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conductor by a moving or nonuniform magnetic field.
eddy current damping. Decreasing the amplitude of oscillations by the interaction of magnetic fields. In
the case of a vertical-card magnetic compass, flux from the oscillating permanent magnet produces eddy
currents in a damping disk or cup. The magnetic flux produced by the eddy currents opposes the flux from
the permanent magnet and decreases the oscillations.
eddy current inspection (nondestructive inspection method). A form of nondestructive inspection used
to locate faults in a metal part. Eddy currents are induced into the part being inspected and also into a
similar part known to be sound. The presence of a defect is indicated by a difference in the amount of
current needed to induce the eddy current in the two parts.
eddy current losses (electrical machinery). The loss of electrical power caused by eddy currents induced
into the cores of transformers and the armatures of generators and motors. This lost power produces heat.
edge distance (sheet metal measurement). The distance from the center of a bolt hole or rivet hole to the
edge of the metal sheet.
edge-grain wood. Wood that has been sawed from the tree in such a way that the edges of its grain are
visible in the wide part of the plank. Edge-grain wood is also called quarter-sawed wood.
edge thickness (sheet metal measurement). The thickness of the edge of a sheet of material.
EDM (electric-discharge machining). A method of machining complex contours in a piece of metal by
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 213
allowing a controlled electric arc to erode, or eat away, the metal. Electric-discharge machining (EDM) is
used to form the dies used for certain types of plastic molding.
eductor. A form of jet pump used to pick up one liquid and mix it with another. Eductors are used in some
aircraft fuel systems to remove fuel from a vent-drain tank and return it to the main tank. Fuel from the
boost pump flowing through the eductor produces a low pressure that pulls fuel from the vent-drain tank
and carries it back into the main tank.
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 overspeed and overtemperature.
effective pitch (propeller parameter). The actual distance a propeller moves through the air in one
revolution. Effective pitch is the difference between the geometric pitch of the propeller and the slip. See
geometric pitch, and slip.
effective value (AC electricity). The value of sine wave alternating current needed to produce the same
amount of heat as this value of direct current. The effective value of sine wave AC is 0.707 time its peak
value. This means that AC having a peak value of one amp will produce as much heat as , or 0.707 amp of
direct current.
Effective value, also called root mean square, or rms, value of alternating current is found by: (1)
squaring all the instantaneous values of the current or voltage in one alternation; then (2) averaging these
values; and then (3) finding the square root of this average. Most AC voltmeters are calibrated to show the
effective value of the voltage they measure.
efficiency. A measure of the effectiveness of a system or device. Efficiency is found by dividing the output
of the device by its input, and it is usually expressed as a percentage.
If the output of a device is exactly the same as its input, the device has an efficiency of 100%. If
its output is only one half of its input, its efficiency is 50%.
EFIS (electronic flight instrument system). A complete electronic flight instrumentation system that
includes the EICAS (engine indicating and crew alerting system) and the ECAM (electronic centralized
monitoring) system. See EICAS and ECAM.
E-gap angle (magneto measurement). 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.
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.
EGT indicating system (gas turbine engine). An indicating system used with a gas turbine engine to
measure the temperature of the exhaust gases as they enter the tail pipe, after passing through the turbine.
　
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