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— the blade is twisted.
blade wrench (propeller maintenance tool). A paddle-like tool with an airfoil-shaped cutout that is
slipped over the propeller blade. A handle on the blade wrench is used to apply a twisting force to the blade.
Blade wrenches are also called blade beams.
blanket method of aircraft covering. The method of installing fabric on an aircraft structure in which the
fabric is applied in the form of a sheet, or blanket, wrapped around the structure and fastened by sewing or
cementing it in place.
The other method of installing fabric is the envelope method, in which the fabric is sewed into the
form of an envelope and slipped over the structure. The ends are then secured by sewing or cementing.
blast fence. A barrier installed on an airport to divert or dissipate jet or propeller blast.
bleed air. Compressed air taken from one or more stages of the compressor of a gas turbine engine. Bleed
air is used for anti-icing, deicing, cabin pressurization, and cabin heating or cooling.
bleed orifice. A calibrated orifice, or hole, used in some fluid power systems to allow a controlled flow of
fluid while the system is in operation. When the system is shut down, all of the pressure bleeds off through
the bleed orifice.
bleed valve (gas turbine engine). A valve in the compressor case of an axial-flow gas turbine engine that
allows some of the air to bleed off.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 79
By bleeding off some of the pressure, the airflow through the engine is improved, and there is less
danger of compressor stall or surge.
bleeder (composite structure component). A material such as glass cloth or mat placed over a composite
layup to absorb the excess resin that is forced out of the ply fibers when pressure is applied.
bleeder current. A steady current that flows from the output of a power supply through a bleeder resistor
to ground. Bleeder current improves the voltage regulation of a power supply.
bleeder resistor (electrical circuit component). A high-resistance resistor placed between the output of an
electrical power supply and ground.
The function of a bleeder resistor is to draw a fixed current for improved regulation, or
stabilization, and to bleed off high-voltage charges from the capacitors when the equipment is shut off.
bleeding brakes (maintenance procedure). A maintenance procedure in which air is removed from the
hydraulic fluid in an aircraft brake system. Air in the fluid will compress when the brakes are applied, and
the brakes will feel spongy and will not be effective.
To bleed the brakes, a bleeder hose is installed in the brake cylinder, and fluid is pumped through
the system until no trace of bubbles appears in the fluid.
bleeding dope. Aircraft finishing materials containing certain types of pigments that bleed through any
finish applied over them. Bleeding dopes can sometimes be successfully covered with a coat of
aluminum-pigmented dope applied before the final topcoats.
blemish. A visible imperfection that damages an object or destroys its value.
blending (turbine engine maintenance). A method of repairing damaged compressor and turbine blades.
The damage is removed and the area is cleaned out with a fine file to form a shallow depression
with generous radii. The file marks are then removed with a fine abrasive stone so the surface of the
repaired area will match the surface of the rest of the blade.
blimp. The name given to a cigar-shaped, nonrigid airship. Nonrigid airships were originally called limp
airships.
blind flight. A term used in the early days of aviation to refer to flight by reference to instruments when the
natural horizon is not visible. The term blind flight has been replaced by the more accurate term instrument
flight.
blind rivet. A special rivet used in a sheet metal structure that can be installed when there is access to only
one side of the metal.
The most widely used type of blind rivet has the end of its hollow shank upset by pulling a tapered
plug up into the shank.
blind speed (air traffic control). The rate of departure or closing of a target relative to the radar antenna at
which the cancellation of the primary radar target by moving target indicator (MTI) circuits in the radar
equipment causes a reduction or complete loss of signal.
blind spot (radio operation). An area from which radio transmissions and/or radar echoes cannot be
received.
blind spot (visual operation). An area on an airport not visible from the control tower.
blind velocity (ICAO). The radial velocity of a moving target, such that the target is not seen on primary
radars fitted with certain forms of fixed echo suppression.
blink Zyglo. A form of nondestructive inspection of parts subject to vibration. In this method of inspection,
　
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