REFLECTOR: Shimmy and Nose Gear Pivot Bushings

[John Dibble]

Chuck,
I agree with you.  There are two kinds of "shimmy".  The nose shimmy is
very violent and won't stop until the plane is stopped.  The gear leg
shimmy will "stop" if you let off the brakes.  My right main shimmys,
and my left doesn't.  I videotaped it during a high speed taxi.  It
shimmys at around 20-30kn (just a guess as my AI doesn't register at
that speed) both during acceleration and deceleration.  With the brakes
off, I can't feel it, but it shows up on the videotape real clear.  It's
a front to back oscillation like you said.

John

Chuck Jensen wrote:

> 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, 200512:41 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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