Fixed biases, Variable biases, and Random errors.
Explain fixed bias error sources.
Error sources induced by ammunition, weapon, and fire control system design and manufacturer that at any given range will cause the round to miss the desired aiming point in a constant direction. These errors are predictable, and therefore can be compensated for.
What is parallax?
The difference in apparent direction of an object as seen from two different points not on a straight line with that object.
What is system parallax?
The vertical and horizontal distance between the axis of the bore (AOB) and the line of sight (LOS).
Explain ballistic drift correction.
GPS - the computer offsets drift in the ballistic solution.
GAS - Ballistic reticle.
Explain mean jump.
The average difference between the impact of a group of rounds fired over many occasions and the intended strike of those rounds, given that all inputs to the FCS are correct or within tolerance.
What is a CCF?
Computer Correction Factor. Horizontal and Vertical offsets needed to null out mean jump.
How do we correct for mean jump?
GPS - CCF
GAS - Precision alignment of the GAS or sight correction factors (SCF's) if the system is degraded.
What are the fixed bias error sources?
System Parallax, Mean Jump, and Ballistic drift? (Superman's Balls)
Explain Variable Bias Errors.
Errors whose value remains nearly constant when firing one type of ammunition at a particular target at a given range (single engagement), but can change considerably from one engagement to the next.
What are the variable bias errors?
Optical Path Bending
(C.R.A.C. B.O.B. is a Mother Facking Vicious Zombie!)
What are the boresight/ boresight retention error causes?
(There are 7)
1. Gravitational Bending (gun tube droop)
2. Thermal Bending
3. Turret deformation
4. Inaccurate MRS update
5. MBD tolerance
6. Round-off errors (mean readings)
7. Gunner and/or TC not sighting on the same exact point (gun/sight).
(GT-TIM-RG... need to come up with a better acronym)
How do we correct for boresight/boresight retention errors?
What is the correction for CANT?
GPS - POS/NAV AND HTPS. (CANT Unit as backup)
GAS - Manual correction 1/2 target form in opposite direction of CANT for HEAT and DM11 in AZ only. (no correction for KE/MPAT)
What is the correction for crosswind errors?
GPS - Crosswind sensor
GAS - No correction
Explain Fire Control as it pertains to Variable Bias Errors.
Error and stresses of both physical and environmental nature. The FCS cannot compensate for most of these stresses such as design tolerances, metal fatigue, and vehicle vibrations.
When referring to variable bias errors of the fire control system what can be compensated for?
Muzzle displacement which consists of gun tube droop, and thermal bending.
How does the thermal shroud help with thermal bending?
The thermal shroud reduces Thermal bending caused by uneven heat distribution BY UP TO 50%, but does nothing about the gravitational effect.
What is air density?
The weight of a certain volume of air which consists of water vapor in the air, air temperature, and barometric pressure.
How does the computer compensate for air density?
It accepts manual inputs for barometric pressure and air temperature, but there is no correction for water vapor.
Explain errors associated with ballistic solution.
Errors associated with calculating a ballistic solution based on incorrect information applied to the computer by the crew or the automatic inputs.
What are some of the incorrect inputs associated calculating a ballistic solution?
Incorrect ammunition selected
incorrect range determined
unknown failure of an automatic input
HTPS not aligned
Incorrect Ammo SUBDES
Incorrect manual inputs (Manuel)
How do we correct ballistic solution as an error source?
Crews must be trained properly on conduct of fire, and maintenance.
What are muzzle velocity variations?
Changes in the velocity of the projectile due to characteristics of the ammunition or weapon.
What are the muzzle variation causes?
- Tube Wear
- Change of loading density
- Tube length
- Loss of MV when employing the canister round in cold weather.
How do you correct for Muzzle Velocity variation?
Good cannon maintenance
Ammo Temp input
Good manufacturing procedures and quality control
Good manufacturing and design
Explain range estimation errors.
Errors associated with incorrect determination of a range to a specific target. When incorrect range is introduced to the ballistic solution there will be an elevation error.
How do we correct for range estimation errors?
What is optical path bending?
The apparent illusion of target movement created by emitted solar radiation (refraction).
What are the conditions under which refraction may occur?
Day- clear skies, flat terrain, wind less than 10mph, ranges over 1500m.
Night - clear skies, flat terrain, wind less than 4mph, ranges over 1500m.
What is the correction for optical path bending?
Find an elevated firing position at least 10m above intervening terrain, or...
Day- aim 1/2 target form high.
Night - aim 1/2 target form low.
Explain variable jump.
Variable jump is the average difference between actual impacts for a particular occasion and the intended strike of those rounds, given all inputs to the FCS are correct or within tolerance.
How do we correct for variable jump?
Standard sight adjustments after subsequent round misses.
What is zeroing?
The firing technique used by the crew to align direct fire sights to the center of a shot group.
How do we correct for zeroing errors?
Explain Random Error.
Random error sources are those that vary for each round fired, they cannot be predicted from one round to the next, nor can the crew compensate for them.
What are the random errors?
Round-to-round dispersion, and gunner lay error.
Explain round-to-round dispersion.
refers to the spread between impacts of 2 or more rounds in relation to the MPI when fired under identical conditions.
What factors may cause dispersion?
How do we correct for round to round dispersion?
Explain Gunner Lay Error
The gunner fails to make a correct lay to the target aiming point while either boresighting or engaging targets.
Gunner lay errors are influenced by what?
- Inability to identify the center of the target
- Inability to properly superimpose the reticle onto the center of the target
- Firing too quickly due to the criticality of time
- Optical path bending
How do you correct for gunner lay errors?
Gunner lay errors are primarily a training problem. You correct it with training.
What does gun tube wear result in?
Lowered muzzle velocity and increased dispersion.
What are the causes of in-bore balloting?
There are 7.
- Projectile Center of Gravity and Principal axis offset from bore centerline.
- Projectiles are not perfectly concentric
- Projectile/gun tube clearances may exist at projectile surfaces.
- Insufficient stiffness of the projectile/gun tube interface.
- Projectile wear produces or widens gaps between the projectile bourrelet surfaces and the bore.
- Gun tube curvature
- Gas dynamics produce irregular pressures at the projectile base.
What factors limit the length of a KE penetrator?
The ability of the penetrator to withstand launch forces while in the bore, as well as forces applied along its length at impact.
What are the Gun/Sight offsets?
GPS - Up 20in, Right 29in
TIS - Up 20 in, Right 35in
CITV - Up 26in, L 28in
GAS - Down 5in, Right 12in
What is erratic firing?
When the strike of any two rounds are separated by more than the height or width of the circle on the ST-5 panel.
What causes thermal bending?
Normally caused by uneven cooling of a warm or hot barrel. It can be caused by cold wind or rain striking one side of the barrel, with the result that one side cools more quickly than the other.
What causes gun tube droop?
Gun tube droop is caused by gravity acting on the gun, and can disturb the gun/sight relationship established through boresighting.
What are the prerequisites for the screening test?
PMCS, AAC's, Boresighting with an MBD, Collimation checks of the MBD, Plumb and Sync.
What is an MBD?
Muzzle Boresight device - an optical instrument used to accurately define the axis of the bore of a gun at the muzzle end.
Tell me the specifications of the MBD.
10x Magnification, 4.5deg field of view, Reticle crosshair with a 1 mil circle, and .06mil line width.
What do you do if an MBD cannot be collimated to a particular tank?
If it collimates on a second tank proceed with training, if it doesn't collimate on the second tank, turn the MBD in for repairs.
What does boresighting establish.
A base of information to make a system parallax correction by establishing a relationship between the axis of the bore and the sights. When the proper tank to target range is entered into the computer during boresighting, this gives the computer the baseline from which all later system parallax corrections will be made.
What are the two methods of boresighting?
MBD, and String Method
How much movement does the GPS allow for?
7.5 mils in any direction while in boresight mode. Less than 3 mils should be necessary to boresight. If more than 5 mils of movement are required, recheck the procedure.
What are the frequency and conditions to boresighting?
1. Change of TC or gunner
2. Loss of boresight or demonstrated loss of accuracy
3. In training, before each gunnery table
4. In combat:
- before anticipated contact
- After extensive road movement
- As the tactical situation permits.
What do CCF's do?
Refine and improve the ballistic solutions.
What are the two ways to enter information into the CEU?
Keypad and RATS (Reticle Adjust Toggle Switch)
What is the purpose of a proofing team?
At home station, assist training crews in procedures for live fire gunnery. During screening test assist in the preparation and conduct of the test.
What does proofing team success depend on?
Eliminating mechanical faults and crew errors before the first round is fired.
What must a tank do to pass the screening test?
The tank must hit one out of the first two rounds fired fully within the circle for each type of ammunition being screened.
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