Nicks in propeller?

mistercrisp

mistercrisp

Filing Flight Plan
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mistercrisp
I was pre flighting a Cessna 172 before a flight with my instructor. I was stunned to find a significant dent in the leading edge of the prop, about 8" in from the tip. What was strange was that it was a perfect semi-circular dent. It looked as if it had been hit with a 3/8" bolt or something. I had never seen anything like that before. It was a perfectly smooth semi circle in the leading edge. So the mechanic came out and said that was beyond spec and there was no way to use a file to fix that large a dent. And then he said, he thought that someone had taxied over a tie down strap which at this FBO has steel "S" hooks on both ends of the nylon straps! Yikes!

So my question is just because I am curious about this, is, what can be done with a prop damaged like that? It is a MacCauley fixed pitch prop. Can damage like this be repaired with a weld in the leading edge and then some kind of heat treatment, or does that kind of damage mean the end of that propeller? Just curious. Thanks for any answers.
 
It can't be welded. The propeller manufacturer (or AC43-13) will have specs on how deep a dent or nick may be before it can't be repaired by filing smooth.
 
Sorry for your misfortune.

A Blade Drawing is needed here to determine condition at each station

from the hub. Measurements are taken from the Trailing Edge forward

to determine if it meets the Minimum Chord Specification for that

station. If it is too short you have a paperweight.


But it doesn‘t end there. It sounds like you have a Prop Strike but not

a Sudden Stoppage. So how do you address this with the engine?

Your Hull Insurance will pay for a tear down. It is not an overhaul though

so rust and wear items are excluded.

The Crankshaft should be checked with a Dial Indicator for starters.

Lycomings require removal for the Accessory Case to check the

Crankshaft Gear per the AD. This may be considered minimum action.
 
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Magman said:
But it doesn‘t end there. It sounds like you have a Prop Strike but not

a Sudden Stoppage. So how do you address this with the engine?
Click to expand...
Lycoming requires a teardown in the event of a "sudden rpm reduction". This doesn't sound like that.
Magman said:
Towbar
Click to expand...
He said it was a tiedown hook.
 
Agree with the rpm factor as not a Sudden RPM Reduction and a complete

teardown is not required. The AD ( if Lycoming) still would apply though.

The Insurance Company May be a major driver here.
 
Sounds like not his plane, not his problem.

The operator can be thankful it is not a CS prop though.
 
mistercrisp said:
what can be done with a prop damaged like that?
Click to expand...
Some fixed props can be re-profiled to a different dimension and even re-pitched to a different spec. So depending on extent of the damage, the base model of the prop, and the economic side of the equation, it could be repaired. However, if the prop is beyond those extended limits then its scrap or becomes a wall decoration.
 
Dana said:
It can't be welded. The propeller manufacturer (or AC43-13) will have specs on how deep a dent or nick may be before it can't be repaired by filing smooth.
Click to expand...
Wow! Thanks so much for the reference to AC43-13! What amazing reading. I will be reading this for a while, absolutely fascinating. I was particularly interested in the section about aircraft immersed in water. There was a warbird that had to ditch in shallow water along an Atlantic ocean beach here. Pilot OK, airplane in salt water. I always wondered what it would take to keep that aircraft airworthy. AC43-13 tells us everything! Thanks for the reply and the reference!
 
Magman said:
Sorry for your misfortune.

A Blade Drawing is needed here to determine condition at each station

from the hub. Measurements are taken from the Trailing Edge forward

to determine if it meets the Minimum Chord Specification for that

station. If it is too short you have a paperweight.


But it doesn‘t end there. It sounds like you have a Prop Strike but not

a Sudden Stoppage. So how do you address this with the engine?

Your Hull Insurance will pay for a tear down. It is not an overhaul though

so rust and wear items are excluded.

The Crankshaft should be checked with a Dial Indicator for starters.

Lycomings require removal for the Accessory Case to check the

Crankshaft Gear per the AD. This may be considered minimum action.
Click to expand...
Not my misfortune. Not my aircraft. A nick in the blade only. No sudden stoppage. Apparently previous pilot had no idea they had had something hit the prop.
 
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Thanks for carefully reading my question... Not my plane. Aircraft belongs to the FBO. It is their problem, and I wasn't flying the plane. I was doing my preflight when I discovered the nick. I am just a curious person and wondered about the extent of the nick. I mean, I have seen small nicks in my time flying, but this was something else! I just remembered I did a photograph of the nick.
Ed Haywood said:
Sounds like not his plane, not his problem.

The operator can be thankful it is not a CS prop though.
Click to expand...
 

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It depends upon the depth, and if it is smooth and small, should be ok to continue flying. If it’s beyond the maximum depth allowed then you can have a mechanic fix it.
 
Good job with the preflight, had you missed it and flown it, you would have, or your insurance would have owned it. I always do a thorough preflight. I don't taxi over tie down ropes either.
 
PaulS said:
I don't taxi over tie down ropes either.
Click to expand...
I don't either, always afraid of the rope laying just right, picking up the end of the rope, and wrapping around a prop somehow. I know, probably not possible, but not possible if you don't taxi over them.
 
mandm said:
It depends upon the depth, and if it is smooth and small, should be ok to continue flying. If it’s beyond the maximum depth allowed then you can have a mechanic fix it.
Click to expand...
None of the prop manufacturers say anything like that. Any damage disrupts the lines of stress in the blade, bunching them up at the damage and eventually causing a crack. If that crack is not caught in time, a chunk of the blade departs, throwing the prop balance way off. If enough of the blade breaks away, the vibration can be serious enough to tear the engine off the airplane, and what happens to the CG when hundreds of pounds fall off the nose? The airplane won't even glide.

Prop nicks are all serious; the smaller ones just take longer to kill, that's all. That "nice, rounded ding" has compressed the metal there, work-hardening it and making it more brittle and prone to cracking. The edges of that ding are sharp and will crack easily, and the crack will travel into the blade.

From a McCauley manual:

1705000394799.png
1705000448087.png

Daily inspection:

1705000529844.png

A prop that broke. Note the remains of a small ding at the leading edge. A SMALL ding. Note also the other numerous dings and scratches that were ignored. Small wonder that the prop gave up.

1705000844501.jpeg
 
Last edited:
mistercrisp said:
Thanks for carefully reading my question... Not my plane. Aircraft belongs to the FBO. It is their problem, and I wasn't flying the plane. I was doing my preflight when I discovered the nick. I am just a curious person and wondered about the extent of the nick. I mean, I have seen small nicks in my time flying, but this was something else! I just remembered I did a photograph of the nick.
Click to expand...

At least we know one thing. The nick was caused by a tiny elf wearing a weird hat and holding some kind of weapon in one hand:

elf.jpg
 
I expect the mechanic would pull the prop and send it to a proper shop for evaluation and overhaul. The PropShop can determine if it is serviceable and complete the proper work to return the prop to service. Or they may not approve the prop and remove it from service.
 
Faced a similar issue just a couple of months ago and did the same as you - posted a pic and asked for advice. Suffice it to say it was close to consensus my propeller was junk.

But then I took it to a prop shop and it had it evaluated pretty much how Magman described in post #3. Turns out there was plenty of meat on the prop to file the ding out. It would have left a pretty good divot but it would have been airworthy. A more proper repair would be to overhaul the prop and have the leading edge reprofiled to remove the divot then reprofile the undamaged blade to match.

Moral of the story. You ain't gonna know what you got until you take it to a prop shot and get it evaluated per the manufacture's recommendations. You just can't eyeball these things.

By the way, the evaluation took about 15 min and the prop shop did it for free.
 
There is an AD on Lycoming engines regarding the Crankshaft Gear.

If the damage to the Prop requires it being sent out then the the AD must

be complied with. This is mandatory even if the damage resulted from a

hangar door hitting the installed Prop!
 
They do have a procedure at the FBO where you unclip the tail tie down, and bunch up the nylon strap, and then put it over by one of the wing tie downs. Really a great idea, but I never realized how important it was NOT to taxi over the tiedown. But I am guessing that the pilot who had the plane before me, maybe gunned the engine as he was going over the tail tie down, and that would do it.
schmookeeg said:
I do that all the time... :oops:. this thread has me rethinking that practice.
Click to expand...
 
mistercrisp said:
They do have a procedure at the FBO where you unclip the tail tie down, and bunch up the nylon strap, and then put it over by one of the wing tie downs. Really a great idea, but I never realized how important it was NOT to taxi over the tiedown. But I am guessing that the pilot who had the plane before me, maybe gunned the engine as he was going over the tail tie down, and that would do it.
Click to expand...
That's good possibility, and if that's what actually happened I think it would be considered a form of prop strike resulting in an abrupt reduction in RPMs, which would likely require a teardown and inspection. If this is a rental plane, I'd be reluctant to fly it with a new prop but no inspection.
 
ANY nick should be looked at by a mechanic and filed smooth.
 
Pinecone said:
ANY nick should be looked at by a mechanic and filed smooth.
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And filed smooth in accordance with the relevant prop maintenance manuals. I have encountered way too many "repairs" that were no safer than if they had just left it alone.
 
Id still be checking the towbar....or setting glue traps for a Leprechaun so he can't do it again
 
If you have the time, take a picture with a penny, dime, or quarter next to the ding. This gives the picture scale.
 
Best practice is preflight the airplane (incl propeller), [this part is usually taught well]

…and postflight the airplane [not taught enough]. This prevents the next flight from having issues (ranging from delays to accidents), and protects you from being blamed for stuff that happened after you walked away.
 
Absolutely! Including a post - flight run- up!

Mags fail in flight but not discovered till next flight attempt.

The Postflight is to determine if in good mechanical condition.

Preflight should really be for oil, fuel and tire pressures.
 
They do have a procedure at the FBO where you unclip the tail tie down, and bunch up the nylon strap, and then put it over by one of the wing tie downs. Really a great idea, but I never realized how important it was NOT to taxi over the tiedown. But I am guessing that the pilot who had the plane before me, maybe gunned the engine as he was going over the tail tie down, and that would do it.
schmookeeg said:
I do that all the time... :oops:. this thread has me rethinking that practice.
Click to expand...

Dan Thomas said:
None of the prop manufacturers say anything like that. Any damage disrupts the lines of stress in the blade, bunching them up at the damage and eventually causing a crack. If that crack is not caught in time, a chunk of the blade departs, throwing the prop balance way off. If enough of the blade breaks away, the vibration can be serious enough to tear the engine off the airplane, and what happens to the CG when hundreds of pounds fall off the nose? The airplane won't even glide.

Prop nicks are all serious; the smaller ones just take longer to kill, that's all. That "nice, rounded ding" has compressed the metal there, work-hardening it and making it more brittle and prone to cracking. The edges of that ding are sharp and will crack easily, and the crack will travel into the blade.

From a McCauley manual:

View attachment 124270
View attachment 124271

Daily inspection:

View attachment 124272

A prop that broke. Note the remains of a small ding at the leading edge. A SMALL ding. Note also the other numerous dings and scratches that were ignored. Small wonder that the prop gave up.

View attachment 124273
Click to expand...
Wow! thanks so much for the detailed information from the McCauley manual! THAT information answers my question! So this impact damage was a big deal - way beyond any ability for a mechanic to fix in the field. Thanks so much for this! Much appreciated.
 
Mikey52 said:
If you have the time, take a picture with a penny, dime, or quarter next to the ding. This gives the picture scale.
Click to expand...
REALLY good point and I never thought to add a coin for scale. I should know better, to add something for scale. :-( They took the airplane into the shop before we left in another airplane, so I'm sorry, I can't photograph it now.
 
Better yet, don't use tiedowns with metal hooks. And don't even get me started on ratchet straps...:no:
 
Magman said:
Absolutely! Including a post - flight run- up!

Mags fail in flight but not discovered till next flight attempt.

The Postflight is to determine if in good mechanical condition.

Preflight should really be for oil, fuel and tire pressures.
Click to expand...
Or if a p lead is no longer making a good connection. Caught that on a post flight once.
 
Dana said:
Better yet, don't use tiedowns with metal hooks. And don't even get me started on ratchet straps...:no:
Click to expand...
So I have always been fascinated by knots. When I learned the tiedown knot I was amazed at what a cool knot is was because you could put the rope under tension, and then tie the knot and the tension stayed! I use that knot all the time. I was disappointed that that the FBO that I rent from they use nylon straps with metal hooks ( ! ) AND nylon straps! But tell me about ratchet straps, please. I don't think I have seen racket straps used for tiedowns before. This FBO uses nylon straps through a metal fitting and you pull the tail end of the strap through the fitting and the tension stays. And, yes, the strap sometimes jams in the fitting...
 
Let'sgoflying! said:
…and postflight the airplane [not taught enough]. This prevents the next flight from having issues (ranging from delays to accidents), and protects you from being blamed for stuff that happened after you walked away.
Click to expand...
In order to protect you from being blamed for stuff that happened after you walked away, how would you prove that you did the postfight?
 
Palmpilot said:
In order to protect you from being blamed for stuff that happened after you walked away, how would you prove that you did the postfight?
Click to expand...
You could take a short video, just like I do after every rental car.
I’m in a good situation in which the managers/owners and i trust each other; if I say I did a clean post flight, they believe me. I report every defect, and if I’m responsible, I tell them. They often see me do it, so they know it’s happening.
 
Palmpilot said:
In order to protect you from being blamed for stuff that happened after you walked away, how would you prove that you did the postfight?
Click to expand...
Back in the day knew several FBOs that had you sign out/in rental aircraft with your signature equating your acceptance of the preflight and post flight. Within a few months it helped them lower some of their scheduling/mx costs.
 
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