REFLECTOR: Shimmy Damper Settings

Thu Sep 19 14:18:19 CDT 2013

Hi Bob,
I should have mentioned that the Jorge Bujanda nosegear strut bumper mod is for FG's. Certainly it is in the archive. 
Worth looking up for the FG folks... 
Vibration sets off shimmy people. An out of balance nose wheel/tire combo sets off vibration. A sloppy  fitment of a nose gear strut sets off vibration.
This from Scott Swing. After 2 nearly catastrophic nose gear shimmy episodes, this rings true for my bird.
Orig shimmy damper on the cone washers: 8lbs tension. No shimmy. Super easy ground turns.
PEACE OUT

Mark B. Magee
N34XL XLFG
Sent from IPhone 4S

On Sep 19, 2013, at 12:53 PM, "Bob Jackson \(Jax Tech\)" <bobj at jaxtechllc.com> wrote:

> 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
>  
> 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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