Main Landing Gear Shimmy at 10-20kts (with video)

[nickw9815]

On landing roll, we are getting a shimmy from the gear. Originally we thought it was caused by the nose gear so the nose wheel was re-balanced and the bearings were re-machined. Today, I stuck a camera under the wing and videoed a landing, and it looks like it is the main landing gear that is shimming. What could be causing this?

 

[rockyfatcat]

RV Gear Leg Stiffener Set

These wooden Gear Leg Stiffeners provide a simple, inexpensive, and easy-to-install solution to dampen the damaging and uncomfortable vibrations that your main gear legs experience at various speeds. These Gear Leg Stiffeners will fit aircraft using the tapered rod spring steel gear. This...

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[rockwoodrv9]

Is there a chance your wheels are not lined up correctly? To me it looks more line the legs may be turned in a bit too much and and they cause the wheels to skip across the surface. If your tires wear out quickly or different than other 6A planes, that may be the issue. I would check the alignment first with your normal weight in the plane. If it all checks out, then out of round or unbalanced tires would be the next check. Maybe even the first. Leg stiffeners of wood or the new aluminum design that I cant remember who came up with would be the next option I would try. I havent had much issue with shimmy on my mains but at times my main gives me a little thrill. Good luck.

 

[rocketman1988]

Is there a chance your wheels are not lined up correctly? To me it looks more line the legs may be turned in a bit too much and and they cause the wheels to skip across the surface. If your tires wear out quickly or different than other 6A planes, that may be the issue. I would check the alignment first with your normal weight in the plane. If it all checks out, then out of round or unbalanced tires would be the next check. Maybe even the first. Leg stiffeners of wood or the new aluminum design that I cant remember who came up with would be the next option I would try. I havent had much issue with shimmy on my mains but at times my main gives me a little thrill. Good luck.

I have a similar issue on my -10 between 31-34 kts. I have the wooden stiffeners wrapped with two layers of 9 ounce cloth.

 

[Stevea]

Before installing gear leg stiffeners, I would first check the mains for two conditions:

1. Are the wheels statically balanced?
2. Are the tires permanently out of round?

If either of these conditions exist, they can cause the wheel shimmy you are seeing. Adding gear leg stiffeners may minimize the shimmy....but it can also mask an out of balance/out of round condition that may still be present. If the wheels are balanced and round, there is very little forcing function to excite the wheel shimmy (always in the same speed range) like you are seeing.

As for wheel alignment.....there is no alignment adjustment on the 6A mains. You're kind of stuck with whatever the original builder or the factory did when drilling the gear leg to gear mount bolt hole.

 

[blaplante]

What tire pressures are you running? If I recall correctly (?) running on the high side can make this more likely.