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RV-10 Main Wheel Pressure / Shimmy

vic syracuse

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Main Gear shimmy

I thought I would ask if any of the flying RV-10's are having any of the main gear shimmy we have seen on the other RV's. I am, and it's driving me nuts (no comments about it being a short drive, please). :) It appears to be getting worse, so I'm thinking it might be the tires. I've rotated the tires, and put the wood dampeners on the main gear legs as well. It is very pronounced upon landing and decelerating through 32-34 knots. It is hardly noticeable on takeoff, probably because we accelerate so quickly. But upon landing, it almost wants to shake the airplane apart. It's fine faster than 34 or slower than about 28. I have verified it is the mains by having another pilot stand outside the airplane as I went by with the shake occuring. It is only noticeable on pavement. I fly off of grass 90% of the time, and have about 500 hours on the original tires, which are still showing about 1/8" of tread, deeper in the middle, and shallower on the insides and outsides (due to rotating the tires). I've had the right main brake line fail at the fuselage joint, and I'm thinking that it is most likely due to the shimmy.
Thanks in advance.

Vic
 
Not a direct reply to your question Vic, but worn (flat spotted and/or out of balance) tires are THE driving factor when I have shimmy on my -6.
 
Main Gear Shimmy

I had the exact same problem on my 6A - main gear shimmy between 26 & 33 mph on rollout. I never installed the wood dampers on mains or nose legs.

The solution is to static balance all the tires and apply self-adhesive weights as needed.

tirebal.jpg


Use a balancer like this http://www.desser.com/accessories.html and search for these weights "BALANCE TAPE ON WEIGHTS PACKAGE 10 STICKS" at Desser Tire, ~$15.

I just replaced all my tires before OSH and used Desser Recaps (with Michelin Airstop tubes) for the mains and a new "Lamb" tire & tube from Van's on the nose.

My nose tire took 1oz, one main took 3oz and the other took 4.25oz, the original tires took about the same amount.

The results are impressive - I have no noticeable shimmy at any speed.

See this page http://www.desser.com/mounting.html for more info about balancing.
 
RV10 Main gear shimmy

I experienced the same maingear shimmy and, like Vic, had someone watching when I landed. The right main looked like a basketball being dribbled down the court. I removed it and it took almost 4 oz of weight to get it close to being balanced. The shimmy is all but gone now.


Bill Stegemann
RV10 N545RV
116 hours
 
Thanks, guys. I will get new tires on order and balance them and let everyone know the results.

Vic
 
RV-10 Nose Wheel Shimmy

There is a certain taxi speed when I get a shimmy. Faster and it stops, slower it stops. Any ideas? Is the nose gear like the other RVs needing a certain "break out" value for wheel tightness? I did not build this plane.
 
I'm sure you checked the obvious, bearing torque and wheel balance.

Almost all nose wheels have a speed where some vibration is more apparent, kinda a harmonic thing, but it shouldn't be severe. Has the vibration gotten worse over time?
 
Use the search

This has been addressed a few times already in this forum, use the search function, or just scroll through old posts.

There seems to be 3 main causes------tire balance/out of round, loose bearing crush/pre load, and fork breakout force.

The Matco wheel provided is not too tolerant of things being out of whack.

Here is one example http://www.vansairforce.com/community/showthread.php?t=17878

Good luck,
 
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Larry,

Did you buy an RV10? Fill me in on the details..........gonna be at the next York Breakfast with it? Inquiring minds wanna know.................:)

Dean 805HL
 
Thanks to all who posted. I'll work on all of the "Big 3".

I sure do like this site when guys who have 'been there, done that" help out. I really appreciate it guys.

Yes, I did buy the KC 10, no I won't be in York, family stuff weekend. ;) It needs alittle more "dressing up" to get to the level of your 10. That is one FINE aircraft you built.
 
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I'm sure you checked the obvious, bearing torque and wheel balance.

Almost all nose wheels have a speed where some vibration is more apparent, kinda a harmonic thing, but it shouldn't be severe. Has the vibration gotten worse over time?

Seems to be fairly steady, worse with the more weight in the plane. I just built my wing jacks last night, and I'm working on the front wheel this AM. The weather here has been great for duck hunting, but not good for flying.
 
Nose wheel shimmy

This is just a thought on the nose wheel shimmy. I read an article about pipers having shimmy problems and they replaced dampers and tires etc.
Someone recommended balancing the wheel pant using the axel as
the CG. They added a little weight to either the nose or tail as needed and seemed to cure his shimmy. I am building a 10 also and just thought I would pass this on.
 
I have had a shimmy in my mains every since my first flight. I know I have posted before on this but I was talking with another RV-10 builder who mentioned that a higher tire pressure has fixed this. Not only that but that the 42 psi that Van's recommends may be too low for our tires and that 60 psi might be better and what the stock tires recommend.

First the shimmy issue, I have done some research on this and have found that landing gear shimmy is typically poor alignment and wheel balancing and tire pressure will not affect it much. In fact, there are many that say to decrease tire pressure to decrease shaking in the landing gear. My mains shimmy around 30 mph. It is worse if I brake through the 30 mph which makes sense as it causes toe-out.

As for the tire pressure, I am currently running Goodyear Flight Custom III and their technical specs have a rated inflation pressure of 68 psi.

I might try increasing the tire pressure as another RV-10 pilot increased his and saw an improvement in the main wheel shaking.

Any thoughts on this? Where did Van's come up with 42psi?
Any harm in running 55-60 psi?
 
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I have it also at around 30MPH........ My plane partner tells me that Qantas SOP required taxi speeds less than that :rolleyes:

Seriously though..... more pressure, less rubber on the road so less effect from misalignment.

I cant see a problem, and may well try it in fact!

I would rather find out how to get a few more knots out of the machine!

DB
 
One thing that I think gets overlooked with shimmy sometimes is the bearings. If the axle nut is too tight pressing the bearings into the races or the bearings are poorly greased it can cause shimmy. The shimmy in my case was what I would categorize as "severe"...as in the airplane felt like it was coming apart. The axle nuts were too tight. I had the shimmy develop and I jacked the airplane and tried to spin the tires but the left one was obviously too tight. I pulled the wheels, very carefully inspected the bearings and races and repacked the bearings and reassembled. Everything worked perfectly and has been working perfectly for 230 hours since and no signs of shimmy.
 
Out of round..

....Was the cause for our shaking. I thought it was the nosegear but on landing, I happened to look out the right side while my buddy landed and saw the shadow of the right wheel move back and forth what appeared to be a foot!

On closer inspection, it was really worn out of round with some grooves only going half way around the tire. A new one resolved the problem.

Regards,
 
Nose wheel shimmy

Our 10 suffers from a bad shimmy for a long time which appears to be the nose leg.
On landing there is no problem but it always starts when decellerating to about 35 knots. It feels like the plane is coming apart.
A short firm brake kick dropping the nose stops the vibration.
The nose wheel is staticcally balanced and by exiting it fast by a handdrill no out of roundness or vibration is shown.

Someone looking at the nose gear along the runway reported strong bouncing of the leg.

Could permanent compression of the damping rubber rings be the cause ?
When we lift the nose the vertical play of the leg is about 1/2 inch.
I ordered new rings at VANs to make sure.

Any ideas ?
 
Our 10 suffers from a bad shimmy for a long time which appears to be the nose leg.
On landing there is no problem but it always starts when decellerating to about 35 knots. It feels like the plane is coming apart.
A short firm brake kick dropping the nose stops the vibration.
The nose wheel is staticcally balanced and by exiting it fast by a handdrill no out of roundness or vibration is shown.

Someone looking at the nose gear along the runway reported strong bouncing of the leg.

Could permanent compression of the damping rubber rings be the cause ?
When we lift the nose the vertical play of the leg is about 1/2 inch.
I ordered new rings at VANs to make sure.

Any ideas ?

Have you checked the bearing pre-load? This can be challenging if not using the matco axle, which I recommend.

Larry
 
I have had a shimmy in my mains every since my first flight. I know I have posted before on this but I was talking with another RV-10 builder who mentioned that a higher tire pressure has fixed this. Not only that but that the 42 psi that Van's recommends may be too low for our tires and that 60 psi might be better and what the stock tires recommend.

First the shimmy issue, I have done some research on this and have found that landing gear shimmy is typically poor alignment and wheel balancing and tire pressure will not affect it much. In fact, there are many that say to decrease tire pressure to decrease shaking in the landing gear. My mains shimmy around 30 mph. It is worse if I brake through the 30 mph which makes sense as it causes toe-out.

As for the tire pressure, I am currently running Goodyear Flight Custom III and their technical specs have a rated inflation pressure of 68 psi.

I might try increasing the tire pressure as another RV-10 pilot increased his and saw an improvement in the main wheel shaking.

Any thoughts on this? Where did Van's come up with 42psi?
Any harm in running 55-60 psi?


I didn’t have any shimmy with the kit tires until I replaced them with the same Goodyear tires Scott has.

When I first replaced them I used that factory pressure settings and had the stereotypical shimmy. I increased the pressure and the shimmy went away.
 
With the standard axle and spacer bushings there is not much you can change to pre-load.
I find the pre-load is quite low and I can wiggle the wheel a bit left to right.
The only way to increase the pre-load is to machine the bushings sltghtly shorter, but how much ? How do you measure this ?

I have not seen the Matco and will have look.

I have experimented with tire pressures from low to very high , but there is no difference at all.
 
If you can wiggle the wheel and feel it moving, there is a decent chance that could be your issue. In all my years, I have never been able to move a wheel side to side if the tapered bearings were set correctly. The matco axle is only $70 and I would definitely buy it if I could wiggle my wheel side to side.

Larry
 
No success

I have tried all you guys tips but nothing works
Its is keeping me busy for two years now..

It only happens in decelleration during landing around 25 to 30:knots when the plane shakes violently and it feels like it is falling apart.
I keep the nosewheel off the ground as long as I can but shortly after dropping the vibration starts.

On the camera attached to the fuse it looks like the wheel is bouncing up and down instead of sideways, but its difficult to see when the whole plane shakes.

I have modified the wheel shaft so I can adjust the bearing pre-load. No change
Removed play of the leg hinge and put filler rings between the damper blocks. No change
Varied sideforce and tire pressure. No change
Fitted a new tyre and had it dynamiccally balanced and checked roundness.. No change
Flew without wheelpant to change eigen frequency. No change

My last but not favorite ideas are stiffen the nose leg and install a damper, but these require quite a lot of work.

Any ideas ?
 
Have you tried 50psi in the tires? I have a slight shimmy at that same speed, but it’s the main gear, not the nose gear.
 
Full disclosure - I don't have a -10, but my Wheeler Express nose gear is a castoring design almost identical to the -10 fork and and I have had to resolve the same kind of shimmy issues discussed here, including front shimmy in certain taxi speed ranges, and the violent shake like the plane is coming apart on landing as brakes begin to get applied. So, here are some comments:
1) In general, I personally wouldn't give much credence to tire pressure, small amounts of slop in bushings, bearings, etc. being the primary shimmy cause. If changes in those areas "fix" a shimmy problem, I would contend that it has merely moved a resonance to a different frequency without actually fixing the root cause, and you'll just re-find the problem at a different speed or condition.
2) That said, these main tires should in fact be run at 68 PSI, and the nose at 35. Lower increases your take off roll and tire wear.
3) Nose wheel shimmy, if the fork geometry is designed right with a negative upward rake angle (which I believe the -10 has correct - i.e. moving the fork and wheel sideways from center lifts the nose up, so gravity has a natural tendency to center the wheel) is primarily the result of insufficient friction in the turning force. Needs to be tightened to where about 20 to 25 pound force at the back of the fork is needed to turn it.
4) There may be more that goes on with the -10, but in my case the severe shimmy/shake on landing turned out to be a lack of toe in. Toe in was set many years ago to 1.5 degrees, but it turned out over time the gear legs, with many - some hard - landings - had lost their toe in, in fact gone to about 1 degree toe out - which is a disaster for landing roll straight line stability and tendency to shake violently at the drop of a hat.

So, I would advise highly to check toe in. Yes, I believe there is no adjustability for it on the -10, but if you don't have toe in, I'll bet that is the cause for the shakes, and there will need to be found a way to get toe in.
 
I had the same problem at same speeds but maybe not to the degree you describe. When I replaced the Vans tires with Desser retreads the problem mostly went away.
 
My last but not favorite ideas are stiffen the nose leg and install a damper, but these require quite a lot of work.

Any ideas ?

I solved similar problem (mine happened decelerating through about 35 knots as I recall) by adding wooden shimmy dampers to the aft side of each main gear leg.

Van's RV-6 plans (attached) include instructions on making a damper. For my RV-10, I only made the aft portion, using Lowes molding. I sized my RV-10 shimmy dampers so they fit inside the standard RV-10 gear leg fairing. I taped them on with fiberglass reinforced strapping tape. Problem solved.

After several years, the shimmy started to return as the strapping tape stretched. I reapplied strapping tape, problem disappeared.
 

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Shimmy

The tyre has been changed and was perfectly balanced dynamically and was checked for roundness. This is not the cause to me.
i have set side force to many values as well as tyre pressure. No effect
Now side force is 25 lbs, tyre pressure 35 psi and main to 68 psi on the main.

I am pretty convinced the problem is the nose gear. Shimmy starts shortly after the nose wheel drops on the runway after holding off as long as possible and decelleration from sat 65 to 35 knots..

Maybe I should check again with the camera if its really the nose causing it.
The main leg stiffening looks simple but I have never hard of Lowes molding or window molding over in Europe. The shape is no problem but what material or wood type is it ?

The toe in is a very interesting one. i noticed the problem got worse over the last 250 flying hours possible losing the toe in on imperfect landings. That is worth cheching and seems a viable cause to me.

Anyway new ideas to keep me busy.
Thanks very much.
 
The toe in is a very interesting one. i noticed the problem got worse over the last 250 flying hours possible losing the toe in on imperfect landings. That is worth checking and seems a viable cause to me.

I'm going to play devil's advocate on this being the cause.

If it fixed N49EX's problem, then maybe there's a dynamic at play I'm unaware of. However, I was an auto mechanic for 15 years that specialized in alignments and suspensions on cars. I realize a car suspension and airplane suspension are different, but toe-in (or out) on a car will NEVER cause a vibration on it's own. If toe is off (in or out) the two sides will always "equalize" themselves simply by steering the car straight, or in the case of a plane, steering it straight via rudder or brakes. The toe-in (or out) will always be equal between the 2 sides, therefore the effects are equally opposed and because of this, not felt by the driver. (Even though it will wear tires if improperly set.) The exception to this is if toe-in is significantly off. By significant, I mean 1/2" (visible to the eye) not the normal 1/16" that is only detectable by measurements.

It IS true that toe-in or out can create uneven wear patterns that affect tire balance.... but toe-in by itself can't be felt by the driver.

Again, this is based on years of auto experience, not a planes landing gear. But, since changing toe angle on an RV-10 would be a significant task to correct, thought I'd offer this up as food for thought before you chase a rabbit down a hole that might not make a difference.
 
If it fixed N49EX's problem, then maybe there's a dynamic at play I'm unaware of. However, I was an auto mechanic for 15 years that specialized in alignments and suspensions on cars. I realize a car suspension and airplane suspension are different, but toe-in (or out) on a car will NEVER cause a vibration on it's own. If toe is off (in or out) the two sides will always "equalize" themselves simply by steering the car straight, or in the case of a plane, steering it straight via rudder or brakes.

.....before you chase a rabbit down a hole.....

Agree for a car. In a car the steering has a pretty tight grip on the direction of the wheels and there is no mechanism for the wheels to move in or out. And brake force inherently gets applied equally to both front wheels. And the fixed back wheels add another component of straight line restoring force.

On a plane with spring or tubular struts, the wheels have a lot more motion latitude. Forward motion with toe in slightly raises the plane as the gear moves inward, while with toe out the plane lowers slightly. The feedback loop between brake or rudder action and wheel/plane directional response is relatively loose and certainly capable of energizing instabilities in a number of ways, and certainly doesn't have any capability of suppressing an oscillation the way that car steering has a hold on the wheel direction. Toe out in a plane with any kind of gear leg lateral flex capability will definitely result in squirrely weaving down the runway.

In any case, all I was suggesting is that if you have a main wheel oscillation, at least check the toe in - that's not a rabbit hole.
 
The main leg stiffening looks simple but I have never hard of Lowes molding or window molding over in Europe. The shape is no problem but what material or wood type is it ?

Lowes is a U.S. home supply store. I think I used Ash.
 
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