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616jim
03-11-2012, 09:39 AM
Anyone have ideas as to eliminating residual magnetism in a rag/tube LSA? I've tried different methods but no luck. My compass likes to read east, all the time. Tried 3 compasses. All the same. Ive tried to "chase" the residual magnetism with magnets, no success. I made an ac electromagnet, nope. That did not work either. http://eaaforums.org/images/icons/sad.gif

Bill Greenwood
03-11-2012, 12:12 PM
All I can say is that maybe it is divine guidance and if you follow it you'll arrive at Mecca.

I had an a plane with a large vintage British compass, like a ships compass. For some silly reason, I tried to put a modern one in as a backup. Never could get it swung right, too much interference, and I finally removed it and realized that the old style compass was dead accurate and worked just fine, you just had to look down at the floor to read it.

nrpetersen
03-11-2012, 01:02 PM
Funny - I've been fooling with using a large dia AC excited coil to see how much it takes to demagnetize 4130 steel. It seems to take about 30 ampere-turns in free air to generate enough magnetic flux to reset everything as the 4130 steel is pulled away slowly.

The next step inder personal consideration is to take a 100 ft coil of 3 conductor #14 Romex wire, roll it into a 1 ft dia coil, splice the ends together so that the whole mess of wires is in series, and excite that with a Variac with a few volts to get ~ 4 amps of current thru it. Of course you could use a 500 Watt series heating element to limit the current to 3-4 amps too.

Or a long extension cord of say 100 ft of # 16 - cobble a suicide plug system to series the three wires & bring a power cord out.

This is all strictly not UL approved. :)

Operation would be to hold it near the area to be degaussed and slowly withdraw it to at least 5 to 10 feet away before taking the power off.

Has anyone else fooled with this sort of approach? and how much will a compass take before it becomes demagnetized? or a tachometer? or a magneto (much more I'd think).

616jim
03-12-2012, 12:18 PM
I did something like that. I took a piece of iron, a foot or so of re-rod, wrapped about 100 turns of #14 around it. I first bent the re-rod in the shape of a horseshoe. Then I connected it in series with 2 heaters each pulling about 1200 watts. When energized I moved it around the area and pulled it back, then shut the juice off. No luck so far. Sounds like were doing much the same.




Funny - I've been fooling with using a large dia AC excited coil to see how much it takes to demagnetize 4130 steel. It seems to take about 30 ampere-turns in free air to generate enough magnetic flux to reset everything as the 4130 steel is pulled away slowly.

The next step inder personal consideration is to take a 100 ft coil of 3 conductor #14 Romex wire, roll it into a 1 ft dia coil, splice the ends together so that the whole mess of wires is in series, and excite that with a Variac with a few volts to get ~ 4 amps of current thru it. Of course you could use a 500 Watt series heating element to limit the current to 3-4 amps too.

Or a long extension cord of say 100 ft of # 16 - cobble a suicide plug system to series the three wires & bring a power cord out.

This is all strictly not UL approved. :)

Operation would be to hold it near the area to be degaussed and slowly withdraw it to at least 5 to 10 feet away before taking the power off.

Has anyone else fooled with this sort of approach? and how much will a compass take before it becomes demagnetized? or a tachometer? or a magneto (much more I'd think).

martymayes
03-12-2012, 12:37 PM
Anyone have ideas as to eliminating residual magnetism in a rag/tube LSA? I've tried different methods but no luck. My compass likes to read east, all the time. Tried 3 compasses. All the same.

Yours is an example of where degaussing should work. Do you have a magnometer? If not, what are you using to determine the source of the magnetic interference?

martymayes
03-12-2012, 12:39 PM
Has anyone else fooled with this sort of approach? and how much will a compass take before it becomes demagnetized? or a tachometer? or a magneto (much more I'd think).

Only with CRT's. All the instructions I have on degaussing says to keep it away from delicate instruments and such.

nrpetersen
03-12-2012, 03:26 PM
616jim - How wide (far apart) were your pole pieces? I'm thinking that the loop should be maybe 1 ft in dia & maybe more if we had more wire. Do you suppose it is necessary take all the extension cords one can find, put them together & make a loop big enough to go around the fuselage? Obviously an AC current limiter within the capabilities of the extension cords is necessary.

Otherwise we are on similar pages w similar techniques.

Trying to do anything constructive with a DC magnet would be absolutely hopeless.

I played w 4130N tube using a cheap compass as a polarity indicator. Just approach from the e-w direction & see what it takes to make the needle swing in the opposite direction with different materials.

616jim
03-13-2012, 07:09 AM
pole pieces about 1.5" apart. I tried loops of extension cords. Did not work/help. But the current flowing in one wire would cancel out the field caused by the other wire correct? Might try again today.

Hiperbiper
03-13-2012, 10:20 PM
http://www.sacskyranch.com/degaussi.htm

Some of the things I've found under panels (including a magnet taped to a coax cable to "drain interference" might boggle the mind...) mean you first need to point to the section of the aircraft you need to work on. A cheap compass moved around the panel will point to an magnetic field and therefore point you to your problem.
If I might ask for more info; what LSA, what's in the panel does the problem change if the radios/electrical system are on/off?
Also; you say you've tried 3 compasses and none would read correctly (assuming with the compensators tweeked). What compasses have you tried?

Chris in Shreveport

douglish
03-17-2012, 06:05 PM
About twenty years ago I had a Debonair with a compass which suddenly 'went loopy'.

Took a long time to track the source (yep eventually used a cheap boy scout compass), it turned out to be our tacho cable had 'gone magnetic'.

Removed the compass from harms way, pulled the tacho (no problems detected with it), and got the local TV repair man out with his de-gaussing coil. He activated it in the tacho hole beside the cable and circled it continuously as he withdrew to a few feet away. Repeated this twice more, then went and circled the main instrument panel once, said "try that". No more problems. Did it need the main panel circled?, he said not but did it to placate the LAME (A&P to you yankees).

All looked very 'black magic' to me, but it worked.

Track the source of the magnetism first, sometimes that can be just ONE hole in a bit of steel that was drilled too slowly. Yep, ever taken too long with a blunt drill bit and seen the chips attracted around the drill bit and site? One magnetic hole!

n3pup
03-17-2012, 07:26 PM
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
03-18-2012, 07:21 AM
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
04-28-2012, 06:17 PM
Wow, sounds kind of like the apparatus used to get rid of evil spirits.
Maybe talk to your priest/minister/rabbi:rollseyes:

616jim
07-19-2012, 05:36 PM
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
07-19-2012, 07:08 PM
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
07-19-2012, 07:09 PM
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.