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snow crystals. The grains are fairly flat or elongated with diameters generally less than 0.04 inch (1 mm).
snow pellets (meteorology). Precipitation consisting of white, opaque ice particles that are approximately
round or sometimes conical. The particles have a snow-like structure and are about 0.08 to 0.2 inch in
diameter. Snow pellets differ from snow grains in that they are crisp and easily crushed, and they rebound
from a hard surface and often break up.
snubber (fluid power system component). A component in a hydraulic or pneumatic actuator that slows
the motion of the actuator piston. The snubber absorbs the shock when the actuator piston reaches the end
of its travel.
snubber (instrument component). A restrictor fitting installed between an oil pressure gage and the
pressure pump. A snubber prevents the indicator pointer from fluctuating.
soak (metal heat treatment). The procedure in which metal being heat-treated is held in an oven at an
elevated temperature until it is heated uniformly throughout.
soap. A material used for cleaning or as an emulsifier. Soap is made by the chemical action between the
salt of a metal, such as sodium or potassium, and a fatty oil. Soap assists water in penetrating a film of
grease or dirt on a surface so it can be washed away.
SOAP (Spectrometric Oil Analysis Program). An oil analysis program in which a sample of oil is burned
in an electric arc and an examination is made of the wavelength composition of the resulting light. Each
chemical element in the oil, when burned, produces light containing a unique band of frequencies.
A computer analyzes the amount of each band of frequencies and prints out the number of parts of
the element per million parts of the entire sample. SOAP can predict engine problems by warning the
engine operator of an uncharacteristic increase in the amount of any of the elements in the oil.
soap bubble test. A type of test used to check for leaks in almost any kind of system in which a gas is held
under pressure. A soap solution is brushed over all areas of a pressurized system where a leak could occur,
and if there is a leak, the escaping gas will form bubbles in the soap film.
soapstone. A soft, grayish-white stone composed of talc and chlorite, a mineral similar to mica. Soapstone
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 537
has a slick, or soapy, feel that gives it its name.
soaring (aircraft flight). A type of flight in which the aircraft, usually a glider or sailplane, flies without
the use of engine power. The aircraft is normally pulled into the air with a powered airplane and, when
released, it glides down. The pilot circles in a column of rising air, and as long as the air is rising faster than
the aircraft is descending, the aircraft goes up in altitude. As soon as an altitude is reached where the air is
no longer rising, the pilot leaves that column and searches out another, to continue the flight.
socket-head bolt. A bolt with a socket, usually hexagon-shaped, formed in its head. A hexagon wrench
that fits into the socket is used to turn a socket-head bolt.
socket wrench. A type of wrench used to turn a nut or bolt. The socket is a small cylinder of high-strength
chrome-vanadium steel. One end of the cylinder has either a 6-point or 12-point opening that fits the nut or
bolt head. The other end has a square hole that fits the handle used to drive the socket. These drive holes
are usually 1/4-inch, 3/8-inch, 1/2-inch, or 3/4-inch square, depending on the size nut the socket is designed
to turn.
Ratchet handles, breakover handles, and speed handles can be used to drive the socket. Extensions
of various lengths, and universal joints may be used between the socket and the drive handle to allow the
socket to fit squarely on the nut and be turned by the handle.
sodium. A soft, light, malleable, ductile, silvery-white, metallic chemical element that has a waxy feel.
Sodium’s symbol is Na, its atomic number is 11, and its atomic weight is 22.9898. Sodium is in the alkaline
metal group and is extremely active, combining readily with other chemical elements.
Pure sodium metal combines instantly with oxygen when it is exposed to air, and it causes water
to decompose with a violent reaction. Because of this, sodium metal must be kept covered with kerosine.
sodium bicarbonate. A white, powdery salt of sodium. When mixed with water, sodium bicarbonate forms
a weak alkaline solution. Sodium bicarbonate is useful for neutralizing spilled battery acid and as a fire
extinguishing agent. When sodium bicarbonate is heated, it releases carbon dioxide that smothers the fire.
Other names for sodium bicarbonate are baking soda and saleratus.
sodium-filled exhaust valve (reciprocating engine component). A hollow exhaust valve that is partially
　
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