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"A" Model Nose Wheel Shimmy

C

Chofrock

Active Member
I am going to order my RV kit soon, and thought I had decided on a Tri-cycle landing gear, better visiblity, it is what I am used to, etc. Then, I spent a Saturday helping out at Home Wing Fly-In in Scapoose. I had the chance to watch several RVs land, and I noticed that many of the tri-cycled landing gear planes had a shimmy in the nose wheel.

Frankly, this scares me a lot.

Is this something that is completely normal and should not bother me? Does this shimmy cause any problems? Is there any way to keep this from happening to my plane?

Thanks
Clay
 
Any potential shimmy is controlled by keeping the correct axle nut torque. I'm pretty sure that's covered in the preview plans book somewhere.
 
The previous post is exactly Right

I have experienced the shimmy, that is actually an understatement. it shakes so bad I thought I had blown the nose tire the first time it happened. Then I thought I had let the nose down too soon and on my next landing I rolled the mains on with nary a squeek and held the nose off until it couldn't be held off any more - bang-bang-bang-bang-bang all the way until the plane stopped moving. Then it taxied like a pussy cat. I had torqued the nose gear and set the breakout force as described in section 10 to 23 lbs (the book actually says 22 lbs) and I have no holes in the nose fairing for an easy way to check the breakout force so checking it is not high on my things I like to do list. Off came the fairing and sure enough the the breakout force was way down (I don't remember the number if it even registered on my coarse fish scale). I retorqued and tested until I had it up to 24 lbs. and the problem went away completely! Several months later after I had retired and moved to Arkansas it happened again. There was no hesitation this time I removed the fairing retorqued the nut and kept testing until the breakout force was back up to 24 lbs and there has been no recurrence so far. The manual gives a detailed procedure that allows you to get rid of some of the "give" in the system but with wear and "settling" it probably will recur less and less frequently as the system ages. If it happens check and reset it immediatly (or as soon as you get home) and check it annually during the condition inspection is my humble recommendation. It is a heck of an airplane and nosewheel shimmy is NOT something that you "just have to live with." All of the reasons for the emergence of tricycle landing gear as the landing gear configuration of choice for production airplanes are just as valid for the RV series. The tricycle landing gear configuration is harder to build on the RV-6 and I assume the RV-7 is the same; the extra big wheeled prong probably makes it a little slower; if you lose brakes you also lose taxi steering; etc. etc. I went with the tricycle gear strictly because my wife insisted on it and during the build process I cussed the unnecessary complications I had to deal with because of that choice. Now that I am done with it, having spent 50 years in aerospace, I wonder at the wisdom of this little lady who knew the right choice for us and her elevation above my petty belly aching about it. You will not be disapointed if you prefer tricycle gear and build one. Don't let the shimmy shake your resolve.

Bob Axsom
 
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They all shimmy

If you ask me, given the right conditions, they all shimmy. Watch a Grumman land some time and you're liable to see the same thing. Castoring nosewheels shimmy -- it's the nature of the beast. Most of the time you don't even know it's doing it and it's not hurting anything.

But that bone-jarring, machine-gun shimmy that Bob's talking about can definately be controlled with the proper nose gear torque and low air pressure -- and one other thing.

That other thing is the bolt at the top of the gear that holds the gear in the engine mount. I don't know if this what they ship nowdays, but Vans gave me a nylon stop nut to use on that bolt. That nut sits right over the exhaust stacks. The heat would cause it to loosen up every 25 hours or so, which would let the gear leg rotate a little in the socket and cause a severe shimmy. I replaced that nut with an all-steel stopnut (that should have been in the kit to begin with), and haven't had a shimmy that I could feel in the cockpit in the last 100 hours.

But every now and then, someone will still come up to me all concerned and ask me, "Did you know your nose gear was shimmying on that last landing?". I just tell them they all shimmy.
 
Nosewheel Shimmy

I have to disagree with Mr Baker, they don't ALL shimmy. Mine did when I first bought it because the builder didn't have the proper tension torqued in on the nosegear nut.
It's a very easy adjustment that took about five minutes using a digital fish scale to measure the resistance.
Now, 300 hours later, I NEVER have nosewheel shimmy at any landing speed.
 
mrreddick said:
I have to disagree with Mr Baker, they don't ALL shimmy. Mine did when I first bought it because the builder didn't have the proper tension torqued in on the nosegear nut.
It's a very easy adjustment that took about five minutes using a digital fish scale to measure the resistance.
Now, 300 hours later, I NEVER have nosewheel shimmy at any landing speed.
Click to expand...

It's impossible to build this plane without being aware of the procedure to set the nose gear torque -- fish scale and all. But if it's such a slam-dunk fix, how-come the issue comes up so much?

In my post, I suggested two explanations.

1) Some shimmying might be caused by a nylon stop-nut used in the high-heat area over the exhaust stacks. That's what was causing mine.

2) All castoring nosewheels shimmy a little, given the right conditions. But if you can't feel it in the cockpit, I say don't worry about it.
 
My 6A was good for a couple of hours initially then developed a terrible shimmy. Checked fork breakout force and it was down to about 10 lbs. Tightened nut up to get 22lbs. again and shimmy went away and has stayed away now for 90 hours. It was so bad a one point that I thought I would strike the prop, the whole leg went into an orbital motion and the wheel pant touched on the leg fairing which was over a 1/4 inch away! The panel was a blur. Scared the crap outta me.

The nose leg itself is a bit on the spindley side and does not offer great dampening when the nose touches down, you get some bouncey, bouncey happening sometimes. It does work well enough if the breakout force is within specs.

Having a fair amount of time in Grummans, these can be really bad as well. One thing I have found in both aircraft, watch having yaw present on touchdown, the nose gear and fairing want to weathercock into the relative wind. If the nosewheel touches down, cocked, it can set off this wicked orbital motion.

I think if you set it up right, you will be happy with the tri-gear. Probably safer for most people in the long run. There are a lot of ground loop accidents in the NTSB database on tail wheel RVs. I would consider this aspect more important unless you are a really skilled tail dragger pilot.
 
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Nose wheel Shimmy

I read a post somewhere (can't remember where at the moment) about balancing wheelpants to help eliminate shimmy. The technique is to epoxy lead shot in the nose section of the pant to balance it about the axle line. I think they recommended doing the main gear also.
I'm just building my empennage, so I can't report on whether, or how well, it works...

Dennis Glaeser
7A Empennage
 
The trick of balancing wheel pants actually came from the Grumman crowd many years ago. It does work, but also adds weight (obviously).
Mel...DAR
 
How to?

I'm not a builder (yet! :) ) but was wondering if someone has a reference of how to ballance the wheel pants to help minimize they shimmies! Would probably help out the whole group.

Thanks,

Greg
 
I don't want to question what is said to work

I don't want to question what is said to work but I have to. The nose wheel fairing is like a feather compared to the mass and arm of the rest of the pivoting system. Based on my experience with the system as reported earlier I simply can't see the source of improvement nor can I see that there is any improvement that could be sensed and therefore be worth pursuing. The nose gear fairing is already balanced at its CG so where do you move the CG to achieve an improvement? Ther is no way to add enough weight in the nose cone to move the CG of the whole wheel assembly to the pivot point but if you did what is the effect on function? If you only move the CG of the fairing to the pivot point what effect will that have? I want to believe but I need some rationale at least.

Bob Axsom
 
Bob Axsom said:
I don't want to question what is said to work but I have to. The nose wheel fairing is like a feather compared to the mass and arm of the rest of the pivoting system. Based on my experience with the system as reported earlier I simply can't see the source of improvement nor can I see that there is any improvement that could be sensed and therefore be worth pursuing. The nose gear fairing is already balanced at its CG so where do you move the CG to achieve an improvement? Ther is no way to add enough weight in the nose cone to move the CG of the whole wheel assembly to the pivot point but if you did what is the effect on function? If you only move the CG of the fairing to the pivot point what effect will that have? I want to believe but I need some rationale at least.

Bob Axsom
Click to expand...
I think that the "balancing" by adding weights does not actually balance anything as much as it lowers the natural frequency of the oscillation down below the frequency of the excitation.

The wheel/gearleg/friction block system is simply vibrating due to an input excitation. When the excitation frequency is very close to the shimmy mode, the wheel responds ever more violently until your speed slows to the point that excitation is outside of the resonance.

You can do several things to change/ reduce the shimmy. Increase damping (tighten nut), change frequency response of wheel (add weights to fairing. It's like a spinning skater putting out their arms to slow the spin rate) or change the spring rate of the nose gear itself (use a larger or smaller diameter gear leg). Change the castering geometry (I actually think this has the most promise for a real solution but it also has the problem of testing new designs that most of us can't easily undertake).

Some of these are easy, some aren't but the bottom line is to do something that changes the resonant frequency of the wheel oscillations given that we have to live with the current caster geometry.

Study shopping carts and try to determine what makes some of their wheels shimmy. Then avoid that condition on your nosewheel.

-Mike
 
OK - good input

Basically, that says control the breakout force by tightening the retaining nut to control the breakout force as described in the manual is the practical solution - I couldn't agree more.

Bob Axsom
 
Ever since I became a member of VAF (April 2005) I have read with great interest all the threads related to the design of the "A" model nose gear. I have seen the pictures of collapsed nose gears and watched the videos showing the oscillations of the nose strut. I pondered the various theories, but never really thought about what could be causing this problem. The recent thread about using 3D CAD software to model and analyze the nose wheel really got me thinking about how this could be anlayzed. This in turn has me really thinking about what might be causing these failures.

Some background about me: I'm a mechanical engineer and have worked in the aerospace industry for the past 13 years. I use Pro Engineer just about everyday to design and model hardware. While I'm not proficient at using them, I am familiar with both NASTRAN and Pro Mechanica, which are structural analysis software packages. I work very closely with structural analysts who are masters of this software, to run detailed computer analysis of my designs.

I haven't done any analysis to back this up, so take this as anecdotal information at best. It appears to me the "A" model nose gear is designed with to much caster which allows the nose wheel to shimmy. With the exception of the Bellville washers applying a friction load, there is no mechanism to damp out nose wheel shimmy. Nose wheel shimmy can cause two things to happen: 1) impart an oscillating load into the nose gear leg which can couple with the natural frequency of the strut causing large oscillations (as seen in the videos) 2) The loads imparted by this motion can cause fatigue cracking and eventual failure over time.

In several pictures of failed nose gears the nose wheel appears to be 90 degrees to the strut. This could indicate nose wheel shimmy prior to the failure of the gear leg. If the nose wheel begins to shimmy and is not damped it could turn and at some critical angle (maybe 45 degrees?) cause the nose gear to collapse.

Here is an interesting read on nose wheel shimmy and the efforts that have gone into controlling it: http://www.triplanebuilder.com/cgi/articles.cgi?which=wheelshimmy.

Just a theory.
 
So far, I've been in seven different "A" models and no shimmy. That's five 6A's, and two 9A's. Some had the wood dampeners, and some didn't.

Therefor, I don't think it's an across the board design problem.

L.Adamson -- RV6A
 
The Belleville washers impart the damping to the fork. If the preload is correct, I've never had shimmy. If too loose, you sure can get it under the right conditions. If the motion diverges and reaches high enough deflection on the leg, failure will result. I doubt if many suffer fatigue failures. If you always have a shimmy, you better find out why and fix it.

The leg itself if not particularly stiff in any direction, designed to spring up and down with the forward raked angle, it can deflect just as easily laterally.

The leg failures on soft or uneven ground are hardly a mystery- aircraft traveling at X velocity has considerable inertia, the fork nut hits something solid and stops, aircraft keeps going, leg folds up. Most of these are not proceeded by shimmy.

The Grumman AA series use a castoring fork and are equally prone to shimmy when the preload is too low. The leg itself is far stiffer and stronger however so you rarely hear of one folding up.

I've had severe shimmy in both aircraft and it scares you. You can only pray it stops and does not fold up on you.
 
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rv6ejguy said:
The Belleville washers impart the damping to the fork. If the preload is correct, I've never had shimmy. If too loose, you sure can get it under the right conditions. If the motion diverges and reaches high enough deflection on the leg, failure will result. I doubt if many suffer fatigue failures. If you always have a shimmy, you better find out why and fix it.

The leg itself if not particularly stiff in any direction, designed to spring up and down with the forward raked angle, it can deflect just as easily laterally.

The leg failures on soft or uneven ground are hardly a mystery- aircraft traveling at X velocity has considerable inertia, the fork nut hits something solid and stops, aircraft keeps going, leg folds up. Most of these are not proceeded by shimmy.
Click to expand...


Thanks for the data point Ross. These thoughts are based upon my looking at photos and what's on Van's site. I haven't actually seen an A model in real life or the plans for that matter. So as I said before this is analysis is anecdotal at best.

The failures where the nose wheel hits a pot hole causing the fork nut to hit are obviously a no brainer. It's the ones like the recent failure in San Diego that are a mystery to me.
 
It's a "systems problem"

and the system includes all components from the tire to the motor mount (and probably a little bit more ) plus the operating environment (including the pilot and runway surface). I'm and engineer too, but have no experience with design of similar systems. However, it seems to me that the solution is to change the natural frequency of the system so that it is is far removed from the "driving frequency". Drivers can include nose wheel speed, pilot technique, imbalance, out-of-round, tire pressure, drag in the nose-wheel bearings (Grove nose gear solution?), pilot induced loads, and probably more.

A secondary set of solutions can be found in dampening of the system. As I recall, dampening a system is OK, but it's capability of preventing a failure is secondary to designing so that the natural frequency is far removed from the drivers' "operating frequency" being close to the "system" natural frequency. Tacoma Narrows Bridge anyone? Dampening in the system includes yoke preloads, wheel bearing drag, and the gear leg itself (with or without the wooden "stiffener").

Bottom line, is we can do lots of things that will improve dampening, but my first approach will be the Grove nose-wheel, followed by a wooden/graphite stiffener to change the frequency of the system...

I'll let you know how it goes in a few months...

90% done, 90% to go...
 
Good Point!

frazitl said:
and the system includes all components from the tire to the motor mount (and probably a little bit more ) plus the operating environment (including the pilot and runway surface). I'm and engineer too, but have no experience with design of similar systems. However, it seems to me that the solution is to change the natural frequency of the system so that it is is far removed from the "driving frequency". Drivers can include nose wheel speed, pilot technique, imbalance, out-of-round, tire pressure, drag in the nose-wheel bearings (Grove nose gear solution?), pilot induced loads, and probably more.

Bottom line, is we can do lots of things that will improve dampening, but my first approach will be the Grove nose-wheel, followed by a wooden/graphite stiffener to change the frequency of the system...
Click to expand...

I completely agree with all the statements above. It is a "systems" problem. The goal of the engineering is to as much as possible insulate the mechanical system from the human system, if you will. What I mean by this is the design should be robust enough to handle pilots who are less than graceful. I'm in no way passing judgment on this design, I'm stating that this is a goal of a well engineered design.

Raising the natural frequency of the gear leg is a good thing, I'm guessing that solid tube has a pretty low resonance. However, the damping I believe is needed in the design is not damping of the nose gear leg, but rather the nose wheel bracket assembly (All caveat's I've stated before apply, this is just a theory, and I don't know if you can even call it that). In one of the videos you see the nosewheel shimmy back and forth as the airplane accelerates. It is this motion which I think needs to be damped.
 
I don't see anything wrong with the fork design and the Belleville washers. The standard wheel bearing setup is poor IMO and I've commented on this before. Not too hard to fix that properly.

The leg is not robust for ham fisted pilots nor rough terrain. It has very poor damping and acts like a pogo stick under certain conditions. I question how much spring is really needed on the nose leg. We shouldn't be landing on it and I don't care much how an airplane "rides". A larger diameter tubular leg along the lines of the RV10 leg would be much stiffer but the -10 has rubber donuts doing the springing via pivots and linkage. This design is not easily retrofitable to the existing mount structure.

It is hard to come up with a better design which would simply bolt on to existing mounts- without some welding. The first person to come up with a better design and offer the parts as a kit at a reasonable price would sell hundreds I'd guess.

Wood stiffeners will change the resonant frequency of the leg to a small degree but make almost no significant difference in stiffness or consequent deflection. I think spring steel has about 20 times the elastic modulus of most woods. I would be very interested to see what computer analysis or actual testing would show in this area.

Finally there has been talk of improper heat treating of some of the legs with "mystery" failures. Did the one fellow here on VAF ever follow through on getting his leg tested?
 
beating that jar of glue

jtrusso said:
Some background about me: I'm a mechanical engineer and have worked in the aerospace industry for the past 13 years. I use Pro Engineer just about everyday to design and model hardware. While I'm not proficient at using them, I am familiar with both NASTRAN and Pro Mechanica, which are structural analysis software packages. I work very closely with structural analysts who are masters of this software, to run detailed computer analysis of my designs.
Click to expand...


John,
Have you looked at what loading would cause the gear to fail due to eccentric loading on the landing gear, causing column failure? (as compared to just exceeding a "design load" in bending) Seems to me there could be a number of items that cause the loading 1.) drag of matco wheel 2.) FAA says Van was wrong and fairing would not cause drag.. but 3.) landing occurred while drifting and side load started a sequence of increased drag/load of nose gear (wonder how that Matco does in such condition) 3.) the "bump" taken at speed caused significant axial loading,.. beyond the expected rolling resistance... with spike in axial,.. then failure tree started.

Did the gear fail and nut dig in, or did nut dig in and gear fail? We might also look at how we decide to go across those bumps,.. either straight on or at angle

So,..ASSUMING this WILD guess could be right,... if one were to calc the required failure loading, and then go looking for ways to reach it,... we might decide how to stay inside the envelope.
 
Your looking at the wrong video

jtrusso said:
In one of the videos you see the nosewheel shimmy back and forth as the airplane accelerates. It is this motion which I think needs to be damped.
Click to expand...

Although the video is interesting, it has nothing to do with real "A" model operation. It shows slowly going to a high speed taxi. This is not a recommended thing to do with a RV and most other small planes. RV are designed to fly and not drive.

Check out the videos that I made. I show both paved and grass takeoff and landing. No high speed taxi.

http://www.vansairforce.com/community/showthread.php?t=19641&highlight=kent+video

How to take off:
1. Line up to runway heading.
2. Hold stick full back.
3. Apply full power (note that planes nose raises some, less weight on front wheel)
4. When nose wheel leaves ground (about 3 seconds latter), ease back on stick, but keep nose off ground.
5. Leave ground and don't return until your ready to land.

How to land:

1. Line up to runway heading. (Your on final)
2. Maintain speed at 1.3 x stall.
3. Pull back on stick and reduce power as you enter ground effect.
4. Keep the nose wheel off the ground.
5. Let the plane settle on the MAIN wheels only.
6. Hold the nose up (but not high) and don't use brakes unless necessary.
7. Keep pulling the stick back as you slow down.
8. When the stick is almost all the way back, it is time to lower the nose to the ground by easing forward on the stick. Let the wheel touch lightly.
9. Slow to taxi speed (5 to 10 mph).

You need to practice the above to be good at it.
If you miss some of the above steps your plane might not last as long and you made need to replace more then your nose wheel.

I am all for coming up with a better wheel/gear, but not if it compromises the flying characteristic of my plane. After all I built it to fly not drive down the runway.

Kent
 
kentb said:
Although the video is interesting, it has nothing to do with real "A" model operation. Kent
Click to expand...

The video was relevent to real "A" model operation on that RV because the shimmey still happened on that RV during takeoff and landing with the airplane flown as per Kents procedures. The shimmey was not as long as in the video but it was still there. The nose wheel has to come down at some point and then it would shimmey even with full back stick.
 
A little misleading...

rvator51 said:
The video was relevent to real "A" model operation on that RV because the shimmey still happened on that RV during takeoff and landing with the airplane flown as per Kents procedures. The shimmey was not as long as in the video but it was still there. The nose wheel has to come down at some point and then it would shimmey even with full back stick.
Click to expand...

There seem to be a number of people that after seeing this video conclude that the nose wheels on all A model are on the verge of destruction. I don't doubt that the plane has a shimmy problem. I sometimes feel a little shimmy in my gear, but it by no means make the plane unsafe to fly.

I just want others to realize that the video shows that bad shimmy in a mode of operation that is not under normal usage.

What ever happened to this plane? Did the shimmy problem get resolved and how?

Kent
 
I'm curious

I wonder what the use of full flaps during take-offs and landings contributes to these problems? It seems to me that the increased downward pitch moment plus decreased elevator authority in this configuration could increase the load on the nose gear directly, and indirectly by longer contact with the ground at higher than desired speeds.

So far, I haven't seen this issue addressed either in the NTSB investigation or on-going discussions in the forums here. Inasmuch as I have frequently encountered comments by pilots here who routinely use both full flaps plus carry an extra 10kts or more "insurance" on final, I am curious if that has any bearing on what is happening here and on tip-overs. Anyone else?

Cheers, Joe.
 
I doubt if many RV pilots use full flaps on takeoff and there is really no need to use full flaps on landing most of the time. If you do landings clean most of the time then switch to a full flap landing, the attitude is quite different and could cause the inattentive pilot to touch nosewheel first. This is certainly pilot error. RVs can be landed nicely with any flap configuration using the right technique.

I personally prefer clean landings and just use half flaps if I need to fly slow behind some Cessnas on approach.
 
Hi Joe

Don't know the answer, but my guess is that it doesn't matter that much when you are at takeoff or touchdown speeds.

I don't use flaps for takeoff. I get off the ground so quickly that I don't think it would make much difference in time before airborne.

On landing I use full flaps (unless a very strong x-wind). The idea is to be at the slowest flying speed when on final approach. When in the flair and holding the nose up, the plane will slow to below stall speed in ground effect before the mains touch the runway. I don't know what this speed is because I am always looking outside at this point. My best guess is about 40 or so knots. The front wheel settles at around 25kts.
The next time I take someone for a ride I'll ask them to note the speed at touchdown and front wheel let down.

At the speed of the front wheel let down, I don't think that the speed would be much different, but maybe I could do a little testing of this. The other problem with testing at these speeds it the accuracy of the indicator is falling off.

Kent
 
kentb said:
I sometimes feel a little shimmy in my gear, but it by no means make the plane unsafe to fly.
Click to expand...

It is possible that nose whell shimmy, similar to that observed in this video, could be imparting large loads into the nose gear strut if the frequency of the oscillation of the nose wheel is near the natural frequency of the gear leg. Over time this could lead to weakening of the gear leg and eventual failure. Some alloys of aluminum have a very load fatigue limit (I'm not sure if this is a problem or not as I do not know what alloy of aluminum the nose gear strut is made from).

Again, this is just a theory and has in now way been verified by analysis or inspection, but if this is a common occurrence it could be weakening the nose gear strut over time. This may have been a contributing cause to the mysterious failures of the nose gear legs on hard pavement that have happened (I can think of two off the top of my head).

I plan on doing some basic analysis of this, if anyone can give me details of the design I'll see what I can do. As I'm not building an RV yet I don't have a set of plans.
 
As for full flap landing procedures, I raise the flaps (ok, I start to raise the flaps) just after touchdown. Raising the flaps is just about as effective as continuing to pull back on the stick, and you can keep the nose up longer. I almost always use full flaps on landing as I believe it saves tires and brakes and gives a better view over the nose. I am not saying this is the only way, or even the preferred way to land. It just works for me. I have never had any shimmy.

Bob Kelly
 
kentb said:
What ever happened to this plane? Did the shimmy problem get resolved and how?

Kent
Click to expand...

Hi Kent,

I agree with you. Some RV-6As seem to shimmy a lot and others don't seem to have a problem. It varies a lot from plane to plane.

After trying every other remedy, a wood shim was placed on the nose gear leg which reduced the shimmy a lot.
The owner recently did the nose gear leg/fork SB. He told me the new nose gear and fork combo reduced the shimmy dramatically and he doesn't need a wood shim anymore on the gear leg.
 
rvator51 said:
Hi Kent,

I agree with you. Some RV-6As seem to shimmy a lot and others don't seem to have a problem. It varies a lot from plane to plane.

After trying every other remedy, a wood shim was placed on the nose gear leg which reduced the shimmy a lot.
The owner recently did the nose gear leg/fork SB. He told me the new nose gear and fork combo reduced the shimmy dramatically and he doesn't need a wood shim anymore on the gear leg.
Click to expand...

LOOK AT IT THIS WAY.............. http://www.vansairforce.com/community/showpost.php?p=231999&postcount=176

TRY A GROVE WHEEL AND YOU WILL SEE A CHANGE.
 
nose wheel shimmy

I still have nose wheel shimmy at about 40 mph. I have tightened the tension on the the nose wheel caster beyond the vans recommended and it halped some but still does not go away. Any one else with this problem?
 
Which RV do you have? Do you have the Cleveland, Matco or Grove nosewheel?

Have you had anyone observe the shimmy before from outside the airplane? Is it a side-to-side shimmy or a fore-aft shimmy?

FWIW: My Grove nosewheel is smooth and nice and light weight.

BTW: My nose is never on the ground at 40mph. I have it off the ground at 27kts and higher, take-off and landing -- especially when I'm operating from grass. I have a Hartzell C/S prop too (heavy nose), so I know that anyone can do it.
 
I agree with Jamie that the nosewheel shouldn't be on the ground at that speed. Also, do balance your wheel. it REALLY makes a difference.

Vic
 
Just balanced my RV-10 original Matco nose wheel yesterday. I painted the rim first then placed the wheel on two parallel rails with a 3/8" rod thru it. How do you determine exactly where to put the weights ? Of coarse you let the wheel settle heavy on the bottom. But then do you put the weight directly on center and on each side or two weights off to each side of center (on one side)? How fussy does one get? Does the wheel have to stay absolutely still, no mater where you place it in the 360 degree location?
Thanks Ron
 
The Seager method, beat into my head because I'm a slow learner...that nosewheel needs be lifted as soon as it can on the takeoff roll and stabilized at that point until the wing lifts the mains off the runway.
For landing, you should be in the same attitude you were right before takeoff, ie, that nosewheel should be in the air and the stick should be way back. If you land that way every time, it will do a lot to eliminate all the stress on that nosegear assembly. The other thing that helped me eliminate what shimmy I did have was to inflate the nosewheel tire higher than what Van's recommends. I'm running 42 lbs of air in that tire and it doesn't shimmy. Balance and breakout strength are also an important component of the mixture...you should check the breakout strength at least as frequently as every condition inspection. Follow the "Seager Landing Rules" above, then have someone shoot some video of your nosewheel touching down on landing and look it over. As soon as I machine an adapter for RV wheels that will allow you to take your wheels to the local Les Schwab (or whatever your local tire dealer is), put your RV wheel assy on their fancy balancing machine and have them dynamically balanced...I think a lot of gear leg shimmy (even on the mains) will go away. But...as others have said, keep that nosewheel in the air for as long as it will stay there.
 
Be careful on pulling the stick all the way back when landing these RV's, you could balloon back in the air. I found the best landing are to fly it to the runway, have 70kts on final. When the wheels touch, believe it, the nose WILL be off the runway. Than start pulling the stick back slowely as well as pull off all throttle. Your goal is to have the stick all the way back in your lap. Than as you slow, move the stick slowely forward until the nose touches. If you hit the brakes and have the stick all the way back you could have the nose come down with a slam, that's no good either. Go by feel and make sure the speed is down before you let the nose down.
 
Jamie said:
BTW: My nose is never on the ground at 40mph. I have it off the ground at 27kts and higher, take-off and landing -- especially when I'm operating from grass. I have a Hartzell C/S prop too (heavy nose), so I know that anyone can do it.
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Russ's is a 6A. The 6A's are a bit trickier in regards to lifting the nosewheel, because they are already sitting nose high, compared to 7 & 9As. If you did the same as in a 7/9, the plane will just take off as if you're doing a soft field takeoff.

On my very first landing (RV6A first flight), I let the nose gear down too fast. It shimmied like crazy. I re-torqued the nut, and have not had a shimmy like that since. On occasion, I've got a bit of shimmy after landing, but can get rid of it fast by changing the speed a bit. More than not, there is none.

As to my takeoffs these days, I have the stick back, but move it somewhat forward as the airspeed builds. I'm right on the edge of having the nosegear barely touching the surface or just above. This is really important when carrying a passenger; because if you lift it a hair too high, the plane will take off prematurely. As I said previously, the 6A is closer to a takeoff attitude, when the nosewheel is still firmly planted on the ground. Of course, this does look cooler than the longer legged RV's; and even better if you have the shorter "classic" tail! :D

L.Adamson --- RV6A
 
Main gearleg shimmy (6A)

Thought I would submit my experience to the data base for others to reference.

I developed main gearleg shimmy in my left gear (6a) after I swapped tires due to wear. These are the original tires that came with the kit, and did not have a reference spot to align the stem with. So as a result, when I remounted the left tire, it was not in proper balance. I borrowed a static tire balancer and sure enough, the left wheel/tire was WAY out of balance.

I balanced the wheel with the stick on weights you can get at an auto parts store, and then further secured them with high speed tape. Checked to make sure the bearings were well packed, and properly seated.

I cannot believe how much of a difference it has made. Rollouts are now smooth as a baby's bottom, where before I would get shimmy at around 40mph. If I ever see the need to remove the wheel again, I may deflate the tire, crack the seal and re-clock the tire to get it in better balance. For now, I will go with the weights in place.

Your mileage may vary, but I would suggest you check your wheels/tires for balance.
 
Nose wheel

Yeah maybe the single wheel is at the wrong end but it's the only one I've got!

Greg can you give me the procedure on checking the "breakout force"? I suspect that we are well shy of 20lbs.
 
Phlyan Pan said:
Shouldn't someone throw out the obligatory "you put the single wheel on the wrong end of the plane" ? :D
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No...............Sixes look like "squatting dogs" when viewed with their short fat wings from certain angles... :D

Other than that, the 22 lb. or slightly more, side force is important. Air pressure, out of balance or out of round tires also can have an effect. Keep the nose wheel off as much as possible. I have had severe landing shimmy in the past. Once and a while, I'll get a slight shimmy at a certain speed while taxiing after landing. It's very infrequent these days.

L.Adamson --- RV6A
 
I suspect that you do not know if it is shimmy or out of balance/out of round. Have someone knowledgeable observe the tire when it is doing whatever it is doing.
 
Trying to get an "A" model that doesn't shimmy is like trying to find a smooth shopping cart at WalMart.
Breakout force, tire pressure, type of tire and weight on front wheel all affect.
I had a lot of experience with a Velocity trying to eliminate shimmy which is a much more difficult issue due to no weight on wheel and lower breakout forces (you can't go too tight as the wheel slides in turns)--Also, there's no stops so when shimmy gets a good wiggle going it can literally destroy the fairing and even the fork assembly. My eventual fix was a locking nosewheel. (Here's a link)
http://www.velocityaircraft.com/newsV5/images/noselock/Mishler Nosewheel Lock.pdf

Breakout force--Grummans, Velo, RVs, etc all call for at least 22lbs of pull before the fork moves. Get the nosewheel off the ground and pull with a luggage or fish scale at (or even with) the axle. On an RV you can go significantly higher--your only concern is to keep it loose enough that the nosewheel swivels in flight otherwise you'll have an uncontrollable rudder out front. We've got a few RVs here with 30+ pounds on the pull with no adverse affect. This is the most common issue as they tend to loosen up over time. Take several readings as it will vary.

Tire pressure--key here is amount of rubber on the runway. On some tires as you increase the pressure, the tire eggs and lower/outer portions of the tire no longer contact the ground. The small amount of wobbling this can cause may initiate a shimmy. (Less side to side movement resistance)

Weight on wheel--larger engines and constant speed props get more tread on the nosewheel contacting the surface as well as providing more movement resistance.
 
nose gear bolt

You might also want to check the bolt that holds the nose gear leg on. Best thing to do is have someone hold the back down to get the front wheel off the ground. Then try to see if you can rotate the leg in the engine mount. If so you may have to one of the two fixes. Taper pin or next size up on the bolt. Search the forums and you will find the instructions on the fix.

Here is a link to the wiki instructions.
http://www.matronics.com/wiki/index.php/Nose_Gear_Strut
 
As a purchaser of my 7A and now also someone who doesn't feel a thing in the cockpit, but has an observer on the ground telling me I have a bad nosewheel shimmy.... Can someone lead me to the procedure for checking the breakout force? I see it referred to on a LOT of different threads but no actual reference to the procedure. Thanks.
 
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