the Aviation Dictionary

blizzard - blue arc
products of corrosion. 2. In composites, an undesirable
rounded elevation of the surface of a plastic, and
somewhat resembling in shape a blister on the human
skin.
blizzard - A severe weather condition characterized by
low temperatures and strong winds bearing a great
amount of snow, either falling or picked up from the
ground.
block - To secure from, or release an airplane for flight.
It includes actions by ground crew personnel who aid
the pilot in parking, mooring, or releasing by handling
the wheel chocks, gear pins, etc.
block diagram - A functional diagram of a system in
which the units are represented by squares that describe
the functions of the unit and show its relationship to the
other units of the system. Arrows between the blocks
show the direction of the flow of energy or information
within the system. Block diagrams do not show any of
the actual components.
block heater - An electrical heater embedded in die that
is used for hot dimpling sheet metal.
block plane - A small, hand-held carpenter's tool used
for smoothing the surface of wood.
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block test - An operational test of an aircraft engine
when the engine is installed in a test cell to determine
its condition.
blocked - Phraseology used to indicate that a radio
transmission has be% distorted or interrupted due to
multiple simultaneous radio transmissions.
hlocking capacitor - A capacitor that has high
impedance to DC and low frequency AC. However, it
has low impedance to the AC signal being passed
through the circuit.
block-to-block time - The lapsed time between an
airplane leaving the ramp for the purpose of flight and
its returning after landing.
bloom - A bar of iron or steel hammered or rolled from
an ingot.
blow molding - A plastic molding process in which a
hollow tube of thermoplastic material is heated inside a
mold. Air pressure is applied to the inside of the tube,
and the soft plastic material is forced out against the
walls of the mold. The outside of the part takes the
form of the inside of the mold.
blowback - In rotorcraft, the tendency of the rotor disc
to tilt aft in forward flight as a result of flapping.
blowdown turbine - A power recovery device used on
the Wright R-3350 engine that is driven by the exhaust
gases from the engine, and coupled through a clutch to
the engine crankshaft. Also referred to as Powerrecovery
turbine (PRT).
blower - 1. A mechanical device such as a fan that is
used to move a column of air. 2. An internal geardriven
supercharger in an aircraft reciprocating engine.
Blowers are used to increase the pressure of the fuellair
mixture after it has passed through the carburetor, and
to improve the distribution of the fuel-air mixture to all
of the cylinders.
blower clutch - A unit in a two-speed supercharger
system of a reciprocating engine that can be driven at
two different speeds by means of a clutch.
blower section - The blower section of an aircraft
reciprocating engine crankcase that houses the internal,
gear-driven supercharger.
blow-in doors - In gas turbine engines, spring-loaded
doors located ahead of the first stage of the
compressor. These doors are spring-loaded to hold
them closed, but under conditions of low airspeed and
high engine power, they open automatically to allow
more air to enter the compressor. Blow-in doors help
prevent compressor stall. Also referred to as auxiliary
air-intake doors.
blowing dust - Dust particles picked up locally from the
surface and blown about in clouds or sheets.
blowing sand - Sand picked up locally from the surface
and blown about in clouds or sheets.
blowing snow - Snow picked up from the surface by the
wind and carried to a height of 6 feet or more.
blowing spray - Water particles picked up by the wind
from the surface of a large body of water.
blown boundary layer control - A system used to
decrease aerodynamic drag on the surface of a wing.
Blown boundary layer control uses high-velocity air
blown through ducts or jets to energize the boundary
layer.
blow-out plug - A safety plug or disc on the outside
skin of an aircraft fuselage near the installation of high
pressure oxygen and COz, or other fire extinguisher
agents. It is designed to rupture and discharge its
contents overboard if, for any reason, the pressure of
the gas in the cylinders rises to a dangerous value.
Colored disks in the blow-out plugs identify the system
that has been relieved in this manner.
blowtorch - A small burner having a device to intensify
combustion by means of a blast of air or oxygen.
Usually includes a fuel tank pressurized by a hand
pump. Used for soldering, welding, and glass blowing.
blue arc - An instrument marking that indicates an
operating range. For example, the blue arc might
indicate the manifold pressure gauge range in which an
engine can be operated with the carburetor control set
at automatic lean.
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