Fighter Combat - Tactics and Maneuvering

50 FIGHTER WEAPONS
racy being about the norm. The difficulty is compounded with hardmaneuvering
targets, since missile envelopes are generally based on the
direction of the target's velocity vector, not on its attitude, which is the
only visual reference available to the attacking fighter pilot. These two
references may vary widely with high target angle of attack (AOA). (The
concept of AOA is discussed in the Appendix.)
In addition to the restrictions imposed by their operating envelopes,
AAMs also usually have aiming requirements. Since guided missiles can
correct for some aiming error, the aiming restrictions for them are much
looser than those for unguided weapons, but there are restrictions nevertheless.
Some missiles, including many heat seakers, must be launched
along the LOS in order to detect and guide on the target. Others may be
launched with lead or lag, i.e., pointing ahead of or behind the target. A lag
heading at launch is seldom beneficial for missile guidance since it requires
a larger turn to establish a collision course and usually results in
greater LOS rates. Lead heading can be quite helpful, however, particularly
for min-range launches, by reducing the required missile maneuver. Firecontrol
computers often provide the pilot with an indication of the optimum
lead heading, ideally allowing the missile to fly a straight path to
target intercept. These inputs often make the assumption that the target is
nonmaneuvering, and they may or may not account for the effect of the
shooter's angle of attack on apparent lead heading, an effect that can be
considerable during heavy maneuvering. AOA is a factor since missiles
usually weathercock toward the relative wind immediately after launch.
Although each missile design has its own set of unique problems, most
missiles are affected to a greater or lesser degree by difficulties in distinguishing
the target from its background. Even though Doppler-radar guidance
has largely eliminated the clutter obstacle for forward-hemisphere
targets, the hypothetical maneuvering missile envelope demonstrates that
limitations remain. The guidance performance of radar missiles is, in
general, enhanced when the missile is looking up at a target with only sky
in the background. Because of the effects of SLC, the performance of such
missiles may also be degraded at low altitudes, even with look-up.
The effects of clutter are sometimes bewildering and difficult to predict.
However, it usually can be said that the impact varies with the roughness
of the earth's surface along the target LOS and the "grazing angle," or
degree of look-down. Over land, particularly rough terrain, clutter is usually
a greater factor than it is over water.
Background is also a serious problem for heat-seeking missiles, with the
sun being the culprit, either directly or indirectly. The sun is much more
intense than any target exhaust and will "capture" the missile seeker if the
target LOS approaches too near at any point from launch to intercept.
(Don't worry; nobody has hit it yet.) Reflections of the sun off water, snow,
clouds, etc., can also cause problems. These produce a wide area of background
IR noise, as opposed to a point source, reducing target acquisition
ranges and degrading guidance through a decrease in signal-to-noise ratio.
Look-down may have much the same effect, especially against hot desert
backgrounds. As with radar missiles, a clear, blue sky is the optimum
background for heat-seeking missile employment.