board-foot. A unit of measurement commonly used for lumber. One board-foot is the amount of lumber in a piece of wood one foot long, one foot wide, and one inch thick. A board-foot is also used for the dimensions of any piece of board whose volume is equal to 144 cubic inches.
bob weight (aircraft control system component). A mechanical weight in the elevator control system of some airplanes.
The bob weight is used to apply a nose-down force on the elevator control system. This force is counteracted by an aerodynamic force caused by the elevator trim tab.
If the aircraft slows down enough that the aerodynamic force on the trim tab is lost, the bob weight forces the nose down, and the airplane picks up speed.
bogie landing gear (aircraft landing gear). The landing gear of an aircraft that uses tandem wheels mounted along the center line of the aircraft fuselage.
Some aircraft having bogie landing gear are supported while parked by outrigger wheels mounted far out on the wing.
bogus parts. Parts not approved for use in aircraft maintenance.
Bogus parts are normally made to look like legitimate parts. They carry the same part number as the legitimate part, and are often packaged in boxes that look like the box in which the original part was sold.
When bogus parts are installed in an aircraft, safety is often compromised.
boiling point. The temperature at which a liquid begins to change into a gas.
The boiling point of a liquid varies with the pressure of the air above it.
The boiling point of water, under standard sea level conditions, is 212°F, or 100°C.
bolt. A threaded fastener which has an enlarged head on one end and threads on the other. Bolts used in aircraft normally have hexagonal heads, but some high-strength bolts have a round head with a hexagonal-shaped hole. These special bolts are turned with an Allen wrench.
Bolts fasten pieces of material together by clamping them between the bolt head and a nut screwed onto the bolt threads.
bomb tester (spark plug tester). A shop tool used to test spark plugs after they have been cleaned and gapped.
After a spark plug has been serviced, it is screwed into the bomb tester, and about 200-psi air pressure is applied to the firing end. High voltage is directed into the terminal cavity of the spark plug, and the electrodes are observed to see the type and amount of spark being produced.
If a spark plug operates properly in a bomb tester, it will almost always work properly when it is installed in an aircraft engine.