Loss of oil pressure - will it feather?
Regarding multi engine piston aircraft with fully feathering, single-acting prop governor systems, will losing all oil pressure move the blades to the feather position?
I've seen a number of articles that say the propeller will go all the way to feather and I've seen some that say that it will go to a coarse setting but will require manually selecting feather with the prop lever. Maybe they're both correct and it depends on manufacturer?
I would say I'm pretty familiar with the governor operation including when the prop is on the start locks, low pitch stops, high pitch stops (the IO-360 doesn't seem to have high pitch stops). I'm familiar with how the governor operates during overspeed, underspeed and on speed conditions. I'm familiar with governing range.
Say for example, the engine instantaneously dumped all oil. Assuming the engine was still making the same power, wouldn't the prop pitch remain the same since the oil is 'trapped' inside the hub? Obviously, the engine would seize eventually which would begin to slow the engine and prop governor and open the line for oil to go into the prop hub. Since there would be no pressure at this point in the line, as soon as the engine slowed a bit, I believe the propeller would actually dump all oil from the hub into the sump, and go to the feather position.
If anyone has some detailed diagrams with discriptions of the prop system I'd love to see them. I've gone through a number myself including Pelican's Perch and read a few excerpts from textbooks.
EDIT: I think it could also feather when it has low oil pressure vs zero oil pressure. As long as the pressure supplied to the prop pitch change piston, through the governor and its gear pump, is less than the force from the feathering spring and/or nitrogen on the opposite side - it would go to feather. Is that correct?