REFLECTOR: Shimmy and Nose Gear Pivot Bushings

[John Dibble]

Good point.

John

steve korney wrote:

> John...
>
> If you use your GPS, you can get a good reading of your ground speed...
>
> Best... Steve
>
> ----Original Message Follows----
> From: John Dibble <aminetech at bluefrog.com>
> Reply-To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
> Date: Fri, 18 Nov 2005 16:13:32 -0600
>
> 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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