REFLECTOR: Shimmy Damper Settings

Thu Sep 19 12:53:45 CDT 2013

Hello Mark,

I'm not sure what you're referring to with Jorge Bujuanda's 'nose gear strut
bumper mod' - can you describe a little more, or find and reference the
post.

At least with our Bellevilles, there can be a little 'deadband' play in the
nosewheel turning, before the resistance of the Belleville's takes over - at
least as you're tightening down the nose strut nut and putting tension on
the Bellevilles.  If this is what you're referring to in your 'tight
bumper-bushing' comment below, then I agree 100% -- that little bit of loose
play and free turning movement (that can occur just before the Belleville's
are properly tensioned) can be a killer and instigator of shimmy.  And I
also agree that good balance is important, but I've had less luck achieving
it.

Thanks,

Bob

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Mark Magee
Sent: Thursday, September 19, 2013 12:03 PM
To: Velocity Aircraft Owners and Builders list
Cc: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Shimmy Damper Settings

With a balanced front tire/wheel combo and Jorge Bujanda nose gear strut
bumper mod, I have 8lbs on the bellville washer-damper and no shimmy with
great ground handling.

The importance of a well balanced wheel/tire combo and a tight
bumper-bushing cannot be overstated.

Mark B. Magee

N34XL XLFG

Sent from IPhone 4S

On Sep 19, 2013, at 7:18 AM, Ron N VelocityXLFG <velocityxl at fastmail.fm>
wrote:

When I flew with just the belleville springs I had my front wheel set with
14-16 lbs of pull at the back of the wheel. Were are you measuring 
35 lbs of pull? Now with the steering dampener I have the springs set to
8lbs of pull . This so far allows me to steer with the winglets on take off.
That was my main goal for the dampener. Brakes on take of make the take off
roll last to long:( 

Ron

On 9/18/2013 10:14 PM, Bob Jackson wrote:

Thanks for the steer, Patrick!

I found and read Andy's excellent VOBA article.  Andy did a great job on the
article.  It was very informative and included his modifications and
settings:

*	Replace the shear pin with the much stronger one Jorge Bujanda found
(from McMaster Carr and described in Andy's VOBA article)
*	Set the damper Low Speed valve -- 1 1/2 turns back from full CW
'Hard'
*	Set the damper High Speed valve -- 1 turn back from full CW 'Most
Sensitive'

But what Andy didn't discuss was the relationship between his settings of
the Scott's Damper and the old Belleville washers.  When I measured the
nosewheel 'break-out' force required to just begin to turn the nosewheel
(with no Belleville washer tension) and the Damper set as Andy describes
above -- the 'break-out' force was only 5-10 lbs.

Prior to adding the Damper, we used to set our Belleville washer tension so
that the nosewheel break-out resistance to wheel turn was about 35 lbs.  I
know Andy said that the value of the Damper was in it's resistance to high
speed or 'impulse' shocks, but I'm skeptical that the Damper alone will
provide enough resistance and damping to prevent shimmy from these impulses.
My inclination would be to continue to use the Belleville washers, still
tensioned to provide something very close to the 35 lbs break-out force
resistance, along with the Damper as in Andy setup, or even a little
'harder' and 'more sensitive'.

-- Andy -- if you're monitoring the Reflector -- could you please comment on
my conclusions above, and also describe how you're setting up the Belleville
washer tension in conjunction with your Damper settings.

Thanks,

Bob Jackson
N2XF

  _____  

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Patrick Sieders
Sent: Friday, September 13, 2013 4:00 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Shimmy Damper Settings

There was an excellent write up on the shimmy dampener on the VOBA
newsletter written by Andy Millin.

Great article !

Patrick

Patrick & Dana Sieders

7244 Sugarloaf Drive

Nashville TN 37211

Tel. 615-250-2304

Cell P. 615-918-2698

Email. Js3201 at comcast.net

Http://www.sieders.com/sieders

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