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blowing snow (meteorology). Snow picked up locally from the surface by the wind and carried to a height
of six feet or more.
blowing spray (meteorology). Water particles picked up by the wind from the surface of a large body of
water.
blown boundary layer control (aerodynamics). A method of decreasing aerodynamic drag on the surface
of an airplane wing. The boundary layer is the layer of air which flows in a random fashion directly over
the surface of the wing.
Blown boundary layer control uses high-velocity air blown through ducts or jets to energize, or
add energy to, the boundary layer. Energizing this air speeds it up and causes it to flow straight across the
wing.
blowout plug. A safety plug on the outside skin of an aircraft fuselage near the installation of high-pressure
oxygen or fire extinguisher agent. If, for any reason, the pressure of the gas in the cylinders rises to a
dangerous level, the blowout plug will blow out and relieve the pressure.
Colored disks in the blowout plugs identify the system that has been relieved in this manner.
blowtorch. A hand-held torch that uses liquid gasoline as a fuel. Air is pumped into the fuel tank, and the
liquid fuel sprays out into the burner where it becomes a vapor. The air compressed in the tank blows
through the flame and intensifies it.
Gasoline blowtorches have been replaced, to a great extent, by torches using propane or other
liquified petroleum products as their fuel.
bluckets (turbofan engine component). The portions of aft-fan blades that are in the exhaust of the core
engine. Bluckets drive the fan by energy received from the hot gases leaving the core engine.
blueprint. A type of engineering drawing used in the design and manufacture of aircraft, aircraft engines,
and various components. Lines in the drawing appear white on a dark blue background.
The original drawing is made with black ink on translucent drawing paper or cloth. This drawing
is then used as a negative, and sensitized paper is exposed through the drawing by exposing it to a
high-intensity light. After the exposure, the print is developed by washing it in water.
Blueprints have been replaced in many engineering departments by prints made by the Ozalid
process, in which the exposed sensitized paper is developed by exposing it to ammonia fumes.
blush (aircraft finishing system defect). A defect in a lacquer or dope finish caused by moisture
condensing on the surface before the finish dries.
If the humidity of the air is high, the evaporation of the solvents cools the air enough to cause the
moisture to condense. The water condensed from the air mixes with the lacquer or dope and forms a dull,
porous, chalky-looking finish. This is called blush. A blushed finish is neither attractive nor protective.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 82
BMEP (brake mean effective pressure). The average pressure inside the cylinder of a reciprocating
engine during the power stroke.
BMEP, measured in pounds per square inch, relates to the torque produced by the engine, and can
be calculated when the brake horsepower and RPM of the engine are known.
B-nut. A type of tubing nut used to attach a piece of flared tubing to a threaded fitting. B-nuts are used with
a sleeve slipped over the tubing before the tubing is flared. The B-nut forces the sleeve tight against the
flare, which seals against the flare cone of the male fitting.
board-foot. A unit of measurement commonly used for lumber. One board-foot is the amount of lumber in
a piece of wood one foot long, one foot wide, and one inch thick. A board-foot is also used for the
dimensions of any piece of board whose volume is equal to 144 cubic inches.
bob weight (aircraft control system component). A mechanical weight in the elevator control system of
some airplanes.
The bob weight is used to apply a nose-down force on the elevator control system. This force is
counteracted by an aerodynamic force caused by the elevator trim tab.
If the aircraft slows down enough that the aerodynamic force on the trim tab is lost, the bob weight
forces the nose down, and the airplane picks up speed.
bogie landing gear (aircraft landing gear). The landing gear of an aircraft that uses tandem wheels
mounted along the center line of the aircraft fuselage.
Some aircraft having bogie landing gear are supported while parked by outrigger wheels mounted
far out on the wing.
bogus parts. Parts not approved for use in aircraft maintenance.
Bogus parts are normally made to look like legitimate parts. They carry the same part number as
the legitimate part, and are often packaged in boxes that look like the box in which the original part was
sold.
　
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