Fighter Combat - Tactics and Maneuvering

32 FIGHTER WEAPONS
Missile Propulsion
The propulsion system of a missile may be of any type suitable for airborne
vehicles, but because of the typically high speeds of their targets, AAMs
and SAMs are generally rocket or jet powered. Rockets are usually preferred
for shorter-range missiles, since rocket engines provide very high
thrust-to-weight, generating great acceleration and high speeds during the
short duration of the flight. Solid-fuel rockets are generally preferred because
small engines of this type usually have higher thrust-to-weight, are
simpler, and seldom require throttling.
As range requirements for the missile increase, so does the complexity
of the motor design. Simply increasing the size of the rocket to provide
greater endurance would cause the missile size and weight to grow rapidly,
so more propulsive efficiency is required. For medium-range missiles this
is sometimes accomplished by a solid-fuel rocket designed to produce two
levels of thrust: an initial high-thrust booster and a longer-lasting, lowthrust
sustainer. As the rocket grows in size to provide greater range,
liquid-fuel designs become more competitive in thrust-to-weight while
also providing convenient thrust control. Ramjet propulsion, however, is
usually preferable to liquid-fuel rockets in this application as long as the
missiles can remain within jet atmospheric limits. Often, particularly
with SAMs, a solid rocket booster will be provided to assist the missile in
initial acceleration to efficient ramjet operating speed.
Missile Control
The control system causes the missile to maneuver in response to inputs
from the guidance system. Missiles are often controlled aerodynamically,
like conventional aircraft, but they may also use thrust-vector control or
an arrangement of fixed control jets. The aerodynamic controls of missiles
vary little from aircraft controls. Since anti-air missiles are usually supersonic
vehicles, they often use all-moving irreversible control surfaces.
They also make frequent use of canard controls for improved maneuverability,
as well as sophisticated autopilots to maintain stability. As with
aircraft controls, missile aerodynamic controls are subject to the lift
limitations of airfoils and the results of induced drag. Unlike fighters,
however, missiles are seldom restricted to a limiting structural load factor,
i.e., they generally operate at speeds below their corner velocities. (See the
Appendix for a discussion of aerodynamics and performance.) Aerodynamically
controlled missiles, therefore, often have their best turn performance
at their highest speeds. With many rocket-powered missiles
there is a short period of rocket thrust followed by "gliding," or unpowered
flight, for the remainder of their operation. Maximum speed, minimum
weight (due to fuel exhaustion), and therefore greatest maneuverability for
this type of missile would generally occur near the time of motor burnout.
One of the advantages of aerodynamic controls is that they can provide
control during the gliding portion of the missile's flight.
Thrust-vector control is provided by altering the direction of the exhaust
gases to change the thrust line. This may be accomplished by