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enough that it was completely burned out before it reached the ground.
flare (rigid fluid lines). A cone-shaped expansion on the end of a piece of rigid fluid line tubing. The
fitting to which the flared tubing attaches has a cone-shaped end that exactly mates with the flare, and when
the tubing nut is tightened onto the fitting, the flare and the flare cone form a fluid-tight seal.
Tubing used in automotive fluid lines is flared at an angle of 45°, and tubing used in aircraft fluid
lines is flared at an angle of 37°.
flareless fitting (fluid lines). A type of fitting used on a fluid line that forms its seal without being flared.
Flareless fittings use a compression sleeve around the end of the tube. The sleeve fits into a recess in the
fitting, and when the nut is tightened, the sleeve is forced tightly between the tube and the fitting, making a
fluid-tight seal.
flashback (welding problem). A problem in oxy-gas welding in which the flame burns back into the
mixing chamber of the torch. A clogged or overheated tip can cause the flame to disappear from the tip and
burn back into the mixing chamber.
A flashback is always accompanied by a shrill hissing or squealing, and the flame does not
reappear at the tip as it does with a backfire. Flashback is extremely dangerous, and if the fuel gas, the
acetylene or hydrogen, is not turned off at the regulator, the fire can burn back through the hose and cause
an explosion.
flasher (electric lights). An automatic switch installed in a light system to turn the lights on and off in a
definite sequence. Flashers may be operated by a thermal switch, or they may have a motor that drives a
selector switch.
In a thermally operated switch, the current used in the lights passes through a strip of bimetallic
material and heats it. When the strip gets hot, it warps and separates the contacts, opening the circuit.
Current stops flowing, and the lights go out. When the strip cools, it snaps back to its original shape and
closes the contacts, and the lights turn back on.
flashing off (finishing system). A step in the curing process of a finishing system. The finishing material is
thinned with a solvent to get the proper viscosity for spraying. When the finish is sprayed on the surface, it
is shiny because of the solvents. These solvents evaporate very soon and leave the surface of the finish dry
to the touch, but it is not completely cured. The evaporation of the thinning solvents is called flashing off.
flashing the field (generator maintenance). A maintenance procedure for an aircraft generator that
restores residual magnetism to the field frame. DC generators get their field excitation current from the
armature, and the field frame must retain a small amount of permanent magnetism to furnish the magnetic
field to begin producing current in the armature. As soon as current begins to flow in the armature, it
excites the field.
If the field frame loses its residual magnetism, it must be restored before the generator can
produce current. This residual magnetism is restored by flashing the field. A battery is momentarily
connected to the field coil so current flows through it in its normal direction for a few seconds. This current
magnetizes the field frame.
flash line (molded products). The raised line along the surface of a molded part caused by the molten
material flowing into the space formed by the slightly rounded edges of the two halves of the mold.
flashover (reciprocating engine ignition system fault). An ignition system problem in which the high
voltage in the magneto distributor jumps to the wrong terminal. Flashover causes the wrong spark plug to
fire, and this reduces the engine power and produces vibration and excessive heat.
Flashover is often caused by moisture inside the distributor, but it also occurs when flying at high
altitude where the air inside the distributor does not have enough density to act as an effective dielectric.
Physically large distributors, low-tension ignition systems, and pressurized distributors have been used to
prevent flashover.
flash plating (metal finishing). The deposit of an extremely thin coating of metal on a surface. A flash
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 252
coating is only thick enough to give color to the surface.
flash point (petroleum specification). The temperature to which a material must be raised for it to ignite,
but not continue to burn, when a flame is passed above it.
flash resistant. 14 CFR Part 1: “Not susceptible to burning violently when ignited.”
flat-compounded generator. A compound-wound generator (a generator that has both a series and a
parallel, or shunt, winding) in which the effect of the two fields are balanced so they hold the output
　
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