Flow over a feathered propeller

LaxeyT

The propeller of a turboprop engine is started with the propeller blades feathered (in-line with the flow): see video: http://www.youtube.com/watch?v=h-V5jzSslZo. As the propeller speeds up and reaches idle speed while still feathered, and the incidence onto the blades is very high, does this mean that the flow over the blades is separated? Is this why they are started feathered, so that there is little load from the propeller?

Thanks.

Danger

I have no idea about separation. Sorry.
I can only speculate as to why they're keeping the prop feathered. The load upon the engine is actually higher that way, but it would minimize the linear strain upon the mounting system.

HowlerMonkey

It would be super hard on the starter for the TPE-331s if they were started feathered so they aren't started in the feathered position.

PT-6 have a very different design than the single spool TPE331 which allows them to be started feathered.

If you've ever seen a mitsibushi MU2 starting, you will understand why the PT6 guys start feathered.

They do it because they can and the benefit is a propeller that isn't screaming away it idle but rather gently turning.

LaxeyT

Yes, I think the PT6 (http://www.youtube.com/watch?v=7QAISlqA9Us) and the PW120 as well (http://www.youtube.com/watch?v=MtRTaBL9VIU) have separate power turbines, where I think it is common to start the turboprop feathered. On these engines the starter doesn't turn the propeller directly, but my question is is the propeller unloaded or loaded by starting feathered. I think you are saying it is loaded a little, so it doesn't overspeed while coming to idle. However, I am wondering what is the condition of the flow over the propeller, and whether these engines could be started in a fine pitch as well, for a low load condition?

Danger

I'm out of here now; I was never turbine-rated. My only thought was about the prop drag on the gearbox vs. thrust on the staunchion. That was based upon it being a static engine test. (At least, I hope that's what it was, because otherwise it was the ugliest aeroplane that I've ever seen in my life. )