Cessna 414 Prop Feathering Problem

seethru

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Howdy, I have been having a problem lately with a propeller on our 414A. This is like one of those Puzzlers you might hear on Car Talk on NPR. :D

Ours is a 1978 414A with the Ram VII upgrade that was completed in 2003. It has the Continental TSIO-520 335HP engines and Hartzell Scimitar 3-Blade Props.

The problem is that occasionally, after we shut down both engines after our flight, the right propeller will feather all on its own, which clearly it should not do this.

Oil pressures and temperatures are all within normal operating limits. The Prop levers are moved to full forward after landing. The throttles are reduced to Idle power before engine shutdown with the mixtures.

We have never had an issue during the Before Takeoff check or flight that caused us to be concerned about either propeller. They both attain equal RPM on takeoff and adjust appropriately in cruise.

History of troubleshooting:

Our shop, which BTW we have enjoyed their quality and attention to our concerns, had the right propeller looked at by the local Hartzell people. They did not find anything to be out of adjustment.

We continued to fly and found a few flights later that the problem occurred again. This time RAM was involved because they found that the right engine was damaged by this. There was something about where the prop and engine connection was made that grooves had been worn into the engine, necessitating a new overhauled engine (at RAM's expense).

At the same time the right prop was removed and sent to the Hartzell shop for a complete overhaul (at RAM's expense). As before, nothing was found on the prop to be wrong.

It was decided to swap propellers. So the right prop went on the left engine, and the left prop got mounted on the right engine. We flew this way without problems for over six months, at which time the props were swapped back to their original positions (right prop, right engine; left prop, left engine).

This last week I got the airplane back from annual inspection, and low and behold the right prop is feathering again! It is back for inspection at Hartzell, but I am not confident that they will find any problems. Again, RAM has agreed to pay for the overhaul.

Has anybody experienced anything like this, or maybe could offer some suggestions? I know my shop is working hard on it, but I think they are stumped as well. I am sure that there is a lot of other checks/inspections they have performed, such as oil pressure and prop governor issues.

Thanks,

Greg

BTW, as good as RAM has been in backing up their products, Hartzell won't even talk to us. Nice to see some corporate responsiblity...
 

erj-145mech

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The only time that I have seen that problem (3 times) has been the feathering pins in the hubs sticking. They are supposed to keep the blades from feathering below 1000 revs (or some where in that region). They are slung out by centrifical force be rotation, and spring pressure pushes them in at low RPM's.
 

seethru

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erj-145mech said:
The only time that I have seen that problem (3 times) has been the feathering pins in the hubs sticking. They are supposed to keep the blades from feathering below 1000 revs (or some where in that region). They are slung out by centrifical force be rotation, and spring pressure pushes them in at low RPM's.

OK, I know what you are referring to. These were checked by the Hartzell guys both times they worked on our machine and found them to be operating properly.

Thanks for the suggestion.
 

Say Again Over

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Well oil pressure in the hub must be dropping prematurely, moving toward the feather position while centrifugal force is still counteracting spring pressure in the pins?:confused:




(no I am not an engineer)
 

JediNein

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Had a similar problem on a 421 where the prop would feather and recover during the run-up, but no other place. RAM and Hartzell could not find a problem. They attempted several different fixes with several maintenance test flights and plenty of lost revenue.

When the right engine feathered in flight, the owner followed this procedure:
1. Remove right engine oil dipstick
2. Remove and replace right engine.
3. Replace old engine oil dipstick with new.

Both engines had recording JPIs on them which clearly showed the right engine feathering then recovering in flight.

The engine shop sent the engine and JPI data to RAM and we've heard no further word on the cause. The new engine works just fine.

This is only the second engine in a decade in numerous airplanes where the engine shop stated "remove and replace, do not attempt an overhaul".

The other engine, an O-360, would seize after shut-down as the thing heat-soaked. The crankshaft clearance was zero until about 30 minutes afterward. It was a few hours away from seizing in flight. The blame was an improper overhaul, but that mechanic was never pursued.

Fly SAFE!
Jedi Nein
 

seethru

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Fortunately we haven't had this happen with the engines running... yet. I am curious about the dip stick thing. What was the thoughts on keeping it (or were you just kidding)?

I should have the prop back from overhaul Monday or Tuesday, so I'll pass along what they find, if anything.

Thanks for the help everybody.

Greg
 

USMCmech

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If it's not the locking pins, then I wouldn't have a clue without actually examining the engine. Sounds like you've got a gremlin on your hands.


seethru said:
I am curious about the dip stick thing. What was the thoughts on keeping it (or were you just kidding)?

Common joke, called the oil cap solution.

Remove oil cap,

Drive new car under oil cap,

Replace oil cap,

Problem solved.

In other words, you need a new car (or engine, airplane, boat, whatever).
 

seethru

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USMCmech said:
Common joke, called the oil cap solution.

Remove oil cap,

Drive new car under oil cap,

Replace oil cap,

Problem solved.

In other words, you need a new car (or engine, airplane, boat, whatever).

Hehe, I hadn't heard that one before. Very funny. :D
 

helimech

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I would say the feathering pins are sticking, but they are each independent aren't they? so if they are, then what are the chances of them all sticking? what is the engine idling at when it is shut down?? Just a thought, but if the prop governor is set a little to loose (by loose I mean a little towards the high pitch side of things) and the engine is idling above the feathering pin activation rpm, let's say 1000. won't the prop think that it should be feathering after the oil pressure is rapidly dropped and the engine was idling somewhere around that range, if not above it? do you notice anything in flight once you pull the props back for cruise and get the mp set, does it "hunt" at all or do the pilots just switch on the sync? Just a thought, I could be completely wrong, please let me know if I am, It's been awhile since i got my hands on a recip engine, always curious for info, so let us know what you guys find out....
thanks
 

seethru

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Howdy, thanks for following up.

In the previous inspections by the prop shop they have determined that the feathing pins are functioning appropriately. I'm not sure yet what they found on our most recent encounter, but I am not betting any money that they will find an issue there this time either.

Normally, but not always, we pull the throttles back to idle before cutting off fuel at the mixtures. This yields an RPM in the neighborhood of 700-800. Occasionally we will forget and will kill the engine at 1000 RPM, however that was not the case on this occurance.

I'll be asking about the prop governor settings on Monday or Tuesday to get a better description of what they are set at. As you say, this could be causing the problem.

I have not noticed any problems while in flight. Often we don't even turn on the prop sync in cruise because the darn things align themselves and just stay that way.

I'll keep you posted.

Thanks,

Greg
 

Hung Start

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Had the same problem in one of our 402's, normal operation, but after shutdown it would self-feather in about 15 minutes. Happened only in very cold weather, and it was a sticking locking pin. For what it is worth.
Hung
 

seethru

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Update 2-16-06.

Well, I wasn't surprised, but our maintenance guys called and said that the prop shop didn't find any particular problems with our propeller. Just as I suspected.

Interestingly, they did decide to replace the spring that goes around the locking pins. I am almost 100% convinced this whole problem is related to those pins, so I hope that by replacing the spring that we won't see this again.

We'll get the prop reinstalled later next week and be up and running again, monitoring for any problems. We'll keep our fingers crossed.

Thanks for all the info.

Greg
 

NoPax

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Completely different engine, but similar problem - Aero Commander 500Bs, with Lycoming IO-540 and a Hartzell prop (rather than a McCauley prop) would, according to my Director of Mainenance, feather at idle (<1000 RPM), or after shutdown.

To cut a long story short, it turned out the N2 charge in the prop hub was too high. It was within the manufacturer's settings, however, during certain atmospheric conditions the prop would feather. We got permission from Hartzell to lower the N2 pressure, to prevent this from happening.
 

seethru

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So the final word, at least so far, is that Hartzell has decided to reduce the nitrogen pressure in the prop dome, as NoPax was hinting at above. Good call!

I hope this will do the trick.

Clear skies.

Greg
 
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