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When maximum current flows in the control winding, its magnetic field saturates the core with a
steady magnetic flux. This flux decreases the permeability of the core so much that the changing flux
caused by the secondary current does not affect the core. There is less inductive reactance, so the secondary
current has less opposition, and it increases.
saturate (meteorology). To combine to such an extent that there is no more tendency to combine. Dry air
absorbs water vapor. But when the air becomes saturated, it will not absorb anymore. The amount of water
the air can hold before becoming saturated depends upon its temperature.
saturated adiabatic lapse rate (meteorology). The rate of decrease of temperature with altitude as
saturated air is lifted with no gain or loss of heat from outside sources. The saturated adiabatic lapse rate
varies with temperature, being greatest at low temperature.
saturated vapor. The condition of the vapor above a liquid that will not allow any more of the liquid to
evaporate.
saturation (meteorology). The condition of the atmosphere when the actual water vapor present in the air
is the maximum the air can hold at the existing temperature.
saturation current (electron control current). The plate current flowing in an electron tube circuit when
all of the electrons emitted from the cathode are attracted to the plate. In a transistor circuit, saturation
current is the current flowing between the emitter and collector when an increase in the forward bias
between the base and emitter causes no further increase in the emitter-collector current.
sawtooth waveform. The waveform of voltage produced by a relaxation oscillator. The voltage across the
capacitor in a relaxation oscillator rises relatively slowly because it flows through the series resistor. But,
when the voltage rises to the ionization potential of the gas discharge tube, the tube fires and the voltage
across the capacitor drops off immediately.
The slow rise and rapid fall produce a sawtooth-shaped voltage wave. See relaxation oscillator.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 503
“Say again” (air traffic control). A phrase used by ATC to request a repeat of the last transmission. This
usually specifies the transmission or the portion that was not understood or received, such as “Say again all
after Abram VOR.”
“Say altitude” (air traffic control). A phrase used by ATC to ascertain an aircraft’s specific altitude or
flight level. When the aircraft is climbing or descending, the pilot should state the indicated altitude
rounded off to the nearest 100 feet.
Saybolt universal viscosity. A measure of the viscosity (resistance to flow) of a lubricating oil. The
number of seconds needed for 60 milliliters of the liquid, at a specified temperature, to flow through a
calibrated orifice is measured and is called the Saybolt Seconds Universal (SSU) viscosity of the liquid.
The viscosity number used for commercial aviation engine lubricating oil relates closely to the
SSU of the oil at 210°F. Aviation 80 engine oil has an SSU viscosity at 210°F of 79.2, and Aviation 100 oil
has an SSU viscosity of 103.0 at the same temperature.
“Say heading” (air traffic control). A phrase used by ATC to request an aircraft heading. The pilot should
state the actual heading of the aircraft.
S-band radar. Radar that operates in the frequency band between 1,550 and 5,200 megahertz. In this
frequency band, the wavelengths are between 19.35 and 5.77 centimeters.
scale model. A copy of something made in the same proportions as the original, but of a smaller size.
When an airplane is designed, a scale model is built and tested in a wind tunnel. The model has the same
shape as the actual aircraft, but it is much smaller. It is a scaled-down copy of the real thing.
scalene triangle. A closed, three-sided, plane (flat) figure that has no two sides of the same length, nor are
any of the angles the same.
scandium. A silvery-white, very lightweight, rare-earth, metallic chemical element. Scandium’s symbol is
Sc, its atomic number is 21, and its atomic weight is 44.956. A radioactive isotope of scandium is used in
petroleum exploration.
scarfed patch. A type of patch made to a thin plywood structure. The damaged area is cleaned out and the
edges of the hole tapered, with the length of the taper about 12 times the thickness of the plywood.
Temporary backing blocks support the area while the patch is glued in place. A scarfed patch is the most
difficult to make, but it is the preferred patch for aircraft plywood skins.
scarf joint (woodworking). A joint in a wood structure in which the ends to be joined are cut in a long
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航空术语词典Dictionary of Aeronautical Terms 下(35)
