safety wire. Soft wire used to secure fasteners (bolts, pins, and clips) so they will not vibrate loose in operation. Safety wire (also called lockwire) is made of galvanized low-carbon steel, annealed stainless steel, or brass.
sailplane (aircraft type). A high-performance glider. Sailplanes normally have a high-aspect-ratio wing, are lightweight, and very strong. Sailplanes glide so well that they ride upward on rising air currents. They can stay airborne for hours and can travel long distances.
Saint Elmo’s fire (meteorology). A discharge of static electricity often seen on airplanes flying through stormy weather. Static electricity from the clouds collects on the airplane structure and discharges from sharp points in the form of visible light.
sal ammoniac. A name commonly used for ammonium chloride. Ammonium chloride is one of the components of the moist-paste electrolyte used in carbon-zinc flashlight batteries.
salient pole (electrical machine). A field pole of an electrical generator or motor that has its own pole shoe protruding radially inward from the field frame. A field coil is wound around this pole shoe. Salient poles are often used instead of distributed poles which do not have separate pole shoes.
salt. A product of a chemical reaction in which a metal displaces the hydrogen in an acid. If sulfuric acid (H2SO4) reacts with sodium hydroxide (NaOH), sodium sulfate (Na2SO4) and water (H2O) are produced. Sodium sulfate is a salt. The food seasoning called “salt” is sodium chloride (NaCl).
samarium. A pale gray, rare-earth, metallic chemical element. Samarium’s symbol is Sm, its atomic number is 62, and its atomic weight is 150.35. Samarium is used in laser technology and as an ingredient in infrared-absorbing glass.
sandbag (sheet-metal-working tool). A heavy canvas or leather bag filled with sand. A sandbag is used to shape sheet metal parts by forming a depression in the sand and hammering the metal into it with a soft-face mallet.
sand casting (metal forming). A method of casting metal parts in a mold made of sand. A pattern that duplicates the part to be molded is made of wood and is covered with a special casting sand that contains a resin to bind it together.
The mold is separated along a special parting line, and the pattern is removed. The mold is put back together, and the cavity is poured full of molten metal. When the metal cools, the sand is broken away from the molded part. Sand casting is less expensive than permanent-mold casting.
sanding coat (finishing system). A coat of heavy-bodied surfacer material sprayed over a surface to be painted. After the sanding coat has thoroughly dried, it is sanded to give a smooth surface over which the subsequent coats of finishing material are applied.
sandpaper. An abrasive paper made by bonding grains of sharp sand to the surface of a piece of paper. Sandpaper is used for abrading (wearing away) rough surfaces or unwanted material.
sandwich construction. A type of laminated structure used where high strength, light weight, and rigidity are required. One commonly used type of sandwich construction is made of a fiberglass or metal honeycomb core bonded between two sheets of resin-impregnated fiberglass or metal.
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