Silicone rubber.  An elastomeric material made from silicone  elastomers. Silicone rubber is compatible with fluids that  attack other natural or synthetic rubbers. Slow-blow fuse.  An electrical fuse that allows a large amount  of current to flow for a short length of time but melts to open the  circuit if more than its rated current flows for a longer period. Single-acting actuator.  A linear hydraulic or pneumatic  actuator that uses fluid power for movement in one direction  and a spring force for its return. Smoke detector.  A device that warns the flight crew of the  presence of smoke in cargo and/or baggage compartments.  Some smoke detectors are of the visual type, others are  photoelectric or ionization devices. Single-action hand pump.  A hand-operated fluid pump  that moves fluid only during one stroke of the pump handle.  One stroke pulls the fluid into the pump and the other forces  the fluid out. Snubber.  A device in a hydraulic or pneumatic component that  absorbs shock and/or vibration. A snubber is installed in the line  to a hydraulic pressure gauge to prevent the pointer fluctuating. Softwood.  Wood from a tree that bears cones and has needles  rather than leaves. Single-disk brakes.  Aircraft brakes in which a single steel  disk rotates with the wheel between two brake-lining blocks.  When the brake is applied, the disk is clamped tightly  between the lining blocks, and the friction slows the aircraft. Soldering.  A method of thermally joining metal parts with  a molten nonferrous alloy that melts at a temperature below  800 °F. The molten alloy is pulled up between close-fitting  parts by capillary action. When the alloy cools and hardens,  it forms a strong, leak-proof connection. Single-servo brakes.  Brakes that uses the momentum of the  aircraft rolling forward to help apply the brakes by wedging  the brake shoe against the brake drum. Sintered metal.  A porous material made by fusing powdered  metal under heat and pressure. Skydrol hydraulic fluid.  The registered trade name for a  synthetic, nonflammable, phosphate ester-base hydraulic  fluid used in modern high-temperature hydraulic systems. Slat.  A secondary control on an aircraft that allows it to fly  at a high angle of attack without stalling. A slat is a section  of leading edge of wing mounted on curved tracks that move  into and out of the wing on rollers. Slip roll former.  A shop tool used to form large radius curves  on sheet metal. Slippage mark.  A paint mark extending across the edge of  an aircraft wheel onto a tube-type tire. When this mark is  broken, it indicates the tire has slipped on the wheel, and  there is a good reason to believe the tube has been damaged. Slipstream area.  For the purpose of rib stitch spacing,  the slipstream area is considered to be the diameter of the  propeller plus one wing rib on each side.  Slot (aerodynamic device).  A fixed, nozzle-like opening  near the leading edge of an airplane wing ahead of the aileron.  A slot acts as a duct to force high-energy air down on the  upper surface of the wing when the airplane is flying at a  high angle of attack. The slot, which is located ahead of the  aileron, causes the inboard portion of the wing to stall first,  allowing the aileron to remain effective throughout the stall. Speed brakes.  A secondary control of an airplane that  produces drag without causing a change in the pitch attitude  of the airplane. Speed brakes allow an airplane to make a  steep descent without building up excessive forward airspeed. Specific heat.  The number of BTUs of heat energy needed  to change the temperature of one pound of a substance 1 °F. Sonic venturi.  A sonic venturi in a line between a turbine  engine or turbocharger and a pressurization system. When  the air flowing through the sonic venturi reaches the speed  of sound, a shock wave forms across the throat of the sonic  venturi and limits the flow. A sonic venturi is also called a  flow limiter. Solution heat treatment.  A type of heat treatment in  which the metal is heated in a furnace until it has a uniform  temperature throughout. It is then removed and quenched in  cold water. When the metal is hot, the alloying elements enter  into a solid solution with the base metal to become part of its  basic structure. When the metal is quenched, these elements  are locked into place. Solidity (helicopter rotor characteristic).  The solidity of  a helicopter rotor system is the ratio of the total blade area  to the disc area. Solenoid.  An electrical component using a small amount of  current flowing through a coil to produce a magnetic force  that pulls an iron core into the center of the coil. The core  may be attached to a set of heavy-duty electrical contacts, or  it may be used to move a valve or other mechanical device.  G-32