Replacing nose wheel inner tube. How do I balance?

stevenhmiller

stevenhmiller

Pre-takeoff checklist
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Steve's Archer
I have to replace the nose wheel inner tube. Once done, how do I check the balance on the tire? I want to be sure it's balanced, so upon takeoff or landing, it's not shimmying all over the place do to out-of-balance.
 
Balancing aircraft tires really doesn't seem to be common practice. Folks I've seen tend to set the balance indexes of the wheel and tire 180deg apart so it's close, though.
 
mkosmo said:
Balancing aircraft tires really doesn't seem to be common practice. Folks I've seen tend to set the balance indexes of the wheel and tire 180deg apart so it's close, though.
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Balance indexes? Where are those?
 
Now we know why they shimmy. Do they even make weights that go on there? What Ive done is, try it and if it shimmies, move the tire 90 degrees and try it again?
 
I've been known to take mine to the local motorcycle shop and use stick on weights. They have a dynamic balancer that can do my aircraft wheels/tires.

Alternately, my mechanic has a static balancer.

Both seem to work just fine but, yes, I balance.
 
For the amount of times I'll be doing this, I don't think it pays for me to buy a balancer. I'll just bring it to a motorcycle shop and have it done for me.

Thanks!
 
Not all bike shops can do it. I do it manually, spinning the wheel on its axle and driving it with a wire wheel, and experimenting with weights on either side and in different clock positions. We have a static balancer that's fine for the mains, but if you want to eliminate shimmy, you need it dynamically balanced.
 
Dan Thomas said:
Not all bike shops can do it. I do it manually, spinning the wheel on its axle and driving it with a wire wheel, and experimenting with weights on either side and in different clock positions. We have a static balancer that's fine for the mains, but if you want to eliminate shimmy, you need it dynamically balanced.
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A slightly out of balance tire is causing noticible shimmy in a GA piston single?

I've flown tons of small planes where no one ever balances a tire, only time I've felt shimmy is when a student was screwing up, or didn't tap the brakes after wheels up.
 
James331 said:
A slightly out of balance tire is causing noticible shimmy in a GA piston single?

I've flown tons of small planes where no one ever balances a tire, only time I've felt shimmy is when a student was screwing up, or didn't tap the brakes after wheels up.
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What's that doing for the nose wheel? :D
 
Checkout_my_Six said:
What's that doing for the nose wheel? :D
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You gotta have a huge nose wheel if you're feeling it shimmy due to balance.

Most all nose wheel shimmy I've felt was due to low experience folks holding the nose wheel down too long, pranging the nose wheel down on landing, bad shimmy damper (often due to the prior two causes), etc.


If you got the machine and time, go for it, but balancing a 172/PA28/etc tire seems a little excessive and unnecessary, I'd wager if you got shimmy 45% it's pilot induced, 45% other mechanical like a damper, 10% balance. YMMV
 
trust me....once the wheels are off the ground....tapping the brakes will do nothing for the nose wheel. :no:

and mains stop within a second or three....with no brakes applied.
 
Enough of a difference I've noticed it :dunno:
 
So thats what those little pieces of metal on the runway are? Balance weights! How do you log that? Oh, I know, you don't.
 
James331 said:
You gotta have a huge nose wheel if you're feeling it shimmy due to balance.

Most all nose wheel shimmy I've felt was due to low experience folks holding the nose wheel down too long, pranging the nose wheel down on landing, bad shimmy damper (often due to the prior two causes), etc.


If you got the machine and time, go for it, but balancing a 172/PA28/etc tire seems a little excessive and unnecessary, I'd wager if you got shimmy 45% it's pilot induced, 45% other mechanical like a damper, 10% balance. YMMV
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Some airplanes are notoriously prone to nosewheel shimmy, and one can replace lots of nosegear parts and fool with shimmy dampeners and so on, but the real solution--and the only one that works, in the end--is to dynamically balance that nosewheel. I've stopped shimmy on numerous airplanes, none of them with huge nosewheels, by dynamically balancing them.

Why do you think tire shops left off static balancing tire/wheel assemblies 40 years ago in favor of dynamic balance? So the steering wheel would stop shaking in cruise. And that's in a vehicle with big heavy steering components, not a lightplane with minimal and rather flexible steering structure and nosegear mounting.

Shimmy should not have to be dealt with using pilot technique. It shouldn't be there at all, period.
 
I don't know about NEVER shimmy. Everything has a vibrational frequency. What usually kicks it off is the tire is cocked a bit when it comes to the pavement, then it continues to vibrate. Tailwheels shimmy too. I'm in the camp that MOST shimmy can be reduced or eliminated with balancing, but am not sure how to go about balancing. Aircraft mechanics don't seem to do it because there is no certified way to attach the weights? Only way I know how to do it is by turning the tire on the wheel to a different spot and trying it there.

Saying its pilot technique is a bit like telling a driver of a car whose front wheels shimmy that it's technique. Not true. Its either wheel and tire balance or alignment. Ditto aircraft. Could be adjustment of caster camber and toe in, could be balance. Depends.
 
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coloradobluesky said:
I don't know about NEVER shimmy. Everything has a vibrational frequency. What usually kicks it off is the tire is cocked a bit when it comes to the pavement, then it continues to vibrate. Tailwheels shimmy too. I'm in the camp that MOST shimmy can be reduced or eliminated with balancing, but am not sure how to go about balancing. Aircraft mechanics don't seem to do it because there is no certified way to attach the weights? Only way I know how to do it is by turning the tire on the wheel to a different spot and trying it there.
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Cessna has a Service Bulletin telling mechanics to use stick-on weights for balancing, and Aviall sells Goodyear stick-ons for aircraft service. I don't know what more a guy would need.

Nosewheels are designed with some caster to them. That's to get them to trail properly. When they shimmy, it's due to a dynamic imbalance getting an oscillation going that gets worst at a resonant frequency, with the weight of the wheel and nosegear itself figuring into that. Without the imbalance, the wheel will trail just fine. When it starts to oscillate, its contact with the pavement varies as it swings from side to side, with the most contact in the straight-ahead position, and that will tend to damp the shimmy. A wheel that shimmies badly is WAY out of balance. Touching down with the wheel cocked a bit to one side should simply pull the wheel into alignment with the airplane's track. It shouldn't start any shimmy.

Tailwheels can also be dynamically balanced, but in many cases the tailspring has lost its proper curve and the caster axis has tipped forward so that the tire contacts the pavement most firmly at the ends of the travel, and it bounces back and forth once it get started. New or re-arced tailsprings are the only way to fix that. It's the same geometry as a bent shopping cart caster that shimmies.
 
Dan Thomas said:
Cessna has a Service Bulletin telling mechanics to use stick-on weights for balancing, and Aviall sells Goodyear stick-ons for aircraft service. I don't know what more a guy would need.

Nosewheels are designed with some caster to them. That's to get them to trail properly. When they shimmy, it's due to a dynamic imbalance getting an oscillation going that gets worst at a resonant frequency, with the weight of the wheel and nosegear itself figuring into that. Without the imbalance, the wheel will trail just fine. When it starts to oscillate, its contact with the pavement varies as it swings from side to side, with the most contact in the straight-ahead position, and that will tend to damp the shimmy. A wheel that shimmies badly is WAY out of balance. Touching down with the wheel cocked a bit to one side should simply pull the wheel into alignment with the airplane's track. It shouldn't start any shimmy.

Tailwheels can also be dynamically balanced, but in many cases the tailspring has lost its proper curve and the caster axis has tipped forward so that the tire contacts the pavement most firmly at the ends of the travel, and it bounces back and forth once it get started. New or re-arced tailsprings are the only way to fix that. It's the same geometry as a bent shopping cart caster that shimmies.
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What is the Cessna Service Bulletin number?
 
I've replaced a main and a nose wheel without balancing. I never noticed anything but it may be one of those situations where it would be noticeably smoother had I done it.:dunno:
 
Usually it is backlash in the linkage to the damper that causes shimmy. Cessna nose gears have an automatic centering lock when the nose gear extends fully, that releases when the nose strut is compresses. It is necessary to defeat this lock when looking for nose gear damper mechanism backlash.

I've gotten around this lock this by venting all gas out of the strut, then tying the tail down raising the wheel off the ground, and then bleeding in a small amount of atmospheric air to once again let the wheel extend to the middle of its travel. The slight vacuum in the strut holds the wheel off the ground.

Now look at the linkage backlash. Shims etc are available to fix this.

After rebuilding, reassemble and recharge the strut normally. This trick didn't used to be in the Cessna Manual.
 
nrpetersen said:
Usually it is backlash in the linkage to the damper that causes shimmy. Cessna nose gears have an automatic centering lock when the nose gear extends fully, that releases when the nose strut is compresses. It is necessary to defeat this lock when looking for nose gear damper mechanism backlash.

I've gotten around this lock this by venting all gas out of the strut, then tying the tail down raising the wheel off the ground, and then bleeding in a small amount of atmospheric air to once again let the wheel extend to the middle of its travel. The slight vacuum in the strut holds the wheel off the ground.

Now look at the linkage backlash. Shims etc are available to fix this.

After rebuilding, reassemble and recharge the strut normally. This trick didn't used to be in the Cessna Manual.
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ANd there are some things still not in the manuals. For instance, the inner bushing ("spacer") in the torque links was designed to be pinched tight by the bolt between the ears of the nosewheel fork and the steering collar, but many mechanics leave it loose. The bolt then lets the spacer mover around, and the ends of the spacer chomp depressions in the ears and the bolt wallows out the holes in the ears, and no amount of new shims or bearings is going to change it much. Furthermore, all-new stuff is soon beat up by a dynamically imbalanced nosewheel. The shimmy damper is at the top of the whole affair, and the movement has to travel through two torque links and three joints and the steering collar to get to it. The steering collar itself has shims and if it gets worn, it rocks, and allows movement that the shimmy damper never feels. If it rocks long enough, the steel ridge around the lower end of the nosegear tube gets worn on its sides and you can't shim that wear out. If you try, you end up with a jammed steering collar.

So the only real solution I have found is to dynamically balance that nosewheel. That's impossible with static balancers, and a bubble balancer is just another static balancer.

Nobody tries to ride a motorcycle that has a dynamically imbalanced front wheel. Nobody driving a car will put up with a front-end shimmy. But in aviation we're expected to tolerate it (we're even told that it's a "normal" thing) and are taught all sorts of pilot tricks to stop it. Dumb. And what motorcycle or car has a shimmy dampener??
 
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1600vw said:
In a modified form I use this to balance my props. It can be used out of the box for balancing your wheels. 40 bucks.

http://www.harborfreight.com/motorcycle-wheel-balancing-stand-98488.html
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That's a static balancer. This is a dynamic balancer:

eewb700dm.jpg


It costs a lot more, which is one reason why we don't see them in aircraft shops. The other reason is the lack of understanding that dynamic balancing is the real answer.

Look a this:

image812.jpg



The only way to dynamically balance a wheel is to spin it at some speed to determine where the imbalance lies. If the machine isn't spinning it, it's not a dynamic balancer.

This issue has been discussed here ad nauseum numerous times. Do a forum search on "dynamic nosewheel balance."
 
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I've noticed with Castering nose wheels if you let the nose wheel down at excessive speed they will tend to shimmy.
 
Dan Thomas said:
That's a static balancer. This is a dynamic balancer:

eewb700dm.jpg


It costs a lot more, which is one reason why we don't see them in aircraft shops. The other reason is the lack of understanding that dynamic balancing is the real answer.

Look a this:

image812.jpg



The only way to dynamically balance a wheel is to spin it at some speed to determine where the imbalance lies. If the machine isn't spinning it, it's not a dynamic balancer.

This issue has been discussed here ad nauseum numerous times. Do a forum search on "dynamic nosewheel balance."
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I don't believe I called what I posted a static or dynamic balance. I just showed a way to balance a wheel. Nothing more, nothing less. To balance a wheel like we are speaking, not many want to spend the thousands on that computer controlled balance machine. Why I posted what I did. For what we are working on this balance machine for 40 bucks will do just fine.
 
You could take it one step farther. Before you use the 40 dollar unit I posted, you could use a bubble machine and bubble balance your wheel. Then use the other unit to put a static balance on it.

You would have around 120 bucks invested in the equipment going this route. But in my opinion this is a little over the top for what we are working on.
 
Tires can be out of round as well... I have had one with 1/4" difference between high and low spot, and it wasn't really that bad...
 
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