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On full-feathering (hydraulic) constant speed propellers in general, and specifically Hartzell and McCauley props, does the propeller governor have a high-pitch stop (like non-feathering propellers, at 20-30°) or can the governor go up to the feather pitch stop if needed ?

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Yes the high pitch stops are there, but on a feathering version, they are removed centrifugally when the RPM gets above 500 after starting. They are only there to prevent the prop from moving into feather when you shut down on the ground.

Actual blade angle is controlled by governor oil pressure driving the blades to fine pitch, opposed by the counterweights on the blade roots wanting to drive the propellers to coarse pitch. On a feathering prop, coarse pitch movement from the counterweights is helped by an internal feathering spring for when it's necessary to go all the way to feather.

The engine feathers by dumping the oil from the governor so that the counterweights and the internal feathering spring are the only forces acting on blade angle, and they move to feather (as long as the engine is spinning above 500 RPM when you feather so that the high pitch stops are disengaged).

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    $\begingroup$ What is undesirable about going to feather when shut down or at low speed on the ground? IIRC, the Hamilton Standard props on C-130's (up to the H model, dunno about the J's) could go to feather without limitation on prop speed, but different hardware has different capabilities & limitations. Thanks! $\endgroup$
    – Ralph J
    Sep 15, 2023 at 18:26
  • $\begingroup$ Many turboprops do feather on shutdown. $\endgroup$
    – TheEagle
    Sep 15, 2023 at 22:12
  • $\begingroup$ So the counterweights could drive the blades all the way to the feather pitch if the advance ratio is high enough, right ? $\endgroup$
    – TheEagle
    Sep 15, 2023 at 22:14
  • $\begingroup$ If the oil pressure in the hub is not there, and the prop is spinning, there's nothing stopping the counterweights from driving the blades to feather other than friction and possible opposing aerodynamic forces as the weights move to where their influence is weakest. The feathering spring helps it along to make sure. $\endgroup$
    – John K
    Sep 16, 2023 at 2:23
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    $\begingroup$ @RalphJ Those are "hydramatic" props, where hydraulic pressure drives the blades in both directions. For feathering, they will dump oil from the fine pitch side so oil on the coarse pitch side can drive the blades to feather. Since they are dependent on oil pressure to feather, they use a feathering pump that takes oil from an emergency sump in the propeller gearbox if there is no main oil pressure. TP propellers feather on shutdown to prevent windmilling in the breeze, there being little resistance. Not necessary with a piston engine. $\endgroup$
    – John K
    Sep 16, 2023 at 2:36

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