Formative 5 - ballistics Flashcards
Internal Ballistics:
Define
What is the study if ballistics
The scientific study of the motion of projectiles.
Internal Ballistics:
Define
Define internal ballistics
The scientific study of the operating process within the gun moment that the propellant is ignited until the projectile leaves the barrel.
Internal Ballistics:
List
What are the objectives of internal ballistics - 3 points
Launch the Projectile Safely
Consistent performance between shots
Achieve the highest possible muzzle velocity
Internal Ballistics:
List
Define the following terms:
All burnt point Peak pressure shot start shot exit Ignition temp Explosion heat Flame temp Chamber press specific gas volume (L/kg) muzzle pressure solid residue(%)
All Burnt Point.: The point where all the propellant has been consumed.
Peak Pressure (MPa): The point where the Max pressure is reached.
Shot Start.: The point where the projectile begins to move.
Shot Exit: The point at which the projectile exits the muzzle.
Ignition Temp ( C): Temperature required to ignite propellant.
Explosion Heat (Qex): Amount of heat liberated in the combustion of 1kg of propellant.
Flame Temp (C): Peak chamber temperature upon combustion of propellant.
Chamber Press (MPa): Pressure at the case mouth.
Specific gas vol (L/kg)” Amount of gas produced from 1kg of propellant.
Muzzle Press (MPa): Peak overpressure at the muzzle upon breakage of the projectile bore seal.
Solid residues (%).: w/w% of solid matter remaining after combustion.
Internal Ballistics:
List
What are the 4 phases of internal ballistics
Charge Ignition.
Combustion prior to projectile motion.
Combustion up to the all burnt point.
Gas flow and Projectile motion after all burnt point to muzzle.
Internal Ballistics: Primers
List
Why do primers need to be consistent?
What two things must the primer do, in cased cartridge ammunition?
Irregular initiation will lead to misfires and variations between shots.
cartridge cased ammunition primers must
- Provide rearward obturation to pressure loss, known as primer leakage.
- Withstand the initiation forces (Firing Pin impact), Pierced Primer.
Internal Ballistics:
Define
Define Piobert’s law
The surface of deflagrating propellants will recede layer by layer in a direction normal to the surface.
Internal Ballistics: Burning characteristics
List
List the burning characteristics of propellants, of both composition (4) and the granule (2)
Propellant Composition:
- Burning Rate.
- Pressure Index.
- Co Volume.
- Force Constant.
- Propellant Granule:
- The Ballistic Size.
- The Form Function.
Internal Ballistics: Burning propellants
Define
Define the following burning characteristics
- Burning Rate.
- Pressure Index.
- Co Volume.
- Force Constant.
- Propellant Granule:
- The Ballistic Size.
- The Form Function.
- Burning Rate: Is the rate at which a granule reduces in size as the burning of that granule occurs on all sides.
- Pressure Index: Coefficient which relates to changes in burning rate to changes in pressure.
- Co Volume: The volume occupied by the molecules of a kilogram of propellant in a gaseous state.
- Force Constant: A measure of the pressure which a unit mass of propellant produces in a fixed volume.
Force constant = (Max pressure x Eff volume of closed vessel) / mass of propellant - Ballistic Size: Is the shortest distance between any two points on the surface of a propellant granule.
- Form Function: How the surface area of a propellant grain of a particular shape changes during combustion.
Internal Ballistics: Firing sequence
List
List the steps in the firing sequence
Initiation of the primer.
Propellant combustion.
Increase in Pressure and Temperature thereby
Increasing the Burn Rate.
Shot Start.
Acceleration of the projectile.
Peak pressure:
1/10 of the Barrel length.
Increase in volume
- Decrease in pressure.
All burnt point.
Acceleration increases:
-Slightly.
Pressure is 1/6 of peak pressure when the projectile is at the muzzle.
Entire process from initiation to muzzle exit takes less than 15 milliseconds
Internal Ballistics:
List / define
Understand the effects on max pressure and all burn point of the following possible variations:
Charge Weight. Propellant size. Chamber Capacity. Ignition Temperature. Shot start. Bore Area. Multiple Variations.
Reference the graphs in the presentations.
- increase in ignition temperature causes increased
The burning rate.
Pressure.
Temperature.
All burnt point moves closer to the breech.
Increase in muzzle velocity.
- increase in shot start pressure increases Burn Rate. Temperature. All Burnt Point moves rearward. Increase in muzzle velocity.
Internal Ballistics:
List / define
What is fall back?
Why can it happen - 4 points
what are the consequences - 4 points
Why: Mis match Driving Band Forcing Cone. Dirt or fouling. Insufficient Ramming force. Misaligned Projectile.
Consequence: Round Falls well Short. Round Breaks up on Exit. In bore detonation. Blackened round.
Internal Ballistics:
List
Define the following ballistic anomalies
Occasion to occasion Effect.
The Warmer (Cold Gun) Effect.
Order of Fire.
Ballistic Hump.
Occasion to occasion Effect.
- All guns experience MV variation.
- Day to day variation currently unpredictable. up to 5m/s.
- Lot to lot change of charge/projectile.
The Warmer (Cold Gun) Effect.
- Initial round has greater range.
- Can occur between fire missions.
- As low as several minutes of cooling.
Order of Fire.
- made no sense
Ballistic Hump.
- MV of a new barrel rises rapidly.
- Continues over number of rounds.
- Peaks at point indeterminable.
- Returns to MV comparable with state of wear.
Internal Ballistics:
define
What effect does having an earlier all burn point have?
improved round regularity and MV
Internal Ballistics:
List
List the 6 places where energy is distributed in during internal ballistics
Projectile (translational & rotational) = 32%.
Residual heat of the gases = 42%.
Recoil of the gun = 0.2%.
Engraving the driving band/barrel friction = 2.8%.
Unburnt charges and gases = 3%.
Heat lost to the gun = 20%.
Internal Ballistics:
List
List the 6 places where energy is distributed in during internal ballistics
Projectile (translational & rotational) = 32%.
Residual heat of the gases = 42%.
Recoil of the gun = 0.2%.
Engraving the driving band/barrel friction = 2.8%.
Unburnt charges and gases = 3%.
Heat lost to the gun = 20%.
Intermediate Ballistics:
Define
Define intermediate ballistics
The study of the transition from internal to external ballistics that occurs in the vicinity of the muzzle
Intermediate Ballistics: Muzzle energy
Define
Define muzzle energy
Majority energy carried by propellant gases
Give rise to blast and flash, and have considerable influence on projectile and gun motions
high pressure causes a Blast Shock Wave.
creates a sonic boom, as wave travels from away from gun
Intermediate Ballistics: Gas flow field
Define
Define a gas flow field
The muzzle gas flow field during firing consists of two phases:
- The precursor blast field that precedes the projectile exit from the muzzle
- The main blast field that follows as high pressure propellant gases are ejected into the air
Intermediate Ballistics:
Define
Further define precursor field
Precursor blast shock wave - standard spherical shock wave
includes bottle shock - pushed air and propellant gas in a piston like effect
- barrel shock - sides
- mach disc - forward flat edge of the pressure wave
Intermediate Ballistics: Main blast field
Define
Define the main blast field
What effects can the main blast have?
Once the projectile leaves the barrel there is the formation of another bottle shock, which has a Mach disc and barrel shocks
The blast shock is not spherical unlike the precursor blast shock, but rather distorted by the presence of the projectile and the hot propellant gases
Gases have higher velocity than projectile and can cause small amounts of acceleration, however primarily cause the projectile to yaw
Intermediate Ballistics: Flash
Define
Define flash, and list their types
Flash is the light emitted in the vicinity of the muzzle by the hot propellant gases and the chemical reactions that occurs as the propellant gases mix with the surrounding air.
Pre flash. Primary flash. Muzzle glow Intermediate flash. Secondary flash.
Intermediate Ballistics: Flash
Define
Define Pre-flash
Before the projectile exits the barrel, a small pre flash may occur due to the small amount of hot gases and propellant gases that leaked out in front of the projectile
Intermediate Ballistics: Flash
Define
Define Primary Flash
After the projectile has left the muzzle, the temperature of the gases may be high enough to allow for the emission visible radiation.
This radiation is known as the primary flash.
Intermediate Ballistics: Flash
Define
Define muzzle glow
I s the illumination caused by gas inside the bottle shock.
Intermediate Ballistics: Flash
Define
Define intermediate flash
As the gases pass through the Mach disc, they are re-compressed.
This can cause very high temperatures which can produce a flash, known as the intermediate flash.
Intermediate Ballistics: Flash
Define
Define Secondary flash
Hot combustible material mixes with the oxygen in the air.
An ignition of a very large flash.
Brightest form of flash.
Flash leaves a large signature.
Intermediate Ballistics: Flash
Define
Define the difference for secondary flash for small calibre weapons
Temperature and the amount of combustible material is not sufficient to cause a secondary flash.
Hot particles may then appear as a long streak behind the projectile.
Intermediate Ballistics: Flash reduction methods
List
List 3 methods of flash reduction
Muzzle devices (Flash Suppressors).
Type of propellant.
Propellant additives.
Intermediate Ballistics: Flash reduction
List
List the 3 reason we use muzzle devices
Reduce recoil.
Suppress flash.
Decrease report.
Intermediate Ballistics: Flash suppression
List
What are the 2 reasons for flash suppresion
Reduce signature.
Reduces possibility of temporary blindness.
Intermediate Ballistics: Flash reduction
Define / list
Define flash suppressors and list 3 types
Designed to minimise the intermediate flash and thus reduce the possibility of the ignition of secondary flash.
Conical tube
Slotted tube
Bar type
Intermediate Ballistics: Flash reduction methods
List
What type of propellant can reduce flash?
Tripe base propellants
Intermediate Ballistics: Flash reduction
Define
What propellant additives reduce flash?
Potassium and sodium inhibit the formation and burning of hydrogen gases however do create more smoke.
Intermediate Ballistics: Blast
List
What are the two main sources of muzzle blast?
Blast Shock wave
Flash blast
Intermediate Ballistics: Blast
Define
What causes flash blast?
The flash blast is caused by the rapid raising of temperature and consequent gas pressure caused by the secondary flash.
Intermediate Ballistics: Blast
List
What ancillary can reduce blast?
What 3 kinds are there?
Silence
Three types of silencers are:
Blast absorption.
Blast dissipation.
Blast containment and controlled release.
Intermediate Ballistics: Bore evacuator
Define
Define an evacuator
Prevents propellant fumes from entering crew compartments.
Works be creating pressure differentials during and after firing.
Intermediate Ballistics: Bore evacuator
List
List the steps of functioning of a bore evacuator
High pressure propellant gases are stored in the evacuator as the round passes through the barrel.
As the round exits the muzzle, the high pressure gases flow out the muzzle.
This may moment increase the secondary flash.
Intermediate Ballistics: Recoil
Define
define is recoil?
Recoil is the rearward motion of the gun in reaction to the forward motion imparted by the projectile and propellant gases.
Intermediate Ballistics: Recoil
List
What way is there to reduce recoil?
Braking system,
Muzzle brakes:
deflect propellant gases
Can reduce recoil up to 50 percent
- however can cause damage to gunners
Normally reduction of 25%
Intermediate Ballistics: Recoil
List
What is the disadvantage of a muzzle break?
No sabot round can be fired as the break up of propellant gases interfere with the sabot discarding action.
External Ballistics:
List
List the 4 properties of a projectile
Mass.
Calibre.
Nose Shape.
Spin Rate.
External Ballistics:
List
List the 3 properties of the atmosphere
Air Density
Temperature
Pressure
External Ballistics:
Define
Define trajectory
The trajectory is the path taken by the centre of gravity of the projectile.
External Ballistics: Air resistance
List
List the 4 aspects of drag forces
Skin Friction.
Pressure Drag.
- Base drag.
Forebody Drag (Shock Waves).
Excrescence Drag.
External Ballistics: Air resistance
Define
Define Drag forces
Average static pressure greater at nose.
it is minimised by smooth shapes and rounded nose and avoidance of sharp corners
The boundry layer effect causes wake, (base drag)
External Ballistics:
Define
Define excrescence drag
The final form of resistance arises from protuberances from the shell.
Normally only the driving band is unavoidable and this must be carefully designed.
External Ballistics: Drag
List
What is the drag equation?
D = Cd * (pv^2)/2 * A
D = ? p - Air density v - velocity A- cross sectional area Cd - Drag coefficient
External Ballistics:
Define
Define ballistic coefficient
The measure of a projectile’s ability to overcome drag.
External Ballistics:
Define
Define CRH and fractional CRH
Well done
External Ballistics:
Define
What nose shape can significantly reduce drag in a sub-sonic round
Any suitable smooth nose shape
External Ballistics:
Define
Under what design conditions will a projectile have static stability, and what will cause static instability
Stability: Cg forward of Cp
Instability: Cg rearward of Cp
External Ballistics:
Define
Explain why we spin a projectile.
To overcome yaw effects, and improve the stability of a projectile.
External Ballistics:
Define
External Ballistics:
Define
Why do we spin stabilise artillery rounds?
The base is required to be heavy to withstand firing force and,
the nose is pointed or streamlined to reduce drag.
This causes the the Cg to be rear of the Cp, requiring us to spin the projectile in order to stabilise it
External Ballistics: Drift
Define
Define drift
A projectile will deviate laterally from the original direction imparted to it by the
gun.
This lateral deviation is called drift.
Made up of two parts:
- Drift due to equilibrium yaw - for spun projectiles.
- Drift due to rotation of the earth.
