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Originally Posted by mistarose
Lets get this straight, if you loose oil pressure, the propeller will only go into feather w/out manually feathering it if the oil is lossed quickly. Why does it matter how fast/slow you loose the oil pressure in the system?
The thought is that as long as the RPM does not drop below 950 it will feather, but once it drops to or below 950 it will be impossible to feather.
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Whats the proper name for these locks that engage somewhere between 700 and 950 rpms? Do you prevent these pins from locking by moving the prop lever past the feather detent? Because at some point you will be reducing the RPMs past the 700-950 range when they are supposed to engage.
They engage at 950 RPM and are called Feather Locks, according to the Seminole POH (might be something you might want to look into investing in). The locks will move into place automatically when the RPM reaches 950, the only way to prevent the locks from moving into place is to keep RPM above 950 on each engine. If you have the Prop Lever in the feather detent the Prop will feather no matter what the RPM is, unless it is 950 or below when you move the prop lever to feather. The locks PREVENT the Propellers from feathering.
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Now to a related topic, during the runup, what are we checking during the feather check? We increase RPM's to 1500, then move each prop lever individually to the feather detent momentarilly and back to full forward again. I have been told and believe that we are verifying the feather locks do not engage, and the prop acts as if it is going to feather (rapid decrease in RPM and whop whop whop). I have also been told we do not know if its the locks or oil pressure keeping them from feathering. I am very confused and will figure all of this out eventually during ground training, but am interested in others thoughts.
Thanks in advance!
When you do the feather check you are making sure that the propellers will feather, the reason they do not feather on you is because you go to the feather position for a short period of time before moving them back to full forward. If you were to leave the prop lever in the feather position it would feather, what is preventing it from feathering is that you are only going to feather for a moment, then right back to full forward, not allowing the oil pressure to drop enough to completely feather the propeller.
The oil pressure helps in allowing you to change the pitch of the propeller. A lack of oil pressure will move the props toward a feather position.
The feather locks prevent the propellers from feathering when shutting down and starting up the engine, because oil pressure may not be enough to prevent the propeller from feathering.