Aviation Maintenance Terms beginning with E
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.
Eddy current
Current induced into a conductor due to a mobbing or non-uniform magnetic field.
Effective pitch
The actual distance a propeller advances in one revolution through the air.
Elastic limit
The maximum amount of tensile load, in pounds per square inch, that a material is able to withstand without permanent deformation.
Electrical potential
The electrical force caused by a deficiency of electrons in one location and an excess of electrons in another. Electrical potential is measured in volts.
Electrical steel
A low-carbon iron alloy that contains some silicon It is used as the core for transformers, field frames 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.
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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