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break line (aircraft drawings). A wavy line or a line containing a series of zig-zags, used to show that a
part of the component has been left off the drawing.
breakdown voltage (electrical component rating). The voltage that must be placed across the dielectric
in an electrical or electronic component to cause the dielectric to break down and conduct current.
breaker-point bounce. A condition in which the breaker points in an aircraft magneto bounce open, rather
than remaining closed when the cam follower moves off of the cam lobe. Breaker-point bounce is caused
by a weak breaker-point spring.
breaker points (magneto component). Electrical contacts in the primary circuit of an aircraft magneto
that are opened by a cam turned by the engine. The breaker points are timed to open at the instant the
ignition spark should occur. When the points open, the primary current stops flowing, and its magnetic field
collapses.
The lines of flux from the collapsing primary magnetic field cut across the many turns of the
secondary winding and induce a high voltage in the secondary circuit. It is this high secondary voltage that
causes a spark to jump across the gap in the spark plug.
breakers (tire component). Layers of reinforcing fabric (cords) in an aircraft tire between the casing plies
and the tread rubber. Breakers protect the casing plies and strengthen the tire.
breakout (air traffic control). A technique used to direct aircraft out of the approach stream. In the
context of close parallel operations, a breakout is used to direct threatened aircraft away from a deviating
aircraft.
breast drill. A hand-held drill motor used to drill relatively large holes in wood or metal. The handle of the
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 89
drill motor is fitted with a curved plate that allows the user to apply a pushing force with his upper body as
the drill cuts the hole.
breather (engine lubricating system). A vent line in an aircraft engine that allows the air pressure inside
the engine crankcase to be the same as the pressure of the surrounding air.
An effective breather system prevents pressure building up inside the engine and forcing oil out of
the crankcase.
breather-pressurizing valve (turbine engine lubrication system component). An aneroid-operated valve
in the overboard vent line of the lubrication system of some turbine engines.
The breather-pressurizing valve is open at sea level, but closes with increasing altitude to maintain
sea level pressure inside the vent system as the aircraft goes up in altitude.
breech chamber (cartridge-pneumatic starter). A locking chamber in a cartridge starter that holds a
pyrotechnic cartridge (a powder charge). The cartridge is placed in the breech, the breech is closed and
locked, and the cartridge is fired. The expanding gases produced by the burning powder spin the turbine in
the starter.
breeder reactor (nuclear energy). A reactor that produces fissionable material as well as consuming it.
bridge circuit (electrical circuit). An electrical circuit containing four impedances connected in such a
way that their schematic diagram forms a square. One pair of diagonally opposite corners is connected to
an input device, and the other two corners are connected to the output device.
See illustration for balanced bridge.
bridge-type rectifier. An electrical rectifier circuit using four diodes to change alternating current into
full-wave rectified direct current.
bright band (radar meteorology). A narrow, intense echo on the range-height indicator scope resulting
from water-covered ice particles of high reflectivity at the melting level.
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brine (heat treatment of metal). A solution of salt (sodium chloride) and water, used as a quenching
medium in the heat treatment of metal.
Steel parts quenched in brine are harder than parts quenched in either water or oil.
Brinell hardness test. A method of measuring the hardness of metal. A hardened steel sphere is pressed
into the surface of the metal by a specific force and is held for a specified period of time.
The force is removed and the diameter of the indentation caused by the ball is measured with a
special microscope. The larger the diameter of the dent, the softer the metal.
brinelling (bearing damage). A form of damage to the hardened surface of a bearing roller or race caused
by excessive radial loads on the bearings.
When a bearing is overloaded, the rollers are forced into the race, and they leave small dips
(indentations) in the race or flat spots on the surface of the roller. Bearings that have been brinelled must be
replaced.
　
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