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Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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axial-centrifugal compressor (gas turbine engine component). A combination axial and centrifugal
compressor used in a gas turbine engine.
The axial-flow portion of the compressor serves as the low-pressure stage, and the centrifugal
portion serves as the high-pressure stage.
axial-flow compressor (gas turbine engine component). A type of compressor used in gas turbine
engines in which the air passes through the compressor in essentially a straight line, parallel to the axis of
the compressor.
The compressor is made of a number of stages of rotating compressor blades between stages of
stationary stator vanes. The compression ratio is determined by the number of stages of compression.
axial-lead resistor (electrical component). A discrete electrical component which provides a given
amount of resistance to a circuit.
The wire leads of an axial-lead resistor extend from the ends in a direction parallel to the axis of
the resistor. The resistance value and tolerance is indicated by a series of colored bands See illustration for
resistor color code.
axial load (bearing load). The load on a bearing parallel to the shaft on which the bearing is mounted.
Axial loads are usually carried by ball bearings or tapered roller bearings.
The thrust load produced by a propeller is an axial load, and it is carried into the engine crankcase
through the thrust bearing.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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axial loading (gas turbine engine compressor force). An aerodynamic force that tries to move the
compressor forward in its case. Axial loading is supported in a gas turbine engine in ball bearings.
axial turbine (gas turbine engine component). A turbine turned by a fluid flowing through it in a
direction approximately parallel to the shaft on which the turbine wheel is mounted.
axis. A straight line about which a body can rotate.
axis of rotation (helicopter rotor). The line through the rotor head of a helicopter at right angles to the
plane of rotation. The blades rotate around this axis.
axis of rotation (propeller). The center line about which a propeller rotates.
axis of symmetry. An imaginary center line about which a body or object is symmetrical, or has the same
shape on either side.
axle. The shaft on which a wheel is mounted and about which the wheel is free to rotate.
axonometric projection (aircraft drawings). A projection used in mechanical drawing that shows a solid,
rectangular object inclined in such a way that three of its faces are visible. An isometric projection is a form
of axonometric projection.
azimuth. Angular measurement made in a horizontal plane and in a clockwise direction from a fixed
reference direction to an object.
B
babbitt. A soft, silvery alloy of tin, lead, copper, and antimony used for main bearing inserts in some
aircraft reciprocating engines.
Babbitt has a very low coefficient of friction, and its dimensions change very little with changes in
its temperature.
back (propeller nomenclature). The curved surface of a propeller blade. The back of a propeller blade
corresponds to the upper surface of an airplane wing.
back course (instrument flight). The reciprocal of the localizer course for an ILS (Instrument Landing
System).
When flying a back-course approach, an aircraft approaches the instrument runway from the end
on which the localizer antennas are installed.
back current (semiconductor device). Current that flows in a semiconductor when the junction is
reverse-biased. Back current is also called reverse current.
backfire (reciprocating engine). A loud noise, or explosive sound, made by a reciprocating engine when
the fuel-air mixture in the induction system is ignited by gases which are still burning inside the cylinder
when the intake valve opens.
A lean fuel-air mixture burns more slowly than a rich mixture, and it can still be burning during
the time of valve overlap (the time when both the intake and the exhaust valves are open). This causes a
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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backfire.
backfire (welding). A condition in which the flame burns back inside the tip of an oxy-gas torch. If a
backfire occurs, the gases must be shut off at the regulator to stop the fire inside the torch.
background noise (electronic equipment). Any noise heard or seen in a piece of electronic equipment
when no signal is present. Background noise in a radio receiver is normally heard as a steady hiss.
backhand welding. A method of welding in which the flame is directed back over the finished weld, rather
　
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