REFLECTOR: Compass split resoved

[Terry Miles]

Lar,

Thanks.  I know that.  I was pushing the fuselage by hand, and getting an
otherwise valid mag track read out, and it would respond to minor heading
changes correctly, just 40+ degress out of sync w/ North.  
Terry

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Laurence Coen
Sent: Friday, November 30, 2007 1:24 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Compass split resoved

Terry,

A GPS can only tell direction when it is in motion.  When it's sitting still

it has no idea which way north is.

Larry Coen
N136LC

----- Original Message ----- 
From: "Terry Miles" <terrence_miles at hotmail.com>
To: "'Velocity Aircraft Owners and Builders list'" <reflector at tvbf.org>
Sent: Friday, November 30, 2007 3:34 AM
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
>
> _______________________________________________
> To change your email address, visit 
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
> 

_______________________________________________
To change your email address, visit
http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html