曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
turn is to neutralize the air rudder and allow the seaplane
to weathervane into the wind. If taxiing directly
downwind, use the air rudder momentarily to get the
turn started, then let the wind complete the turn.
Sometimes opposite rudder may be needed to control
the rate of turn.
Stronger winds may make turns from upwind to downwind
more difficult. The plow turn is one technique for
turning downwind when other methods are inadequate,
but this maneuver is only effective in certain seaplanes.
It takes advantage of the same factor that reduces a
floatplane’s yaw stability in flight: the large vertical area
of the floats forward of the center of gravity. In the
plowing attitude, the front portion of each float comes
out of the water, presenting a large vertical surface for
the wind to act upon. This tends to neutralize the weathervaning
force, allowing the turn to proceed. At the
same time, the center of buoyancy shifts back. Since
this is the axis around which the seaplane pivots while
Wind Force
Centrifugal
Force
Wind Force
Centrifugal
Force
Centrifugal
Force
Wind
Force
Centrifugal
Force
Wind
Force
Figure 4-8. Wind effects in turns. When the wind and centrifugal force act in the same direction, the downwind float can be
forced underwater. When the wind is countered by centrifugal force, the seaplane is more stable.
Ch 04.qxd 8/24/04 10:49 AM Page 4-6
4-7
on the water, more of the fuselage is now forward of
the axis and less is behind, further decreasing the
weathervaning tendency. In some seaplanes, this
change is so pronounced in the plowing attitude that
they experience reverse weathervaning, and tend to
turn downwind rather than into the wind. Experienced
seaplane pilots can sometimes use the throttle as a
turning device in high wind conditions by increasing
power to cause a nose-up position when turning downwind,
and decreasing power to allow the seaplane to
weathervane into the wind. [Figure 4-9]
To execute a plow turn, begin with a turn to the right,
then use the weathervaning force combined with full
left rudder to turn back to the left. As the seaplane
passes its original upwind heading, add enough power
to place it into the plow position, continuing the turn
with the rudder. As the seaplane comes to the downwind
heading, reduce power and return to an idle taxi.
From above, the path of the turn looks like a question
mark. [Figure 4-10]
Plow turns are useful only in very limited situations
because they expose the pilot to a number of potential
dangers. They should not be attempted in rough water
or gusty conditions. Floatplanes are least stable when
in the plowing attitude, and are very susceptible to
capsizing. In spite of the nose-high attitude, the high
power setting often results in spray damage to the
propeller. In most windy situations, it is much safer
to sail the seaplane backward (as explained in the
next section) rather than attempt a plow turn.
When the seaplane is on the step, turns involve careful
balancing of several competing forces. As the rate of
turn increases, the floats are being forced to move
somewhat sideways through the water, and they resist
this sideways motion with drag, much like an airplane
fuselage in a skidding turn. More power is required to
overcome this drag and maintain planing speed. This
skidding force also tends to roll the seaplane toward
the outside of the turn, driving the outside float deeper
into the water and adding more drag on that side. To
prevent this, use aileron into the turn to keep the outside
wing from dropping. Once full aileron into the
step turn is applied, any further roll to the outside can
only be stopped by reducing the rate of turn, so pay
careful attention to the angle of the wings and the feel
of the water drag on the floats to catch any indication
that the outside float is starting to submerge. When
stopping a step turn, always return to a straight path
before reducing power.
At step taxi speeds, the centrifugal force in a turn is far
greater than at idle taxi speed, so the forces involved in
turning from downwind to upwind are proportionately
more dangerous, especially in strong winds. Chances
are, by the time a pilot discovers that the outside float
is going under, the accident is almost inevitable.
However, immediate full rudder out of the turn and
power reduction may save the situation by reversing
Engine Idling
Water Rudder Down
Elevator Full Up
Add Power to Assume
Plowing Attitude.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
Seaplane, Skiplane, and FloatSki Equipped Helicopter Operati(21)
