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Sep 16, 2019, 03:18 PM
The runway used to be longer
Mad_Mike's Avatar
Thread OP
Question

Weird wear on prop


I have the cowl sticking out too far so the prop rubs on it.
I'm fixing it but I don't understand why the wear is only on one blade. You can see tiny wear on the APC opposite blade but it dramatically wears only one side.

Can anyone tell me what is happening?
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Sep 16, 2019, 03:28 PM
Build a scale plane already!!!
scale_only's Avatar
I'd say your holes are not bored out square to the prop,, what do you use to enlarge the holes?
Sep 16, 2019, 03:31 PM
Registered User
Only thing I can think of is an out-of-balance prop causing the engine to vibrate laterally slightly so that it's always 'leaning' towards the heavy blade and causing it to rub.
Sep 16, 2019, 05:48 PM
Registered User
DGrant's Avatar
Are those pusher props by some chance? Something about those pics lead me to believe they are.

Although the wear is definitely bad on one side, on the APC, I can see a light scuff on the opposite blade as well. I sure hope you don't try and use those again. Once an APC prop is breached in any way they become very unstable.

How about a pic of the cowling and engine install as well... We're just seeing the props. As far as what's causing it might be found in another area obviously.

I wouldn't rule out a slightly bent crank.. although its low on the list of suspicion. Balance.. hmm... that creates more of an oscillation then an outright alignment issue.

If these are pusher props, that would explain why the scuffs are on the back side of the hub, judging by the APC hub, the scuff is on the side that goes to the thrust washer, same with the woody prop. Also the impression of the thrust washer is in both props. Also if they are pushers, that would explain something too. As the engine spools up and pushes, the thrust is pushing the blade forward into whatever is interfering and scraping the props.

What does a simple hand rotation tell you other then the cowl scrapes? If you get a good prop on the engine, get it started at an idle, and carefully watch how the prop tracks.

Best thing already asked here though is what/how do you ream your props?... If your simply drilling them, well... that's not good. There's prop reams specific for getting the holes precise... and then balancers to further get them in tune. So there's a few thoughts for you.

So get some more pics of then engine/mount/cowl/etc.. and tell us what kind of plane and engine you're working on. The more info you give, the more feedback you'll get. At this point what you gave in info of your problem only leaves us asking more questions. So lets really find out what's going on if you want to.
Sep 16, 2019, 05:52 PM
The runway used to be longer
Mad_Mike's Avatar
Thread OP
Quote:
Originally Posted by scale_only
I'd say your holes are not bored out square to the prop,, what do you use to enlarge the holes?
That makes sense but I didn't have to bore out the props, they were already 8mm.
Thanks, I see how it could happen like that.

Quote:
Originally Posted by abenn
Only thing I can think of is an out-of-balance prop causing the engine to vibrate laterally slightly so that it's always 'leaning' towards the heavy blade and causing it to rub.
I did balance with a static balancer but I also see how that could make it hit one side and not the other.
Thanks for that.
Sep 16, 2019, 06:06 PM
Build a scale plane already!!!
scale_only's Avatar
Well,,, if you look at the wood prop it seems the thrust washer is digging in more on the side with the burn mark,,, must be a bad drill job from the factory,,

Two fluke bad props from the factory,, who knows?? seems unlikely,, but possible

good luck
Sep 17, 2019, 04:00 PM
Registered User
earlwb's Avatar
It could be that the driver washer is just a hair crooked on the crankshaft too. But it looks like the back of the propellers isn't straight, thus causing one side of the prop to be more close to the cowl then. I think they had a fancy name for it where the prop is crooked like that.
Sep 17, 2019, 04:37 PM
Build a scale plane already!!!
scale_only's Avatar
"cadywampass"
Sep 17, 2019, 05:03 PM
Dinosaur
Twodor's Avatar
Very interesting...…. but suspicious. (spoken with a German accent)

I need to see the props mounted on the plane, with the cowling installed and photographed from above looking down.

Tom
Last edited by Twodor; Sep 17, 2019 at 07:52 PM.
Sep 17, 2019, 06:28 PM
Registered User
exf3bguy's Avatar
Combination right thrust and bent crank?
Sep 17, 2019, 07:16 PM
Registered User
DGrant's Avatar
Quote:
Originally Posted by Twodor
Very interesting.... but very suspicious. (spoken with a German accent)

I need to see the props mounted on the plane, with the cowling installed and photographed from above looking down.

Tom
I know right. I mentioned that in an above post, as well as asking what plane these props were on, and a few other questions... It's a mystery thing I guess. Oh well. It's always perplexing when someone asks for advice, but doesn't give much to go on.

Seriously a picture of a few props with nicks in them really doesn't say much other then... there's props with nicks in them. Cool. Fix it.
Sep 17, 2019, 07:25 PM
A man with a plan
Balsaworkbench's Avatar
Quote:
Originally Posted by Mad_Mike
I have the cowl sticking out too far so the prop rubs on it.
I'm fixing it but I don't understand why the wear is only on one blade. You can see tiny wear on the APC opposite blade but it dramatically wears only one side.

Can anyone tell me what is happening?
Theoretically a bent crank could cause this wear pattern, but you probably would have mentioned vibration if that was the case. That leaves a slant-wise hole as the only possible explanation.
Sep 17, 2019, 07:45 PM
Registered User
exf3bguy's Avatar
Quote:
Originally Posted by Balsaworkbench
Theoretically a bent crank could cause this wear pattern, but you probably would have mentioned vibration if that was the case. That leaves a slant-wise hole as the only possible explanation.
The prop would still clamp straight between the thrust washer and prop washer. Even if it did not, it would produce an excessive amount of vibration just the same a bent crank would. Perhaps the OP can bolt on a prop and run up the engine and let us know if there are two visible prop disks at the tip or just one. Of course as safely as possible.
Sep 18, 2019, 12:30 AM
A man with a plan
Balsaworkbench's Avatar
I'm pretty sure it would cause some vibration, but not as much vibration as a bent crank. But now you have me wondering about the prop clamping down flat. Do you suppose it would clamp flat and distort the hole, or would the shaft stay straight in the hole and the prop would compress unevenly?

The fact that two propellers had the same problem really makes me think about the possibility of a bent crankshaft again. I'm hard pressed to think of any other way that this wear pattern could happen, other than these two scenarios.

Mike, do you have a similar engine? If so, swap the engine out and use a new prop, and see if the symptoms disappear.
Sep 18, 2019, 06:06 AM
Registered User
earlwb's Avatar
That is a good point. It is possible that the airframe itself may be developing a odd pattern like that from the vibration at certain specific RPMs. Resonance.

As mentioned already, checking the blade tip tracking would show if the blades were bent or warped, or if the back of the prop was not straight too. The blade tips would not be tracking true with each other.


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