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beam. This beam can be oriented in any direction needed.
beam-power tube (electron tube). A form of tetrode (four-element) electron tube that uses two
beam-forming electrodes, or plates, to shape the flow of electrons so they travel from the cathode to the
plate in definite beams.
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The screen grid is wound in such a way that its wires are in the shadow cast by the control grid,
and keeping the screen grid out of the path of the electrons helps minimize screen current.
Beam power tubes are power amplifier tubes, rather than voltage amplifiers.
beam resolution (radar technology). The ability of radar to distinguish between targets at approximately
the same range but along different azimuths.
bearing (mechanical equipment). A device fitted into a hole to reduce the friction present when a shaft
rotates in the hole. Plain bearings are liners for the hole made of a material such as bronze or babbitt metal
which have a low coefficient of friction. Antifriction bearings consist of a pair of hardened and polished
steel races, with either hardened steel rollers or balls rolling between them.
bearing (navigation). The horizontal direction to one object from another. True bearing is the direction
measured in degrees clockwise from true north. Relative bearing between two objects is the direction
measured in degrees clockwise from a reference point on the first object, such as the nose of an aircraft, to
the second object.
bearing cage (antifriction bearing component). A thin sheet metal separator that keeps the rollers or balls
in an antifriction bearing evenly spaced around the races. The bearing cage should never touch either of the
bearing races.
bearing cone (antifriction bearings). The tapered bearing races used with some roller bearings.
For wheel bearings, the inner cone is slipped over the axle, and the outer cone fits into a recess
inside the wheel. Hardened steel rollers ride between the two cones.
bearing failure (riveted structural failure). A type of failure of a riveted joint in a sheet metal structure.
A joint fails in bearing when the metal tears at the rivet holes before the rivets shear.
bearing race. The hardened steel surface upon which the balls or rollers of an antifriction bearing ride.
bearing rollers. Hardened steel rollers that support a rotating shaft. The rollers ride between two hardened
steel races and are usually spaced evenly around the races by a thin sheet metal separator.
bearing strength (sheet metal specification). The amount of pull needed to cause a piece of sheet metal to
tear at the points it is held together with rivets.
The bearing strength of a material is affected by both its thickness and the diameter of the rivet.
bearing support (gas turbine engine component). The portion of the case of a gas turbine engine in
which the main bearings are mounted.
bearing surface. A surface which supports a moving load.
Bearing surfaces are normally treated in some way to decrease the friction between the surface and
the load being moved.
beat (vibration). A low-frequency sound, or vibration, produced when two sources of vibration having
almost, but not exactly, the same frequency, act on an object at the same time.
For example, in a multi-engine airplane, if one engine is turning at 1,850 RPM and the other is
turning at 1,880 RPM, the airframe vibrations caused by these engines will produce a very noticeable beat
of 30 cycles per minute. This beat is caused by the difference in the frequency of the two vibrations.
beat frequency. The frequency of vibration produced when two sources of vibration act on a common
body. The beat frequency is the difference between the frequencies of the two original vibrations.
Beaufort scale. A number rating from zero to 12, used by the weather bureau to describe wind speed.
Beaufort Velocity
Force (knots) Indication
0 less than 1 smoke rises vertically
1 1 – 3 wind blows smoke
2 2 – 7 wind felt on face
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3 8 – 12 leaves in motion
4 13 – 18 raises dust and loose paper
5 19 – 24 sways small trees
6 25 – 31 moves large branches of trees
7 32 – 38 whole trees in motion
8 39 – 46 breaks twigs off of trees
9 47 – 54 slight structural damage
10 55 – 63 uproots trees
11 64 – 72 widespread damage
12 73 – 136 devastation
beef up. To strengthen.
beehive spring (riveting gun component). A hard steel, coil-spring retainer used to hold a rivet set in a
pneumatic rivet gun.
A beehive spring, which gets its name from its shape, screws onto the end of the rivet gun and
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航空术语词典Dictionary of Aeronautical Terms 上(46)
