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  #1  
Old 11-16-2017, 11:16 AM
13brv3's Avatar
13brv3 13brv3 is offline
 
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Location: Tellico Plains, TN
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Default Gear shimmy video

Greetings,

I purchased an RV-3B a few months ago, and I'm finally getting around to looking at the gear leg shimmy. I mounted a GoPro on one of the tie down attachments just to see what this actually looks like, then intentionally provoked it. Pretty interesting if you've never seen it.

https://youtu.be/GaKSJmu1zgw

BTW, this is a good angle to critique landings, so no videos of that :-)

FWIW, I'm familiar with the shimmy causes and fixes, so this is mainly being posted for your entertainment. Don't say I never gave you anything :-)

Cheers,
Rusty
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  #2  
Old 11-16-2017, 12:15 PM
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Default

Fun times. Good example. Now, let's see those landings
(You can always just share your best ones)
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  #3  
Old 11-16-2017, 12:27 PM
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Ironflight Ironflight is offline
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Default

That's a classic! great video Rusty - thanks for sharing.
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  #4  
Old 11-16-2017, 01:22 PM
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13brv3 13brv3 is offline
 
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Default

Quote:
Originally Posted by JonJay View Post
Fun times. Good example. Now, let's see those landings
(You can always just share your best ones)
OK, this is all you get :-)

https://youtu.be/4GbggShsGdE

Rusty
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  #5  
Old 11-16-2017, 01:29 PM
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Quote:
Originally Posted by 13brv3 View Post
OK, this is all you get :-)

https://youtu.be/4GbggShsGdE

Rusty
Excellent, perfectly executed, ....
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  #6  
Old 11-16-2017, 03:51 PM
Dmadd Dmadd is offline
 
Join Date: Jul 2008
Location: Camas, WA
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Default

Daaaaaaammmmnnnnn :-)

Quote:
Originally Posted by 13brv3 View Post
OK, this is all you get :-)

https://youtu.be/4GbggShsGdE

Rusty
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  #7  
Old 11-16-2017, 07:25 PM
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CAVU Mark CAVU Mark is offline
 
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Default Haw many takes?

Must have been more than one?

And if anyone can point me to the gear fix thread I would appreciate it. I too bought a RV3 with enough shimmy for the rocketts!
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  #8  
Old 11-16-2017, 09:22 PM
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13brv3 13brv3 is offline
 
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Quote:
Originally Posted by CAVU Mark View Post
And if anyone can point me to the gear fix thread I would appreciate it. I too bought a RV3 with enough shimmy for the rocketts!
There's no single thread, but a search will find a bunch of different threads.

Bottom line is that the shimmy happens at the resonant frequency for your gear legs. The primary factors for the frequency are the weight of the wheel/brake/pants, and the stiffness of the gear leg. For the most part, the weight of the wheel assembly can't be changed too much, so the main thing we can change is the stiffness of the gear legs. If you do some searches for gear leg stiffeners, or dampers, you'll find more info, but most people end up with a wood strip wrapped in epoxy to stiffen the gear leg. The idea is to raise the resonant frequency to a point higher than normal taxi speeds.

Another "fix" you see a lot is the recommendation to lower the tire pressure. I'm thinking that also changes the frequency by effectively making the tire smaller, but it may also add some dampening by raising the rolling resistance.

The other recommendations are usually along the lines of making sure your tires are as close to perfectly round as possible, and balanced. These go along the lines of trying to prevent the vibration that will get amplified by the resonance. Tuning forks are quiet if you don't hit them :-)

This plane has some form of gear leg stiffeners, but I haven't taken the aluminum gear leg fairings off to see how they're constructed. Adding the stiffeners totally resolved the shimmy on my previous RV-3B, so I'm hoping I can rework them and have the same success. I'll also be getting rid of those aluminum fairings and replacing them with fiberglass. They guy who built this plane had a thing for polished aluminum.

Cheers,
Rusty
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  #9  
Old 11-17-2017, 06:17 AM
Jab Jab is offline
 
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Location: Knoxville, TN
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Beautiful landing Rusty, thanks for posting those videos. Let me know if you plan to sell those aluminum fairings, I am actually looking for some.

Cheers, Gary
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  #10  
Old 11-17-2017, 07:41 AM
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13brv3 13brv3 is offline
 
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Quote:
Originally Posted by Jab View Post
Beautiful landing Rusty, thanks for posting those videos. Let me know if you plan to sell those aluminum fairings, I am actually looking for some.

Cheers, Gary
Thanks Gary. I'll let you know about the fairings. I guess they would probably work on a 4 if it's the short gear version.

Rusty
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A&P - 2018
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