Refinish Glass Face in Airpath Compass

How to keep the Cessna 170 flying and airworthy.

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MoonlightVFR
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Refinish Glass Face in Airpath Compass

Post by MoonlightVFR »

I have been advised by AP I/A that Airpath Compass has crazed glass face unable to read numerals.

Can they be refinished like an automobile headlight lens?
My compass hangs down from center Strip of windscreen 54 170B s.n. 26433

What should I do?
gradyb, '54 B N2890C
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c170b53
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Re: Refinish Glass Face in Airpath Compass

Post by c170b53 »

Yep, parts are available from aircraft spruce, have a look at their website for price details. Your glass might just be dirty on the inside. I "rebuilt" mine over 20 years ago and still have 1/2 quart of compass fluid left over. I can't even give it away to boaters on my crew.
From your recent posts on your plane, it sounds like the extensions on your MEL's have run out ! :)
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
hilltop170
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Re: Refinish Glass Face in Airpath Compass

Post by hilltop170 »

I saw a compass lens one time that was also “crazed” looking. A compas rebuild kit was bought from the a/c supply store and when disassembled, it was obvious the glass was just covered with a tough scum. A microfiber towel was used with Dawn dishwashing soap and hot water to scrub it clean. The kit was installed, refilled the fluid, and it looked and worked like new.
Last edited by hilltop170 on Tue Jan 08, 2019 6:49 pm, edited 3 times in total.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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ghostflyer
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Re: Refinish Glass Face in Airpath Compass

Post by ghostflyer »

We use a good grade whisky as a compass fluid. It doesn’t last 20 years around here . I marked the bottle with marker pen “urine ‘’. It still avaporated.
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Bruce Fenstermacher
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Re: Refinish Glass Face in Airpath Compass

Post by Bruce Fenstermacher »

Chances are your glass is fine but it has a haze of filth on it.

The only way to clean it is to disassemble, clean, glass, reassemble.

If there has ever been a statement easier said than done, it is my last statement.

1. Many from the Friendly Folks Assoc. think one must be specially trained and licensed to perform such magic as disassembly and glass cleaning. Neither you OR your mechanic has this mysterious certificate in their possession.

2. Assuming #1 isn't enough to stop you, you must be confident enough to evaluate this precision mechanical piece of fluid filled equipment and decide on a disassembly scheme. My method with this type equipment is to only disassemble what is absolutely necessary. I would not try to remove the compass card inside for example, but removing the back is within most tinkerers ability. Once the back is of and the fluid spread all over your bench, a swab of towel with simple glass cleaner inserted around the card will clean the glass. While your at it your likely to notice the numbers on the card are a bit yellow. DO NOT be tempted to clean them as you will totally remove the numbers as the paint is likely soft. Just take my word for it.

3. Reassemble. I Assume you determined and bought a new diaphragm if your compass requires such. And I assume you bought enough of the secret sauce that goes inside the compass. This sauce can be lots of things including a clear whiskey and your compass will work fine just keep what ever you use secret. Your likely to buy the special sauce from Spruce with the new diaphragm you got.

4. Now the hard part. Filling every crevice in the compass with fluid and leaving it void of air. Let me give you a clue right now. You will not be able to do it. The secret is those that have the secret certificate I spoke about in #1 have a tub of the special sauce the completely submerge the compass into and rotate it at every angle to release the air. Bet you didn't buy enough of that sauce from Spruce to do this did you.

My suggestion is, if your IA really insists, remove and send that compass to an instrument shop and ask to trade it and some cash for one they have 'overhauled", which means they cleaned the glass, replaced the diaphragm and submerged it in their special sauce and removed all the air bubbles. You'l be much better off.

For extra credit, since you read all this an are now more determined to clean your own glass, start reading MSDS sheets for the "compass fluid" Spruce and others sell. You'll start seeing familiar ingredients if you've ever researched the MSDS sheets for Marvel Mystery Oil. Then start reading ingredients on stuff at your local hardware store. After all, at this point, there is no way in heck your paying $50 a gallon for the necessary quantity to submerge your compass, for something someone else bought for $2 and stamped "compass fluid on it".
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Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
hilltop170
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Re: Refinish Glass Face in Airpath Compass

Post by hilltop170 »

I am not suggesting anyone take this advice. I have heard this procedure works well though.

Bruce makes it sound much more onerous than it is if you want to rebuild it yourself. Strictly legal? No. Easy? Yes. Better to rebuild it than look at a tilting card that doesn’t work? Absolutely! Besides that, when is the last time you actually USED the compass for navigation? I can’t remeber when I did but it is required equipment so there you go.

The rebuild kit that is commonly sold includes a new diapghram for the rear and a paper gasket for the front lens. Bruce is correct in saying do not try to remove the compass card/rotor. 99 and 44/100 % chance nothing is wrong with the card/rotor.

As Bruce described, the lubber line paint will fall off when it is lightly touched while cleaning so do not touch the rotor AT ALL with ANYTHING.

The lubber line is brass and what can be done to correct the missing paint is carefully and completely remove the paint then carefully scrape it with a blade to give it a bright reflective surface which is actually easier to see than the old paint.

Now for the messy part: refilling the fluid. It is not hard at all, just messy. Every home improvement and hardware store in America sells 99% pure, odorless, premium lamp oil which is really a very good grade of kerosene and sells for $5-10 for a 1/2 gallon. The left over fluid can be used to start your charcoal barbeque grill or refill your Alladin lamps the next time you want to get romantic. 8O

Completely assemble and snug down the back side of the compass with the new diapghram installed. Assemble the front side of the compass and leave the lens screws loose and facing up. Find a wide mouth Mason jar or glass big enough to completely contain the compass body and place the compass in the container. Fill the container with fluid and completely submerge the compass. Gently tap and manulate the lens/face letting all the air escape while filling the compass completely with fluid. When all the bubbles are gone, snug the front face screws while still submerged in the fluid. It’s going to make a mess but all the air will then be gone.

When done, simply sop up all the spilled fluid and let it drip dry facing up on a stack of towels. The rear vent hole will weep for awhile so don’t get in a hurry.

Then all you need to do is leak check, reinstall, and go swing the compass to confirm accuracy.
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
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GAHorn
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Re: Refinish Glass Face in Airpath Compass

Post by GAHorn »

I suggest that you ignore all the jokes and commentary about using whiskey, whisky, kerosene, or anything from a hardware store and purchase the compass rebuilt kit and the compass fluid directly from Aircraft Spruce and follow the directions after cleaning the backside of the glass. As already warned, avoid any attempt to improve the scripting on the compass card or lubber line (and beware that some old compasses have radium in that paint so simply don't mess with it.)

When refilling the compass...the simple solution is as Richard suggests... but I use a plastic Tupperware bowl full of the quart of fluid you bought from Spruce and completely submerge the compass and letting all the bubbles out before closing up the gasketed back.

Being absolutely respectful of all regulations regarding things that use the word "whiskey".... I only used the Airpath compasses I've rebuilt in things like boats, off-road vehicles and experiments, etc. 8) I've done a half dozen of them and it's not hard at all. (There are excellent articles online also that will guide you in re-calibration if necessary, but if you don't mess with that it should not be an issue.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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MoonlightVFR
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Re: Refinish Glass Face in Airpath Compass

Post by MoonlightVFR »

Where can I send my Airpath Compass out for a rebuild?

I read all the post. I think my compass works well but the I A A/P has reservations.

Can these be rekitted at reasonable rate and turn around time?
gradyb, '54 B N2890C
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Bruce Fenstermacher
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Re: Refinish Glass Face in Airpath Compass

Post by Bruce Fenstermacher »

You can send it to any number of places. Keystone Instruments. http://www.keystoneinstruments.com/ is one.

As, in this case, I doubt your Airpath is special, I'd call them, send a picture of yours, and ask them to send you a cleaned duplicate replacement. They have hundreds of them sitting there. Ask if yours has a core value and return yours as a core if it does.

I guess your A/P has already told you he doesn't have the proper license to service these then. If not ask him why you can't buy readily available diagrams, and fluid and you clean and fill it under his supervision or he do it himself.
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GAHorn
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Re: Refinish Glass Face in Airpath Compass

Post by GAHorn »

A replacement will certainly require re-swinging the compass. If Keystone doesn't mess with the compensators you can probably just reinstall yours once they repair it.
I'd do it myself, If I were you. Spruce sells the materials. Its a fun job. To get rid of air bubbles, simply submerge the entire compass into a bowl of their compass fluid as you put it back together. Another expensive aircraft item...almost Twelve-bucks. :twisted: https://www.aircraftspruce.com/catalog/ ... cfer=22939
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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