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coils, two condensers, and two distributors. A dual magneto is considered to be the equivalent of two
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 207
separate ignition systems for an aircraft engine.
dual rotor system (helicopter rotor system). A system of helicopter rotors in which there are two main
rotors driven by coaxial drive shafts. The rotors turn in opposite directions so their torques counteract each
other.
dual-spool gas-turbine engine. An axial-flow turbine engine that has two independent compressors, each
driven by its own stage or stages of turbines.
The high-pressure, or N2, compressor is speed governed by the fuel control, but the low-pressure,
or N1, compressor is not governed but seeks its own best speed as the ambient air density changes.
duckbill pliers (mechanic’s hand tools). A special type of pliers used to twist safety wire. Duckbill pliers
have long handles and wide, flat jaws with serrations to grip the wire, but they do not have jaws for cutting
the wire.
duct (air conditioning and heating component). A thin-wall tube installed in an aircraft to carry heated or
cooled air for distribution at the proper locations.
ducted-fan engine (aircraft engine). A form of aircraft engine in which a propeller or fan is enclosed in a
specially shaped shroud, or duct. A ducted-fan engine has a high degree of propulsive efficiency.
duct heater. A thrust augmentation system similar to an afterburner in which fuel is added to the fan
discharge air and burned.
ductility (metal characteristic). The property of a material that allows it to be drawn into a thin section
without breaking. Because copper has a great deal of ductility, it is possible to draw it into very fine wires.
duct losses (gas turbine engine losses). A decrease in pressure of the air flowing into a gas turbine engine
caused by friction.
dummy load. A noninductive, high-power resistor that can be connected to a transmission line in place of
the antenna. The transmitter can be operated into the dummy load without transmitting any signal.
dump chute (aircraft fuel system component). A specially shaped duct, or tube, used to carry fuel away
from the aircraft when it is dumped from the fuel tanks.
Some large aircraft are permitted to take off with a greater weight than they are allowed to have
when they land. However, if such an aircraft must make an emergency landing before it has burned off
enough fuel to reduce its weight to its legal landing weight, it must dump enough fuel to get rid of this
excess weight. The dump chute is designed to carry the fuel away from the aircraft so it will not be ignited
by the engine exhaust or by static electricity.
duo-servo brakes (type of aircraft shoe brakes). A form of shoe brake that uses the weight of the aircraft
to wedge the shoes tightly against the drum when the aircraft is rolling either forward or backward.
duplex fuel nozzle (gas turbine engine component). A type of fuel nozzle that discharges its fuel into the
combustor, or burner, at two different rates and flow patterns; one for low airflow and the other for high
airflow.
These flow patterns determine the shape of the flame inside the burner and both flow patterns keep
the flame centered in the burner so it will not touch the thin metal of which the burner is made.
duplex operation (electronic communications). A method of communications in which each end can
simultaneously transmit and receive. Communication by telephone is duplex operation. Duplex operation
by radiotelephone requires the use of two frequencies.
durability. A measure of engine life. Durability is normally measured in hours of time between overhauls,
or TBO.
duralumin. The trade name for one of the original alloys of aluminum, magnesium, manganese, and
copper. Duralumin, which is the same as modern 2017 aluminum alloy, was first used by the Germans to
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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build the Zeppelins of World War I. The term dural, which was at one time used for almost all the
high-strength aluminum alloys, was taken from the name duralumin.
dust (meteorology). Fine particles of dry matter suspended in the atmosphere.
dust devil (meteorology). A small, vigorous whirlwind, usually of short duration. Dust devils are made
visible by dust, sand, and debris picked up from the ground.
dust storm (meteorology). An unusual, frequently severe weather condition in which strong winds and
dust-filled air cover an extensive area.
Dutchman shears (mechanic’s hand tool). A common name for compound-action sheet metal shears.
Dutchman shears come in three types: those that cut straight, those that cut to the right, and those that cut to
　
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