Nose wheel shimmy c182H

[benyflyguy]

I have a nosewheel shimmy mid speed. On take off and landing. It a a specific speed range. I keep back pressure elevator to minimize and it still does it. We have had the tire replaced-balanced-shimmy damper refurb you name it. It shook apart a wheel pant on us. Finally got a vid or it
Fast forward to 10 minute mark for takeoff.
any thoughts???

I started to think about rudder trim. If the rudder is trimmed differently will that trim the nose gear as well? We’ve spent thousands trying to get this right.

 

[NordicDave]

This is popcorn topic.

Usual suspects in order of likelihood:

• Loose scissors joint links, need McFarlane link rebuild it
• Shimmy dampener rebuilt
• Worn locking collar
• Sometimes Tire issues

Personal experience with a few planes, it's commonly all the above replaced or overhauled one part at a time hoping not to have to dive into the whole set-up. Tire is least suspect unless there is uneven wear pattern. It's more expensive to take a piecemeal approach. Though sounds like to may have done all this already.

I'd remove the wheel pant and see if the shimmy goes away. Sometimes the pant will catch, shake, and release air in a cycle.

I'm sure the next 3 posts will disagree widely.

 

[wheaties]

This post agrees with @NordicDave. Nose wheel shimmy is, unfortunately, common and can be aggravated by a hard landing (or a series of rough landings.)

 

[Dan Thomas]

I have stuck my oar in on this plenty of times. I have cured numerous cases of nosewheel shimmy by simply dynamically balancing that nosewheel, without touching anything else. Dynamically, not statically, which is about all any airplane wheel gets. If it isn't dynamically balanced, all those expensive parts can only mask the problem for awhile until they're worn out again in short order.

Finding someone to dynamically balance it is the problem. Motorcycle shops often have a dynamic balancer that will fit a nosewheel. The seals and bearings must be out of the wheel. I built my own balancing machine when I went to work in another shop, based on an old machine that I had converted to do nosewheels in the flight school.

You have to think about it. When you buy new tires for your car, what do they do to them before they install the wheels back on the car? They dynamically balance them. That wheel has to be spun to determine the amount and location of the imbalance, and simple static balancers cannot do it, despite what some vendors of static balancers tell you. I, and a lot of other old guys here, remember the days when tire shops had only static balancers, and the steering wheel would shake constantly in cruise, with some speeds being very bad. ANd that was in cars, where the suspension and steering stuff is far heavier and rigid than that in an airplane. The shimmy damper in the airplane is just an attempt to stop shimmy caused by dynamic imbalance and dates from the old days when static balancing was standard practice. Cars NEVER used any shimmy dampers at any time, and dynamic balancing eliminates the need for them. It's funny how we complain about the archaic technology still being used in GA aircraft, and then go and use archaic methods to try to cure shimmy.

Do a search on POA for nosewheel shimmy. I'm not going to redefine it here anymore.

If there are guys posting here giving advice on what to fix, and they have never done a dynamic balance and experienced the result, their advice is badly lacking.

See this: http://www.aircraftmaintenancespecialties.com/tech.php?id=3

TLDR? An excerpt:

Nose Wheel Tire & Wheel Assembly Balance
Balancing the nose wheel/tire assembly is the most important point to check in trying to solve a shimmy problem. Aircraft tire and tube manufacturers paint a red dot on the tire for the "light" spot. A yellow stripe on the tube, or the valve stem should be aligned with the red dot for coarse balance during tire buildup. Then the tire/wheel assembly is balanced with a static type (bubble) balancer and generally does an acceptable job.

However, the preferred method, and sometimes the only method that can solve persistent shimmy problems, is dynamic balancing. (Dynamic balancing is when the wheel/tire/bearing assembly is spun and the proper weights and locations determined electronically). Very few light aircraft maintenance shops have the capability to do spin balancing, so AMS suggests that local motorcycle shops be contacted until one with a spin balancer is found. Usually these shops have the necessary mandrels to mount an aircraft tire/wheel assembly. Balance is achieved by affixing lead weights to the wheels.

Bold emphasis mine.

 

[benyflyguy]

I have stuck my oar in on this plenty of times. I have cured numerous cases of nosewheel shimmy by simply dynamically balancing that nosewheel, without touching anything else. Dynamically, not statically, which is about all any airplane wheel gets. If it isn't dynamically balanced, all those expensive parts can only mask the problem for awhile until they're worn out again in short order.

Finding someone to dynamically balance it is the problem. Motorcycle shops often have a dynamic balancer that will fit a nosewheel. The seals and bearings must be out of the wheel. I built my own balancing machine when I went to work in another shop, based on an old machine that I had converted to do nosewheels in the flight school.

You have to think about it. When you buy new tires for your car, what do they do to them before they install the wheels back on the car? They dynamically balance them. That wheel has to be spun to determine the amount and location of the imbalance, and simple static balancers cannot do it, despite what some vendors of static balancers tell you. I, and a lot of other old guys here, remember the days when tire shops had only static balancers, and the steering wheel would shake constantly in cruise, with some speeds being very bad. ANd that was in cars, where the suspension and steering stuff is far heavier and rigid than that in an airplane. The shimmy damper in the airplane is just an attempt to stop shimmy caused by dynamic imbalance and dates from the old days when static balancing was standard practice. Cars NEVER used any shimmy dampers at any time, and dynamic balancing eliminates the need for them. It's funny how we complain about the archaic technology still being used in GA aircraft, and then go and use archaic methods to try to cure shimmy.

Do a search on POA for nosewheel shimmy. I'm not going to redefine it here anymore.

If there are guys posting here giving advice on what to fix, and they have never done a dynamic balance and experienced the result, their advice is badly lacking.

See this: http://www.aircraftmaintenancespecialties.com/tech.php?id=3

TLDR? An excerpt:

Nose Wheel Tire & Wheel Assembly Balance
Balancing the nose wheel/tire assembly is the most important point to check in trying to solve a shimmy problem. Aircraft tire and tube manufacturers paint a red dot on the tire for the "light" spot. A yellow stripe on the tube, or the valve stem should be aligned with the red dot for coarse balance during tire buildup. Then the tire/wheel assembly is balanced with a static type (bubble) balancer and generally does an acceptable job.

However, the preferred method, and sometimes the only method that can solve persistent shimmy problems, is dynamic balancing. (Dynamic balancing is when the wheel/tire/bearing assembly is spun and the proper weights and locations determined electronically). Very few light aircraft maintenance shops have the capability to do spin balancing, so AMS suggests that local motorcycle shops be contacted until one with a spin balancer is found. Usually these shops have the necessary mandrels to mount an aircraft tire/wheel assembly. Balance is achieved by affixing lead weights to the wheels.

Bold emphasis mine.

You are right. I have heard this before and I just checked with our shop and is static balancer. We aren’t flying too much right now so I’ll have the wheel pulled and take to a motorcycle
Shop. This is the only thing we really haven’t tried- really should be the first thing I guess. I will keep you posted.

 

[Dan Thomas]

You are right. I have heard this before and I just checked with our shop and is static balancer. We aren’t flying too much right now so I’ll have the wheel pulled and take to a motorcycle
Shop. This is the only thing we really haven’t tried- really should be the first thing I guess. I will keep you posted.

A static balance can actually make things worse. If the imbalance is on one side of the wheel, as in left or right (it's seldom in the center), and the tech installs the weight opposite the heavy area but on the wrong side of the wheel, it's statically balanced but now the dynamic imbalance is even worse. Static balancers think in two dimensions, while the problem is in three dimensions.

 

[ktup-flyer]

PM'd

 

[Larry Korona]

Finding someone to dynamically balance it is the problem. Motorcycle shops often have a dynamic balancer that will fit a nosewheel. The seals and bearings must be out of the wheel.

Good idea, but would the weights that a non-aviation repair shop put on the wheel be acceptable?

 

[Dan Thomas]

Good idea, but would the weights that a non-aviation repair shop put on the wheel be acceptable?

It's the standard practice. Aviall sells Goodyear stick-on weights for this purpose. The wheel has to be really clean and dry, but they stay put. The only time I had any fall off was on our R182, and that nosewheel retracts into the well immediately below the engine and gets pretty warm. The weight stickum can let go. The hubcaps kept them from escaping altogether.

As the nose tire wears it might be necessary to rebalance. Getting those weights off can be fun; the tape usually stays stuck to the wheel and weight and delaminates through its center. Then you have to carefully scrape the tape off the wheel and clean it.


The weights go inside the wheel's cavities and centrifugal forces help keep them there, too.

Cessna published a Service Information Letter long ago on this subject. CE-84-21, IIRC, Can't find it now. An older one, NL-81-5, describes the Goodyear static balancer and the self-sticking wheel weights. Straight from Cessna, still listed in their service document listing, so it carries more authority than I do. https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=37619

Remember, that balancer will not solve nosewheel shimmy problems. It's not a dynamic balancer, yet shops keep using it on nosewheels and have no success dealing with shimmy. We used it to balance main wheels to stop common wheel hop. With the brake discs on the inside of the main wheel you can't dynamically balance it anyway. Can't put weights in that side.

 

[nrpetersen]

Assuming the strut assembly is similar to a 172, there is a design feature that locks it to center when it is fully extended. This has to be defeated when analyzing the lost motion in the linkage connecting strut yaw to the to the steering/shimmy damper. This is easiest done by:

1) Vent all the charge from the nose strut until the strut fully collapses.
2) Raise the nosewheel by tying the tail down.
3) Bleed in enough atmospheric air to allow the strut to extend about half ways. This allows the nose gear to be manually wiggled similar to shimmy, and the linkage can be more correctly evaluated for lost motion between the steering damper and the wheel shimmy.
4) Chances are there is excess roll motion in one of the elements of the linkage that is not obvious unless you do this half way extension test. Shims spacers etc are available. Spend $$ on same.
5) Fill the shimmy damper, reassemble, and recharge.

This is based on a MechEngr w 50 years of 172 experience. YMMV.

 

[Larry Korona]

It's the standard practice. Aviall sells Goodyear stick-on weights for this purpose. The wheel has to be really clean and dry, but they stay put.

Good information! Thanks!

 

[gdwinc]

I'm curious to know if anyone has tried using Dynabeads to balance a nosewheel? Might be easier than tracking down a motorcycle shop to do a dynamic balance.

 

[Dan Thomas]

I'm curious to know if anyone has tried using Dynabeads to balance a nosewheel? Might be easier than tracking down a motorcycle shop to do a dynamic balance.

They'll statically balance a wheel, but will they move to the sides to dynamically balance it?

 

[gdwinc]

I don't know about moving to the sides, but this is a quote from their website:

The way we do this is by offering a Dynamic Balancing Solution, a high-density ceramic bead that, when easily installed, continuously balances your tires as you drive. The amount of material will distribute itself in weight and position dependent on the balance requirements of the individual tire.
​

Again, I'm not advocating this as a solution, just curious if anyone has tried...

 

[nrpetersen]

I think theoretically Dynabeads will gradually migrate to a constant rotating radius of the interior of the tire. Yes, that may in time improve the static balance assuming constant tire tread thickness, but I don't see how it will do anything at all for the dynamic balance. It also requires time to work its way around the tire inside, something that is not available in a tire that rolls only a little bit before called on to spin like hell - and a widely varying speeds.

I would also question the balance after a wheel has been parked for some time. It probably actually be worse, when suddenly spun up.

 

[Dan Thomas]

With our oh-so-modern inner-tube tires, getting the balancing beads in there would be fun. And inner tubes often develop wrinkles that would hamper bead movement.

 

[GaryV]

Sometimes a shimmy isn’t a shimmy.

I’ve been fighting a ‘shimmy’. I couldn’t find anything else wrong so I took my nose wheel to a local motorcycle shop to have it dynamically balanced. The guy that does the balancing at the shop is a pilot that owns a Maule.

He pointed out how out of round the tire was and helped me use a belt sander to get it back in round. The first time he checked it, the balance was off by more than an ounce on one side. After we removed the high spots, and got it back to round, it didn’t need weights to balance.

The tire is new enough that I couldn’t see any obvious issues until watching the tire while it was spinning. When it was turning quickly you could see that it had a high spot. I used a great pencil to lightly touch the contact surface as it was spinning and it turned out that there were several high spots before we touched it up.

Thinking back I did have a light ‘shimmy’ shortly after installing the tire. Obviously that should have been a red flag but I missed it. My tire guy said that as time went on the problem just got worse to the point where the tire was bouncing on each rotation when the tire was lightly loaded like shortly after touchdown or just before rotation. I interpreted the bounce as a shimmy.

Now that the tire is round my ‘shimmy’ went away. I never checked a new tire for out of round before but will be checking them in the future. I did check my mains while I was at it an they are round.

gary

 

[brien23]

Cessna did not balance the nose wheel with weights when new and your C-182 aircraft when new did not have that problem. You along with others have parts worn out in the nose gear that are causing the problem. Find someone to fix it right and get away from the idea that the nose tire needs weights to balance it will fix all.

 

[Dan Thomas]

Cessna did not balance the nose wheel with weights when new and your C-182 aircraft when new did not have that problem. You along with others have parts worn out in the nose gear that are causing the problem. Find someone to fix it right and get away from the idea that the nose tire needs weights to balance it will fix all.

This overlooks something really important. When Cessna built that airplane, all the parts were new and the tolerances were all very close. The tires were US-made, not from Asia like so many are now. Those tight clearances and good-quality tires meant that you felt nothing even if there was a bit of imbalance. Now, a mechanic can replace the shimmy damper mounting bolts and bushings but he can't economically replace the oleo housing with its wallowed-out mounting hole or the oleo strut with its wallowed-out hole. He can't economically replace the shimmy damper cylinder with its wallowed-hole either. He can take the oleo apart and re-shim the steering yoke to reduce the rocking on the housing, but he can't replace the metal worn off the top side of the support flange and so he can't remove all the rocking. He can replace the torque link bushings and bolts but he can't economically replace the nosewheel fork that has the wallowed-out torque link mounting holes in it, nor the oleo housing with its wallowed-out holes. (Edit: those holes get wallowed out because the mechanic doesn't torque the bolts up properly.The bolts pass through a bushing (sometimes called a spacer) that is inside the torque link bushings, and the bushings are supposed to run on the spacer, which is supposed to be pinched between the lugs on the oleo and fork or strut collar so it can't move. They get left loose, and the bolt ends up pounding the holes out on those aluminum castings and the spacer's ends eat divots in the inboard sides of the lugs. There is nothing in Cessna's manuals or service bulletins about it. From an engineering pespective it's an adequate setup if the thing is assembled right. Most aren't.)

A guy could spend vast sums on all this stuff. And even if he did, a dynamically-imbalanced wheel will wear it all out again in short order. I learned to fly in a six-year-old 172 in 1973 that had awesomely horrible nosewheel shimmy. Less than 2000 hours on it, likely. So bad it blurred your vision when it happened. With a US-made tire, too.

Now we have "aviation quality" bias-ply tires that aren't round sometimes and have high spots off-center sometimes. An off-center high spot moves the center of the contact footprint around and makes the wheel want to turn one way or the other. That's one issue, but the other is that these tires are often way out of dynamic balance. Having inner tubes doesn't help. They're not uniform either.

Still no radials for light airplanes. It's silly.

If the tire/wheel assemblies on a brand-new 1970 Cessna had been dynamically balanced and kept that way, it would still be on its original steering stuff and it would still be tight.

Cars always get dynamic balancing and have for a lot longer than you younger guys have been alive. You have never experienced the runaway front-end shimmy we older guys sometimes did when the wheels got a static balance only, and constant steering-wheel shake in cruise. And steering stuff that was worn out as a result. And, like I said before, if you have never fixed nosewheel shimmy by dynamically balancing that nosewheel, your experience is deficient. You can argue against it all you like but it means nothing if you haven't tried it.

 

[denverpilot]

This overlooks something really important. When Cessna built that airplane, all the parts were new and the tolerances were all very close. The tires were US-made, not from Asia like so many are now. t.

You complained about Chinese made parts, then listed off a majority of stuff the mechanic couldn’t afford to replace... all made by Cessna in ... Mexico.

LOL.

Mechanic “can’t” afford to replace because Cessna jammed all liability costs for everything into parts costs in GA. Especially landing gear parts. The retractable system parts are ludicrous.

But “can’t” is more on the owner/operator. Sorry, these parts costs rising isn’t new. Can’t afford to pay to maintain these ancient designs... is mostly because of wishful thinking that it’s still the 70s and people still work on things with cheap parts. Of course it breaks every week in heavy service but we have ten cheap mechanics, too!

These machines are speciality/novelty nostalgia things now. Like maintaining a classic car.

Sadly most of these parts *could* be made to better tolerances AND cheaper by a solid company that knows how to MANAGE a Chinese vendor, but we can’t have competition in these magical “certified” chunks of aluminum dumber than any car part made today for any automotive suspension system.

Hell... there’s a local shop in every city that can turn out a better version of almost all these parts on their mid range CNC mill in a few hours, tops. Cheap. Don’t even need China.

But not allowed... easily anyway. Magic certification fairies didn’t tinkle on the aluminum. LOL.

 

[Dan Thomas]

You complained about Chinese made parts, then listed off a majority of stuff the mechanic couldn’t afford to replace... all made by Cessna in ... Mexico.

LOL.

Read my post again. I said that the tires were often made in Asia. I didn't say that Cessna's parts were.

That whole nosegear could be designed a lot stronger, but it would end up heavier, too. Cessna made it light so it would fly better. Heavier stuff, made so that it's idiot-proof, really hurts performance, and the world just comes up with better idiots. That shimmy problem, started by an imbalanced nosewheel, involves the entire nosegear, not just shimmy dampers and torque links. The whole gear flexes a little on the airframe, and the airframe flexes, too. The tire flexes and adds to the confusion. None of it is anywhere near as rigid as it looks. The physics of shimmy involve the dynamic imbalance, the tire's footprint, the gear and airframe flex, the resonant RPM of the wheel and its imbalance, the brake index (traction) of the runway surface, the slop in the torque links and shimmy damper stuff, and a lot of other little things. The whole thing can be mostly cancelled by getting rid of the instigator: the dynamic imbalance. As I've said before, I've cured numerous cases of shimmy by doing nothing but dynamically balancing that nosewheel. I've done it with tailwheels, too. Fiddling only with all the shimmy damper and torque link stuff is like trying to cure cancer with aspirin. You're suppressing the symptoms instead of the disease. You're going to go through a lot of expensive aspirin.

 

[denverpilot]

I’m kinda not thinking these shopping cart tires were any great shakes in the 70s from a bunch of American bubbas making them vs Chinese and Korean bubbas. LOL.

They’re not radials or expensive as you’ve mentioned. Crap is crap.

Lots of marketing money in the 80s trying to tell folks the Goodyear ones were better after everyone realized they all sucked. Ha. Goodyear probably did make a slightly better and three times the price, option. Paid for the full page magazine ads.

Nowadays all you hear rental owners recommending and using are retreads from Monster and such.

Cheap junk still just like the heyday of the 70s.

Nowadays you have wear and slop at every single component interconnect point that’s worse than the intrinsic factory slop 40 years ago — on our beer can airplanes.

Silly things are sometimes just going to shimmy and turn into a hunting ground until that particular problem is found. Could be tire, could be wheel, could be wear, could be fat pilot sat on left side instead of right today and poor quality retread. Ha.

Old fairly low quality junk — when it was all brand new. We’re just keeping it all alive.

Cirrus mimicked am actual shopping cart for a reason... LOL!

 

[Checkout_my_Six]

replace the bolts in your nose wheel scissor link and shim gaps to tighten up.....that will fix 99% of the problem.

Dan Thomas wants you to remove the strut and re-bush everything....that works too, but is very expensive. If the bolts are examined you'll see step wear and new hardware does tighten up the assembly and stop the shimmy. I've done it a few times....

 

[deadeye99]

FWIW. My 182 had a shimmy when I bought it in 2018. It had a new lord dampener already. I had the McFarlane scissor kit installed and it was still there. Asked for the tire to be balanced and they said it was terrible, too bad to work with. Since I don’t like to play with tires or batteries I got a new flight custom 3 and new Michelin tube. No shimmy now for a year.

 

[Doug Reid]

IMO, getting the nose wheel balanced is probably the easiest and least expensive option on the list. No reason not to give it a try.

 

[Dan Thomas]

replace the bolts in your nose wheel scissor link and shim gaps to tighten up.....that will fix 99% of the problem.

Good grief. All I typed and we still get this sort of advice. A few posts back I said this:

He can replace the torque link bushings and bolts but he can't economically replace the nosewheel fork that has the wallowed-out torque link mounting holes in it, nor the oleo housing with its wallowed-out holes. (Edit: those holes get wallowed out because the mechanic doesn't torque the bolts up properly. The bolts pass through a bushing (sometimes called a spacer) that is inside the torque link bushings, and the bushings are supposed to run on the spacer, which is supposed to be pinched between the lugs on the oleo and fork or strut collar so it can't move. They get left loose, and the bolt ends up pounding the holes out on those aluminum castings and the spacer's ends eat divots in the inboard sides of the lugs. There is nothing in Cessna's manuals or service bulletins about it. From an engineering pespective it's an adequate setup if the thing is assembled right. Most aren't.)

Using new bolts does absolutely nothing if the spacer bushings aren't pinched between the lugs as per design. I have found those stupid assembles loose time after time, the holes wallaowed out because if it, and I've found those brass shims in there too, trying to take up the slop that cannot be taken up if the spacer is loose in there. The spacer and torque link bushings are precision made, with the bushings being reamed to size and the spacer ground to size, to an absolute minimum clearance and still allow free rotation. Putting it all together on an AN bolt that is .005 or more smaller than the inside of the spacer, and letting the spacer rotate on the bolt, means that you just spent a pile of money on parts and labor for absolutely no gain. I ahve taken these things apart and found that the bushing and spacer clearances are like new because all the rotation was on the bolt, and the spacer's ends instead have eaten divots in the lugs and wallowed out the bolt holes.

I've had a lot of these apart. Spent plenty of money on parts, too, before I realized out why they were always so loose. I was in machine-shop work before that, running precision machinery, designing and building precision production machinery, some of it automated, overhauling precision stuff, and so on. I recognize what Cessna intended for that nosegear assembly, and I wish they had put a bunch of detail into the service manuals about it. Of course, if mechanics don't read the manuals......

There's a similar engineering idea in the tails of the 180, 185 and old 182s. The trim in those airplanes moves the stabilizer's leading edge up and down, and the stab has small aluminum brackets on its aft spar that have nyldon bushings in then, and there are steel spacer bushings in the nylon bushings. Those steel spacers fit down between long aluminum angles on the outboard sides and formed aluminum brackets on their inboard sides. The angles are attached to the inside of the fuselage and run forward about six feet, and have a bend in them a couple of feet up from the aft end. They get called hockey sticks because of that bend. The inboard brackets are riveted to the side skins, top diaphragm under the stab bay, and the aft bulkhead. Two AN4 bolts go through the angles, pivot spacers, and inboard brackets to hold the stab to the tail, and those bolts are to be tightened to 70 inch-pounds. And yet, mechanics leave them a bit loose, thinking that the stab pivots on that bolt, not realizing that the nylon bushing is supposed to pivot on the spacer, which is supposed to be solidly clamped between the angle and bracket. That's what 70 inch-pounds torque is for. They don't read the manual. Those bolts end up taking the tail loads, and the stab wrenches around a lot in turbulence and propeller blast, and the bolts wallow out the holes in the aluminum hockey sticks and brackets, making the stab loose and sloppy. You would not believe the prices of those formed angles. Many thousands per piece. There is no way to repair a wallowed-out bolt hole, so the entire length has to be replaced, along with its opposing bracket, which isn't cheap either. For the price of those four pieces you could by a flyable 150. Add the labor, and it gets really obscene.

The elevator and rudder in Cessnas up to the 177 are also mounted this way, and loose bolts wallow those out, too.

 

[Checkout_my_Six]

so you jump to the expensive solution....right out of the gate? lol

 

[Dan Thomas]

so you jump to the expensive solution....right out of the gate? lol

Tell me: have you ever worked on this stuff? Wallowed-out holes on critical parts? Ever looked for an approved repair scheme? Ever?

 

[Checkout_my_Six]

Tell me: have you ever worked on this stuff? Wallowed-out holes on critical parts? Ever looked for an approved repair scheme? Ever?

I guess you think not......but, you'd be wrong.