the Aviation Dictionary

bag side . ball joint
over a rigid mold in as many layers as are needed. A
sheet of flexible, air-tight plastic material is placed
over the mold and the edges are sealed to form a bag
over the part. The entire assembly is then placed in an
autoclave for curing. In the absence of an autoclave, a
vacuum pump can be attached to the bag, and the air
pumped out. The atmospheric pressure pressing on the
outside of the bag supplies the needed force.
bag side - In composites, the side of a part that is cured
against the vacuum bag.
bagging - In composites, applying an impermeable layer
of film over an uncured part and sealing the edges so
that a vacuum can be drawn.
bailout bottle - Small oxygen cylinder connected to the
oxygen mask supplying several minutes of oxygen. It
can be used in case of primary oxygen system failure
or if an emergency bailout at high altitude became
necessary.
Bakelite - A phenol resin, often used as electrical
insulation, made by the Bakelite Corporation.
baking soda - The common term for bicarbonate of
soda O\TaHCO3).
balance - A state of equilibrium.
balance bridge - A method of measuring resistance. It
consists of three known resistances and an unknown
resistance. When the known resistances are adjusted so
the bridge is balanced, the output is zero. The unknown
resistance can then be calculated using the relationship
RI:R2=R3:R4. See also Wheatstone bridge.
balance chamber - An internal air chamber in a turbine
engine used to absorb some of the compressor axial
loading "thrust."
balance checks - A check or series of inspections
performed on rotating components after overhaul to
statically and dynamically check for correct balancing.
balance point - 1. A point within an object at which the
sum of all its components have zero rotation. 2. The
point about which an object will balance.
balance pressure torch - A welding torch where the
oxygen and acetylene are both fed to the torch at the
same pressure. The openings to the mixing chamber for
each gas are equal in size, and the delivery of each gas
is independently controlled.
balance tab - An auxiliary control mounted on a
primary control surface, which automatically moves in
the direction opposite the primary control to provide an
aerodynamic assist in the movement of the control.
Sometimes referred to as a servo tab.
balance, static - 1. A condition of balance which does
not involve any dynamic forces. 2. When a body will
stand in any position as the result of counterbalancing
andlor reducing the heavy portions, it is said to be in
standing or static balance.
balanced actuator - A hydraulic or pneumatic actuator
having the same area on each side of the actuator
piston. Fluid power into the actuator produces the same
amount of force in either direction of piston movement.
balanced amplifier - An electronic amplifier that has
two output circuits that are equal, but opposite in
phase. Also referred to as a push-pull amplifier.
balanced control surface - A primary control surface
with an overhang ahead of the hinge line that provides
an aerodynamic assist to reduce control pressures.
balanced design - In filament-winding of composites, a
winding pattern so designed that the stresses in all
filaments are equal.
balanced laminate - In composites, each layer except
the 0/90° is placed in plus and minus pairs around the
centerline. These plies do not have to be adjacent to
each other.
balanced transmission line - A radio frequency
transmission line matched in impedance between each
conductor and ground, and between conductors and the
electronic equipment to which the conductors are
connected. Neither conductor is grounded.
balancing - The act of performing a balance procedure
using prescribed methods.
ball bearing - An anti-friction bearing consisting of
grooved inner and outer races and one or more sets of
steel balls held in a sheet metal retainer. Ball bearings
can be designed to support thrust loads as well as radial
loads.
ball bearing assembly - Consists of grooved inner and
outer races, one or more sets of balls, and, in bearings
designed for disassembly, a bearing retainer. They are
used for supercharger impeller shaft bearings and
rocker arm bearings in some engines. Special deepgroove
ball bearings are used in aircraft engines to
transmit propeller thrust to the engine nose section.
ball check valve - A check
valve in a fluid power
system that uses a springloaded
steel ball and a seat
to allow flow in one
direction only. The ball is forced tightly against its seat
by fluid flowing into the valve from the end that
contains the spring, thereby stopping the fluid flow
through the valve. Fluid flowing into the valve from
the ball end forces the ball off its seat, allowing flow
through the valve.
ball joint -A flexible expansion joint used in an aircraft
engine exhaust system to allow relative movement of
the parts as a result of their expansion and contraction.
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