REFLECTOR: Compass split resolved

[Andy Millin]

Way to go Terry!  If it had all gone well from the start you would probably
be wondering what you had done wrong?  :)

Glad this is on track.  Now go fly!

Andy

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Terry Miles
Sent: Friday, November 30, 2007 10:35 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: REFLECTOR: Compass split resoved

Hi all,

First thanks for all the good ideas.  This sharing of ideas is my best
working resource by far and away.

Here's what I had, my mistake, how I fixed it, and a guess at what was going
on.

INITIAL ISSUE
When I went to do the book magnetometer calibration on my GRT EFIS I found
myself outside of tolerances.  I didn't doubt my N reference or my properly
following the calibration procedure so I was left with looking at the
magnetic interference or alignment between the magnetometer and the AHRS box
as possible issues issues.  

It turns out the magnetometer was fine, what I had done was give it bad
North reference.  I was off by the full 40 plus degrees. I used my GNS480
(GPS) as my N reference and it was out of whack big time.    

Across the last year or so the GPS box has been turned on and fully fired up
in MN, PA, and SC.  I travel a lot and was taking panel parts with me.  The
airplane was built about 3 miles from the ramp where it sits now and that
too could have been a player.  I can't say for sure, but other GPS equipment
I have worked with does retain a last known present pos on shutdown and goes
thru and internal comparison to next start up.  I have seen GPS boxes act up
when relocated from the city to city and turned back on again.  Maybe that
was a player for me.  At any rate after another couple of hours powered up
in one place the GPS is back responding correctly.  It could also have been
acacerbated by the GRT being so badly misaligned by me originally and
whatever crosstalk goes on between the GRT EFIS and Garmin GPS.  I do not
have the internal GRT GPS.    

Moral of the story:  go to the compass rose and use what's painted into the
concrete.  Had I done that to start with it would have saved me a week of
hand wringing.  

Thanks to every one for their time and guidance.

Terry Miles
Velocity XLRG-5
Flying

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