User manual

Section Appendix A.4 Part B
08 TAKEOFF
Choice of Takeoff Path
Choice of Takeoff direction and planning the takeoff is more complicated then for
operations on land. The following need to be considered:
Shape and size of the Takeoff area. Because visual estimates are inaccurate it is best to
examine the area well from the air before landing. If that is not possible an assessment
from charts plus inspection by taxiing or by boat before take off is desirable.
Submerged obstacles are best identified by aerial inspection (if water clear) chart, local
knowledge (if available) or by slow back taxi over the full length of the takeoff run.
Wind direction and speed should be estimated and in almost all cases take off should be
made into the wind. Tailwind takeoffs are particularly risky in hull type seaplanes such as
PBY due to the exaggerated tendency to porpoise and the reduced elevator effectiveness
to counter this. Signs to help read the wind direction include;
1) the aeroplane itself by weather cocking,
2) Moored boats,
3) Sails, flags and sailing direction of boats,
4) Shoreline trees, flags, smoke etc,
5) Wind vanes on the water.
Wind strength is best assessed by a combination of factors. These were introduced in
01/08 of this section
Surface Conditions including waves, wave form and direction, glassy water areas,
potential for boat wakes to disturb the takeoff, surface markers and obstructions must all
be studied to determine the best takeoff area and direction.
Currents can be used to advantage and where a down current takeoff run is into wind that
should be chosen. If wind and current direction are the same, choose a takeoff direction
into wind even though that is against the current.
09 PERFORMANCE CONSIDERATIONS
For a standard takeoff in light winds at sea level and ISA conditions and with the aircraft at
11999 kg AUW (26485 lbs) PBY requires 1200m (4000ft) for takeoff. This basic value will
be affected by:
Density Altitude
which will increase the takeoff distance as DA increases. Propeller efficiency decreases,
wing efficiency decreases, T AS is higher for the same lAS, even though engine power
loss is compensated for by supercharging. Allow 12% longer Takeoff run for each 1000 ft
increase in DA. Allow 12% longer for each 8 deg C above standard for the pressure
altitude.
Weight reduction
below MAUW will improve takeoff performance and shorten the takeoff run.
Allow 10% less for takeoff run for each 5% reduction in AUW.
Wind strength
affects takeoff run as it does on land. A down wind takeoff is undesirable due to the longer
period of time in contact with the water and the greater speed through the water for a given
IAS. Thus forces on the aircraft are much more severe downwind while elevator control is
poorer. Allow 10% reduction in Takeoff run for each 10 knots headwind component.
Rev No: 02 Stichting Catalina PH-PBY
Page: 4 01 April, 2006