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 counterweights 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 fuel-air mixture inside the cylinder at two  locations provides more efficient combustion of the fuel-air  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. EGT.  Exhaust gas temperature. The temperature of the gases  as they leave the cylinder of a reciprocating engine or the  turbine of a gas turbine engine. E-gap angle.  The position of the rotating magnet in a  magneto when the breaker points are timed to open. The  E-gap (efficiency gap) angle is several degrees of magnet  rotation beyond the magnet’s neutral position. At this point,  the magnetic field stress is the greatest, and the change in  flux is the greatest, inducing the maximum voltage in the  secondary winding. Effective pitch.  The actual distance a propeller advances in  one revolution through the air. EEC.  Electronic engine control. An electronic fuel control for  a gas turbine engine. The EEC senses the power-lever angle  (PLA), engine RPM, bleed valve, and variable stator vane  position, and the various engine pressures and temperatures.  It meters the correct amount of fuel to the nozzles for all  flight conditions, to prevent turbine over-speed and over- temperature. Eddy current.  Current induced into a conductor due to a  mobbing or non-uniform magnetic field. 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. 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. 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. 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. Durability.  A measure of engine life. Durability is usually  measured in TBO hours. Duct losses.  A decrease in pressure of the air flowing into a  gas turbine engine caused by friction. ∆P (delta P).  Differential pressure.  G-10