Aviation Maintenance Terms beginning with D
Data
The input for computer processing in the form of numerical information that represents characters or analog quantities.
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.
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.
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.
Delta P ∆P
Differential pressure.
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.
Dirigible
A large, cigar shaped, lighter-than-air flying machine. Dirigibles differ from balloons in that they are powered and can be steered.
Distributed pole stator winding
Alternator stator windings wound in a series of slots in the stator frame. A distributed pole stator is distinguished from a salient pole stator whose coils are wound around separate pole shoes that project inward from the field frame toward the rotor.
Distributor
A high-voltage selector switch that is gear- driven from the shaft of the rotating magnet in a magneto. The distributor rotor picks up the high voltage from the secondary winding of the coil and directs it to high-voltage terminals. From here, it is carried by high-tension ignition leads to the spark plugs.
Divergent duct
A duct that has an increased cross-sectional area in the direction of flow.
Downdraft carburetor
A carburetor that mounts on the top of a reciprocating engine. Air entering the engine flows downward through the carburetor.
Droop
A progressive decrease in RPOM with load in a gas turbine engine whose speed is governed with a fly-weight- type governor in the fuel control. As the load increases, the pilot valve drops down to meter more fuel. The lower position of the valve decreases the compression of the speeder spring and allows the flyweights to assume an on-speed position at a lower rpm.
Dry-sump engine
An engine that carries its lubricating oil supply in a tank external to the engine.
Dual ignition
An ignition system of an aircraft reciprocating engine that has two of every critical unit, including two spark plugs in each cylinder. Dual ignition provides safety in the event of one system malfunctioning, but more important, igniting the air/fuel mixture inside the cylinder at two locations provides more efficient combustion of the air/fuel mixture in the cylinder.
Dual-spool gas turbine engine
An axial-flow turbine engine that has two compressors, each driven by its own stage or stages of turbines.
Duct heater
A thrust augmentation system, similar to an afterburner, where fuel is added to the fan-discharge air and burned.
Duct losses
A decrease in pressure of the air flowing into a gas turbine engine caused by friction.
Durability
A measure of engine life. Durability is usually measured in TBO hours.
Duty cycle
A schedule that allows a device to operate for a given period of time, followed by a cooling down period before the device can be operated again.
Dwell chamber
A chamber in a turbine engine into which the scavenged oil is returned. Entrained air separates from the oil in the dwell chamber before it is picked up by the pressure pump.
Dynamometer
A device used to measure the amount of torque being produced by an engine. The drive shaft of the engine is loaded with either an electric generator or a fluid pump, and the output of the generator or pump is measured and converted into units of torque. Torque at a specific rpm can be converted into brake horsepower.
Dyne
The unit of force that imparts an acceleration of one centimeter per second, per second to a mass of one gram. One dyne is equal to 2.248 ∙ 10-6 pounds.
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