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  #1  
Old 12-03-2017, 10:49 PM
Norcalrv7 Norcalrv7 is offline
 
Join Date: Jan 2015
Location: McKinleyville CA
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Default Rv8 Main landing gear bracket bolt

Found this wollowed out hole on a landing gear bracket on partially built RV-8. Thoughts?

1130171509b by Caleb Lesher, on Flickr

1130171603 by Caleb Lesher, on Flickr
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Last edited by Norcalrv7 : 12-04-2017 at 02:47 PM.
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  #2  
Old 12-03-2017, 11:13 PM
Robin8er Robin8er is offline
 
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I think that because that bolt primarily has tension on it, it is probably ok. I am very much an amateur, so take that into consideration. I would check with vans to be sure.
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  #3  
Old 12-04-2017, 12:17 PM
scsmith scsmith is offline
 
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First of all, STEP ONE - get rid of those lousy stamped nuts. Use the high-strength12-point nuts. Lots in the archives but if you can't find the info, then PM me.

Second, although it is a tension application, the design of the saddles precludes sufficient bolt pre-load to clamp the assembly tight. So, I'm afraid that a poor hole will allow movement of the joint. Basically, the saddles are fit so that when torqued to the rather light pre-load, the ends of the saddle are not supposed to touch the bearing plate. There is supposed to be a gap. With that assembly, a sloppy hole is going to allow movement at every landing.

I think I recall that edge clearances are kind of marginal through the aluminum parts, but the real bolt contact that matters is the steel weldment. I would consider reaming that hole smooth with an adjustable reamer, to the very minimum amount needed to get a clean hole, and then turning a thin-walled sleeve on a lathe that would be a light drive fit into the hole and provide normal close clearance hole for the bolt.

I have the tools to do this, so if you need help, I'm not too far away. If weather would cooperate, I could fly over, we could ream the hole and then I would fly home, machine the sleeve, and then deliver it to you.

Oh, and maybe a moderator knows how to re-size your pictures so the thread window is normal size?
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Last edited by scsmith : 12-04-2017 at 12:22 PM.
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  #4  
Old 12-04-2017, 02:54 PM
Norcalrv7 Norcalrv7 is offline
 
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Photo size fixed!

This is not my airplane or project thus far. Using the correct hardware would definitely happen. I'm glad you mentioned reaming and sleeving this joint, as that was one of my ideas for a fix. I was unaware that this bracket had an intentional light preload. I wish when I was looking at the project, I would have taken pictures of the inside of this joint.


I might take you up on the offer if this becomes my project!

Caleb
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  #5  
Old 12-09-2017, 06:23 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by scsmith View Post
snip...
Second, although it is a tension application, the design of the saddles precludes sufficient bolt pre-load to clamp the assembly tight. So, I'm afraid that a poor hole will allow movement of the joint. Basically, the saddles are fit so that when torqued to the rather light pre-load, the ends of the saddle are not supposed to touch the bearing plate. There is supposed to be a gap.
snip...
I should probably qualify this. The proper torque is supposed to be the normal torque that you would look up on a table for the NAS close-tolerance bolts. If you watch as you torque, you will see that the bracket is just starting to bend and close the gap on the ends as you reach that torque.

I call it a lower than normal pre-load based on general engineering practices for high-strength fasteners in applications with fluctuating load in both shear and tension. The general practice is to torque to a preload that produces roughly 60--80% of yield stress in the bolt. Experience has shown that this gives the best bolt protection to fatigue and joint movement. The normal tables for AN and NAS bolts have torque values that are quite a bit lower than a general engineering torque table for equivalent strength bolts.

This lower torque, in combination with the flexibility of the U-803 bracket, means that the joint is not clamped very tight. It relies on a good fit of the bracket on the gear leg, and close tolerance fit of the bolts, to minimize movement of the joint.
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WW 200RV
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Hobbs 470 in 8 years
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  #6  
Old 12-10-2017, 08:40 AM
BillL BillL is online now
 
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Quote:
Originally Posted by scsmith View Post
. . . I would consider reaming that hole smooth with an adjustable reamer, to the very minimum amount needed to get a clean hole, and then turning a thin-walled sleeve on a lathe that would be a light drive fit into the hole and provide normal close clearance hole for the bolt.
+1 Perfect!
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