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. 

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. 

Cleco fastener.  A patented spring-type fastener used to hold metal sheets in position until they can be permanently riveted together. 

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. 

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. 

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. 

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. 

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 disk. 

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. 

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. 

