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multipliers.
frequency synthesizer (electronic circuit). An electronic circuit used to produce alternating current
having an accurately controlled frequency. One type of frequency synthesizer uses a crystal-controlled
oscillator to produce a single accurate frequency. Frequency multipliers and dividers change the crystal
frequency into the required frequencies.
freshening charge (battery servicing). A constant-voltage charge given to dry-charged batteries to get
them ready for installation. Most lead-acid batteries are shipped from the manufacturer in a dry-charged
state. The battery was charged at the factory, the electrolyte was drained, and the cells were sealed.
When the battery is ready to be put into service, electrolyte having the proper specific gravity is
poured into the cells, and the battery is given a constant-voltage freshening charge. The battery is
considered ready for service when the specific gravity of the electrolyte does not change in three hours of
charging.
fretting. A type of mechanical damage to the surface of an object. Fretting is caused by one object rubbing
against another and wearing part of it away.
fretting corrosion. A form of corrosion between two surfaces which have a slight amount of relative
motion between them. The protective oxide coating that forms on aluminum or magnesium alloys is rubbed
away by the movement of the parts. New oxides must be continually formed to replace those that are worn
away and these oxides act as an abrasive to further damage the metal.
friction. Opposition to the relative movement between two objects.
friction brake. A mechanism used with a rotating wheel or shaft in which friction is used to slow its
rotation.
friction clutch. A device used to connect a motor to a mechanical load. A plate or cone on the load is
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 266
driven by a mating device on the motor. A lining made of a material that causes a good deal of friction
separates the two surfaces, and a spring forces the surfaces and lining tightly together, allowing the motor
to drive the load. The spring force can be released to disconnect the motor from the load.
friction error (instrument indications). The error caused by friction in an instrument mechanism. The
amount of friction error is found by reading the instrument, vibrating it, and then reading it again. The
difference between the two indications is the amount of friction error.
friction horsepower (reciprocating engine specification). The amount of horsepower used to turn the
crankshaft, pistons, gears and accessories in a reciprocating engine, and to compress the air in the cylinders.
The brake horsepower actually delivered to the output shaft of the engine is the total horsepower
developed by the engine, less the friction horsepower.
friction loss. The loss of mechanical energy in a mechanism caused by friction changing mechanical
energy into heat.
friction measurement (runway condition). A measurement of the friction characteristics of the runway
pavement surface, using continuous self-watering friction measurement equipment in accordance with the
specifications, procedures, and schedules contained in AC 150/5320-12, Measurement, Construction, and
Maintenance of Skid-Resistance Airport Pavement Surfaces.
friction tape. A type of electrical insulating tape that was commonly used in the past, but is being replaced
by more effective types of tape. Friction tape is a cloth tape impregnated with a black, sticky, tar-like
material.
friction welding. A method of joining thermoplastic materials by rubbing the mating surfaces together
while applying a large amount of pressure. Heat caused by the friction softens the material, and the pressure
fuses the softened edges together.
Frise aileron (airplane control). A type of aileron used for lateral control of an airplane. The hinge line of
a Frise aileron is set back from the leading edge so a portion of its surface is ahead of the hinge line. When
the aileron is raised, to lower the wing on which it is mounted, the portion ahead of the hinge line protrudes
below the wing and causes parasite drag. This parasite drag counteracts the induced drag produced on the
opposite wing when its aileron is lowered. Frise ailerons minimize adverse yaw.
front (meteorology). A surface, interface, or transition zone of discontinuity between two adjacent air
masses having different densities. More simply, a front is the boundary between two different air masses.
frontal zone (meteorology). A front or zone with a marked increase-of-density gradient. The term frontal
zone is used because fronts are not truly a ‘surface’ of discontinuity, but, rather, a ‘zone’ of rapid transition
　
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