raymondj(at)frontiernet.n
Guest
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 Posted: Fri Jan 04, 2013 8:07 am Post subject: Advisability of using anti-corrosion lubricant on contact |
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Greetings Bob,
May I suggest that you try "3M Marine Adhesive Sealant 5200" instead of RTV for your tests. I have used it under many fittings above and below the waterline on boats with excellent results. They also make a 4200 that is easier to remove which might be more appropriate for antenna installations.
| Quote: | Raymond Julian
Kettle River, MN.
"And you know that I could have me a million more friends,
and all I'd have to lose is my point of view." - John Prine |
On 01/04/2013 09:17 AM, Robert L. Nuckolls, III wrote:
[quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> (nuckolls.bob(at)aeroelectric.com)
At 07:06 AM 1/4/2013, you wrote:
| Quote: | --> AeroElectric-List message posted by: "toddheffley" <public(at)toddheffley.com> (public(at)toddheffley.com)
Wow....Talk about the subject that will not die!
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Not sure why anyone would want it to 'die' . . .
| Quote: | I have watched this controversy in my industry (large cabin executive jet maintenance) for some time now, and much like the discussion here, it will not die.
Some airframers do not want corrosion inhibitors between the antenna and the airframe.
Conversely, I worked for a MRO that requires Pentrox Type 2 (grey) for every antanna installation. (conductive paste, feels like toothpaste, non-hardening)
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There's a BIG difference between the situation you
are citing and the conversations we've had here on
the list.
| Quote: | My anecdotal experience tells me that antenna footprints are the first and worst hideouts for corrosion on many aircraft. Particularly lower antennas. My experience is 1 to 1 without exception. If a removed antenna has Pentrox under the foot print, it has no corrosion. I come down as a strong advocate for adding Penetrox.
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Absolutely. But the identification of successful
remedies for specific issues does not translate
into a general applicability as a prophylactic
measure. I.e. using Penetrox to offset a specific
vulnerability does not suggest that dipping the
whole airplane into Penetrox is a good idea.
| Quote: | I have two theories: one is that Airframers live in perfectly clean factories with brand new airplanes that never corrode. Antennas are installed on perfectly clean ground planes, and that thinking is inviolate. MRO's live with 30 year old airplanes, thus the difference between the two.
Theory number 2 is that the clamp up force of an antenna is very low because of the large size of the footprint. Use of some type of "magic goo" seems more reasonable, because one can never achieve a vapor tight fit up over the entire footprint of the antenna.
I doubt there is a wooden stake for this vampire, but I would like Bob's thoughts related to HBC background vs. OBAM background.
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Some years ago I published this drawing
http://tinyurl.com/6rwodso
that spoke to the value of high mate-up forces
in the vicinity of mounting hardware along
with a suggestion that paint be removed from
skin ONLY around the holes. It was a toss-up
then as to how moisture might be prevented from
taking up long term residence under the antenna.
THIS is a problem. I suggested a bead of RTV on
the outside because it can be inspected and renewed
as needed. A gasket is NOT called for because it upsets
the design goal for gas-tight bonding at the bolt holes.
Silicon grease would be good for protecting the bonds
and is probably the preferred technique . . . but that
stuff is a high viscosity liquid with very good wetting
properties. This means that the stuff migrates out from
under the antenna base and stains surrounding surface
while adding dust collection. Looks like (at)#$(at)#.
| Quote: | I come from a maintenance background , not a build background, so ....grain of salt....
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So you're quite right that there's a unique and
challenging problem to seek the elegant process
by which long-lived antenna installations can
be made . . . certainly more than a 'grain of salt'.
In retrospect, given that electronic grade
RTV in the uncured state has no significant
compression strength, It would be interesting
to try an overall, liquid gasket approach
under the antenna using the silicone sealant.
I think it would extrude out of the gas-tight
contact areas as the bolts are torqued up. Squeeze-
out around the base is easily cleaned after
the bolts are tightened. Overall water tightness
should be quite good.
I'll put that into my list of experiments to
try . . . One could overlap 3" wide strips of
say 1/8" and equivalent thicknesses for skin
and doubler. Do the 'bonding' thing around 4
holes with 10-32 hardware in them. Dope the
interface between 1/8" and 'skin' with rtv
and clamp it up.
Do a test on bonding integrity of the two
surfaces after the RTV has cured. Repeat
without RTV and compare.
Bob . . .
[b]
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