the Aviation Dictionary

selection-type test items . semi-monocoque
selection-type test items - Questions where the student
chooses from two or more alternatives provided. Truefalse,
matching, and multiple-choice type questions are
examples of selection-type test items.
selective call system (SELCAL) - A system that
permits the selective calling of individual aircraft over
radiotelephone channels linking a ground station with
the aircraft.
selective plating - A process of electroplating only a
section of a metal part.
selectivity - The ability to select or choose from among
several choices.
selector switch - A multi-pole switch that takes the
place of several switches. It is used to connect a single
conductor to one of several other conductors.
selector valve - A hydraulic flow control valve that
directs hydraulic pressure to one side of an actuator and
connects the other side to the system return line.
selenium - A chemical element in the sulfur family with
a symbol of Se and an atomic number of 34. Used in
photoelectric devices because it changes its
conductivity with a change in temperature.
selenium rectifier - A rectifier using laminated plates of
metal, usually iron, that have been coated with
selenium on one side. It is designed to develop a
unidirectional current-carrying characteristic. The flow
of electrons from the conductive metal to the selenium
occurs more readily than the flow in the opposite
. direction.
self concept - A perception factor that ties together how
people feel about themselves with how well they will
receive further experiences.
self-accelerating - The ability of a turbine engine to
produce enough
-.
power to accelerate.
self-aligning bearing - A rod end bearing consisting of
a ball fitted into a socket that maintains alignment
between the operating control and the unit- being
controlled.
self-centering - chuck - A drill motor chuck with
interconnecting jaws. They move at the same time to
hold a drill bit when loosening or tightening.
self-concept - A perception factor that ties together how
people feel about themselves with how well they will
receive further experiences.
self-demagnetization - The process in which a magnet
loses its magnetism if allowed to sit for long periods
- -
without a keeper bar.
self-excited generator - A generator whose field
excitation is taken directly from the armature rather
than from an outside source. A self-excited DC
generator depends on residual magnetism. Without
residual magnetism, it would be impossible to start a
self-excited generator once stopped.
self-extinguishing - The ability of a material to
automatically stop burning as soon as the outside
source of the flame is remo;ed.
self-fulfdment needs - Occupy the highest level of
Maslow's pyramid. They include realizing one's own
potential for continued development, and for being
creative in the broadest sense. Maslow included
various cognitive and aesthetic goals in this echelon.
self-healing capacitor - In electronics, an electrolytic
capacitor that restores the dielectric film if it is
damaged by over-voltage.
self-induction - The generation of back voltage in a
conductor. This occurs when lines of flux created by
the AC current in the conductor alternately expand and
contract across the conductor. The moving lines of flux
create a back voltage opposite in direction to the
original voltage.
self-launch glider - A glider equipped with an engine,
allowing it to be launched under its own power. When
the engine is shut down, a self-launch glider displays
the same characteristics as a non-powered glider.
self-locking nut - A nut designed with a built-in locking
device that grips the threads of a bolt when the nut is
tightened. This prevents the nut from loosening
because of vibration. Locking devices can be fiber or
non-fiber depending on their intended purpose.
self-tapping screw - A wood or metal screw that cuts its
own threads as it is screwed into sheet metal or wood.
Selsyn system - A DC-type of synchro remote indicator
system.
selvage edge - A manufactured woven edge on fabric
that runs the length of the fabric or in the warp
direction. It is removed for all fabrication and repair
work.
semi - A prefix meaning a half or part of something.
semiautomatic operation -A device that is partially
automatic and partially manual in its operation.
semi-cantilever - An externally braced wing.
semicircular - In the form of a half circle.
semiconductor - An insulating material treated with
certain impurities that add free electrons to act as
current carriers, carrying the flow of current in one
direction and blocking it in the other.
semiconductor diodes - A semiconductor type of
electron check valve. A device that allows the flow of
electrons in one direction but not the opposite.
semi-monocoque - A stressed-skin structure in which
the skin is supported by a lightweight framework to
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