Compass Issues and Airframe Magnetization

[Cubdet]

I am a new (1 year almost to the day) owner of Sport Cub No. 15 (the second owner of this Cub). The airplane came with a compass that was simply inaccurate. Eventually, I had a mechanic look at it last fall. After a long session attempting to re-swing it, the mechanic gave up and said the compass needed to be replaced.

At annual time this year, a different mechanic (at a CubCrafters Authorized Service Center) attempted to re-swing the compass just to make sure. Still no luck. Ordered a new compass, and before installing it, walked around the ramp with the old and new compasses in hand. The new one was generally working fine, the old one, no go. So, we knew the old one was indeed bad.

Got the new compass installed, went for a test flight, and lo and behold, the new compass suddenly looked as bad as the old one! Now it's getting interesting. Took the compass off its mount, and put it in his lap--it suddenly performed like a good new compass should. Finally determined that the airframe has actually become magnetized over time. The old compass must have been in that field for so long that it finally threw it off for good.

The mechanic is now waiting for a tool (used by CubCrafters as well) to de-magnetize the tubes in the area around the compass. Apparently, it does not throw off enough of a field to upset any other instruments or radios, at least not permanently. This is apparently a known issue, with some airframes at least, and hopefully, this will do the trick. I'll try to post some updates as I know more, and hope to post a picture of the tool itself for those that might be interested, but wanted to at least get the party started on this topic. I thought I had seen some other posts here about compass issues in the past, but couldn't seem to come across them on my search today. Maybe this will help solve issues for some other folks out there having similar problems.

[ncshp]

I degaussed serial#21 and it did fine for a while but returned over time.

[cityrancher]

I have tried to re-swing mine several times, without much luck.

[mikesutton]

Two things to consider, one is that while you can remove magnetism with degaussing, you cant remove the fact that a compass is still attracted to anything with iron in it. Admittedly the fact that iron will become magnetized only makes things more complicated, but often its just the presence of iron that causes much of the problem and its pretty hard to eliminate iron from a steel tube fuselage.

We had been using an old hand held demagnetizer that came from radio shack or somewhere, its been around here forever, to degauss tubes. I forget its original purpose but essentially you plug it in, its an ac magnetic field and you run it along the tubes in question and move it away from them as you go, to gradually lessen the field strength. Sometimes you get it on the first try, other times you dont. Sometimes you swap compasses or you get one with stronger compensating magnets in the compass.

Wish I had a better outcome to the story, out of the sheer number of aircraft that go out the door we do seem to get them dialed in pretty well, just not always on the first try. I see the guy on the line still occasionally have to swap one to get one that works best.

Good luck

Mike Sutton
Cubcrafters Avionics

[Pete D]

We had been using an old hand held demagnetizer that came from radio shack or somewhere, its been around here forever, to degauss tubes. I forget its original purpose but essentially you plug it in, its an ac magnetic field and you run it along the tubes in question and move it away from them as you go, to gradually lessen the field strength.
Mike Sutton
Cubcrafters Avionics

I was always told it was a VHS tape or magnetic tape eraser. Not sure if that is true, just the story that has been passed down.

[mikesutton]

I think you're right Pete, that seems like what I remember as well. Now if a person could find one might be another story.

Good memory on your part

Thanks much

Mike

[ceslaw]

Reserecting this old thread

Final step before completing the Cub is swinging the compass before the DAR arrives.

Compass points southwest no matter which direction the plane faces. Remove the compass from the plane, or even move it away from the windscreen still in the plane, and it works fine.

Looks like I need to degauss the frame members in proximity to the top of the windscreen. Questions:

1. Any recommendations on a degausser? There is an inexpensive $20 on amazon, wonder if it would suffice:

https://www.amazon.com/Degausser-Deg...10084963&psc=1

2. Is there any issue with harming the ADHARS located behind the G3X when degaussing the frame members three feet away?

3. Is there any issue with harming the magnetometer located at the outboard end of the right wing when degausing within the cockpit?

The DAR is coming, so need to get this sorted ASAP

[Daveembry]

interesting article here ?……. https://www.holladayaviation.com/ind...ic-compass-qa/

4A0312B3-905F-475C-9C22-5BE5AAC5FC25.jpg

Reserecting this old thread

Final step before completing the Cub is swinging the compass before the DAR arrives.

Compass points southwest no matter which direction the plane faces. Remove the compass from the plane, or even move it away from the windscreen still in the plane, and it works fine.

Looks like I need to degauss the frame members in proximity to the top of the windscreen. Questions:

1. Any recommendations on a degausser? There is an inexpensive $20 on amazon, wonder if it would suffice:

https://www.amazon.com/Degausser-Deg...10084963&psc=1

2. Is there any issue with harming the ADHARS located behind the G3X when degaussing the frame members three feet away?

3. Is there any issue with harming the magnetometer located at the outboard end of the right wing when degausing within the cockpit?

The DAR is coming, so need to get this sorted ASAP

[mikesutton]

I can't say with certainty that the degaussing would harm the Adhars unit or the magnetometer in the wing, the adahars is attitude and air pressure inputs and the magnetometer is not much more than a very modernized remote compass feed. That said, what's the harm in removing them to be safe versus the cost of replacing them? The magnetometer is pretty far out in the wing unless they found a new place to put them so it's quite a ways from whatever iron isin the tubes. That's why we put them where they are, to stay away from ferrous metals. Remember, even if it isn't a magnet it still affects magnets.

Best of luck,

Mike

[ceslaw]

[QUOTE=Daveembry;29217]interesting article here ?……. https://www.holladayaviation.com/ind...ic-compass-qa/


Dave:

Very interesting article indeed. As I read it, it appears the current regs require a 'magnetic direction indicator', and presumably the G3X with its magnetometer would fulfill that requirement. The regulation requiring a compass deviation card no longer exists. So the magnetic compass can simply be put back in the box and call it done.

Are we missing something? Does the G3X and its GMU-22 magnetometer indeed constitute a 'magnetic direction indicator'?

Anyone else want to chime in??

Thanks for the info.

Chuck