shot peening (metal treatment). A method of strengthening the surface of a metal part by blasting it with steel shot. The blows from the steel shot produce a compressive stress on the surface of the metal which must be overcome by a tensile stress of a greater intensity before the tensile stress can cause the surface of the metal to crack.
shoulder bolt. A special type of fastener used to prevent damage to a structure that could be caused by squeezing the surfaces together when the nut is tightened on the bolt. The diameter of the shank is larger than the diameter of the threaded portion of the bolt. The length of a shoulder bolt is chosen so its shank is the same length as the thickness of the material being fastened together.
shoulder-wing airplane. A monoplane in which the wing is mounted near the top of the fuselage, but not on the top.
The classifications of a monoplane with regard to the placement of the wing are: low-wing, midwing, shoulder-wing, high-wing, and parasol-wing.
show. A term meaning to demonstrate, confirm, validate, or substantiate something. In legal documents it means to plead or allege. 14 CFR Part 1: “Unless the context otherwise requires, means to show to the satisfaction of the Administrator.”
shower (meteorology). Precipitation from a cumuliform cloud. Showers are characterized by the suddenness of beginning and ending, by the rapid change of intensity, and usually by the rapid change in the appearance of the sky. Showery precipitation may be in the form of rain, ice pellets, or snow.
Shower of Sparks ignition system (aircraft reciprocating engine ignition system). The registered trade name for a type of magneto ignition system. When the ignition switch in a Shower of Sparks ignition system is placed in the START position, the primary circuit of the right magneto is grounded, and pulsating direct current from a vibrator flows into the primary winding of the left magneto to ground through a set of retard breaker points. When the crankshaft turns far enough for the retard points to open, the pulsating DC in the primary winding induces a high voltage in the secondary winding of the left magneto. This high voltage causes the spark plugs connected to the left magneto to produce a “shower of sparks.”
show-type finish (aircraft finish). A type of finish put on some aircraft that are built for show. A show-type finish is usually made up of many coats of dope or lacquer, with much sanding and rubbing of the surface between coats.
shrink fit. An interference fit between pieces of an assembly. The hole into which a part is to fit is enlarged by heating it, and the piece to fit into the hole is shrunk by chilling it. The two pieces are assembled while their temperatures are different. Then, when they reach the same temperature, the fit is so tight no relative movement can take place between the parts.
shrinking blocks (sheet metalworking tool). A pair of wooden blocks used to clamp a sheet of metal to keep it from buckling when it is hammered with a mallet to shrink it.
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