Baron BE55 Prop feather question

[philly3229]

Hi guys!

I am flying a baron 55 for my multi commercial add on training. I have a question on feathering the engine.

I understand the concept of feathering and why we do it but my question is: In these multi-engine props, they are different from, say, a piper arrow in that when oil pressure leaves the prop hub it changes the pitch to be more coarse, correct? I believe that if there is a loss of oil pressure then the props will fail to the feather position. Does this mean in this plane a loss of oil pressure will automatically put the prop in feather, without the pilot having to use the prop control to put it into the feather position?

Also- when I am doing my run-ups with my instructor and we have high RPM, he is very adamant about not letting the prop RPM drop very far when we test the feather (put the leaver into the D-tent and then up very quickly) is this because the prop WILL feather if we leave it there too long and this puts terrible stress on the engine?

Thanks so much.

Phil

 

[AcroBoy]

In. B-55 (which I own and fly), the pitch will go flat upon loss of oil pressure. However, on my Extra 300L the pitch will go to coarse upon loss of oil pressure. It all depends on the system. Your instructor should know this answer.

 

[Cpt_Kirk]

I don't know the exact intricacies of the Baron-specific systems, but when there is a loss of oil pressure, the propeller will move towards a feathered position. I don't know if it will completely feather itself or if the locks will prevent it from completely feathering in flight until pilot input is made. Have you noticed that when you shutdown, the propellers don't feather even though there is a natural loss of oil pressure? There are locks that prevent the feather from occurring and, if I'm not mistaken, there difference between feathering and not feathering has to do with the rpm on shutdown. Like I said, I can't give you an exact reason, but I hope that you will look into this further.

 

[Fearless Tower]

In. B-55 (which I own and fly), the pitch will go flat upon loss of oil pressure. However, on my Extra 300L the pitch will go to coarse upon loss of oil pressure. It all depends on the system. Your instructor should know this answer.

You have it reversed. In a light twin the loss of oil pressure will cause the blades to go coarse, not flat. But the lock pins in the hub keep the blades from going fully feathered unless you put the prop lever in the feather detent.

 

[unsafervguy]

You have it reversed. In a light twin the loss of oil pressure will cause the blades to go coarse, not flat. But the lock pins in the hub keep the blades from going fully feathered unless you put the prop lever in the feather detent.

first off you feather a prop, not an engine.
the above is not not quit true. the pins are only engaged below about 800 RPM. they are held out by centrifical force, if the engine looses oil pressure when the the RPM is above that the prop will go into feather. the pins are to keep the prop from going into feather when shutting the engine down normally.

 

[hindsight2020]

first off you feather a prop, not an engine.
the above is not not quit true. the pins are only engaged below about 800 RPM. they are held out by centrifical force, if the engine looses oil pressure when the the RPM is above that the prop will go into feather. the pins are to keep the prop from going into feather when shutting the engine down normally.

The functionality of the feathering stop pins in these piston props has to do with the gradient of oil pressure loss, not the RPM at the time of loss. This is why pulling the mixture above 800-950RPM (depending on the manufacturer) does not automatically lead to a feathered prop like you suggest. Plenty of youtube videos demonstrating that an engine shutdown in flight by pulling the mixture, merely windmills in the wind, where by your logic it would feather upon loss of ignition and oil pressure.

The reason the feathering dump works, is that the gradient of oil loss by manual feathering is steep, thereby allowing the feathering spring to go full bore and bends those blades into full stop feather, well before the RPM catches up to the stop pin popout range circa 800-950RPM. By the time the propeller reaches that trigger RPM on a large oil pressure gradient loss, the blades already got sprung past the stop pin positions, thereby not being caught by the pins when they pop out.

Conversely, if the oil pressure loss is graaaaaadual, such as is the case of a mixture pulled, loss of ignition, or normal engine shutdown, the hub will retain residual oil and thus oil pressure, and not allow the feathering spring sufficient "delta force" to bottom out aggressively and get those blades into feathered position before the stop pins pop out at 800-950RPM. In this event the blades never get pushed past the stop pin position before the RPM reaches the popout range, at which point they get naturally caught by the pins. It is at THAT point, that even feather dumping won't work, no delta left to make the "dumping" effective anymore.

Clear as mud? And F.Tower is a Baron owner, I'm willing to give him the benefit of his understanding of the feathering specifics of the props in his spam can. I'm positive he understands the nomenclature behind feathering a prop and not an engine, as do you and most of us twin drivers on here. Let's all hold hands and get along now.

 

[unsafervguy]

sorry, but you are wrong. rate of loss has nothing to do with it. from hartzell manual 115N (it the same for M type props)
3)
If oil pressure is lost during operation, the propeller will
feather. Feathering occurs because the air charge, spring,
and blade counterweights are no longer opposed by
hydraulic oil pressure. The air charge, spring and blade
counterweights are then free to increase blade pitch to
the feathering (high pitch) stop.

also from the same manual:
(7)
When the engine is stopped on the ground, it is
undesirable to feather the propeller, as the high blade
angle inhibits engine starting. To prevent feathering during
normal engine shutdown on the ground, the propeller
incorporates spring energized latches. If propeller rotation
is approximately 800 RPM or above, the latches are
disengaged by centrifugal force acting on the latches
to compress the springs. When RPM drops below 800
RPM (and blade angle is typically within 7 degrees of the
low pitch stop), the springs overcome the latch weight
centrifugal force and move the latches to engage the high
pitch stops, preventing blade angle movement to feather
during normal engine shutdown

the reason why pulling the mixture does not feather the prop in flight is that as long as the prop is windmilling, the oil pump is working and you do not loose oil pressure. as you well know, the oil pump is a gear driven pump and as long as the crank is turning, if there is not leaks and oil in pan, there will be oil pressure against the piston and springs. trust me, if you really loose oil pressure, it will feather no matter where the prop control is set.

I have no doubt that f tower knows his aircraft, but the lock pins have no connection to the prop control and their only function is to stop the prop from feathering on shut down. as i have said, loose oil pressure in flight and the prop WILL feather no matter where the prop control is.

bob