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  #1  
Old 06-10-2021, 11:36 AM
rv6cardinal rv6cardinal is offline
 
Join Date: Jun 2016
Location: calico rock ar
Posts: 16
Default Broken engine/gear leg mount

Iím not sure if there is anyone out there who can help but itís worth a try. I have an RV-6 that I built and have been flying for 19 years. I have a little over 1100 hours on it and almost 2300 landings logged, at least half of them on grass. On Memorial Day I landed at my home airport in North Arkansas and noticed when taxiing to the hangar that the right wing was significantly lower than the left. I first thought I might be getting a flat so I got to the hangar as soon as I could before it went completely down. Unfortunately it turned out to be the engine mount which surprised me since I have not experienced any landings lately that I would consider rough. I am thinking now that it may have been cracked for a while and the last landing was the straw that broke the camelís back.

At any rate, here is my problem. The technical advisors at Vanís looked at the pictures and have recommended not attempting to have it welded, but to replace it with a new mount and new gear legs which are match drilled by the manufacturer. I have ordered it but received an email yesterday stating that the parts will not be available until September 13. Ií m wondering if anyone near me would have the mount in their kit but might not be ready to use it in the near future, and might be willing to swap out with me. The mount that I have coming is the 7 DYNA-1 O-360 for the 6,7, or 9. If not too far away I would be willing to come after it and pay a little extra to make it worth your trouble. I could have Vanís ship my new one to you. Oshkosh is coming up and I sure would like to take my RV for the 18th time. Sorry for the long post.
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  #2  
Old 06-10-2021, 11:56 AM
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Sam Buchanan Sam Buchanan is offline
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Join Date: Dec 2004
Location: North Alabama
Posts: 4,455
Default photos please

Sorry to hear about your -6 being grounded but glad you were able to return to the hangar under power.

I can't help with the mount but would love to see some photos of your cracked mount. Am interested if the root of the failure appears to be from the same area where small cracks are often found.
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  #3  
Old 06-10-2021, 12:09 PM
rv6cardinal rv6cardinal is offline
 
Join Date: Jun 2016
Location: calico rock ar
Posts: 16
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I have never posted a picture so will have to figure out how to do so. If you like I would be happy to text or email pictures to you directly.u
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  #4  
Old 06-10-2021, 12:30 PM
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azrv6 azrv6 is offline
 
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Posts: 304
Default

rv6cardinal check you PM's, I sent you my email address so you can send me pics and I will post them for you. Like Sam, I am interested in seeing them. Thanks,
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1932 Monocoupe 110, Warner 145 (http://gobinkley.com)
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  #5  
Old 06-10-2021, 12:44 PM
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azrv6 azrv6 is offline
 
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Posts: 304
Default Pics of Mount

Received these pics of the mount from the OP.

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  #6  
Old 06-10-2021, 04:19 PM
agent4573 agent4573 is offline
 
Join Date: Aug 2019
Location: Mountain view
Posts: 372
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I'll be the first one to jump in and say, holy ****. My first assumption was cold weld that separated, but the weld didn't fail, it pulled the entire tube apart and cracked another one. If your based on a grass strip, I would go walk it looking for gopher holes, cuz you hit something hard at some point. Sorry I can't help with the new mount, but that one needs to go on the wall, cuz thats an impressive level of damage. Super happy that it didn't take anything else out with it.
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  #7  
Old 06-10-2021, 04:45 PM
Eric Minnis Eric Minnis is offline
 
Join Date: Feb 2020
Location: Burlington, NC
Posts: 93
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The new mount that you will receive has additional gussets welded in areas that the older 6 mounts did not have. If you do find one to get before yours arrives, I'd make sure it is the latest generation.
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  #8  
Old 06-10-2021, 04:46 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,626
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From a picture, it is hard to tell what caused the failure.

BUT, what seems apparent is that painting the engine mount black could have made it much harder to identify a crack.

Think about that if you're re-painting an engine mount or are painting one of the older ones that wasn't factory powder coated.
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  #9  
Old 06-10-2021, 06:11 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,589
Default Mount

Failure from stresses in excess of design limits should have occurred on the diagonal tube from the top of the firewall to the top of the gear socket. The diagonal tube should be lesser wall thickness than the socket tube.
This is indicative to me of air hardened weld of the diagonal to the gear socket. Any failure should be well away from the weld.
The tube to the engine mount portion is a secondary failure due to excessive movement from initial weld failure.
This raises the question of whether the socket doubler would be better on the outside of the main socket tube as Steve Wittman originally designed it. While the inner socket makes it much easier to fit and install the gear leg I decided on the outer socket for my Wittman Tailwind. I have a ittermittent shimmy on the left side only that can sometimes get quite violent. I have tried all the standard fixes including balance weights in the wheel pant with limited results. Low tire pressure has helped. Rough paved runway is a problem. Most of my local flying has been with the aft portion of the left wheel pant removed. No wheel pant has not made much difference.
An interesting test would be to file the failed weld with a very fine tooth file. If it doesn't file easily but instead seems like glass, it is an air hardened weld.
Similar failures have occurred from time to time on Pitts aircraft and on the Christen Eagle. On those failures cold weld shop temperatures could be an issue. Too much heat and moving too fast with the TIG torch is also a possible cause. I can produce near identical TIG welds where one is ok and the other is air cooled and will fail.
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  #10  
Old 06-10-2021, 06:14 PM
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Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by Sam Buchanan View Post
Sorry to hear about your -6 being grounded but glad you were able to return to the hangar under power.

I can't help with the mount but would love to see some photos of your cracked mount. Am interested if the root of the failure appears to be from the same area where small cracks are often found.
Wow....that is a catastrophic failure. However, it is not at the same location as the small compression fatigue cracks we sometimes see in RV-6 mounts and have been addressed with gussets in later mounts.

This mount appears to have been severely over-stressed at some point....or cracks with unknown origins went undetected for a very long time. My guess (speculation) is that the gear suffered a huge hit (or repeated punishment?) which created cracks that propagated over a period of time until failure occurred. I really doubt this is due to design flaws or poor workmanship.

Thank you for posting the photos, they are very helpful.
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