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Date: Tue, 20 Feb 2007 15:35:46 -0500
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Subject: RE: [LML] Re: Outboard elevator hinge bleeding
In-Reply-To: <list-1850507@logan.com>
Thread-Topic: [LML] Re: Outboard elevator hinge bleeding
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References: <list-1850507@logan.com>
From: "Zavatson, Christopher J \(US SSA\)" <Christopher.Zavatson@baesystems.com>

John,

Comments/replies/questions are inserted:=20

.....He does not include Carbinge in his test.....

Send me a small sample and I'll add it.  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.  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.
   =20
.....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?
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.
 =20
 =20
.....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.   =20
 =20

   .....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? =20
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=20
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. =20
 =20

Regards,
Chris Zavatson
N91CZ
360std
www.N91CZ.com