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. 

