i am experiencing rudder shimmy through right pedal just after lift off.

My 601 is 6yo, 350 hrs Jabiru 3300.  My hrs 800.

i have checked cable tensions, all ok.  It settles after about 5 seconds of applying rt and or left rudder.

ball is in centre

i have removed wheel pants, no change.

any suggestions?

Bob Emery, Perth W Aus

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Comment by Robert Emery on April 22, 2018 at 9:52pm

Thanks to all who responded.

I am happy to say balancing the nose wheel with stick on weights resolved the vibration issue.

Back to normal.

Bob Emery

Comment by David Krakowsky on April 9, 2018 at 2:33pm
Harbor freight motorcycle wheel balancer does a great job do $40.00
There are always 20% off coupons available
I found I need to epoxy the weights on the wheels. Makes a huge difference in my plane. The cheap Aero Trac tires I used are always way out of balance.
I have all three balanced and redo it any time I replace a tire.
Dave
Comment by Bob Pustell on April 9, 2018 at 11:55am

Very few people bother to balance airplane tires but it makes a difference. If your shimmy after liftoff goes away when you apply the brakes in flight then it is a main gear tire shaking. If it keeps on with the brakes applied then it's the third tire. This is all immediately after take off, since the wheel stops rotating (and therefore stops shaking from imbalance) shortly after take off.

Some people choose to just ignore the shake, which works in the short term. It will, usually, lead to a flat spotted tire in the longer term. If your wheel/tire assembly has enough of a heavy spot to shake the plane the heavy spot will usually settle to the bottom while the plane is airborne. Therefore, upon touchdown it is always the same spot on the tire that absorbs the impact and the little chirp of a skid until the tire starts rotating. That will wear out that spot on the tire long before the rest of the tire is worn. People always assume a flat spotted tire was skidded with the brakes badly enough to flat spot the tread, but frequently the flat spot is due to one spot on the tire absorbing every landing the plane makes. If your wheel/tire is balanced (or even fairly close to balanced, it does not need to be exact) then the tire stops rotating in a random manner and you have different sections of tread absorbing different landings and even wear occurs.

I recommend using fairly small stick-on wheel balance weights, the quarter ounce size. Larger ones cannot follow the fairly sharp curve of a small diameter aircraft wheel unless you carefully bend them to the radius of the wheel. If you need a lot of weight you can apply some of the weights on each side of the wheel to get more weight at the light spot of the wheel - just be careful not to locate weights where they conflict with the brake caliper or other structure.

If you do not have access to a static wheel balancer your can do it on the aircraft's axle. Remove and clean the wheel bearings and wheel hub, then lube the wheel bearings with just a little bit of light oil. Mount the wheel on the axle and just barely snug up the bearings so the wheel rotates very easily on the oiled bearings. The heavy spot will settle to the bottom. You will need to add enough weight opposite the heavy spot to make the wheel balanced. When it is balanced, the wheel will stop at any position and stay there - there is no heavy spot to pull that part of the wheel down to the bottom.

Tape weights into place to get an idea how much weight is needed at what location, then mark the location on the tire sidewall with chalk, remove the wheel, clean the weight locations well (the adhesive on the stick on weights will not stick well to dirty and/or oily surfaces) and stick on the weights. Reinstall and check to see if there is still a heavy spot. Install more weight if needed until the heavy spot is gone and the wheel will happily stay in any spot you stop the rotation. Then, grease up your wheel bearings and install the balanced wheel/tire assembly normally.

By the way, on the main gear wheels it is good to mount the wheels for balancing with the brake pads either removed or pulled back so they don't touch the disk - you need the wheel assembly to rotate very freely and easily, no drag from grease in the bearings or brakes rubbing the disk. Some folks mount the wheel for balancing without having the grease seals in the wheels to avoid the little bit of drag the grease seals induce.

Comment by Robert Emery on April 7, 2018 at 8:43am
Thanks guys, I will check my front wheel balance, may even change tyre first since it the original. I will advise the outcome. Regards Bob
Comment by Bob McDonald on April 7, 2018 at 7:28am

Balance front tire. I had a front end shake on take off so bad I first thought it was an engine failure.

Comment by Randy Boykin on April 6, 2018 at 9:53pm

I had the same problem on my 750. It ended up the tire was out of balance. After take off the tire is still turning, severely out of balance. After balancing it problem solved no more vibration. It took several ounces to balance. It is not hard to make your own balancer. Hope this helps

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