bayonet fueling nozzle. A type of nozzle used to fuel aircraft with a pressure, or single-point, fueling system. The nozzle is connected to the fueling receptacle in the aircraft, and the handles are turned a portion of a turn to lock it in place.
bayonet gage. A term for a dip stick, such as that used to measure the quantity of a liquid in a tank or a reservoir.
bayonet thermocouple probe. A thermocouple pickup used to measure cylinder head temperature on an air-cooled aircraft engine.
The bayonet probe fits into an adapter screwed into the cylinder head and a spring holds the end of the probe tightly against the cylinder head.
B-battery. A source of high-voltage direct current needed for vacuum tubes. Vacuum tubes must have a high positive DC voltage on their plates and screen grids to pull electrons across the vacuum from the cathode. This high voltage is called B plus (B+) voltage.
BBC. See before bottom center.
BCD (binary coded decimal). A system used for changing decimal numbers into binary numbers. Each digit from 0 through 9 is represented with four binary digits:
Decimal Binary Decimal Binary
0 = 0000 5 = 0101
1 = 0001 6 = 0110
2 = 0010 7 = 0111
3 = 0011 8 = 1000
4 = 0100 9 = 1001
The decimal number 126 for example, expressed in BCD, is: 0001 0010 0110.
B-check. See maintenance checks.
BDC. See bottom dead center.
bead (tire component). The high-strength carbon-steel wire bundles that give an aircraft tire its strength and stiffness where it mounts on the wheel.
bead (tubing). A rounded ridge formed near the end of a piece of rigid tubing used for carrying fluids in an aircraft.
A hose is slipped over the end of the tube, and a hose clamp is installed between the end of the hose and the bead. The bead keeps the tube from being pulled out of the hose.
bead (welding). The ridge of filler metal that sticks up above the surface of metal that has been welded.
The appearance of the bead usually indicates the condition of the weld. The bead of a good weld is uniform in height, has a smooth, uniform ripple on its surface, and blends evenly into the base metal.
bead seat area of a wheel. The flat surface of an aircraft wheel on which the bead of the tire seats.
The bead seat area of wheels that have tubeless tires installed on them must be very smooth and free of damage. Only then can the tire form an airtight seal with the wheel.
bead thermistor (fire detection system component). A component in a fire detection system that signals the presence of a fire or overheat condition.
Beads of a thermistor material (a material, such as germanium, whose resistance changes with its temperature) support a wire that forms part of the fire detection circuit. The bead-supported wire is enclosed in a metal tube routed through the area to be protected.
If the tube is heated by a fire, the thermistor material changes from an insulator into a conductor and completes an electrical circuit between the central wire and the tube. This completed circuit initiates the fire-warning procedure by turning on the fire-warning light and sounding the fire-warning bell.
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