REFLECTOR:Nose wheel shimmy

[Brian Michalk]

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