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Prop Overhaul... when do you?


Gerbil

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Props have a flight hour and calendar recommendation for overhaul. As I understand it operating under part 91 this TBO interval is not required but is recommended.

How many of you out there are sending the prop in to be done when the calendar limit comes? Who of you is waiting until it is slinging grease?

Gerbil

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6 minutes ago, neilpilot said:

Do you mean IRAN when you say overhaul?  My understanding is that an overhaul often will result in the blades being ground below limits and/or discarded.

You are correct about overhaul.  They grind the blades.  Funny thing about the calender requirement is that it's from the time the prop is installed, not manufacture.  It could be sitting in a box for 10 years, but not need overhaul due the calender.  However, if you install the prop and let it the aircraft sit for 10 years, it does.

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1 hour ago, neilpilot said:

Do you mean IRAN when you say overhaul?  My understanding is that an overhaul often will result in the blades being ground below limits and/or discarded.

My intent was to ask how often folks remove their prop and send it in for reseal OR overhaul. A follow up question is for those who don't send them in for a long time, are there a lot of parts that need replaced from wear or corrosion?

I am starting to think the calendar recommendation is not being observed by many. 

Gerbil

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There are hub issues, and there are blade issues, that require specific maintenance... Calendar issues typically don't coincide with GA in the US.

We have seen photos of cracked and broken hub castings and corrosion at the base of the blades.  The most common killer of blades around here is probably ground strikes of various sorts...

Anything else?

+1 for Cody's insight and support...

Best regards,

-a-

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6 hours ago, Gerbil said:

I am starting to think the calendar recommendation is not being observed by many. 

This is as true for propellers as for engines, at least for those of us who fly Part 91. I've heard that some planes withiut constant speed prop will go two or more engine overhauls before doing anything wjth the prop . . .

Personally, I've always thought that prop overhaul was done at the same time as the engine.

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"Personally, I've always thought that prop overhaul was done at the same time as the engine."

The flight hour requirements for both are similar so this makes sense. The risk is that moisture can cause corrosion if the prop is not overhauled for a long time and this could lead to expensive parts being out of limits when inspected.

Is anyone sending them in on a calendar basis?

Gerbil

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Several posters have mentioned blade grinding.  IMO, there's undue concern about this, if you're using a reputable shop.  It's true an overhaul requires blade profiling, but the amount of material removed is very small - again assuming a reputable shop.

Our prop was new in 1991.  It was overhauled in 2005 (primarily to take advantage of the deal Hartzell was offering on new hubs), and again in 2016 (because it was throwing grease).  So the blades have been reprofiled twice.  At the 2016 overhaul, I asked how close the blades were to limits.  The service tech said the prop was nearly guaranteed to make two more reprofilings assuming continued operation on normal airport surfaces, and possibly three.  Given our history of about 12 years between overhauls, that means the blades will almost certainly be OK for another roughly 36 years, and maybe for another 48 years.

I'm sure there are poor/disreputable shops that grind blades into oblivion for no good reason, but I don't really buy the argument not to overhaul your prop because it's likely your blades will be condemned.  Just my $0.02.

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2 hours ago, Vance Harral said:

years.

I'm sure there are poor/disreputable shops that grind blades into oblivion for no good reason, but I don't really buy the argument not to overhaul your prop because it's likely your blades will be condemned.  Just my $0.02.

If you've had previous nick repairs I think you end up with a lot of grinding. The prop shops I've used have always recommended against overhaul because of this. They still do a full service, replace bearings etc 

-Robert 

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Being Part 91 it's clear complying with Manufacturers TBO is optional.

There is no doubt the propeller is one of the most highly stressed parts on an Aircraft, however they are built like Tanks.

Very Robust.

To the actual Question now.

Propeller Overhaul.

Overhaul is a word used loosely in the aviation community.

But when you request Overhaul in a Repairstation like mine, your propeller will be put through the rigors of the Manufacturers O/H Manuel for your propeller.

There are many steps, many procedures, many measurements, many mandatory new parts.

When grinding the blades, all damage is to be removed from the blades. A lot of material has to be removed.

After all of this is complete, you will have a fresh O/H Propeller, a Large Invoice an Thinner blades.

Thats the truth of the matter, with no BS.

 

Propeller IRAN

With an IRAN(Inspect Repair As Necessary) the repairman doesn't have his hands tied.

We can remove only the material needed to do what needs to be done. Corrosion Nicks Galding ect.

Your looking for Airworthiness Issues, anything that could compromise safety of flight.

With this, the propeller will have certain parts replaced.

We look at high stress parts an Wear parts: Counter weight bolts, Ball bearings, Actuating pin bolts, ect. They are replaced with new parts, An of course new Orings an seals.

If at any point in the IRAN process something shows the need for MT, PT or ET inspection, we do it.

When complete, the propeller will look like new agin, like an Overhaul.

You will have a Smaller invoice, an thicker blades.

The Catch:

IRAN doesn't Satisfy an O/H.

So if you IRAN, it will be continued time on the previous O/H or New.

Generally speaking, most people wait for a visual cue before removing a propeller for service.

Grease Leak, Red Oil, Loose blade.

I think that weighting a little to long, However I have taken props apart that were almost 30 yrs old, that looked New on the inside.

Then I have taken them apart that weren't even to their TBO(5-6yrs) yet, that I ended up throwing in the trash.

How often it's operated, an how often it's serviced plays a big roll in this.

Hartzell an Oil Filled McCauley propellers seem to have the best life expectancy.

Hartzells can be greased, An the Oil Filled McCauley has a Quart of SAE 30 Oil in it.

Its the McCauleys that have grease in them, that have problems.

They can't be service in the field.

So after 8-10 yrs they spit a little grease out then stop.

When it stops its out of Grease, an corrosion starts.

I will attach a few pictures of a Cessna C-421 Propeller.

The stuff that looks like mud, is actually What's left of the grease.

Bearings show signs of heavy pitting on the surfaces.

 

 

 

IMG_2459.JPG

IMG_2465.JPG

IMG_2467.JPG

IMG_2468.JPG

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3 hours ago, Vance Harral said:

Several posters have mentioned blade grinding.  IMO, there's undue concern about this, if you're using a reputable shop.  It's true an overhaul requires blade profiling, but the amount of material removed is very small - again assuming a reputable shop.

Our prop was new in 1991.  It was overhauled in 2005 (primarily to take advantage of the deal Hartzell was offering on new hubs), and again in 2016 (because it was throwing grease).  So the blades have been reprofiled twice.  At the 2016 overhaul, I asked how close the blades were to limits.  The service tech said the prop was nearly guaranteed to make two more reprofilings assuming continued operation on normal airport surfaces, and possibly three.  Given our history of about 12 years between overhauls, that means the blades will almost certainly be OK for another roughly 36 years, and maybe for another 48 years.

I'm sure there are poor/disreputable shops that grind blades into oblivion for no good reason, but I don't really buy the argument not to overhaul your prop because it's likely your blades will be condemned.  Just my $0.02.

With all Due Respect Vance, it depends what blades a person has an what the New to Scrap delta is.

You taken advantage of the B hub deal from Hartzell, means you have F7666A-2 Blades.

A very thick blade design. It's one of their older designs an in my opinion the best blade they have ever produced for a LYCOMING 360.

When a Tech makes the statement 2-3 O/H remaining , he's really sticking his neck out.

His opinion is based off of what he's looking at Now.

But that propeller has several Takeoffs to endure, an 12 Annuals to deal with.

To Many variables are involved ,an have to be considered when it comes to a blade.

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Cody, thank you for sharing your expertise. You're an asset to MS.

The prop is probably one of those things that's not discussed much around here. Certainly not as much as avionics and engines.

I do have a question regarding the oil filled McCauley in my J. You mention that there's a quart of oil in it. How many times should it be cycled in order to completely flush and freshen up the oil to be sure it doesn't get stagnant over time? I always wonder about that every time I cycle the prop. I typically cycle it three times. Is this enough? Does the oil circulate much on its own while in operation maintaing RPM in flight?

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PTK

To answer your question, no the oil does not circulate with a Constant-Speed propeller.

The Red-Oil I was referring to is a lubricantion oil only, Its separate from the engine oil that actuates the propeller.

With a CS propeller there is very little oil circulation, if any.

With a CS propeller, its blade angle travel is very little often between +12.5 degrees increasing to +28.0-30.0 of movement.

that only takes around an inch of Travel from the piston in the Propeller.

so very little oil moving.

Cycling the propeller is more to verify a working Governor.

As far as how many tims to cycle, I can't answer that question.

I can tell you this, no mater how many times you cycle it you will never get a 100% oil exchange.

There just isn't enough movement for that to happen.

With a Feathering propeller, there is much more movement in the hydraulic assembly, hints the larger cylinder.

Twins, Rocket an Missile owners can do a deep cycle towards Feather or onto Feather an pretty well clear out all the oil in the hydraulic unit.

PTK, I'm at the shop this morning( I know Labor Day Sunday) waiting on an AOG propeller to come in, I will get you a video of the blade travel on a straight Constant speed Propeller.IMG_3964.MOVIMG_3964.MOV

Its not much

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11 hours ago, Cody Stallings said:

With all Due Respect Vance, it depends what blades a person has an what the New to Scrap delta is.

This is a fair point, thanks for emphasizing that the type of propeller makes a difference.

My purpose in giving the particulars of our propeller was just to put some actual data out there, vs. lore.  I've met owners who are afraid to overhaul their propeller under any circumstances, because they're convinced it will almost always result in their blades being condemned.  I think that's over the top, and not fair to the prop shops.  One can certainly look up the service limits for a prop, compare them with the state of a single specimen, and reasonably estimate the likelihood of future condemnation assuming normal operations.  Perhaps it's true the service tech I spoke with was "sticking his neck out" in giving such an estimate.  But I like to think I convinced him I'm a reasonable customer and human being, not a simpleton who would interpret his statement as a guarantee of anything at all.  As a person in the business, I'm sure you've dealt with customers of the latter variety, and I don't blame you for being conservative in your statements.  We certainly appreciate your posts here on the forums.

For what it's worth, I'm a fan of IRAN for props and other components, and would have preferred to do instead of having our prop overhauled last year.  Unfortunately, I could not find a prop shop anywhere in Colorado at the time, that would agree to perform an IRAN on a prop with more than 10 years since the last overhaul.  Faced with a choice between the risk and expense of a full overhaul locally, vs. the risk, expense and additional down time of shipping the prop out of state, we chose a full overhaul.  I wouldn't criticize someone for choosing to ship out of state for an IRAN instead.  It was a tough call for us.

Edited by Vance Harral
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18 hours ago, Vance Harral said:

Several posters have mentioned blade grinding.  IMO, there's undue concern about this, if you're using a reputable shop.  It's true an overhaul requires blade profiling, but the amount of material removed is very small - again assuming a reputable shop.

Our prop was new in 1991.  It was overhauled in 2005 (primarily to take advantage of the deal Hartzell was offering on new hubs), and again in 2016 (because it was throwing grease).  So the blades have been reprofiled twice.  At the 2016 overhaul, I asked how close the blades were to limits.  The service tech said the prop was nearly guaranteed to make two more reprofilings assuming continued operation on normal airport surfaces, and possibly three.  Given our history of about 12 years between overhauls, that means the blades will almost certainly be OK for another roughly 36 years, and maybe for another 48 years.

I'm sure there are poor/disreputable shops that grind blades into oblivion for no good reason, but I don't really buy the argument not to overhaul your prop because it's likely your blades will be condemned.  Just my $0.02.

The problem is you won't know your blades have been ground to limits and condemned until after it's already happened and then you're out $7000 for a prop.  

This happens quite frequently I don't know percentagewise but when you called in some shops to drop your engine off to have an overhaul,  the price is pretty well known and barring the crank or the case being bad the price is the price... the problem with the prop is they opened it up and do a bunch of stuff to it and then they call you with a price and sometimes it doesn't include a prop when you're done

 For example I called my local prop shop when I had to change the engine out the prop was nine years old and had 1200 hrs. on it and they told me it must be overhauled to be airworthy. I told him the service history of it it was new when it was put on the airplane in and it never hit the ground or been seriously filed on and he said "I don't know it's very iffy send it in and will call you after we find out if the blades pass or not". Repeated questions trying to pin him down he's being very evasive and frankly I had just about zero confidence that I will see a prop at the end of this deal. So I sent it to San Antonio propeller $650 later it was painted static balance and reassembled and it's been going strong for six years now. 

 

Edited by jetdriven
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1 hour ago, jetdriven said:

The problem is you won't know your blades have been ground to limits and condemned until after it's already happened and then you're out $7000 for a prop.

I guess I just don't understand how this happens, at least not "frequently".  Seems like only a completely disreputable shop would behave this way, and that word would quickly spread not to use them.  The shops I've worked with would call before doing any such thing (or at least that's what was specified in the written contracts I signed - in my case there was never any doubt the blades would be within limits after grinding).  I only have an N of 2 prop shops, though.

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  • 3 weeks later...
On September 3, 2017 at 1:39 AM, Cody Stallings said:

With all Due Respect Vance, it depends what blades a person has an what the New to Scrap delta is.

You taken advantage of the B hub deal from Hartzell, means you have F7666A-2 Blades.

A very thick blade design. It's one of their older designs an in my opinion the best blade they have ever produced for a LYCOMING 360.

When a Tech makes the statement 2-3 O/H remaining , he's really sticking his neck out.

His opinion is based off of what he's looking at Now.

But that propeller has several Takeoffs to endure, an 12 Annuals to deal with.

To Many variables are involved ,an have to be considered when it comes to a blade.

 

Cody, thank you very much for being on the forum and enlightening all of us !

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