distributor finger (magneto ignition system component). A term for a magneto distributor rotor. The
finger, or rotor, is the device inside a distributor that picks up the high voltage from the magneto coil and
directs it to the terminal inside the distributor block to which the ignition lead for the correct spark plug is
attached.
distributor valve (Hamilton Standard Hydromatic propeller component). A valve which screws into
the end of the propeller shaft on which a Hydromatic propeller is mounted.
For all normal operations of the propeller, including feathering, the distributor valve acts only as
an oil passage. But when the propeller is being unfeathered, the distributor valve shifts and directs
high-pressure oil to the side of the piston in the propeller dome that moves the blades toward their
unfeathered position.
distributor valve (pneumatic deicer system component). A rotary selector valve in a pneumatic deicer
system. The distributor valve, installed between the air pump and the deicer boots, sequences the inflation
and deflation of the boots to break the ice that has formed on the leading edges of the wings and tail
surfaces. Air flowing over the surface gets under the broken ice and blows it away.
disturbance (meteorology). An area in which weather, wind, pressure, etc., show signs of cyclonic
development.
dither signal (automatic control signal). An oscillating, or alternating, signal sent into the servo motors of
an automatic pilot. The dither signal does not produce rotation of the motor when there is no directional
signal. But, as soon as the directional signal is sent to the motor, the dither signal adds to it and helps
overcome the effect of friction or hysteresis.
diurnal. Daily. This term applies to a cycle complete within a 24-hour period and which recurs every 24
hours.
dive (flight maneuver). A steep descending flight path.
dive flaps (airplane auxiliary control surfaces). Surfaces on either the wings or fuselage of an airplane
that can be extended in flight to create enough parasite drag to keep the airplane from reaching an excessive
speed in a dive.
Dive flaps, also called speed brakes or dive brakes, are designed to produce a minimum amount of
pitch change when they extend.
divergence (meteorology). A condition that exists when the distribution of winds within a given area is
such that there is a net horizontal flow of air outward from the region.
In divergence at lower levels, the resulting movement of air away from the surface is compensated
for by subsidence of air from aloft. The air is heated and the relative humidity is lowered, making
divergence a warming and drying process. Low-level divergent regions are areas in which clouds and
precipitation are unlikely to form. Divergence is the opposite of convergence.
divergent duct (fluid flow passage). A duct, or passage, whose cross-sectional area increases in the
direction of fluid flow. When fluid flows through a divergent duct at a subsonic rate, its velocity decreases,
and its pressure increases.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 196
divergent oscillation. Oscillations whose amplitude increases with time. The oscillations of an airplane
that has positive static stability but negative dynamic stability are divergent oscillations.
diverse vector area (air traffic control). That area, in a radar environment, in which a prescribed
departure route is not the only suitable route to avoid obstacles. The area in which random radar vectors
below the minimum vectoring altitude/minimum IFR altitude (MVA/MIA), established in accordance with
the terminal instrument procedures (TERPS) criteria for diverse departures, obstacles and terrain avoidance,
may be issued to departing aircraft.
dividend (mathematical term). The number in a division problem that is to be divided. The components
of the problem 36 ÷ 3 = 12 are: 36 is the dividend, 3 is the divisor, and 12 is the quotient.
dividers (layout tool). A sheet metal layout tool that looks much like a drafting compass. Dividers are used
to lay out circles or arcs of a circle and to divide a line into equal spaces.
divisor (mathematical term). The number in a division problem that is used to go into, or to divide, the
dividend. The dividend is divided by the divisor. See dividend.
DME (distance measuring equipment). A pulse-type electronic navigation system that shows the pilot, by
an instrument-panel indication, the number of nautical miles between the aircraft and a ground station.
The DME transmitter in the aircraft transmits a specific pulse of electrical energy. This pulse is
received by the ground station and retransmitted on another frequency. When the pulse is received back in
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