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Please help with nose wheel vibrations

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15 May 2019 13:24 #1977 by Ronald Raty
Replied by Ronald Raty on topic Please help with nose wheel vibrations
SM-15 provides some guidance on this. Note that it recommends taking your front tire to a local automotive shop for balancing.

www.univair.com/content/ERC_SM15.pdf

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12 May 2019 17:07 #1962 by Tad Daughters
Replied by Tad Daughters on topic Please help with nose wheel vibrations
From the Aircoupe Service Manual - Models F-1 and F-1A - Dated 1 February 1965:

Vibration and Shimmy
An improperly maintained nose landing gear
may tend to shimmy in ground operations, and
to vibrate immediately after take-off.
If the wheel and tire are out of balance, rota-
tion of the wheel after take-off will cause the
gear and engine mount to vibrate; this may be
corrected by proper dynamic balancing of the
nose wheel.
Vibration due to unbalance of the main wheels
can be identified, since it will stop upon applica-
tion of the brakes after take-off.
If the steering system of the nose wheel or
strut attachment is loose, wheel unbalance or
ground roughness can be a disturbing influence
which will induce shimmy.
Shimmy may usually be eliminated by tighten-
ing the various joints in the nutcracker, steering
push rod, and in the control system. Shimmy is
sometimes caused by looseness in the nose gear
attaching bolts, and in the two countersunk
screws which retain the outer cylinder head.

=======================

Hope this helps.

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20 Mar 2019 21:34 #1882 by Gene Bunt
Replied by Gene Bunt on topic Please help with nose wheel vibrations
I have found that uneven wear on the nose wheel will cause the shimmy. However the coupes I have did not have a fork it had the one side with the single ball bearing. The uneven wear could be caused by a balance problem. The side load pressure on landing in a crab also causes uneven tire wear. On both coupes I had and have. changing the tire eliminated the shimmy. Since these tires are expensive I plan to send my old tire to have it re-treaded.

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18 Mar 2019 09:45 #1876 by Bob Thompson
Please help with nose wheel vibrations was created by Bob Thompson
This may turn into a series of posts as I evaluate specific details but I am looking for some help on the famous nose wheel shimmy / vibration causes and solutions. First, I have read all the summary articles on what to look for and have addressed with my mechanic most of them but there are still a few details I can not find online.

I have owned the plane for 1-year and never experienced this until I picked it up after annual. Initially we noticed that the nose wheel had less play in it than before due to the main nut being reinstalled a little tighter. this was loosened and the issue when away for 4 take-offs and landings...3-days later is showed back up but much milder than the original shimmy. Next we inspected the wheel itself and found severe flat spots, uneven tread wear cracks from age so shimmy or not it was time to replace. That was done over the weekend with a new 5.00-4 which also behaved the same way on rotation...vibration as the weight was coming off the nose wheel.

One detail I can not find a quantitative answer to is exactly how tight or loose the nose wheel nut should be. I understand (maybe incorrectly) that there should be a good amount of movement of the wheel that was intended to aide in x/wind operations in the original plane. Is there a spec tolerance to determine the limits of this movement? Also, I have rudder pedals and can control the rudder independently from the nose wheel...would this imply that my wheel nut should be tighter since using the rudder I can eliminate all side load from the wheel above about 40-MPH? I have not flown the plan any differently than over the last year and I can't find any mention or mechanic's memory of adjustments made to the steering rigging; if I can find a spec on how tight the nose wheel should be, that would help in this process.

THX

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