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earth’s magnetic field and the horizontal plane.
Dip is caused by the vertical component of the earth’s magnetic field, and to correct for dip, a
weight is often put on one end of the magnet to keep it horizontal. This weight is the cause of two errors
found in aircraft magnetic compasses: acceleration error and northerly turning error. See acceleration error
and northerly turning error.
dipcoating (insulation application). A method of electrically insulating the handles of certain tools, such
as pliers, that are used in electrical work. The handles are dipped into a liquid plastic resin. The resin that
sticks to the handle hardens and forms a comfortable, attractive, nonconductive grip.
diplexer (aircraft radio component). A coupling system used with an aircraft radio antenna. A diplexer
allows two different transmitters to use the same antenna.
diplex operation (communications operation). A method of communicating which allows transmission
and reception of two signals at the same time. Diplex operation uses a single antenna or a single carrier.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 192
dipole antenna (radio antenna). A straight-wire, half-wavelength, center-fed radio antenna. The length of
each of the two poles of the antenna is approximately one quarter of the wavelength of the frequency for
which the antenna is designed.
dip soldering. The method of soldering component leads to a printed circuit board. The ends of the
component leads pass through holes in the printed circuit board and stick out through the bottom. The
board is floated on the top of a bath of molten solder, and the solder joins the component leads to the
printed conductors.
dipstick. A gage, made in the form of a thin metal rod, used to measure the level of a liquid in a reservoir.
The dipstick is pushed into the reservoir until it contacts a built-in stop; then it is removed and visually
inspected. The level of the liquid in the reservoir is indicated by the amount of the dipstick wet by the
liquid.
A dipstick is the normal method used for measuring the amount of lubricating oil in the sump of
an engine and the amount of hydraulic fluid in a reservoir.
direct (flight operation). Straight-line flight between two navigation fixes.
direct-arc furnace (metallurgy). A type of electric furnace used to melt metal. The metal is placed in a
container lined with a material that can withstand extremely high temperatures, and a carbon rod is lowered
to contact the metal. Electrical current is then forced to flow between the rod and the metal.
While current is flowing, the rod is slowly pulled away, and as it breaks contact, an intensely hot
arc forms between the rod and the metal. This arc melts the metal.
direct-cranking electric starter (reciprocating engine starter). A high-torque DC motor used to crank a
reciprocating engine for starting.
directional antenna (radio antenna). An antenna which radiates stronger signals in one direction than in
others.
directional gyro. A flight instrument used in airplanes and helicopters, using a gyro-stabilized compass
card to show the direction in which the nose of the aircraft is pointed.
A directional gyro does not align itself with magnetic north, and it must be set to point to magnetic
north either by hand or by driving it with some form of magnetic compass.
directionally solidified (turbine blade manufacturing). A method of manufacturing turbine blades in
which the blades are cast and removed from the casting furnace in such a way that all of the crystals in the
metal form columnar grains extending along the length of the blade.
directional stability (aircraft stability). The stability of an aircraft about its vertical axis. Directional
stability causes an aircraft to return to straight flight after it has been disturbed by a yawing or side-slipping
action.
direction finder. See DF.
dirigible. A large, steerable, cigar-shaped, self-propelled lighter-than-air craft. Dirigibles are made of a
rigid truss structure covered with fabric. Gas bags inside the structure contain the lifting gas, which may be
either hydrogen or helium.
discontinuity. In nondestructive inspection, any interruption in the normal physical structure or
configuration of a part. A discontinuity may or may not affect the usefulness of a part.
discreet. Having good judgment. A discreet action is one that gives the desired results without being showy
or calling attention to itself.
discrete. Separate, not continuous. A discrete change is made in a number of separate steps, rather than in a
continuous, smooth movement.
discrete code (air traffic control). As used in the air traffic control radar beacon system (ATCRBS), a
　
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