Man, thanks but all that is the basic of Constant Speed prop operation
I understand very well that below the governed range, when the blades are resting against the Flight Idle stops, the Power Lever now directly affect Np
Now, how you enter into Bęta mode, or if you prefer, the one used to brake.
Because on the PC-6 the Flight Idle max fine pitch is 9°30' at 30 inches station ( position of the blade that the measure of the angle was taken ), I can tell you there is no brake effect, or at least not the one we're lookin' for.
So, what allow the blades to come at around -0°30'..
There is a good scheme here :
http://aerosolution.ca/inside/courscaravan/PT6-3.jpg
But, if it's work like that, when you start your PT-6, pushing all the way forward the Prop Lever after start, as the Power Lever is fully retarded, the prop should be in Beta Range, AND Beta angle, so, viewing from the sides, the blades would be really flat, having the flat part in the center.
To show you what angles I mean, I used this PC-6 prop I modelled :
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