Turbo props running in feather before shutdown

I did a little research in my systems book and asked someone else and came to this conclusion --

In the Dash-8 there is a prohibited/yellow RPM range (500-780rpm) which the ECU will keep Nh set as such to either be above or below it. Above feather/disc the ECU will keep the Nh up to keep the RPM above 780rpm. Going to feather allows the Nh to stabilize temperatures for fuel cut off.
 
Procedures I use are:

van- feather, 400 Prop RPM condition cutoff

200- cutoff, feather during spool down.
 
A feathered prop is also much quieter than an unfeathered one on a prolonged taxi. Also in the Saab you will see your prop gearbox oil temps spike in the unfeathered position if you are sitting still on the ground on a warm day. Feathering allows oil back to the reservoir which = cooler oil.

As previously mentioned, CJC's procedure to help keep the cabin cool is to run the high pressure bleed valves with one engine feathered and the compressor spooled up a bit. This is why so often you see the Saabs taxiing with one engine unfeathered and one feathered. We are in there sweating like a cub scout at neverland ranch. ;)
 
Also on the Dash we do it for the purpose of the mighty quick turn...If we didn't let the engine cool at feather for 30 seconds in all likelihood, especially in the summer, we'd have to motor the engine to bring the ITT down within starting limitations before adding fuel. That's really hard on the starter and batteries even with the APU running. And it's also time limited to 30 seconds which may not be adequate.
 
But being a free power turbine, the engine temps don't really change with with prop in feather. The NH and ITT are about the same. That is the point that has me confused about this temp stabilization thing.
 
smig said:
But being a free power turbine, the engine temps don't really change with with prop in feather. The NH and ITT are about the same. That is the point that has me confused about this temp stabilization thing.
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You said the answer - Stabilization. I understand it to be primarily for cooling of bearings etc (not temps that you find on a gauge). You are not producing thrust which I suppose is good if you are parked at a gate. Realistically at idle with props unfeathered, it really doesn't matter though.
 
I remember the dash mx manual saying something about leaving them at start/feather for 30 seconds before shut down, so that you can get an adaquate oil check.

Also, know that if you dont wait the 30 seconds, the prop will be hard to spin by hand. Noticeable when spining the blades during preflight.
 
In Phoenix in the summer its not uncommon to have to wait till around 25% Nh to introduce fuel, or slightly higher than that. Usually I wait until the ITT is below 200' then introduce fuel.
 
Polar742 said:
Free-power turbines, such as the PT-6 on the King Air and the GE on the SAAB, don't require that the prop turns in order to start the engine. So it's easier to let them bleed off to feather, or some procedures (I'm reaching way back) and systems are designed to place the prop to feather prior to shutdown. Usually bringing the condition levers to cutoff will feather the engine as it shuts down (I think this is the way it was in the King Airs - again, I'm reaching deep in the memory, so I could be completely off base)
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Yes, this is correct WRT the PT6. On the -25A the prop will return to feather somewhere in the 10-12 psi oil pressure range, so as the engine is shut down by pulling the cond. lever back to FUEL-OFF, the prop will slowly return to feather as the oil comes back out of the hub and pitch-change assembly.
 
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