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location to another, or moving an aircraft to and from a maintenance base.
Ferry flights, under certain conditions, may be conducted under terms of a special flight permit.
ferry permit. A special flight permit issued by the Federal Aviation Administration that allows an
unlicensed aircraft to be flown from its present location to another location where it can be repaired,
inspected, or otherwise prepared for licensing.
FET (field effect transistor). A high-impedance semiconductor device in which the flow of load current
between the source and drain is controlled by variations in voltage on the gate, rather than current, as is
done with a bipolar transistor.
Load current flowing between the source and the drain, through a semiconductor channel, is
switched and regulated by the effect of an electric field exerted by the voltage on the gate. An FET is
sometimes called a unipolar transistor.
FHP (friction horsepower). The amount of horsepower used to turn the crankshaft, pistons, gears, and
accessories in a reciprocating engine and to compress the air inside the cylinders.
fiberglass. Thin fibers of glass used to reinforce plastic resins in the manufacture of strong, lightweight
structural components. The glass fibers have diameters between 0.005 mm and 0.2 mm (0.0002 inch and
0.008 inch).
fiber locknut (self-locking nut). A type of self-locking nut used on a bolt that is subject to vibration — it
cannot, however, be used on a bolt that is subject to rotation. A collar of resilient, or springy, fiber is locked
into the end of the threads in the nut. The hole in the fiber is slightly smaller than the major diameter of the
threads on the bolt on which it fits.
When the nut is screwed onto the bolt, the threads press, but do not cut, into the fiber and cause so
much friction that the nut cannot vibrate loose from the bolt. A fiber locknut can be reused as long as a
wrench is needed to turn it onto the bolt.
fiber optics. The branch of technology that deals with the transmission of light through long, slender,
flexible fibers of glass or transparent plastic material. Transparent fibers arranged in a compact bundle have
the ability to transmit an image from one end to the other, even if the bundle is bent around a corner.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 242
Fiber optic borescopes are used to inspect the inside of a structure without requiring any major
disassembly. These instruments may be fitted with a light source to illuminate the inside of the device
being inspected, and a camera to make a permanent record of what is seen through the eyepiece.
fidelity. The accuracy with which an amplifier reproduces the signal applied to its input.
field (electrical). A space across which electrical lines of force exist.
field (magnetic). A space across which magnetic lines of force exist.
field cleaning (turbine engine maintenance procedure). Cleaning the compressor blades, casings, and
inlet guide vanes of a turbojet engine by spraying them with an emulsion-type cleaner, followed by a rinse
with distilled or demineralized water. Field cleaning is done while the engine is motored by the starter or
operated at a low RPM.
field coil (electrical machine). A coil of insulated wire wound around a laminated steel pole shoe in an
electrical motor or generator. Each motor or generator has two or more field coils that may be connected
either in parallel or in series with the armature.
Direct current flowing through the field coils of a generator produces magnetic flux which induces
a voltage in the conductors of the armature as they pass in front of the pole shoes. The amount of voltage
induced in the armature is determined by the strength of the magnetic field. A voltage regulator is normally
used to control the amount of current flowing in the field coils, and thus the strength of the magnetic field.
In a motor, torque is produced by the reaction between the magnetic flux produced by current
flowing in the field coils and the flux produced by current flowing through the armature coils.
field effect transistor. See FET.
field excitation (aircraft generator). Direct current supplied to the field coils of a generator to produce the
magnetic field in which the armature rotates. DC generators are normally self-excited. This means that the
field excitation current comes directly from the armature.
Self-excited generators depend upon residual magnetism in the field frame to produce the initial
excitation current as soon as the generator begins to turn.
field frame (generator component). The steel housing of a generator in which the field coils are mounted.
The field frame provides a low reluctance path for the magnetic flux from the field coils, and it retains
　
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