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simply an up-and-down motion of the water surface—
the water itself is not moving sideways. To maintain a
straight path through the water, pick a spot on the shore
as an aim point for the takeoff run. On the other hand,
some crosswind techniques involve describing a
curved path through the water. Experience will help
determine which technique is most appropriate for a
given situation.
CONTROLLED WEATHERVANING
In light winds, it is easy to counteract the weathervaning
tendency during the early part of the takeoff run by
creating an allowance for it from the beginning. Prior
to adding takeoff power, use the water rudders to set up
a heading somewhat downwind of the aim point. The
angle will depend on the speed of the wind—the higher
Begin Takeoff by
Aiming Downwind of
the Intended Takeoff Path
Airplane
Weathervanes to
Intended Path
During Takeoff Run
Intended Takeoff Path
Figure 4-15. Anticipate weathervaning by leading the aim point, setting up a somewhat downwind heading prior to starting the
takeoff. Choose an aim point that does not move, such as a buoy or a point on the far shore.
Ch 04.qxd 8/24/04 10:49 AM Page 4-13
4-14
the wind, the greater the lead angle. Create just enough
of a lead angle so that when the water rudders are raised
and power is applied, the seaplane weathervanes to the
desired heading during the time it gains enough speed
to make the air rudder and ailerons effective. As the
seaplane transitions to the plowing attitude, the weathervaning
tendency decreases as the fronts of the floats
come out of the water, adding vertical surface area at
the front of the seaplane. Use full aileron into the wind
as the takeoff run begins, and maintain enough aileron
to keep the upwind wing from lifting as airspeed builds.
[Figure 4-15 on previous page]
USING WATER RUDDERS
Another technique for maintaining a straight takeoff
path involves leaving the water rudders down to assist
with steering. Using the water rudders provides added
directional control until the aerodynamic controls
become effective.
To use this technique, align the seaplane with the aim
point on the shore, hold full aileron into the wind, and
apply takeoff power. As the seaplane accelerates, use
enough aileron pressure to keep the upwind wing
down. The downwind float should lift free of the water
first. After lift-off, make a coordinated turn to establish
the proper crab angle for the climb, and retract the
water rudders.
This takeoff technique subjects the water rudders to
high dynamic water pressures and could cause damage.
Be sure to comply with the advice of the float manufacturer.
[Figure 4-16]
DOWNWIND ARC
The other crosswind takeoff technique results in a
curved path across the water, starting somewhat into the
wind and turning gradually downwind during the takeoff
run. This reduces the actual crosswind component at the
beginning of the takeoff, when the seaplane is most susceptible
to weathervaning. As the aerodynamic controls
become more effective, the pilot balances the side loads
imposed by the wind with the skidding force of an intentional
turn, as always, holding the upwind wing down
with the ailerons. [Figure 4-17]
The pilot plans a curved path and follows this arc to
produce sufficient centrifugal force so that the seaplane
tends to lean outward against the wind force. During
the run, the pilot can adjust the rate of turn by varying
rudder pressure, thereby increasing or decreasing the
centrifugal force to compensate for a changing wind
force. In practice, it is quite simple to plan sufficient
curvature of the takeoff path to cancel out strong
crosswinds, even on very narrow rivers. Note that the
tightest part of the downwind arc is when the seaplane
is traveling at slower speeds.
The last portion of a crosswind takeoff is somewhat
similar to a landplane. Use ailerons to lift the downwind
wing, providing a sideways component of lift to
counter the effect of the crosswind. This means that the
downwind float lifts off first. Be careful not to drop the
upwind wing so far that it touches the water. When
using a straight takeoff path, keep the nose on the aim
point with opposite rudder and maintain the proper step
attitude until the other float lifts off. Unlike a landplane,
there is usually no advantage in holding the seaplane
on the water past normal lift-off speed, and doing
so may expose the floats to unnecessary pounding as
they splash through the waves. Once airborne, make a
coordinated turn to the crab angle that results in a
　
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