Turboprop - Prop Position Prior to Start?

M

meritflyer

Well-Known Member
Why is it on a turboprop engine, the prop is feathered during shut down?

Secondly, what actually controls the prop position in flight (ie governor?)
 
My understanding is if the prop is full feathered it means it is a free turbine. Otherwise there would be too much load on start. The props that are connected directly to the turbine (through gears) do not go to full feather on shut down.
 
A couple of reasons

1. the condition levers and prop levers could be the same thing, ala Dash 8 style, so when you put the prop levers in fuel cutoff it also feathers the prop.
2. King air style where you have seperate prop and condition levers you feather the prop before shutting down simply to help the engine spool down quicker after you move the condition levers to cutoff.
3. On direct drive applications, Garrett engines for example the props do not feather on shutdown because the feathered prop on startup is too much load on the engine (imagine a big paddle swinging through the air).
 
400A said:
A couple of reasons


2. King air style where you have seperate prop and condition levers you feather the prop before shutting down simply to help the engine spool down quicker after you move the condition levers to cutoff.
Click to expand...

Not to mention the oil pump i.e. accessory case is run by the compressor section which spins down almost immediately while the power section does not. So, no oil pump no lube.
 
To your unanswered question, in flight the props are controlled by a governor, same as a recip.

On the ground, they're controlled by a beta valve, which functions to reposition the low pitch stop.
 
The SAAB only had Condition Levers, which controlled the prop and the start functions. It was always started in feather, as it was a free turbine. They also could sit in feather all day, versus the 1900, allowing you to have air conditioning (what little it had) on the ground. Plus, if you wanted to run the HP Bleed (for more air or heat), it had to be in feather, as you had to run the NG up to 76%.

The engines also had to run in feather for 1 minute prior to shut down.
 
First you need to know what kind of turbine your referring to:

King Air Style w/ PT-6's is a Free / split turbine. (IE the "power" section (prop and prop reduction gearbox shaft) is completely split from the Compressor turbine, Compressor stages and accessory gearbox drive shaft):

The prop does not have to be feathered for shut down, BUT it Can be feathered for shutdown.. which one to use is typically operator preference.
My operator prefers us NOT to feather before shutdown. We bring the Condition lever to fuel shutoff. at 30% N1 we bring the props into feather. 1. This puts less "load" on the prop blades 2. provides additional "suction" on the turbine side to help w/ cool down, 3. Removes all of the oil from the prop hub to eliminate the chance of a "dry start" in the prop reduction gearbox. 4. Helps eliminate any hot exhaust gases from collecting and heat soaking any fuselage skins and the windscreens during prolonged ground feather operations.

The Primary governor is responsible for controlling the prop in cruise. The overspeed governor is responsible for controlling the prop in a overspeed condition (2288rpm). The Fuel topping governor is responsible for controlling the prop if the Primary and Overspeed governor fails (2333 rpm i believe) and for Beta and reverse thrust operations.


Mu2's, Turbo Commanders, etc w/ garrets are a direct drive (prop is driven directly by the reduction gearbox that is connected to the compressor/turbine shaft)

Prop is still controlled by the primary governor and i would assume (b/c i'm not familiar with these) that they also have a fuel topping and overspeed governor.
The prop is left in an unfeathered condition b/c they are directly connected to the compressor and turbine shaft. This helps in quicker starts and lower battery drain during starts.
 
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