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the airplane to sink even more rapidly.
The airplane must be retrimmed on the final approach
to compensate for the change in aerodynamic forces.
With the reduced power and with a slower airspeed,
the airflow produces less lift on the wings and less
downward force on the horizontal stabilizer, resulting
in a significant nosedown tendency. The elevator must
then be trimmed more noseup.
It will be found that the roundout, touchdown, and
landing roll are much easier to accomplish when they
are preceded by a proper final approach with precise
control of airspeed, attitude, power, and drag resulting
in a stabilized descent angle.
ESTIMATING HEIGHT AND MOVEMENT
During the approach, roundout, and touchdown, vision
is of prime importance. To provide a wide scope of
vision and to foster good judgment of height and
movement, the pilot’s head should assume a natural,
straight-ahead position. The pilot’s visual focus should
not be fixed on any one side or any one spot ahead of
the airplane, but should be changing slowly from a
point just over the airplane’s nose to the desired
touchdown zone and back again, while maintaining a
deliberate awareness of distance from either side of
the runway within the pilot’s peripheral field of vision.
Accurate estimation of distance is, besides being a
matter of practice, dependent upon how clearly objects
are seen; it requires that the vision be focused properly
in order that the important objects stand out as clearly
as possible.
Speed blurs objects at close range. For example,
most everyone has noted this in an automobile
moving at high speed. Nearby objects seem to merge
together in a blur, while objects farther away stand
out clearly. The driver subconsciously focuses the
eyes sufficiently far ahead of the automobile to see
objects distinctly.
The distance at which the pilot’s vision is focused
should be proportionate to the speed at which the
airplane is traveling over the ground. Thus, as speed is
reduced during the roundout, the distance ahead of the
airplane at which it is possible to focus should be
brought closer accordingly.
If the pilot attempts to focus on a reference that is too
close or looks directly down, the reference will
become blurred, [Figure 8-5] and the reaction will be
either too abrupt or too late. In this case, the pilot’s
tendency will be to overcontrol, round out high, and
make full-stall, drop-in landings. When the pilot
focuses too far ahead, accuracy in judging the
closeness of the ground is lost and the consequent
reaction will be too slow since there will not appear to
be a necessity for action. This will result in the
airplane flying into the ground nose first. The change
of visual focus from a long distance to a short distance
requires a definite time interval and even though the
time is brief, the airplane’s speed during this interval is
such that the airplane travels an appreciable distance,
both forward and downward toward the ground.
Figure 8-5. Focusing too close blurs vision.
If the focus is changed gradually, being brought progressively
closer as speed is reduced, the time interval
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and the pilot’s reaction will be reduced, and the whole
landing process smoothed out.
ROUNDOUT (FLARE)
The roundout is a slow, smooth transition from a normal
approach attitude to a landing attitude, gradually
rounding out the flightpath to one that is parallel with,
and within a very few inches above, the runway. When
the airplane, in a normal descent, approaches within
what appears to be 10 to 20 feet above the ground, the
roundout or flare should be started, and once started
should be a continuous process until the airplane
touches down on the ground.
As the airplane reaches a height above the ground
where a timely change can be made into the proper
landing attitude, back-elevator pressure should be
gradually applied to slowly increase the pitch attitude
and angle of attack. [Figure 8-6] This will cause the
airplane’s nose to gradually rise toward the desired
landing attitude. The angle of attack should be
increased at a rate that will allow the airplane to continue
settling slowly as forward speed decreases.
When the angle of attack is increased, the lift is momentarily
increased, which decreases the rate of descent.
Since power normally is reduced to idle during the
roundout, the airspeed will also gradually decrease.
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(80)
