REFLECTOR: Shimmy Damper Settings

Craig Woolston cdwoolston at sbcglobal.net
Fri Sep 20 07:20:52 CDT 2013


Bob, it might help to understand where the shimmy damper comes from.  It was designed to go between the handle bars and the front fork of a motorcycle, imagine Baja racers running over washboard desert at a 100 mph.  It,s not suppose to provide ANY friction at low rotation speeds.

Most people use a fish scale attached to end of the nose tire to measure breakout force, so I think your 35 pounds is an "apples to oranges" comparison.  Might be interesting to measure yours with a fish scale and see what that equates to because I'm sure the moment arm is not the same.

Sent from my iPad

On Sep 19, 2013, at 10:48 AM, "Bob Jackson \(Jax Tech\)" <bobj at JaxTechLLC.com> wrote:

> 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
>  
> 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
>>  
>> 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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