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does the amount of drag on the remaining wetted area.
Drag increases as the square of speed, and eventually
drag forces would balance the power output of the
engine and the seaplane would continue along the surface
without further acceleration.
Seaplanes have been built with sufficient power to
accelerate to takeoff speed this way, but fortunately the
step was invented, and it makes further acceleration
possible without additional power. After passing over
the hump, the seaplane is traveling fast enough that its
weight can be supported entirely by hydrodynamic lift.
Relaxing the back pressure on the elevator control
allows the float to rock up onto the step, and lifts the
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rear portions of the floats clear of the water. This eliminates
all of the wetted area aft of the step, along with
the associated drag.
As further acceleration takes place, the flight controls
become more responsive, just as in a landplane.
Elevator deflection is gradually reduced to hold the
required planing attitude. As the seaplane continues to
accelerate, more and more weight is being supported
by the aerodynamic lift of the wings and water
resistance continues to decrease. When all of the
weight is transferred to the wings, the seaplane
becomes airborne.
Several factors greatly increase the water drag or
resistance, such as heavy loading of the seaplane or
glassy water conditions. In extreme cases, the drag may
exceed the available thrust and prevent the seaplane
from becoming airborne. This is particularly true when
operating in areas with high density altitudes (high elevations/
high temperatures) where the engine cannot
develop full rated power. For this reason the pilot should
practice takeoffs using only partial power to simulate
the longer takeoff runs needed when operating where
the density altitude is high and/or the seaplane is heavily
loaded. This practice should be conducted under the
supervision of an experienced seaplane instructor, and in
accordance with any cautions or limitations in the
AFM/POH. Plan for the additional takeoff area required,
as well as the flatter angle of climb after takeoff, and
allow plenty of room for error.
Use all of the available cues to verify the wind direction.
Besides reading the water, pick up clues to the
wind’s direction from wind indicators and streamers
on the masts of moored boats, flags on flagpoles, or
rising smoke. A boat moored to a buoy points into the
wind, but be aware that it may have a stern anchor as
well, preventing it from pointing into the wind.
Waterfowl almost always align themselves facing into
the wind.
Naturally, be sure you have enough room for takeoff.
The landing distance of a seaplane is much shorter than
that required for takeoff, and many pilots have landed
in areas that have turned out to be too short for takeoff.
If you suspect that the available distance may be inadequate,
consider reducing weight by leaving some of
your load behind or wait for more favorable weather
conditions. Atakeoff that would be dangerous on a hot,
still afternoon might be accomplished safely on the following
morning, with cooler temperatures and a brisk
wind.
In addition to wind, consider the effects of the current
when choosing the direction for takeoff. Keep in mind
that when taxiing in the same direction as the current,
directional control may be reduced because the seaplane
is not moving as quickly through the water. In rivers or
tidal flows, make crosswind or calm wind takeoffs in the
same direction as the current. This reduces the water
forces on the floats. Suppose the seaplane lifts off at 50
knots and the current is 3 knots. If winds are calm, the
seaplane needs a water speed of 47 knots to take off
downstream, but must accelerate to a water speed of 53
knots to become airborne against the current. This difference
of 6 knots requires a longer time on the water
and generates more stress on the floats. The situation
becomes more complex when wind is a factor. If the
wind is blowing against the current, its speed can help
the wings develop lift sooner, but will raise higher
waves on the surface. If the wind is in the same direction
as the current, at what point does the speed of the wind
make it more worthwhile to take off against the current?
In the previous example, a wind velocity of 3 knots
would exactly cancel the benefit of the current, since the
air and water would be moving at the same speed. In
most situations, take off into the wind if the speed of the
　
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