a problem with compass swing

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photofly
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a problem with compass swing

Post by photofly »

I'm having trouble with my compass. With the aircraft aligned magnetic north, the compass is adjusted to read 360. Then with the aircraft aligned south, the magnetic compass reads 150 degrees, 30 degrees off. That's twenty degrees too much error to pass.

With the compass on my bench I have no such issue, there's only about five degrees error between N and S.

So I conclude the aircraft steel parts in the vicinity of the instrument panel have too much residual magnetism. Is that likely to be the explanation? Any ideas how to improve things?
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cgzro
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Re: a problem with compass swing

Post by cgzro »

Yup- The compas has little adjustable magnets in it and a procedure for compensating by moving the magnets around. Also make sure the electronics are turned on and dont use magnetic screwdrives anywhere near the compas. Real pain.

Also possible to degauss but ugh
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photofly
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Re: a problem with compass swing

Post by photofly »

The magnets will centre the error, but 30 degrees between north and south would mean the corrections would be +15° and -15° which is beyond the allowed value.

Any ideas about degaussing?
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GyvAir
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Re: a problem with compass swing

Post by GyvAir »

Is the aircraft new to you? If not, was anything changed recently? Windshield retaining screws driven with a magnetic driver can be close enough to influence things a bit.

If you haven't already, try verifying that the compensator magnets are both moving properly and set to neutral, then try another swing from scratch. I trust you’ve verified it’s full of fluid, if applicable.
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photofly
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Re: a problem with compass swing

Post by photofly »

GyvAir wrote:Is the aircraft new to you? If not, was anything changed recently? Windshield retaining screws driven with a magnetic driver can be close enough to influence things a bit.

If you haven't already, try verifying that the compensator magnets are both moving properly and set to neutral, then try another swing from scratch. I trust you’ve verified it’s full of fluid, if applicable.
The airplane is new to me... I'm slowly working my way through the inevitable list of squawks. Random compass headings in flight is just one of them :-)

The compass is not brim full of fluid, but the cup floats freely. I will be topping it up when I find something suitable.
I'm also going to try relocating it.
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GyvAir
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Re: a problem with compass swing

Post by GyvAir »

Good luck! It can be a frustrating search for the culprit, sometimes.
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helicopterray
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Re: a problem with compass swing

Post by helicopterray »

Check that the compass mounting screws are brass or stainless, and not steel screws. Or steel screws spray painted black...
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who me ?
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Re: a problem with compass swing

Post by who me ? »

confirm ,
that you are using a Brass screwdriver ? not a steel screwdriver ?
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DonutHole
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Re: a problem with compass swing

Post by DonutHole »

Good, they finally added compass swing to 625 app a
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robertw
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Re: a problem with compass swing

Post by robertw »

DonutHole wrote:Good, they finally added compass swing to 625 app a
Ummm... Really? Where?

I just read through the list of elementary work 3 times and did not see anything related to the compass anywhere.
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photofly
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Re: a problem with compass swing

Post by photofly »

Actually it was an AME who was unable to get the compass to line up. Donuthole can rest assured that his brethren were being well compensated for their time.
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gwagen
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Re: a problem with compass swing

Post by gwagen »

What kind of airplane?
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gwagen
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Re: a problem with compass swing

Post by gwagen »

Maybe you could use an old handheld cassette tape degausser?

https://www.amazon.com/RADIO-SHACK-POWE ... B000T9ZEK8

Cheap to try anyways.

I used to use a desktop one at a radio station. Trick is to slowly pull the tape away from the degausser or likewise the degausser from what you are trying to demagnetize.
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DonutHole
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Re: a problem with compass swing

Post by DonutHole »

photofly wrote:Actually it was an AME who was unable to get the compass to line up. Donuthole can rest assured that his brethren were being well compensated for their time.
Is it possible the compass is fucked?

Usually when I can't get it to line up I just replace it with one that works.
robertw wrote:
DonutHole wrote:Good, they finally added compass swing to 625 app a
Ummm... Really? Where?

I just read through the list of elementary work 3 times and did not see anything related to the compass anywhere.
Lol *shakes head*
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DonutHole
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Re: a problem with compass swing

Post by DonutHole »

Photo.

Seriously though. You're not the kind of guy that's going to use an ame who doesn't know how to swing a compass. From what I know of the you you present out here I can see you probably wouldn't suffer a fool.

They know how to do it properly, you know how to do it properly... If it doesn't work it's the instrument or the earth... So.. which one of those can you fix?
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photofly
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Re: a problem with compass swing

Post by photofly »

I asked my AME guy to look at it briefly, at the end of a long day working on other stuff. With the equipment available it was fairly clear there was a big error. He suggested cutting our losses and buying a new compass. They're about $200, so that's not the worst outcome, but when removed from the airplane this compass doesn't seem so bad so perhaps a new compass will have the errors when installed in the same place in the same way.

I had a close look at the mounting hardware, and although the nuts and bolts are brass, there were steel washers used, which are now removed. Also the location is on top of the panel, not higher up the windshield, so there may be some stray magnetic fields from hardware there.

It's not clear where to apply a degausser - pretty much everything in the vicinity is aluminium. Again, there's more work for me to do going around with a magnet on a stick checking, to be sure.

i just want to do a bit of checking myself, before buying a replacement, and I appreciate everyone's suggestions.
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robertw
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Re: a problem with compass swing

Post by robertw »

DonutHole wrote:
robertw wrote:
DonutHole wrote:Good, they finally added compass swing to 625 app a
Ummm... Really? Where?

I just read through the list of elementary work 3 times and did not see anything related to the compass anywhere.
Lol *shakes head*
Ah... I see. That was tongue in cheek. Humor on a forum is sometimes hard to detect for me... :oops:
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Broken Slinky
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Re: a problem with compass swing

Post by Broken Slinky »

Was the compass swing performed on the ground with the aircraft near the same location each time? Did you try it in the air?
I had one that was just out of tolerance on the ground but in the air was fine. Ended up being something magnetic located where we were doing the swing on the ground.
Other compasses checked fine but this one was just more sensitive I guess?
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groncher
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Re: a problem with compass swing

Post by groncher »

Is there any way you might be able to try another compass from a different aircraft, before buying a new one?
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digits_
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Re: a problem with compass swing

Post by digits_ »

Does it make a difference when the radio/battery master is on/off?

Does it make a difference if you physically unhook the battery? It shouldn't, but at least takes all the power out of the trouble shooting.

How often did you test it? Was there a cell phone or other powered equipment in the plane somewhere? Is there a tool hidden/forgotten in the dash (magnetic screwdriver - like things)?
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