Builders,

I have been flying my CH750 for over 5 yrs now. Have a Precision model vertical card compass that I have never been able to keep within 25-30 degrees of correct. I recently bought a new Air Path Whiskey compass and installed it with the same results. Got to researching a bit, and discovered the "degaussing" phenomenon with regards to the magnification of welded steel parts and its effect on a compass. I've read everything from where you can use a TV monitor-type degausser, to you must use a massive industrial degausser, to wrapping the cord of an extension light around your steel parts and leave the light on for 24 hrs will demagnify the steel.

Do any of you guys have any actual sucessful experience with degaussing steel parts in your plane you could share, and has anyone else had this same compass inaccuracy issue with their Zenith?

Jimmy Young

Houston TX

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Just curious if you have ever performed a compass swing and used the adjustment screws on the compass to correct for any magnetic interference.

As long as your interference remains constant and doesn't change when other electronics are turned on or off, you should be able to adjust for it using a compass rose or a calibrated master compass which can be rented to you.

https://www.eaa.org/en/eaa/aviation-communities-and-interests/homeb...

Yes, I've done that procedure with the original vertical card compass. I can't remember the exact routine, but I do know when I get it dialed in N & S, then do E & W, when I go back to N & S it will be off again. It also varies in accuracy from day to day while flying, as in one day it may be off 30 degrees, and a week later its 20 degrees.

The fact that I have tried two brand new compasses with the same results is what makes me think I've got a magnetized engine mount or cabin frame.

Jimmy - Here is some data from Mooney for how they recommend degaussing the airframe.

http://www.mooney.com/en/si/M20-23A.pdf

Another possible alternative.

http://www.aircraftspruce.com/catalog/inpages/compensator.php?click...

Degaussing Coil
My Vertical Compass had a 150 degree error when it was mounted on the top of the instrument panel. I made a Degaussing Coil to de-magnetize the struts. I pulled the Degaussing coil out of an old tube type TV and wired up a push button switch to activate the coil. Use the coil to go over the metal struts but be sure to remove your compass first and keep it away. Also activate the coil for only short periods due to the overheating of the coil. You can “Google” the procedure on how to make a Degaussing Coil, or borrow a “Growler Coil” from your A&P friends. The welding of the struts causes the struts to become magnetized, the coil worked great and my compass now reads correctly.

http://www.zenith.aero/photo/degaussing-coil?context=user

Any coil of wire will work fine to degauss the parts. Wrap the parts with insulated wire or magnet wire. Then the key piece, use an AC transformer connected to the wire to demagnetize the tube. 24v transformers from HVAC or a door bell would both work fine.  This same circuit works to magnetize parts as well, just wrap the part and hook the wire to a DC supply. No real magic here, just remember the more current flow the stronger the effect will be.

you might try shielding the compass with aluminum foil or sheet to see if it corrects. If so then fab up some sort of AL shield. a nice little box?

Joe, I've never heard of that one before. If it works, that will be great. Going to try it, will post the results.

JY

Really don't think aluminum shields a magnetic field.  Be sure to let everyone know if it does. 

Remember the AHRS and remote compass units set inside of an aluminum airplane and they pick up earth's magnetic field just fine.

I don't know either but it's free to try. I wonder about stainless too.

The coil works, 30 seconds and you are done! Find an old tv repair shop and they should have a coil you could borrow, be sure to level the coil and step away from the plane before turning it off. 

What does "level the coil" mean? Are you saying to hold it level with the ground and walk away from the plane, then turn it off? Sounds weird to me, but when you don't know, you have to ask!

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