Aviation Maintenance Terms beginning with C
Calendar month
The measurement of time used by the FAA for inspection and certification purposes. One calendar month from a given date extends from that date until midnight of the last day of that month.
Cam
An eccentric, or lobe, on a rotating shaft that changes rotary motion into linear motion. A cam is mounted on the magnet shaft in a magneto to push upward on the insulated breaker point to separate, or open, the points when the magnet is in a particular location.
Cam engine
A reciprocating engine with axial cylinders arranged around a central shaft. Rollers on the pistons in the cylinders press against a sinusoidal cam mounted on the shaft to produce rotation of the shaft.
Cam-ground piston
A reciprocating engine piston that is not round, but is ground so that its diameter parallel to the wrist pin is slightly smaller than its diameter perpendicular to the pin. The mass of metal used in the wrist pin boss, the enlarged area around the wrist pin hole, expands when heated, and when the piston is at its operating temperature, it is perfectly round.
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 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.
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.
Chordline
An imaginary line, passing through a propeller blade, joining the leading and trailing edges.
Cigarette
A commonly used name for a spark plug terminal connector used with a shielded spark plug.
Circular magnetism
A method of magnetizing a part for magnetic particle inspection. Current is passed through the part, and the lines of magnetic flux surround it. Circular magnetism makes it possible to detect faults that extend lengthwise through the part.
Circumferential coil spring (garter spring)
A coil spring formed into a ring. This type of spring is used to hold segmented ring-type carbon seals tightly against a rotating shaft.
Claret red
A dark purplish pink to a dark gray purplish red color.
Class A fire
A fire with solid combustible materials such as wood, paper, and cloth as its fuel.
Class B fire
A fire that has combustible liquids as its fuel.
Class C fire
A fire which involves energized electrical equipment.
Class D fire
A fire in which a metal such as magnesium burns.
Closed-loop control
A type of control in which part of the output is fed back to the input. This allows the input to continually compare the command signals with the output to determine the extent to which the commands have been complied with.
Coke
The solid carbon residue left when all volatile parts of a mineral oil have been evaporated by heat.
Cold section
The portion of a gas turbine engine ahead of the combustion section. The cold section includes the inlet, compressor, and diffuser.
Cold-cranking simulation
A method used for specifying the characteristics of a lubricating oil at low temperature. Oils rated by this test have the letter W (standing for Winter) in their designation. For example, SAE 15W50.
Cold-tank lubrication system
A turbine engine lubricating system in which the oil cooler is in the scavenge subsystem.
Collector ring
A ring made of thin corrosion-resistant steel tubing that encircles a radial engine and collects exhaust gases from each cylinder. The ring ends with a connection to the exhaust tail pipe.
Combustor (combustion chamber)
The section of a gas turbine engine in which fuel is injected. This fuel mixes with air from the compressor and burns. The intense heat from the combustion expands the air flowing through the combustor and directs it our through the turbine. Combustors are also called burners.
Commutator
A mechanical rectifier mounted on the armature shaft of a DC generator or motor. It consists of a cylindrical arrangement of insulated copper bars connected to the armature coils. Carbon brushes ride on the copper bars to carry current into or out of the commutator, providing a unidirectional current from a generator or a reversal of current in the motor coils.
Compensating winding
A series winding in a compound- wound DC generator. The compensating windings are embedded in the faces of the field poles and their varying magnetic field works with the fields from the interpoles to effectively cancel the field distortion caused by armature current.
Composite propeller blade
A propeller blade made from several materials such as metal, graphite, glass or aramid fibers, and foam.
Compression ratio (reciprocating engine)
The ratio of the volume of a cylinder of a reciprocating engine with the piston at the bottom of its stroke engine to the volume of the cylinder with the piston at the top of its stroke.
Compression ratio (turbine engine)
The ratio of the pressure of the air at the discharge of a turbine engine compressor to the pressure of the air at its inlet.
Compressor (air conditioning system component)
The component in a vapor-cycle cooling system in which the low- pressure refrigerant vapors, after they leave the evaporator, are compressed to increase both their temperature and pressure before they pass into the condenser. Some compressors are driven by electric motors, others by hydraulic motors and, in the case of most light airplanes, are belt driven from the engine.
Compressor bleed air
Air that is tapped off from a turbine engine compressor. Compressor bleed air is used for anti- icing the inlet ducts and for cooling the turbine inlet guide vanes and first stage turbine blades. Bleed air is also used for certain airframe functions. See customer bleed air.
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.
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.
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.
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.
Convergent duct
A duct that has a decreasing cross section in the direction of flow.
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.
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.
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.
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.
Cryogenic fluid
A liquid which boils at a temperature lower than about 110°K (-163°C) under normal atmospheric pressure.
Curtiss Jenny (Curtiss JN4-D)
A World War I training airplane powered by a Curtiss OX-5 engine. It was widely available after the war and helped introduce aviation to the general public.
Customer bleed air
Air that is tapped off a turbine engine compressor and used for such airframe functions as the operation of air conditioning and pressurization systems.
Cylinder
The component of a reciprocating engine which houses the piston, valves, and spark plugs and forms the combustion chamber.
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