backup system. A reserve, or substitute, system that can be put into effect if the main or primary system should fail.
back voltage (counter-electromotive force). Voltage induced in a conductor when it is carrying a changing current. As the magnetic field produced by the changing current builds up and decays, it cuts across the conductor and induces a voltage in it.
The polarity of this induced voltage is opposite that of the voltage which caused the original current to flow.
bacteria. Microscopic plant life that lives in water entrapped inside aircraft fuel tanks. The growth of bacteria in jet aircraft fuel tanks forms a film of scum which holds water against the aluminum alloy surfaces and causes corrosion to form.
bactericide. A material used to destroy bacteria.
baffle. A part of a structure used to impede, regulate, or alter the rate or direction of flow of a fluid, light, or sound.
baffle (air-cooled engine component). A sheet metal shield used to direct the flow of air between and around the cylinders of an air-cooled reciprocating engine.
Forcing this air to flow through the fins on the cylinders removes the maximum amount of heat from the engine.
baffle system (fuel tanks). A series of baffles, or partitions, inside an aircraft fuel tank. These baffles have holes in them that allow the fuel to feed to the tank outlet, but prevent the fuel from surging enough to uncover the outlet.
Aircraft fuel tanks carry such large quantities of fuel that the sloshing (surging back and forth) of the fuel in a partially full tank could cause severe control problems.
bag molding. A method of applying pressure to a piece of laminated plastic material so all the layers are held in tight contact with each other. The reinforcing material is impregnated with liquid resin and laid up over a rigid mold in as many layers as are needed.
A sheet of flexible, airtight plastic material is placed over the mold, and the edges are sealed to form a bag over the part. The entire assembly is then placed in an autoclave, and the air pressure is increased to force the layers of material tightly together.
If an autoclave is not used, a vacuum pump can be attached to the inside of the bag and the air pumped out. The atmospheric pressure pressing on the outside of the bag supplies the needed force.
bail out. To jump from an aircraft in flight and use a parachute for descent.
bail-out bottle (oxygen supply). A small high-pressure oxygen bottle attached to a parachute harness. The bail-out bottle supplies the oxygen used during a parachute descent.
Bakelite. The registered trade name for a phenol resin often used as an electrical insulation.
baking soda. The common term for bicarbonate of soda (NaHCO3). A solution of baking soda and water can be used to neutralize electrolyte spilled from a lead-acid battery.