From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] Re: Outboard elevator hinge bleeding
To: lml
Date: Wed, 21 Feb 2007 05:18:04 -0500
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Posted for "John Barrett" <2thman@cablespeed.com>:

  Chris,
  
  Thanks for your response.
  
  My Answers embedded with leading "....."
  
  
  Regards,
  John
  
  John,
  
  Comments/replies/questions are inserted:
  
  .....He does not include Carbinge in his test.....
  
  Send me a small sample and I'll add it.  I will send you one soon.  Several
  years ago, while visiting a Legacy project, I did have chance to examine a
  short section of Carbinge.  I noted movement much like a standard MS hinge
  so I didn't pursue it further.  Our early prototypes were quite sloppy
  because they were layed up by hand on a bench and the notches were cut on a
  jigged tablesaw.  Now the tolerances are very close and there is little if
  any play in the hinges. I don't know how you could have found a sloppy piece
  of Carbinge in a Legacy project as we have been past the prototype materials
  for quite a few years.  It is my understanding that the diameter of the
  hinge pin was changed at some point.  I do not know which vintage I had in
  my hands.a

  .....The fact is there is no play discernable in Carbinge when pulled back
  and forth as it appears he did in the video.....
  
  What is the ID of the Nylon and OD of the pin you are currently using?  The
  ID of the tubing is nominally 3/32" or .0925".  The pins are .085" OD.
  There is some variance in the tubing ID, but this seems to be the best match
  to date.   For cowling attachments some builders need to go to a smaller
  diameter pin that we provide.
  That is what really determines the movement one sees in the video.  The
  Carbinge section I saw had noticeable play(~4 years ago).  Something must be
  different in newer hinges since you report no discernable play.
  Again, if you send me a short section, I'll add it to the video clip.
  If a photo is worth a thousand words, a video has got to be worth ten times
  that.
  
  
  .....From the video it would be instructive to know how long the segment of
  hinge was in each sample and how much pressure was applied.....
  
  The sections are short, four or five segment pairs long (I'd have to check
  to make sure), and the load very light, about 5 lbs.  This was not a stress
  test in any way.  It was just meant to visually record the relative
  movement.  The sections were clamped between 1/4" steel plates to keep the
  hinge sections flat.  Ironically, if the hinge mounting surface is not flat
  and true, less play will be observed in a loose
  hinge while stiffness will be noted in a close tolerance hinge.
  
  
    .....You also stated that ".....Teflon and Nylon are very soft and will
  flow and deform if subjected to high loads."....
  
  This is based on the low modulus of both Teflon and Nylon, Teflon being the
  softer of the two.  This makes tight tolerances between the pin OD and the
  Nylon or Teflon insert ID all the more critical.  If the fit is very good,
  you'll have decent load carrying capability.  If there is any difference in
  diameters, the local stresses will deform the material until the load is
  carried.  This is really no different than with any other material except
  that plastic materials are handicapped by lower physical properties.  Since
  the Carbinge fully captures the Nylon OD, the only interface of concern is
  with the pin.  Starting off with a larger pin OD also helps.  BTW, what type
  Nylon are you using?
  
  
  ... it does not deform, even when subjected to over a million cycles...
  
  Deformation will depend on the load rather the number of cycles.  What load
  was applied during the cycle test?
  Worth noting is that many hinges are not loaded evenly across the span.
  The 'outback' flaps are good examples of this.  Actuation occurs outside the
  first hinge.  The highest stress will be on the most inboard hinge element
  of the inboard hinge.  This can really skew the lb/in number that should be
  applied during testing.
  
  ...I tend to agree with you that Teflon does flow significantly when point
  loads are applied, but I have not tested that theory myself...
  
  Again, this is very much load dependent.  In our case, the diametrical
  tolerance of the pin to hinge interface is a big driver in determining the
  stress on the bearing material, be it metal, Nylon, or Teflon.
  
  
  The genesis of my investigation into alternative hinge options stemmed from
  the desire to minimize play in trim tabs i.e. unbalanced controls surfaces.
  During this same period I was also trying out the Teflon option in ailerons
  and flaps.  After the Teflon failed in my flap hinges, the reaming solution
  that worked well in the trim tab was applied to ailerons and flaps.  (I have
  the MKII tail)  They have held up perfectly over the years and now have
  hundreds of hours on them.  The relationship between play and wear has
  become quite clear.  I clean and lube them, along with all the rod end and
  spherical bearings, once a year.
  
  
  Regards,
  Chris Zavatson
  N91CZ
  360std
  www.N91CZ.com