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  #51  
Old 05-02-2018, 07:35 PM
Jolly Jolly is offline
 
Join Date: Nov 2016
Location: San Francisco, CA
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This bracket breaks because of vibration. Putting a thicker bracket on is a
band-aid to the main problem. We need to fix the cause and not the result.
This vibration is usually from poor carb sync, gearbox vibration (maybe it needs to be shimmed), the prop (either blades out of pitch from each other or the prop is out of balance). It can also be bad or old rubber engine mounts or engine mount bolt torque too lose. These are the common causes. There are over 50+K engines out there with well over 5 million run hours and most don't have this issue. Best to find the cause because if it breaks this bracket it's working on other parts to. You may not feel a vibration as a human, but all engines vibrate. It you can feel it then it may be bad. Even if you think an engine feels smooth it just has a fine vibration that a human can't feel.
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  #52  
Old 05-03-2018, 08:17 AM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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I agree that vibration is the problem, however, 4-cyl engine behaving as two separate, but coupled power sources, is difficult to minimize vibration especially at harmonic frequencies. I could have easily bought a Rotax replacement bracket and begin a process to reduce vibration but Iíd rather not wait for same bracket design to fail again and perhaps end with a bad day. My new bracket gives me confidence that ignition coils will not shake loose.

Rubber engine mounts and mounting bolt torque, prop pitch, and carb synch will be checked again at next condition inspection. Prop balancing is outside of my budget and not specifically required by Vanís or Rotax.
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  #53  
Old 05-03-2018, 03:37 PM
RFSchaller RFSchaller is offline
 
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Brad, everything you said about vibration causes is correct. However, what does not make sense to me is that all LSA models with 912s should have the same issues, but from the two ROTAX mechanics I have talked to it seems only the RV-12 is having a common bracket problem. I wonder if Scott would comment about whether the prototype ever had these bracket failures. If it didnít with all the hours it has I would be nclined to agree itís not specific to the RV-12.

Rich
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  #54  
Old 05-04-2018, 05:40 AM
PilotBrent PilotBrent is offline
 
Join Date: Dec 2011
Location: Hackettstown, NJ
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Unfortunately, without a larger sample of data on failures/flight hours by model, one cannot support claims that the RV-12 is any worse that other 912ULS installations. All the reports on here are anecdotal. That said, my carbs are (and always are) balanced with gauges, prop pitch is within 0.1 degrees etc... I've done everything expect having the prop balanced which I'll probably do in next few weeks. I'm glad that this possible failure was noted on VAF as I likely would have missed it.
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  #55  
Old 05-04-2018, 09:02 AM
DHeal DHeal is online now
 
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Location: Windsor, California
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Here's an "out-of-the-box" thought: Builders of early RV-12s were required to partially disassemble the ignition modules to install the fiberglas engine plenums. When the builders reinstalled the modules did they inadvertently induce a torquing stress on the module mounting bracket? Could such a twisting stress contribute to premature failure of the bracket?
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  #56  
Old 05-04-2018, 11:09 AM
RFSchaller RFSchaller is offline
 
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Brent, I agree it is certainly not a comprehensive sample from which positive conclusions can be made. Thatís why I thought it would be helpful to know if the Vans prototype had bracket failures. Would that have prompted a service bulletin on the brackets?
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