REFLECTOR: shimmy

Fri Feb 20 06:57:57 CST 2009

Sid, thanks for the plot showing the two types of friction.  The drag force
shown on the plot is measured where?  Is it at the axel, parallel to the
center line or ??  Also how did you get these values?

All, I am writing a little code to show the effect of the different factors
on shimmy.  It will take a couple of weeks of an-hour-here type work to get
some real answers (if I am successful). It will be able to run both
Belleville and viscous (i.e. hydraulic) dampers, wide and narrow tires, bent
and straight struts.

Some data I need:
1) since my plane is not finished, I have little idea of the load (vertical
weight) carried on the front wheel.  Can someone give me a range, with pilot
only and with one passenger.  
2) does shimmy mainly occur on take off or landing?
3) if on take off, at what speed does it kick in?
4) if on landing, does it go away as you slow down?
5) any feel for the frequency of the vibration? Even answers like "It feels
like a car with unbalanced wheel at XX mph will be helpful.

David G. Ullman PhD ME
Robust Decisions
ullman at robustdecisions.com
541-754-3609

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Today's Topics:

   1. Re:  FW:  GPS for IFR (David Staten)
   2. Re:  wheel shimmy (Sid Knox)

----------------------------------------------------------------------

Message: 1
Date: Thu, 19 Feb 2009 23:24:36 -0600
From: David Staten <david.staten at gmail.com>
Subject: Re: REFLECTOR: FW:  GPS for IFR
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Message-ID: <499E3E94.7060804 at gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

You can use a Non IFR GPS to help maintain situational awareness.

Like.. you have a VOR, ILS and NDB in your plane, and a handheld GPS.

With a non-IFR GPS
You cannot file /G.
You cannot accept GPS approach clearances.
You cannot LEGALLY use the GPS device in lieu of the primary equipment - 
i.e. it must be working, not disabled.
You cannot LEGALLY use the GPS device in lieu of DME if the DME is 
required equipment for the approach you are cleared on.

You CAN use the non IFR GPS to help keep you heading towards the NDB, on 
the approach centerline, navigating over fixes, markers and whatever 
else while you use the VOR, ILS, NDB etc as your "primary means of 
navigation"

An IFR GPS automatically increases the sensitivity of the display from 1 
mile = 1 dot in non approach airspace to 1 dot = 0.3 miles in the 
terminal end of the approach. Any gps can be adjusted, but the IFR ones 
do this as you progress down the approach

You must have an annunciator or GPS display on or near the centerline of 
your field of view (in the 6 pack, essentially) that indicates whether 
GPS is armed or in approach mode, and the database must be up to date.

I may have missed something because I'm running off memory here, but was 
at one point assisting with Chris Barber's build, and had acquired a 
King KNS 89B IFR capable GPS and had obtained the hardware to make it an 
IFR legal and capable installation..

aminetech at bluefrog.com wrote:
> That's very helpful.  I'll have to check the centerline distance.  I 
> understand my plane is IFR approved for VOR.  If my GPS is not 
> approved, can I fly IFR with it, or only if the VOR is not working?  
> I'm looking for the meaning of "additional source".
>  
> John
>
> --- ljepstein at hotmail.com wrote:
>
> From: lawrence epstein <ljepstein at hotmail.com>
> To: Reflector Reflector <reflector at tvbf.org>
> Subject: REFLECTOR: FW: GPS for IFR
> Date: Mon, 16 Feb 2009 22:51:31 +0000
>
> I forgot, it must have an up to date database.
>
> Btw: you can use any GPS (even a handheld with an old database) as an 
> "additional source" of Nav. Info, as long as you have IFR approved 
> Nav. equipment as your "primary source of navigation)
>
> ------------------------------------------------------------------------
> From: ljepstein at hotmail.com
> To: reflector at tvbf.org
> Subject: RE: REFLECTOR: GPS for IFR
> Date: Mon, 16 Feb 2009 22:47:25 +0000
>
> GPS must be TSO'ed for IFR enroute, approach +/or WAAS. The box itself 
> must be an approved box and the installation must meet certain specs 
> to use it IFR (eg; CNX 480 display has to be no more than 13.4" (I 
> think that is the number) from the "centerline" (center in front of 
> the pilot) or a remote annunciator has to be added in that space (for 
> WAAS approaches).
>
> Larry Epstein
>
> ------------------------------------------------------------------------
> Date: Mon, 16 Feb 2009 14:38:34 -0800
> From: aminetech at bluefrog.com
> To: reflector at tvbf.org
> Subject: REFLECTOR: GPS for IFR
>
> My plane came with an Apollo GPS and I was told that it was not 
> suitable for IFR.  Someone recently told me that any GPS can be made 
> suitable for IFR.  If so, I'd like to know how as I'm working on my 
> IFR ticket.
>  
> John
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------------------------------

Message: 2
Date: Fri, 20 Feb 2009 01:23:23 -0600
From: "Sid Knox" <sbjknox at earthlink.net>
Subject: Re: REFLECTOR: wheel shimmy
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Message-ID: <011201c9932c$1f6226a0$a941fea9 at texastornado>
Content-Type: text/plain; charset="iso-8859-1"

From: "Al Gietzen" <ALVentures at cox.net>

> So what you are saying is the Sticktion is what we are fighting  right.
> So if we over come this then we would not need toe Hydraulic dampener?
>
> Ron
>
> "Sticktion" is only part of the problem.  I find the sticktion force only
> about 2-3 lbs more that the steady state.  What we want is a freely
> castoring nose wheel that does not shimmy - or as close to that as 
> possible.
>
Here is the graphic of what you are saying... this data was taken some years

back.  You can see and compare the stiction of the two systems in the 
near-zero Angular Velocity region. (yes, I know now that it should say 
"Belleville").

Sid
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