Aviation Maintenance Terms beginning with C
Cable (electrical)
Assembly of one or more conductors within an enveloping protective sheath so constructed as to permit use of conductors separately or in a group.
Cage (verb)
To lock the gimbals of a gyroscopic instrument so it will not be damaged by abrupt flight maneuvers or rough handling.
Calendar month
A measurement of time used by the FAA for inspection and certification purposes. One calendar month from a given day extends from that day until midnight of the last day of that month.
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.
Calibrated airspeed
The indicated airspeed of an aircraft, corrected for position and instrument error. Calibrated airspeed is equal to true airspeed in standard atmosphere at sea level.
Calibrated airspeed (CAS)
Indicated airspeed corrected for position error. See position error.
Calibration
A set of operations, performed in accordance with a definite document procedure, which compares the measurements performed by an instrument or standard, for the purpose of detecting and reporting, or eliminating by adjustment, errors in the instrument tested.
Calorie
The amount of heat required to change the temperature of 1 gram of water by 1 degree Centigrade.
Calorie
The amount of heat energy needed to raise the temperature of one gram of pure water 1 °C.
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.
Camber
The curvature of a wing as viewed by cross section. A wing has upper camber on its top surface and lower camber on its bottom surface. The upper camber is more pronounced; the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing.
Camber (wheel alignment)
The amount the wheels of an aircraft are tilted, or inclined, from the vertical. If the top of the wheel tilts outward, the camber is positive. If the top of the wheel tilts inward, the camber is negative.
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.
Canard
A horizontal control surface mounted ahead of the wing to provide longitudinal stability and control.
Canard
The forward wing of a canard configuration and may be a fixed, movable, or variable geometry surface, with or without control surfaces.
Canard configuration
A configuration in which the span of the forward wing is substantially less than that of the main wing.
Canted rate gyro
A rate gyro whose gimbal axis is tilted so it can sense rotation of the aircraft about its roll axis as well as its yaw axis.
Cantilever wing
A wing that is supported by its internal structure and requires no external supports. The wing spars are built in such a way that they carry all the bending and torsional loads.
Cap strip
The main top and bottom members of a wing rib. The cap strips give the rib its aerodynamic shape.
Capacitance (C)
The property of an electric conductor that characterizes its ability to store an electric charge.
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.
Capacitance-type fuel quantity measuring system
A popular type of electronic fuel quantity indicating system that has no moving parts in the fuel tank. The tank units are cylindrical capacitors, called probes, mounted across the tank, from top to bottom. The dielectric between the plates of the probes is either fuel or the air above the fuel, and the capacitance of the probe varies with the amount of fuel in the tank. The indicator is a servo-type instrument driven by the amplified output of a capacitance bridge.
Capacitive reactance (Xc)
The measure of a capacitor’s opposition to alternating current.
Capacitor
An electrical component that stores an electric charge.
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 soft copper tube with a small inside diameter. The capillary tube used with vapor-pressure thermometer connects the temperature sensing bulb to the Bourdon tube. The capillary tube is protected from physical damage by enclosing it in a braided metal wire jacket.
Capillary tube
A glass or metal tube with a tiny inside diameter. Capillary action causes the fluid to move within the tube.
Carbon monoxide detector
A packet of chemical crystals mounted in the aircraft flight deck or cabin where they are easily visible. The crystals change their color from yellow to green when they are exposed to carbon monoxide.
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.
Carbon-pile voltage regulator
A type of voltage regulator used with high-output DC generators. Field current is controlled by varying the resistance of a stack of thin carbon discs. This resistance is varied by controlling the amount the stack is compressed by a spring whose force is opposed by the pull of an electromagnet. The electromagnet’s strength is proportional to the generator’s output voltage.
Carburizing flame
An oxyacetylene flame produced by an excess of acetylene. This flame is identified by a feather around the inner cone. A carburizing flame is also called a reducing flame.
Carcass (tire component)
The layers of rubberized fabric that make up the body of an aircraft tire.
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.
Case hardening
A process in which the surface of a metal is changed chemically by introducing a high carbide or nitride content. Case hardening produces a hard, wear-resistant surface, or case, over a strong, tough core.
Case pressure
A low pressure that is maintained inside the case of a hydraulic pump. If a seal becomes damaged, hydraulic fluid will be forced out of the pump rather than allowing air to be drawn into the pump.
Casing
The structural part of a tire.
Catalyst
A substance used to change the speed, or rate, of a chemical action without being chemically changed itself.
Category
(2) As used with respect to the certification of aircraft, means a grouping of aircraft based upon intended use or operating limitations. Examples include: transport, normal, utility, acrobatic, limited, restricted, and provisional. Category A,with respect to transport category rotorcraft, means multiengine rotorcraft designed with engine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landing operations under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight in the event of engine failure. Category B,with respect to transport category rotorcraft, means single-engine or multiengine rotorcraft which do not fully meet all Category A standards. Category B rotorcraft have no guaranteed stay-up ability in the event of engine failure and unscheduled landing is assumed. Category II operations,with respect to the operation of aircraft, means a straight-in ILS approach to the runway of an airport under a Category II ILS instrument approach procedure issued by the Administrator or other appropriate authority. Category III operations,with respect to the operation of aircraft, means an ILS approach to, and landing on, the runway of an airport using a Category III ILS instrument approach procedure issued by the Administrator or other appropriate authority.
Cathode-ray tube (CRT)
A display tube used for oscilloscopes and computer video displays. An electron gun emits a stream of electrons that is attracted to a positively charged inner surface of the face of the tube. Acceleration and focusing grids speed the movement of the electrons and shape the beam into a pinpoint size. Electrostatic or electromagnetic forces caused by deflection plates or coils move the beam over the face of the tube. The inside surface of the face of the tube is treated with a phosphor material that emits light when the beam of electrons strikes it.
Caution
The level or category of alert for conditions that require immediate flight crew awareness and subsequent flight crew response.
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.
Cavitation
A condition that exist in a hydraulic pump when there is not enough pressure in the reservoir to force fluid to the inlet of the pump. The pump picks up air instead of fluid.
CDTI Assisted Visual Separation (CAVS)
The CDTI is used to assist the flight crew in acquiring and maintaining visual contact during visual separation on approach. The CDTI is also used in conjunction with visual, out-the-window contact to follow the preceding aircraft during the approach. The application is expected to improve both the safety and the performance of visual separation on approach. It may allow for the continuation of visual separation on approach even if visual contact out-the-window is momentarily lost.
Center of gravity
The location on an aircraft about which the force of gravity is concentrated.
Center of gravity
That point about which the aircraft would balance if suspended. For field weight and balance purposes/control, the center of gravity is normally calculated only along its longitudinal axis (nose to tail), disregarding both the lateral and vertical location.
Center of gravity (CG)
The point about which the nose-heavy and tail-heavy moments are exactly equal in magnitude.
Center of gravity range
The center of gravity range for an aircraft is the limits within which the aircraft must balance. It is identified as a forward-most limit (arm) and an aft-most limit (arm).
Center of lift
The location of the chord line of an airfoil at which all the lift forces produced by the airfoil are considered to be concentrated.
Center of pressure
The point on the chord line of an airfoil where all of the aerodynamic forces are considered to be concentrated.
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.
Centering cam
A cam in the nose-gear shock strut that causes the piston to center when the strut fully extends. When the aircraft takes off and the strut extends, the wheel is straightened in its fore-and-aft position so it can be retracted into the wheel well. Charging stand (air conditioning service equipment). A handy and compact arrangement of air conditioning servicing equipment. A charging stand contains a vacuum pump, a manifold gauge set, and a method of measuring and dispensing the refrigerant.
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.
Centrifugal force
The apparent force occurring in curvilinear motion acting to deflect objects outward from the axis of rotation. For instance, when pulling out of a dive, it is the force pushing the pilot down in their seat.
Centripetal force
The force in curvilinear motion acting toward the axis of rotation. For instance, when pulling out of a dive, it is the force that the seat exerts on the pilot to offset the centrifugal force.
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.
Certification
Implies that a certificate is in existence which certifies or states a qualification.
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.
Charles’ Law
States that all gases expand and contract in direct proportion to the change in the absolute temperature, provided the pressure is held constant.
Chatter
A type of rapid vibration of a hydraulic pump caused by the pump taking in some air along with the hydraulic fluid.
Check
A lengthwise separation of the wood, the greater part of which occurs across the rings of annual growth.
Check (wood defect)
Longitudinal cracks that extend across a log’s annual rings.
Check valve
A hydraulic or pneumatic system component that allows full flow of fluid in one direction but blocks all flow in the opposite direction.
Cheek (crankshaft)
The offset portion of a crankshaft that connects the crankpin to the main bearing journals.
Chemical conversion coating (Specification MIL-C-81706)
A chemical surface treatment used on aluminum alloys to inhibit corrosion and to provide a proper surface for paint finishing.
Chemical energy
Energy released from chemical reactions.
Chemical oxygen candle system
An oxygen system used for emergency or backup use. Solid blocks of material that release oxygen when they are burned are carried in special fireproof fixtures. When oxygen is needed, the candles are ignited with an integral igniter, and oxygen flows into the tubing leading to the masks.
Chevron seal
A form of one-way seal used in some fluid- power actuators. A chevron seal is made of a resilient material whose cross section is in the shape of the letter V. The pressure being sealed must be applied to the open side of the V.
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.
Chord
The distance from the blade leading edge to the trailing edge.
Chord
An imaginary straight line joining the leading and trailing edges of an airfoil.
Chord line
A straight line drawn between the leading and trailing edges of the blade.
Chordline
An imaginary line, passing through a propeller blade, joining the leading and trailing edges.
Chromel
An alloy of nickel and chromium used as the positive element in a thermocouple for measuring exhaust gas temperature.
Cigarette
A commonly used name for a spark plug terminal connector used with a shielded spark plug.
Circle
A closed plane figure with every point an equal distance from the center. A circle has the greatest area for its circumference of any enclosed shape.
Circuit
A closed path or mesh of closed paths usually including a source of EMF.
Circuit breaker
An electrical component that automatically opens a circuit any time excessive current flows through it. A circuit breaker may be reset to restore the circuit after the fault causing the excessive current has been corrected.
Circuit breaker
A protective device for opening a circuit automatically when excessive current is flowing through it.
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.
Circular magnetization
The induction of a magnetic field consisting of concentric circles of force about and within a part, which is achieved by passing electric current through the part.
Circumference (of a circle)
The linear measurement of the distance around a circle. The circumference is calculated by multiplying the diameter of the circle by 3.1416.
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.
Civil aircraft
Aircraft other than public aircraft.
Clad aluminum
A sheet of aluminum alloy that has a coating of pure aluminum rolled on one or both of its surfaces for corrosion protection.
Clamp-on ammeter
An electrical instrument used to measure current without opening the circuit through which it is flowing. The jaws of the ammeter are opened, slipped over the current- carrying wire, and then clamped shut. Current flowing through the wire produces a magnetic field which induces a voltage in the ammeter that is proportional to the amount of current.
Claret red
A dark purplish pink to a dark gray purplish red color.
Class
(2) As used with respect to the certification of aircraft, means a broad grouping of aircraft having similar characteristics of propulsion, flight, or landing. Examples include: airplane; rotorcraft; glider; balloon; landplane; and seaplane.
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.
Cleco fastener
A patented spring-type fastener used to hold metal sheets in position until they can be permanently riveted together.
Close-grained wood
Wood with narrow and inconspicuous annual rings. The term is sometimes used to designate wood having small and closelyspaced pores, but in this sense the term “finetextured” is more often used.
Close-quarter iron
A small hand-held iron with an accurately calibrated thermostat. This iron is used for heat- shrinking polyester fabrics in areas that would be difficult to work with a large iron.
Closed angle
An angle formed in sheet metal that has been bent more than 90°.
Closed assembly time
The time elapsing between the assembly of glued joints and the application of pressure.
Closed-center hydraulic system
A hydraulic system in which the selector valves are installed in parallel with each other. When no unit is actuated, fluid circulates from the pump back to the reservoir without flowing through any of the selector valves.
Closed-center selector valve
A type of flow-control valve used to direct pressurized fluid into one side of an actuator, and at the same time, direct the return fluid from the other side of the actuator to the fluid reservoir. Closed-center selector valves are connected in parallel between the pressure manifold and the return manifold.
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.
Coast Interval
The elapsed time since a report from any source has been correlated with the track.
Coaxial
Rotating about the same axis. Coaxial rotors of a helicopter are mounted on concentric shafts in such a way that they turn in opposite directions to cancel torque.
Coaxial cable
A special type of electrical cable that consists of a central conductor held rigidly in the center of a braided outer conductor. Coaxial cable, commonly called coax, is used for attaching radio receivers and transmitters to their antenna.
Cockpit Display of Traffic Information (CDTI)
The pilot interface portion of the Aircraft Surveillance Applications System. This interface includes traffic display(s) and all the controls that interact with such a display. At a minimum, CDTI includes a graphical plan-view (top down) traffic display. Additional graphical and non-graphical display surfaces may also be included. The CDTI receives position information of traffic and Ownship from the airborne surveillance and separation assurance processing (ASSAP) function. The ASSAP receives such information from the surveillance sensors and Ownship position sensors.
Code of Federal Regulations (CFR)
Established by law to provide for the safe and orderly conduct of flight operations and to prescribe airmen privileges and limitations.
Coefficient of drag
A dimensionless number used in the formula for determining induced drag as it relates to the angle of attack.
Coefficient of lift
A dimensionless number relating to the angle of attack used in the formula for determining aerodynamic lift.
Coil shot
Production of longitudinal magnetization accomplished by passing current through a coil encircling the part being inspected.
Coin dimpling
A process of preparing a hole in sheet metal for flush riveting. A coining die is pressed into the rivet hole to form a sharp-edged depression into which the rivet head fits.
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.
Collective pitch control
The helicopter control that changes the pitch of all of the rotor blades at the same time. Movement of the collective pitch control increases or decreases the lift produced by the entire rotor disc.
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.
Collodion
Cellulose nitrate used as a film base for certain aircraft dopes.
Combustion heater
A type of cabin heater used in some aircraft. Gasoline from the aircraft fuel tanks is burned in the heater.
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.
Commercial operator
A person who, for compensation or hire, engages in the carriage by aircraft in air commerce of persons or property, other than as an air carrier or foreign air carrier or under the authority ofPart 375 of this title. Where it is doubtful that an operation is for “compensation or hire”, the test applied is whether the carriage by air is merely incidental to the person’s other business or is, in itself, a major enterprise for profit.
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.
Compass
A device used to determine direction on the Earth’s surface. A magnetic compass utilizes the Earth’s magnetic field to establish direction.
Compass fluid
A highly refined, water-clear petroleum product similar to kerosene. Compass fluid is used to dampen the oscillations of magnetic compasses.
Compass rose
A location on an airport where an aircraft can be taken to have its compasses “swung.” Lines are painted on the rose to mark the magnetic directions in 30° increments.
Compass swinging
A maintenance procedure that minimizes deviation error in a magnetic compass. The aircraft is aligned on a compass rose, and the compensating magnets in the compass case are adjusted so the compass card indicates the direction marked on the rose. After the deviation error is minimized on all headings, a compass correction card is completed and mounted on the instrument panel next to the compass.
Compensated fuel pump
A vane-type, engine-driven fuel pump that has a diaphragm connected to the pressure regulating valve. The chamber above the diaphragm is vented to the carburetor upper deck where it senses the pressure of the air as it enters the engine. The diaphragm allows the fuel pump to compensate for altitude changes and keeps the carburetor inlet fuel pressure a constant amount higher than the carburetor inlet air pressure.
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.
Compensator port (brake system component)
A small hole between a hydraulic brake master cylinder and the reservoir. When the brakes are released, this port is uncovered and the fluid in the master cylinder is vented to the reservoir. When the brake is applied, the master-cylinder piston covers the compensator port and allows pressure in the line to the brake to build up and apply the brakes. When the brake is released, the piston uncovers the compensator port. If any fluid has been lost from the brake, the reservoir will refill the master cylinder. A restricted compensator port will cause the brakes to drag or will cause them to be slow to release.
Composite
Something made up of different materials combined in such a way that the characteristics of the resulting material are different from those of any of the components.
Composite propeller blade
A propeller blade made from several materials such as metal, graphite, glass or aramid fibers, and foam.
Compound curve
A curve formed in more than one plane. The surface of a sphere is a compound curve.
Compound gauge (air conditioning servicing equipment)
A pressure gauge used to measure the pressure in the low side of an air conditioning system. A compound gauge is calibrated from zero to 30 inches of mercury vacuum, and from zero to about 150-psi positive gauge pressure.
Compressibility effect
The sudden increase in the total drag of an airfoil in transonic flight caused by formation of shock waves on the surface.
Compression failure
A type of structural failure in wood caused by the application of too great a compressive load. A compression failure shows up as a faint line running at right angles to the grain of the wood.
Compression ratio
The ratio of the volume of a cylinder with the piston at the bottom of its stroke to the volume of the cylinder with the piston at the top of its stroke.
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.
Compression strut
A heavy structural member, often in the form of a steel tube, used to hold the spars of a Pratt truss airplane wing apart. A compression strut opposes the compressive loads between the spars arising from the tensile loads produced by the drag and antidrug wires.
Compression wood
A defect in wood that causes it to have a high specific gravity and the appearance of an excessive growth of summerwood. In most species, there is little difference between the color of the springwood and the summerwood. Any material containing compression wood is unsuited for aircraft structural use and must be rejected.
Compression wood
Identified by its relatively wide annual rings, usually eccentric, and its relatively large amount of summer wood, usually more than 50 percent of the width of the annual rings in which it occurs. Compression wood shrinks excessively lengthwise as compared with normal wood.
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 (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.
Computer aided design (CAD)
Using a computer in the design of a product.
Computer aided design drafting (CADD)
Using a computer in the design and drafting process.
Computer aided engineering (CAE)
Using a computer in the engineering of a product.
Computer aided manufacturing (CAM)
Using a computer in the manufacturing of a product.
Computer graphics
Drawing with the use of a computer.
Con-di ducts
The British name for a convergent-divergent duct. See convergent-divergent duct.
Concave surface
A surface that is curved inward. The outer edges are higher than the center.
Condenser
See capacitor.
Condenser (air conditioning system component)
The component in a vapor-cycle cooling system in which the heat taken from the aircraft cabin is given up to the ambient air outside the aircraft.
Conduction
The transfer of heat which requires physical contact between an object that has a large amount of heat energy and one that has a smaller amount of heat energy.
Conductor
A material that will carry electric current.
Conductor
A wire or other material suitable for conducting electricity.
Conductor (electrical)
A material that allows electrons to move freely from one atom to another within the material.
Conduit
A rigid metallic or nonmetallic casing, or a flexible metallic casing covered with a woven braid or synthetic rubber used to encase electrical cables.
Configuration, Maintenance, and Procedures (CMP) document
A document approved by the FAA that contains minimum configuration, operating, and maintenance requirements, hardware life-limits, and Master Minimum Equipment List (MMEL) constraints necessary for an airplane-engine combination to meet ETOPS type design approval requirements.
Conformal
A desirable property of map projections. A map projection (a function that associate points on the surface of an ellipsoid or sphere representing the earth to points on a flat surface such as the CDTI display) is said to be conformal if the angle between any two curves on the first surface is preserved in magnitude and sensed by the angle between the corresponding curves on the other surface.
Coning angle
The angle formed between the plane of rotation of a helicopter rotor blade when it is producing lift and a line perpendicular to the rotor shaft. The degree of the coning angle is determined by the relationship between the centrifugal force acting on the blades and the aerodynamic lift produced by the blades.
Constant (mathematical)
A value used in a mathematical computation that is the same every time it is used. For example, the relationship between the length of the circumference of a circle and the length of its diameter is a constant, 3.1416. This constant is called by the Greek name of Pi (π).
Constant differential mode (cabin pressurization)
The mode of pressurization in which the cabin pressure is maintained a constant amount higher than the outside air pressure. The maximum differential pressure is determined by the structural strength of the aircraft cabin.
Constant-displacement pump
A fluid pump that moves a specific volume of fluid each time it rotates; the faster the pump turns, the more fluid it moves. Some form of pressure regulator or relief valve must be used with a constant- displacement pump when it is driven by an aircraft 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-speed drive (CSD)
A special drive system used to connect an alternating current generator to an aircraft engine. The drive holds the generator speed (and thus its frequency) constant as the engine speed varies.
Constant-volume cycle of energy release
The cycle of energy transformation of a reciprocating engine. See Otto cycle.
Constantan
A copper-nickel alloy used as the negative lead of a thermocouple for measuring the cylinder head temperature of a reciprocating engine.
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.
Contact
Electrical connectors in a switch, solenoid or relay that controls the flow of current.
Contactor (electrical component)
A remotely actuated, heavy-duty electrical switch. Contactors are used in an aircraft electrical system to connect the battery to the main bus.
Continuity tester
A troubleshooting tool that consists of a battery, a light bulb, and test leads. The test leads are connected to each end of the conductor under test, and if the bulb lights up, there is continuity. If it does not light up, the conductor is open.
Continuous Airworthiness Inspection Program
An inspection program that is part of a continuous airworthiness maintenance program approved for certain large airplanes (to which 14 CFR Part 125 is not applicable) turbojet multi-engine airplanes, turbopropeller-powered multi-engine airplanes, and turbine-powered rotorcraft.
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.
Continuous-duty solenoid
A solenoid-type switch designed to be kept energized by current flowing through its coil for an indefinite period of time. The battery contactor in an aircraft electrical system is a continuous-duty solenoid. Current flows through its coil all the time the battery is connected to the electrical system.
Continuous-flow oxygen system
A type of oxygen system that allows a metered amount of oxygen to continuously flow into the mask. A rebreather-type mask is used with a continuous-flow system. The simplest form of continuous- flow oxygen system regulates the flow by a calibrated orifice in the outlet to the mask, but most systems use either a manual or automatic regulator to vary the pressure across the orifice proportional to the altitude being flown.
Continuous-loop fire-detection system
A fire-detection system that uses a continuous loop of two conductors separated with a thermistor-type insulation. Under normal temperature conditions, the thermistor material is an insulator; but if it is exposed to a fire, the thermistor changes into a conductor and completes the circuit between the two conductors, initiating a fire warning.
Contrarotating
Rotating in opposite directions. Turbine rotors are contrarotating when the different stages have a common center, but turn in opposite directions.
Control horn
The arm on a control surface to which the control cable or push-pull rod attaches to move the surface.
Control panel
An upright panel, open or closed, where switches, rheostats, meters, etc., are installed for the control and protection of electrical machinery.
Control stick
The type of control device used in some airplanes. A vertical stick in the flight deck controls the ailerons by side-to-side movement and the elevators by fore- and-aft movement.
Control yoke
The movable column on which an airplane control wheel is mounted. The yoke may be moved in or out to actuate the elevators, and the control wheel may be rotated to actuate the ailerons.
Controllability
The characteristic of an aircraft that allows it to change its flight attitude in response to the pilot’s movement of the flight deck controls.
Controller Pilot Data Link Communication (CPDLC)
Provides direct data communication between the pilot and the air traffic controller through a data link.
Convection
The process by which heat is transferred by movement of a heated fluid (gas or liquid).
Conventional current
An imaginary flow of electricity that is said to flow from the positive terminal of a power source, through the external circuit to its negative terminal. The arrowheads in semiconductor symbols point in the direction of conventional current flow.
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.
Converging duct
A duct, or passage, whose cross-sectional area decreases in the direction of fluid flow.
Conversion coating
A chemical solution used to form an airtight oxide or phosphate film on the surface of aluminum or magnesium parts. The conversion coating prevents air from reaching the metal and keeps it from corroding.
Convex surface
A surface that is curved outward. The outer edges are lower than the center.
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.
Coriolis effect
The change in rotor blade velocity to compensate for a change in the distance between the center of mass of the rotor blade and the axis rotation of the blade as the blades flap in flight.
Cornice brake
A large shop tool used to make straight bends across a sheet of metal. Cornice brakes are often called leaf brakes.
Correlation
The process of determining that a new measurement belongs to an existing track.
Corrosion
The deterioration of metal by chemical or electrochemical attack.
Corrosion
Deterioration of a metal because of reaction with its environment. For further references see AC 43-4, Corrosion Control for Aircraft.
Corrosion
The electrochemical deterioration of a metal resulting from chemical reaction to the surrounding environment.
Corrosion, intergranular
Intergranular corrosion occurs in the grain boundaries of some alloys of aluminum. The presence of intergranular corrosion may be the result of fatigue, stress, or the continued presence of moisture such as under a decal, or in a fastener hole. Sometimes called exfoliation corrosion, when it occurs in forgings, extrusions or rolled sheets.
Corrosion, pitting
Visible cavities extending inward from the metal surface due to chemical or electro-chemical action.
Corrosion, surface
Surface loss of metal due to chemical or electro-chemical action. On polished surfaces begins as a dulling of surface, soon becoming frosted, followed by widespread pitting.
Corrugated metal
Sheets of metal that have been made more rigid by forming a series of parallel ridges or waves in its surface.
Cosine (cos)
A trigonometric function comparing two sides of a right triangle as follows: Cos = adjacent side hypotenuse Coulomb. A measure of electrical output. One coulomb is 6.24 × 1018 electrons.
Cotter pin
A split metal pin used to safety a castellated or slotted nut on a bolt. The pin is passed through the hole in the shank of the bolt and the slots in the nut, and the ends of the pin are spread to prevent it backing out of the hole.
Countersink
A tool that cuts a cone-shaped depression around a hole in order to allow a rivet or screw to set flush with the surface of the material.
Countersinking
Preparation of a rivet hole for a flush rivet by beveling the edges of the holes with a cutter of the correct angle.
Coverite surface thermometer
A small surface-type bimetallic thermometer that calibrates the temperature of an iron used to heat-shrink polyester fabrics.
Cowling
The removable cover that encloses an aircraft engine.
Crabbing
Pointing the nose of an aircraft into the wind to compensate for wind drift.
Crack
A physical opening or fissure within the body of a material. May be either internal within the material or at the surface (surface breaking). On a propeller, cracks can be started by cuts, nicks, or corrosion.
Crack
A partial separation of material caused by vibration, overloading, internal stresses, nicks, defective assemblies, fatigue, or rapid changes in temperature.
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.
Crazing
A form of stress-caused damage that occurs in a transparent thermoplastic material. Crazing appears as a series of tiny, hair-like cracks just below the surface of the plastic.
Creep
The deformation of a metal part that is continually exposed to high centrifugal loads and temperatures.
Creepage
The conducting of electrical current along a surface between two points at different potentials. The current’s ability to pass between two points increases with higher voltage and when deposits of moisture or other conductive materials exist on the surfaces.
Crewmember
A person assigned to perform duty in an aircraft during flight time.
Critical altitude
The maximum altitude at which, in standard atmosphere, it is possible to maintain, at a specified rotational speed, a specified power or a specified manifold pressure. Unless otherwise stated, the critical altitude is the maximum altitude at which it is possible to maintain, at the maximum continuous rotational speed, one of the following: (1) The maximum continuous power, in the case of engines for which this power rating is the same at sea level and at the rated altitude. (2) The maximum continuous rated manifold pressure, in the case of engines, the maximum continuous power of which is governed by a constant manifold pressure.
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 whose failure would most adversely affect the performance or handling qualities of an aircraft.
Critical engine
The engine of a twin-engine airplane whose loss would cause the greatest yawing effect.
Critical Mach number
The flight Mach number at which there is the first indication of supersonic airflow over any part of the aircraft structure.
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.
Cross coat
A double coat of aircraft finishing material in which the second coat is sprayed at right angles to the first coat, before the solvents have evaporated from the first coat.
Cross coat
A double coat of dope or paint. It is sprayed on in one direction, and then immediately after the solvent flash-off, it is sprayed at right angles to the first coat.
Cross grain
Grain not parallel with the axis of a piece. It may be either diagonal or spiral grain or a combination of the two.
Cross-feed valve (fuel system component)
A valve in a fuel system that allows any of the engines of a multi-engine aircraft to draw fuel from any fuel tank. Cross-feed systems are used to allow a multi-engine aircraft to maintain a balanced fuel condition.
Cross-flow valve
An automatic flow-control valve installed between the gear-up and gear-down lines of the landing gear of some large airplanes. When the landing gear is released from its uplocks, its weight causes it to fall faster than the hydraulic system can supply fluid to the gear-down side of the actuation cylinder. The cross-flow valve opens and directs fluid from the gear-up side into the gear-down side. This allows the gear to move down with a smooth motion.
Cryogenic fluid
A liquid which boils at a temperature lower than about 110°K (-163°C) under normal atmospheric pressure.
Cryogenic liquid
Aliquid which boils at temperatures of less than about 110 °F (–163 °C) at normal atmospheric pressures.
Cuno filter
The registered trade name for a particular style of edge-type fluid filter. Cuno filters are made up of a stack of thin metal discs that are separated by thin scraper blades. Contaminants collect on the edge of the discs, and they are periodically scraped out and allowed to collect in the bottom of the filter case for future removal.
Cure
To change the properties of a thermosetting resin irreversibly by vulcanization or chemical reaction. May be accomplished by the addition of curing (cross-linking) agents, with or without a catalyst, and with or without heat or pressure.
Curing temperature
Temperature to which a resin or an assembly is subjected in order to cure the resin.
Current
The flow of electrical charge
Current
A general term used for electrical flow. See conventional current.
Current limiter
An electrical component used to limit the amount of current a generator can produce. Some current limiters are a type of slow-blow fuse in the generator output. Other current limiters reduce the generator output voltage if the generator tries to put out more than its rated current.
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.
Cusp
A pointed end.
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.
Cut
A deep, long, narrow fissure usually caused by a sharp object.
Cutting torch
A device used in gas cutting of metals.
Cyclic pitch control
The helicopter control that allows the pilot to change the pitch of the rotor blades individually, at a specific point in their rotation. The cyclic pitch control allows the pilot to tilt the plane of rotation of the rotor disc to change the direction of lift produced by the rotor.
Cylinder
The component of a reciprocating engine which houses the piston, valves, and spark plugs and forms the combustion chamber.
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