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power strokes. An airplane engine does not need a flywheel, because the propeller serves the same purpose.
flywheel effect (electronic circuit). One of the characteristics of an LC circuit, a circuit that contains both
inductance and capacitance. If a class-C amplifier supplies an LC circuit with short pulses of energy at the
proper time, the magnetic field around the inductor will build up and decay, and the capacitor will charge
and discharge.
The LC circuit acts as a flywheel, and a continuous flow of alternating current is maintained
between the inductor and capacitor, even though the energy is supplied in short pulses. Energy stored in the
electromagnetic and electrostatic fields is supplied to the circuit during the time it is not being supplied by
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the amplifier.
FM (radio modulation). See frequency modulation.
FMC (flight management computer). An electronic flight instrumentation system that allows the flight
crew to initiate and implement a given flight plan and monitor its execution.
FMS (flight management systems) (air traffic control). A computer system that uses a large data base to
allow routes to be preprogrammed and fed into the system by means of a data loader. The system is
constantly updated with respect to position accuracy by reference to conventional navigation aids.
The sophisticated program and its associated data base insures that the most appropriate aids are
automatically selected during the information update cycle.
foamed plastic. A synthetic resin filled with millions of tiny bubbles. Foamed plastic is lightweight and
resilient (soft and pliable) and is used as a packing material and a thermal (heat) insulator. Foamed plastic
is sometimes called expanded plastic.
foaming (lubrication system malfunction). A condition in a lubrication system in which oil passing
through the engine picks up air which causes thousands of tiny bubbles to form. Foaming oil does not
lubricate efficiently, neither does it adequately pick up heat. Foam is removed from the lubricating oil by
passing the oil through a deaerator system.
foam rubber. A form of rubber filled with millions of tiny air bubbles. These bubbles were beaten into the
latex before it was vulcanized.
FOD (foreign object damage). Damage to the components in the gas path of a turbine engine that is
caused by ingesting objects that are not part of the engine.
Technicians tools carelessly left in the intake ducts as well as debris from the runways or taxiways
can cause FOD when the engine is being run on the ground. In flight, the ingestion of ice and birds can
cause FOD.
foehn (meteorology). Warm, dry downslope wind whose warmness and dryness is caused by adiabatic
compression upon descent. Foehns are characteristic of mountainous regions. See adiabatic process,
Chinook, Santa Ana.
fog (meteorology). An obscuration to visibility caused by water droplets that are small enough to remain
suspended in the air. Fog differs from drizzle in that it does not fall to the surface, and it differs from cloud
only because it extends all the way down to the surface.
foil. A form of metal rolled out into very thin sheets. Foil is normally thought of as a sheet of metal with a
thickness of less than 0.15 millimeter (0.006 inch).
folded fell seam (machine-sewed fabric seam). A type of machine-sewed seam in which the edges of the
fabric are folded back and a double row of stitches used to form the seam. The stitches pass through three
thicknesses of material.
follow-up signal. A signal in an autopilot system that nulls out the input signal to the servo when the
correct amount of control surface deflection has been reached.
footcandle (illumination). The amount of illumination on a surface when all points are one foot from a
uniform light source of one candela, the amount of light produced by one international candle.
foot-pound (measurement of torque). The amount of torque produced when one pound of force is applied
one foot from the point of rotation.
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foot-pound (measurement of work). The basic measure of work in the English gravitational system. One
foot-pound is the amount of work done by one pound of force when it causes a movement of one foot in the
direction of its application. One foot-pound is equal to 1.355818 joules.
foot-poundal (measurement of work). The basic measure of work in the English absolute system. One
foot-poundal is the amount of work done when one poundal of force causes a movement of one foot in the
direction of its application. One foot-poundal is equal to 0.0421 joule. The difference between a foot-pound
　
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