REFLECTOR: Shimmy Damper Settings

Thu Sep 19 12:48:44 CDT 2013

Ron,

We use an old fashioned bathroom 'spring' scale, turn it vertical, reset the
zero, and then push it against the back outside/inside edge of the nosewheel
tire for the friction settings I described below.  Ours is an XL/RG and we
fly it about 500 pounds heavier than most XL's - that may account for some
of our use of higher friction settings.  We have no trouble taxiing it with
the Belleville's set for a breakout friction of ~35 lbs, and very little, if
any braking at the start of the take-off run to keep it aligned on the
runway.

Using the above spring scales, like I said, I don't see that the damper
provides more than 5 lbs of turning friction, and at least with my hand, I
can't feel much resistance even to 'impulse hits' with the High Speed
setting in CW essentially all the way.  Maybe you just can't apply fast and
hard enough of an impulse with your hand to test it.  Still, the damper does
provide some turning resistance and we've kept ours set with both Low & High
Speed knobs at ~1 turn back from full CW.  No issues with shimmy so far with
more than 25 landings.

Bob

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Ron N VelocityXLFG
Sent: Thursday, September 19, 2013 8:18 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Shimmy Damper Settings

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

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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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