This was back at post 700.
Originally Posted by NickLappos
No clutches, guys. The whole drive system is tied together, rotors and prop shaft. My guess is that the "permanently" geared prop is a variable pitch assembly that can run at flat pitch, as well as positive (forward push) and negative (aft pull) pitch. If no prop thrust is desired, the pitch is flattened. Prop thrust could be done with a separate thrust lever in the cockpit, near the collective.
The engine governors automatically increase power as prop pitch is increased.