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  #161  
Old 12-23-2014, 04:57 PM
Malndi Malndi is offline
 
Join Date: Sep 2014
Location: Sydney Australia
Posts: 116
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Quote:
Originally Posted by 1001001 View Post
Would it be possible for you to clean and dye penetrant inspect the removed bolt and post the results? That may help add to the body of knowledge on this issue.
It's probably doable, however I am still waiting for the replacement NAS bolt to arrive. Hope to complete this work sometime in January and will report back with the findings.
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  #162  
Old 12-27-2014, 06:53 PM
Rob's RV9A Rob's RV9A is offline
 
Join Date: Dec 2010
Location: WASh, DC
Posts: 26
Default SB 14-12-22

Finally started my CI today with a friend and RV builder and found SB 14-12-22 and Mr. Blanks posts very timely. The nose stop flange was reversed. So turned it around and ordered new replacement bolts, washers and nuts including for the engine mount socket attachment. We also replaced the 2 U-611 Disk Spring Washers. N994KS has 851.3 hours on the Hobbs. I'll make this minimally part of the CI.
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  #163  
Old 01-16-2015, 08:11 PM
Malndi Malndi is offline
 
Join Date: Sep 2014
Location: Sydney Australia
Posts: 116
Default Sorry no crack test

Quote:
Originally Posted by 1001001 View Post
Would it be possible for you to clean and dye penetrant inspect the removed bolt and post the results? That may help add to the body of knowledge on this issue.
Update:
After waiting many weeks for the NAS bolt to arrive my maintenance provider replaced upper and lower nose leg bolts yesterday. They didn't do a detailed inspection of the upper bolt because we discovered in the logbook it had been replaced only last June as part of an unrelated engine mount repair. They didn't believe there was enough time on the bolt for a crack test to be worthwhile.

My suspicion is that the stop plate may have been installed backwards when the nose leg and fork SB was carried out in 2008. If I'm right, the upper bolt survived without incident from mid 2008 to mid 2014 and 200-odd hours.
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  #164  
Old 01-16-2015, 08:53 PM
Martin Sutter Martin Sutter is offline
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Join Date: Jan 2005
Posts: 266
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Performed the SB on my 7A with 1100 hrs TT recently. Nose fork stop collar was installed backwards (can't beleive I did that!). The old gear leg to engine mount bolt was in there tight but was easy enough to remove. It was pristine with absolutely no nicks or stress marks. This makes me think that movement in the assembly is as much a factor in bolt failures as a stop collar installed backwards. Installed new bolts and turned the stop collar around to be in compliance with the SB.

Martin Sutter
Building and flying RV's since 1988
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  #165  
Old 01-16-2015, 09:51 PM
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1001001 1001001 is offline
 
Join Date: Dec 2014
Location: Just Minutes from KBVI!
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Quote:
Originally Posted by Malndi View Post
Update:
After waiting many weeks for the NAS bolt to arrive my maintenance provider replaced upper and lower nose leg bolts yesterday. They didn't do a detailed inspection of the upper bolt because we discovered in the logbook it had been replaced only last June as part of an unrelated engine mount repair. They didn't believe there was enough time on the bolt for a crack test to be worthwhile.

My suspicion is that the stop plate may have been installed backwards when the nose leg and fork SB was carried out in 2008. If I'm right, the upper bolt survived without incident from mid 2008 to mid 2014 and 200-odd hours.
Thanks for the follow-up. It would probably be interesting if others who find the plate installed backwards over longer periods of time could do a DPI and report out on whether they see any signs of incipient cracking.
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  #166  
Old 01-17-2015, 11:40 PM
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az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
Exclamation Another data point

We did the SB check on a friends recently purchased RV-6A and found the collar installed backwards.

The gear leg attachment to the motor mount was solid and firm, but in this case the wear point was the hole and bolt in the collar -



The softer steel of the collar had distorted and then split under the loading -



In this case it looked like the collar was the weak point.
We don't know the history, but it looks like the bolt was not fully clamping the collar, and the softer collar sleeve wore against the harder bolt each time the turning radius was exceeded.
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EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ

Last edited by az_gila : 01-17-2015 at 11:46 PM.
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  #167  
Old 01-17-2015, 11:50 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by az_gila View Post


In this cse it looked like the collar was the weak point.
We don't know the history, but it looks like the bolt was not fully clamping the collar, and the softer collar sleeve wore against the harder bolt each time the turning radius was exceeded.
In a bolted joint like this, the clamping load of the bolt is not what takes the load, and if it was slightly loose, would make a very minimal difference in the over strength of the joint.
It is the shear strength of the bolt being acted upon by the ring and the leg that takes all of the load.
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Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #168  
Old 01-18-2015, 12:08 AM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
Posts: 10,011
Smile

Quote:
Originally Posted by rvbuilder2002 View Post
In a bolted joint like this, the clamping load of the bolt is not what takes the load, and if it was slightly loose, would make a very minimal difference in the over strength of the joint.
It is the shear strength of the bolt being acted upon by the ring and the leg that takes all of the load.
The bolt held up relatively undamaged but the collar obviously rotated a lot - not clamped down tight? - and elongated the collar hole in a major fashion.

Could this be caused more by tow bar damage rather than "pirouetting" using the brakes and Lycoming for power? Would this put the load on the collar bolt rather than the upper mount bolt?
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Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ

Last edited by az_gila : 01-18-2015 at 12:13 AM.
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  #169  
Old 01-18-2015, 12:18 AM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by az_gila View Post
The bolt held up relatively undamaged but the collar obviously rotated a lot - not clamped down tight? - and elongated the collar hole in a major fashion.

Could this be caused more by tow bar damage rather than "pirouetting" using the brakes and Lycoming for power? Would this put the load on the collar bolt rather than the upper mount bolt?
It could be a combination of any instances that cause the fork to hit the stop, but damage like that is usually the result of a nose wheel shimmy event. The pivot angle during a shimmy event can easily reach the limit of the stop if it is installed backwards.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #170  
Old 01-18-2015, 03:55 PM
gerrychuck gerrychuck is offline
 
Join Date: Jun 2011
Location: Moose Jaw, SK, Canada
Posts: 550
Default

I am currently waiting for my new hardware to arrive to complete the SB. I had Vans throw in a new stop collar as well, and after having a closer look at it (still installed on the plane) today, and now seeing this post, I'm glad I did. My collar shows signs of exactly the same deformation; it appears it has split on both sides above the bolt, just as this one has, and also shows the deformation at the front resulting in space between the front of the leg and the collar.

Yes, my collar is on backwards as well. Having bought my airplane flying, of course, affords me the luxury of being able to blame the builder and absolve myself of any responsibility! Seriously, the guy who built my plane did an exemplary job; if he made this mistake, anyone could.
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Gerry Julian
Moose Jaw Saskatchewan
RV6A "Second Wind" C-GERZ (born N242UL)
O-360 A1A, Sensenich FP prop

Those who think any system is foolproof greatly underestimate the ingenuity of fools
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