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Shake rattle and roll ...

wcalvert

Well Known Member
I realize this has been discussed recently in other contexts, and likely known by many, but here's my story.

My -7 had a main wheel shimmy since it was new 200+ hours ago. It would reliably shake as it slowed on landing at 18-21 kts, seemingly dependent on a/c weight and mostly tire pressure. All the talk of the need for gear leg stiffeners had me believing that it was an inherent issue with the aircraft, so I decided to live with it.

Then a few weeks ago I was doing a section takeoff with Ken out to the islands. On return he mentioned that the shake I was feeling was likely my left main, he could see it shudder after liftoff.

So that made me suspect that the issue may not be with the gear leg, but with the tire balance. Given the tiny size of the wheel and the low speed when the issue occurred, I just didn't suspect tire balance as the culprit.

Off to HF and got the static balancer they sell for motorcycle tires, with a horizontal rod on bearings. It did take some searching to find large enough cones to fit the bearings, but with all the tools together I balanced both sides. For sure the left was well out of balance, and as a side note, has no mark on the tire for the stem location, so it's most likely in the wrong place on the rim.

Test flight resulted in super smooth operation during taxi out, and no shimmy or shake on roll out! What a difference. That and the new tailwheel with sealed bearings made the taxi out very nice and smooth.

Long story short, if you're having the shakes, check your balance. Worth a try.

Cheers
 
did take some searching to find large enough cones to fit the bearings

Mmmmh, were you able to buy those commercially, and if yes any reference, thanks.

Otherwise I'll dust off my lathe, good exercise :)


PS
Pity I missed you during my short stay at K74S on July 4th, best to the gang!
 
I realize this has been discussed recently in other contexts, and likely known by many, but here's my story.

My -7 had a main wheel shimmy since it was new 200+ hours ago. It would reliably shake as it slowed on landing at 18-21 kts, seemingly dependent on a/c weight and mostly tire pressure. All the talk of the need for gear leg stiffeners had me believing that it was an inherent issue with the aircraft, so I decided to live with it.

Then a few weeks ago I was doing a section takeoff with Ken out to the islands. On return he mentioned that the shake I was feeling was likely my left main, he could see it shudder after liftoff.

So that made me suspect that the issue may not be with the gear leg, but with the tire balance. Given the tiny size of the wheel and the low speed when the issue occurred, I just didn't suspect tire balance as the culprit.

Off to HF and got the static balancer they sell for motorcycle tires, with a horizontal rod on bearings. It did take some searching to find large enough cones to fit the bearings, but with all the tools together I balanced both sides. For sure the left was well out of balance, and as a side note, has no mark on the tire for the stem location, so it's most likely in the wrong place on the rim.

Test flight resulted in super smooth operation during taxi out, and no shimmy or shake on roll out! What a difference. That and the new tailwheel with sealed bearings made the taxi out very nice and smooth.

Long story short, if you're having the shakes, check your balance. Worth a try.

Cheers

Yup
It is the very first thing on my suggestion list...
after doing something to confirm where the shaking is at, such as using a camera mounted on the aircraft or have someone watch from outside during a landing. A lot of people assume they are feeling nose whee shimmy(if an A model) when it is really main gear or visa versa.

#2 is to check tire roundness. It is not unusual for an airplane that never had a gear shake issue, but that has been sitting un-flown for a while, to develop one.
 
Tire Shop Balance

I've never looked in to this but it seems that a 1st class tire shop could spin balance a/c tires.
My local shop handles everything from wheelbarrow tires to road and farm tractors.
It would be worth a try.

Glenn Wilkinson
 
Huh. I'm in the same position, always thought it was just an inherent nosewheel vibration around the same speed on roll out. Which size cones did you need from Marc Parnes? And what did you use for balancing weights? My first instinct is to just order some of those adhesive rim weights from Amazon.
 
Huh. I'm in the same position, always thought it was just an inherent nosewheel vibration around the same speed on roll out. Which size cones did you need from Marc Parnes? And what did you use for balancing weights? My first instinct is to just order some of those adhesive rim weights from Amazon.

Ever see pics of the damage a stick-on weight can do if it becomes "unstuck"?

-Marc
 
Which size cones did you need from Marc Parnes?

I ordered and have used his “Portable Motorcycle Wheel Balancer” kit since 2017. I would recommend calling him as I ordered the universal size and he called me to suggest a different size. How’s that for great customer service! Works great on our RV wheels and nothing else to buy.
 
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Ever see pics of the damage a stick-on weight can do if it becomes "unstuck"?

-Marc

No, and we have been doing it for many many years. Including on the certified SLSA RV-12’s.
With the shape of most aircraft wheels you can stick the weights on in such a way that when the wheel spins up centripetal force is sticking the weight harder to the wheel, not trying to pull it off. Just need to make sure the surface is cleaned really well before the weights are installed.
 
Turns out it wasn't their hesitation to work on an "aircraft" wheel, but rather that their machine was not able to accurately balance a tire that small. They recommended a motorcycle shop, that might be another option. In the mean time, static balance seems to be sufficient.

Cheers
 
I radius bend my weights with a hammer, and split the weight from side to side. Lead is hard to get (here?).

I use the bearings so the HF cones fit just fine. YMMV

I have considered spinning the wheel to validate the static balancing but have not invested the time.
 
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