曝光台 注意防骗
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200 Ft. (Dry Runway)
500 Ft. (Wet Runway)
2,000 Ft. (Air)
Figure 15-25. Extended flare.
Ch 15.qxd 5/7/04 10:22 AM Page 15-23
15-24
TOUCHDOWN AND ROLLOUT
A proper approach and flare positions the airplane to
touch down in the touchdown target zone, which is
usually about 1,000 feet beyond the runway threshold.
Once the main wheels have contacted the runway, the
pilot must maintain directional control and initiate the
stopping process. The stop must be made on the
runway that remains in front of the airplane. The
runway distance available to stop is longest if the
touchdown was on target. The energy to be dissipated
is least if there is no excess speed. The stop that begins
with a touchdown that is on the numbers will be the
easiest stop to make for any set of conditions.
At the point of touchdown, the airplane represents a
very large mass that is moving at a relatively high
speed. The large total energy must be dissipated by the
brakes, the aerodynamic drag, and the thrust reversers.
The nosewheel should be flown onto the ground
immediately after touchdown because a jet airplane
decelerates poorly when held in a nose-high attitude.
Placing the nosewheel tire(s) on the ground will assist
in maintaining directional control. Also, lowering the
nose gear decreases the wing angle of attack,
decreasing the lift, placing more load onto the tires,
thereby increasing tire-to-ground friction. Landing
distance charts for jet airplanes assume that the
nosewheel is lowered onto the runway within 4
seconds of touchdown.
There are only three forces available for stopping the
airplane. They are wheel braking, reverse thrust, and
aerodynamic braking. Of the three, the brakes are most
effective and therefore the most important stopping
force for most landings. When the runway is very
slippery, reverse thrust and drag may be the dominant
forces. Both reverse thrust and aerodynamic drag are
most effective at high speeds. Neither is affected by
runway surface condition. Brakes, on the other hand,
are most effective at low speed. The landing rollout
distance will depend on the touchdown speed and what
forces are applied and when they are applied. The pilot
controls the what and when factors, but the maximum
braking force may be limited by tire-to-ground
friction.
The pilot should begin braking as soon after
touchdown and wheel spin-up as possible, and to
smoothly continue the braking until stopped or a safe
taxi speed is reached. However, caution should be used
if the airplane is not equipped with a functioning
anti-skid system. In such a case, heavy braking can
cause the wheels to lock and the tires to skid.
Both directional control and braking utilize tire ground
friction. They share the maximum friction force the
tires can provide. Increasing either will subtract from
the other. Understanding tire ground friction, how
runway contamination affects it, and how to use the
friction available to maximum advantage is important
to a jet pilot.
Spoilers should be deployed immediately after
touchdown because they are most effective at high
speed. Timely deployment of spoilers will increase
drag by 50 to 60 percent, but more importantly, they
spoil much of the lift the wing is creating, thereby
causing more of the weight of the airplane to be loaded
onto the wheels. The spoilers increase wheel loading
by as much as 200 percent in the landing flap
configuration. This increases the tire ground friction
force making the maximum tire braking and cornering
forces available.
Like spoilers, thrust reversers are most effective at
high speeds and should be deployed quickly after
touchdown. However, the pilot should not command
significant reverse thrust until the nosewheel is on the
ground. Otherwise, the reversers might deploy
asymmetrically resulting in an uncontrollable yaw
towards the side on which the most reverse thrust is
being developed, in which case the pilot will need
whatever nosewheel steering is available to maintain
directional control.
Ch 15.qxd 5/7/04 10:22 AM Page 15-24
16-1
EMERGENCY SITUATIONS
This chapter contains information on dealing with
non-normal and emergency situations that may occur in
flight. The key to successful management of an
emergency situation, and/or preventing a non-normal
situation from progressing into a true emergency, is
a thorough familiarity with, and adherence to, the
procedures developed by the airplane manufacturer and
contained in the FAA-approved Airplane Flight Manual
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AIRPLANE FLYING HANDBOOK 飞机飞行手册下(88)
