REFLECTOR:Nose wheel shimmy

[Mike Pollock]

I agree with you Brian.  We have gone through 3 sets of tires so far and we
have never balanced any of them. We have not had any shimmy at all except
during the second flight of the plane (6 years ago) when we loosened the
nose gear axle nut to steer easier.  After the first shimmy, we tighten it
back up and everything works as designed.  The dynamics of the system has
more to do with maintaining the shimmy, whereas the statics of the system
only helps to keep the system from starting the shimmy.  There are other
forces acting on the system that can cause shimmy other than just a tire out
of balance.

Mike Pollock




-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Brian Michalk
Sent: Monday, August 11, 2003 8:53 PM
To: reflector@tvbf.org
Subject: RE: REFLECTOR:Nose wheel shimmy


All this talk about balancing tires:

Don't forget that if a tire is in balance, that is only for that static
situation.

A thought problem:
Take the following structure:


A-----------B
            |
            |
            |
            C
            |
            |
            |
            D------------E

Let the AB distance be 1 foot, the BD distance be one foot and the DE
distance be one foot.
Now, let's balance this structure at C with weights at A and E, oh, let's
say 10 kilograms, with the rest of the structure weighing 1Kg.  Okay it's
balanced, now let's rotate it about point C such that B, C and D stay in the
same plane.  What happens is that A and D will want to turn the plane of
rotation.  For a tire, imagine BC and D being exactly in the denter of the
tire.  If you cut the tire along this line you would have two donuts.  A and
E could represent opposing counterbalance weights applied to the rim of the
tire.  The correct balancing schematic would look more like this:

A-----------B
            |
            |
            |
            C
            |
            |
            |
E-----------D

I'm sure everyone is confused now.  A sloppy nosewheel bearing would
aggravate this problem.

A way to test this would be to mount the wheel on some sort of bearing that
could be held by hand.  Bring it up to speed like someone mentioned with a
die grinder.  It it vibrates (wobbles about the bearing axis), it could
cause a shimmy.

On the other hand, what do I know.  I'm still building.

 Brian Michalk  <http://www.michalk.com>
Life is what you make of it ... never wish you had done something.
Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
musician, home-brewer, entrepreneur and mostly single

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of
Alexander Balic
Sent: Monday, August 11, 2003 8:08 PM
To: reflector@tvbf.org
Subject: RE: REFLECTOR:Nose wheel shimmy


Another way to do it is to pull the tire, and the axle and support the
axel/tire assembly on the edge of 2 single edge razor blades- there will be
almost no rolling friction on the almost perfect edge- and add the weights
until the tire no longer wants to find any particular favorite place to
rest.
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of
Dave Scharfenberg
Sent: Monday, August 11, 2003 1:46 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Nose wheel shimmy


My nose tire was way out of balance as it came.  I was able to balance it by
jacking up the front of the plane and spinning up the tire with an air
powered die grinder.  I used one of those 1" drum sander attachments without
the sandpaper drum installed.  You can really get that tire spinning!  Then
using stick-on lead weights and trial and error, I was able to get it to run
smoothly.  I used double stick tape on the weights until they were where I
wanted them and then used the self adhesive tape on the weights.  So far the
weights seem to be staying put.


Dave Scharfenberg


on 8/9/03 9:54 AM, SlvEgl99@aol.com at SlvEgl99@aol.com wrote:


When I had shimmy I also had an out of balance front wheel. I removed it and
reinserted the axle in the bearings. I then bought two aluminum angle irons
about 3 feet long and set them up on my workbench, and levelled them in
every direction. I placed the wheel between the aluminum L's supported by
the axle and watched. The wheel turned. I got some aluminum weights from Big
"O" tires and applied them on the light side of the wheel, on the inner side
of the wheel. After installing about 3 weights I had a balanced wheel and
tire.

The weights are held on by adhesive that is on the weights when I got them.
None have dropped off, due I suppose to the fact that they are held on by
centrificial force when the wheel is spinning.

This in addition to keeping the fork tight seems to have resulted in a very
much smoother front gear.

I suppose this is not as precise as spin balancing, but it worked for me.

Bob Wood

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