PA25 Specific Information Take-Off Climb Descent Red Lining Approach & Landing Shut Down Wind Limits
PA25 Specific Information
Engine / Throttle handling:
The PA25 is fitted with a 260HP Lycoming 0-540 engine.
Glider towing is very hard on engines due to the alternate use of high and low power settings. Cylinder head cracking can happen when rapid changes (temperature ‘shocks’) or differential changes in temperature occur in an engine. More detailed information can be found under Operations – General Information and Pawnee Ground Operations.
The engine suffers damage if the RPM is constantly varied – it’s important to minimise throttle changes when taxying, so plan ahead. Do not open the throttle quickly – take a full 3 seconds from idle to full throttle.
Fuel management:
The fuel gauge is unreliable. Fuel consumption is higher than the Robin, and also more variable depending on the descent route taken. Guidance of 22 000’ from full tank is approximate and you may achieve less on the day. If in ANY doubt, refuel. Owing to the high fuel burn, efficiently planned towout/descent routeings bring a significant cost benefit.
Visual picture:
Seating position is high and the nose slopes down, so forward visibility is reasonable when taxying and the visual attitude when flying looks more nose-down than you may expect, so monitor airspeed after lift-off. Final approach is moderately steep but looks even more so. Make a note of the ‘picture’ on the ground before take-off, because this shows you the landing attitude.
Take-Off
Pre Take-Off
Use pre-take-off scan to ensure the aircraft is ready for flight. This should include:
- Check fuel again – the gauge is somewhat unreliable. Ensure you refuel when 22,000′ worth of towing has been completed.
- Check door latches again
- Mags on ‘both’, alternator on, lights on
- Carb heat cold, mixture rich
- Trim set to approx letter ‘U’ or slightly aft
- Flaps up (flaps are not used for take off)
Look over your shoulder at the elevator – it will be ‘up’ from the neutral position. Push the stick forward until the elevator is neutral; this is approximately the correct position for the early take-off roll and is approximately in line with the guillotine handle. Now pull the stick hard back until take-off power is set and the combination is rolling.
As above, the take-off is a critical time for the engine. It is therefore important that opening the throttle at the start of the ground run should be gradual and take at least 3 seconds (the O-540 has counterbalance weights on the crankshaft and rapid or frequent RPM changes can cause expensive damage to crankshaft and bearings). On reaching full throttle check the RPM. This is very important and will give the first clue on engine problems. If RPM is low, check the carb heat is OFF before considering rejecting the take-off. Once at 20-30 knots, look in the mirror to ensure the gliders air-brakes are closed. See the ‘Emergencies’ page for actions in the event of a rejected take off.
Elevator and rudder are effective immediately, tailwheel steering helps at lower IAS. Set stick as described above then raise the tailwheel slightly off the ground. There is good rudder authority for crosswinds but be careful not to inadvertently apply brakes with rudder. The attitude looks nose-down as described in section 1.
The aircraft will tend to lift off and climb away at low speed – check the ASI straight away and adjust attitude as necessary.
On first flight of the day, it is normal for oil px to reach or slightly exceed the maximum.
Climb
Basic towing patterns are the same as the Robin, but a bit of planning can bring marked efficiency benefits. The PA25 burns more fuel than a Robin and its descent is quite steep, so a long distance back to the airfield will use significant extra fuel. Commensurate with the type of flight you are towing, try to minimise long returns at higher power. For example; you can be confident a one-day-course or Trial Flight will go to 2000’ so can arrange to drop them in a position that optimises your descent. This is often not possible, especially with a heavy single-seater on a soaring day, but try to take the chances that arise while also dropping the glider in a position that suits its requirements. Being sat behind much of the wing, it is a little more difficult to judge distance from NA areas.
ASI accuracy:
PA25 ASIs commonly overread at towing speeds – in ‘TN use 80mph for unballasted/club gliders and up to 95mph for heavier machines (85mph should be plenty). Keep an eye on the RPM redline at higher speeds, you may need to slow down
Descent
At glider release, stop the climb, acknowledge release with a short turn to the right, reduce power VERY SLOWLY to 2200 rpm, whilst accelerating to 110mphs. This is the most critical part of engine operation and it is very important that the power reduction is achieved in NOT LESS THAN 40 SECONDS.
If necessary, descent speed can be maintained until base leg because the aircraft slows readily, or can be reduced to no less than 80mph to fit in with traffic. Plan to have a little power applied on base leg if possible, as this reduces wear on the thrust-bearing. The base leg and approach angle is steeper than the Robin. Flaps may be applied directly to ‘full’ or in two stages, as you wish – they are reasonably effective and induce a slight nose-up trim change.
‘Red Lining’
The PA25 is fitted with a four bladed propeller. The advantage of this is that high rpm at full throttle minimises the ground run and produces an efficient climb profile. The downside is that it operates very close to the 2700 rpm red line limit which will be reached at full power at around 95mph and very quickly after the glider releases if the correct power reduction technique is not applied. It is also possible during strong convection or heavy turbulence to see surges towards the red line, it is usually sufficient to just slow down, however, reducing the throttle setting may be needed.
Approach & Landing
Final approach looks steeper than it is – regularly check the ASI. Until ‘in practice’ it is probably better to make approaches with a little power applied, to moderate the Rate of Descent.
It is possible for the RoD to get high at the end of the approach, especially if speed reduces and/or in thermic/windy conditions. If you get this impression, promptly add power; it is possible to make very heavy landings otherwise.
Flare as for any taildragger but, when you achieve the attitude you saw when taxying, stop holding off and let the aircraft fly onto the ground in this attitude (if fully held-off, it lands tailwheel first which can break the springs) and roll out straight ahead until jogging/walking pace; turns made at excessive speed tend to tighten-up uncontrollably.
Be aware that if landing along a slope (e.g. near the base of the hill on SW run) the aircraft may tend to turn up the slope. Consider any crosswind affecting the required stick position as you make turns then taxy as before, applying due caution to taxying downwind and/or downslope.
Check the door latches again if carrying out a series of tows. Between tows you will probably need to hold on the toe-brakes – take care when your attention is inside the cockpit that the aircraft doesn’t creep forward. If it does, close the throttle before braking.
Shut Down
The tug should be stopped and brakes applied. Allow the engine to idle at 1000 rpm for a short time to allow it to adequately cool, check carb heat during this phase.
Switch ALL electrics off including the stobes & radio.
Shut down as per the Robin.
After the engine stops, switch the magnetos OFF and remove the key. Turn the master switch OFF.
The park brakes rely on trapped fluid pressure which may reduce with time to the point they become ineffective. Choose a parking position with minimal slope, if left unattended on a slope for any time use the chocks kept in the hopper.
Unless only a very few tows have been made it is best to refuel now, owing to the limited number of tows per tankful.
Annotate ‘refuelled’ on the log card for the benefit of the next pilot.
Wind Limits
It is possible to operate the Pawnee is relatively strong winds, however, there is little point in taking the risk of using a taildragger in these conditions when there are Robins in the hangar.
Return to ‘Pawnee Ops’ Return to ‘Operations’ Return to ‘Front Page’
