How old is too old for a propeller?

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Stigmon

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Stigmon
Assuming the propeller is maintained and is not warped or otherwise damaged and in theory would pass an inspection, is there some age at which beyond this age it would be unsafe or unwise to use a propeller.

Assume also that the propeller has been maintained, but not overhauled more than 1x or 2x because that would eventually grind it down to uselessness.

Maybe it has flown for 4000, 8000, 12000 hours ...but nicely, no strikes, regular repair and reseal / IRAN. For arguments sake, it has seen no knicks, dings, or corrosion that has required redressing (material removed).

When is it too old?
 
Thanks and that is what I thought. We have a club plane and one of the folks helping with maintenance commented that the propeller was old. I don't believe the age matters and I don't know of any material weaknesses, of significance, that have to do with the age of the aluminum. as noted, it is usually the other things that would cause a prop to die. Including, doing overhauls per manufacturer specifications and recommendations because this will thin the prop and might be done 2 or 3 times as far as my understanding goes.
 
Stigmon said:
I don't know of any material weaknesses, of significance, that have to do with the age of the aluminum.
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Just to add, aluminum can be suseptible to fatigue cycling which can be directly related to age and hours. However with props these issues are normally dealt with by using life-limits or restricting certain operational limits like RPM ranges. Regardless preventative maintenance is key to getting the most out of any prop.
 
“Reseal” tells me this is a Constant Speed Prop.

I would have some concern with steel components of the hub rusting and
impacting operation.
 
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Owners and pilots need to know what that propeller has to withstand before they start to realize how important propeller maintenance is. We'll start with the five basic forces. Centrifugal forces are easily the highest, and a pull of up to 40 tons must be taken at the hub. Thrust bending forces are normally mitigated somewhat by designing the prop with the center of outer blade mass lightly ahead of the center of mass at the hub so that centrifugal forces tend to pull that blade back into line with the hub, against the thrust forces. Center of pressure forces try to increase the pitch, so the prop has to be strong enough to resist that, and the centrifugal twisting force tries to decrease it; that force is used in some constant-speed props to default to low pitch. That little notation "Center of rotation" is pointing at the wrong spot; the right spot is the dot in the middle of the blade airfoil.

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But that isn't all of it.

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In the climb, or in slow flight, those blades are being yanked forward on the right with every rotation. It causes vibration, and stresses the hub and crankshaft, and pulls the airplane to the left.

More yet. The gyroscopic forces are fairly large whenever the airplane pitches or yaws. Those forces have been known to break crankshafts during aerobatics, or cranks that have corrosion pitting. It also results in the blades being yanked around with every rotation.

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That propeller is probably the most highly-stressed component on the whole airplane. it would never, for instance, withstand 3.8 times its normal loading without failing, as the rest of the airframe can. It's why propeller manufacturers have directions for inspection and NDI procedures after an engine overspeed situation.

Anything that compromises the strength cannot be tolerated. Corrosion pitting or, more commonly, nicks in the blades, must be dressed out in accordance with manufacturer's instructions and limits. We used to do a lot of off-airport training, and gravel would regularly nick our props. Those nicks got dressed out promptly to preclude any cracking that could lead to blade failure and a resulting imbalance that could tear the whole engine off the airplane. That sort of maintenance tends to reduce prop life, but in our case we were training pilots for overseas work where they'd be on some pretty rough strips and it had to be done and we had to absorb some propeller costs. Canada has regulations demanding five-year corrosion inspections on fixed-pitch metal props, and ten-year internal corrosion inspections on CS props. The CS props just got an overhaul to cover that. Corrosion inside the hub is deadly and has caused blade loss.

Here's something someone spotted just in time. See where that crack started?

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That's a deep nick that might not have been repairable within blade station width limits, but even so, dressing it properly could have prevented the crack from starting. It was obviously ignored for awhile. Don't ignore nicks! Look at the rest of that prop's leading edge. No maintenance at all. You really don't want this happening:

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Stigmon said:
Assuming the propeller is maintained and is not warped or otherwise damaged and in theory would pass an inspection, is there some age at which beyond this age it would be unsafe or unwise to use a propeller.

Assume also that the propeller has been maintained, but not overhauled more than 1x or 2x because that would eventually grind it down to uselessness.
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A general comment:
There's bit of myth and legend about edge grinding. More wear typically actually occurs from normal use than repair or overhaul. Many of the newer props also have additional "meat" on the blades like Hartzell Top Props. My low time prop just came back from IRAN and the edges were dressed and blades balanced and repainted. The prop had good nick and dressing it out with non-destructive testing. Needed the hub flushed before remounting on newly overhauled engine.

A prop will withstand more than "1 or 2 prop shop dressings". Talk to a couple of shops and see what the collective wisdom maybe for a given situation.

I threw a "like" to @Dan Thomas post above. Hidden corrosion, improperly dressed nicks, or hub wear is the lurking danger not worth flirting with to avoid fear of the blades being dressed below minimums at the prop shop.

To the OP:
Really depends upon what was inspected/not inspected during the IRAN and how long ago. Was the prop continuously hangared or parked outside? Makes a difference.
 
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Dan, ....... Nevermind, just read what I wrote, and came to the realization that I was almost confused.
 
I had a PM from a fellow employed with a major prop manufacturer. He has seen plenty of broken blades. It's amazing that there aren't more crashes due to them.

He also pointed out the RPM range limitations in some airplanes. You can pass through that range, but you don't stay there. At all. The prop can experience destructive vibrations in that range, and what pilot wants increased risk?

Propellers are being viewed far too casually by both pilots and maintainers. You need to remember that props are one of the three things on the airplane that has its own type certificate, the others being the airframe and the engine. Props have to be pretty good to get certification, but if you don't keep them good like the engine and airframe, it could cost you an awful lot.
 
From discussions w a McCauley engr - A prop at takeoff is 3/32" to 1/8" inch bigger in diameter. It is a non-redundant fatigue-loaded component that can down an airplane if it fails.
 
Very relevant question I’m interested in.

A friend is dealing with a purchased airplane where the owner sustained a prop strike when he drove his airplane into “mud.” The propeller was replaced new, and the airplane was not flown more than 3 hours since. The propeller is just over 12 years old. Should it merit an overhaul? Should it overhaul a reseal? What’s the IRAN process here?


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Llk said:
A friend is dealing with a purchased airplane where the owner sustained a prop strike when he drove his airplane into “mud.” The propeller was replaced new, and the airplane was not flown more than 3 hours since.
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The bigger question: Was the engine torn down for a propstrike inspection?
 
If the prop strike was more than 12 years ago, and flown for 4 hours in 12 years, the engine tear down then may be moot, as there may be a need to overhaul the engine due to corrosion.

At a minimum dial indicate the flange and do the accessory section inspection mandated in the SB. Also, a good borescope exam of all the cylinders.

You may consider pulling a cylinder to inspect the cam, but you could also just fly it and do oil analysis every 10 hours for a while to check for metal from pitted lifters grinding on the cam.
 
Pinecone said:
If the prop strike was more than 12 years ago, and flown for 4 hours in 12 years, the engine tear down then may be moot, as there may be a need to overhaul the engine due to corrosion.

At a minimum dial indicate the flange and do the accessory section inspection mandated in the SB. Also, a good borescope exam of all the cylinders.

You may consider pulling a cylinder to inspect the cam, but you could also just fly it and do oil analysis every 10 hours for a while to check for metal from pitted lifters grinding on the cam.
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In the flight school we had several propstrikes over the years. The cranks were still straight, but the teardown found cracked crankshafts. It's been known for a long time that the crank can flex enough to start a crack, and spring back to within the flange runout specs. Insurance companies often demand a teardown, and they'll pay for it, simply because it will usually save them a big payout in the future when the thing fails in flight. Besides the crank, the rods can distort, the pistons can crack, gear teeth can crack, magnetos can be damaged, and so on.

I have seen engines that sat for many years, and have no corrosion inside. The 12-year thing was more of a CYA policy. People ground-running their engines are filling them with damaging moisture.
 
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