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, and the other as a pusher behind the cabin. The empennage is mounted on booms.

center of gravity. See CG.
center of gravity envelope (aircraft weight and balance). An envelope drawn on a graph included in aircraft Type Certificate Data Sheets and aircraft flight operations manuals showing the center of gravity limits for all weights up to the maximum allowable gross weight of the aircraft.
Any combination of weight and center of gravity location that falls within the envelope is an approved loading condition for the aircraft.
center of gravity limits (aircraft weight and balance). The specified forward and aft points beyond which the CG must not be located during flight. These limits are indicated in the Type Certificate Data Sheets (TCDS) for the aircraft.
center of gravity range (aircraft weight and balance). The distance in inches between the forward allowable center of gravity and the rearward allowable center of gravity.
The allowable center of gravity range changes with the gross weight of the aircraft, and the gross weight must be specified for the center of gravity range to be meaningful.
In most modern aircraft, this center of gravity range is shown in the aircraft Type Certificate Data Sheets in the form of a center of gravity envelope.
center of lift (aerodynamic parameter). The location along the chord line of an airfoil at which all the lift forces produced by the airfoil are considered to be concentrated.
center of mass. The location within a body at which its entire mass is considered to be balanced.
center of pressure (aerodynamics). The point on the chord line of an airfoil (a line through the airfoil that joins the leading edge and the trailing edge) where all the aerodynamic forces are considered to be concentrated.

center of pressure coefficient (airfoil data). The distance between the leading edge of an airfoil and the location of the center of pressure expressed as a ratio of this distance to the length of the airfoil chord line.
If the center of pressure coefficient, which is expressed as “cp” on a set of airfoil characteristic curves, is 0.3, the center of pressure is located 30% of the chord line length behind the leading edge of the airfoil.
center punch. A small, metalworking punch used to make an impression in a piece of metal to hold the point of a twist drill so it can start cutting without walking over the surface of the metal.
The point of a center punch forms an angle of approximately 60°. This angle allows the drill to
start cutting easily.
center radar ARTS presentation/processing (air traffic control). A computer program developed to provide a backup system for airport surveillance radar in the event of a failure or malfunction. The program uses air route traffic control center radar for the processing and presentation of data on the ARTS IIA or IIIA displays.