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which a wing stalls regardless of
airspeed, flight attitude, or weight.
CRITICAL ENGINE—The engine
whose failure has the most adverse
effect on directional control.
CROSS CONTROLLED—
A condition where aileron deflection
is in the opposite direction of rudder
deflection.
CROSSFEED—Asystem that allows
either engine on a twin-engine
airplane to draw fuel from any fuel
tank.
CROSSWIND COMPONENT—
The wind component, measured in
knots, at 90° to the longitudinal axis
of the runway.
CURRENT LIMITER—A device
that limits the generator output to a
level within that rated by the
generator manufacturer.
DATUM (REFERENCE
DATUM)—An imaginary vertical
plane or line from which all
measurements of moment arm are
taken. The datum is established by the
manufacturer. Once the datum has
been selected, all moment arms and
parasite drag to compensate for the
additional induced drag caused by the
down aileron. This balancing of the
drag forces helps minimize adverse
yaw.
DIFFUSION—Reducing the velocity
of air causing the pressure to increase.
DIRECTIONAL STABILITY—
Stability about the vertical axis of an
aircraft, whereby an aircraft tends to
return, on its own, to flight aligned
with the relative wind when disturbed
from that equilibrium state. The
vertical tail is the primary contributor
to directional stability, causing an
airplane in flight to align with the
relative wind.
DITCHING—Emergency landing in
water.
DOWNWASH—
Air deflected perpendicular to the
motion of the airfoil.
DRAG—An aerodynamic force on a
body acting parallel and opposite to
the relative wind. The resistance of
the atmosphere to the relative motion
of an aircraft. Drag opposes thrust and
limits the speed of the airplane.
DRAG CURVE—
A visual representation of the amount
of drag of an aircraft at various
airspeeds.
DRIFT ANGLE—Angle between
heading and track.
DUCTED-FAN ENGINE—
An engine-propeller combination that
has the propeller enclosed in a radial
shroud. Enclosing the propeller
improves the efficiency of the
propeller.
DUTCH ROLL—A combination of
rolling and yawing oscillations that
normally occurs when the dihedral
effects of an aircraft are more
powerful than the directional stability.
Usually dynamically stable but
objectionable in an airplane because
of the oscillatory nature.
the location of CG range are measured
from this point.
DECOMPRESSION SICKNESS—
A condition where the low pressure at
high altitudes allows bubbles of
nitrogen to form in the blood and
joints causing severe pain. Also
known as the bends.
DEICER BOOTS—Inflatable rubber
boots attached to the leading edge of
an airfoil. They can be sequentially
inflated and deflated to break away ice
that has formed over their surface.
DEICING—Removing ice after it
has formed.
DELAMINATION—The separation
of layers.
DENSITY ALTITUDE—
This altitude is pressure altitude corrected
for variations from standard
temperature. When conditions are
standard, pressure altitude and density
altitude are the same. If the temperature
is above standard, the density altitude
is higher than pressure altitude. If
the temperature is below standard, the
density altitude is lower than pressure
altitude. This is an important altitude
because it is directly related to the
airplane’s performance.
DESIGNATED PILOT
EXAMINER (DPE)—An individual
designated by the FAA to administer
practical tests to pilot applicants.
DETONATION—
The sudden release of heat energy
from fuel in an aircraft engine caused
by the fuel-air mixture reaching its
critical pressure and temperature.
Detonation occurs as a violent
explosion rather than a smooth
burning process.
DEWPOINT—The temperature at
which air can hold no more water.
DIFFERENTIAL AILERONS—
Control surface rigged such that the
aileron moving up moves a greater
distance than the aileron moving
down. The up aileron produces extra
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G-6
DYNAMIC HYDROPLANING—A
condition that exists when landing on
a surface with standing water deeper
than the tread depth of the tires. When
the brakes are applied, there is a
possibility that the brake will lock up
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AIRPLANE FLYING HANDBOOK 飞机飞行手册下(109)
