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JonathanMilbank
Joined: 14 Apr 2012
Posts: 384
Location: Aberdeen area
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 Posted: Mon May 21, 2018 8:08 am Post subject: Airmaster thrust bearing witness marks |
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My Airmaster AP308 propeller hub has served me well for about 17 years, fitted to 3 different Rotax engines and with 4 different sets of Warp Drive blades attached. The latest set of replacement blades have done over 250 hours and I did a routine servicing and inspection yesterday.
As always after removing each blade, I slide the thrust bearing assembly and spacer away from the blade root spigot to reveal the surface of the ferrule and look closely for a witness line caused by the inner edge of the bearing assembly.
On one of the ferrules there is no visible line. On the next, scratching back and forth with my fingernail across a faint line all the way around the ferrule circumference doesn't result in any groove being felt. On the third, the line is more easy to see and for about 10% of the circumference my fingernail detects a very slight groove, maybe less than half a millimetre deep.
On previous sets of blades, I can recall deeper grooves being seen and felt around much of the circumference on all of the blades. Anyone I've ever asked about this doesn't seem to have anything to offer, by way of an opinion on how much of a groove is acceptable and whether it constitutes a significant stress riser.
So who of you has similar observations and what's your feeling about it?
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Remi Guerner
Joined: 14 Dec 2010
Posts: 284
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| Posted: Tue May 22, 2018 3:35 am Post subject: Re: Airmaster thrust bearing witness marks |
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Jonathan,
I had a similar symptom on my prop years ago. I questioned Airmaster and they answered that it was not critical (see below). I have 1100 hours on this prop now and there are a few more scratches on the ferrule. I am considering replacing the blade/ferrule assembly in a near future.
Regards
Remi
Hi Remi
The ferrules are not anodised, but are painted. This is to ensure the surface is not hardened and made susceptible to fatigue failure. This is relatively soft and gets scratched by the thrust bearings that slide against it. FEA analysis has shown this area to be of relatively low stress compared to the adjoining radiused area which is the area that should be inspected.
Even thought the scratching is visually obvious, it is not subject to corrosion since the area is surrounded by grease. We have had no reports of any failures from this scratching.
Our advise at this stage is that the scratching from the thrust bearings is not of concern, however keep an eye on this when you do your inspections and let us know if you feel the surface scuffing deteriorates.
Regards,
Martin Eskildsen
GM
Airmaster Propellers Ltd
Phone: +64 9 8360065
Fax: +64 9 8360069
View our web-site at www.propellor.com
E-mail us at support(at)propellor.com or sales(at)propellor.com
-----Original Message-----
From: Remi Guerner [mailto:air.guerner(at)orange.fr]
Sent: Tuesday, May 12, 2009 7:30 AM
To: support(at)airmasterpropellers.com
Subject: Questions to Product support
Dear sirs,
I have a few questions regarding discrepancies discovered during inspection of my propeller today.
The ferrule is marked (black anodization removed showing bare aluminum alloy) probably due to the thrust bearing and retention nut rubbing on the surface of the ferrule. See attached pictures of blades # 1 and 3. The ferrule on blade 2 looks the same as on blade 3. The ferrules are marked on about one third to one half of the circumference. The marked area is not deep but it can be felt with your finger nail.
The prop is an AP332 serial 386 with AC200 controller serial 486
Blades number: N14998
Installed on my Europa by myself in April 2006
Engine: Rotax 912ULSFR
Prop total time 267 hours
No damage history
Maintenance done according to the Airmaster Manual
Everything else on the prop is ok: no problem in flight, no play in the blades, no humidity, no corrosion.
Questions:
1. What may have caused this wear after a so short time?
2. How to determine if it is safe or not?
3. How to avoid the wear to continue?
4. How to protect the the bare aluminum alloy?
Any advice wil be welcome
Looking fwd to read you soon.
Regards
Remi Guerner
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JonathanMilbank
Joined: 14 Apr 2012
Posts: 384
Location: Aberdeen area
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| Posted: Tue May 22, 2018 5:30 am Post subject: Re: Airmaster thrust bearing witness marks |
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Hi Remi,
A couple of hours before your reply appeared, I cut and pasted my post above to Martin Eskildsen at Airmaster NZ. If I'd seen your reply first I probably wouldn't have done that, because Martin has already given you a satisfactory answer.
As I've already mentioned, I observed similar marks on my previous sets of blades and they were more obvious with deeper grooves around some of the ferrule circumferences.
Thus far I've never become aware of anyone in the world making it known that they had to change blades because of this phenomenon. I wonder if Martin will have anything different to suggest, but I guess not.
I'm comforted by the fact that the ferrule material is quite thick under the thrust bearing witness lines/grooves and that corrosion in that area would be very unlikely due to the presence of grease.
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Duncan McFadyean
Joined: 18 Jan 2011
Posts: 218
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| Posted: Tue May 22, 2018 2:19 pm Post subject: Airmaster thrust bearing witness marks |
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Similar to DUC, who don't consider that a cracked ferrule is significant (and decline to replace under warranty).
Duncan McF.
----Original Message----
From: air.guerner(at)orange.fr
Date: 22/05/2018 12:35
To: <europa-list(at)matronics.com>
Subj: Re: Airmaster thrust bearing witness marks
--> Europa-List message posted by: "Remi Guerner" <air.guerner(at)orange.fr>
Jonathan,
I had a similar symptom on my prop years ago. I questioned Airmaster and they answered that it was not critical (see below). I have 1100 hours on this prop now and there are a few more scratches on the ferrule. I am considering replacing the blade/ferrule assembly in a near future.
Regards
Remi
Hi Remi
The ferrules are not anodised, but are painted. This is to ensure the surface is not hardened and made susceptible to fatigue failure. This is relatively soft and gets scratched by the thrust bearings that slide against it. FEA analysis has shown this area to be of relatively low stress compared to the adjoining radiused area which is the area that should be inspected.
Even thought the scratching is visually obvious, it is not subject to corrosion since the area is surrounded by grease. We have had no reports of any failures from this scratching.
Our advise at this stage is that the scratching from the thrust bearings is not of concern, however keep an eye on this when you do your inspections and let us know if you feel the surface scuffing deteriorates.
Regards,
Martin Eskildsen
GM
Airmaster Propellers Ltd
Phone: +64 9 8360065
Fax: +64 9 8360069
View our web-site at www.propellor.com
E-mail us at support(at)propellor.com or sales(at)propellor.com
--
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Remi Guerner
Joined: 14 Dec 2010
Posts: 284
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| Posted: Tue May 22, 2018 11:04 pm Post subject: Re: Airmaster thrust bearing witness marks |
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Duncan,
There is no cracks on my ferrules, just surface marks. I made a dye penetrant inspection recently during my annual which confirmed that assumption.
Remi
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