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Main wheel shimmy / vibration

WingnutWick

Well Known Member
Hello all,

Been trying to eliminate a vibration in the new 10 since I got it. Did the anti-splat nose bearing mod/balance, checked breakaway force, and balanced the mains. Thought this would take care of the problem but no effect. Mounted a GoPro onto the bottom of the plane for a high speed run. You can see it's the mains that begin to shudder at certain speeds. There are plenty of post about this with other models but the 10 I seem to only have found posts about the nose wheel. Any ideas why I'm getting this?

You can watch the video here, shimmy can be seen most noticeably at 00:35 when I begin to apply brakes but it occurs at taxi speeds as well with no brakes applies (will actually reduce when I apply brakes when it's happening at taxi speeds):

https://drive.google.com/file/d/17xOd6MbU6q8g5R6l5Ixb9ld9cvv5R17n/view?usp=sharing
 
What are the main tire pressures?

+1

I have no issues with this on my 10 and haven't seem many others post about it either. I do believe that tire pressure can calm or excite this issue on the smaller models. I run 45 PSI on the mains and suggest you try 40-50 and see if it changes. I have seen some state that lower pressures seem to reduce shimmy, but caution is required here, as the lower the pressure, the greater the risk of a pinched tube. I just replaced a nose wheel tube for a guy that didn't heed the warnings of low pressure and tube popped on landing.

Larry
 
My tire pressures are high, I keep them around 45 as I’ve had punctured tubes on my 8 from not doing so. Likewise I haven’t heard of 10s doing this so I’m wondering what’s causing it.

+1

I have no issues with this on my 10 and haven't seem many others post about it either. I do believe that tire pressure can calm or excite this issue on the smaller models. I run 45 PSI on the mains and suggest you try 40-50 and see if it changes. I have seen some state that lower pressures seem to reduce shimmy, but caution is required here, as the lower the pressure, the greater the risk of a pinched tube. I just replaced a nose wheel tube for a guy that didn't heed the warnings of low pressure and tube popped on landing.

Larry
 
Mine has always done this, regardless of tire pressure (I run 45-50). It seems less with new tires, especially the Goodyear flight custom III's, but between 14-18 knots they will vibrate/shimmy some. I always balance them.

Vic
 
My 9A has a "taxi too fast" warning shimmy that occurs at exactly 23 knots ground speed. 22 is fine, 24 is fine, 23 gives a resonance and a shimmy on the nosewheel despite having it well balanced.
 
me too

Our RV10 has a shimmy like Vic's at about 20 or so, either as you speed up on take off or slow down on landing. Wheels been balanced, gone through several different tires in last 12 years, still got the shimmy. Flys great!!
 
Mine is more than just noticeable. I really would like to take care of it. Next steps for me: tire pressure to 50psi - if that doesn't fix, tire pressure to 35 (not sure I want to go lower). If that doesn't work, then new tires and anti-splat mod. If THAT doesn't work, some sort of leg stiffener. If that doesn't work - light the plane on fire. Any other suggestions before the fire option?
 
I don't know the solution for your -10, but every time I had repetitive shimmy on my -6, it was because of out of round or out of balance tires.
 
Gear shimmy........

If that doesn't work - light the plane on fire. Any other suggestions before the fire option?

Before you set it alight, call me! I'll come take that shaky jake off of your hands!:D

Are the tires balanced? Is your stem where the RED DOT is on the tire?

It is a little bit of a PITA to balance them (somewhat harder than setting the airplane on fire....:D) but easily done. I used the motorcycle tire balancing jig from Harbor Freight and a bag or two of their weights. Weights come in two sizes: get the larger ones. I bent the weights to conform more to the curvature of the wheel and, once I knew where they were going, JB Welded them in place. The sticky stuff the weights come with are good for attracting Cat hair; otherwise not enough stickiness but is good enough to get them initially placed. It is a do it again do it again do it again affair before you get the weights placed where they do the most good. You will take them completely off several times.....:mad: Disclaimer: they will not be perfectly in balance but much closer than just the stock tire.
 
My -10

I have a shimmy at 34-35 kts when braking. Tires are at 45 psi. I have had it since the first flight with standard bearings. Had the Anti splat mod done to all wheels, no change to this specific shimmy. I have the wooden gear stiffeners installed as well.

If I do not brake, there is no shimmy. If I brake to 36 kts, release the brakes and coast to 33 kts, then continue braking, no shimmy.

I would like to get a video of it but do not have an action cam yet...
 
I eliminated most of my shimmy in the 33 to 38kt range by going with desser retreads. It seems the heavier tire changes the resonant frequency of the system. I run 50psi in the tires. It’s not totally gone, but close to it. I also meticulously balance the tires
 
I eliminated most of my shimmy in the 33 to 38kt range by going with desser retreads. It seems the heavier tire changes the resonant frequency of the system. I run 50psi in the tires. It’s not totally gone, but close to it. I also meticulously balance the tires

My tires are Desser Retreads...and, they were balanced and trued by anti splat...still have the shimmy. It probably isn't going away; likely some resonance as you stated. When I change the tires, I will try a set of Wilkerson retreads and see if that makes any difference...
 
Mine is more than just noticeable. I really would like to take care of it. Next steps for me: tire pressure to 50psi - if that doesn't fix, tire pressure to 35 (not sure I want to go lower). If that doesn't work, then new tires and anti-splat mod. If THAT doesn't work, some sort of leg stiffener. If that doesn't work - light the plane on fire. Any other suggestions before the fire option?

From my reading here, it would seem that from your list, the leg dampers are most likely to reduce it.
 
I can't help but wonder if what makes this so variable (I have none on my 10) is the Toe. Last winter I restored a jeep for my son. We lifted it and did a bunch of front suspension work. WIth big tires, the jeeps get whats called death wobble (tire hits something and starts a motion that begin a pretty violent resonance cycle in the front wheels, which usually happens at the same speed every time, just like the posters here mention). Toe and caster settings seem to have a BIG impact on the frequency of this occuring. It can also be excited by too much slop in the steering (ball joints tie rods, etc.). Wonder how much variance there is in toe settings out there. IN my experience, Vans welded steel parts don't seem to have the tightest of tolerances known to industry

For those getting the shimmy, it may make sense to check the main wheel bearing to be sure they are not on the loose side. My limited experience with the jeep is that ANY looseness can get the cycle started. I suspect that many that did not work on cars back in the 80's or earlier may not have a lot of experience in setting tapered wheel bearings. Not a great deal of art to it, but not necessarily intuitive either.
 
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There are apparently several reasons why the shimmy can occur. One of them appears to be that the fore-aft and vertical stiffnesses are the same, for round gear legs. Adding an aluminum stiffener in trail of the main gear leg has eliminated the shimmy on several airplanes that have done this. It increases the fore-aft stiffness enough to decouple the fore-aft and vertical stiffnesses.

Here's a link to a discussion of it. Don't be dissuaded because it's in the RV-3 section as it's a general technique and has worked on the two-seaters, too.

Dave
 
Do the Grove style legs shimmy?

I know they are not available for the 10 or the 9, but do those that have the Grove flat style legs have shimmy too?

I have wondered why we use round legs. If the leg was designed to reduce drag without fairings it would make things so much easier. I realize it would be heavier but to eliminate the shimmy and the fairing work, it would be worth it for some of us.
 
Hmmmmm.....guess I just have to go down the list. It seems shimmy is a consistent problem in RV's judging from the plethora of posts about it. I am curious what Vans thinks about this. I am also curious if this is a common aircraft problem in the GA world or more prevalent in RV's. I can't think of any other plane I've flown other than my RV's that have these shimmy issues.
 
Yep, just balanced the tires thinking that would fix my issue. Hate to say it but almost seems worse :(
Before you set it alight, call me! I'll come take that shaky jake off of your hands!:D

Are the tires balanced? Is your stem where the RED DOT is on the tire?

It is a little bit of a PITA to balance them (somewhat harder than setting the airplane on fire....:D) but easily done. I used the motorcycle tire balancing jig from Harbor Freight and a bag or two of their weights. Weights come in two sizes: get the larger ones. I bent the weights to conform more to the curvature of the wheel and, once I knew where they were going, JB Welded them in place. The sticky stuff the weights come with are good for attracting Cat hair; otherwise not enough stickiness but is good enough to get them initially placed. It is a do it again do it again do it again affair before you get the weights placed where they do the most good. You will take them completely off several times.....:mad: Disclaimer: they will not be perfectly in balance but much closer than just the stock tire.
 
Hmmmmm.....guess I just have to go down the list. It seems shimmy is a consistent problem in RV's judging from the plethora of posts about it. I am curious what Vans thinks about this. I am also curious if this is a common aircraft problem in the GA world or more prevalent in RV's. I can't think of any other plane I've flown other than my RV's that have these shimmy issues.

Pretty sure vans thinks that if you get shimmy, you should make and install wooden leg dampers. They went so far as to include the drawings and instructions for making and installing them in my 6A build manual. I think they even recommended to put them on the plane during the build, referencing that shimmy was not universal, but also not uncommon. I put them on my 6 and have never had shimmy. I did not put them on the 10 and also never had shimmy.

Larry
 
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Gear leg shimmy........

Hmmmmm.....guess I just have to go down the list. It seems shimmy is a consistent problem in RV's judging from the plethora of posts about it. I am curious what Vans thinks about this. I am also curious if this is a common aircraft problem in the GA world or more prevalent in RV's. I can't think of any other plane I've flown other than my RV's that have these shimmy issues.

To answer a previous post: yes, from an aerodynamic point of view, round anything produces the highest drag component. The post talking about shimmy in a 150/172 would likely be a nose gear, not main gear shimmy. That is likely due to front fork geometry and a dampener was added to stop/lessen that.

To add to your list: are your wheel pants balanced? Not sure if I read that. I balanced mine during the build but did not put the wood stiffeners in. I had wrapped the gear legs with several layers of fiberglass thinking that might do the trick. I had shimmy at various speeds, almost always on landing, not departing, and more annoying than bad. Messed with tire pressures. Different tires: seem the heavier retreads were better. Now, during my multi-faceted list of current modifications, I tried to build the wood stiffeners according to the plans but found they were a major PITA to get the taper right and still fit in the aluminum gear fairings. I finally went with a stiff fiberglass rod behind the gear leg. Did that work? Looks good but I have not flown since putting those on. I'll report back after the first flight with them on.....(insert crossed fingers here....)
 
Might the real cause of shimmy be the braking system? Specifically, the brake discs? I have come to know aircraft, though not RVs, with shimmy problems that were satisfactorily addressed by resurfacing or replacing the brake discs.

Has anyone looked into whether the disc(s) surfaces were actually flat and parallel or not having localized wear depressions? (Or uneven glazing.) Consider that the brake pads are always, if only ever so slightly, touching the disc and that a repeating on-off change in friction at the right frequency (i.e., rotational speed) can excite a sensitive resonant gear leg system.

My hunch would be that if a dial indicator was placed on the disc surfaces, as mounted on the wheel, that some irregularity would be found. It may be that the disc is not wearing evenly over time, slightly warping, and that the surfaces are not uniformly parallel.
 
To answer a previous post: yes, from an aerodynamic point of view, round anything produces the highest drag component. The post talking about shimmy in a 150/172 would likely be a nose gear, not main gear shimmy. That is likely due to front fork geometry and a dampener was added to stop/lessen that.

To add to your list: are your wheel pants balanced? Not sure if I read that. I balanced mine during the build but did not put the wood stiffeners in. I had wrapped the gear legs with several layers of fiberglass thinking that might do the trick. I had shimmy at various speeds, almost always on landing, not departing, and more annoying than bad. Messed with tire pressures. Different tires: seem the heavier retreads were better. Now, during my multi-faceted list of current modifications, I tried to build the wood stiffeners according to the plans but found they were a major PITA to get the taper right and still fit in the aluminum gear fairings. I finally went with a stiff fiberglass rod behind the gear leg. Did that work? Looks good but I have not flown since putting those on. I'll report back after the first flight with them on.....(insert crossed fingers here....)


I am with Michael on this.
Check your wheel pants.

You will be amazed at how much weight you have to put in it
To balance them.
That with aluminum leg dampers will help.

Boomer
 
Shimmy

I have Sam James wheel pants on my Wittman Tailwind. Balanced the left side wheel pant only. No help. Removed the balance weight. Removing the aft portion of the wheel pants reduced the severity or the shake. Removing the wheel pants does not help. Metal stiffner on left gear only helps but still shakes. Landing rollout at 23 knots on GPS. I just use moderate braking to transition thru that speed.
There was a comment some time ago about the cause being overlapping "belts" in the tires which makes them out of round.
 
My -10 is two years old and I’ve had a few periods of time where I would consistently get the shimmy when breaking after landing. For me, I’m pretty sure tire pressures make the difference. I’m running 50 psi and currently have no shimmy.
 
Wheel pant balance - honestly didn't know if that was a thing but it does make sense. I'm guessing they are to be balanced about the attach point (center of wheel)?

So, from the variety of responses it looks like this will be a journey of trial and discovery. I think I'll do the anti-splat mod/balance pants, then move to stiffeners. All part of having experimentals I guess!
 
Check the toe in...

I know from a lifetime of working on race cars that the toe setting are crucial and you should check and make sure you do not have toe out on the main wheels...
 
Wheel fairing balancing......

Wheel pant balance - honestly didn't know if that was a thing but it does make sense. I'm guessing they are to be balanced about the attach point (center of wheel)?

So, from the variety of responses it looks like this will be a journey of trial and discovery. I think I'll do the anti-splat mod/balance pants, then move to stiffeners. All part of having experimentals I guess!

Yes: they are balanced around the attach point of the axel. Mine took some experimenting but have a bunch of lead bird shot in the nose, held in place by fiberglass resin.

Then I wonder if long legs are more of a problem than short legs (early RV-4 and -6). :confused:
 
I've seen one comment about toe in. I was wondering if wheel alignment could be a contributing factor.
I come from the world of backcontry flying where many have shimmy from the tailwheel, most commonly from poor caster angle and wrong pressure on the steering heard, certainly not an issue here, but checking alignment and bearing tightness sounds worth checking.
 
main wheel shimmy / vibration

I have over 800 hours on my -10 and have had to put up with the shimmy since day one. Mine occurs around 15kts on taxi with no brakes. Slowing make the shimmy go away. On landing the shimmy occurs around 35kts quits as I go thru 15-20kts. This problem was discussed in the early days of my build (2008). No one could come up with a solution or cause. I worry that it will lead to other problems with the gear attachment in the fuselage. I'll try the stiffening on the back side of the gear leg to see if this helps.
 
I have over 800 hours on my -10 and have had to put up with the shimmy since day one. Mine occurs around 15kts on taxi with no brakes. Slowing make the shimmy go away. On landing the shimmy occurs around 35kts quits as I go thru 15-20kts. This problem was discussed in the early days of my build (2008). No one could come up with a solution or cause. I worry that it will lead to other problems with the gear attachment in the fuselage. I'll try the stiffening on the back side of the gear leg to see if this helps.

I have the stiffeners, still have the shimmy. Also have the anti splat bearing mod. Still have the shimmy.
 
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