step taxi (float plane operation). To taxi a float plane at full power or high RPM.
step turn (float plane operation). A maneuver used to put a float plane in a planing configuration prior to entering an active sea lane for takeoff.
step-up transformer (electrical transformer). A type of electrical transformer with more turns in the secondary winding than in the primary. The secondary voltage of a step-up transformer is higher than the primary voltage, but the secondary current is less than the primary current.
stiffener (sheet metal structural component). A piece of formed sheet metal or extrusion riveted to a larger piece of thin sheet metal to give it rigidity and stiffness. Some types of aircraft sheet metal structure have large areas of thin sheet metal that vibrate and cause noise and weaken the metal. To prevent this metal from vibrating, a stiffener in the shape of a hat section, a channel, or an angle is riveted across the sheet. This stiffens it enough to stop the vibration.
Stoddard solvent. A petroleum product, similar to naphtha, used as a solvent and a cleaning fluid.
stoichiometric mixture (heat engine fuel-air mixture). The ratio of the mixture of fuel and air that, when burned in a heat engine, leaves no uncombined oxygen nor free carbon. A stoichiometric mixture of gasoline and air contains one pound of gasoline and 15 pounds of air.
STOL (Short TakeOff and Landing). STOL performance of an aircraft is the ability of the aircraft to take off and clear a 50-foot obstruction in a distance of 1,500 feet from the beginning the takeoff run. It must also be able to stop within 1,500 feet after crossing over a 50-foot obstacle on landing.
“Stop altitude squawk” (air traffic control). A phrase used by ATC to inform a pilot to turn off the automatic altitude reporting feature of his transponder. This phrase is used when the verbally reported altitude varies 300 feet or more from the automatic altitude report.
stop countersink (sheet metal tool). A cutting tool used to cut the chamfered holes into which flush rivet heads fit. The cutter, which is driven by a shaft mounted in a hand-held drill motor, fits through a bushing in the body of the stop unit and extends out beyond a fiber collar on the end of the body.
The body is made in two parts threaded together to allow the length of the body to be adjusted. The body length determines the amount the cutter protrudes, and this, in turn, controls the depth of the hole made by the cutter. A fiber collar prevents the stop scratching the soft metal being countersunk.
stop drilling (method of crack arresting). A method of stopping the growth of a crack in a piece of metal by drilling a small hole at the end of the crack. A crack in a piece of metal subject to vibration will continue to grow because of the stresses concentrated at its end in an extremely small area. Very little force acting on this tiny area will tear the metal.