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Another technique that aids glassy water takeoffs
entails roughening the surface a little. By taxiing
around in a circle, the wake of the seaplane spreads and
reflects from shorelines, creating a slightly rougher
surface that can provide some visual depth and help
the floats break free during takeoff.
Occasionally a pilot may have difficulty getting the
seaplane onto the step during a glassy water takeoff,
particularly if the seaplane is loaded to its maximum
authorized weight. The floats support additional
weight by displacing more water; they sink deeper into
the water when at rest. Naturally, this wets more surface
area, which equates to increased water drag when
the seaplane begins moving, compared to a lightly
loaded situation. Under these conditions the seaplane
may assume a plowing position when full power is
applied, but may not develop sufficient hydrodynamic
lift to get on the step due to the additional water drag.
The careful seaplane pilot always plans ahead and considers
the possibility of aborting the takeoff.
Centrifugal Force
Figure 4-17.The downwind arc balances wind force with centrifugal
force.
Ch 04.qxd 8/24/04 10:49 AM Page 4-15
4-16
Nonetheless, if these conditions are not too excessive,
the takeoff often can be accomplished using the
following technique.
After the nose rises to the highest point in the plowing
position with full back elevator pressure, decrease back
pressure somewhat. The nose will drop if the seaplane
has attained enough speed to be on the verge of attaining
the step position. After a few seconds, the nose will
rise again. At the instant it starts to rise, reinforce the
rise by again applying firm back pressure. As soon as
the nose reaches its maximum height, repeat the entire
routine. After several repetitions, the nose attains
greater height and speed increases. If the elevator control
is then pushed well forward and held there, the seaplane
will slowly flatten out on the step and the controls may
then be eased back to the neutral position. Once on the
step, the remainder of the takeoff run follows the usual
glassy water procedure.
ROUGH WATER TAKEOFFS
The objective in a rough water takeoff is similar to that
of a rough or soft field takeoff in a landplane: to transfer
the weight of the airplane to the wings as soon as possible,
get airborne at a minimum airspeed, accelerate in
ground effect to a safe climb speed, and climb out.
In most cases an experienced seaplane pilot can safely
take off in rough water, but a beginner should not
attempt to take off if the waves are too high. Using the
proper procedure during rough water operation lessens
the abuse of the floats, as well as the entire seaplane.
During rough water takeoffs, open the throttle to takeoff
power just as the floats begin rising on a wave. This
prevents the float bows from digging into the water and
helps keep the spray away from the propeller. Apply a
little more back elevator pressure than on a smooth
water takeoff. This raises the nose to a higher angle
and helps keep the float bows clear of the water.
Once on the step, the seaplane can begin to bounce
from one wave crest to the next, raising its nose higher
with each bounce, so each successive wave is struck
with increasing severity. To correct this situation and
to prevent a stall, smooth elevator pressures should be
used to set up a fairly constant pitch attitude that allows
the seaplane to skim across each successive wave as
speed increases. Maintain control pressure to prevent
the float bows from being pushed under the water surface,
and to keep the seaplane from being thrown into
the air at a high pitch angle and low airspeed.
Fortunately, a takeoff in rough water is generally
accomplished within a short time because if there is
sufficient wind to make water rough, the wind is also
strong enough to produce aerodynamic lift earlier and
enable the seaplane to become airborne quickly.
The relationship of the spacing of the waves to the
length of the floats is very important. If the wavelength
is less than half the length of the floats, the seaplane is
always supported by at least two waves at a time. If
the wavelength is longer than the floats, only one wave
at a time supports the seaplane. This creates dangerous
pitching motions, and takeoff should not be attempted
in this situation.
With respect to water roughness, consider the effect of
a strong water current flowing against the wind. If the
current is moving at 10 knots and the wind is blowing
the opposite direction at 15 knots, the relative velocity
　
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