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PolyFiber silver coats and their effect on radio signals

 
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PostPosted: Sun Jun 06, 2010 9:57 am    Post subject: PolyFiber silver coats and their effect on radio signals Reply with quote

So all those decals on FAA-PMA GPS and transponder antenna radomes saying "Antenna: Do Not Paint" are flooby-dust, as I long suspected...  good to know.

On Sun, Jun 6, 2010 at 12:53 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>



Quote:
 I can see where such a semi-solid layer of aluminum flakes could affect some radio waves.  I chose to not do the bottom surfaces.  (They got their share of sealer/paint, etc)


  Perhaps some consideration of electro-magnetic wave behavior
  is useful here . . .

  If you were to seal yourself up in a 55-gallon drum
  and weld the lid on. A hand held vhf radio would be
  useless in terms of communicating with the
  outside world. If you added a hole in the drum (but
  didn't stick the antenna through the hole), the hole
  would have to be enlarged to about 10% of a wavelength
  (120 MHz is 2.5 meters or 100 inches. 10% is about
  10 inches) to have significant communication with the
  outside world but would become really "transparent" at
  50% or 50 inches in diameter.

  Now consider the effects of suspending particles of
  aluminum, probably less than .001" in diameter, in
  the path between a transmitting and receiving antenna.
  These tiny "shields" are about 1/100,000th of a
  wavelength at VHF comm frequencies and 1/10,000th
  at transponder frequencies. They are a SIGNIFICANT
  part of a wavelength at the frequency of light and
  thus offer useful attenuation by reflection of the
  effects of light on the surface.

  The only way you can make these particle a useful
  tool for affecting VHF radio is to electrically bond
  the particles together such that the sheet resistance
  approaches that of a solid material like aluminum
  skin. This simply cannot and does not happen when
  dispersed throughout a fluid polymer intended to
  be a component of paint.

  Some of you may recall a discussion I had with
  Greg Richter some years ago wherein he offered
  that spray-on conductive coatings were suitable
  for adding a ground plane to the inside surface of
  a non-conducting skin. There too we considered the
  exceedingly difficult task of purposefully increasing
  conductivity of an applied coating. In the case
  of PolyFiber coatings, there's no interest whatsoever
  in the electrical conductivity of the finished
  coating.

  It's the size of aluminum particles compared with
  the wavelength of ultra-violet light that makes
  the coating magic . . . it's effectiveness as
  a conductor at radio frequencies is very low
  and as demonstrated . . . not noticeable in terms
  of antennas buried under the skin.


 Bob . . .


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PostPosted: Mon Jun 07, 2010 3:04 pm    Post subject: PolyFiber silver coats and their effect on radio signals Reply with quote

Mike,

I had originally intended to do what you suggest and just PolySpray
the top. I had the same conversation with them! They were quite
insistent about the need to PolySpray all of the aeroplane. Your
experiences directly contradict what they said, i.e. that the UV
damage will occur all over the plane and not just on top.

James

On Sun, Jun 6, 2010 at 5:09 PM, Mike Welch <mdnanwelch7(at)hotmail.com> wrote:
Quote:
  James,

  In addition to the information you just shared regarding PolySpray, I
thought I'd throw my two cents in......

  Back when I had my Cessna, which spent all of it's life outside, I noticed
that the top-side of the surfaces oxidized a fair amount.  The wings' upper
surfaces, fuselage, etc, really needed those polishes and wax jobs.
  The bottom surfaces didn't!!!!     They were as shiny as the day they got
painted.  A wash and a simple coat of wax to clean any smog residue and they
were "good to go"!
  The tops required plenty of polish and elbow grease!!  I was able to
eventually get a pretty decent shine on the top, but it was real evident
that it oxidizes "significantly" more than the bottom surfaces (the paint
job was about 7 years old, the underside has ZERO oxidation).

  So!!  With this personal experience on my own Cessna, I made the decision
to only spray the Poly Spray silver paint on the upper surfaces of the
airplane I'm building.  The sun does NOT shine on the bottom, so I did't
want to waste the paint.
  I know what the Poly Fiber manual says.  It wants you to spray the entire
plane!!  I talked to Dondi Miller ((at) Aircraft Tech Support...a leading
seller of the P.F. products), and she said as far as she knew, you have to
spray the entire plane.  But, since I get to make the decision on my own
plane....I chose not to.  Others opinions may differ.  I'm ok with that.

  What this may have to do with your post is;  if a guy were planning to
install his antennas inside his Poly Fabric covered plane, he might
seriously consider NOT spraying the Poly Spray silver coats on the bottom
surfaces.
  The Poly Fiber manual suggests that in order to get the best UV
protection, you need to spray the silver coatings thick enough that
virtually zero light shines through.  Plus, according to the manual, a
certified aircraft HAS to be fully covered!!
  I can see where such a semi-solid layer of aluminum flakes could affect
some radio waves.  I chose to not do the bottom surfaces.  (They got their
share of sealer/paint, etc)

  Just my thoughts on the matter....

Mike Welch
Kolb MkIII


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PostPosted: Mon Jun 07, 2010 3:40 pm    Post subject: PolyFiber silver coats and their effect on radio signals Reply with quote

This makes me wonder, does UV energy bounce off of the ground?  I got the impression from somewhere that the fabric degrades in a matter of months when it is exposed without protection, so it may be that a little bit of exposure makes a big difference.  Is this discussion about a fuselage made of wood?  It seems like a steel tube fuselage would cause much more RF concern than the Poly-Spray.
On Mon, Jun 7, 2010 at 7:01 PM, James Kilford <james(at)etravel.org (james(at)etravel.org)> wrote:
[quote] --> AeroElectric-List message posted by: James Kilford <james(at)etravel.org (james(at)etravel.org)>

Mike,

I had originally intended to do what you suggest and just PolySpray
the top.  I had the same conversation with them!  They were quite
insistent about the need to PolySpray all of the aeroplane.  Your
experiences directly contradict what they said, i.e. that the UV
damage will occur all over the plane and not just on top.

James

On Sun, Jun 6, 2010 at 5:09 PM, Mike Welch <mdnanwelch7(at)hotmail.com (mdnanwelch7(at)hotmail.com)> wrote:
>   James,
>
>   In addition to the information you just shared regarding PolySpray, I
> thought I'd throw my two cents in......
>
>   Back when I had my Cessna, which spent all of it's life outside, I noticed
> that the top-side of the surfaces oxidized a fair amount.  The wings' upper
> surfaces, fuselage, etc, really needed those polishes and wax jobs.
>   The bottom surfaces didn't!!!!     They were as shiny as the day they got
> painted.  A wash and a simple coat of wax to clean any smog residue and they
> were "good to go"!
>   The tops required plenty of polish and elbow grease!!  I was able to
> eventually get a pretty decent shine on the top, but it was real evident
> that it oxidizes "significantly" more than the bottom surfaces (the paint
> job was about 7 years old, the underside has ZERO oxidation).
>
>   So!!  With this personal experience on my own Cessna, I made the decision
> to only spray the Poly Spray silver paint on the upper surfaces of the
> airplane I'm building.  The sun does NOT shine on the bottom, so I did't
> want to waste the paint.
>   I know what the Poly Fiber manual says.  It wants you to spray the entire
> plane!!  I talked to Dondi Miller ((at) Aircraft Tech Support...a leading
> seller of the P.F. products), and she said as far as she knew, you have to
> spray the entire plane.  But, since I get to make the decision on my own
> plane....I chose not to.  Others opinions may differ.  I'm ok with that.
>
>   What this may have to do with your post is;  if a guy were planning to
> install his antennas inside his Poly Fabric covered plane, he might
> seriously consider NOT spraying the Poly Spray silver coats on the bottom
> surfaces.
>   The Poly Fiber manual suggests that in order to get the best UV
> protection, you need to spray the silver coatings thick enough that
> virtually zero light shines through.  Plus, according to the manual, a
> certified aircraft HAS to be fully covered!!
>   I can see where such a semi-solid layer of aluminum flakes could affect
> some radio waves.  I chose to not do the bottom surfaces.  (They got their
> share of sealer/paint, etc)
>
>   Just my thoughts on the matter....
>
> Mike Welch
> Kolb MkIII
>
>


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PostPosted: Mon Jun 07, 2010 4:35 pm    Post subject: PolyFiber silver coats and their effect on radio signals Reply with quote

Mike, I hope you haven't misunderstood me -- I meant that your
experience of the Cessna's wings top and bottom are what's most
interesting to me, as they are a direct experience gained over several
years of polishing! I found it a bit surprising at the time, that
PolyFiber said that the plane would receive UV damage all over without
the PolySpray, but figured "hey, they're the experts", and did the PS
all over. Had we had this discussion before, perhaps I wouldn't have
done the PS underneath!

James

On Tue, Jun 8, 2010 at 1:11 AM, Mike Welch <mdnanwelch7(at)hotmail.com> wrote:
Quote:
  James,

  My "experience" comes from from seeing countless thousands of things rot
in the sun and rain.  An item NOT left in the sun and the rain seems to last
a long, long, long time....compared to the same kind of item left in the
elements!
  Whether it's a car, a board, a sheet of sheetrock, just about anything
lasts longer stored inside.  My fabric covered plane will NOT ever sit
openly in the sun, at least not as long as I own it.  I've seen too many
airplanes just rot away, sitting on a ramp.  Not mine.  It will have a
cover, or be in a hangar...period.

  Since the primary purpose of the Poly Spray is to block the sun's rays, I
don't personally see much need for something to be thoroughly "protected"
that will never see direct sunlight.  That's just me, I guess.  It's like
getting travel insurance, and never going anywhere.

  Simple experiment:  take two pieces of fabric, any fabric.  Set one
outside to see lots of sunshine and rain.  Keep the other one indoors in a
dry place.   Let them sit there for a few years, say 4-5.  That ought to do
it.    Look at the outside one.  Tug on it.  Look at the inside one.
That's my "experience".

  Yes, I'm aware of the Miller's position.  They weren't as adamant last
year, but whatever.
Considering their liabilty, how could they say anything else??

  Another experiment:  find someone who is in bad need of a suntan.  Get a
nice, hot sunny day.  Have this pale skinned chap sit underneath a nice
shade tree all day.  How much sunburn did he get?   Probably not a lot, I
guess.

  I'm not trying to be argumentative, just use what I believe to be my own
personal judgement regarding sun protection.

  Thanks for sharing your opinion.

Mike Welch


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