REFLECTOR: Nose Wheel Pivot

michalk michalk at awpi.com
Thu May 18 10:33:23 CDT 2006


Hehe,

I've got the plans for hydraulic steering, but rotational damping would 
be better suited to increase friction as rotational velocity increases.

I think a rheopectic http://en.wikipedia.org/wiki/Rheopecty
solution would work best.  The opposite of thixotropic 
http://en.wikipedia.org/wiki/Thixotropy solution.

Basically, the faster you try to turn it, the more torque is required. 
It seems like a fairly simple pancake damper could be built on this premise.

There would need to be a lot of surface area, so the two halves of each 
pancake would need grooves.

Al Gietzen wrote:
> I have wondered if the 14# spec is break-away or in-motion force.  Also, 
> with the 14# setting with no load on the wheel, what is the force when 
> the wheel is on the ground and you have a couple big bodies in the front 
> seats?  Sounds like Larry has taken a step in the right direction.  I’m 
> waiting for Brian to come up with the hydraulic rotational damperJ.
> 
>  
> 
> Al
> 
>  
> 
>  
> 
>  
> 
> *Subject:* RE: REFLECTOR: Runway Rash
> 
>  
> 
> That is exactly correct- the numbers for static vs sliding are closer 
> with the plastic -  a well lubed washer assy is going in the right 
> direction, but it is difficult to maintain the correct pressure 
> relationship- dirt, grease hardens, slings out ect.
> 
>  
> 
> ------------------------------------------------------------------------
> 
> *From:* reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *Chuck Jensen
> *Sent:* Wednesday, May 17, 2006 3:27 PM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* RE: REFLECTOR: Runway Rash
> 
>  
> 
> Larry,
> 
>  
> 
> Very good explanation of how static v. sliding friction affects our nose 
> wheel steering, but I’m still having difficulty seeing how the plastic 
> washer sharply changes the equation.  Are you saying that the plastic 
> washer reduces the differential between static and sliding, hence the 
> static (aka breakout force) can be set lower without compromising the 
> necessary sliding friction which dampens the shimmy?
> 
>  
> 
> If that’s the theory, its comprehensible why it would reduce the 
> breakout force necessary to still damp the shimmy, but is the 
> change/improvement actually noticeable from a well lubbed Bellevile 
> washer setup?
> 
>  
> 
> Chuck Jensen
> 
> Diversified Technologies
> 
> 2680 Westcott Blvd
> 
> Knoxville, TN  37931
> 
> Phn:     865-539-9000 x25
> 
> Cell:     865-406-9001
> 
> Fax:     865-539-9001
> 
> cjensen at dts9000.com
> 
>  
> 
> -----Original Message-----
> *From:* reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> *On Behalf Of *Laurence Coen
> *Sent:* Wednesday, May 17, 2006 10:07 AM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* Re: REFLECTOR: Runway Rash
> 
>  
> 
> Al,
> 
>  
> 
> The manual tells us to set the force to move the nose wheel at 12 to 15 
> lbs. Mine is set to 14 lbs.  The basic problem comes from the fact that 
> there are two types of friction involved.  The first is static friction 
> which is what we measure during adjustment.  When the fork moves we have 
> sliding friction which is less than the static friction.  With lack of 
> lubrication, rust and/or dirt the difference between the two becomes 
> much greater.  As a result the static or break out force is excessively 
> high when you have enough sliding friction to prevent shimmy.  This 
> gives a plane that is hard to steer with marginal shimmy control.  The 
> idea of the nylon washer is to keep the value of the static and sliding 
> friction as close together as possible.  Think of a rusty hinge that 
> creaks.  What makes the noise is the static friction is so high the 
> hinge starts to flex before it moves.  When it does move the sliding 
> friction is low enough to allow it to spring back to its original shape. 
> the rapid repetition of this process makes the creaking sound.  
> Lubrication is curative.
> 
>  
> 
> My previous description was inaccurate.  When I replaced my original 
> fork with the new thicker one I rearranged the washers.  The current set 
> up is two Belleville washers with the cupped surfaces together above the 
> fork and the nylon washer, flat steel washer and nut below. A word about 
> materials.  Phenolic is not self lubricating and absorbs water.  Teflon 
> is self lubricating but suffers from cold flow which would require 
> constant adjustment.
> 
>  
> 
> Larry Coen
> 
>  
> 
> ----- Original Message -----
> 
>     *From:* Al Gietzen <mailto:ALVentures at cox.net>
> 
>     *To:* 'Velocity Aircraft Owners and Builders list'
>     <mailto:reflector at tvbf.org>
> 
>     *Sent:* Tuesday, May 16, 2006 11:13 PM
> 
>     *Subject:* RE: REFLECTOR: Runway Rash
> 
>      
> 
>     Let me describe my "Oreo" friction damper.  I have two bevel washers
>     (the
> 
>     cracker part)  with a nylon washer making up the creamy filling.  I
>     made the
> 
>     nylon washer from 1/8" flat stock using a couple of hole saws.   The
>     science
> 
>     behind the idea is that nylon is self lubricating so there is no
>     grease to
> 
>     squeeze out or attract dirt.  My experience to date with ground
>     handling has
> 
>     gone slicker than snot on a brass doorknob.
> 
>      
> 
>     Larry Coen
> 
>     N136LC
> 
>      
> 
>      
> 
>     I think there is something missing here.  The ‘drag’ that makes it
>     hard to steer IS the damping force that keeps it from shimmying.  If
>     the wheel pivots easily, where does the damping force come from?
> 
>      
> 
>     Al
> 
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