Chip detector. A warning device that alerts you to any abnormal wear in a transmission or engine. It consists of a magnetic plug located within the transmission. The magnet attracts any metal particles that have come loose from the bearings or other transmission parts. Most chip detectors have warning lights located on the instrument panel that illuminate when metal particles are picked up.

Chord. An imaginary straight line between the leading and trailing edges of an airfoil section.

Chordwise axis. For semirigid rotors, a term used to describe the flapping or teetering axis of the rotor.

Coaxial rotor. A rotor system utilizing two rotors turning in opposite directions on the same centerline. This system is used to eliminated the need for a tail rotor.

Collective pitch control. The control for changing the pitch of all the rotor blades in the main rotor system equally and simultaneously and, consequently, the amount of lift or thrust being generated.

Coning. See blade coning.

Coriolis effect. The tendency of a rotor blade to increase or decrease its velocity in its plane of rotation when the center of mass moves closer to or farther from the axis of rotation.

Cyclic feathering. The mechanical change of the angle of incidence, or pitch, of individual rotor blades, independent of other blades in the system.

Cyclic pitch control. The control for changing the pitch of each rotor blade individually as it rotates through one cycle to govern the tilt of the rotor disk and, consequently, the direction and velocity of horizontal movement.

Degraded Visual Environment (DVE). Any flight environment of reduced visibility in which situational awareness of the aircrew or control of the aircraft may be severely diminished, completely lost, or may not be maintained as comprehensively as they are during flight operations within clear or undiminished visibility. DVE conditions are further categorized into eleven different types: smoke, smog, clouds, rain, fog, snow, whiteout, night, flat light, sand, and brownout.

Delta hinge. A flapping hinge with an axis skewed so that the flapping motion introduces a component of feathering that would result in a restoring force in the flap-wise direction.

Density altitude. Pressure altitude corrected for nonstandard temperature variations.

Deviation. A compass error caused by magnetic disturbances from the electrical and metal components in the aircraft. The correction for this error is displayed on a compass correction card placed near the magnetic compass of the aircraft.

Direct control. The ability to maneuver a helicopter by tilting the rotor disk and changing the pitch of the rotor blades.

Direct shaft turbine. A single-shaft turbine engine in which the compressor and power section are mounted on a common driveshaft.

Disk area. The area swept by the blades of the rotor. It is a circle with its center at the hub and has a radius of one blade length.

Disk loading. The total helicopter weight divided by the rotor disk area.

Dissymmetry of lift. The unequal lift across the rotor disk resulting from the difference in the velocity of air over the advancing blade half and the velocity of air over the retreating blade half of the rotor disk area.

Drag. An aerodynamic force on a body acting parallel and opposite to relative wind.