Nose wheel vibration......advice urgently needed please

[Martin bevelander]

Cessna C177a FG 1969 model refers....
let me explain the issue please...this is not a shimmy problem.....
on landing, taxi & take off role there is no problem......when taking off there are no issues.....once rotated and climbing out the rotation speed on the front wheel reduces....then the crap starts.....its like a rrrrrrrr sound starting to settle in as the rotation speed reduces and then the rrrr sound disappears as the wheel further reduces rotation speed......it send a massive vibration through the firewall seriously vibrating into the firewall shaking the instument panel like crazy....
I replaced the front tyre and tube and since then its a problem....its sucha violent rrrrrr noize and vibration that I am too afraid to fly the plane....its really violent....
had the whole strut services....torque links shimming shimmy damper the lot ......ballanced the front wheel......its like a spanner or something was left inside the tyre......feels like a car with seriously our of ballance wheels.....massive rrrrr sound and high frequency vibration coming right into the firewall and instrument panel....

 

[Martin bevelander]

there are no links in my message

 

[steingar]

Had the same thing on my Mooney. It'd vibrate on landing just as I started rolling out. Turns out it needs some new shock discs and a couple other things, cheap fix. You should get yours to your mechanic, see what he (or she) thinks.

 

[SixPapaCharlie]

I once had a leak in a tire and filled it with that green goop for bike tires and got the same symptoms you describe.
The goop stays liquid so on taxi, it distributes itself evenly so takeoff was a non event.

During flight, the stuff would settle toward the bottom of the tire and when I landed, it shook the holy hell out of the plane.
Just because the wright brothers built bicycles doesn't mean you can use bicycle repair products on planes.

 

[Dan Thomas]

A howl from a wheel indicates corroded wheel bearings, or a cracked bearing cup. Corrosion in bearings is VERY common in airplanes, since their wheel seals are simple felt discs and they allow water and dirt in far too easily. When some people wash the airplane they squirt water directly at the wheel hub and axle, and water is driven through that seal with no effort at all. The water mixes with the oil in the grease and forms acids that eat the bearings.

Raise the nose and spin the wheel. Might be enlightening.

 

[denverpilot]

Tire balance, broken bearing, wheel cracks, all sorts of things can cause that.

I’ll let you know what they say was causing ours once the shop actually comes and gets the airplane and looks at it.

They said they were booked three weeks out, three weeks ago, and they’d get the airplane on Thursday of this week.

Airplane is still in the hangar and no response from the voice mail I left on Thursday just checking that the hangar key we left them worked. Not even a courtesy call saying they’ll get back next week.

 

[Peter Anderson]

It could be the shock dampener is going out. Similar issue at one of the planes in my school. When weight goes onto the front gear on landings it vibrates the whole damn from of the plane. The shock itself I believe is in the body, the dampener looks like a little shock horizontally mounted above it.


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[Peter Anderson]

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[Checkout_my_Six]

probably too much slop (side-to-side play) in the strut links. If you can wiggle them, that's the problem....first thing to try (the cheapest) replace the bolts in the links. 99% of the time fixing the damper doesn't fix the problem, it just masks it.

 

[Salty]

Maybe I can’t read, but I thought the OP was describing a vibration when there was no weight on the front wheel which isn’t what most of the rest of you seemed to read. Sounds like bearings to me.

 

[Salty]

there are no links in my message

Except for the torque links.

 

[mondtster]

A howl from a wheel indicates corroded wheel bearings, or a cracked bearing cup. Corrosion in bearings is VERY common in airplanes, since their wheel seals are simple felt discs and they allow water and dirt in far too easily. When some people wash the airplane they squirt water directly at the wheel hub and axle, and water is driven through that seal with no effort at all. The water mixes with the oil in the grease and forms acids that eat the bearings.

Raise the nose and spin the wheel. Might be enlightening.

Bearings are my first thought too, and I’ve seen many of the same problems with them and the felt seals.

I’m also wondering if the OP possibly installed a retread tire. I’ve seen a number of them that have heavy spots which will cause the exact same kind of shake being described, but not the noise.

 

[hotprops]

if it started with the new tire it could be everything stated above but not the shimmy damp.i would guess the tire is bad ,out of balance or the installer broke the rim or the bearing cup. or did not tighten the axel nut properly or reused the tube . take to someone else to fix and bill the ****head who f ed it up .failure after a repair is no coincidence in this case.buy a new dresser retread they have great quality control and buy the best tube as advised by dresser.

 

[mondtster]

if it started with the new tire it could be everything stated above but not the shimmy damp.i would guess the tire is bad ,out of balance or the installer broke the rim or the bearing cup. or did not tighten the axel nut properly or reused the tube . take to someone else to fix and bill the ****head who f ed it up .failure after a repair is no coincidence in this case.buy a new dresser retread they have great quality control and buy the best tube as advised by dresser.

Desser made the retreads I was referring to. I would not put any retread on the nosewheel of the airplane.

 

[Dan Thomas]

probably too much slop (side-to-side play) in the strut links. If you can wiggle them, that's the problem....first thing to try (the cheapest) replace the bolts in the links. 99% of the time fixing the damper doesn't fix the problem, it just masks it.

It's not the bolts that wear. They just clamp the spacer (bushing) in the forks of the nose fork and the steering collar. If the mechanic doesn't get them torqued properly, they allow the whole thing to slop, spacers and all, and the bolts chomp out the holes in the aluminum forks and make everything much worse. The service manuals are deficient in this; they don't tell the mechanic to bring the bolt and nut to any specified torque, and some mechanics will leave them a bit loose, thinking that the affair pivots on the bolt rather than on the spacer. I have seen the holes badly wallowed out, and the shifting spacer ends eat cavities on the inside faces of the forks, making it almost impossible to repair properly.

The proper wear points are the surfaces between the spacers and the bushings in the torque links. Only the short NAS bolt at the link junction has no spacer. And it's supposed to be an NAS bolt, not an AN bolt. The AN will wear too fast.

The shimmy damper is next to useless. Without dynamically (not statically) balancing the nosewheel assembly, you'll get shimmy with or without the damper.

 

[455 Bravo Uniform]

OP said it only does it after the front tire lifts off the runway at rotation, the highest unloaded speed it sees. And it started after the tire and tube were replaced.

First question: where does the colored dot on the tire line up relative to the valve stem?

 

[Checkout_my_Six]

I've done this many times....the bolts do wear. If bad enough the bushings will need to be replaced. Sometimes the bolts can be a cheap fix.

The damper is commonly reworked....but, as said before, is not the culprit.
These are shear bolts not torques. They wouldn't take more than 5-8 ft-lbs anyways.

It's not the bolts that wear. They just clamp the spacer (bushing) in the forks of the nose fork and the steering collar. If the mechanic doesn't get them torqued properly, they allow the whole thing to slop, spacers and all, and the bolts chomp out the holes in the aluminum forks and make everything much worse. The service manuals are deficient in this; they don't tell the mechanic to bring the bolt and nut to any specified torque, and some mechanics will leave them a bit loose, thinking that the affair pivots on the bolt rather than on the spacer. I have seen the holes badly wallowed out, and the shifting spacer ends eat cavities on the inside faces of the forks, making it almost impossible to repair properly.

The proper wear points are the surfaces between the spacers and the bushings in the torque links. Only the short NAS bolt at the link junction has no spacer. And it's supposed to be an NAS bolt, not an AN bolt. The AN will wear too fast.

The shimmy damper is next to useless. Without dynamically (not statically) balancing the nosewheel assembly, you'll get shimmy with or without the damper.

 

[wilkersk]

I know everyone's focused on the nose gear. But when this happens, have you reached up and stepped on the brakes to rule out the main gear. Usually, I've found the rental 172s with these symptoms have main gear issues like wheels out of balance, worn and bulls-eyed.

 

[denverpilot]

I know everyone's focused on the nose gear. But when this happens, have you reached up and stepped on the brakes to rule out the main gear. Usually, I've found the rental 172s with these symptoms have main gear issues like wheels out of balance, worn and bulls-eyed.

If he’s describing something similar to ours, it’s VERY obvious it’s coming from the nose.

Ours isn’t awful, but we know it’s wrong, so we are having it looked at... once they get around to actually looking at it, that is.

Our mechanic listed off improper torques as a very commonly seen thing on Cessnas. Tire balance. Worn parts. Etc.

He’ll know when he has it up in the air, the wheel pant off, and can look at things.

In a LOT of years as owner and also having attended John Frank’s 182 course, before he passed, the shimmy dampener is a device that HIDES other problems.

Almost 99% of the time, if someone goes straight to shimmy dampener, they’re either being lazy, or the thing is so loose it’s only part of the problem, and the real problem has beat the poor thing to death. It can only do so much.

Watch some of the YouTube videos people have shot with foreward angles from under the belly of anything with a free castering nosewheel. They shimmy. They flop around. Tiny go kart sized tires and high speeds don’t really mix as well as we think they do.

But wobbling after takeoff, unloaded, while the tire is spinning, is enough information to know the thing needs to be put up in the air and inspected. Could be simple. Tire balance. Could be a mess. Broken parts. Could be worn parts. All sorts of possibilities that looking at the components and spinning the tire will find out.

By the way, if the mains are suspected, they’re easy to rule out in this case. Lightly apply the brakes after liftoff and stop and hold their motion. If the vibration continues and winds down with the nose wheel, it’s not the mains.

 

[wilkersk]

By the way, if the mains are suspected, they’re easy to rule out in this case. Lightly apply the brakes after liftoff and stop and hold their motion. If the vibration continues and winds down with the nose wheel, it’s not the mains.

Yep:

I know everyone's focused on the nose gear. But when this happens, have you reached up and stepped on the brakes to rule out the main gear? ...

In the 172s I've flown, I've seen 2 problems (1) Vibration on lift off. Tap the brakes it stops. (2) Shimmy on landing. Everyone thinks shimmy dampner. But, its usually the 40+ year old torque link hardware (bushings, bolts and washers) begging to be replaced.

That has been my experience. Just thought I'd throw it out there. But, I'm sitting in my easy chair and not looking at OPs aircraft.

 

[denverpilot]

That has been my experience. Just thought I'd throw it out there. But, I'm sitting in my easy chair and not looking at OPs aircraft.

Yup that’s why we’re here. Tossing out ideas. We can eliminate soke from his description.

The thing I think he’s saying that isn’t those two scenarios, is that he’s got vibration from the nosewheel after liftoff with the mains stopped. We’ve also developed this on our 182.

In certain conditions we can get it to shimmy during landing, especially with heavy braking, but it’s always there as a vibration on liftoff. Weight off the nose but still rolling on the ground it’s either not there or very weak.

At least if I’m reading his OP correctly, that’s what I think he’s saying. Almost identical to ours, and numerous possibilities listed above are possible.

The best advice is... get a mechanic to look at it. Give a solid description of when and how it happens.

They’ll eliminate a bunch of things with a good description. And/or they’ll find it by looking with a Mark 1 eyeball.

 

[Dan Thomas]

I've done this many times....the bolts do wear. If bad enough the bushings will need to be replaced. Sometimes the bolts can be a cheap fix.

The damper is commonly reworked....but, as said before, is not the culprit.
These are shear bolts not torques. They wouldn't take more than 5-8 ft-lbs anyways.

You'll keep doing it many times until those bolts are tight enough to pinch the spacers between the tabs and stop them from moving. The mechanical design of that system makes it obvious that that is what was intended. If Cessna intended those bolts to be in shear alone, they'd have used just the bolts and left out the spacers, and they'd have used larger bolts. I have torqued those things up snug and had no more wear and slop problems on several flight school airplanes over thousands of hours.

 

[Checkout_my_Six]

interesting....maybe Cessna should update the manuals to reflect this.

 

[bnt83]

OP said it only does it after the front tire lifts off the runway at rotation, the highest unloaded speed it sees. And it started after the tire and tube were replaced.

First question: where does the colored dot on the tire line up relative to the valve stem?

Ballanced and then my next question, is the mud flap scraper thingy (on the nose wheel pant) hitting the tire?

 

[bnt83]

interesting....maybe Cessna should update the manuals to reflect this.

It is pretty obvious, the bushings are plastic on the 177s and its not built like the other 100 series airplanes. It actually works pretty well IMHO.

 

[Daniel F. Smith]

I noticed this thread is from 2012 - probably solved long ago.

What I immediately saw was that he has already rotated and is climbing. The only thing that could be affecting this is aerodynamic forces causing some fluttering of a part.
If he has wheel pants, he should take a look at the attachment. Maybe the nose wheel pant is loose, or changes after takeoff, and is violently resonating up through the plane.
Raise the nose wheel off the ground; get it hanging free. Then spin the tire somehow. That should prove it's not the tire but may cause other parts to strike into resonance. The linkage bushings, or shimmy damper would have to be very loose for airflow to affect it that way. I doubt it. We had to replace all bushings, the damper, and rotate and balance a new tire, but that was roll-out shimmy; totally different problem.

Cowling would be my next guess. It apparently happens as the plane transitions through a particular attitude and airspeed. Maybe the climbing angle causes the wheel pant to flutter. Immediate test and solution would be to remove the wheel pant.

I hope they got this fixed. You certainly don't want the wheel pant coming loose and jamming the nose wheel on landing. Yikes!

Arm chair mechanic,
Dan

So... in retrospect...what was it?

 

[Daniel F. Smith]

Oops! Sorry. Saw the wrong date on the posting. This IS current. Hope I can help somehow.
Dan

 

[Dan Thomas]

interesting....maybe Cessna should update the manuals to reflect this.

Yes, they should, but there are numerous sections and pages of those manuals that still have data that was superseded by service bulletins. They just don't want to spend the time and money to update old manuals, but they'll still charge you for them.

They'll also provide parts manuals, for a price, that are full of part numbers superseded decades ago.

If they wanted that assembly to pivot on the bolt, why did they put in a grease nipple that feeds the interface between the link bushings and the spacer instead of between the spacer and bolt? The grease does no good at all if that spacer is turning on the bolt.

 

[thomasdr72]

Ours did this, until I re-shimmed the NLG scissors, and then balanced the new tire... Considerable improvement.

 

[Daniel F. Smith]

I still don't see how any of the bushings and balancing have effect on this when it has to clear the ground before the vibration starts.