1967 Cessna 150G Nosewheel Shimmy Problem

Bilal

Bilal

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Bilal
Hello All,

I apologize if this was already asked on this forum before. I did not find much on this topic so, here we go:

I recently purchased a 1967 Cessna 150G and noticed that the nose wheel shimmies when taxi. The problem goes away when I take the load off the nose wheel and taxi really slow. I was told that this is a common problem with Cessna 150s? Never heard of this before so not sure how true is this statement :confused:

Did some research online and found solutions ranging from changing the tire and strut to installing MCFARLANE CESSNA TORQUE LINK KIT TL-KT-1. Also, I checked there is no play from Torque link below so I am not sure if that kit will do much good.

Wondering if any of you experienced or dealt with a similar issue and how to fix it? Thank you
 
Yea I think MBDiagman has the right idea as the symptom doesn’t pinpoint the issue, his idea is far better than throwing parts at it which may or may not do it.

but it’s not a bad idea to taxi like a taildragger with the yoke in your lap if winds allow - may as well take the load thus wear off it when you can.
 
There are MANY posts on POA regarding Cessna nosewheel shimmy. And there are MANY opinions as to how to fix it, and one opinion that says "that's what Cessnas do."

Sure, worn torque links and shimmy dampers can let shimmy get severe, but the ROOT CAUSE, as I've said many times, is a dynamically imbalanced nosewheel. No amount of parts replacing will change that. No amount of shimmy damper rebuilding will change it. Static balancing of the nosewheel might improve it somewhat, but can also make it much worse. If the imbalance condition is not corrected, new parts will just get worn out again in short order.

When you get new tires on your car, they dynamically balance them. They've been doing that for over 50 years. Aircraft shops, if they do any balancing, use a cheap static balancer. Automotive tire shops threw those out when they got dynamic balancers. I converted an old mechanical dynamic balancer to balance nosewheels in the flight school, and shimmy totally disappeared. At a subsequent shop I had to build my own dynamic balancer, and it also stopped shimmy, without even replacing any worn parts. So you see, I know that dynamic balancing is the answer.

Find a motorcycle shop that has a dynamic balancer. The balancers for cars can't mount small wheels like nosewheels.
 
As a former C-150 owner, I can tell you that allowing the wheel to shimmy will eventually put a wear pattern on the tire that will make all the other efforts moot.

tighten up the scissors and the damper attach points with washers and put ATF in the damper. Then buy a new tire and static balance it. You can make a fixture to balance the wheel with a few pieces of hardware from Lowe's or Home Depot...

treat the nosewheel like the fragile device it is. Keep the weight off of it at all times when taxiing and landing. Keep your landing and taxi speeds to the absolute minimum required and don't get in a hurry.

Always keep a spare main- and nosewheel tire for those times when you have a bad day.
 
IK04 said:
tighten up the scissors and the damper attach points with washers and put ATF in the damper. Then buy a new tire and static balance it. You can make a fixture to balance the wheel with a few pieces of hardware from Lowe's or Home Depot...
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Like I said, there are lots of opinions, and some are not based in science or experience.

upload_2021-5-24_10-44-52.jpeg

Now, a static balancer can help you with that static imbalance. It can't do anything for the dynamic imbalance shown above. If fact, if the wheel has a heavy spot in one position and it's off to the side like both of those in the dynamic imbalance picture, and you stick a weight on the wrong side of the wheel and get it statically balanced, you have created the exact condition shown in the dynamic imbalance and the shimmy gets much worse and more damaging.

There is NO substitute for dynamic balancing. The wheel HAS to be rotating to determine where weight needs to be installed to stop the shimmy. Sadly, there are no affordable dynamic balancers for aircraft shops, which is why I had to build my own. Static balancers work fine for main wheels, and in fact most can't be dynamically balanced because the brake disc prevents the attachment of any weight on the inboard side. Nosewheels are a different matter. So are tailwheels, and I did those by hand, spinning them on their bearings on an axle using a wire wheel to spin them up a bit, then fooling with various weights in various places until it behaved at any RPM. It paid off, too. Tailwheel shimmy can break airframe components in the tail. Had a Citabria tailpost fail from unresolved shimmy.
 
Thank you everyone for your response. This gives me a starting point and I think I will begin with wheel balancing.
@Dan Thomas - Your last post is very helpful and I see why you are suggesting dynamic balancing. I will try to find someone locally who can do this for me. @IK04 I agree, not a bad idea to have a spare main.
 
Okay, from years of experience chasing vibrations and the like on cars I can tell you this. Balancing the wheel is well and good, but wheel imbalance can cause vibration, but loose parts allow the vibration to transfer into the vehicle and under certain conditions loose suspension and steering components can be completely responsible for the shimmy even with a perfectly balanced wheel. And yes, make sure it is done dynamically. This means weights on both sides of the wheel. Many tire stores have wonderful dynamic balancers but they do a static balance which probably won’t correct the problem even if it is an imbalanced wheel.

You REALLY need to get the nose wheel in the air, find the slack and correct it. Balancing the wheel and trying it is not proper troubleshooting. That is basically like throwing parts at the problem. Analyze and THEN decide on the course of action. I would give wheelbalancing alone a very small chance of curing your problem.
 
MBDiagMan said:
Okay, from years of experience chasing vibrations and the like on cars I can tell you this. Balancing the wheel is well and good, but wheel imbalance can cause vibration, but loose parts allow the vibration to transfer into the vehicle and under certain conditions loose suspension and steering components can be completely responsible for the shimmy even with a perfectly balanced wheel. And yes, make sure it is done dynamically. This means weights on both sides of the wheel. Many tire stores have wonderful dynamic balancers but they do a static balance which probably won’t correct the problem even if it is an imbalanced wheel.

You REALLY need to get the nose wheel in the air, find the slack and correct it. Balancing the wheel and trying it is not proper troubleshooting. That is basically like throwing parts at the problem. Analyze and THEN decide on the course of action. I would give wheelbalancing alone a very small chance of curing your problem.
Click to expand...

I agree ... Probably the most logical first step before spending money/time on getting the wheel balanced. Thanks :)
 
Chased a similar problem on a 172 that ended up as a broken engine mount.
 
I agree about the dynamic balancing, if it’s available. I’ll add that I recently had what I thought was shimmy ( on my Beechcraft), I jacked the nose wheel up enough to spin the tire, and it turned out to be about 3/8” out of round. The tire was almost new. Installed a new tire and problem went away, the shimmy was really a bouncing!


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When balancing, dynamic balancing is the only way to go. Because airplane wheels don’t have a similar mount to an automobile, I expect that you would have to use a motorcycle balancer or something. I have a very good old Coats balancer that would do a great job if you could mount the wheel. I expect that with access to a lathe, it wouldn’t be too difficult to build something to adapt an aircraft wheel.
 
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MGJohnson said:
I’ll add that I recently had what I thought was shimmy ( on my Beechcraft), I jacked the nose wheel up enough to spin the tire, and it turned out to be about 3/8” out of round. The tire was almost new. Installed a new tire and problem went away, the shimmy was really a bouncing!
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Sometimes that's due to leaving the wheel bearings with no preload. If that wheel can turn too freely, it will always stop with the heavy side down, and that's the spot that gets abraded when the airplane lands. That spot, plus maybe another quarter or half a turn as the wheel picks up speed. If the imbalance is big enough it will lose a lot of rubber before it decides to stop in some other position. The solution is proper preload on the bearings.

The rest of the time an out-of-round condition is because the tire manufacturer made it like that. These "aircraft-quality" tires have more runout than the cheapest car tires. And they're tube-type; cars abandoned inner tubes in the 1960s. And they're bias-ply; cars abandoned those for radials in the 1970s. All of it makes dynamic balancing so much more important.

I guess tube-type, bias-ply tires go well with the felt wheel bearing seals. More 1920s technology. There are POAers who whine about Lycoming technology; they don't see the much older, much worse stuff in their airplanes. Felt seals let in dirt and water, causing wear and corrosion. It takes care and labor to prevent that. And never squirt water at the wheel hubs when washing the airplane.
 
kkoran said:
I thought they left the factory with a shimmy. :rolleyes:
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They left the factory with dynamic imbalance, but the entire nosewheel strut and its torque links and shimmy damper were brand-new and very tight, so the shimmy wasn't all that apparent. They would still be good and tight if the wheel had been dynamically balanced at the factory and kept that way. ANd the tires of the day were probably better, too.

Shimmy wrecks this stuff. When I was a PPL student in the early 70s, flying a six-year-old 172, it would sometimes shimmy so bad that you couldn't read the instruments. Everything was vibrating terribly, even your eyeballs. That does the airframe no good, either. Loosens stuff, cracks stuff.
 
On my 12,000hr C150 (1966); shimming the oleo strut inside the mount did the trick.
Actually, my a&p would go through the entire system eliminating every bit of play. This was necessary every 5-6yrs. 800-1000hrs.

Running a bit more air in the strut, and a bit more air in the tire would usually mitigate the biggest part of the shimmy.
 
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