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Compass Fluid Test Report

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Jim Weir

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Oct 21, 2002, 1:45:32 PM10/21/02
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This is an imaginary report. Nothing like this ever happened or will happen
because to do so is to admit modifying an instrument, something that should only
be done by an approved instrument repair shop. This is merely a figment of my
machination and in no way represents reality. I stand shoulder to shoulder with
the FAA and we believe solidly that 1930s technology has been around this long
for a perfectly good reason.


The problems with compass fluid are that is is flammable and that it does not
damp the magnetic compass properly. That is, in turbulent air, that sucker
swings around and is totally worthless for determining what direction you are
headed.

The problem, then, resolves itself to finding a clear viscous ("thick") fluid
that is not flammable.

Several fluids were tried. The most promising to start was mineral oil ("baby
oil") from the drugstore. It was exactly the right viscosity, didn't burn very
well, and damped the compass quite well. Unfortunately, it got real cold here a
couple of weeks ago and the damned compass was beyond viscous -- it took about
ten minutes to come to a heading when making a standard rate 180° turn. I
didn't do any super-scientific measurements, but putting the stuff in the
freezer caused it to freeze solid. Not good.

The freeze problem also held true for corn-sugar based syrups ("Karo") and other
hydrocarbon fluids. I did not try brake fluid (5606) or tranny fluid because of
the color change.

What has worked for the last month or so has been "toner oil" from the local
copy shop. It is actually a silicone based fluid, absolutely nontoxic and
nonflammable, exactly the right viscosity, and has performed exactly as
expected. The CCR tables show it having a freeze point of -40°, and quite
frankly, if the cabin temperature ever gets that low, I'm not much for flying
anyway. The copy shop sold me a pint of it (in my container) for $2.

Yes, it takes almost half a minute for the compass to totally catch up with you
when making a 180° turn. So what? That's what the DG is for. I will take slow
compass reactions for the capability of having a useful instrument when it gets
bumpy.

Like I said, this is all in a dream and would NEVER have made it's way into an
airplane, much less a standard certificated airworthiness airplane. Never, no,
hm'um, unhunh, nope, not here.

Jim



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com j...@rst-engr.com

Bob Olds

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Oct 21, 2002, 8:16:59 PM10/21/02
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Jim Weir <j...@rst-engr.com> wrote in message news:<a9e8ruk165c1npnrt...@4ax.com>...

*************************************************************************

This looks like very good info,Jim. Puff Puff , as soon as I blow all
the SMOKE away I'll finish reading it.
Bob Olds RV-4 N1191X

*************************************************************************

Blanche Cohen

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Oct 21, 2002, 8:36:48 PM10/21/02
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The Navigator compass by S.I.R.S uses the silicone fluid, probably
for the reasons Jim cites.

http://www.sirsproducts.com/page3.html

I've got a compass that's flakey and this looks like a reasonable
replacement.

Kevin M

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Oct 22, 2002, 2:32:24 PM10/22/02
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"Jim Weir" <j...@rst-engr.com> wrote in message
news:a9e8ruk165c1npnrt...@4ax.com...
| What has worked for the last month or so has been "toner oil" from the
local
| copy shop.
| Yes, it takes almost half a minute for the compass to totally catch up
with you
| when making a 180° turn. So what?


Another good suggestion for anyone thinking about rebuilding their
automobile compass is the shock oil from R/C trucks. It's silicone based,
and comes in various viscosities. You can basically custom tailor your
compass to your own liking. More bounce but faster adjustment, or less
bounce and slower to come around.

Just a thought,
Kev


Ben Haas

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Oct 22, 2002, 11:37:46 PM10/22/02
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"Kevin M" <kev...@swball.com> wrote in message news:<YQgt9.22$gB6.12...@newssvr11.news.prodigy.com>...

This is exactly why lists like this are so DAMN great. Thanks to all
you guys for doing some levelheaded R&D. Only in America !!!!!!

Jim Weir

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Oct 23, 2002, 1:32:20 AM10/23/02
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What is an R/C truck? Radio Controlled? And if so, where do you get the shock
oil? Hobby stores?

Jim


benf...@aol.com (Ben Haas)
shared these priceless pearls of wisdom:

->> Another good suggestion for anyone thinking about rebuilding their
->> automobile compass is the shock oil from R/C trucks. It's silicone based,
->> and comes in various viscosities. You can basically custom tailor your
->> compass to your own liking. More bounce but faster adjustment, or less
->> bounce and slower to come around.

Kevin M

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Oct 23, 2002, 9:32:49 AM10/23/02
to
"Jim Weir" <j...@rst-engr.com> wrote in message
news:n1dcrug7j8fikdpae...@4ax.com...

|
| What is an R/C truck? Radio Controlled? And if so, where do you get the
shock
| oil? Hobby stores?


Yes, R/C is Radio Controlled. Any good hobby store near you should carry it.

Kev


Mike Rapoport

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Oct 23, 2002, 10:40:41 AM10/23/02
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While you are at the hobby store, buy some Testors paint pens. They work
like a felt tip marker but have paint instead of ink. They are great for
touching up your panel!

Mike
MU-2


"Kevin M" <kev...@swball.com> wrote in message

news:5yxt9.271$Wf4.13...@newssvr11.news.prodigy.com...

Jay Honeck

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Oct 24, 2002, 11:33:28 AM10/24/02
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> While you are at the hobby store, buy some Testors
> paint pens.

Great tip, Mike (and Jim, and others) -- I never heard of them.

Thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"


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