Nurse or feather that engine??

[svcta]

okay.

 

[Amish RakeFight]

I am still a bit confused about whether or not the prop on a piston twin will feather if oil pressure is completely lost without intervention from the pilot. I know when oil P is lost everytime it is shut down on the ramp the prop goes into the low pitch/windmill position but can't seem to figure out how it will feather if oil P is lost in flight. How does it know the difference? Thanks.

The average light piston twin has a system where below a certain RPM value it will not feather. Gear pins functioning on centrifugal force provided by the windmilling propeller within the hub prevent this. As the centrifugal force decreases, the pins begin to move in and prevent the blade angles from moving to a full feathered position. This is an important piece of knowledge to have if you're flying such an airplane equiped as such. If you don't feather it in time, you might not be able to do so at all.

The reason for this is so that upon normal shutdown on the ramp the blades don't go into a feathered position. This would make it very hard on the starter and battery to turn the prop fast enough so that it catches. Same reason why we verify that the prop control is in the fwd positon upon start up. Less resistence and drag with a lower pitch.

Recall also, that the hub may also contain a counter spring, conunter weights and a nitrogen charged hub as well which assist in the feathering. If oil pressure is lost above a certain RPM, although centrifugal force will normally drive the blades to a low pitch/high RPM setting, the counterweights within the hub will also be working to drive the baldes to an opposite and feathered position.