Compass Calibration

[turbopilot]

I am in the process of troubleshooting some compass calibration issues.

There are two screens displayed as you drill down to the ultimate screen to calibrate the compass. First screen shows when you initially select "Compass Calibration" from the "ADAHRS Calibration" menu item. Second "Compass Calibration" screen displays when you select "Compass Calibration" with a button push.

The first screen displays a "CURRENT MAGNETIC HEADING" value while the second screen displays "CURRENT MAG HEADING" that is noted as "(WITHOUT CALIBRATION)".

Is the magnetic heading displayed in the first page with calibration? For future software releases it would be helpful if both pages displayed magnetic heading with and without calibration along with a table showing the amount of calibration applied to various headings after ground and air calibration.

Here are screen shots of the two pages. Sorry the second one is a little blurry.

 

[dynonsupport]

The only difference between the pages is if you have "entered" the calibration routine. The first page is with mag cal, and then when you enter the cal routine it zeros it out so it's without. We're just warning you in that menu that you're totally uncalibrated.

In what case do you want to see the difference between calibrated and uncalibrated?

 

[turbopilot]

In what case do you want to see the difference between calibrated and uncalibrated?

In my case I am getting good calibrations on westerly headings but getting a 5 to 7 degree error on easterly headings after calibration (ground and in flight) so I am just trying to understand where the calibration offsets have been applied around the heading rose.

This installation is in a Carbon Cub. I did the ground calibration in this airplane tail down with a highly accurate magnetic sight compass. However, the Cub sits 12.5 degrees nose up on the tail wheel. Compass calibration instructions say it should calibrate on the tail wheel, but I am not so sure.

This is my second Carbon Cub. My first Carbon Cub had a D100 system. The only way I could accurately calibrate the compass in that airplane was raise the tail to the flying position for each calibration heading.

So next step will be to do another compass calibration in the flying position and see if that makes a difference.

 

[dynonsupport]

Have you run the in-flight cal where you do turns in flight? This generally leads to a much better calibration.

The calibration on the ground is not a simple adjustment on various headings, so it would be hard to observe the effects on a specific heading. If it's correct on one heading but way off on the reciprocal, then you likely have a very strong interferer in the plane.

Try the in-flight cal, it will likely fix it.

 

[turbopilot]

Have you run the in-flight cal where you do turns in flight? This generally leads to a much better calibration.

The calibration on the ground is not a simple adjustment on various headings, so it would be hard to observe the effects on a specific heading. If it's correct on one heading but way off on the reciprocal, then you likely have a very strong interferer in the plane.

Try the in-flight cal, it will likely fix it.

Yes, I have done the inflight calibration with a score of 122.

I think I found a few degrees of my error. Just discovered that my home airport, KTRM, airport charts use Magnetic Variation from the year 1990 when it was -13. This year KTRM variation is -11.5. So the magnetic heading information for the runways printed on the charts is 1.5 degrees off actual. For instance, RWY 12 is 135 degrees true with the charts showing mag direction of the runway at 122 degrees when the runway is actually pointing 123.5 magnetic based on this year's magnetic variation.

If you used an old compass rose at your airport you might check when it was laid down. The magnetic north pole has been on the move.