the Aviation Dictionary

beat. bend tangent line (BL)
to keep dirt out of the outside bearing. Retainers and
felt seals are supplied inboard of the inner bearing to
prevent grease from reaching the brake lining.
beat - A low frequency vibration produced when two
sources of vibration act on the same object at the same
time. In a multi-engine airplane, if two engines have
slightly different RPMs, the airframe vibrations caused
by these engines will produce a very noticeable beat.
This beat is caused by the difference in the frequency
of the two vibrations.
bellmouth - A turbine engine air inlet duct having a
flared or convergent shape used to direct air into a gas
turbine engine. The shape of the bellmouth increases
the efficiency of the incoming air to the engine.
bellows - Circular, pleated, or corrugated capsules or
compartments used to measure pressure. They may be
either evacuated or filled with a specific pressure of
inert gas and exposed to the pressure to be measured.
Their dimensional change is measured as the pressure
surrounding them varies.
beat-frequency oscillator (BFO) - A variable Bellville washer - A lock washer made in the form of a
frequency electronic oscillator designed to produce a cupped steel washer.
signal frequency that is mixed with another frequency
below minimums - Weather conditions below the
in order to develop an intermediate frequency or an
minimums prescribed by regulation for the particular
audio frequency that can be heard.
action involved; e.g., landing - minimums, takeoff
Beaufort scale - In meteorology, a scale used to minimums.
describe wind force, ranging from 0 to 12, 0 (zero)
belt frame - A circumferential Fuselage frame usually
represents less than 1 MPH, and 12 represents speeds
having a channel or hat section.
of more than 72 MPH, or hurricane force.
beef up - To strengthen or reinforce.
bench check - A functional check performed on a part
that has been removed From an aircraft to determine its
beehive spring - A hard
condition of serviceability. The equipmenl is set up on
steel retaining spring used
a test bench and operated to find out whether or not it
to hold a rivet set in a
is functioning as it should.
pneumatic rivet gun.
bench plate - A flat, cast iron plate built into a bench
Prevents the set from
being driven out of the gun. It derives its name,
used for working sheet metal. Holes in the bench plate
support stakes that are used to form the sheet metal.
beehive, from its shape.
bench timing - A functional procedure to time a
beep button - A switch on the collective control used to
magneto by setting the breaker points, and for checking
trim a helicopter turbine engine by increasing or
the rotor for the E-gap position. This process is done in
decreasing the steady state RPM. Also referred to as a
the shop before installation in the engine.
beeper button.
bend allowance - The amount
beeswax - A substance secreted by bees. It is used to
of material actually used in the
coat rib lacing cord to protect it from moisture and
bend of sheet metal. This
prevent slippage.
amount of metal must be added
before bottom center (BBC) - The degrees of to the overall length of the
crankshaft travel before the piston stops at the bottom layout pattern to assure
of its stroke.
adequate metal for the bend.
end allowance depends on
before top center (BTC)- The degrees of crankshaft
four factors: the degree of the bend, the radius of the
travel before the piston reaches the top of its stroke.
bend, the thickness of the metal, and the type of metal
behaviorism -- Theory of learning - that learning - is used. The amount of material in the bend is usually
dependent on particular behaviors being positively found by using a bend allowance chart.
reinforced by someone other than the student.
bend allowance chart - A chart used to save time in
be1 - A unit used to express the ratio of two values of calculating the bend allowance of sheet metal.
power. The number of bels is the logarithm to the base Formulas and charts for various angles, radii of bends,
10 of the oower ratio. material thicknesses, and other factors have been
bell gear - The large stationary gear used in a spur gearestablished
to make up the chart.
type planetary reduction gearing system.
~- - -
bend radius - The radius of the bend as measured on
~
bellcrank - A double lever in an aircraft control system
the inside of the curve.
used to change the direction of motion. Bellcranks are bend tangent line (BL)- A line made on a sheet metal
commonly used in an aileron system to change layout to indicate the beginning of the bend, and the
spanwise movement into chordwise movement to move line at which the metal stops curving. All the space
the control surface.
between the bend tangent lines is the bend allowance.
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