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stalling speed. As the airplane settles, the proper
landing attitude is attained by application of whatever
back-elevator pressure is necessary.
Some pilots may try to force or fly the airplane onto
the ground without establishing the proper landing
attitude. The airplane should never be flown on
the runway with excessive speed. It is paradoxical that
the way to make an ideal landing is to try to hold the
airplane’s wheels a few inches off the ground as
long as possible with the elevators. In most cases,
when the wheels are within 2 or 3 feet off the
ground, the airplane will still be settling too fast for
a gentle touchdown; therefore, this descent must be
retarded by further back-elevator pressure. Since
the airplane is already close to its stalling speed and
is settling, this added back-elevator pressure will
only slow up the settling instead of stopping it. At
the same time, it will result in the airplane touching
the ground in the proper landing attitude, and the
main wheels touching down first so that little or no
weight is on the nosewheel. [Figure 8-8]
After the main wheels make initial contact with the
ground, back-elevator pressure should be held to
maintain a positive angle of attack for aerodynamic
braking, and to hold the nosewheel off the ground until
the airplane decelerates. As the airplane’s momentum
decreases, back-elevator pressure may be gradually
relaxed to allow the nosewheel to gently settle onto the
runway. This will permit steering with the nosewheel.
At the same time, it will cause a low angle of attack
and negative lift on the wings to prevent floating or
skipping, and will allow the full weight of the airplane
to rest on the wheels for better braking action.
Near-Zero Rate of Descent
15 Feet
2 to 3 Feet 1 Foot
Figure 8-8. A well executed roundout results in attaining the proper landing attitude.
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8-7
It is extremely important that the touchdown occur
with the airplane’s longitudinal axis exactly parallel to
the direction in which the airplane is moving along the
runway. Failure to accomplish this imposes severe side
loads on the landing gear. To avoid these side stresses,
the pilot should not allow the airplane to touch down
while turned into the wind or drifting.
AFTER-LANDING ROLL
The landing process must never be considered complete
until the airplane decelerates to the normal taxi
speed during the landing roll or has been brought to a
complete stop when clear of the landing area. Many
accidents have occurred as a result of pilots abandoning
their vigilance and positive control after getting the
airplane on the ground.
The pilot must be alert for directional control difficulties
immediately upon and after touchdown due to the
ground friction on the wheels. The friction creates a pivot
point on which a moment arm can act. Loss of directional
control may lead to an aggravated, uncontrolled, tight
turn on the ground, or a ground loop. The combination
of centrifugal force acting on the center of gravity (CG)
and ground friction of the main wheels resisting it during
the ground loop may cause the airplane to tip or lean
enough for the outside wingtip to contact the ground.
This may even impose a sideward force, which could
collapse the landing gear.
The rudder serves the same purpose on the ground as it
does in the air—it controls the yawing of the airplane.
The effectiveness of the rudder is dependent on the airflow,
which depends on the speed of the airplane. As
the speed decreases and the nosewheel has been lowered
to the ground, the steerable nose provides more
positive directional control.
The brakes of an airplane serve the same primary
purpose as the brakes of an automobile—to reduce
speed on the ground. In airplanes, they may also be
used as an aid in directional control when more positive
control is required than could be obtained with
rudder or nosewheel steering alone.
To use brakes, on an airplane equipped with toe brakes,
the pilot should slide the toes or feet up from the rudder
pedals to the brake pedals. If rudder pressure is
being held at the time braking action is needed, that
pressure should not be released as the feet or toes are
being slid up to the brake pedals, because control may
be lost before brakes can be applied.
Putting maximum weight on the wheels after touchdown
is an important factor in obtaining optimum
braking performance. During the early part of rollout,
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(82)
