Here’s a Constant Speed prop itself – notice that there is no CSU or Beta valve attached to this! Effectively what you have in this end is a hoofing great spring which attemts to feather the propeller (turn the blades into the airflow), and oil pressure fed through the tube in the middle to the right hand side of the piston to progressively fine the propeller. As has been stated, the pilot requests the pitch of the propeller, and the CSU directs oil into (fine) or out of (coarse) the prop hub. Couple of pictures here: http://www.fly13.co.uk/Tug/VP%20Prop/Prop.htm
Starting up, the prop would be held in ground fine pitch (2-3 degrees), and as the engine runs up, the start locks disengage and allow the pilot to control the pitch. Fine is used for take-off and landing, and coarse would be used to change the speed of the aircraft in the cruise. (OK, it is a little more complex than that, but it’ll do). Further than the coarse range, we have an option to feather the prop (not on Spitfires….). Further back from Fine pitch, turboprop engines usually have a superfine and a reverse pitch…..
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