Compass problems

[n3pup]

If I may be so bold as to quote from another forum without the originator being named, here is how he solved his problem.

"Here is how I fixed it. I got an inexpensive ($43, and that's cheap for this kind of instrument) from a site called Less EMF. Then I got on eBay and grabbed a 13" degaussing coil. These degassing coils were originally intended to degauss television screens, which would sometime develop oddball mag fields. I'm told it gave you purple spots...whatever, these are pretty available. I paid $13 and shipping, you may pay more or less...all depends.

Anyway, I could pinpoint the areas of high magnetic activity and then hold the degaussing coil over it for a few seconds and slooooowly move it away. Rechecking showed a reduction, sometimes complete. I had to do it a couple of times in some spots to reduce it to zero. All in all, very simple and painless.

Wow! Was that simple or what?

Why does the airframe get magnetized? Two most common ways are if you electric weld on it you are sending lots of amperes through the structure, and this will make localized fields. Second, if you have a battery mounted elsewhere than on the firewall, don't take the easy way out and ground it through the fuselage tubing. This will make magnetic fields for you. Instead, use a dedicated grounding cable from battery to starter, and bond all the system grounds to the ground terminal at the starter."

[nrpetersen]

Orienting a piece of steel along the earths magnetic field & then pounding on it a few times will cause the steel to become magnetized too. From there it gets to facing the same direction everytime you park. And then it comes to magnafluxing steel parts - if the inspector forgets to demagnetize (i. e. degauss) everything afterwards you will have a compass problem. A crankshaft is a hardened part so it will be reluctance to release its magnetism.

I had not heard of the poorly cutting drill before but it too makes sense.

Degaussing coils would be present in big conventional picture tube TV sets. There's lots of them in the junkyards etc for those so inclined.

Not using the fuselage frame as a current conductor is important too. Only wires should carry current, structures should carry only forces.

[raytoews]

Wow, sounds kind of like the apparatus used to get rid of evil spirits.
Maybe talk to your priest/minister/rabbi

[616jim]

thanks to all who offered solutions etc. i rented the degaussing tool from Skyranch. it comes with a field meter. i got the area where the compass is located down to one small mark on the meter. i would hold the tool about 4' away, turn it on and then bring it up to the suspect area, then pull it away. the key is to diminish the field gradually. (i have heard of degaussing tools that turn off gradually, -- this one just had a switch). i've installed the PA 700 and after adjusting the N/S and E/W screws, got it to within 10 degrees. now i/ve got to find a compass rose. local airports have been seal-coated and covered the compass roses. (lots of federal money for airports in MN.)
again thanks. ps: I have found John at Skyranch to be most helpful and knowledgeable.

[Hiperbiper]

thanks to all who offered solutions etc. i rented the degaussing tool from Skyranch. it comes with a field meter. i got the area where the compass is located down to one small mark on the meter. i would hold the tool about 4' away, turn it on and then bring it up to the suspect area, then pull it away. the key is to diminish the field gradually. (i have heard of degaussing tools that turn off gradually, -- this one just had a switch). i've installed the PA 700 and after adjusting the N/S and E/W screws, got it to within 10 degrees. now i/ve got to find a compass rose. local airports have been seal-coated and covered the compass roses. (lots of federal money for airports in MN.)
again thanks. ps: I have found John at Skyranch to be most helpful and knowledgeable.

Forget about a compass rose...go find a good looking section of farmland with good square fields! Fly the N/S section lines (keeping the nose parallel to the edge of the line; no wind crab angles!) back and forth gradually adjusting your compass to remove all the error you can. Now find a good E/W section line and rather,rinse,repeat!

Of course you can always use your DG set to a runway heading then use the DG as your Master Compass...
Don't forget to have everything you normally have powered up during flight powered up for your compass swing!.

And yes; Sac Skyranch is a great group!

Chris

[nrpetersen]

We do have an unofficial but well marked compass rose on the main ramp of Shell Lake WI (SSQ). It was laid in by our engineer when the runway was reconstructed 3 years ago so it should be pretty good.