REFLECTOR: Nose wheel shimmy

Chuck Jensen cjensen at dts9000.com
Sat Aug 12 05:49:05 CDT 2006


Al,
 
The optimum time to induce nose shimmy is landing in a bit of a crab.  If in a crosswind, one doesn't get the nose exactly straight with the track, when the nose touches, the nose wheel is 'flipped' to the side when it touches....and then it starts.  Personally, I've never seen an instance induced by high speed taxi and other exercises, just on touchdown and then usually when there is some runway misalignment to kick the nose gear to the side.
 
A sure cure is if you keep in mind a nearby grass strp where you can land and tighten the nut--thought there aren't many of those around and of the proper length.  Ag spraying operations often have a grass strip available so keep an eye out for one of those as a alternate if the nose shimmy starts on touchdown.
 
Chuck
 
 
 -----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Al Gietzen
Sent: Saturday, August 12, 2006 1:37 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Nose wheel shimmy



	 

	Kirk,

	 

	Every time I hear about an "incurable" nose gear shimmy I wonder, what 

	is different.  There are too many flying V's with no problem, like my 

	airplane for this to be a design flaw. 

	 

	I'll propose 4 factors that could influence whether nose wheels shimmy or not:

	 

	1.     Assembly of the wheel hub.  The two halves of the wheel hub are not indexed (at least mine were not), and with the three bolts, it can be assembled in three positions.  I found the only one position that aligned properly so there was no wobble or run-out.

	2.     Wheel balance.

	3.     Vertical alignment - side to side.

	4.     Negative caster angle (Kurt referred to as king pin angle). I think it is supposed to be about 2 ½ degrees - forward of vertical.  Wayne (IIRC) has written about getting it right on his.

	 

	Of course there could be others.

	 

	I set the 'drag' on my nose wheel at 10-12# with the fish scale on the back edge of the tire.  Not much experience yet, but some high speed taxis, nose wheel lift, crow hop, and a 100 kt touchdown from first flight; and no signs of shimmy yet.  Perhaps I got lucky and had the factors come out OK.

	 

	I have some ideas about rotational balance around the vertical axis that could allow lower drag force.  I'll test something after I get through Phase I, or close to it.

	 

	FWIW,

	 

	Al

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