User manual

Part B SectionAppendix A.2
10 SAILING WITH POWER OFF
Once weather-cocked into wind the aircraft will "sail" backwards but direction can be
modified by placing the rudder hard over in the direction required and putting in full down
aileron on the same side. Thus rudder is towards direction of travel and control wheel
turned in the opposite direction. This will turn the aircraft and allow it to "keel sail"
backwards and to one side. The degree to which a sideways component of sailing can be
maintained depends on the rudder and aileron ability to counter the weather-cocking
tendency and so is affected by wind strength.
11 SAILING WITH POWER ON
If conditions allow lateral keel sailing, other directions can be achieved as well. Once nose
direction has been set by the use of rudder and aileron, sailing in most directions can be
achieved by using power to equalise or exceed the backward component of the wind
vector. The forces required are not great so the power needed is often little but
correspondingly the speeds achieved with sailing are low and to achieve and maintain
control requires patience and concentration from the pilots.
12 PLOW TAXI
In a single engine aircraft one advantage of the plow taxi is the ability to turn downwind
especially to the left (see hydrodynamic forces) but in PBY this ability can be provided by
asymmetric thrust and the poor visibility over the nose of the aircraft means the use of the
plow taxi is seldom if ever used.
13 HIGH SPEED TAXI (ON THE STEP)
Once power is applied and the aircraft accelerates it begins to cross its own transverse
waves. This, combined with the presence of a step in the hull allows air and water to mix
under the hull. Small waves on the water surface add to this effect. As speed increases the
control back pressure is relaxed to allow the hull to settle into a planing attitude supported
by the area of hull just forward of the step. An attitude exists for best planing efficiency and
that offers least drag from the water and best acceleration for the aircraft. A lower nose
attitude results in greater drag from the increased hull contact forward of the step and a
higher attitude compromises the air/water mixing behind the step and may prevent the
aircraft getting onto the step at all. This is particularly a problem if heavily loaded, with the
CofG too far rearward or in high density altitude conditions where less power is available.
As acceleration continues and the centre of buoyancy moves rearward some elevator back
pressure will be required to maintain the best attitude. A change as little as 1/2 degree in
attitude can make all the difference to take off performance.
On the step the aircraft is supported by a balance of hydrodynamic and aerodynamic
forces. The wing is set to be at its best low speed angle of attack at the same time as the
hull sits at the best planing attitude. This explains the slight nose down appearance of a
Catalina in cruise flight.
Once on the step and with best attitude achieved the aircraft will continue to accelerate
until it takes off. To keep the aircraft on the step requires a power reduction and 25in
Manifold Pressure is usually sufficient to keep PBY step taxiing.
Directional control can be achieved by the use of the rudder fairly early on in acceleration
(floatplanes have their water rudders raised for operation on the step). Because the aircraft
is being supported by a very small area of hull, small bank angles will produce a horizontal
Stichting Catalina PH-PBY Rev No: 02
01 April, 2006 Page: 3