REFLECTOR:Nose Gear Shimmy

[Chuck Jensen]

At this point, about 12 hours and as many landings with nary a hint of
shimmy.  Lightly loaded and gross.  No difference.

And, the times when the nose drops on a little harder (rare, I assure you),
I'm nearly positive that the "thump" is muted by the softer tire, yet I
don't really see any "squishiness" in the front tire when loaded....and this
at only 16 psi.  And, as John observed, the nose is lightly loaded compared
to the mains, so the low pressure may not result in much tire deformation.

Its fair to say there is some interesting "stuff" associated with this nose
wheel thing.  I grew up on a farm (which probably is a surprise to no one)
and the hay rake had a castering wheel.  Sometimes, for reasons unknown,
it'd shimmy like it had gotten into some bad home brew.  Then other times,
it'd track like a dog.  Who knows.

The wheel balancing is certainly a good idea as that little wheel spins like
the dickens at 80 mph, but I have some doubts that the out of balance issue
is a causative factor in the shimmy problem.  I think the shimmy is likely
initiated when we land and, with a little cross wind, the nose wheel touches
slightly out of alignment with the runway, though in perfect alignment with
the plane.  Upon contacting the pavement, the wheel is kicked in the
opposite direction, which then kicks it back and so on and so forth til it
self destructs and is sliced-an-diced in the prop.

Clearly, the stiff resistance of the tightened washers on the forks kills
this oscillation.  Perhaps, the additional friction of the soft(er) tire
also helps reduce the oscillation vector.  To date the stiff washers
definitely work (even though its a little bit of a cuss to steer) and the
jury is out on the reduced air pressure in the front tire.

I'm just ignorant enough to try the continued loosening of the washers,
and/or, increasing the air pressure to see if I can induce the shimmy, yet
get to a grass field to land and rectify.  Wouldn't it be a kick if all we
had to do was reduce the front tire pressure to 16 psi, then we could loosen
the front forks so a light tap on the brakes would turn the nose ever so
subtly?  There, but for the grace of god, goes a stearable nose wheel.

And, besides, if the test is a failure, MT can always use the extra money!

Chuck



-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of
John Dibble
Sent: Friday, August 08, 2003 8:35 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Nose Gear Shimmy


That's interesting.  My shimmy gets much worse when I brake hard and I
usually let off
to reduce the shimmy.  On a grass strip I have locked the main wheels and
don't recall
noticing much shimmy.  Can the rotors be "turned" like for a car, or should
they just
be replaced?

I'm tempted to try Chuck's low pressure method.  I would think that the tire
turning
on the rim issue would be much less for the nose where the weight is much
less and the
landing impact is much less.  So, tell me Chuck, how many hours do you have
with the
low tire pressure?

John

HYTEC45@aol.com wrote:

> In a message dated 8/6/03 6:34:39 PM Pacific Daylight Time,
> ALVentures@cox.net writes:
>
> <<
>  Perhaps this discussion has gone as far as it can go on one data point.
>  There could have been other factors that caused the shimmy.  We don't
>  really know that is a pressure/shimmy relationship. >>
>
> I have had the Cleveland brakes since day one.  I have been through 2 sets
of
> disks due to warpage from receptive heating (over 600hrs), yet never have
> lost braking.  The symptom is nose shimmy as one brake grabs the warped
disk.
> Changing the disks provides instant relief.  My nose tube is at 50#.
>
> TEC
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