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Fighter Combat - Tactics and Maneuvering

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FIGHTER WEAPONS<br />

swiveling the nozzles, by installing deflector vanes in the exhaust, or by<br />

other means to cause the missile to pivot about its CG in a severe sideslip.<br />

The thrust is then vectored to stop the body rotation at the proper heading,<br />

<strong>and</strong>, finally, it is centered to send the missile off in the desired new<br />

direction. Such a system is highly unstable <strong>and</strong> requires an extremely fast<br />

<strong>and</strong> sophisticated autopilot, but it has the potential for great maneuverability,<br />

such as the ability to turn nearly square corners at low speed. One<br />

obvious disadvantage of thrust-vector control is that the motor must be<br />

burning, making it inoperable during a gliding flight segment. This would<br />

tend to make the missile bigger for a given range <strong>and</strong> may limit its<br />

application to fairly short-range weapons.<br />

Most thrust-vector-controlled vehicles are inherently more maneuverable<br />

at very low speeds, since there is less inertia in the missile to be<br />

overcome by the thrust in producing a change in flight direction. There are<br />

many other factors involved, however, including vehicle weight, moment<br />

of inertia about the vehicle's CG, <strong>and</strong> CG location. These factors generally<br />

tend to increase maneuverability near the point of motor burnout, so such<br />

a missile should remain very agile throughout its powered flight. This type<br />

of control is quite useful for very high-altitude missiles, since, unlike<br />

aerodynamic controls, it is not dependent on the atmosphere.<br />

Fixed control jets, arranged around the missile body to pivot the vehicle<br />

about its CG, are just another method of thrust-vector control; in this case<br />

the thrust line is changed by rotating the entire missile rather than just the<br />

nozzle or exhaust gases. A system of fixed control jets may be lighter than a<br />

straight thrust-vector control system, since no large actuators are required.<br />

Some maneuverability may be lost, however, since greater control power<br />

is usually available from the main engine, but maneuverability characteristics<br />

are essentially the same.<br />

Almost any control system requires actuators of some sort for movement<br />

of control surfaces, nozzles, valves, etc. The power source <strong>and</strong> the<br />

design of these actuators also have an effect on the maneuverability of the<br />

missile. These power sources are usually pneumatic, electric, or hydraulic,<br />

or some combination thereof. Pneumatic power may be provided by bottles<br />

of compressed gas or by a gas generator. Such systems are lightweight<br />

<strong>and</strong> simple, but they are generally fairly slow in reacting, particularly<br />

when heavy control loads are involved, <strong>and</strong> they have a rather limited<br />

endurance. Pneumatic control systems, therefore, are usually found only<br />

in small, short-range missiles.<br />

Electric actuators are generally faster than pneumatic ones. Also, since<br />

virtually all guided missiles already have electrical systems, electric<br />

actuators may simplify the missile by eliminating additional systems.<br />

Electric actuators, however, are expensive <strong>and</strong> tend to be heavy when great<br />

amounts of control power are required.<br />

Hydraulic actuators usually provide the fastest reaction time of these<br />

three methods, <strong>and</strong> they can produce great control forces efficiently. Missile<br />

hydraulic systems may be either "open" or "closed." In an open<br />

system used hydraulic fluid is vented overboard. In a closed system the<br />

used fluid is returned to the reservoir for reuse.<br />

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