Can-annular combustor . A type of combustor used in some large turbojet and turbofan engines. It consists of individual cans into which fuel is sprayed and ignited. These cans mount on an annular duct which collects the hot gases and directs them uniformly into the turbine.

Capacitance afterfiring . The continuation of the spark across the gap in a shielded spark plug after the air/fuel mixture in the cylinder is ignited. Afterfiring is caused by the return of electrical energy stored in the capacitance of the shielded ignition leads. Capacitance afterfiring is eliminated by the use of a resistor in the spark plug.

Capacitor . An electrical component, formerly called a condenser, that consists of two large-area conductors, called plates, separated by an insulator. Electrons stored on one of the plates produces an electrostatic pressure difference between the plates.

Capillary tube . A glass or metal tube with a tiny inside diameter. Capillary action causes the fluid to move within the tube.

Carbon pile voltage regulator . A voltage regulator for a high output DC generator that uses a stack of pure carbon discs for the variable resistance element. A spring holds pressure on the stack to reduce its resistance when the generator output voltage is low. This allows maximum field current to flow. The field from an electro-magnet, whose strength varies directly with the generator voltage, opposes the spring to loosen the stack and increase its resistance when the generator voltage needs to be decreased. The increased resistance decreases the field current and reduces the output voltage.

Carbon track . A trail of carbon deposited by an arc across a high-voltage component such as a distributor block. Carbon tracks have a relatively low resistance to the high voltage and can cause misfiring and loss of engine power.

Cartridge starter . A self-contained starter used on some military aircraft. A cartridge similar in size to a shotgun shell is ignited in the starter breech. The expanding gases drive a piston attached to a helical spline that converts the linear movement of the piston into rotary motion to rotate the crankshaft.

Cascade effect . The cumulative effect that occurs when the output of one series of components serves as the input to the next series.

Catalyst . A substance used to change the speed, or rate, of a chemical action without being chemically changed itself.

Cavitating . The creation of low pressure in an oil pump when the inlet system is not able to supply all of the oil the pump requires. Prolonged cavitation can damage pump components.

Center of pressure . The point on the chordline of an airfoil where all aerodynamic forces are concentrated.

Center-line thrust airplane . A twin-engine airplane with both engines mounted in the fuselage. One is installed as a tractor in the front of the cabin. The empennage is mounted on booms.

Centrifugal compressor . A type of compressor that uses a vaned plate like impeller. Air is taken into the center, or eye, of the impeller and slung outward by centrifugal force into a diffuser where its velocity is decreased and its pressure increased.

Ceramic . Any of several hard, brittle, heat-resistant, noncorrosive materials made by shaping and then firing a mineral, such as clay, at a high temperature.

Channel-chromed cylinders . Reciprocating engine cylinders with hard chromium-plated walls. The surface of this chrome plating forms a spider web of tiny stress cracks. Deplating current enlarges the cracks and forms channels that hold lubricating oil on the cylinder wall.

Cheek (crankshaft ). The offset portion of a crankshaft that connects the crankpin to the main bearing journals.

Chip detector . A component in a lubrication system that attracts and holds ferrous metal chips circulating with the engine oil. Some chip detectors are part of an electrical circuit. When metal particles short across the two contacts in the detector, the circuit is completed, and an annunciator light is turned on to inform the flight crew that metal particles are loose in the lubrication system.

Choke of a cylinder . The difference in the bore diameter of a reciprocating engine cylinder in the area of the head and in the center of the barrel.

Choke-ground cylinder . A cylinder of a reciprocating engine that is ground so that its diameter at the top of the barrel is slightly smaller than the diameter in the center of the stroke. The large mass of metal in the cylinder head absorbs enough heat to cause the top end of the barrel to expand more than the rest of the barrel. At normal operating temperature, the diameter of a choke-ground cylinder is uniform throughout.

Choke nozzle . A nozzle in a gas turbine engine that limits the speed of gases flowing through it. The gases accelerate until they reach the speed of sound, and a normal shock wave forms that prevents further acceleration.