Standpipe.  A pipe which protrudes upward from the base  of an oil tank and through which oil used for normal engine  lubrication is drawn. In the event of a catastrophic leak when  all oil available to the engine-driven pump is lost overboard,  enough oil is available from an outlet below the standpipe to  feather the propeller. Spline.  Parallel slots cut in the periphery of a shaft, parallel to  its length. Matching slots, cut into the hub or wheel that fits  on the shaft, lock the shaft into the device to transmit torque. Sprag clutch.  A freewheeling, nonreversible clutch that allows  torque to be applied to a driven unit in one direction only. Springback.  A condition in the rigging of an aircraft engine  control in which the stop at the engine is reached before the  stop in the flightdeck. The flightdeck control moves slightly  after the stop in the engine is reached, and when it is released,  it springs back slightly. Starter-generator.  A single-component starter and generator  used on many smaller gas-turbine engines. It is used to start  the engine, and when the engine is running, its circuitry is  shifted so that it acts as a generator. Static pressure.  The pressure of an unmoving fluid. Spur-gear pump.  A form of constant-displacement fluid  pump that uses two meshing spur-gears mounted in a close  fitting housing. Fluid is taken into the housing where it fills  the space between the teeth of the gears and is carried around  the housing as the gears rotate. On the discharge side of the  pump, the teeth of the two gears mesh, and the fluid is forced  out of the pump. Static rpm.  The number of revolutions per minute an aircraft  engine can produce when the aircraft is not moving. Steam cooling.  A method of liquid cooling in which the  coolant, normally water, is allowed to absorb enough heat  that it boils. The steam gives up its heat when it condenses  back into a liquid. Squat switch.  An electrical switch actuated by the landing  gear scissors on the oleo strut. When no weight is on the  landing gear, the oleo piston is extended and the switch is in  one position; but when weight is on the gear, the oleo strut  compresses and the switch changes its position. Stellite.  A nonferrous alloy of cobalt, chromium, and  tungsten. Stellite is hard, water resistant, and corrosion  resistant, and it does not soften until its temperature is  extremely high. Stellite is welded to the faces of many  reciprocating engine exhaust valves that operate at very high  temperatures. Squealer tip (compressor blade tip).  See profile tip. Squeeze film bearings.  Another name for oil-damped  bearings. See oil-damped bearings. Stage length.  The distance between landing points in airline  operation. Stepping motor.  A precision electric motor whose output  shaft position is changed in steps by pulses from the control  device. Stepping motors can make high-torque changes in  small angular increments to their output shaft. Stage of a compressor.  One disk of rotor blades and the  following set of stator vanes in an axial-flow compressor. Stoichiometric mixture.  The fuel-air mixture ratio that,  when burned, leaves no uncombined oxygen nor any free  carbon. It releases the maximum amount of heat, and  therefore produces the highest exhaust gas temperature. A  stoichiometric mixture of gasoline and air contains 15 pounds  of air for 1 pound of gasoline. Staggered timing.  Ignition timing that causes the spark plug  nearest the exhaust valve to fire a few degrees of crankshaft  rotation before the spark plug nearest the intake valve. Straight-through combustor.  A combustor in a gas turbine  engine through which the air from the compressor to the  turbine flows in an essentially straight line. Stratosphere.  The upper part of the Earth’s atmosphere. The  stratosphere extends upward from the tropopause, which is  approximately 36,000 feet above the surface of the Earth, to  approximately 85,000 feet. The temperature of the air in the  stratosphere remains constant at -56.5 ºC (-69.7 ºF). Standard day conditions.  Conditions that have been decided  upon by the ICAO for comparing all aircraft and engine  performance. The most basic standard day conditions are:  temperature, 15 ºC or 59 ºF; altitude, mean sea level; pressure,  29.92 inches of mercury. Standard J-1.  A World War I training airplane powered by  a Curtiss OX-5 engine.  G-26