Gas Turbine Glossary

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for generators and alternators, and the magnetic circuit of
magnetos.
Electromagnet. A magnet produced by an electrical current
flowing through a coil of wire. The coil is normally wound
around a core of soft iron which has an extremely low
retentivity, allowing it to lose its magnetism as soon as the
current stops flowing.
Electromagnetic radiation. A method of transmitting energy
from one location to another. Current caused by high voltage
in the secondary winding of a magneto produces electric
and magnetic fields which oscillate back and forth at a high
frequency and extend out into space in the form of waves.
These waves of electromagnetic radiation are received as
interference by the radio receivers in the aircraft.
Electromotive force. A force that causes electrons to move
from one atom to another within an electrical circuit. An
electromotive force, or EMF, is the difference in the electrical
pressure, or potential, that exists between two points. An
EMF may be produced by converting mechanical movement,
pressure, chemical, light, or heat energy into electrical energy.
The basic unit of EMF is the volt.
Emulsion. A suspension of small globules of one material
in another when the two materials will not mix. Oil and
water will not mix, but they can be formed into an emulsion.
An emulsion will separate into its components when it is
allowed to sit.
Engine trimming. A maintenance procedure in which the
fuel control on a gas turbine engine is adjusted to cause the
engine to produce the required EGT or EPR at a specified rpm.
Entrained water. Water suspended in jet fuel. The amount
of entrained water that can be held in the fuel is determined
by the temperature of the fuel. When the fuel becomes cold,
the water precipitates out and forms ice crystals on the fuel
filter element.
Epicyclic reduction gears. A gear train in which a series
of small planetary gears rotate around a central gear. More
commonly called a planetary gear train.
EPR. Engine pressure ratio. The ratio of the turbine discharge
total pressure to the compressor inlet total pressure. EPR is
normally used as the parameter to determine the amount of
thrust an axial-flow turbojet or turbofan engine is producing.
ESHP. Equivalent shaft horsepower. A measure of the
power produced by a turboprop engine. ESHP takes
into consideration both the shaft horsepower delivered
to the propeller and the thrust developed at the engine
exhaust. Under static conditions, one shaft horsepower is
approximately equal to 2.5 pounds of thrust.
Ethanol. Alcohol made from cereal grains such as corn.
Ether. A volatile, highly flammable liquid that may be used
to prime the cylinders of an aircraft engine when starting
under extremely cold conditions.
Ethylene dibromide. A colorless, poisonous liquid
BrCH2CH2Br that is blended with leaded gasoline to help
scavenge lead oxides.
Ethylene glycol. A form of alcohol used as a coolant for
liquid-cooled aircraft engines. It is also used in automobile
engines as a permanent antifreeze.
Eutectic. An alloy or solution that has the lowest possible
constant melting point.
Evaporative cooling. See steam cooling.
Exceedance condition. A condition in which a parameter
sensed by the EICAS exceeds the limits for which it is
programmed.
Exhaust cone. The fixed conical fairing centered in the
turbine wheel. The exhaust cone straightens the flow and
prevents the hot gases from circulating over the rear face of
the turbine wheel.
Exhaust nozzle. The opening at the rear of the exhaust pipe.
Expansion wave. The change in pressure and velocity of
supersonic air as it passes over a surface that drops away from
the flow. As the surface drops away, the air tries to follow it,
and in changing its direction, the air speeds up to a higher
supersonic speed, and its static pressure decreases. There is
no change in the total amount of energy as air passes through
an expansion wave.
External-combustion engine. A form of heat engine in
which the fuel releases its energy outside of the engine.
This released heat expands air which is used to perform
useful work. Steam engines are a popular type of external
combustion engine.
Extreme pressure (EP) lubricant. A lubricant that reacts
with iron to form iron chlorides, sulfides, or phosphides on
the surface of a steel part. These compounds reduce wear and
damage to surfaces in heavy rubbing contact. EP lubricants
are specially suited for lubricating gear trains.
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