Ballistics Flashcards
Ballistics definition
The science of the motion of a projectile and the conditions that influence their motion
Interior Ballistics
Characterisitcs that affect projectile motion inside the barrel or rocket tube. Barrel ear, launcher tube alignment, thrust misaligment, propellant charges, projectile weight. BLT-PP
Barrel Wear
Gaseous action, propellant residue, and projecitle moiton wear away the inner surface of the barrel or cause deposits to build up resulting in lower muzzle velocity or a decrease in accuracy
Launcher Tube Alignment
Alignment/boresight of each tube may vary
Thrust Misalignment
Greatest Cause of error in free flight. A perfectly thrust-aligned free flight rocket does not exsit. Firing rockets above ETL provides a favorable relative wind, helping to counteract thrust misalignment. Rockets spin to counteract.
Propellant Charges
Production variances can cause difference in muzzle velocity and projectile trajectory. Temperature and moisture in the sotrage environment can also affect the way propellants burn.
Projectile Weight
The weight of projectiles of the same caliber may vary
Exterior Ballistics
Characteristics that influence hte motion of a projectile as it moves along its trajectory. Gravity, Air Resistance, Ya, Projectile Drift, wind drift.
Gravity
As range increases, the amount of gravity drop increases. This drop is proportional to the time of flight (dsitance) and inversely proportional to velocity.
Trajectory
The flight path of a projectile as it flies form the muzzle of a weapon to the point of impact.
Air Resistance
Friction between the air and the projectile causes friction, or drag. The bigger and faster a projectile is, the more drag it produces.
Yaw
The angle between the centerline of the projectile and the trajectory
Projectile Drift
Gyroscopic precession causes a clockwise spinning projectile to drift right. As range increases, drift increases.
Wind Drift
The effect of wind on a proectile in flight. The amount of drift depends on the TOF of the projectile and the wind speed acting onthe projectile. Crosswind requires the gunner to fire into the wind. Down/upwind requires range adjustment.
Aerial Ballistics: Common Characteristics
Depend on whether the projectiles are spin stabilized or fin stabilized and whether they are fired from the fixed mode or flexibile mode. Rotor Down-wash error and angular rate error
Rotor Down Wash Error
Rotor downwash acts on the projectile as it leaves the barrel or launcher
Causes the trajecotry to change (most noticeable below ETL)
Most affects rockets
Max error is induced when fired from IGE hover
Causes both lateral and linear (range) errors
If terrain allows drifting with the wind can provide a more consistent rotor down wash for both launcher and allow the aircraft to remain more stable.
Angular Rate Error
The motion of the helicopter as the projectile leaves the weapon
Does not affect hellfire and Stinger missiles
depends on the range to target, the rate of motion, and the airspeed
Occurs when an aircrew fires rockets from a hover using the pitch-up delivery technique
Anytime a pitch-down motion is required, the effect of angular rate error causes the projectile to land short of the target.
Spin-Stabilized Projectiles (M4/.50Cal)
Trajectory shift, port-starboard effect, and projectile jump
Trajectory Shift
The boreline axis of the weapon differs from the flight path of the helicopter, the movement of the helicopter changes the trajectory of the proejctile.
To correct tarjecotry shift the gunner leads the target.
The amount of lead depends on airspeed, angle of deflection, projectile velocity, and target range
Port-Starboard effect
Trajectory shift and projectile drift combine to constitute port-starboard effect.
When targets are on the left, the ffects of drift and shift compound each other; both cause the round to move right (need to fire left of target)
When targets are on the right, the effect of projectile drift (round moves right) tends to cancel the effect of trajectory shift (round moves left). Therefore, when targets are on the right, firing requires less compensation.
The range and airspeed at which a gunner engage a target determine which effect is greater.
At ranges less than 1000 meters, trajectory shift is greater (fire right of target)
At ranges beyond 1,000m, the effect of projectile drift is greater and tends to cancel the effect of trajectory shift.
Projectile Jump (Vertical Plane Gyroscopic Effect)
When a crew fires a weapon from a helicopter in flight and the muzzle is pointing any direction other than into the relative wind of the helicopter, the projectile will experience a jump.
Occurs because of the precession (chagne in axis of rotation) induced by crosswind
The amount that a projectile jumps is proportional to its initial yaw
Firing to the right produces a downward jump (aim slightly above)
Firing to the left produces an upward jump (aim slightly below)
Compensation is not required when firing from a hover
Fin-stabilized projectiles
Center of gravity, propellant force, relative wind effect
Center of Gravity
The CG of a rocket is in front of the center of pressure. As the rocket propellant burns, the CG moves farther forward. The fins of the rocket cause the center of pressure to follow the CG.
Propellant Force
A bullet reaches its maximum velocity at or near the muzzle. A rocket continues to accelerate until motor burnout occurs. As the rocket reaches its greatest velocity, the kinetic energy in the rocket tends to overcome other forces and causes the rocket to travel in a flatter trajectory.
