REFLECTOR: Nose Wheel Pivot
michalk
michalk at awpi.com
Tue Jun 27 09:34:17 CDT 2006
It's vaporware at the moment.
I have drawn up some crude plans which involve a sun gear to increase
the angular distance that a cylinder would need to travel.
I think that damping should be designed in from the start, because
steering control won't be enough to arrest the problem, and it most
likely would rip itself off the airplane before the pilot could react.
It would really be nice to have something that castors 360 degrees, but
that's going to be difficult.
At this time, the steering assembly is on back burner. I'm feverishly
working to get my plane in the air, because I can't stand the thought of
Kurt beating me there.
Hal Smith wrote:
> 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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