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varnish.
dope roping (aircraft finishing problem). A condition of aircraft dope being brushed onto a surface that
causes the dope to form a stringy, uneven surface, rather than flowing out smoothly. Dope roping is caused
by the dope being too cold when it is brushed on.
doping (semiconductor manufacturing). The process of adding small amounts of certain elements as
impurities to a semiconductor element to alter its electrical characteristics.
Doppler effect. The apparent rise in the pitch, or frequency, of a sound as its source approaches the hearer,
and the decrease in pitch as the source moves away.
Doppler radar. An electronic system used to detect the speed of a moving vehicle. Speed is measured by
computing the change in frequency of an electronic signal bounced back from the vehicle.
This change in frequency is related to the speed the vehicle is moving toward or away from the
source of the signal.
dorsal fin (aircraft surface). A fixed vertical fin extending from the top of the fuselage to the leading edge
of the vertical fin. Dorsal fins are used to increase the directional stability of an airplane.
double-acting actuator (fluid power actuator). A linear fluid power (hydraulic or pneumatic) actuator
that uses fluid to move the piston in both directions.
A single-acting actuator, by contrast, uses fluid to move the piston in one direction and some other
type of force, such as a spring, to move it in the opposite direction.
double-acting hand pump. A hand-operated fluid pump that moves fluid during both strokes of the pump
handle.
double-backed tape (adhesive tape). A type of adhesive tape with adhesive on both sides.
double-cut file. A file with two series of parallel cutting teeth. These teeth cross each other at an angle.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 199
double-cut saw. A saw with teeth that cut on both the forward and return stroke.
double-entry centrifugal compressor. A form of centrifugal air compressor with vanes on both sides of
the rotor. Air is taken into both faces of the rotor and discharged from its periphery.
double flare (rigid fluid line component). A flare made on a piece of rigid tubing in which the tubing in
the flare is doubled back on itself to produce two thicknesses of metal in the flare.
A double flare is acceptable in aircraft fluid systems on soft aluminum tubing having an outside
diameter no larger than 3/8 of an inch.
double-loop rib stitching (aircraft fabric attachment). A type of stitch used to attach fabric to an aircraft
structure in which the rib-stitching cord is wrapped around the rib two times to form a double loop before
the knot is tied.
double magneto (reciprocating engine component). An aircraft engine magneto that uses a single
rotating magnet to supply the magnetic flux for two magneto circuits. A double magneto has two coil
assemblies, two sets of breaker points, and two distributors, but only one rotating magnet and one cam.
doubler (sheet-metal structural component). A piece of sheet metal used to strengthen and stiffen an
aircraft skin at the location some component is to be attached. A doubler is normally riveted to the inside of
the aircraft skin where a radio antenna is mounted.
double-row radial engine (reciprocating engines). A radial engine with two rows of cylinders whose
pistons are connected to a single crankshaft.
The crankshaft of a double-row radial engine has two throws, 180° apart. The master rod for the
front row of cylinders attaches to one throw, and the master rod for the rear row of cylinders attaches to the
other throw. Most double-row radial engines have either 14 or 18 cylinders.
double-shear loading (riveted joint). A riveted joint that contains two shear planes. The total shear
strength of the joint is approximately twice the shear strength of a joint with a single-shear load.
double spread (adhesive application). The application of a layer of adhesive to each of the two surfaces
being bonded together.
double-tapered wing (aerodynamic shape). A wing tapered in both planform and thickness. The
planform of a wing is its shape as seen from above, looking down on it, and thickness is the shape as seen
from the front, looking aft.
double-throw switch. An electrical switch with three positions, CIRCUIT 1, OFF, and CIRCUIT 2. A
single-pole, double-throw (SPDT) switch can select one of three conditions in a single circuit, and a
double-pole, double-throw (DPDT) switch can select one of three conditions in two circuits with the
movement of a single control.
dovetail (type of fitting attachment). A method of attaching or joining parts in which the ends to be
joined are shaped in the form of the spread-out tail of a dove. The rotor blades of some turbine engine
　
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