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the wings and engine have to lift and carry useless
water in a float compartment. Even a relatively small
amount of water in one of the front or rear float compartments
could place the airplane well outside of CG
limits and seriously affect stability and control.
Naturally, water also moves around in response to
changes in attitude, and the sloshing of water in the
floats can create substantial CG changes as the seaplane
is brought onto the step or rotated into a climb
attitude.
Some pilots use float compartments near the CG to
stow iced fish or game from hunting expeditions. It is
imperative to adhere to the manufacturer’s weight and
balance limitations and to include the weight and
moment of float compartment contents in weight and
balance calculations.
Density altitude is a very important factor in seaplane
takeoff performance. High altitudes, high temperatures,
high humidity, and even low barometric pressure
can combine to rob the engine and propeller of thrust
and the wings of lift. Seaplane pilots are encouraged
to occasionally simulate high density altitude by
using a reduced power setting for takeoff. This exercise
should only be attempted where there is plenty
of water area, as the takeoff run will be much longer.
An experienced seaplane instructor can assist with
choosing an appropriate power setting and demonstrating
proper technique.
Unbalanced Fuel Load
Figure 5-1. The location of the CG can affect seaplane
handling.
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5-2
CLIMB AND CRUISE
When comparing the performance of an airplane with
wheels to the same airplane equipped with floats, the
drag and weight penalty of the floats usually results in
a reduced climb rate for any given weight. Likewise,
cruise speeds will usually be a little lower for a particular
power setting. This in turn means increased fuel
consumption and reduced range. Unless the airplane
was originally configured as a seaplane, the performance
and flight planning information for a landplane
converted to floats will typically be found in the
Supplements section rather than the Performance section
of the Airplane Flight Manual (AFM) or Pilot’s
Operating Handbook (POH).
In addition to working within the limits of the seaplane’s
range, the pilot planning a cross-country flight
must also consider the relative scarcity of refueling
facilities for seaplanes. Amphibians have access to land
airports, of course, but seaplanes without wheels need
to find water landing facilities that also sell aviation
fuel. While planning the trip, it is wise to call ahead to
verify that the facilities have fuel and will be open at
the intended arrival times. The Seaplane Pilots
Association publishes a Water Landing Directory that
is very helpful in planning cross-country flights.
In flight, the seaplane handles very much like the corresponding
landplane. On many floatplanes, the floats
decrease directional stability to some extent. The floats
typically have more vertical surface area ahead of the
airplane’s CG than behind it. If the floats remain
aligned with the airflow, this causes no problems, but if
the airplane begins to yaw or skid, this vertical area acts
somewhat like a large control surface that tends to
increase the yaw, making the skid worse. [Figure 5-2]
Additional vertical surface well behind the CG can
counteract the yaw force created by the front of the
floats, so many floatplanes have an auxiliary fin
attached to the bottom of the tail, or small vertical surfaces
added to the horizontal stabilizer. [Figure 5-3]
LANDING
Landplane pilots are trained to stay on the lookout for
good places to land in an emergency, and to be able to
plan a glide to a safe touchdown should the engine(s)
fail. An airplane equipped with floats will usually have
a steeper power-off glide than the same airplane with
wheels. This means a higher rate of descent and a
diminished glide range in the event of an engine failure,
so the pilot should keep this in mind when spotting
potential landing areas during cruising flight.
Seaplanes often permit more options in the event of an
unplanned landing, since land can be used as well as
water. While a water landing may seem like the only
choice for a non-amphibious seaplane, a smooth
landing on grass, dirt, or even a hard-surface runway
usually causes very little damage to the floats or hull,
and may frequently be the safer alternative.
Figure 5-2. The side area of the floats can decrease directional
stability.
　
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