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lower layer, and no sky cover can be greater than 1.0 (10/10).
summerwood. The less porous, usually harder portion of an annual ring that forms in a tree during the
latter part of the growing season, the summer of the year.
sump (aircraft engine component). A low point in an aircraft engine in which lubricating oil collects and
is stored or transferred to an external oil tank. A removable sump attached to the bottom of the crankcase of
a reciprocating engine is often called an oil pan.
sump (fuel tank component). A low point in an aircraft fuel tank in which water and other contaminants
collect and are held until they can be drained out.
sump jar (aircraft battery installation component). A small jar located in the vent line of an aircraft
battery box. The sump jar used in a lead-acid battery installation contains a sponge saturated with a solution
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 563
of bicarbonate of soda and water. Acid fumes from the battery pass through the sump jar where they are
neutralized to prevent their causing corrosion in the aircraft structure.
The sump jar in a nickel-cadmium battery installation contains a boric acid solution to neutralize
the alkaline fumes from this battery.
superadiabatic lapse rate (meteorology). A lapse rate greater than the dry-adiabatic lapse rate, greater
than 3°F per thousand feet.
supercharged engine. A reciprocating engine that uses an air compressor to increase the pressure of the air
before it enters the engine cylinders.
supercharger (reciprocating engine component). An air pump used to increase the pressure of the air
taken into the cylinders of a reciprocating engine. The amount of power a reciprocating engine can develop
is determined by the mass, or weight, of the fuel-air mixture taken into the cylinders. By compressing the
air before it enters the cylinders, a greater mass of air can be used, and more power can be developed by the
engine.
Superchargers can be gear-driven from the engine, or they can be driven by a turbine spun by
exhaust gases. Superchargers driven by exhaust gases are called turbochargers or turbosuperchargers.
superconductivity. A condition of certain chemical elements (niobium, tantalum, vanadium, tin, and others)
when they are held at a temperature near absolute zero. At this low temperature, these metals lose almost
all their electrical resistance and become strongly diamagnetic. They try to orient themselves across a
magnetic field, rather than aligning with the field.
supercooled water. Water in its liquid form at a temperature well below its natural freezing temperature.
When supercooled water is disturbed, it immediately freezes.
supercritical airfoil (aerodynamics). An airfoil section that allows an airplane to cruise efficiently at a
speed very near Mach one (the speed of sound). The center portion of the airfoil is nearly flat, and there is a
distinct downward curve, or cusp, near the trailing edge. The lower side of the forward part of the airfoil is
more curved than the upper side.
superheat (refrigeration system). Heat energy added to a refrigerant after it changes from its liquid state
into a vapor. The thermal expansion valve in a refrigeration system meters just enough liquid refrigerant
into the evaporator for all of it to be changed from droplets of liquid into a vapor by the time it reaches the
end of the evaporator coils. If all of the refrigerant vaporizes before it reaches the end of the coils, any
additional heat raises its temperature. This additional heat is called superheat.
superheated water. Water that has been heated to a temperature above that at which it normally changes
its state from liquid into steam. Water may be superheated by holding it under pressure. More heat energy
must be added to it before its molecules move fast enough to leave the surface of the liquid and become
steam.
superheterodyne radio receiver circuit. The type of circuit used in most modern radio receivers. A
radio-frequency signal is received, amplified, and mixed with a signal produced inside the radio by a local
oscillator. The frequency of the oscillator signal is always a fixed amount different from the
radio-frequency signals being received.
When the two signals are mixed, two more signals are produced. The frequency of one is the sum
of the other two, and the frequency of the other is the difference between them. The signal whose frequency
is the difference is called an intermediate frequency, an IF. The IF is amplified and changed into an
audio-frequency voltage that duplicates the AF used to modulate the radio-frequency signal in the
transmitter.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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