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gear leg shimmy

Hitt7A

Member
A little background, I have 120 hours now and love the plane and what it does. I had Anti Splat Aero do all 3 tires bearing and balance mod, I'm lazy and don't want to pack wheel bearings again. the mod works as advertised and the plane was butter smooth, couldn't be happier. My problem started at around 110 hours and over 120 landings, my right main was starting the shimmy and vibration issue I see others have had. Upon inspection I noticed my tire on that side the tread was worn off the outside edge, I rotated the tire on the rim thinking it had too much drag from the tread being gone causing the main gear to oscillate fore and aft and causing the vibration. This helped but did not fix the issue, so like others before I fabricated an Oak wood gear leg stiffener and that fixed the problem. I was not happy with the fix as it also caused the leg to be a little stiffer in the up and down motion also, so I started playing around and came up with a solution that works for both problems. using left over fiberglass and carbon fiber I had, I laid up 10 layers of 3" wide glass cloth with a single layer of carbon on each side. After cure I cut it in half leaving me two pieces 22" long x 1.5" wide and close to 3/16" thick. I then attached the pieces to the back side of the gear leg with 7 stainless steel Adel clamps, this allows the gear leg to still travel up and down with very little restriction and also stop all fore and aft shimmy. It all fits nicely under my gear leg fairings after I cut off the rubber strip on the top and bottom of the clamps, hopefully my photos attach and make this a little better to understand.
 

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Hitt 7A question ?

Why glass with carbon skin ? I have wrapped my 3B with carbon around the gear leg and carbon plate behind the leg ( tapered top to bottom) replacing the vans fairing completely. I might try your approach on my -4 and keep Vans fairing. So how/why did you decide on glass core and carbon skin for rear stiffener element ? Adells and stiffener plate are clever !
 
The fiberglass alone may have let the stiffener flex and bow just a bit in the aft direction. When I clamped the bare piece on the bench and applied force in that direction it tended to flex and bow a small amount, when I added the carbon layer on both sides that disappeared.
 
clever

Very clever!
Any chance you have a weight comparison with the oak ones?
 
I didn’t weigh them, but I would say the fiberglass ones are a little lighter even with all the clamps
 
Smart solution

Is it all glass and carbon fiber, or is there a wooden core. - If yes is it oak or?

Thank you for sharing the idea
 
Seems like an awful lot of work to fix something that a new set of tires most likely would have taken care of?

I replaced one of the antisplat nose wheel mods that was shimming despite installing a new tire and balancing, a new Beringer wheel fixed the problem, it looked like the modified wheel was not running true.
 
new tires

funny you mention that Walt. I put new tires on 5 hours ago and just realized I haven't gotten any shimmy since!
 
I fly mostly solo, I suspect that’s why my right main was worn out on the outside tread only, the left is wearing fairly even. Rotating that tire on the rim put good usable tread on the outside. I’m sure replacing that tire would have stopped the shimmy, I’m just trying to maximize the life of the tires. This is the fun part of experimental for me, tinkering and finding solutions to issues that come up along the way, sharing what I find and also seeing what others have for ideas also.
 
gear shimmy

I have tried everything to stop the shimmy, different tires, pressure, wood slats, wrapping legs with carbon fiber, etc. I just bought a new pair of gear legs, seem to have just a bit more toe in. Can you send me a list of the ADEL clamp sizes and quantity you used?
Please send to: [email protected]
 
CF wrap plus Adel clamps?

We wrapped the main legs on our -7A with carbon fiber as recommended by RocketBob. This reduced the shimmy and made it a lower frequency vibration but did not eliminate it. With two layers of CF on the legs, do you think Adel clamps would still fit under the fairings?
 
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