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becomes so great that the air no longer flows smoothly over the surface but breaks away.
burble point (aerodynamic turbulence). The angle of attack at which air flowing over an aerodynamic
surface no longer flows smoothly, but breaks away and forms a turbulent flow (it burbles).
burn-down coat (aircraft finishing system). A coat of lacquer or dope in which some of the thinner is
replaced with an equal amount of retarder.
When this mixture is sprayed over a blushed surface, the thinner softens and restores the blushed
material. The retarder slows the drying so the new film will not blush.
burner cans (gas turbine engine component). Individual combustion chambers of a gas turbine engine.
burner compartment. The portion of an engine pod or nacelle of a turbojet-powered aircraft that houses
the burner section of the engine.
burner pressure (gas turbine engine parameter). The static pressure inside the combustors, or burners,
of a gas turbine engine. Burner pressure, whose symbol is Pb, is one of the parameters used to compute the
mass airflow through the engine.
burner. See combustor.
burning. The process in which a material is consumed by fire. The material, called the fuel, is consumed
when it reacts with the oxygen in the air to form new compounds. These compounds usually include carbon
dioxide and water. In the process of burning, a large amount of heat and light are usually produced.
burning in (electronic components). A process in the manufacture of sensitive electronic equipment in
which the equipment is operated for a specified period of time. The burning-in period shows up weak or
faulty components, and stabilizes the operating characteristics of the components.
burning point (petroleum specification). The lowest temperature at which a petroleum product in an open
container will continue to burn when it is ignited by an open flame held near its surface.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 94
burnish (verb). To smooth the surface of metal that has been damaged by a deep scratch or gouge.
The metal that has piled up at the edge of the damage is pushed back into the damage with a
smooth, hard steel burnishing tool.
burr (type of metal damage). A sharp, rough edge of a piece of metal left when the metal is sheared,
punched, or drilled.
burst RPM (gas turbine engine parameter). The compressor speed of an engine at which the centrifugal
loads are so high the compressor will fly apart. The engine actually explodes.
bus (electrical system). A point within an electrical system from which the individual circuits get their
power.
bus bar (aircraft electrical system component). A power distribution point in an aircraft electrical
system.
Bus bars are usually strips of metal to which generator or battery power is connected and from
which circuit breakers pick up this power and carry it to the appropriate circuits within the aircraft.
bus tie breaker. A circuit breaker used to connect two electrical bus bars.
bushing. A type of friction bearing consisting of a removable cylinder made of some material, such as
bronze, that has a low coefficient of friction.
The bushing is pressed into a hole, and it is reamed to a size that fits the shaft with the correct
amount of clearance for lubrication.
Some bushings are made of Oilite, a porous bronze material that is impregnated with oil and
requires no additional lubrication.
butt fusion. A method of joining two pieces of thermoplastic material. Butt fusion is done by heating the
ends of the two pieces until they are in a molten state and forcing them together before they cool and
harden.
butt joint (welded joint). A type of welded joint in which the pieces of metal to be joined are placed so
their edges touch, but do not overlap. The edges of both pieces of metal are melted, and filler rod is added
to form a bead between the two pieces.
butt rib (wing rib). The rib at the inboard end of a wing panel.
butterfly tail (airplane control surfaces). A type of tail configuration used on some models of the Beech
Bonanza.
A butterfly, or V-tail, has two fixed surfaces and two movable surfaces, which produce
aerodynamic forces to rotate the aircraft about its vertical and lateral axes in the same way as the three
fixed and three movable surfaces used in the conventional inverted T-tail.
butterfly valve. A flat, disk-shaped valve used to control the flow of fluid in a round pipe or tube. When
the butterfly valve is across the tube, the flow is shut off, and when it is turned parallel with the tube, the
obstruction caused by the valve is minimum, and the flow is the greatest.
Butterfly-type throttle valves are used to control the airflow through a reciprocating engine fuel
　
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