REFLECTOR: Shimmy and Nose Gear Pivot Bushings

[Chuck Jensen]

Larry,

If you stay in the 15-20 ft-lb range for breaking force on the nose
wheel, we wouldn't expect to you to experience shimmy, but you don't
understand...we are GREEDY.  We want perfect, fabulous and fantastic.
Good, okay, it works, is simply not good enough for inveterate tinkers,
which almost by definition, builders are.

Bob, if you build your plane by the plans, and follow Scott's advice
about properly lubing and tensioning the nose gear, you will likely not
have any problem.  Nonetheless, a cheap insurance policy to remedy a
shimmy event is knowing where there's a good grass strip within flying
distance...and having a wrench with you.  

The circumstance that seems to induce the greatest tendency to shimmy is
landing in a slightly crabbed position.  When the nose touches, the
wheel is not aligned with the motion of travel and friction of the
runway will 'kick' the tire toward alignment.  Of course, the kick
always goes past center, then the friction of the runway kicks it back
the other way, ad nauseum.  

Trying to slow rapidly is only mildly effective.  It seems that as you
slow down, the frequency of oscillation also slows but the amplitude
increases.  And hard braking, which shifts weight to the nose, also
seems to aggravate it once started.  Best solution is to lift the nose,
give it gas and go to a grass field.

Chuck



-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of larry
Sent: Saturday, November 19, 2005 4:34 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings

I have a fast build kit.  Wheels were balanced, mains aligned with laser

level, and I maintain 15-20 ft-lb on the nose gear.  No shimmy.



At 12:04 PM 11/19/2005, you wrote:
>Just curious, and haven't seen reference to it....are these
shimmy/gearleg 
>vibrations limited to "scratch-built" kits, or are the fast-build kits 
>similarly afflicted? (Hoping that fix that Duane was mentioned
considering 
>gets included in my fast-build kit due in Jan).
>
>Bob
>
>
>-----Original Message-----
>From: Brian Michalk <michalk at awpi.com>
>To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>Sent: Sat, 19 Nov 2005 10:24:00 -0800
>Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
>
>Alex Balic wrote:
> > There is a viscous coupling that I had to spec years back for a
machine
> > design project- kind of like a tiny torque converter filled with
oil- I
> > have no idea if there is one available that could/would fit the nose
> > gear, but basically, it allows relatively slow turning of the shaft,
but
> > resists rapid turning/oscillation ( shimmy) kind of the same
function
> > that a shock absorber has on the suspension of your car- will see
what I
> > can locate on it and report back........
> > > Alex
> >
>How about a magnetic particle clutch?
><http://www.sdp-si.com/D790/HTML2/D790C13026_2.html>http://www.sdp-si.c
om/D790/HTML2/D790C13026_2.html 
>
>_______________________________________________
>To change your email address, v! isit 
><http://www.tvbf.org/mailman/listinfo/reflector>http://www.tvbf.org/mai
lman/listinfo/reflector 
>
>
>Visit the gallery! <http://www.tvbf.org/gallery>www.tvbf.org/gallery
>user:pw = tvbf:jamaicangoose
>Check new archives:
<http://www.tvbf.org/pipermail>www.tvbf.org/pipermail
>Check old archives: 
><http://www.tvbf.org/archives/velocity/maillist.html>http://www.tvbf.or
g/archives/velocity/maillist.html 
>
>_______________________________________________
>To change your email address, visit 
>http://www.tvbf.org/mailman/listinfo/reflector
>
>Visit the gallery!  www.tvbf.org/gallery
>user:pw = tvbf:jamaicangoose
>Check new archives: www.tvbf.org/pipermail
>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html

_______________________________________________
To change your email address, visit
http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html