supplement of an angle. One hundred and eighty degrees minus the angle. Thirty degrees is the supplement of 150°.
suppressor grid (electron tube component). The grid in a pentode vacuum tube used to suppress secondary emission from the plate of the tube.
surface corrosion. Corrosion that forms on the surface of a piece of metal covered with some form of electrolyte. Surface corrosion shows up as pits filled with a powdery salt.
surface inversion (meteorology). A temperature inversion with its base at the surface. Surface inversions are often caused by the air near the surface being cooled by terrestrial radiation, especially at night.
surface roughness (cylinder wall condition). The condition of the surface of a reciprocating engine cylinder wall that has been honed to make it hold lubricating oil. Surface roughness is measured in microinches rms (μin rms).
surface tape (aircraft fabric material). Strips of aircraft fabric that are doped over all seams and all places where the fabric is stitched to the aircraft structure and over wing leading edges where abrasive wear occurs. The edges of surface tape are pinked, or notched, to keep them from raveling before the dope is applied.
surface tension. The cohesive force that causes molecules of a liquid to hold themselves together. Surface tension tries to keep the area of the surface of the liquid as small as possible. It is surface tension that causes a soap bubble to be shaped like a sphere, since a sphere has the smallest surface area possible for its volume.
surface visibility (meteorology). Visibility observed from eye-level above the ground.
surfactant (fuel system contaminant). A surface active agent, or partially soluble contaminant which is a by-product of fuel processing or of fuel additives. Surfactants adhere to other contaminants and cause them to drop out of the fuel and settle to the bottom of the fuel tank as sludge.
surge. A condition of unstable airflow through the compressor of a gas turbine engine in which the compressor blades have an excessive angle of attack. Surge normally affects an entire stage of compression.
surveillance approach (air traffic control). An instrument approach in which the air traffic controller issues instruction, for pilot compliance, based on the aircraft position relative to the final approach course (azimuth) and the distance (range) from the end of the runway as displayed on the controller’s radar scope. The controller will provide recommended altitudes on final approach if requested by the pilot.
swaged fitting (fluid line fitting). A nonreusable fitting installed on a flexible hose by forcing the material of the fitting into the hose. Swaged fittings are also installed on rigid fluid lines used in high-pressure hydraulic and pneumatic systems.
swaged terminal (control cable terminal). A terminal pressed onto a steel control cable. A swaged terminal is made in the form of a cylinder into which the steel cable is slipped. This steel cylinder is then swaged (hammered into) the cable with special swaging dies.