Core engine.  The gas generator portion of a turboshaft,  turboprop, or turbofan engine. The core engine consists of the  portion of the compressor used to supply air for the engine  operation, diffuser, combustors, and turbine(s) used to drive  the compressor. The core engine provides the high-velocity  gas to drive the fan and/or any free turbines that provide  power for propellers, rotors, pumps, or generators. Compressor pressure ratio.  See compression ratio (turbine  engine). Compressor stall.  A condition in a turbine engine axial-flow  compressor in which the angle of attack of one or more blades  is excessive and the smooth airflow through the compressor  is disrupted. Compressor surge.  A stall that affects the entire compressor  and seriously restricts the airflow through the engine. Con-di ducts.  The British name for a convergent-divergent  duct. See convergent-divergent duct. Condenser.  See capacitor. Cowling.  The removable cover that encloses an aircraft  engine. Crankcase.  The housing that encloses the crankshaft,  camshaft, and many of the accessory drive gears of a  reciprocating engine. The cylinders are mounted on the  crankcase, and the engine attaches to the airframe by the  crankcase. Crankshaft.  The central component of a reciprocating  engine. This high-strength alloy steel shaft has hardened  and polished bearing surfaces that ride in bearings in the  crankcase. Offset throws, formed on the crankshaft, have  ground and polished surfaces on which the connecting rods  ride. The connecting rods change the in-and-out motion of  the pistons into rotation of the crankshaft. “Contact.”  The term used between a person hand-propping  an aircraft engine and the person in the flightdeck. When the  person is ready to spin the propeller, he calls “contact”. The  person in the flightdeck turns on the fuel, slightly opens the  throttle, applies the brakes, and replies “contact”, and then  turns the ignition switch to BOTH. The propeller is then  pulled through to start the engine. Constant-displacement pump.  A fluid pump that moves a  specific volume of fluid each time it rotates. Constant-pressure cycle of energy release.  The cycle of  energy transformation of a gas turbine engine. See Brayton  cycle. Constant-volume cycle of energy release.  The cycle of  energy transformation of a reciprocating engine. See Otto  cycle. Creep.  The deformation of a metal part that is continually  exposed to high centrifugal loads and temperatures. Critical altitude.  The altitude above which a reciprocating  engine will no longer produce its rated horsepower with its  throttle wide open. Critical engine.  The engine of a twin-engine airplane whose  loss would cause the greatest yawing effect. Critical Match number.  The flight match number at which  there is the first indication of air flowing over any part of the  structure at a speed of Mach one, the local speed of sound. Continuous magnetic particle inspection.  A method of  magnetic particle inspection in which the part is inspected  by flowing a fluid containing particles of iron oxide over the  part while the magnetizing current is flowing. Contrarotating.  Rotating in opposite directions. Turbine  rotors are contrarotating when the different stages have a  common center, but turn in opposite directions. CRT.  Cathode ray tube. An electronic display tube in which  a stream of electrons is attracted to the charged inner surface  of the tube face. Acceleration grids and inner surface of the  tube face. Acceleration grids and focusing grids speed the  movement of the electrons and shape the beam to a pin- point size. Electrostatic or electromagnetic forces caused by  deflection plates or coils move the beam over the face of the  tube. The inside of the tube face is treated with a phosphor  material that emits light when the electrons strike it. Convergent-divergent duct.  A duct that has a decreasing  cross section in the direction of flow (convergent) until a  minimum area is reached. After this point, the cross section  increases (divergent). Convergent-divergent ducts are called  CD ducts or con-di ducts. Convergent duct.  A duct that has a decreasing cross section  in the direction of flow. Cryogenic fluid.  A liquid which boils at a temperature  lower than about 110 ºK (-163 ºC) under normal atmospheric  pressure.  G-8