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occur during an actual approach to a landing, since
recovery may be impossible prior to ground contact
due to the low altitude.
The flight instructor should be aware that during traffic
pattern operations, any conditions that result in
overshooting the turn from base leg to final approach,
dramatically increases the possibility of an
unintentional accelerated stall while the airplane is in a
cross-control condition.
ELEVATOR TRIM STALL
The elevator trim stall maneuver shows what can happen
when full power is applied for a go-around and
positive control of the airplane is not maintained.
[Figure 4-8] Such a situation may occur during a
go-around procedure from a normal landing approach
Set up and trim for
final approach glide Apply full power to
simulate go-around.
Allow nose to rise
As stall approaches,
apply forward pressure
and establish normal
climb speed.
Trim to maintain
normal climb
Figure 4-8. Elevator trim stall.
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or a simulated forced landing approach, or
immediately after a takeoff. The objective of the
demonstration is to show the importance of making
smooth power applications, overcoming strong trim
forces and maintaining positive control of the airplane
to hold safe flight attitudes, and using proper and
timely trim techniques.
At a safe altitude and after ensuring that the area is
clear of other air traffic, the pilot should slowly retard
the throttle and extend the landing gear (if retractable
gear). One-half to full flaps should be lowered, the
throttle closed, and altitude maintained until the
airspeed approaches the normal glide speed. When the
normal glide is established, the airplane should be
trimmed for the glide just as would be done during a
landing approach (nose-up trim).
During this simulated final approach glide, the throttle
is then advanced smoothly to maximum allowable
power as would be done in a go-around procedure. The
combined forces of thrust, torque, and back-elevator
trim will tend to make the nose rise sharply and turn to
the left.
When the throttle is fully advanced and the pitch
attitude increases above the normal climbing attitude
and it is apparent that a stall is approaching, adequate
forward pressure must be applied to return the airplane
to the normal climbing attitude. While holding the
airplane in this attitude, the trim should then be
adjusted to relieve the heavy control pressures and the
normal go-around and level-off procedures completed.
The pilot should recognize when a stall is approaching,
and take prompt action to prevent a completely stalled
condition. It is imperative that a stall not occur during
an actual go-around from a landing approach.
Common errors in the performance of intentional stalls
are:
• Failure to adequately clear the area.
• Inability to recognize an approaching stall
condition through feel for the airplane.
• Premature recovery.
• Over-reliance on the airspeed indicator while
excluding other cues.
• Inadequate scanning resulting in an unintentional
wing-low condition during entry.
• Excessive back-elevator pressure resulting in an
exaggerated nose-up attitude during entry.
• Inadequate rudder control.
• Inadvertent secondary stall during recovery.
• Failure to maintain a constant bank angle during
turning stalls.
• Excessive forward-elevator pressure during
recovery resulting in negative load on the wings.
• Excessive airspeed buildup during recovery.
• Failure to take timely action to prevent a full stall
during the conduct of imminent stalls.
SPINS
A spin may be defined as an aggravated stall that
results in what is termed “autorotation” wherein the
airplane follows a downward corkscrew path. As the
airplane rotates around a vertical axis, the rising wing
is less stalled than the descending wing creating a
rolling, yawing, and pitching motion. The airplane is
basically being forced downward by gravity, rolling,
yawing, and pitching in a spiral path. [Figure 4-9]
The autorotation results from an unequal angle of
attack on the airplane’s wings. The rising wing has a
decreasing angle of attack, where the relative lift
increases and the drag decreases. In effect, this wing is
less stalled. Meanwhile, the descending wing has an
Figure 4-9. Spin—an aggravated stall and autorotation.
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increasing angle of attack, past the wing’s critical angle
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(48)
