New Guy from VA

Jarhead

Jarhead

Member
Joined
Apr 24, 2021
Messages
10
Location
Northern Virginia
New guy here from northern Virginia. Just realized a life-long dream of airplane ownership! Flew my 1999 GCAA home from Kansas City a few weeks ago. Couldn’t be happier. I’ve been reading through the archives here and I’m learning a ton here, what a resource this forum is.

I do have a question right off the bat; I’m getting some shimmy during wheel landings…main gear shimmy (tail still up). Even tail-low wheel landings seem to illicit this shimmy and I don’t believe it to be side load chatter. Could it be bearings? Thanks for any insights and great to be here!81DEDEB8-6B31-47DB-B837-9C0ABEBAB721.jpeg
 
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Check first the toe-in with a tape measure front-to-back on the tires. Then check balance of the tires. A possibility is that a tube is pinched between wheel halves - you can see this by observing wobble as you hand-rotate the wheel.
 
Thanks so much for the reply Bob. Just got my jack pad from ACA, I’ll check the balance and potential tube pinch tomorrow. Hoping it’s not toe-in, that sounds a bit more difficult to remedy. Thanks again!
 
Congrats! Concur with Bob, check alignment, balance, worn spots, and proper preload of hubs. Alignment isn't that hard to fix, just a shim between the axle and gear leg, so don't stress too much. But I would bet you just have a wobbly tire.
 
Welcome. Check the tire pressure. Take the wheel pants off for awhile. When were the tires replaced? The tire wear will often tell you about any alignment issue.
 
Howdy,and Welcome,

Question, when you take off and break ground, do you get any vibration? Look out the window at each tire and see if it is bouncing or shaking. This would be a sign of imbalance.

I know as I put 8.50x6 (6 ply) on my Citabria recently, and I get this shimmy. All was mounted correctly with the dot aligned with the valve stem, but one tire still majorly out of balance.

I hit the brakes as soon as I am airborn to stop the shimmy immediately. On landing it is noticeable from touchdown till the tail can not fly anymore and settles down on the runway.

I am putting on my "Smoothie 4 ply" tires as soon as I can get back on the grass and off winter pavement.

Other factors could be alignment as stated above, or just loose/bad wheel bearing, or gear attachment bolts? Give it a good once over,.....Twice!

Ken "COWBOY" Winiarski
Cowboys Air Ranch (84ME)
 
Thanks Ed, Ken and Goodyear, appreciate your advice a lot.
Ed, no vibration after liftoff that I’ve noticed, but I could have just not noticed. I’ll investigate that as well. I’ll also double check the gear attach bolts!

Fun weekend at the hangar ahead of me:p

Many thanks again for all your wisdom guys
 
Welcome Jarhead!

Here's another question, did the plane sit for a long time before you bought it and started flying it? the tires may be old, less pliable and have developed a flat spot that you're feeling on the runway.

also check in/out security of the wheel on the axle, make sure it doesn't move at all when you push and pull it along the axle.

and welcome!
 
Axles added to this diagnosis list thanks Bartman! It flew pretty regularly, but I’ll check for a deformed tire too, good thought
 
While checking your tires check for an out-of-round condition...I can't count the number of times a "vibration" issue turned out to be (after much work, angst, cursing, cussing, goat sacrifice, etc.) a tire with a blown belt.
In the world of radial belted tires we tend to forget our airplane tire technology is as old as our ignition systems and motor designs. Bias ply tires are susceptible to going out of round if one or more of the belts is broken by a hard shock or impact on the tire carcass...the broken belt allows the tire to "egg shape" even though it eyeballs just fine.
While you have the tire on the axle and off the ground rig a block or a pointer next to the tire...give it a spin and see if the tread stays the same distance from the pointer.

Nowadays you can hit a pothole or run over a curb with your radial tires and never give it a thought. The same occurrence in the 1960's would give your car a vibration that lasted until you got a new set of tires...
Just something else to check...

Chris
 
Interestingly, some of the Russian issues in Ukraine have been attributed to tires sitting too long. Apparently many dozens of military trucks have been found abandoned due to being stuck in the mud with flat tires. According to a US blogger who is a DoD quality control inspector for vehicle programs, trucks stored in parking lots must be driven every few months or the tires rot. Such trucks typically have automatic deflation systems to reduce tire pressure for muddy and sandy conditions. When the system is activated on dry rotted tires, the sidewalls rip.
 
That is interesting.

I am delighted that the Russian army appears somewhat thwarted, and hope that soon somebody stops this horrible invasion, but I have heard that logistics is not their strong suit, and that they are running out of everything. Serves them right.
 
Cowboys Air Ranch 84ME said:
Howdy,and Welcome,

Question, when you take off and break ground, do you get any vibration? Look out the window at each tire and see if it is bouncing or shaking. This would be a sign of imbalance.

I know as I put 8.50x6 (6 ply) on my Citabria recently, and I get this shimmy. All was mounted correctly with the dot aligned with the valve stem, but one tire still majorly out of balance.

I hit the brakes as soon as I am airborn to stop the shimmy immediately. On landing it is noticeable from touchdown till the tail can not fly anymore and settles down on the runway.

I am putting on my "Smoothie 4 ply" tires as soon as I can get back on the grass and off winter pavement.

Other factors could be alignment as stated above, or just loose/bad wheel bearing, or gear attachment bolts? Give it a good once over,.....Twice!

Ken "COWBOY" Winiarski
Cowboys Air Ranch (84ME)
Click to expand...

Just as a frame of reference this is what it took to balance one of my wheels. Other isn’t so bad but definitely noticed on takeoff and landing. 7.5oz added. Smooth as butter now. Where new tubes and tires.
 

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Bartman said:
does the ink dot on the tire go with the stem or opposite the stem?
Click to expand...
Red dot 🔴 match’s up with the valve stem or the yellow dot/line on the tube if the valve stem isn’t the heavy spot of the tube. I have only ever seen yellow marks on very large tubes, like on an air tractor.
 
Nice airplane Jarhead! I recently acquired a 1999 GCAA myself. Great aircraft and a lot of fun. Good luck getting rid of your wheel shimmy.
 
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