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the left.
Dutch roll (flight condition). An undesirable, low-amplitude oscillation about both the yaw and roll axes
that affects many swept wing airplanes. Dutch roll is minimized by the use of a yaw damper.
duty cycle. A schedule that allows a device to operate for a given period of time, with a cooling down
period required before the device can be operated again.
D-value (meteorology). The difference, shown on a constant-pressure chart, between the actual height and
the standard atmospheric height of a constant-pressure surface. D-value is the algebraic difference between
true altitude and pressure altitude.
DVFR (defense visual flight rules). Rules applicable to flights within an air defense identification zone
(ADIZ) conducted under visual flight rules as defined in 14 CFR Part 91.
DVFR flight plan (air traffic control). A flight plan filed for a VFR aircraft which intends to operate in
airspace within which the ready identification, location, and control of aircraft are required in the interest of
national security.
dwell chamber (turbine engine lubrication system component). A chamber in a turbine engine oil tank
into which the scavenged oil is returned. Entrapped air can separate from the oil in this chamber before it is
picked up by the pressure pump.
dwell time (penetrant inspection). The length of time a penetrant is allowed to remain on the surface of a
part being inspected. The dwell time is determined by the temperature of the part and the size of the
suspected defect.
dye. A colored substance used to add a more or less permanent color to another object. Dyes are added to
aviation gasoline to give each grade an identifying color. Dyes are also used to add an attractive color to the
oxide film that forms when aluminum alloys are anodized.
dye penetrant inspection. A method of nondestructive inspection used to detect surface defects in metal or
plastic parts. The part to be inspected is soaked in a penetrating liquid for a specified period of time, and
then all the penetrant is washed from its surface. The surface is then covered with a developing powder that
pulls the penetrant from any defects that extend to the surface of the part. The penetrant plainly shows up
on the powder-covered surface, outlining the defect.
dynafocal engine mount (reciprocating engine mount). A special type of mount for an aircraft engine in
which straight lines that pass through the engine mount bolts intersect at the center of gravity of the engine
and propeller assembly. Dynafocal engine mounts absorb much of the torsional vibration caused by the
engine.
dynamic (air traffic control). Continuous review, evaluation, and change to meet demands.
dynamic balance. The balance of a rotating object, such as a wheel or propeller spinner.
The condition of dynamic balance is checked with the object rotating. If an unbalanced condition
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 209
causes vibration, the balancing equipment shows the amount of weight and the location of the weight
needed to stop the vibration. Wheels and tires, as well as propellers, are dynamically balanced.
dynamic braking (electrical braking). Braking of an electric motor done by switching the power leads of
the motor from the source of power to an electrical load. The electrical load consumes power which is
changed to a mechanical force that opposes the rotation of the motor armature.
dynamic damper (reciprocating engine component). Heavy weights mounted on some of the cheeks of a
reciprocating engine crankshaft to absorb torsional vibrations.
The weights are attached to the cheek by small pins that ride in larger holes in the weights. This
arrangement allows the weights to rock back and forth as the crankshaft rotates. It is this rocking motion
that absorbs the torsional vibrations of the engine.
dynamic load (aircraft structural load). The apparent weight of an entire loaded aircraft. The apparent
weight is the actual weight of the aircraft multiplied by the load factor, which is the increase in weight
caused by acceleration.
For example, an aircraft in a properly coordinated 60° banked turn has a load factor of two. This
means that if the loaded aircraft weighs 3,000 pounds, its dynamic load in a coordinated 60° banked turn is
two times 3,000 pounds, or 6,000 pounds.
dynamic microphone. A type of microphone in which sound pressure vibrates a cone on which is mounted
a coil of wire. The coil vibrates in a magnetic field, and a voltage is produced in the coil. The frequency
and waveform of the voltage is similar to that of the sound waves that vibrated the cone.
dynamic pressure, q (aerodynamic parameter). The pressure a moving fluid would have if it were
　
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