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ride in the grooves and support the shaft. The balls are kept spaced evenly in the grooves by a thin
sheet-metal bearing retainer. Ball bearings can be designed to support thrust loads as well as radial loads.
ball check valve (fluid power system component). A type of flow control valve used in a fluid power
system to allow fluid to flow in one direction but not in the other.
A ball check valve contains a spring-loaded ball that seats in one side of the valve. The ball is
forced tightly against its seat by fluid entering the valve from the end containing the spring, and the fluid
cannot flow through the valve. Pressure on the side of the valve containing the ball forces the ball off its
seat and fluid flows through the valve. Fluid flowing through the valve is opposed only by the force of the
spring.
ball joint (exhaust system). A flexible expansion joint used in an aircraft engine exhaust system to allow
relative movement between the parts as heat causes them to expand and contract.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 62
ball peen hammer. A hammer with one side of its head shaped like a ball. The ball is used to peen, or
flatten, the heads of rivets driven in commercial sheet metal.
ballast (aircraft balance). A weight permanently installed in an aircraft to move the center of gravity to a
location within its allowable limits.
ballast lamp (electrical equipment). An incandescent lamp installed in series with an electrical load to
maintain a constant current.
If the current increases, the filament gets hotter and its resistance increases. This brings the current
back to its original value.
ballistic missile. A self-propelled missile which is guided as it goes upward. However, as it comes down, it
follows a ballistic trajectory, its natural curved path.
balloon (aerostatic device). A lightweight aerostatic machine, usually spherical in shape and neither
powered nor steerable. When the balloon is filled with hot air or with a gas that is lighter than air, it
displaces more air than it weighs, and the resulting aerostatic lift causes it to rise.
14 CFR Part 1: “A lighter-than-air aircraft that is not engine driven.”
balsa wood. A soft, strong, lightweight wood from the tropical American balsa tree. Balsa wood is used in
aircraft structure as the core for sandwich-type material. Planks of balsa are cut across the grain and are
bonded (glued) between sheets of thin aluminum alloy. The balsa sandwich is strong, lightweight, and
rigid.
balun. A type of balanced-to-unbalanced radio frequency transformer used in aircraft radio installation. A
balun is used to connect a balanced two-conductor antenna to an unbalanced transmission line.
bamboo. A tropical plant whose stalk (stem) is made up of strong, lightweight, hollow sections with a
tubular shape. The stalks were used as a structural material for some of the very first airplanes.
banana oil. Nitrocellulose dissolved in amyl acetate. Banana oil, so called because of its banana-like smell,
was used as a dope on the fabric covering of some of the early airplanes.
banana plug (electrical component). A device used to make a temporary connection to an electrical
circuit. The contacts of a banana plug are springs having the general shape of a banana. These springs press
out against the walls of the banana jack to make a low-resistance contact.
Banana plugs are installed on the leads of test instruments such as volt-ohm-milliammeters
(VOMs).
band (electrical frequencies). A range of frequencies acceptable to a piece of electronic equipment.
bandpass filter (electronic circuit). An electronic filter that passes a band of frequencies with little
attenuation (loss in power), while attenuating, or blocking, all frequencies above or below the band it
passes.
band-reject filter (electronic circuit). An electronic filter that rejects, or attenuates, a band of frequencies,
while passing with little loss all frequencies on either side of this band.
band saw (power tool). A form of power saw used to cut wood, plastics, or metal. The band saw blade is a
narrow strip of steel with teeth along one edge. The ends of the blade are welded together to form a
continuous loop, and the loop passes over two large wheels, one above and the other below the saw table.
One of the wheels is driven by an electric motor, and its speed is controllable to allow the operator
to match the speed of the blade to the type and thickness of material being cut.
For cutting the inside of a hole, many band saws have an attachment that allows the saw blade to
be cut in two and an end put through a hole in the work. The ends are then welded back together and the
weld ground smooth.
bandwidth (electrical circuit characteristic). The difference between the highest and the lowest
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航空术语词典Dictionary of Aeronautical Terms 上(42)
