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excessive rate of sink, it tends to bounce back into the
air. Though the airplane’s tires and shock struts
provide some springing action, the airplane does not
bounce like a rubber ball. Instead, it rebounds into
the air because the wing’s angle of attack was
abruptly increased, producing a sudden addition of
lift. [Figure 8-36]
The abrupt change in angle of attack is the result of
inertia instantly forcing the airplane’s tail downward
when the main wheels contact the ground sharply. The
severity of the bounce depends on the airspeed at the
moment of contact and the degree to which the angle
of attack or pitch attitude was increased.
Since a bounce occurs when the airplane makes contact
with the ground before the proper touchdown
Figure 8-35. Ballooning during roundout.
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attitude is attained, it is almost invariably accompanied
by the application of excessive back-elevator
pressure. This is usually the result of the pilot realizing
too late that the airplane is not in the proper attitude
and attempting to establish it just as the second touchdown
occurs.
The corrective action for a bounce is the same as for
ballooning and similarly depends on its severity. When
it is very slight and there is no extreme change in the
airplane’s pitch attitude, a follow-up landing may be
executed by applying sufficient power to cushion the
subsequent touchdown, and smoothly adjusting the
pitch to the proper touchdown attitude.
In the event a very slight bounce is encountered while
landing with a crosswind, crosswind correction must
be maintained while the next touchdown is made.
Remember that since the subsequent touchdown will
be made at a slower airspeed, the upwind wing will
have to be lowered even further to compensate for
drift.
Extreme caution and alertness must be exercised any
time a bounce occurs, but particularly when there is a
crosswind. Inexperienced pilots will almost invariably
release the crosswind correction. When one main
wheel of the airplane strikes the runway, the other
wheel will touch down immediately afterwards, and
the wings will become level. Then, with no crosswind
correction as the airplane bounces, the wind will cause
the airplane to roll with the wind, thus exposing even
more surface to the crosswind and drifting the airplane
more rapidly.
When a bounce is severe, the safest procedure is to
EXECUTE A GO-AROUND IMMEDIATELY. No
attempt to salvage the landing should be made. Full
power should be applied while simultaneously maintaining
directional control, and lowering the nose to a
safe climb attitude. The go-around procedure should
be continued even though the airplane may descend
and another bounce may be encountered. It would be
extremely foolish to attempt a landing from a bad
bounce since airspeed diminishes very rapidly in the
nose-high attitude, and a stall may occur before a
subsequent touchdown could be made.
PORPOISING
In a bounced landing that is improperly recovered,
the airplane comes in nose first setting off a series of
motions that imitate the jumps and dives of a porpoise—
hence the name. [Figure 8-37] The problem is improper
airplane attitude at touchdown, sometimes caused by
inattention, not knowing where the ground is, mistrimming
or forcing the airplane onto the runway.
Ground effect decreases elevator control effectiveness
and increases the effort required to raise the nose. Not
enough elevator or stabilator trim can result in a noselow
contact with the runway and a porpoise develops.
Porpoising can also be caused by improper airspeed
control. Usually, if an approach is too fast, the airplane
floats and the pilot tries to force it on the runway when
the airplane still wants to fly. Agust of wind, a bump in
the runway, or even a slight tug on the control wheel
will send the airplane aloft again.
The corrective action for a porpoise is the same as for
a bounce and similarly depends on its severity. When
it is very slight and there is no extreme change in the
airplane’s pitch attitude, a follow-up landing may be
executed by applying sufficient power to cushion the
subsequent touchdown, and smoothly adjusting the
pitch to the proper touchdown attitude.
Small Angle
of Attack
Decreasing Angle
of Attack
Rapid Increase in
Angle of Attack
Normal Angle
of Attack
Figure 8-36. Bouncing during touchdown.
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(101)
