Originally Posted by
SNS3Guppy
Ian,
A typical propeller at that time was a hamilton standard hydromatic prop. This required a dedicated oil pump called a "feather pump," and this pump had to be energized to drive the propeller into feather. The pump was supposed to shutoff when the propeller was feathered. To drive it into the feather position, a button was pushed, and the button was held in by a solenoid. When the feather position was reached, the button was supposed to pop out by itself, interrupting the pump process, and leaving the propeller in feather.
A common problem with the hydromatic prop was that the button wouldn't pop out. The solenoid would hold the button in, and the propeller would feather, then with the pump running, continue to drive itself out of feather again. The solution was to guard against the button, watching the propeller, and popping the feather button out by hand once the prop had feathered.
I was under the impression that if the button did not pop out that it would cause the motor for the aux feathering pump to burn out as it was continuing to try to operate the now feathered prop. I had not heard about the prop coming out of feather by itself in this scenario if the motor continued to run.
In all honesty, I was never 100% comfortable with my knowledge of the inner workings of that complicated prop and it seemed difficult to get answers sometimes, but going from memory, it seems to me that a propeller blade angle switch and a pressure switch in combination would stop the solenoid operating the motor on the pump.
Perhaps our system was different because there was no way to push in that button on the Herc. It went in automatically when the condition lever was placed to feather and then popped out or if necessary was pulled out.
P.S. We had a maximum airspeed of 180 knots for an airstart.