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  #1  
Unread 06-28-05, 10:54 AM
Paul462 Paul462 is offline
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Question Propeller Feather Gates.

Gentle Aviators:

My '68 T337C doesn't appear to have feather gates on the prop controls. The maintenance manual and quadrant placard claim the prop controls should travel back to the gate, then you should have to pull the prop controls up over the gate in order to move them back a little further to feather the props. Mine travel backwards until approx. 1/4 inch short of the rear end of travel wall, then the last 1/4 inch (without having to pull the prop controls up over any gate) feathers the props.

Do ya'll have feather gates? Do they still work? Does it make any difference whether they work or not, that is, is their absence anything to worry about, so long as the props feather OK?

Paul
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  #2  
Unread 06-28-05, 08:35 PM
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As a normal practice during run up I always pull up on the prop control to exercise the blades. I don't think I have ever tried it by not pulling up on the control.
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  #3  
Unread 06-28-05, 10:13 PM
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Same here. I ALWAYS lift up on the prop control, when I retard it during the runup procedure.
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  #4  
Unread 06-28-05, 10:29 PM
kevin kevin is offline
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Guess I am the odd man out. I never lift up on it, because I don't want to put the props in feather during the runup, too much strain on the engine I have been told. I just pull back far enough to cycle the prop, not further.

On my '65, one throttle had a worn out feather gate, and you could feather it by just pulling back all the way. The other gate worked, and you had to life up on it at the end of its travel to get the prop into feather.

Both gates worked correctly on my '73.

FWIW.

Kevin
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  #5  
Unread 06-29-05, 04:27 PM
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Jim Rainer Jim Rainer is offline
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Not a good idea, Kevin. The purpose of checking the feather on the ground is to be sure it is functioning properly in case of a real engine failure. An un-feathered prop in case of an engine failure mean a sure trip to the dirt. The single engine climb performance is based on a feathered prop. Five decades of multi-engine flying tells me that feathering the prop on the ground doesn't harm the engine, if done as called for in the POH. (It's more important to protect the prop from FOD damage on the ground so pick a clean spot to make the check.)
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  #6  
Unread 06-30-05, 01:15 PM
kevin kevin is offline
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Jim,

Like a lot of other things in aviation, I guess there is disagreement on this point. I talked to three folks I respect, all AI's with lots of piston experience, and all three told me that there is no need to go all the way into feather, that moving the control enough to detect significant RPM drop is good enough, that if it will move enough to get a 300 to 400 RPM drop, it will feather, and that going all the way into feather is very bad for the engine. To quote one AI: "There is a small chance that if you don't check it every time, the prop may not go all the way to feather, but checking it like that every time makes it much more likely that you will *need* to feather the engine because of engine abuse. The cost to the engine of such a check is not worth the tiny reduction in risk."

The Cessna checklist for both '65 and '78 337s does indeed say to "check feathering to 1200 RPM" from a runup RPM of 1800. I am not completely sure that one should interpret that sentence to mean "put the propellor all the way into feather" (changing blade pitch can be referred to as feathering), but a 600 RPM drop is only 200 RPM more than the 300 to 400 RPM drop I expect when I follow my procedure without going into the feather position.

You have a different opinion than the folks I have gathered information from, and it does seem to be backed up by the text in the manual, as well as your experience.

Guess everyone will have to decide to do what they think is best.

Kevin

Last edited by kevin : 06-30-05 at 01:19 PM.
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  #7  
Unread 06-30-05, 01:47 PM
Paul462 Paul462 is offline
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Kevin,

So did the worn out feather gate ever cause any problems? Does anyone see any downside to not repairing the feather gates?

Paul
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  #8  
Unread 06-30-05, 03:09 PM
kevin kevin is offline
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It was never an issue for me. But then I flew without an autopilot for 3 years too, and folks have told me that was nuts, so consider the source... ;-)

Kevin
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  #9  
Unread 06-30-05, 03:46 PM
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Kevin, we are saying the same thing. My POH reads the same as yours: "check feathering to 1200 rpm (from 1800)." The difference is in the interpretation. I "check feathering" by pulling up the throttles and placing them in the feather position. I too stop before the rpm drops below 1200.

What I think you are saying is that you check to see if the govenor is working down to 1200 rpm like you would in a single where the prop won't feather no matter what one does.

I think there is a very distinct difference in checking the govenor and checking the feathering mechanism. I stand by my guns!

Further, I very much agree all of your AI friends that the engines should not be feathered on the ground or damage may occur (although I've seen happen a few times without any damage.)
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  #10  
Unread 06-30-05, 04:16 PM
kevin kevin is offline
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No, not the same thing. I only get a 300 to 400 RPM drop. More than that is what they say is bad for the engines.

To each his own.

Kevin
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  #11  
Unread 06-30-05, 04:21 PM
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Jim Rainer Jim Rainer is offline
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Still disagree, 300-400 rpm is fine - I believe AI on that part but still think down to 1200 is OK per the POH, BUT

the difference I am checking the feather mechanism where all you are doing is checking the govenor operation.

I also agree "to each his own" and we're still friends!
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  #12  
Unread 07-01-05, 12:30 AM
Kevin McDonnell Kevin McDonnell is offline
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Exactly what do the AI's say gets damaged in the engine by excessive prop checks?
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  #13  
Unread 07-01-05, 12:57 AM
Keven
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Huh?

Damn, I'm confused! I thought the POH said to pull the prop back from 1800 RPM to 1200 RPM during run up to assure for feathering. Have I misinterpreted something?

Kevin M, what were you referring to when you said that you only get a 300-400 RPM drop?

Sorry for the ignorance.

BTW, I don't care what your answer is, still friends unless . . . well, hell, still friends regardless.

Keven
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Last edited by Keven : 04-23-11 at 05:12 PM.
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  #14  
Unread 07-02-05, 12:34 AM
kevin kevin is offline
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Keven, and Kevin,

The manual says it. However, my flight instructor (who is also an A&P) taught me that it is not necessary to exercise the prop to extent implied in the POH during runup, that in fact it is harmful. So, what I mean by 300 - 400 RPM drop is I only move the lever enough to verify the governor on each engine is working, and that there is warm oil in it. Basically, I move it enough to hear the prop sound change, then move it back. On the first flight of the day I do this three times (I picked that up from the O-2 flight manual), and the rest of the day I do it once.

My instructor told me that if the governor moves that much, it is almost assuredly going to move all the way to the feather position, and that moving it all the way there stresses the engine excessively, and does not test the feather locks anyway, so you are still not sure if it will stay feathered in a real emergency.

When Jim questioned this practice, I checked with three additional AI's in two shops (I only intended two, but a second happened to be visiting a shop that I went to locally). All three listed a litany of problems with running the engine at low RPM and moderate throttle. As best I can remember, they were:

- problems with counterweights
- excessive crankcase pressure
- excessive vibration the engine was not designed for
- more wear and tear on the engine because of all of the above

There was probably more, but I was not taking notes.

As I said in previous message, the book specifies Jim's procedure, so there should be nothing wrong with doing it, in should be something *right* in doing it.

What convinced me originally was my flight instuctor's comment that moving the prop control all the way does not really guarantee the prop will stay feathered, and does not test much more than moving it part way does.

Jim is convinced that testing all the way into feather tests "the feathering mechanism". Maybe he can elaborate more on what that is. I am not a mechanic, and I may misunderstand how feathering works. I thought that when you feathered a prop, the governor was doing nothing more than moving the prop to "feathered" pitch (by removing all oil pressure to the prop) and that there is a locking mechanism that holds the blades feathered on shutdown rather then letting them return to fine pitch as they normally do. But according to the guys I am talking to, you can't really test the locking mechanism unless you shut the engine down completely.

Kevin (everybody on this website seems to be named Kevin)
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  #15  
Unread 07-05-05, 11:24 AM
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I am in Colorado and my plane, POH and Maintenance Manual are in Memphis. I'm not a mechanic but here are my assumptions: the feather position "pull up and back" shuts off all oil pressure to the governor and the engine feathers. I don't think it will come out of feather until oil pressure is restored eithe by an accumulator or by turning the engine over in flight (on the ground is a different matter.) The "feather mechanism" as I describe is whatever valve is activated when the prop control is pulled up and back that shuts off the oil. This valve is not activated by simply pulling the prop control back toward feather.

In any event one controls the drop in rpm no matter which of the two ways you check it. I think it may very well be valid to say that unless one feathers the engine on the ground one will never know if all the oil pressure is cutoff.

I am also following the advice of CFIs and AIs is doing what I do. So I guess we are still "to each his own."

Sorry I'm not more of an expert but the proceedure I have been using has been the same on all the twins with prop feather mechanisms for 4+ decades. There is a difference in engines. Some go to feather like the 337 Continentals but some (most, I think) go to low pitch (high rpm) like the Lycomings on an Aztec. That is when oil pressure is removed for whatever reason.

Not much help, am I?
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