T
RAINING
M
ANUAL
–
L
ANCAIR
IV/IVP
D. Controllability
Factors
(1) Static stability is the inherent flight characteristic of an aircraft to return
to equilibrium after being disturbed by an unbalanced force or
movement.
(2) Controllability is the ability of an aircraft to respond positively to control
surface displacement, and to achieve the desired condition of flight.
(3) At high-flight altitudes, aircraft stability and control may be greatly
reduced. Thus, while high-altitude flight may result in high TAS,
calibrated airspeed is much slower because of reduced air density.
This reduction in density means that the angle of attack must be
increased to maintain the same coefficient of lift with increased
altitude. Consequently, aircraft operating at high altitudes
simultaneously experience problems associated with slow-speed flight
such as Dutch roll, adverse yaw, and stall. In addition, the reduced air
density reduces aerodynamic damping, overall stability, and control of
the aircraft in flight.
(a) Dutch roll is a coupled oscillation in roll and yaw that becomes
objectionable when roll, or lateral stability is reduced in comparison
with yaw or directional stability.
(b) Adverse yaw is a phenomenon in which the airplane heading
changes in a direction opposite to that commanded by a roll control
input. It is the result of unequal lift and drag characteristics of the
down-going and up-going wings.
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40
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©
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2007
LOBO
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