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  #21  
Old 09-27-2020, 01:37 PM
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wcalvert wcalvert is offline
 
Join Date: Jan 2019
Location: Anacortes Wa
Posts: 83
Thumbs down JB Weld

WHY is JB weld being considered here for an oversize hole repair?

Adding material with a compressive/tensile strength of 3.9 KSI compared to the parent material strength of 81 KSI (4130 steel) makes no sense at all.

The best that will do is stabilize the joint temporarily and then fail, leaving you with the impression that the problem is fixed.

Not to bash, but the surfaces designed to bear the loads were designed with the parent material in mind.
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Start 2/19 Emp complete 4/19 Wings complete 11/19 Fuse complete 6/20 Finish kit Complete 8/20 Electric/Avionics complete 9/20 Waiting on a motor...
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  #22  
Old 09-27-2020, 08:11 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by Kyle Boatright View Post
Every time I've gotten into a shimmy problem it was due to air pressure (I keep the mains at 34 psi) and/or tire issues like being flat spotted.
My experience exactly. Anything pushing the high 30's in psi on the mains will cause trouble.

Quote:
Originally Posted by WingsOnWheels View Post
SNIP

I keep my mains at 50psi with no main-gear shimmy.

SNIP
I'd love to run 50psi on the mains, as the plane is so easy to push in/out of the hangar, but it doesn't work on my plane. The internal friction and rolling friction of the tires are the only damping in the spring-mass system (unless one installs some wood behind the gear leg).

It is interesting that this property seems to vary so much from plane to plane, even though the gear legs are the same (in this case 6A to 6A).

Tire brands also make a difference.
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  #23  
Old 09-27-2020, 08:31 PM
WingsOnWheels WingsOnWheels is offline
 
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Location: Plano, TX
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Quote:
Originally Posted by AlexPeterson View Post

It is interesting that this property seems to vary so much from plane to plane, even though the gear legs are the same (in this case 6A to 6A).

Tire brands also make a difference.
I think much of the variation maybe driven by toe-in/toe-out. Also, camber. My left main wears more on the outside than the right. When building, I noticed that the bend in the gear leg was not perfect between the two. The left had slightly less bend.

Also, I run a bit higher bearing preload, not enough to make it hard to roll, but the rollers are well seated, all this may contribute to the variation from one aircraft to another
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Last edited by WingsOnWheels : 09-29-2020 at 05:18 AM.
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  #24  
Old 09-28-2020, 06:09 AM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by WingsOnWheels View Post
I think much of the vaiation maybe driven by toe-in/toe-out. Also, camber. My left main wears more on the outside than the right. When building, I noticed that the bend in the gear leg was not perfect between the two. The left had slightly less bend.

Also, I run a bit higher bearing preload, not enough to make it hard to roll, but the rollers are well seated, all this may contribute to the variation fron one aircraft to another
Colin, very good observations, and quite likely a large (dominant?) the source of variation. I've been threatening to add wood stiffeners for 19 years, one of these days I might... However, if it is the caster that is energizing the resonance, they might not help. You've given me food for further thought.
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  #25  
Old 09-29-2020, 05:21 AM
WingsOnWheels WingsOnWheels is offline
 
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Quote:
Originally Posted by AlexPeterson View Post
Colin, very good observations, and quite likely a large (dominant?) the source of variation. I've been threatening to add wood stiffeners for 19 years, one of these days I might... However, if it is the caster that is energizing the resonance, they might not help. You've given me food for further thought.

You can always do a test. Attach the stiffeners with a couple layers of fiber-reinforced or duct tape, see if it helps before you attach with fiberglass. Someone else wrapped their leg with carbon fiber (without the wood) and said it helped.
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I donate every year on my B-Day (in Dec), but donated early in Sep'19.

Last edited by WingsOnWheels : 09-30-2020 at 04:48 AM.
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  #26  
Old 09-29-2020, 06:17 AM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by WingsOnWheels View Post
You can always do a test. Attach the stiffeners with a couple layers of fiber-reinforced or ducts tape, see if it helps before you attach with fiberglass. Someone else wrapped their leg with carbon fiber (without the wood) and said it helped.
This is a good idea - maybe strapping tape and some oak. The temporary fastening will likely not prevent shear movement between the gear rod and the wood strip, which might be a large component of the damping of fore/aft vibrations.

Will ponder this, thanks.
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  #27  
Old 09-29-2020, 06:24 AM
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Planecrazy232 Planecrazy232 is online now
 
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Quote:
Originally Posted by AlexPeterson View Post
This is a good idea - maybe strapping tape and some oak. The temporary fastening will likely not prevent shear movement between the gear rod and the wood strip, which might be a large component of the damping of fore/aft vibrations.

Will ponder this, thanks.

The strapping tape is permanent enough. I've got wood stiffeners in place with strapping tape for 3 years now, and still in good shape. Easily changed out if necessary. No reason to glass them.
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  #28  
Old 09-30-2020, 12:43 PM
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PerfTech PerfTech is offline
 
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Location: Redlands, Ca.
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Talking

Quote:
Originally Posted by rvbuilder2002 View Post
There is a bunch of different factors that influence the tendency for main gear leg shimmy.

- out of round tire
- out of balance tire
- tire air pressure

This is a lot of the reason some people have had the problem and later don't, or sometimes go for years not having it, and then suddenly do.
... This is all spot-on, and is most likely the source of the issue. One other possibility, and method of checking for it is this.
If the problem gets worse as you slow down to exit the runway, or as you apply braking? This is an indicator of a potato
chipped, glassed, or hot spotted brake rotor / rotors. easy to check and verify! Thanks, Allan...
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