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zero.
analog electronics. Electronics in which values change in a linear fashion.
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Output values vary in direct relationship to changes of input values.
analog indicator. An indicator that shows the value of the parameter being measured by the amount a
pointer moves across a numerical scale.
analog-to-digital conversion. The conversion that changes analog information into a digital form.
Analog-to-digital conversion is done with an analog-to-digital (A-to-D) converter, which changes the
varying values of an analog signal into combinations of conditions that are either on or off. The digital
values can be processed in a digital computer.
anchor light. A white light shown at night on a seaplane, ship, or boat when the vessel is anchored.
anchor nut (aircraft hardware). A nut riveted or welded to a structure in such a way that a screw or bolt
can be screwed into it. An anchor nut does not need to be held with a wrench to keep it from turning.
AND gate. A logic device in which the logic condition (zero or one) of its single output is one only when
the conditions of all of its inputs are logic one.
anechoic room (radar test facility). A special room whose walls are covered with radar absorbing
materials. Anechoic rooms are used for testing radar components in an environment in which there are no
echoes.
anemometer. An instrument used to measure the velocity of moving air. A cup-type anemometer uses a
series of hemispherical metal cups mounted on arms on a shaft. The air blows the cups and rotates the shaft.
A counter measures the number of revolutions the shaft makes in a given period of time and converts this
into wind speed.
A fan-type anemometer uses a small, multibladed propeller, turned by the air moving through it.
The faster the air flows, the faster the fan turns.
The dial on the anemometer may be marked in feet per second, meters per second, kilometers per
hour, miles per hour, or knots.
aneroid. The sensitive component in an altimeter or barometer that measures the absolute pressure of the
air. An aneroid is a sealed, flat capsule made of thin disks of corrugated metal soldered together and
evacuated by pumping all of the air out of it.
Evacuating the aneroid allows it to expand or collapse as the air pressure on the outside changes.
The pressure of the air can be found by measuring the amount the aneroid expands or collapses.
aneroid barometer. An instrument that measures the absolute pressure of the atmosphere by balancing the
weight of the air above it against the spring action of a specially shaped evacuated metal bellows.
AN flared tube fittings. A series of flare-type fittings for fluid lines installed in an aircraft. AN fittings
have a 37° flare angle and a short shoulder between the ends of the flare cone and the first thread.
angel (radar meteorology). An echo caused by a physical phenomenon that is not necessarily discernible
to the eye. Angels may be observed when abnormally strong temperature and/or moisture gradients exist,
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and they are sometimes attributed to insects or birds flying in the radar beam.
angle. The plane figure formed when two lines extend from the same point. A right angle has 90° between
the lines.
angle drill. A type of drilling tool in which a twist drill is held in a chuck mounted at an angle to the
spindle of the drill motor. Angle drills are often used in aircraft sheet metal work to drill holes in locations
where a normal drill cannot be used.
angle of arrival (radio propagation). The angle, measured at the receiving antenna, between the line of
propagation of a radio wave and the surface of the earth.
angle of attack (α). The acute angle formed between the chord line of an airfoil and the direction of the air
that strikes the airfoil.
angle of attack (gas turbine engine compressor). The acute angle formed between the chord line of the
compressor blades and the direction the air strikes the blades. This angle of attack is affected by both the
velocity of the air flowing through the compressor and the RPM of the compressor.
If the RPM of the compressor is too high for the velocity of the air flowing through the engine, the
angle of attack will be excessively high, and the compressor blades can stall.
angle of attack (propeller). The acute angle between the chord line of a propeller blade and the relative
wind.
The angle of attack is affected by both the engine RPM and the forward speed of the aircraft.
angle of attack indicator (aircraft flight instrument). An instrument that measures the angle between the
　
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