Gear shimmy video

[rv8guy]

Sweet. I can remeber all two or so like that in 10 years with my RV8

[JonJay]

Originally Posted by rv8guy

Sweet. I can remeber all two or so like that in 10 years with my RV8

I quit counting landings as I had way more than one per flight!

[13brv3]

My first landing of the day would have required Benny Hill music :-)

Rusty

[ALagonia]

Originally Posted by 13brv3

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

Rusty,

What causes the shimmy and what is the fix?

Thanks
Angelo

[13brv3]

Originally Posted by ALagonia

Rusty,

What causes the shimmy and what is the fix?

Thanks
Angelo

I discussed it some in post #8 of this thread. There's also a ton of info available if you search for shimmy as well.

Rusty

[Bevan]

Shimmy is caused by a combination of things being present at the same time. Excitation force repeating at the same frequency as the resonant frequency of the overall structure (spring gear with a weight (tire) on the end of it. Minimal dampening (absorption) of the vibrational energy. Removing/change anyone of them will "fix" (reduce the tendency of) the shimmy. On our airplanes, the easiest thing to change is the tire pressure. Maintaining pressure between 25-30psi did the trick for me. Lower pressure would work too but that may cause other problems.

My tire gauge was way out of calibration resulting in tire pressures way higher than I was reading. Higher pressure caused (amount other things) less drag, less contact with the runway surface. Drag aids to dampen shimmy.

At least this is how I understand it.

Bevan.

[N13BN]

I currently have a -3 that I built. I also had one that I bought. Both had major shimmy. Both were "cured" by installing Desser Monster Retreads maintaining tire pressures of 20-25 psi.

Bill Newkirk

[13brv3]

Originally Posted by N13BN

I currently have a -3 that I built. I also had one that I bought. Both had major shimmy. Both were "cured" by installing Desser Monster Retreads maintaining tire pressures of 20-25 psi.

Bill Newkirk

It would be interesting to know how the weight of those tires compared to what you were using. Changing the weight should change the frequency. Also I'd wonder if retreads are different enough in diameter to make a difference? The tires have plenty of wear on them, and I'd be up for changing them if that's all it takes.

Rusty

[N13BN]

The Monster retreads are a little heavier but their main feature is a really stiff sidewall. My current -3 shook so violently on landing that the engine would stop because of fuel starvation, even after adding gear stiffeners.

Bill

[Marc DeGirolamo]

Rusty,
By your video it looks like you have the stock aluminum fairing. Do you have the wood leading edge wrapped in fiberglass installed?
I have an RV-4 and opted to not use the lighter AL gear leg fairings supplied with the kit but went with a wood/fiberglass leading edge (as recommended in the plans, wrapped with 2" fiberglass cloth) and then foam behind the gear leg and then all wrapped with 3 layers of fiberglass ( I think 6oz....its been a while) cloth, so ending up with 6 layers of fiberglass on the leading edge.
I have never had any issues with shimmy or cracks in the legs and I have had many rough strip and/or rough landings.

Marc