Fighter Combat - Tactics and Maneuvering

FIGHTER WEAPONS 7
reliability, cost-effectiveness, simplicity, and flexibility in comparison
with many other weapons systems, make the gun a formidable asset of the
modern fighter.
Regardless of the lethality of a given gun system, it is of little value
unless it can be brought to bear on the target. The fact that even the
relatively benign systems of World War I were effective in their time
demonstrates that lethality is certainly not the only factor, and probably
not even the most important factor, in gun effectiveness. The ability to
achieve a hit initially is probably more relevant. By this reasoning, a simple
comparison of rates of fire among the various guns and gun installations is
likely to be a better measure of their effectiveness, since this factor is more
closely related to the probability of a hit. Lethality and target vulnerability
are still important, however, since they determine the number of hits
required for a kill. Additionally, for the guns to be placed in a reasonable
firing position, aircraft peformance and pilot ability must be adequate. The
location of this position is very much dependent on the effectiveness of the
gunsight, as is discussed later.
Air-to-Air Gunnery Principles
The air-to-air gunnery problem is a difficult one; it involves hitting a
moving target from a moving platform with projectiles that follow curved
paths at varying speeds. This complicated problem can be better understood
if each part of it is isolated in turn.
Most people who have fired a gun or an arrow or have thrown a rock at a
stationary target realize that the projectile takes a finite length of time to
reach that target. During this period the projectile is acted on by gravity,
which causes it to curve downward. The longer the projectile time of flight
(TOP), the farther the projectile drops. In the first second this gravity drop
is about 16 ft. During its flight the projectile is also subjected to aerodynamic
drag, which causes it to decelerate at a rate dependent on its shape,
size, weight, and speed, as well as the density of the air. In general, the
greater the muzzle velocity of a bullet, the shorter the TOP and the smaller
the gravity drop at a given range. As range, and therefore TOP, increases,
however, the rate of gravity drop also increases. Gravity drop may be
negligible at very short ranges, but it becomes increasingly important as
TOP increases.
This finite TOP also poses a problem if the target happens to be moving,
since the target's position will change somewhat from firing of the projectile
to its impact; thus lead is required for the projectile and target to arrive
at the same point in space at the same instant. This will come as no
surprise to anyone who has ever shot at flying birds or skeet. The lead
required is roughly proportional to the crossing speed of the target, so if its
track is directly toward or away from the shooter, no lead is necessary, but
maximum lead is called for when the target's track is 90° to the line of sight
(LOS) from shooter to target.
As shown in Figure 1-1, lead usually is described as a "lead angle." Lead
angle is sensitive to target crossing speed and average bullet speed. Range is
also a factor, since average bullet speed decreases with greater TOP. Lead