Degaussing sliding canopy

As I fly my new RV-7A and set up stuff on the panel, I was able to swing my magnetic compass on the ground using our airport's compass rose without much trouble. My procedure was done on the ground with the sliding canopy open. I then noticed that when I closed the canopy, the compass moved and was in error about 10 degrees.... Has anyone had this problem? Am I supposed to degauss the sliding canopy somehow? Or do I just swing the compass as best as I can with the canopy closed?

Any help with this issue and any suggestions will be greatly appreciated!

Thanx.

Victor

I don't think you're "supposed" to degauss the canopy, but you can certainly do it...I had a similar problem with my control stick. Compass would swing 30 degrees when I moved the stick closer to the panel (nose down).

My parents had a floppy disk degausser from years and years ago, which cleared the problem after some experimentation. Repeated applications at various points along the stick worked, wheras waving it along the full length of the stick did not.

Radio Shack sold it, maybe they still sell them? If not, search around for one to buy...there are also roll-your-own plans out there, but watch out for excessive heating. Even the store-bought ones get really hot and have a limited duty cycle.

Paul

Magnetic personality

vasrv7a said:

Am I supposed to degauss the sliding canopy somehow? Or do I just swing the compass as best as I can with the canopy closed?, Victor

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Yes by all means. By its very nature steel gets magnetized. You know that. You need a degausser. How do you do it?

http://www.sacskyranch.com/degaussi.htm

Rent it
http://www.sacskyranch.com/degauss.htm

(get 5 guys and it cost $20 each with shipping?)

Now can a big canopy frame or canopy roll bar bow be demagnetized, degaussed with this thing? I don't know for sure? At least beg borrow or buy a magnetometer and see if the frame is magnetized. I would guess if we really where serious about it, we would make a big plywood box and use coils around it to demagnetize the whole thing at once. That would be a project for a physics major who knows magnetic theory real well.

Look at Grounded for a long time (dated 2005-08-09)
http://www.megginson.com/blogs/lahso/archives/2005/08/09/grounded-for-a-long-time/

This guy claims his plane got magnetized by a lightning strike while parked. Could be. He also says if a plane with a steel tube frame becomes magnetized it may be scrap because of difficulty in degaussing! Hummm never heard that but could also be true.

I don't know but we know steel tube can be magnetized and you can degauss it. Now how effective I don't know. What equipment do you need? You may want to talk to an avionics shop or write Sacramento Sky Ranch.

In WWII whole ships where degaussed (remove residual magnetism) to make them less susceptible to magnetic mines. They wrapped coils around the boat or floated over coils in the sea bed. So degaussing of large steal structure can be done.

Last I will say you don't need compass. Yes I said it. Forget it. You have a GPS that gives you track, which is better than heading in every way. Unless you want to do dead reckoning with the GPS turned off, than the compass does what for you. Also as an experimental VFR at least you don't need it despite what part 91.205 says. To be honest I am not saying to leave it out altogether, only that do the best you can, it is not super critical. Swing it and write a deviation card. If it is 20 degrees off it is 20 degrees off. Remember it is engine running and electrical on.

Magnetic airframes

As a very young child I remember touring the Aeronca plant in Middletown, Ohio. It is my earliest memory. Aeronca was the only plant where the assembly line was laid out north to south. As all the aircraft came down the line, the welders (my dad included) hammered on them to get tubing to fit tighter. Simply striking the metal aligned with the Earth's magnetic field was enough to build a small amount of magnetism, enough to make Aeronca compasses harder to correct than on other planes of their day. As I recall, only Champs were made there and I don't think the Chief had this problem.

Bob Kelly

Don't know where you are located but Lancaster Avionics in Lancaster, PA deguassed my 8's roll over hoop. The compass on the glare shield would always point to 120 deg no matter which direction I was pointed until I had it deguassed by Lancaster.

Jody

N40RV8Pilot said:

The compass on the glare shield would always point to 120 deg no matter which direction I was pointed

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It's good to know I'm not alone in this.
My RV6 compass always wants to point north. If you point the aircraft south it will tend to read about 50 degrees off north - E or W, depending on which way you steered to turn the plane round!

I'm going to try some of the degaussing techniques mentioned elsewhere on the forum, as my plane is now complete and I don't want to disassemble the sliding canopy and rollover bar.

Degauss/Demag

I would bet something inexpensive like a tape head demagnetizer would would work also.


You can find these on ebay for 10-20 bucks.

Here are a bunch of tips:

http://www.vansairforce.com/community/showthread.php?t=40673&highlight=degauss

Where is the magnetic source?

Find that out first, but that is a little difficult on a finished canopy. I checked my slider frame using my field compass which kept me from getting lost in the woods for 25 years. The fore-aft tube across the top is a pretty strong magnet and it moves the compass needle when it is within a foot or more. The bow across the front does almost nothing--the compass needle center has to be withing about 4 inches for the compass to respond. The canopy brace under the windshield is magnetic.

All those tubes are basically bar magnets. The midpoint has basically no magnetism, being midway between the north and south poles. Their propensity for being magnetic depends on the alloy and mild steel won't hold magnetism, so differences in alloys may be why I am finding differences.

You might be able to solve your problem by simply moving the compass to the midpoint of the canopy brace--or maybe a little farther forward to get it away from that top tube. If your compass is near the top end this could be the quick and simple solution.