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gmcjetpilot(at)yahoo.com
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 Posted: Thu Jul 27, 2006 7:39 am Post subject: VHF antenna mounting (more hair splitting) |
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Rumen:
Excellent point, that is why this list is great, input from everyone
and splitting hairs or not that is a GREAT IDEA. I have just made
note of this and put it into my RV-7 builders instructions. Thanks
Another hair to split, not that anyone on the list would ever do
that, is not to use stainless steel screws? Why? The base of
the antenna is aluminum alloy. Aluminum and SS is far apart
on the galvanic corrosion chart. Boeing uses passivated/cadmium
plated fasteners not stainless steel. I think the engineers at
Boeing and Cessna might have a clue. Dang engineers what
do they know.  All those years in school wasted.
Cheers George M., MSME, ATP/CFII-MEI
| Quote: | From: rd2(at)evenlink.com (rd2(at)evenlink.com)
Bob,
Speaking of the magic (grounding the base) - looking at the
Antenna_Installation.gif , I have seen toothed lock washers used
between the doubler plate and skin.
This was on a Cessna. The doubler plate was not riveted to the
skin (it came with with the antenna replacement kit). The lock
washer assured better el contact (grounding). They used externally
toothed lock washers, as per attached. Maybe a better idea would
be to use the external-internal toothed type washers (also attached).
Opinions?
Rumen
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Hopperdhh(at)aol.com
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| Posted: Fri Jul 28, 2006 4:32 am Post subject: VHF antenna mounting (more hair splitting) |
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George and fellow listers,
Well said George. Stainless steel is extremely difficult to make electrical contact to. Once I tried playing around on a curve tracer with a piece of stainless. The oxide coating that grows on stainless (just like aluminum) to protect itself is really hard and tough. I had to really scratch hard with a piece of copper wire to see conduction on the curve tracer. By the way, a curve tracer is an oscilloscope with a built in power supply to allow you to see volts vs. amps on the screen. A short looks like a vertical line and an open looks like a horizontal line. You can see visually whether you have contact or not, and try it at different voltages. Higher voltages (like 100 volts or more!) punch through the oxide much better.
I have always been leery of the ground to the firewall on RVs. I think the real ground is on the inside to the aluminum angle. For this reason I used a cad plated washer and nut instead of the platenut there. I don't think that an all metal locknut is necessary. The threads will contact to the metal part of the nut just fine. I don't know of any problem of conduction through the platenut. I just prefer the nut and washer. YMMV
do not archive -- not many will agree with this!
Dan Hopper
RV-7A
In a message dated 7/27/2006 11:44:28 A.M. Eastern Daylight Time, gmcjetpilot(at)yahoo.com writes:
| Quote: | Another hair to split, not that anyone on the list would ever do
that, is not to use stainless steel screws? Why? The base of
the antenna is aluminum alloy. Aluminum and SS is far apart
on the galvanic corrosion chart. Boeing uses passivated/cadmium
plated fasteners not stainless steel. I think the engineers at
Boeing and Cessna might have a clue. Dang engineers what
do they know. All those years in school wasted.
Cheers George M., MSME, ATP/CFII-MEI
|
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http://www.matronics.com/Navigator?AeroElectric-List |
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