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in the transmitter and the indicator. These synchro motors have a three-phase stator and a single-phase rotor.
The stators and rotors of the transmitter and indicator are connected in parallel, and alternating current is
used to excite the rotors.
The AC exciting the rotor induces a voltage in the three phases of the transmitter stator, and since
the two stators are connected in parallel, the magnetic fields in the indicator are the same as those in the
transmitter. The magnetic fields in the indicator stator pull its rotor around so it assumes the same position
as the rotor in the transmitter. An Autosyn system is a form of synchro system. See Autosyn system.
synoptic chart (meteorology). A chart, such as a weather map, which shows the distribution of
meteorological conditions over an area at a given time.
synthetic oil. A type of engine lubricating oil made by chemical synthesis (changing) of a mineral-,
animal-, or vegetable-oil base. Synthetic oils have appropriate additives that give them such characteristics
as low volatility, low pour point, high viscosity index, good lubricating qualities, low coke and lacquer
formation, and low foaming.
Synthetic oils are superior to natural mineral oils because they resist oxidation better, and they are
able to be used over a wider range of operating temperatures. Synthetic oils are used in almost all gas
turbine engines and are used to some extent in reciprocating engines.
system pressure regulator (hydraulic power system component). A type of hydraulic system-pressure
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control valve. When the system pressure is low, as it is when some unit is being actuated, the output of the
constant-delivery pump is directed into the system. When the actuation is completed and the pressure
builds up to a specified kick-out pressure, the pressure regulator shifts. A check valve seals the system off
and the pressure is maintained by the accumulator. The pump is unloaded and its output is directed back
into the reservoir with very little opposition. The pump output pressure drops, but the volume of flow
remains the same. When the system pressure drops to the specified kick-in pressure, the regulator again
shifts and directs fluid into the system.
Spool-type and balanced-pressure-type system pressure regulators are completely automatic in
their operation and require no attention on the part of the flight crew. A system pressure regulator is also
called an unloading valve.
T
tab (auxiliary flight control). A small, movable control hinged to the trailing edge of one of an airplane’s
primary flight control surfaces. Tabs can be used to help the pilot move the primary control surface, or they
can be used to produce an aerodynamic load on the primary surface that trims the aircraft for a hands-off
flight condition. See antiservo tab, balance tab, servo tab, spring tab, trim tab.
TACAN (electronic navigation system). An electronic navigation system, operating in the ultrahigh
frequency (UHF) range. The name TACAN is an acronym for TACtical Air Navigation. TACAN is used
by military aircraft to give the pilot both the distance and direction from the transmitting stations on the
ground.
Civilian aircraft have equipment that use the TACAN ground facilities to show the distance to the
navigational fix. The equipment used in civilian aircraft is called DME (Distance Measuring Equipment).
tachometer. An instrument used to measure the rotational speed of an object. Tachometers are usually
calibrated in revolutions per minute, RPM, or percentage of the maximum rated RPM.
tachometer cable. The flexible drive used to connect the rotating magnet inside a tachometer indicator to
the tachometer drive gear inside an engine. A tachometer cable is made of a core of steel wire, around
which are wound two concentric coils of steel wire, wound in opposite directions.
tachometer generator. A small alternating current generator, mounted on and driven from the tachometer
drive pad on an engine. The frequency of the AC produced by the tachometer generator is proportional to
the speed of the engine.
tack coat (aircraft finishing system operation). A coat of finishing material sprayed on a surface and
allowed to dry until the solvents evaporate. As soon as the solvents evaporate from the tack coat, a wet,
full-bodied coat of the material is sprayed over it.
tackle. An arrangement of ropes and pulleys used to gain a mechanical advantage. Tackle is most
frequently spoken of as block and tackle.
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Page 568
tack rag (finishing system component). A clean, lintless rag, slightly damp with thinner. A tack rag is
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