Break lines. Line on a drawing indicating that a portion of the object is not shown on the drawing.

British thermal unit (Btu). The amount of heat required to change the temperature of 1 pound of water by 1 degree Fahrenheit.

Buoyancy. The upward force that any fluid exerts on a body submerged in it.

Buttock line (BL). The longitudinal axis of the aircraft that serves as the reference location for positions to the left and right of center. The positions are usually dimensioned in inches.

Calorie. The amount of heat required to change the temperature of 1 gram of water by 1 degree Centigrade.

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.

Capacitance (C). The property of an electric conductor that characterizes its ability to store an electric charge.

Capacitive reactance (Xc). The measure of a capacitor’s opposition to alternating current.

Capacitor. An electrical component that stores an electric charge.

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.

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).

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.

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.

Chemical energy. Energy released from chemical reactions.

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.

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.