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compressors are attached to the disk by a dovetail joint. The periphery of the disk is cut with a series of
triangular-shaped slots, and the blade roots are made with a dovetail-shaped end that fits into the slots in the
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 200
disk.
The dovetail method of blade attachment holds the blades firmly against centrifugal force,
dampens vibration, and compensates for the effect of temperature change.
dovetailing (woodworking). A method of joining pieces of wood to form the sides of a box or drawer.
The ends of one piece of wood are cut with triangular-shaped cutouts that look like the spread-out
tail of a dove. These cutouts are called the mortises. The other piece of wood is cut with tenons that are
shaped so they exactly fit into the mortises. When the tenons are fitted into the mortises, they form a solid
joint.
dowel. A round wooden peg used to fasten pieces of wood together without the use of metal fasteners.
Holes are drilled into each of the pieces to be joined, and a short dowel is pressed into the holes to hold the
pieces together.
dowel rod. A round piece of wood used to make dowels for holding pieces of wood together.
Dow metal. The registered trade name for a series of magnesium alloys produced by the Dow Chemical
Corporation.
downburst (meteorology). A strong downdraft which induces an outburst of damaging winds on or near
the ground. The sizes of downbursts vary from one-half mile or less to more than 10 miles.
An intense downburst often causes widespread damage. Damaging winds, lasting from five to 30
minutes, could reach speeds as high as 120 knots.
downdraft (meteorology). A relatively small-scale downward current of air. Downdrafts are often
observed on the lee side of large objects that restrict the smooth flow of the air or in precipitation areas in
or near cumuliform clouds.
downdraft carburetor. A carburetor that mounts on the top of a reciprocating engine. Air entering the
engine flows downward through the carburetor.
downlocks (aircraft landing gear component). Mechanical locks used to hold a retractable landing gear
in its down position. Downlocks prevent the landing gear from accidentally retracting when there is no
hydraulic pressure on the actuating cylinder.
downtime (aircraft operation). Any time during which an aircraft is out of commission and not able to be
operated.
downwash (aerodynamics). Air forced down by aerodynamic action below and behind the wing of an
airplane or rotor of a helicopter. Aerodynamic lift is produced when air is deflected downward. The upward
force on the aircraft is the same as the downward force on the air. When the mass of air in the downwash is
equal to the weight of the aircraft forcing it down, the aircraft rises.
downwash angle (aerodynamics). The angle formed between the direction of air movement as it
approaches an airfoil and its direction as it leaves.
An airfoil produces lift by deflecting air downward. The upward component of lift is equal to the
downward component created by the mass of the down-washed air.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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downwind. The direction measured relative to the way the wind is blowing. Downwind means the
direction in which the wind is moving.
downwind landing (aircraft operation). A landing in which the aircraft is moving in the same direction
the wind is blowing. Normal landings are made into the wind, or upwind, allowing the wind to slow the
ground speed of the aircraft.
When an aircraft lands into the wind, its ground speed is its airspeed minus the speed of the wind.
When it lands downwind, its speed over the ground is equal to its airspeed plus the speed of the wind.
DPDT switch (double-pole, double-throw electrical switch). A type of electrical switch with six
terminals. It can be used to select any one of three conditions in two separate circuits. See double-throw
switch.
DPST switch (double-pole, single-throw electrical switch). A type of electrical switch having four
terminals. It can select either of two conditions in two separate circuits. See double-throw switch.
draft of a mold. The taper in the sides of a part cast in a mold. Draft makes it easy to remove the solidified
part from the mold.
draftsman. A person who uses the process of mechanical drawing to make plans or sketches of machinery
or structures.
A draftsman functions differently from an artist in that the draftsman uses templates and other
mechanical devices to assure technical accuracy of the drawing. Drawings made by an artist are normally
done freehand, and they convey thoughts and impressions, rather than objective representation of specific
　
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