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Garmin G3X Touch - Interesting Issue

bjdecker

bjdecker

Well Known Member
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[Dual G3X touch, GTN 650Xi, GMC 307, GMU 11, some other stuff...]

In flight, AP set to "TRK" mode via the PFD AP status bar & on screen menu. HDG knob used to select TRK course. Selected TRK selected is shown on the PFD, the GTN Xi active navigation screen.

After the flight, I downloaded the .CSV log file and noticed a discrepancy between what I had selected for TRK and what was shown in the log file -- exactly 4° off to the right; e.g. TRK selected was 210°, log showed 214°. TRK was 320° log showed 324°, TRK was 080°, log showed 084° and so on.

Here's where gets interesting, FlightAware's track log of the flights also show the 4° discrepancy, so the ADS-B is also sending out the "wrong" info. It's not winds aloft -- as the deviation is ALWAYS to the right; I was flying 3 leg patterns to determine TAS error.

Anyone know what the G3X "GPS Ground Track (deg), TRK" parameter is, where it comes from, and why it would be entered into the log 4° right of what was displayed EVERYWHERE else?
 
bjdecker said:
[Dual G3X touch, GTN 650Xi, GMC 307, GMU 11, some other stuff...]

In flight, AP set to "TRK" mode via the PFD AP status bar & on screen menu. HDG knob used to select TRK course. Selected TRK selected is shown on the PFD, the GTN Xi active navigation screen.

After the flight, I downloaded the .CSV log file and noticed a discrepancy between what I had selected for TRK and what was shown in the log file -- exactly 4° off to the right; e.g. TRK selected was 210°, log showed 214°. TRK was 320° log showed 324°, TRK was 080°, log showed 084° and so on.

Here's where gets interesting, FlightAware's track log of the flights also show the 4° discrepancy, so the ADS-B is also sending out the "wrong" info. It's not winds aloft -- as the deviation is ALWAYS to the right; I was flying 3 leg patterns to determine TAS error.

Anyone know what the G3X "GPS Ground Track (deg), TRK" parameter is, where it comes from, and why it would be entered into the log 4° right of what was displayed EVERYWHERE else?
Click to expand...

Brian,

If you want to see aircraft magnetic GPS TRK from the log file data, add the TRK and Mag Var columns.

Steve
 
Thank you Steve and Matthew, it does appear to be Magnetic Declination (Variation) playing havoc with my mental processes.

What I found "odd" was the displayed value on all of the screens (G3Xt, GTN) was the corrected/desired TRK WITHOUT compensation for MagVar.

I suppose that then ties to how I have the GTN XI configured for Magnetic Variation & NAV Angle. What do most folks have selected here -- Magnetic, True, User or External?
 
bjdecker said:
Thank you Steve and Matthew, it does appear to be Magnetic Declination (Variation) playing havoc with my mental processes.

What I found "odd" was the displayed value on all of the screens (G3Xt, GTN) was the corrected/desired TRK WITHOUT compensation for MagVar.

I suppose that then ties to how I have the GTN XI configured for Magnetic Variation & NAV Angle. What do most folks have selected here -- Magnetic, True, User or External?
Click to expand...

Brian,

Nothing odd about showing magnetic instead of true track, because that is how most of us have the Position Setup configured on our G3X Touch systems.

PositionSetup1.png

When the heading parameter is setup for Auto Mag. Variation (instead of True), the HDG, TRK, CRS, and Wind angles are shown as Magnetic instead of True degrees as shown in this example.

HSIMag.png

If the heading parameter on the position setup page is set to True, all of these values are shown with a "T" indicating the units are true degrees.

HSITrue.png

The data log file always has TRK logged in true degrees regardless of the position setup page so that everyone's log files are always in the same units.

The GTN settings have nothing to do with this.

Steve
 
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