REFLECTOR: Shimmy and Nose Gear Pivot Bushings

[Chuck Jensen]

            TEC,
 
            I believe this has been explored before, but I'll ask again,
"are you sure it is the nose wheel that is causing the shimmy you are
feeling?"  The symptoms you describe sounds more like
harmonics/resonance/vibration in your main gear legs from the pulsing of
the brakes as the pads alternate between high and low spots on your
disk.  It would be real interesting to have someone stand beside the
runway in the zone where you normally would expect the shimmy and watch
your nose gear and mains.  The odds seem good that your nose wheel will
be 'dead steady' but your main legs will be cycling forward and back
rapidly due to the uneven braking from your brake discs.  It may feel
like a nose gear shimmy but it's probably a gear leg vibration parallel
with your line of travel. 
 
            Just a thought and something to consider.
 
            Chuck
 
            
 
-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of HYTEC45 at aol.com
Sent: Friday, November 18, 2005 12:41 PM
To: reflector at tvbf.org
Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
 
After 700 hours flying my STDRG, I find that I only have a shimmy (nose
wheel) problem when my Cleveland brake disks get some time(braking) on
them.  They seem to warp just enough to cause a shaking (however slight)
in the main gear leg, which in turns produces the nose shimmy.  This
only happens on landings while decelerating through 30 mph and below.
If I have the room (proper runway management), I let off the brakes, and
the shimmy stops immediately.  On landing, immediately after touch down
of the nose wheel, I apply steady, firm and somewhat aggressive breaking
to approximately 35/40 mph.  Then I let off, and coast as much as the
available runway will allow. This does tow things.  First it confirms
that I in fact do have good breaking capability's while I still have
runway and airspeed to go around, and second (I feel) limits the amount
of time the pads are in contact with the disk.  I know the argument that
this causes more heat, but I am on them less.  This technique seems to
eliminate the "brake caused shimmy" once the symptoms start which is
after about 50 (normal breaking )landings on new disks.  When it bothers
me to much, I either turn the disks, or replace them.
 
Right now, the right brake causes some nose shimmy, so I will probably
turn that disk, and that will be that for a while.
 
TEC
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