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straight track toward the aim point, and pitch to obtain
the desired climb airspeed.
Again, experience plays an important part in successful
operation during crosswinds. It is essential that all seaplane
pilots have thorough knowledge and skill in these
maneuvers.
DOWNWIND TAKEOFFS
Downwind takeoffs in a seaplane present a somewhat
different set of concerns. If the winds are light, the
water is smooth, and there is plenty of room, a downwind
takeoff may be more convenient than a long
downwind taxi to a position that would allow a takeoff
into the wind. In any airplane, the wing needs to attain
a specific airspeed in order to fly, and that indicated
airspeed is the same regardless of wind direction.
Start Takeoff Run with Water
Rudders Down.
Retract Water Rudders
After Lift-Off.
Continue Takeoff Using
Appropriate Aerodynamic
Controls
Figure 4-16. Remember to retract the water rudders after
takeoff to avoid damage during the next landing.
Ch 04.qxd 8/24/04 10:49 AM Page 4-14
4-15
However, when taking off downwind, obtaining the
airspeed means accelerating to a proportionately higher
groundspeed. Naturally, the takeoff run is longer
because the wings must first be accelerated to the speed
of the wind, then accelerated to the correct airspeed to
generate the lift required for takeoff. So far, this is
identical to what occurs with a landplane during a
downwind takeoff. But in addition, a downwind takeoff
run in a seaplane is further lengthened by the factor of
float drag. The speed of the floats in the water corresponds
to the higher groundspeed required in a landplane, but the
drag of the floats increases as the square of their speed.
This increase in drag is much greater than the increase
in rolling resistance of tires and wheel bearings in a
landplane. A tailwind may lengthen the seaplane’s
takeoff distance much more dramatically than the same
tailwind in a landplane.
Nevertheless, there are situations in which a downwind
takeoff may be more favorable than taking off into the
wind. If there is a long lake with mountains at the
upwind end and a clear departure path at the other, a
downwind takeoff might be warranted. Likewise, noise
considerations and thoughtfulness might prompt a
downwind takeoff away from a populated shore area if
plenty of water area is available. In areas where the
current favors a downwind takeoff, the advantage
gained from the movement of the water can more than
compensate for the wind penalty. Keep in mind that
overcoming the current creates far more drag than
accelerating a few extra knots downwind with the current.
In all cases, safety requires a thorough knowledge
of the takeoff performance of the seaplane.
GLASSY WATER TAKEOFFS
Glassy water makes takeoff more difficult in two
ways. The smoothness of the surface has the effect of
increasing drag, making acceleration and lift-off
more difficult. This can feel as if there is suction
between the water and the floats. A little surface
roughness actually helps break the contact between
the floats and the water by introducing turbulence and
air bubbles between water and the float bottoms. The
intermittent contact between floats and water at the
moment of lift-off cuts drag and allows the seaplane
to accelerate while still obtaining some hydrodynamic
lift, but glassy water maintains a continuous
drag force. Once airborne, the lack of visual cues to
the seaplane’s height above the water can create a
potentially dangerous situation unless a positive rate
of climb is maintained.
The takeoff technique is identical to a normal takeoff
until the seaplane is on the step and nearly at flying
speed. At this point, the water drag may prevent the
seaplane from accelerating the last few knots to lift-off
speed. To reduce float drag and break the grip of the
water, the pilot applies enough aileron pressure to lift
one float just out of the water and allows the seaplane
to continue to accelerate on the step of the other float
until lift-off. By allowing the seaplane to turn slightly
in the direction the aileron is being held rather than
holding opposite rudder to maintain a straight course,
considerable aerodynamic drag is eliminated, aiding
acceleration and lift-off. When using this technique, be
careful not to lift the wing so much that the opposite
wing contacts the water. Obviously, this would have
serious consequences. Once the seaplane lifts off,
establish a positive rate of climb to prevent inadvertently
flying back into the water.
　
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