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their jigs and joined together to form a single unit.
assembly drawing. An aircraft drawing which shows a group of parts laid out in the relationship they will
have when they are assembled.
assembly line (aircraft manufacturing). An arrangement of work stations in an aircraft factory that
allows a certain function to be performed on all aircraft at a particular physical location.
Special tools and specially trained personnel stay in one location, and each aircraft is moved to
this location for the function to be performed.
assigned frequency (radio communications). The frequency of the carrier signal produced by a radio
transmitter.
This carrier frequency is assigned by the Federal Communications Commission (FCC) for the
particular transmitter or the particular type of transmission.
astable. Not stable; “a” means not. An astable electronic device has two conditions of temporary stability,
but no condition of permanent stability.
astable multivibrator. An electronic oscillator that has no stable condition. Astable multivibrators, also
called free-running multivibrators, contain two devices such as transistors to control the flow of electrons.
When one transistor is conducting, the other is not conducting. The two transistors alternate between
conditions of conducting and not conducting.
astatine. A highly unstable radioactive chemical element. Astatine’s symbol is At, and its atomic number is
85. Astatine is the heaviest of the halogen elements.
astern. A location or direction measured from an aircraft.
Astern means to the rear of, or behind. This term comes from “stern,” which is the aft, or rear part,
of a ship.
ASTM (American Society for Testing Materials). An organization which sets various standards, called
ASTM standards, used in the aircraft industry.
astrocompass. A navigational instrument that determines direction relative to the stars. Astrocompasses
are not affected by the errors inherent in magnetic compasses and gyrocompasses.
astrodome. A transparent hemispherical dome in the upper skin of an aircraft, over or near the navigator’s
station. The navigator uses the astrodome to make observations of the sun or stars when navigating by
celestial navigation.
astronaut. A person who travels beyond the earth’s atmosphere.
astronautics. The branch of science that deals with space flight. Astronautics includes the design,
construction, and operation of space vehicles and their related support equipment and activities.
astronomical twilight. The period of time before sunrise and after sunset when the sun is not more than
18° below the horizon.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 48
astronomical unit. A unit for measuring distance in astronomy. One astronomical unit is the average
distance between the earth and the sun. This is approximately 93 million miles.
astrophysics. The branch of science which deals with the physical characteristics of the heavenly bodies.
These characteristics include their mass, density, temperature, size, luminosity, and origin.
ASU (altitude sensing unit — turbine engine fuel control). A subsystem in a turbine engine fuel control
that regulates the fuel scheduling as a function of altitude changes.
asymmetrical. A condition of a body in which its shape is not the same on both sides of its center line.
asymmetrical airfoil. An airfoil section that is not the same on both sides of the chord line.
Asymmetrical airfoils are the most commonly used type for fixed-wing aircraft, but because the
location of the center of pressure changes as the angle of attack changes, they are seldom used for
rotary-wing aircraft.
asymmetrical lift (helicopter flight). A condition of uneven lift produced by the rotor system of a
helicopter when it is in forward flight.
When a helicopter is hovering in still air, the lift is uniform across its rotor disk. But when it is
moving in flight, the blade traveling in the same direction as the helicopter, the advancing blade, has a
speed equal to its own speed plus the speed of the helicopter. The blade on the other side, the retreating
blade, has a speed equal to its own speed minus the speed of the helicopter.
Since the amount of aerodynamic lift is determined by airspeed, the difference between the
airspeed over the rotor blades on the two sides of the helicopter causes the lift on the side of the advancing
blade to be greater than the lift produced by the retreating blade.
asymmetrical loading (propeller thrust). The loading of a propeller disk in such a way that one side
produces more thrust than the other side.
asymptote (mathematics). A curve that comes nearer and nearer to a given line without ever touching it.
　
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