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indicates pressure altitude. When it is set to the existing altimeter setting, the altimeter reads indicated
altitude.
barometric tendency (meteorology). The change of barometric pressure within a specified period of time.
For aviation weather observations, the time period is normally three hours.
barrage balloon. A tethered, gas-filled balloon used during wartime to protect an area from low-flying
airplanes. An airplane is prevented from making a strafing run in an area protected by barrage balloons by
the danger of flying into the tethering cables.
barrel roll (airplane flight maneuver). A flight maneuver of an airplane in which the airplane rolls
around its longitudinal axis.
The term barrel roll has been replaced in modern usage; the maneuver is now called an aileron roll,
or slow roll.
barrier voltage (semiconductor parameter). The voltage across a forward-biased PN junction in a
semiconductor diode or transistor. When the mobile charges are drawn away from the junction, ionic
charges are left. These ionic charges cause a voltage, or potential difference, to exist across the junction.
The positive barrier voltage is in the N-material, and the negative barrier voltage is in the P-material.
The barrier voltage across the junction in a silicon diode is about 0.7 volt, and approximately 0.3
volt in a germanium diode.
base (mathematics). The number in an exponential expression that is multiplied by itself the number of
times shown by the exponent.
base (transistor electrode). The electrode of a bipolar transistor between the emitter and the collector.
Controlling a small flow of electrons moving into or out of the base controls a much larger flow of
electrons between the emitter and the collector.
The base of a transistor compares with the grid of a vacuum tube.
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baseball stitch. A type of hand stitch used to join two pieces of fabric that butt together, but do not overlap.
Baseball stitches are used to sew together the edges of a tear in the fabric used to cover an aircraft
structure.
The baseball stitch gets its name from this type of stitch being used to sew the cover on a baseball.
base line. A line used as a datum, or reference line, for measuring.
base metal (metallurgy). Metal to which alloying agents are added.
base metal (welding). The metal to be welded, soldered, or brazed.
BASIC (computer language). A commonly used high-level language for digital computers. The
commands used in BASIC are similar to commands used in the English language.
The acronym BASIC comes from Beginners All-purpose Symbolic Instruction Code.
basic operating weight. See BOW.
bastard file. A double-cut, metalworking file with the next to the coarsest teeth. There are five grades of
double-cut files based on their teeth. From the coarsest to the finest, these are: coarse-cut, bastard-cut,
second-cut, smooth-cut, and dead-smooth-cut.
bathtub capacitor (electrical component). A type of capacitor sealed in a metal container. The bathtub
capacitor takes its name from its shape, which is similar to that of a bathtub.
battery (electrical component). An electrochemical device, normally made of a number of individual cells.
Electrical energy is stored in a battery by changing it into chemical energy.
Chemical energy in the battery causes a potential difference between the negative and the positive
terminals, and when a conductor joins the two terminals, electrons flow from the negative terminal to the
positive terminal.
battery analyzer. A special transformer-rectifier unit used to charge nickel-cadmium batteries. In addition
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to a source of direct current, the analyzer has a built-in load bank, timers, indicators, and controls for
deep-cycling and recharging these batteries.
battery bus. A tie point in an aircraft electrical system to which the battery is connected.
Electrical loads connected to the battery bus get their power from the bus.
battery charger. A transformer-rectifier unit that changes alternating current into direct current of the
proper voltage to charge storage batteries.
The battery charger is connected to the battery with the positive terminal of the charger connected
to the positive terminal of the battery, and the battery is charged until its voltage is the same as that of the
charger.
baud (computer operation). A unit of speed for binary data transmission equal to one bit per second.
bauxite. A type of clay or rock, the source of aluminum. To extract the aluminum, the bauxite is changed
into alumina (aluminum oxide). Then, the alumina is reduced to metallic aluminum by an electrolytic
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航空术语词典Dictionary of Aeronautical Terms 上(44)
