REFLECTOR: Nose Wheel Pivot
Hal Smith
h.smith61 at verizon.net
Tue Jun 27 09:05:56 CDT 2006
How did you do the hydraulic steering? I am not interested in rotational
damping only the steering since I am considering a new nose wheel design and
would like to use an existing steering system if possible.
Thanks
Hal
h.smith61 at verizon.net
----- Original Message -----
From: "michalk" <michalk at awpi.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Thursday, May 18, 2006 8:33 AM
Subject: Re: REFLECTOR: Nose Wheel Pivot
> 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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>>
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>
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