communications satellite. A man-made satellite that orbits the earth at an altitude of 22,300 miles (35,900 kilometers), appearing at this altitude to remain stationary over a given location.
Communications satellites receive radio and television transmissions from earth stations and re-transmit them. Three satellites in essentially the same orbit are able to cover almost the entire earth with the signals they re-transmit.
commutation (electrical machine). The process by which DC voltage is taken from an armature that has had AC voltage induced into it.
commutator (electrical machine component). 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 coils of a motor.
comparator (electronic circuit). An electronic circuit that compares two signals and produces a third signal that indicates whether the first two are the same or different.
compartment (structural component). An enclosed area, or space, in an aircraft structure. An engine compartment is an enclosed area in which the engine is mounted.
compass (drafting instrument). An instrument used to draw circles or portions of a circle. A compass is made of two legs, hinged in the center. One leg is fitted with a sharp point to hold it at the center of the circle, and the other leg can be fitted with a lead holder or ink pen to draw the circle.
compass (navigation instrument). A navigation instrument that indicates the direction to the earth’s magnetic north pole.
The simplest compasses use a small permanent magnet mounted on a pivot and free to turn. It aligns itself with the magnetic lines of flux that extend across the earth from the magnetic north pole to the magnetic south pole.
compass card (magnetic compass component). A drum-like scale, marked in degrees, from 0° to 360°, fastened around the float in an aircraft magnetic compass.
The magnets align the float with the earth’s magnetic field, and the compass card, which is read opposite a fixed lubber line, shows the pilot the direction the nose of the aircraft is pointed relative to magnetic north.
compass compensation. A maintenance procedure that corrects a magnetic compass for deviation error.
The aircraft is aligned on a compass rose, and the compensating magnets in the compass case are adjusted to get the compass to align with the direction marked on the rose. After the deviation error is minimized on all headings, a compass correction card is filled out and mounted on the instrument panel next to the compass.
Compass compensation is also called compass swinging.
compass correction card. A small card mounted near the magnetic compass to show the pilot the amount of deviation error for each heading.
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