Mag Compass Mounted on Center Bar Way Off

Great thread here: http://www.vansairforce.com/community/showthread.php?t=5792&highlight=degauss.

I tried to swing my compass and correct it, but after trying the A&P agreed we actually made it worse. I'll check tomorrow if it's magnetized, suspect it is. I have a GRT EFIS in it so believe it has a magnetomoter and understand the plane probably doesn't even require the mag compass, but thought I'd try to de-magnetize the roll bar and center bar. My hesitation is if I use a growler (1940s model) will it damage any of the avionics (430, EFIS, garmin radio stack)?

Has anyone done something similar to this before with avionics installed right below the bars?

Thanks in advance for any thoughts and blue skies to all,
Tim

p.s. - eventually I hope to do my IFR cert in it, but need to continue trying to get it up to snuff equipment wise in that regard. Think the magnetometer will suffice for the magnetic direction indication requirement, but still trying to get the VOR on the EFIS (ARINC 429 mod) to work. Almost have the PPL and loving the plane.

Hi Tim

The roll bar brace is stainless...non-magnetic.

You're correct in that you don't need a separate compass...the EFIS's magnetic tape is acceptable.

Best,

Thanks

Pierre,

Thanks for the help with the mag compass. My instructor is thinking for an IFR capable plane, which mine is supposed to be, it needs a mag compass. Do you know of a FAR that clears this up, that is you don't need a compass if you have a magnetometer (though it requires electricity to operate)?

Tim

"magnetic direction indicator"

twcroy said:

... My instructor is thinking for an IFR capable plane, which mine is supposed to be, it needs a mag compass. Do you know of a FAR that clears this up, that is you don't need a compass if you have a magnetometer (though it requires electricity to operate)?

Click to expand...

The pertinent requirement in the FARs that I'm aware of, which by the way is for VFR as well as IFR operations, is that you're required to have a "magnetic direction indicator". This is FAR 91.205(b)(3).

An EFIS that shows you your magnetic heading that it derives using a magnetometer should meet this requirement.

Nowhere that I'm aware of do the FARs specifically require you to have a wet compass. If there is such a requirement, then your instructor should be able to point you to it in the FARs (in which case, please post it here).

There is no FAR requiring an "independent" compass. As noted above, Part 91.205(b)(3) calls for a "magnetic direction indicator".

Thanks for everyone's help, Tim

I think we're tracking now.

I work for a large manufacture of business jet aircraft that have every conceivable type of navigation equipment and they all still have a whiskey compass. I know that at 51,000 ft and .82 mach they are not using the whiskey compass and I believe the only reason they are still installing the compass is to meet the regulations?

The picture is where I ended up locating my compass on the instrument panel. You can see on the roll bar brace where I tried locating it, but there was too much residual magnetism.



This is just my two cents worth.

Hi twcroy,

So did you de-magnetize the rollover bar to get your problem sorted?

If so - did you leave the radios and other equipment in place?

I de-magnetized my roll over bar and all the steel nuts and bolts without the instruments installed and my panel mounted PAI vertical card compass seems to track well.

I am yet to do the formal compass swing.

To answer your question - I would remove the instruments. Simply not worth the risk.

Doug

Next Step in Trying to Receive Accurate Mag Indicator

Doug,

I haven't done it yet, but thanks for the advice. I tend to agree with you, not worth the risk. In the meantime, I was hoping to rely on my magnetometer in the tail. Only problem is when I transmit on either radio it swings 130 deg. Not sure if it's an issue, but my instructor thinks it may be or maybe I read it in the GRT EFIS manual. The builder mentioned he thought the ELT wiring may be contributing to the swing. I disconnected it and still same problem; however the coaxial was still in place and close to the radio antenna leads, it may be easier pull the coax out and put a whisker antenna on the ELT.

I need to continue troubleshooting..

Thanks for the email and help,
Tim

pierre smith said:

The roll bar brace is stainless...non-magnetic.

You're correct in that you don't need a separate compass...the EFIS's magnetic tape is acceptable.

Best,

Click to expand...

When I installed mine I also had a problem. I discovered while the bar is stainless there was a residual magnitism in the weld areas. Anyway I demagnetized with a hand held degauss tool and was able to calibrate the Wiskey compass.