CSD.  Constant-speed drive. A component used with either  aircraft gas turbine or reciprocating engines to drive AC  generators. The speed of the output shaft of the CSD is held  constant while the speed of its input shaft caries. The CSD  holds the speed of the generator, and the frequency of the  AC constant as the engine speed varies through its normal  operating range. CTF. Centrifugal twisting force.  The force acting about  the longitudinal axis of a propeller blade, and which tries to  rotate the blade to a low-pitch angle. As the propeller rotates,  centrifugal force tries to flatten the blade so all of its mass  rotates in the same plane. Curtiss Jenny (Curtiss JN4-D).  A World War I training  airplane powered by a Curtiss OX-5 engine. It was widely  available after the war and helped introduce aviation to the  general public. Customer bleed air.  Air that is tapped off a turbine engine  compressor and used for such airframe functions as the  operation of air conditioning and pressurization systems.  Cylinder.  The component of a reciprocating engine which  houses the piston, valves, and spark plugs and forms the  combustion chamber. Data.  The input for computer processing in the form of  numerical information that represents characters or analog  quantities. Dataplate specifications.  Specification of each gas turbine  engine determined in the manufacturer’s test cell when the  engine was calibrated. This data includes the engine serial  number with the EPR that produced a specific RPM. The  technician refers to this information when trimming the engine. Dataplate performance.  The performance specifications  of a turbine engine observed and recorded by the engine  manufacturer or overhauler and recorded on the engine  dataplate. This data includes the engine speed at which a  specified EPR is attained. When trimming the engine, the  technician uses this data as the goal. DC. Direct current.  Electrical current in which the electrons  always flow in the same direction. Deaerator.  A component in a turbine engine lubrication  system that removes air from the scavenged oil before it is  returned to the tank. Deceleration.  The amount the velocity of an object,  measured in feet per second, is decreased by a force during  each second it is acted upon by that force. Deceleration is  usually expressed in terms of feet per second, per second  (fps²). DeHaviland DH-4.  An English designed observation  airplane built in large quantities in the united States during  World War I. After the war, surplus DH-4s were used for  carrying the U.S. Mail.  Deicing.  The removal of ice that has formed on a surface. Density altitude.  The altitude in standard air at which the  density is the same as that of the existing air. Detergent oil.  A type of mineral oil with metallic-ash- forming additives that protects the inside of an engine from  sludge and varnish buildup. Used in automotive engines, it  has proven unsuitable for use in aircraft engines. Detonation.  An uncontrolled explosion inside the cylinder of  a reciprocating engine. Detonation occurs when the pressure  and temperature of the fuel inside the cylinder exceeds the  critical pressure and temperature of the fuel. Detonation may  be caused by using fuel that has a lower octane rating or  performance number than is specified for the engine. Dewar bottle.  A special container used to store liquid oxygen  and liquid nitrogen. A Dewar bottle has an inner and an outer  container, and the space between them forms a vacuum. The  two surfaces within the vacuum are silvered to reflect heat  away from the container walls. Differential pressure.  A single pressure that is the difference  between two opposing pressures. Diffuser.  A component in a gas turbine engine that decreases  the velocity of air flowing through it and increases its pressure. Digitized image.  A modified image picked up by the  miniature TV camera in the end of a fiber-optic probe.  This image is converted into a digital electronic signal that  eliminates unwanted portions of the viewed area and allows  the desired image to be enhanced for a clearer view of the  inside of a turbine engine. Dipstick.  A gage, in the form of a thin metal rod, used to  measure the level of liquid in a reservoir. The dipstick is  pushed into the reservoir until it contacts a built-in stop; then  it is removed and visually inspected. The level of liquid in  the reservoir is indicated by the amount of the dipstick wet  by the liquid. G-9