Compensator port (brake system component).  A small  hole between a hydraulic brake master cylinder and the  reservoir. When the brakes are released, this port is uncovered  and the fluid in the master cylinder is vented to the reservoir.  When the brake is applied, the master-cylinder piston covers  the compensator port and allows pressure in the line to the  brake to build up and apply the brakes. When the brake is  released, the piston uncovers the compensator port. If any  fluid has been lost from the brake, the reservoir will refill  the master cylinder. A restricted compensator port will cause  the brakes to drag or will cause them to be slow to release. Compressor (air conditioning system component).  The component in a vapor-cycle cooling system in which  the low-pressure refrigerant vapors, after they leave the  evaporator, are compressed to increase both their temperature  and pressure before they pass into the condenser. Some  compressors are driven by electric motors, others by  hydraulic motors and, in the case of most light airplanes, are  belt driven from the engine. Concave surface.  A surface that is curved inward. The outer  edges are higher than the center. Composite.  Something made up of different materials  combined in such a way that the characteristics of the  resulting material are different from those of any of the  components. Compound curve.  A curve formed in more than one plane.  The surface of a sphere is a compound curve. Compound gauge (air conditioning servicing equipment). A pressure gauge used to measure the pressure in the low  side of an air conditioning system. A compound gauge is  calibrated from zero to 30 inches of mercury vacuum, and  from zero to about 150-psi positive gauge pressure. Compressibility effect.  The sudden increase in the total drag  of an airfoil in transonic flight caused by formation of shock  waves on the surface. Compression failure.  A type of structural failure in wood  caused by the application of too great a compressive load. A  compression failure shows up as a faint line running at right  angles to the grain of the wood. Compression strut.  A heavy structural member, often in  the form of a steel tube, used to hold the spars of a Pratt  truss airplane wing apart. A compression strut opposes the  compressive loads between the spars arising from the tensile  loads produced by the drag and antidrug wires. Compression wood.  A defect in wood that causes it to have  a high specific gravity and the appearance of an excessive  growth of summerwood. In most species, there is little  difference between the color of the springwood and the  summerwood. Any material containing compression wood  is unsuited for aircraft structural use and must be rejected. Condenser (air conditioning system component).  The  component in a vapor-cycle cooling system in which the  heat taken from the aircraft cabin is given up to the ambient  air outside the aircraft. Conductor (electrical).  A material that allows electrons to  move freely from one atom to another within the material. Coning angle.  The angle formed between the plane of  rotation of a helicopter rotor blade when it is producing lift  and a line perpendicular to the rotor shaft. The degree of the  coning angle is determined by the relationship between the  centrifugal force acting on the blades and the aerodynamic  lift produced by the blades. Constant (mathematical).  A value used in a mathematical  computation that is the same every time it is used. For example,  the relationship between the length of the circumference of  a circle and the length of its diameter is a constant, 3.1416.  This constant is called by the Greek name of Pi (π). Constant differential mode (cabin pressurization).  The mode of pressurization in which the cabin pressure is  maintained a constant amount higher than the outside air  pressure. The maximum differential pressure is determined  by the structural strength of the aircraft cabin. Constant-displacement pump.  A fluid pump that moves a  specific volume of fluid each time it rotates; the faster the  pump turns, the more fluid it moves. Some form of pressure  regulator or relief valve must be used with a constant- displacement pump when it is driven by an aircraft engine. Constant-speed drive (CSD).  A special drive system used to  connect an alternating current generator to an aircraft engine.  The drive holds the generator speed (and thus its frequency)  constant as the engine speed varies. Constantan.  A copper-nickel alloy used as the negative  lead of a thermocouple for measuring the cylinder head  temperature of a reciprocating engine. G-9