User manual

Section Appendix A.2 Part B
06 ASYMMETRIC EFFECTS IN TAXIING
Although not affected as much as in a single engine floatplane the Catalina is acted on by
forces producing turning moments. These are; propeller torque; propeller slipstream;
asymmetric thrust of the propeller disc; and gyroscopic precession. All but the last will
result in a left turn in the Catalina. The result of these is a slight left turning tendency as
power is applied although the gyroscopic precession wants to command a right turn as the
nose rises. As the nose is lowered once the aircraft comes up onto the step there is a
gyroscopic force commanding a left turn. Considerable right rudder is required to keep
straight, even in steady headwind or no wind conditions.
07 ASYMMETRIC EFFECTS OF WIND ON CONTROL SURFACES
It takes very little force to turn an aircraft on the water in calm conditions. The effect of
wind on the large fin and rudder of the Catalina easily yaws the aircraft into wind. The
greater drag provided by a downward deflected aileron can be used to provide a turning
moment or to counter the tendency to weathercock into wind.
08 ATTITUDES ON THE WATER WHEN STATIONARY
The aircraft will position itself in an attitude that puts the CofG and. C.of.B on the same
vertical line. This will be affected to a degree by loading and by water conditions. Rotations
round the C.of.B can occur but those about the longitudinal axis are resisted by the wingtip
floats and those about the transverse axis are countered by the CofG and C.of.B returning
to their co-axial relationship. Force applied transversely at the C.of.B will tend to move the
aircraft sideways but force applied ahead of or behind the C.of.B will rotate the aircraft
about the vertical axis.
An aircraft not moving through the water can not be steered even if water rudders were
fitted. It is the effects of wind that will dictate how the aircraft rests on the water in any
given conditions.
09 LOW SPEED TAXIING
The attitude is determined as above plus the pitch down of thrust and the pitch up of
hydrodynamic forces as forward movement begins. The pitch up is reinforced by airflow
over the up elevators. Pitch up increases in intensity with speed but acts further back on
the hull so its moment arm reduces. At low speed taxi it can be considered constant and
only alters significantly as the aircraft accelerates through the plow configuration to
achieve the step. Control of rotation about the vertical axis is by differential power use to
overcome the weather cocking tendency since the Catalina has no water rudder. The
inertia of the aircraft must be remembered and effects of power and wind anticipated.
Power changes need to be made ahead of the desired course. Directional stability can be
enhanced by lowering the landing gear (greater keel effect) but the danger of salt water in
wheel bearings must be considered if operating in the sea.
Taxi speed will be <5 knots and engine power settings kept as low as possible. Any cross
wind component during the taxi will cause drift which must be taken into account especially
if operating in confined areas. Drift may also be caused by movement of the body of water
in which the aircraft is floating.
Rev No: 02 Stichting Catalina PH-PBY
Page: 2 01 April, 2006