Greetings esteemed UAV-ers...

I'm running an APM2.5 board in a ParkZone Radian (3 controls - throttle/rudder/elevator).

My initial manual flights were successful, including running in Stabilize and Loiter Modes (using my Spektrum DX7s 3-position flap toggle).

The logical NEXT step toward full automation is manually operating the plane, but monitoring the telemetry coming from the plane (the APM2.5 module) via telemetry into the my USB antenna into my laptop running APM Mission Planner v1.2.62...

The APM IS oriented with RC servo inputs aligned toward the NOSE of the plane.

The APM module is easily 12" from the prop motor. It doesn't get much better than that.

ALL the key GPS-related telemetry coming in appears 100% accurate & stable:
- LAT is accurate (+/- 25 feet) and stable;

- LONG is accurate and stable;
- ALT is accurate and stable;

- Artificial Horizon Level/Right Bank/LeftBank/Pitch appear 100% accurate.

My only PROBLEM appears to be with the ON-BOARD COMPASS:
- on power-up with the plan facing due north:
-- the Artificial Horizon's heading shows "N" (perfect orientation);

-- the Red Ray in the Map View emanates out from the plane DUE NORTH (perfect orientation).

SO FAR SO GOOD - THEN...

- even as I LEAVE the plan on the back patio (a full 9 GPS sats visible and NO metal within 20+ FEET of the plan):
-- the plane's heading (the red Heading Ray) starts to drifts counterclockwise (it appears to be a repeatable pattern) a few degrees every minute;

-- after about 30 minutes, the PLANE is STILL pointed NORTH (I NEVER moved it),

   BUT the red Heading Ray is now pointing a FULL 180 deg DUE SOUTH !!!

WHAT GIVES?

I've checked and re-checked the Params and AdvParams - thus far I'm running ALL defaults, NO corrections.

WITHOUT the compass to show actual headings, the plane becomes untrustworthy on a mission, particularly if manual control needs to be resumed.

ANY IDEAS?

Cheers,

-Mark