REFLECTOR: Shimmy on landing...Some clarifications please THANX!

[Richard Riley]

At 10:10 PM 4/9/2006, you wrote:
>I don't know if you ever owned an EZ or Cozy but I have over 1500 
>hours in them.  I fist changed out the nose wheel tensioner in 1983 
>and it was never used again.  After the bevel washer idea was used 
>the major problem of shimmy went away.  If there was a problem with 
>shimmy it was not the design it was the user.  Once a year I checked 
>the tension on mine and they never changed.  The only problem that I 
>ever found to cause shimmy after this was too low of tire pressure. 
>I kept between 50 and 60 psi in my nose tire.  In most cases it 
>would cause the tire and complete casting to leave the plane and 
>most times through the prop.  So let's not blame it on the design 
>but the lack of care on the operator that causes most of the 
>problems with a good design.

My point wasn't that the Davenport design was bad, it was just that 
EZs and Cozys aren't immune.

I put 400 hours on my Long, and I ran the Berkut factory for 4 years, 
and I have a 540 Berkut now.  We used Cozy Mk4 nose gear parts from 
Brock.  The Davenport damper is a huge improvement over the original, 
but it still subject to shimmy with:

1) Low tire pressure
2) Too little OR too much tension on the nut
3) Inadequate or contaminated grease on the large washer
4) Out of balance nose wheel/tire
5) Loose axle bolt
6) Too much play at the NG-6 upper gear pivot point
7) Inadequate grease in the nose wheel bearings
8) Wrong geometry in the NG6, NG 15, or NG3/4

I've seen shimmy in Davenported nose gears from all those.  I agree, 
it's all inadequate maintenance or construction.  The Davenport 
system is good, but it's not perfect.  I like to see enough margin in 
these designs that they can tolerate bad owners.

Now, some bad craftmanship you just can't design around.  I recently 
saw a V-173 retract that was being rebuilt.  The original owner 
thought that a good way to support tube and wire bundles and such was 
an adel clamp held by a self tapping screw into the internal skin of 
the fuselage.

There was a fuel line that went from the inside of the fuselage 
through the firewall. It was supported by an adel clamp, and the 
screw went into the front edge of the upper spar cap, just off 
center.  That one gives me bad dreams at night.