Seneca Propeller Feathering

[matt152]

For the sake of discussion, answer the question. You seem to be the expert on the subject, so I'd like to learn more. I have about 30 hours in piston twins, so I've forgotten most of what I learned 5 years ago.

I don't claim to be an expert. But I have some basic knowledge on the Seneca.

Frankly, what was described in the NTSB report was odd. I am not sure why they would design a system that had stops to prevent it from going to feather. But also I am not familiar with the particular aircraft mentioned there.

 

[matt152]

Edit: Maybe the stops are to prevent the governor from attempting to exceed the governing range?

 

[matt152]

Another thought: the high speed stop is a low pitch position. Perhaps this is the lock to prevent feathering on the ground?

 

[esa17]

The 310 had ZERO oil pressure, the oil left the engine in mere seconds. The props did NOT feather, they went to low RPM.

Full feather MUST be commanded if there is an abscence of an auto-feather system.

 

[matt152]

The 310 had ZERO oil pressure, the oil left the engine in mere seconds. The props did NOT feather, they went to low RPM.

Full feather MUST be commanded if there is an abscence of an auto-feather system.

Ok. But what is mechanically going on to prevent the props from going to feather when oil pressure is lost? Since the information we have on full feathering props seems to contradict what you experienced?

 

[TFaudree_ERAU]

Ok. But what is mechanically going on to prevent the props from going to feather when oil pressure is lost? Since the information we have on full feathering props seems to contradict what you experienced?

High pitch stops. You have to mechanically move them out of the way to get the prop to feather. That mechanical linkage is the last bit of prop lever movement when you move them over the low stop on the throttle quadrant.

Why would you want a prop to feather on its own if there is a good chance that switching tanks or turning on a boost pump may bring the dead engine right back to life? Now you've got an engine that is perfectly capable of running, but the prop is feathered and it is of no use to you or the performance of the airplane.

We all know how difficult it can be to bring a prop out of feather without an accumulator.

 

[matt152]

High pitch stops. You have to mechanically move them out of the way to get the prop to feather. That mechanical linkage is the last bit of prop lever movement when you move them over the low stop on the throttle quadrant.

Why does the Seneca POH specifically say it will go to feather in the event of loss of oil pressure EXCEPT for the feathering lock? Just because you lose an engine does not mean you lose oil pressure.

Why would you want a prop to feather on its own if there is a good chance that switching tanks or turning on a boost pump may bring the dead engine right back to life? Now you've got an engine that is perfectly capable of running, but the prop is feathered and it is of no use to you or the performance of the airplane.

Worst case scenario is that you lose an engine. You WANT it to feather. If you can restart, great. If the prop is windmilling, it most likely has oil pressure and will not feather.

We all know how difficult it can be to bring a prop out of feather without an accumulator.

It's not overly difficult. I do it most days of the week. Prop to high RPM (which does not take it out of feather, BTW) and hit the starter. The crankshaft turns, the oil pump turns, oil pressure is created, the prop comes out of feather.

Now if the starter has failed, you are not restarting without an unfeathering accumulator.

 

[KSCessnaDriver]

It's not overly difficult. I do it most days of the week. Prop to high RPM (which does not take it out of feather, BTW) and hit the starter. The crankshaft turns, the oil pump turns, oil pressure is created, the prop comes out of feather.

Now if the starter has failed, you are not restarting without an unfeathering accumulator.

Eh, it depends on the engine. Both of the planes I've flown with IO-360's had no problem restarting without accumulators in the air. The one I flew with IO-540's was a bear to start in the air. Didn't matter what you did, you needed at least 4 hands to start that thing on the first try.

 

[matt152]

Eh, it depends on the engine. Both of the planes I've flown with IO-360's had no problem restarting without accumulators in the air. The one I flew with IO-540's was a bear to start in the air. Didn't matter what you did, you needed at least 4 hands to start that thing on the first try.

We fly a Seneca I. O-360. It's never been a problem.

 

[matt152]

Eh, it depends on the engine. Both of the planes I've flown with IO-360's had no problem restarting without accumulators in the air.

You were using the starter, right?

 

[KSCessnaDriver]

You were using the starter, right?

Yup, hard to start them otherwise.

Should have clarified. I've flown a Aztec with IO-540's that was a bear to start, even with the starter. Something about old starters, a weak battery, and a big engine doesn't work out to well

 

[minitour]

Why does the Seneca POH specifically say it will go to feather in the event of loss of oil pressure EXCEPT for the feathering lock?

It doesn't. It says the prop will move toward the high pitch position.

Worst case scenario is that you lose an engine. You WANT it to feather. If you can restart, great.

Not at all. Unless I'm going to get some nasty asymmetrical thrust coming from the prop windmilling (like during takeoff or go-around....which is why you arm the autofeather system if you have one for such events) I only want it to feather when I command it to do so. Even if the engine loses all oil and seizes with the prop not feathered, it's stopped...which removes most of the drag. Feathering it removes more, but just stopping the engine removes QUITE a bit of drag.

It's not overly difficult.

Then you don't have enough experience flying airplanes without accumulators...

-mini

 

[CoffeeIcePapers]

Feathering it removes more, but just stopping the engine removes QUITE a bit of drag.

Do you have any reference for that?

 

[TFaudree_ERAU]

Do you have any reference for that?

A windmilling propeller can be compared to a solid disc mounted to the crank shaft, perpendicular to the relative wind, with LOTS of drag. Stop the prop, and now you have 2, sometimes 3 blades with very little area opposing the relative wind.

 

[minitour]

A windmilling propeller can be compared to a solid disc mounted to the crank shaft, perpendicular to the relative wind, with LOTS of drag. Stop the prop, and now you have 2, sometimes 3 blades with very little area opposing the relative wind.

:yeahthat:

I'm trying to find ya a good reference, mojo, but all google is coming up with is .com sites and.......those aren't necessarily the greatest references.

I didn't believe it either until I experienced it.

-mini

 

[matt152]

It doesn't. It says the prop will move toward the high pitch position.

Read above. This was already covered.

Not at all. Unless I'm going to get some nasty asymmetrical thrust coming from the prop windmilling (like during takeoff or go-around....which is why you arm the autofeather system if you have one for such events) I only want it to feather when I command it to do so. Even if the engine loses all oil and seizes with the prop not feathered, it's stopped...which removes most of the drag. Feathering it removes more, but just stopping the engine removes QUITE a bit of drag.

Asymetrical thrust comes from the engine producing power, not the windmilling prop. You want to reduce drag on the inop engine.

If you lose oil pressure, there is more than likely enough residual lubrication to keep the engine going enough to get the prop into feather prior to the engine seizing and the RPM going below the feathering lock speed.

Then you don't have enough experience flying airplanes without accumulators...

I am willing to admit my experience is limited. However, in my experience with the Seneca (topic of this thread) my experience is sufficient to make a claim as to getting the prop to come out of feather.

BTW, I have not yet heard anything that would contradict what is in the Seneca POH.

 

[bLizZuE]

So where do high pitch stop pins come into play? How do you overcome them?

I believe what you're referencing are the anti feathering pins?

Otherwise I'm not sure. Each controllable pitch propeller system generally contains a low pitch and a high pitch stop. This is the full extent the blade is allowed to rotate.

Generally the anti feathering pins are activated at lower RPMs to disable the feathering of an engine when shutting it down while on the ground. This allows easier restarting of the engines and prolongs the life of the starter.

 

[bLizZuE]

The 310 had ZERO oil pressure, the oil left the engine in mere seconds. The props did NOT feather, they went to low RPM.

Full feather MUST be commanded if there is an abscence of an auto-feather system.

I disagree.

I'm completely unfamiliar with the 310 prop governing system, however the Hartzell system installed in the Seneca clearly states that a complete loss of oil pressure will feather the propeller.

I do not argue what happened in your scenario, however I don't believe it to be the case with the Seneca, or it to be the normal result of a loss of oil pressure.

 

[minitour]

Read above. This was already covered.

I scrolled all the way back to the first page where the Seneca I POH exerpt was "attached" into the thread. It says nothing of the prop going into feather.

It says the propeller will go "toward the low RPM or feather position". Nothing about it feathering.

Is there something I missed that you'd like to point out?

Asymetrical thrust comes from the engine producing power, not the windmilling prop.

True. I should have said "drag" and not "thrust". Believe it or not, you'll get quite a bit of asymmetrical thrust from the prop windmilling and ..... not producing thrust, but "technically" speaking you are correct. The asymmetrical thrust comes from the good engine, not the bad one.

You want to reduce drag on the inop engine.

Depends on what you're trying to do.

If you lose oil pressure, there is more than likely enough residual lubrication to keep the engine going enough to get the prop into feather prior to the engine seizing and the RPM going below the feathering lock speed.

Are you willing to bet your certificates on "more than likely" or your life?

Are you saying that a prop/engine cannot completely stop with a loss of oil pressure/total oil? Because I've had one stop without the loss of oil. I'm just wondering where that residual lubrication was.

I am willing to admit my experience is limited. However, in my experience with the Seneca (topic of this thread) my experience is sufficient to make a claim as to getting the prop to come out of feather.

Surely you don't think that only Senecas have this type of propeller system? Or that every plane but a Seneca without an unfeathering accumulator is "not overly difficult" to unfeather? The question may have been about the Seneca, but it applies across the board to all piston twins with this type of propeller installation.

BTW, I have not yet heard anything that would contradict what is in the Seneca POH.

No one is saying the prop won't move towards the feather position (what the POH says). What are you trying to get us to say?

Further, if you read in Paragraph 3 Line 2, "Feathering of a propeller is accomplished by moving the control fully aft through the low RPM detent, into the feather position."

That's Piper's own POH saying that to feather a propeller you must move the control fully aft into the feather position. It doesn't get much more clear.

-mini

 

[bLizZuE]

High pitch stops. You have to mechanically move them out of the way to get the prop to feather. That mechanical linkage is the last bit of prop lever movement when you move them over the low stop on the throttle quadrant.

Why would you want a prop to feather on its own if there is a good chance that switching tanks or turning on a boost pump may bring the dead engine right back to life? Now you've got an engine that is perfectly capable of running, but the prop is feathered and it is of no use to you or the performance of the airplane.

We all know how difficult it can be to bring a prop out of feather without an accumulator.

The scenarios you describe do not include oil pressure loss. Keep in mind that a wind milling propeller is generating oil pressure because most oil pumps are geared to the crank.