LO5 Ballistics Flashcards
What is ballistics?
The scientific study of the motion of projectiles
What’s happening inside the chamber?
- Since the projectile isn’t moving, the volume in the chamber is constant.
- The temperature and pressure are increasing, causing the burn rate to increase.
High pressures and temperatures will increase the burn rate - The propellant’s performance characteristics will dictate how long this phase will last.
The pressure required to force the projectile to move is known as the shot start pressure. - The pressure must be sufficient to force the engraving band into the lands of the rifling.
- The Burning Rate of the propellant will have an effect of when the shot start pressure will be reached.
Burning characteristics
- Propellant Composition
Burning Rate
Pressure Index
Force Constant
Co Volume - Propellant Granule
The Ballistic Size
The Form Function
Burning characteristics explanation
- Propellant Composition
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
Force Constant - A measure of the pressure which a unit mass of propellant produces in a fixed volume
Co Volume - The volume occupied by the molecules of a kilogram of propellant in a gaseous state - Propellant Granule
The Ballistic Size - Is the shortest distance between any two points on the surface of a propellant granule
The Form Function - How the surface area of a propellant grain of a particular shape changes during combustion.
Objectives of Internal Ballistics
- Launch the Projectile safely
- Consistent performance between shots
- Achieve the highest possible muzzle velocity
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
Percentages of distribution of energy during firing sequence
- 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%
Ballistic Abnormalities
- Occasion-to-occasion Effect
- The Warmer (Cold Gun) Effect
- Order of Fire
- Ballistic Hump
Define Internal ballistics
The scientific study of the operating process within the gun from the moment that the propellant is ignited until the projectile leaves the barrel
Define Pioberts Law
The surface of a Burning propellant recedes layer by layer in a direction normal to the surface.
Propellant form functions
**Granual Shape Approx Form Function
Random Chip Positive Most Degressive
Spherical Positive
Cylindrical Cord Positive
Disc Positive Near Zero
Tube/SlottedTube Positive Near Zero Neutral
Ribbon Positive Near Zero
Solid (Suppressed outer layers) Near Zero
Multi tube Near Zero
Tube (Inhibited Ign of outer surface) Negative Most Progressive
What happens to the rate of burning of propellant if the pressure is increased?
It increases.
How can the round to round regularity of muzzle velocity be improved?
If burning finishes while the shell is still well back in the bore.
What is the effect of an increase in charge weight?
Pressure increases, ABP moves back, muzzle velocity increases, regularity in fall of shot improves.
For the same weight of charge, what is the effect of increasing the propellant size?
Total initial burning surface of the propellant decreases.
Pressure is lower at first, ABP moves forward in the bore, muzzle velocity decreases, regularity in fall of shot decreases.
What is the effect of using a multi tubular propellant on internal ballistics?
The peak pressure is reduced but the projectile still gets good energy levels.
What is the effect on internal ballistics of using a projectile of normal weight, but shorter and of larger diameter than normal?
The same muzzle velocity is achieved with a pressure which is everywhere less than with the standard shot.
Definition of Intermediate Ballisitics
The study of the transition from internal to external ballistics that occurs in the vicinity of the muzzle
What is blast shock wave?
When high pressure gas is suddenly released from the muzzle, the out going noise primarily takes the form of an abrupt increased pressure known as blast shock wave. It is caused by the high-pressure propellant gases.
The flash blast is caused by the rapid raising of temperature and consequent gas pressure caused by the secondary flash.
2 phases of gas flow field
- the precursor blast field that proceeds the projectile exit from the muzzle.
- the main blast field that follows as high pressure propellant gases are ejected into the air
Define Muzzle flash
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
REMEMBER THIS QUESTION
Types of muzzle flash
- 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
- 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
- Muzzle glow - Is the illumination caused by gas inside the bottle shock
- Intermediate flash - As the gases pass through the mach disc, they are recompressed. This can cause very high temperatures which can produce a flash, known as the intermediate flash.
- 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.
Methods of flash reduction/ 3 ways to minimise muzzle flash
- Muzzle devices ( flash suppressors)
- Type of propellant - triple based propellant is used to reduce flash
- Propellant additives - Potassium and sodium inhibit the formation and burning of hydrogen gases however do create more smoke.
What are muzzle devices used for?
- Reduce recoil
- Suppress flash
- Decrease report
Resaons for flash suppression
Reduce signature
Reduces possibility of temp blindness
Explain flash suppressors and differnet types
- Flash suppressors are designed to minimise the intermediate flash and thus reduce the possibility of the ignition of secondary flash.
- Types:
Conical tube
Slotted tube
Bar type
what are the sources of Muzzle Blast?
- Blast Shock wave
- Flash blast
How can the Blast shock be reduced
- Silencers can be effective in reducing blast.
- Three types of silencers are
Blast absorption
Blast dissipation
Blast containment and controlled release
Define recoil
Recoil is the rearward motion of the gun in reaction to the forward motion imparted by the projectile and propellant gases
How do most flash suppression devices reduce flash?
- Break up the Barrel Shock
- Mach Disc
What 2 elements make up bottle shock?
- Barrel Shock
- Mach Disc
Properties of a projectile
- Mass
- Calibre
- Nose Shape
- Spin Rate
Properties Of The Atmosphere
- Air Density
- Temperature
- Pressure
2 methods of stabilising a projectile in flight
- Spin Stabilisation
- Fin Stabilisation
Definition of trajectory
The trajectory is the path taken by the centre of gravity of the projectile
What are the different drag forces?
- Skin Friction
- Pressure Drag (Base drag)
- Forebody Drag (Shock Waves)
- Excrescence Drag
What is Pressure drag IRT air resistance and how can it be minimised?
- Average static pressure greater at nose
- Minimised with:
Smooth shapes and rounded nose (subsonic)
Avoidance of sharp corners
Define Excrescence Drag
- The final form of resistance arises from protuberances from the shell.
- Normally only the driving band is the cause amd is unavoidable and this must be carefully designed.
Drag coefficient (Cdd)
- Quantifies the drag of an object through a fluid (Air or Water).
- Cd comprises of two drag comprises of two drag effects
Skin Friction
Form Drag
Define ballistic co-efficient
The measure of a projectile’s ability to overcome drag
How to reduce base drag?
- Base bleed
- Boat tailing
Different forces acting on a projectile
- Stability
- Angle of attack (Yaw) -
Crosswind
Drag - Stability
- Gyroscopes
- Drift
- Metereological conditions
- Rotation of the Earth
What is meant by base drag acting on a projectile in
flight?
Base Drag is caused by turbulent, low pressure region immediately behind the base of the projectile.
What angle gives the maximum range to a projectile?
45 degrees
