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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