High magnetic heading deviation on the EFIS D100

[mgp]

I was to take delivery earlier this week of a new LSA "Sport Cruiser" built in the Czech Republic by CZAW but during the test flight we noticed a high deviation in the magnetic heading of the EFIS D100 - more than 10 degrees when compared with the G496 GPS and with the TruTrak Digiflight IIVS AP heading indication.
We have the new firmware vs 4.0. Recalibration was done in-flight and on the ground fore more than one time. The magnetic sensor was moved to keep it far from the AP servos.
What is strugling eveyone involved in solving this problem is the fact of once in the ground and after calibration the deviation is around 2 to 3 degrees in the different headings sectors. Going airborn in-flight reading is again more than 10 degrees deviation. In-flight recalibration in-flight and the 2 to 3 degrees deviation come back again. After landing...and the magnetic heading deviation once again more than 10 degrees!

Any idea of what can cause this stange behavior of the magnetic heading?

Manuel Gomes Pereira

 

[dynonsupport]

Re: High magnetic heading deviation on the EFIS D1

Wind.

(Your 496 doesn't know about heading - it generates a GPS "ground track" based on positional differences from moment to moment. The EFIS is measuring magnetic heading, which is where the aircraft is pointed. Imagine a 50 knot wind from your left while you're flying pointed north. While your magnetic heading would 360, your gps track would be somewhere between 001 and 090 from the push you get from the wind)

A few other notes:
The Trutrak just displays the track the 496 sends it. It's not a separate source of heading info. It will always "match" the 496, since it IS the 496.

You can't calibrate the EDC in flight. It assumes that there is is not a lot of dynamic motion - ie, that you are on the ground. On top of this, when you calibrate it in flight against GPS track, you're putting a wind offset in your mag heading. When the wind changes or you land, it's suddenly off, just like you saw.

Your GPS might be displaying true headings, not magnetic. Check your setup. In some parts of the world this might be just a few degrees of error, in others this is 20+ degrees.

Magnetic heading within 2-3 degrees is considered pretty good.

 

[Etienne]

Re: High magnetic heading deviation on the EFIS D1

Also, when calibrating on the ground, keep the engine running, and at about 1300-1500 rpm. I found that this corrected a very large error that I was getting... Just watch that prop