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between the water and the wind is 25 knots, and the
waves will be as high as those produced in still water
by a wind of 25 knots.
The advisability of canceling a proposed flight because
of rough water depends on the size of the seaplane, wing
loading, power loading, and, most importantly, the
pilot’s ability. As a general rule, if the height of the
waves from trough to crest is more than half the height
of the floats from keel to deck, takeoffs should not be
attempted except by expert seaplane pilots. Chapter 8,
Emergency Open Sea Operations, contains more
information on rough water operations.
CONFINED AREA TAKEOFFS
If operating from a small body of water, an acceptable
technique may be to begin the takeoff run while
headed downwind, and then turning to complete the
takeoff into the wind. This may be done by putting the
seaplane on the step while on a downwind heading,
then making a step turn into the wind to complete the
takeoff. Exercise caution when using this technique
since wind and centrifugal force are acting in the same
direction and could result in the seaplane tipping over.
The water area must be large enough to permit a wide
step turn, and winds should be light.
In some cases, the water area may be adequate but
surrounding high terrain creates a confined area. The
terrain may also block winds, resulting in a glassy
water situation as well. Such conditions may lead to
a dangerous situation, especially when combined with
a high density altitude. Even though landing was not
difficult, careful planning is necessary for the takeoff. If
the departure path leads over high terrain, consider circling
back over the water after takeoff to gain altitude. If
air temperatures have increased since landing, make the
proper allowance for reduced takeoff performance due
to the change in density altitude. Think about spending
the night to take advantage of cooler temperatures the
next morning. Although the decision may be difficult,
consider leaving some cargo or passengers behind if
takeoff safety is in question. It is far better to make a
second trip to pick them up than to end your takeoff in
the trees along the shore.
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5-1
PERFORMANCE CONSIDERATIONS
FOR TAKEOFF, CLIMB, CRUISE, AND
LANDING
Since many pilots are accustomed to a certain level of
performance from a specific make and model of land
airplane, the changes in performance when that same
airplane is equipped with floats can lead to trouble for
a careless or complacent pilot. Floats weigh somewhat
more than the wheeled landing gear they replace, but
floats are designed to produce aerodynamic lift to offset
some of the weight penalty. Generating lift
inevitably creates induced drag, which imposes a small
reduction in overall performance. By far the greatest
impact on performance comes from the parasitic drag
of the floats.
TAKEOFF
In a landplane, takeoff distance increases with additional
takeoff weight for two reasons: it takes longer
for the engine and propeller to accelerate the greater
mass to lift-off speed, and the lift-off speed itself is
higher because the wings must move faster to produce
the extra lift required. For seaplanes, there are two
more factors, both due to water drag. As seaplane
weight increases, the floats sink deeper into the water,
creating more drag during initial acceleration. As with
the landplane, the seaplane must also accelerate to a
higher airspeed to generate more lift, but the seaplane
must overcome significantly more water drag force as
speed increases. This extra drag reduces the rate of
acceleration and results in a longer takeoff run.
Naturally, the location of the additional weight within
the seaplane affects center of gravity (CG) location.
Because of the way the floats respond to weight, the
CG location affects the seaplane’s handling characteristics
on the water. If the CG is too far aft, it may
be impossible to put the seaplane on the step. If the
CG is located to one side of the centerline, one float
will be pushed deeper into the water, resulting in
more water drag on that side. Be sure to balance the
fuel load between left and right wing tanks, and pay
attention to how baggage or cargo is secured, so that
the weight is distributed somewhat evenly from side
to side. [Figure 5-1]
The importance to weight and balance of pumping out
the float compartments should be obvious. Water
weighs 8.34 pounds per gallon, or a little over 62
pounds per cubic foot. Performance decreases whenever
　
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