Odd shimmy problem...

For the first four years we flew our -6, we never had a shimmy problem. Recently, my dad said that he's occasionally gotten shimmy on rollout, which doesn't stop until he's basically stopped the airplane. I never experienced it before today, when he was landing. He did a three-point, and the shimmy started soon after he pinned the tail. On the next (wheel) landing, no shimmy. Like I said, he's had this happen before (first time, he thought it was a blown tire), but it's never happened to me when I fly it. We tried straightening out the tailwheel, since it was maybe two degrees from vertical, and tightening the axle nuts on the mains, but it didn't seem to help.

Anyone have insight on this? Thanks

I never had it happen on my RV8, but got quite a dose of tailwheel shimmy on my trip home in my new C-180 with 10" tailwheel. I'm pretty sure it was initiated by my (poor and inexperienced) technique. I must have put it on a bit crooked, three-point, and too fast. It wouldn't stop until the plane was basically stopped. Once a resonance is set up, there isn't much you can do except get on the binders and ride it out. You've already checked the hardware, so try to pay special attention to technique; no crab, no side drift and not too fast. Wheelies for me always work out better, by not bringing the tail down until the elevator quits.

Maybe your tail wheel is out of balance or the bearings are worn. They're pretty cheap so maybe just swap it out and see if it changes the overall behavior of the tailwheel assembly.

Check the bolt torque on the gear leg attach bolts at the top of the leg (in the engine compartment). Also after a number of years your wheel pant's attach screws may be allowing some play and this can also 'induce' shimmy.

It is also certainly possible that the shimmy is initiating at the tailwheel. You didn't say if it is the original tailwheel, may it is worn so much that it's wear pattern charateristics are influencing the main gear.

Anything else changed? New tires? Air pressure? Wheel bearing adjustment?

There are lots of variables which change the vibration characteristics.

The tailwheel is brand new... we've had to replace it every year because the bearings were wearing out and the tire got lopsided (we think both were because it was mounted crooked).

We'll check the bolts in the gear mount and the wheel pant mountings next.

Brian Denk said:

I never had it happen on my RV8, but got quite a dose of tailwheel shimmy on my trip home in my new C-180 with 10" tailwheel. I'm pretty sure it was initiated by my (poor and inexperienced) technique. I must have put it on a bit crooked, three-point, and too fast...

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I wouldn't be so sure Brian. I don't see any possible way to be too fast in a three point attitude; crooked, well that's possible.

My experience is that factory tailwheel gear(s) is much more complicated than the simple Vans tailwheel system, which does have a few issues itself. Get a few worn parts and shimmy can ensue.

Congratulations on your new airplane!