REFLECTOR: Paul Calhoun's nose gear incident

[Pat Shea]

I recently had a shimmy event after 140 hours of
flying w/ no prior shimmy issues. My geometry checked
out okay and my nut was still tight. I started asking
around and it turns out others have had similar
problems during bad landings. Scott Baker indicated
that if you land hard (i.e. bounce the nose gear),
especially with any drift component, it's possible for
the nose wheel to get cocked off to one side a little.
I believe this is what happened to me. When I set the
nose down again (same landing), it was cocked off and
all set up to shimmy, which it did.

Until then, I felt the combination of the latest and
greatest bellvilles along w/ a properly tightened nut
would keep the shimmy away. However, the potential for
this problem exists no matter how tight the nut is.
Also, I assumed continuing to tighten the nut would
improve shimmy dampening but of course make steering
harder. It's seems possible that over tightening the
nut can lead to other unintended consequences like
Paul experienced.  

I tested my nose gear guides to make sure the gear
couldn't get caught up. The guides need to be tall and
wide enough and there can't be any lip. They required
some modification, but eventually I got it so that no
matter how I pushed, pulled, or twisted I couldn't get
the nose wheel to hang up. However, if the nut was
tight enough and the wheel got cocked off during take
off, it seems possible the additional friction could
cause a problem.

I previously hadn't recognized these failure modes. I
ordered the nose wheel locking pin system from Ken. I
haven't installed it yet but will report back once
i've got some hours on it.

FWIW, Pat 


  
--- Phil Hooper <phil at hdmnet.com> wrote:

> Paul plans to try to simulate what happened, take
> photos and advise.  The
> picture in my mind is pressed rubber, tight against
> edges, like a bad
> parking job against the curb.




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