Test 5 - Ballistics Flashcards
What are the goals of Internal Ballistics?
- Launch the projectile safely (crew and weapon)
- Consistent performance between shots
- Achieve the highest possible muzzle velocity.
What is ballistics?
- The scientific study of the motion of projectiles
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 Piobert’s Law?
- The burning of a solid state propellants.
- The surface of deflagration propellants will recede layer by layer in a direction normal to the surface.
What happens to the rate of burning of propellant if pressure is increased?
As pressure increases, the rate of burning increases
How can the round to round regularity of muzzle velocity be improved?
If the All Burnt point occurs while the shell is still well back in the bore
What are the 6 areas of distribution of energy when the gun is fired?
- 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%
What is the effect of an increase in charge weight? (4)
- Pressure increases
- ABP moves back
- MV 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
- MV decreases
- Regularity in fall of shot decreases.
What is the effect of using a multi-tubular propellant on internal ballistics?
Peak pressure is decreased however the projectile still receives good energy levels.
What is the effect on internal ballistics of using a projectile of normal weight but shorter and a larger diameter?
Same muzzle velocity but less pressure everywhere compared with standard shot
Define intermediate ballistics
- The study of the TRANSITION from internal to external ballistics that occurs in the vicinity of the muzzle
What are 3 methods/types which can be used to suppress flash?
- Conical tube
- slotted Tube
- bar type.
How do most flash suppression devices reduce flash?
Break up the barrel Shock, Mach disc
What two elements make up bottle Shock?
Barrel Shock and Mach Disc
What are 3 main ways to minimise muzzle flash?
- Muzzle Devices
- Choice of Propellant
- Propellant Additives
What can you use to reduce blast in small calibre weapons?
Silencers
What are the 5 different types of flash?
- Pre-flash
- Primary Flash
- Muzzle Glow
- Intermediate Flash
- Secondary Flash
For a projectile fired in Vacuo, what angle of projection gives you maximum range?
45 degrees
What is meant by base drag acting on a projectile in flight?
A turbulent, low pressure region immediately behind the base of the projectile in flight.
What are the four types of drag?
- Skin Friction
- Pressure/Base Drag
- Forebody Drag (shock waves)
- Excrescence Drag
What two methods reduce base drag?
- Boattailing
- Base Bleed
What is meant by ballistic Co-efficient?
A scientific measure of a projectile’s carrying ability.
What are two major aerodynamic forces acting on the projectile, depending on Yaw?
- Crosswind
- Drag
What are the two common means of Stabilisation?
- Spin stabilisation
- Fin Stabilisaiton
Define Trajectory
The path taken by the centre of Gravity of a projectile
Name two effects of muzzle gas on a projectile.
Slight acceleration and Yaw
What does Cd (Drag coefficient) comprise of?
- Skin Friction
- Form Drag
4 Properties of the Projectile:
- Mass
- Calibre
- Nose Shape
- Spin Rate
Define External Ballistics?
Transition from intermediate to terminal ballistics
Define External Ballistics?
Transition from intermediate to terminal ballistics
4 Phases of Internal Ballistics:
1 - Charge Ignition
2 - Combustion prior to proj motion
3 - Combustion up to the all burnt point
4 - Gas flow and proj motion after all burnt point to muzzle.
7 Effects of Variation to Internal Ballistics
B - Bore Area I - Ignition Temperature C - Charge Weight C - Chamber Capacity S - Shot Start P - Propellant Size M - Multiple Variations
What are the 4 Ballistic Abnormalities?
B - Ballistic Hump
O - Occasion-to-occasion Effect
O - Order of Fire
C - Cold Gun Effect
Why does Fallback occur? (4)
- Mis-Match
- Dirt or fouling
- Insufficient Ramming force
- Misaligned Projectile
What are the consequences of Fallback? (4)
- Round falls well short
- Round breaks up on exit
- In bore detonation
- Blackened round
Explain the 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
What are the Burning Rate characteristics and sub categories
- Propellant Composition
- Burning Rate
- Pressure Index
- Force Constant
- Co Volume
- Propellant Granule
- The Ballistic Size
- The Form Function
How can you reduce forebody drag?
- Sub-sonically, forebody drag can be significantly reduced by any suitable smooth nose shape.
- Avoid Sharp edges
What is Yaw/Angle of Attack?
the angle between the axis of the longitudinal projectile and that of the velocity vector/trajectory
12 Common terms in Internal Ballistics:
- All Burnt Point (propellant has been consumed)
- Peak Pressure (MPa) (max pressure reached)
- Shot Start (projectile begins to move)
- Shot exit (projectile exits the muzzle)
- Ignition Temp (C) (temp required to ignite propellant)
- Explosion Heat (Qex) (amount of heat liberated in the combustion of 1kg of propellant)
- Flame Temp (C) (peak chamber temp upon combustion of propellant)
- Chamber Press (MPa) (Pressure at the case mouth)
- Specific gas vol (L/kg) (gas produced from 1kg propellant)
- Muzzle Press (MPa) (peak pressure at the muzzle upon breakage of the projectile-bore seal)
- Solid Residues (%) (w/w% of solid matter remaining after combustion)
- muzzle velocity (m/s) (proj speed at exit from barrel)
In cartridge cased ammunition, the primer must:
- Provide rearward obturation to pressure loss (primer leakage)
- Withstand initiation forces (pierced primer)
What do variations in Shot Start Pressure result in an increase in?
- Peak pressures are greater when a greater shot start pressure is required.
- Burn Rate
- Temperature
- All burnt point moves rearward
- Increase in MV
(Eg squeeze bore)
Explain Order of Fire Abnormality?
- Multi charge gun systems
- Barrel temperature deviation
- High Charges followed by low charges
- MV several m/s less
- Period of inactivity
- First round on a low charge
- Series average MV several m/s less
- High charge followed by low charge
- Low charge should be unaffected.
- First round on a low charge
- Barrel temperature deviation
Explain 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/proj
- May enhance or diminish effect
Explain the “Cold Gun” Effect?
- AKA ‘Warmer Effect’
- Initial round has greater range
- Can occur between fire missions
- As low as several minutes of cooling.
- Once warmed, can achieve greater consistency
Explain Ballistic Hump Abnormality?
- MV of a new barrel rises rapidly
- Continues over a number of rounds
- Peaks at point undetermined
- Returns to MV comparable with state of wear
2 Phases of Gas flow field?
- Precursor: proceeds the projectile exit from muzzle
- Main Blast field: follows as high pressure prop gases ejected into air
Parts of the Precursor Field?
- Blast Shock
- Bottle Shock
- Barrel Shock
- Mach Disc
What are the three main reasons we use muzzle devices for?
- Reduce recoil
- Suppress flash
- Decrease report
What are the three ways in which a silencer reduces blast?
- Blast Absorption
- Blast Dissipation
- Blast containment and controlled release
Parts/components of Projectile?
Picture:
- Forebody
- Ogive
- Midbody
- Cannelure
- CG and CP (static Margin)
- Afterbody
- Base
- Boattail
Explain Skin Friction?
The air closest to the projectile is dragged with it the further you move away from the projectile the air starts to move in the opposite direction
Explain Excrescence Drag?
- Resistance that arises from protuberances from the shell
- Normally only the driving band is unavoidable and this must be carefully designed
2 Parts that make up Drift?
- Drift due to equilibrium yaw - for spun projectiles
- Drift due to rotation of the earth
