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  #11  
Old 10-11-2015, 12:22 PM
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WingedFrog WingedFrog is offline
 
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Location: Raleigh, NC
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Quote:
Originally Posted by curtis View Post
I see two possible issues with your new bracket;
1 - It looks like it is not the structural Al angle, no radius in the inside corner
2 - There appears to be a notch in the inside corner of the new angle, which may be a new failure point.

My questions are only based upon the image and may not be accurate.
I fabricated the bracket in my hangar from an angle scrap. I had to shave some material to provide clearance for the bolt head. It's quite possible that there are some weak spots. One sure thing, I will keep an eye on it and if it fails I will know how to make the repair.
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  #12  
Old 10-11-2015, 01:32 PM
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DaleB DaleB is offline
 
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Maybe it's just me, but given the long term performance of aluminum under vibration and flex loads, I'd be more tempted to make a replacement from stainless or maybe primed/painted 4130 sheet. AL seems to be a less than ideal choice for a mounting bracket like that. But I'm no engineer, so don't take my word for it.
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  #13  
Old 10-11-2015, 01:37 PM
RFSchaller RFSchaller is offline
 
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Seems like the original bracket probably had a lot of residual stress from forming the 90 degree bend. At least the extruded angle used for the repair won't have that. I'm not a metallurgist, but any metal is subject to fatigue effects.
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  #14  
Old 10-11-2015, 07:46 PM
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chrishalfman chrishalfman is offline
 
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Location: LaVista, NE
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I'm going with improper primer selection and application.

Depending upon how much load there is (I have no idea.....) the aluminum might be fine. If it sees a lot of vibration/load, steel might be the ticket.
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  #15  
Old 10-21-2015, 06:07 PM
Tom Delaney Tom Delaney is offline
 
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Default Another one!

At 150 hours total time found the same bracket broken. Thanks for the heads up.
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  #16  
Old 10-23-2015, 07:35 AM
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WingedFrog WingedFrog is offline
 
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Quote:
Originally Posted by Tom Delaney View Post
At 150 hours total time found the same bracket broken. Thanks for the heads up.
Good (or bad?) to know my case is not isolated, this might motivate other RV-12/912 ULS users to take this warning into account. Did you order a replacement part from Lockwood or did you fabricate one? (I am just curious to find out if Rotax is still using the same part.)
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Sport Pilot
Kit # 120395 N124BX
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Builder's Blog:http://vieilleburette.blogspot.com/
EAA 1114
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  #17  
Old 10-23-2015, 10:38 AM
sblack sblack is offline
 
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Quote:
Originally Posted by curtis View Post
I see two possible issues with your new bracket;
1 - It looks like it is not the structural Al angle, no radius in the inside corner
2 - There appears to be a notch in the inside corner of the new angle, which may be a new failure point.

My questions are only based upon the image and may not be accurate.
Yes it looks like decorative architectural angle. It will likely fail as well. Structural angle has a generous fillet which will improve fatigue life.
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  #18  
Old 10-23-2015, 05:40 PM
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WingedFrog WingedFrog is offline
 
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Quote:
Originally Posted by sblack View Post
Yes it looks like decorative architectural angle. It will likely fail as well. Structural angle has a generous fillet which will improve fatigue life.
I do not believe you need a structural angle here. The ignition boxes are light and stacked on the angle, they are also supported by two rubber dampers on the opposite side of the bracket and the bracket itself is attached to a third rubber block. This is probably the reason Rotax chose to make the angle out of a bent aluminum bar. It is why the broken brackets are difficult to detect as there is no consequence beside a rubbing of the two broken pieces of the bracket. I suspect the original bracket failed from the thermal cycles, not under mechanical stress.
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Builder's name: Jean-Pierre Bernoux
Sport Pilot
Kit # 120395 N124BX
Flying as of 9/11/2013

Builder's Blog:http://vieilleburette.blogspot.com/
EAA 1114

Last edited by WingedFrog : 10-23-2015 at 05:59 PM. Reason: adding details
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  #19  
Old 10-23-2015, 08:21 PM
RFSchaller RFSchaller is offline
 
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I agree. This seems like a low usage application. My guess is the failure is due to high residual stress from bending, more than in service cycles.
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  #20  
Old 10-23-2015, 08:24 PM
Tom Delaney Tom Delaney is offline
 
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Location: St. Louis, MO
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Quote:
Originally Posted by WingedFrog View Post
Good (or bad?) to know my case is not isolated, this might motivate other RV-12/912 ULS users to take this warning into account. Did you order a replacement part from Lockwood or did you fabricate one? (I am just curious to find out if Rotax is still using the same part.)
I ordered a length of 0.125" T-316 Stainless Angle to fabricate a new bracket. If anyone sees a problem with this material for the new bracket please let me know.

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