Compass Calibration Problems

mmarien

Murray M.
Joined
Dec 26, 2009
Messages
1,206
Location
Saskatoon SK CAN
I had my first flights since the panel rebuild. The SV display is just fantastic. I'm still hunting for info and noticing new things every time I go up but starting to get more comforatble and familiar with it.

I tried to do my compass calibration today but found out that I can only go in two directions. North seems to work, but all the other directions point west on the calibration screen.

I hung the ADAHRS from the top of the fuselage (Glasair II) behind the AFT bulkhead. I used aluminum sheeting and brass crews for the mount assuming that neither would affect the magnetometer. The only active attenna within three feet is the ELT but I assumed that it is mute unless activated. There is another antenna built into the fuselage near the ADAHRS but it's not functional or connected to anything.

More than the direction function is affected. I checked the matrix in the Pilot's User Guide but couldn't determine if the magnetometer is affecting the other functions. It appears to only be required for direction.

What appears to work: Altitude, BARO, OAT, DA, VSI, ASI, TAS, horizon, SV, slip/skid ball and the HSI is updated when I do a GOTO in the GPS495. The SV also outputs altitude to the GTX327.

What doesn't work:

Magnetic direction: as noted when I try and calibrate, north is north and any other direction I fly shows west.

Flight path indicator: I caught a glimps of it a couple of times coming out of the left side of the screen turning left base (east to north). I don't believe it showed up in the climbing left turn (west to south) but then I wasn't specifically looking for it. It's MIA otherwise.

Wind speed and direction: The direction arrow is there although I didn't check it against ATIS. The wind speed shows 99K.

Is this a magnetometer problem and should I be checking for magnetic interference at the ADAHRS or does this point to other problems?
 

dynonsupport

Dynon Technical Support
Staff member
Joined
Mar 23, 2005
Messages
13,226
Definitely a magnetometer problem of some kind, either actual or interference-based. When you're in the calibration screen, are you saying it never lets you take data for any direction other than North or West? Any chance you ADAHRS is installed in an orientation other than tabs down, pneumatics forward?
 

mmarien

Murray M.
Joined
Dec 26, 2009
Messages
1,206
Location
Saskatoon SK CAN
I'm pretty sure it's installed correctly. I used installation guide and the pictures on this forum as a guide to mount it. If the aluminum mount is not a problem, I'll start looking for magnetic interference. I don't think I did a proper compass check where I mounted it.

Now that I think about it, it's getting more obvious. The compass generally points to 320 degrees and probably can be swayed to the north or west. If I draw a line from the ADAHRS to 10 or 11 o'clock I'd trip over the ELT and the antenna. The ELT is on the floor so the ELT battery is probably not a problem, but the antenna is up the inside of the fuselage and the top is about the ADAHRS level.

I'll do a better compass check of the area. Thanks for narrowing the seach.
 

dynonsupport

Dynon Technical Support
Staff member
Joined
Mar 23, 2005
Messages
13,226
One thing to try - but a simple boy scout or wet compass on top of the ADAHRS, then walk the airplane around a bit with the electrical system on. Does the boy scout compass agree with the ADAHRS? If yes, likely interference. If not, might be the ADAHRS.
 

mmarien

Murray M.
Joined
Dec 26, 2009
Messages
1,206
Location
Saskatoon SK CAN
This is solved.

I did the compass test on top of the ADAHRS and got different readings. The compass on top had correct readings. I really didn't want to have to send the ADAHRS back and ground my plane so I did do some further scouting with the compass and found out that the bolts I used to attach the ADAHRS were magnitized. They would swing the compass if I put it right on the bolt. Not strong enough to affect the boy scout compass when it was on top of the ADAHRS but too much for the ADAHRS itself.

I replaced the bolts with brass ones and the ADAHRS compass now works. Thanks to support for persisting.
 

llacy

Member
Joined
Nov 6, 2008
Messages
65
After installing 2.5 my compass is off about 15 degrees reads 15 degrees greater than mag at all headings. Does installing version 2.5 mean I have to recalibrate the compass. It was indicating correctly befroe I did the upgrade.
Lou Lacy
 

dynonsupport

Dynon Technical Support
Staff member
Joined
Mar 23, 2005
Messages
13,226
We haven't heard of any other reports of this. If you happen to have a settings backup before and after, you can send them our way at support at dyonavonics . com and we can take a look for you. Otherwise, does a recalibration fix it?
 
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