5. Ballistics Flashcards
What is Ballistics?
The scientific study of the MOTION OF PROJECTILES
Define Internal Ballistics
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OPERATING PROCESS within the gun
from propellant ignition
until projectile leaves the barrel
Goals/Objectives of Internal Ballistics (3)
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Launch the projectile SAFELY
CONSISTENT performance between shots
Achieve the HIGHEST possible muzzle velocity
Define Piobert’s Law
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The surface of a deflagrating (burning) propellant recedes layer by layer in a direction normal to the surface.
Common Terms (cont’d)
- All burnt point
- Peak Pressure (MPa)
- Shot Start
- Shot exit
- Ignition Temp (oC)
- Explosion Heat (Q ex)
- Flame Temp (oC)
- Chamber Pressure (MPa)
- Specific Gas Volume (L/1kg)
- Muzzle Pressure (MPa)
- Solid Residues (%)
- All propellant has been burnt
- maximum pressure is reached
- The point when the shot initially moves
- Shot exits the muzzle
- Temperature required to ignite the propellant
- amount of heat liberated in the combustion of 1kg of propellant
- PEAK chamber temperature upon combustion of propellant
- Pressure at the case mouth
- Amount of gas produced 1kg propellant
- peak overpressure at the muzzle upon breakage of the projectile-bore seal
- % of solid matter remaining after combustion
4 Phases of Internal Ballistics
- Charge ignition (by the primer)
- Combustion prior to projectile motion
- Combustion up to ALL BURNT POINT
- Gas flow and projectile motion after all burnt point to muzzle
Burning Characteristics of Propellant Composition (4)
..of a propellant granule? (2)
COMPOSITION - Burning rate - Pressure index - Force Constant - Co-volume GRANULE - Ballistic size -The Form Function
Pressure Index
Co-efficient which relates to changes in burning rate to changes in pressure
(Burning increases pressure, which in turn, increases burn rate)
Co-Volume (vol/1kg)
The volume occupied by the molecules of a kilogram of propellant in a gaseous state
CV =
Force Constant
A measure of the pressure which a unit mass of propellant produces in a fixed volume
= Max pressure x effective volume of closed-vessel / Mass of propellant
Single vs Double Based Propellant
Single based propellant has a single burn which results in a higher pressure for a short
period.
Double based’s double burn results in lower pressures for a longer duration, but reaches that quicker
Firing Sequence (11)
- 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
Distribution of (propellant) Energy by % (6)
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Projectile - 32% Residual Heat of the gases - 42% Recoil of the gun - 0.2% Engraving the driving band - 2.8% Unburnt charges & gases - 3% Heat lost to the gun - 20%
What are the types Effects of Variations on Propellant and explain their effect
- Charge Weight
- Propellant size
- Propellant Shape
- Chamber Capacity
- Ignition Temperature
- Shot start
- Bore Area
- Multiple Variations
What are the differences to
Peak Pressure, Temp,
Velocity, ABP,
and results due to Effects of Variations on Propellant
-Charge Weight -Propellant size -Propellant shape(standard is degressive.) Chamber Capacity -Ignition Temperature -Shot start pressure -Bore Area -Multiple Variations
-Pressure Temp Velocity ABP
+Charge Weight: more, more, increase, Sooner
- more consistency and accuracy to fall of shot
+Propellant size: less, decrease, decrease, later
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(Neutral) Propellant Shape: less, decrease, slight increase, sooner
+Chamber (gas)Capacity: less, decrease
Ignition Temperature: increased all, sooner ABP
Shot start Pressure: increased all, sooner ABP
Bore Area (short, fatter): decrease, decrease, increased Vel, late ABP
Multiple Variations:
How can the round-to-round regularity of muzzle velocity be improved?
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An all burnt point where the shell is still well back in the bore
What is Fall Back?
When does it occur (4)
Consequences(4)
Occurs when the shell fails to remain in it's 'seating' on loading 1. Mismatched driving band to forcing cone 2. Dirt or fouling 3. insufficient ramming force 4. misaligned project goal A. Round fall well short B. Round breaks up on exit C. In bore detonation D. Blackened round
Ballistic Abnormalities
Occasion-to-occasion effect
The Warmer (Cold gun effect)
Order of fire
Ballistic hump ( re: new barrel)
What happens to the rate of burning of propellant if the pressure is increased?
It increases the burn rate
Extra q for int bal.
If bung finll wek ie
re.
What are the six (6) areas of distribution of
energy when the gun is fired?
Projectile, translational and rotational Heat in the gas Gun recoil Driving band engraving and overcoming friction of the bore. Unburnt charge and gases Heat in the gun
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? (5)
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- 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 are the effects 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.
Define INTERMEDIATE ballistics?
The study of the transition from internal to
external ballistics
What are 3 muzzle methods which can be used to
suppress flash?
How do they work
Conical tube
Slotted tube
Bar type
Break up the barrel shock and mach disc
What are the 2 phases of the muzzle GAS FLOW FIELD during firing?
Precursor blast field
Main blast field
What 2 elements make up bottle shock?
As part of the Precursor field
Barrel Shock (the sides) Mach Disc (the front)
What are the 3 main ways to minimise muzzle
flash?
Muzzle Devices Choice of Propellant Propellant Additives
What is flash?
name the types of Flash (5; in order)
The light emitted in the vicinity of the muzzle that occurs as the propellant gases mix with the surrounding air
Pre flash Primary flash Muzzle glow Intermediate flash Secondary flash
Flash Reduction Methods (3)
Muzzle devices ( flash suppressors) Type of propellant (eg. Triple-based (with NQ)) Propellant additives (eg. flash inhibitors)
We use muzzle devices for three main
reasons:
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Reduce recoil Suppress flash Decrease report
What is Blast
the effects produced by gas pressure waves in both intermediate and terminal ballistics
Properties of the Projectile
External Ballistics
Mass
Calibre
Nose Shape
Spin Rate
Trajectory
The path taken by the CENTRE OF GRAVITY of the projectile
Air Resistance Drag Forces
Skin Friction (# Boundary layer)
Pressure Drag
- Base drag
Forebody Drag (Shock Waves)
Excrescence Drag (stuff sticking out eg. Driving band)Drag Coefficient (Cd)
Drag coefficient (C d ) quantifies the drag of an object through a fluid (Air or Water). C d comprises of two drag effects - Skin Friction - Form Drag
Define Yaw
Angle bxn axis of the proj and that of he velocity vector (Traj) is the Yaw, or angle of attack
What are methods to reduce the effect of base drag?
Base bleed
Boat tail
What are the two common means of
stabilisation?
Spin stabilisation
Fin stabilisation
Define trajectory?
The path taken by the Centre of Gravity of a
projectile
now explain how each works?
Boat tailing:
Base bleeding:
Boat tailing: a truncated cone reducing the area of low pressure behind the projectile
Base bleeding: a method of burning propellant at the rear of the projectile IOT increase the air pressure and reduce Base drag
What are the two major aerodynamic forces acting on
the projectile, depending on Yaw?
Crosswind
Drag
What is meant by the Ballistic Coefficient?
A scientific measure of a projectile’s CARRYING ABILITY
What is recoil?
Recoil is the rearward motion of the gun in reaction to the forward motion imparted to the Projectile and propellant gases
What are 2 possible affects that the muzzle gas flow can have upon the Projectile
Slight acceleration
Slight yawing
How does most Flash suppression devices reduce Flash?
They are designed to Break-up barrel shock
Mach disc
What is the problem to adding potassium or sulphate salts to propellant?
increases the production of smoke
What are the 2 sources to make up blast?
-What can be used to reduce blast in small calibre weapons?
Name the 3 types
blast shock waves and flash blast -Silencers Blast absorption Blast dissipation Blast containment and controlled release
What is Pre Flash and why does it occur
The Flash prior to projectile exit, escaping gases in front of the projectile
What is secondary flash
-Why is it important to minimise?
The large flash caused by mixing the hot combustible material in the air
- It will indicate the position of the gun and may cause temporary blindness
What is Fallback
-When does it happen
What are the consequences
When a loaded projectile fails to remain in its seating in the forcing cone
- mismatched driving band and forcing cone
- Dirt or fouling
- Insufficient ramming force
- Misaligned projectile
Round falls short
Round breaks up on exit
Bore detonation
Blackened round
What is muzzle flash
the light emitted from the vicinity of the muzzle by the chemical reaction when hot propellant gases mixing with the air
What items can be used to reduce blast in small calibre weapons?
Name the 3 types
Silencers
Blast dissipation
Blast absorption
Blast containment and controlled release
What is base drag
the turbulent, low pressure pocket immediately behind the projectile base
Properties of the projectile?(4)
Mass
Calibre
Nose shape
Spin rate
