shock stall (high-speed aerodynamics). A type of stall that affects some airplanes as they fly in the transonic speed range. In the transonic range, some air flowing over the aircraft surface is moving faster than the speed of sound, while other air is moving at a speed slower than the speed of sound.
When a shock wave forms on the upper surface of a wing, it gets in the way of the air flowing behind it, and this air breaks away from the wing surface. The shock wave causes the wing to stall. Shock stalls can cause control problems as an airplane is passing from subsonic flight into supersonic flight.
shock strut. See shock absorber.
shock wave. A pressure wave formed in the air as an object, such as a flight vehicle, passes through the air at a speed greater than the speed at which sound can travel. As the vehicle moves through the air, it creates disturbances, and sound waves spread out in all directions from the disturbance. Since the vehicle is flying faster than the sound waves are moving, they build up and form a shock wave at the front and the rear of the vehicle.
As air passes through a shock wave, it slows down and its static pressure increases. The energy in the air is decreased. See oblique shock wave and normal shock wave.

shop head (rivet head). The head of a solid rivet which is formed when the shank is upset.

Shore Scleroscope. A form of hardness tester used to determine the hardness of such material such as rubber, metal, or plastic. A metal weight is dropped through a glass tube onto the surface of the material being tested, and the height of the rebound of the weight is measured. The harder the material, the higher the weight will bounce.
short circuit (electrical circuit). An electrical circuit in which there is a fault that causes electrons to flow across a portion of the circuit that should act as an insulator. The electrons find a short path to ground. Fuses and circuit breakers protect the circuit from damage that could be caused by excess current flowing through a short circuit.
shorting switch. A type of make-before-break switch. A make-before-break switch is a multipole switch in which one circuit is completed before another circuit is opened. A shorting switch is used in circuits that must never operate, even for a microsecond, without an electrical load being connected.
short stacks (reciprocating engine exhaust system). The exhaust system of an aircraft reciprocating engine made of short pipes that direct the exhaust gases from each individual cylinder of the engine away from the aircraft.
short wave (radio waves). Waves of electromagnetic radiation that are shorter than 60 meters, or about 197 feet. The frequencies used for short-wave radio communications are above about five megahertz.