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degrees the metal is bent. The amount of material in the bend is usually found by using a bend allowance
chart.
bend radius (sheet metal layout). The radius of the inside of a bend in a piece of sheet metal, tubing, or
wire bundle.
bend tangent line (sheet metal layout). A line made in a sheet metal layout that indicates the point at
which the bend is started. The material on one side of the bend tangent line is the flat surface, and the
material on the other side is the bend allowance.
bending strength. The resistance a piece of material offers to bending stresses.
bending stress. The type of stress that tries to pull up or push down on one end of a beam while the other
end is held stationary. When a beam is bent down, the top is under a tensile stress, and the bottom is under
a compressive stress.
benzene. A colorless, volatile, flammable, aromatic hydrocarbon liquid which has the chemical formula
C6H6. Benzene, sometimes called benzoil, is used as a solvent, as a cleaning fluid, and as a fuel for some
special types of reciprocating engines.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 71
berkelium. A synthetic, radioactive chemical element in the actinide series. Berkelium’s properties
resemble those of cerium. Berkelium’s symbol is Bk, and its atomic number is 97.
Bernoulli’s principle. A fundamental principle of physics that explains the relation between kinetic and
potential energy in a fluid in motion.
When the total energy in a column of moving fluid remains constant, any increase in the kinetic
energy of the fluid (its velocity) results in a corresponding decrease in its potential energy (its pressure).
beryllium. A high-melting-point, lightweight, corrosion-resistant, steel-gray metallic chemical element.
Beryllium’s symbol is Be, its atomic number is 4, and its atomic weight is 9.0122. Beryllium’s main
importance is in its use as an alloying agent for copper.
beryllium bronze. An alloy of copper combined with about three percent beryllium. Beryllium bronze is
used for making springs, bellows, and diaphragms for pressure-measuring instruments.
best angle-of-climb airspeed (VX). The airspeed at which an aircraft will gain the greatest amount of
altitude in a given distance.
best-economy mixture (reciprocating engine fuel-air mixture ratio). The fuel-air mixture ratio used in a
reciprocating engine that gives the aircraft its greatest range of flight.
The best-economy fuel-air mixture ratio, which is in the range of 0.055 to 0.065 (18:1 to 15:1
air-fuel ratio). This mixture ratio does not provide any additional fuel for cooling, so it can be used only
when the engine is operating with reduced power.
best-power mixture (reciprocating engine fuel-air mixture ratio). The fuel-air mixture ratio used in a
reciprocating engine that allows the engine to develop its greatest amount of power.
The best-power fuel-air mixture ratio, which is in the range of 0.074 to 0.087 (13.5:1 to 11.5:1
air-fuel ratio), is richer than the ratio used for the best economy. The additional fuel in this mixture is used
to remove some of the heat from the cylinders when the engine is producing its best power.
best rate-of-climb airspeed (VY). The airspeed at which an aircraft will gain the greatest amount of
altitude in a given unit of time.
beta (electronic measurement). The current gain of a transistor connected as a grounded-emitter (common
emitter) amplifier.
Beta is the ratio of the change in collector current to the change in base current when the collector
voltage is held constant.
beta control range (turboprop engine operation). The range of operation of a turboprop powerplant
normally used for in-flight approach and ground handling of the engine and aircraft.
Typically the beta mode includes operations from 65% to 95% of the engine’s rated RPM.
beta particle (nuclear particle). A particle emitted from the nucleus of an atom during radioactive decay.
A negative beta particle is the same as an electron, and a positive beta particle (called a positron) has the
same mass as an electron, but has a positive charge.
beta tube (turboprop control). A tube in a Garrett TPE331 turboprop engine that extends into the
propeller pitch control to act as a follow-up device. It provides proportional movement of the propeller
blades with movement of the power lever.
bevel gears. A pair of toothed wheels with the teeth cut on a surface at an angle other than 90° to the axis
of the shaft on which the wheels are mounted. Bevel gears allow one shaft to drive another shaft that is not
parallel to it.
bevel. The angle formed by one surface with another surface when the angle is not a right angle.
　
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