Electron current.  The actual flow of electrons in a circuit.  Electrons flow from the negative terminal of a power source  through the external circuit to its positive terminal. The  arrowheads in semiconductor symbols point in the direction  opposite to the flow of electron current. Dynamic stability.  The stability that causes an aircraft to  return to a condition of straight and level flight after it has been  disturbed from this condition. When an aircraft is disturbed  from the straight and level flight, its static stability starts it back  in the correct direction; but it overshoots, and the corrective  forces are applied in the opposite direction. The aircraft  oscillates back and forth on both sides of the correct condition,  with each oscillation smaller than the one before it. Dynamic  stability is the decreasing of these restorative oscillations. ELT (emergency locator transmitter).  A self-contained  radio transmitter that automatically begins transmitting on  the emergency frequencies any time it is triggered by a severe  impact parallel to the longitudinal axis of the aircraft. Elevator downspring.  A spring in the elevator control  system that produces a mechanical force that tries to lower the  elevator. In normal flight, this spring force is overcome by the  aerodynamic force from the elevator trim tab. But in slow flight  with an aft CG position, the trim tab loses its effectiveness and  the downspring lowers the nose to prevent a stall. EADI.  Electronic Attitude Director Indicator. ECAM.  Electronic Centralized Aircraft Monitor. Eccentric brushing.  A special bushing used between the  rear spar of certain cantilever airplane wings and the wing  attachment fitting on the fuselage. The portion of the bushing  that fits through the hole in the spar is slightly offset from that  which passes through the holes in the fitting. By rotating the  bushing, the rear spar may be moved up or down to adjust  the root incidence of the wing. Elevons.  Movable control surfaces on the trailing edge of a delta  wing or a flying wing airplane. These surfaces operate together  to serve as elevators, and differentially to act as ailerons. EMI.  Electromagnetic interference. Empennage.  The tail section of an airplane. Eddy current damping (electrical instrument 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. Edge distance.  The distance between the center of a rivet  hole and the edge of the sheet of metal. EFIS.  Electronic Flight Instrument System. EHSI.  Electronic Horizontal Situation Indicator. EICAS.  Engine Indicating and Crew Alerting System. Ejector.  A form of jet pump used to pick up a liquid and  move it to another location. Ejectors are used to ensure that  the compartment in which the boost pumps are mounted is  kept full of fuel. Part of the fuel from the boost pump flowing  through the ejector produces a low pressure that pulls fuel from  the main tank and forces it into the boostpump sump area. Elastic limit.  The maximum amount of tensile load, in  pounds per square inch, a material is able to withstand without  being permanently deformed. Electromotive force (EMF).  The force that causes electrons  to move from one atom to another within an electrical  circuit. Electromotive force is an electrical pressure, and it  is measured in volts. Ethylene dibromide.  A chemical compound added to  aviation gasoline to convert some of the deposits left by  the tetraethyl lead into lead bromides. These bromides are  volatile and will pass out of the engine with the exhaust gases. Equalizing resistor.  A large resistor in the ground circuit  of a heavy-duty aircraft generator through which all of the  generator output current flows. The voltage drop across this  resistor is used to produce the current in the paralleling circuit  that forces the generators to share the electrical load equally. Epoxy.  A flexible, thermosetting resin that is made by  polymerization of an epoxide. Epoxy has wide application  as a matrix for composite materials and as an adhesive that  bonds many different types of materials. It is noted for its  durability and its chemical resistance. Energizing brake.  A brake that uses the momentum of the  aircraft to increase its effectiveness by wedging the shoe  against the brake drum. Energizing brakes are also called servo  brakes. A single-servo brake is energizing only when moving  in the forward direction, and a duo-servo brake is energizing  when the aircraft is moving either forward or backward. Enamel.  A type of finishing material that flows out to form  a smooth surface. Enamel is usually made of a pigment  suspended in some form of resin. When the resin cures, it  leaves a smooth, glossy protective surface.  G-14