G3X Data "Ground track" True?

Whilst analysing the Data Log downloaded from my G3X touch I noticed a split between the heading and "Ground track" parameters, even when the airplane is on the ground and tracking down a runway, when both should be the same. After initially thinking I may have a compass calibration problem I soon realised that the heading closely matches the published headings of all three runways I have used so far, and the difference with the ground track is approximately equal to the local magnetic variation indicating that the "ground track" parameter is in fact a Track(True). Can anyone, hopefully G3expert, confirm that this is the case? and if so why?

I am away from my airplane for a while so cannot confirm but I am pretty sure that the "Track" displayed on the PFD at the top of the compass rose in "Auto Trk/Hdg" mode is Track(Magnetic). Track (True) would make no sense here.

Me Too

On my Garmin Pilot app, when I hand fly, my ground track wanders all over the place compared to my flight plan. It is really noticeable. It must be the magnetic variation too.

No seriously, where I fly, there are areas that the map said had magnetic variations. I wonder if this is affecting the accuracy of the ground track? Good question. Next time, I will fly on auto pilot in same area and see if track improves.

Z-EDD said:

Whilst analysing the Data Log downloaded from my G3X touch I noticed a split between the heading and "Ground track" parameters, even when the airplane is on the ground and tracking down a runway, when both should be the same. After initially thinking I may have a compass calibration problem I soon realised that the heading closely matches the published headings of all three runways I have used so far, and the difference with the ground track is approximately equal to the local magnetic variation indicating that the "ground track" parameter is in fact a Track(True). Can anyone, hopefully G3expert, confirm that this is the case? and if so why?

I am away from my airplane for a while so cannot confirm but I am pretty sure that the "Track" displayed on the PFD at the top of the compass rose in "Auto Trk/Hdg" mode is Track(Magnetic). Track (True) would make no sense here.

Click to expand...

Ed,

I am sure Justin will be along soon, but to start off, how do you have this configured in your G3X Touch system? It would be very unusual for anyone to not be using magnetic GPS track (Auto Mag Variation) since that is the default configuration.





Personally, I have almost no value for Heading. I only use it as a backup for GPS Track or when being Heading Vectored by ATC. In the unlikely event that I fly into an area with no GPS support, I am happy to be able to push the HDG button on the GMC 507 autopilot control panel to either continue the current path or to take heading vectors from ATC out of the affected area.

In general, I couldn't care less where the nose of the aircraft is pointed (Heading), but care a lot about whether or not GPS track equals GPS course since I am almost always flying a flight plan or approach and want to keep the aircraft on the course line.

If you look at the TSO requirements for heading and the acceptable precision, you realize that measuring the earth's magnetic field in a small aircraft to obtain heading is very difficult and error prone and the resultant measurement can't hold a candle to the typical 1 degree precision of GPS track.

Like you, I always use the GPS Track based HSI where the HSI course pointer is always pointing straight up when the CDI is centered and the aircraft is on course to the next waypoint regardless of the direction and magnitude of winds aloft.



Steve

Thanks for your thoughts Steve, I will admit that I have never seen that setup page, must get to know my system better! But I can only assume that it is in the default/ Auto setting. I have never been concerned with the displayed track on the PFD, I only have 13 hrs on her so far and have been focused outside the canopy mostly, but I'm pretty sure the Track displayed has always made sense. My query is mostly about the recorded data in the Data log which appears to be a true Track.

This came to light after a crosswind landing when I thought it would be fun to replay the data on flygarmin.com to watch the relationship between the Heading and Track. But it didn't make any sense and I suspect it is only recording true track in the data log. Variation where I am is around 9 degrees.

G3X Touch GPS Track

Z-EDD said:

Thanks for your thoughts Steve, I will admit that I have never seen that setup page, must get to know my system better! But I can only assume that it is in the default/ Auto setting. I have never been concerned with the displayed track on the PFD, I only have 13 hrs on her so far and have been focused outside the canopy mostly, but I'm pretty sure the Track displayed has always made sense. My query is mostly about the recorded data in the Data log which appears to be a true Track.

This came to light after a crosswind landing when I thought it would be fun to replay the data on flygarmin.com to watch the relationship between the Heading and Track. But it didn't make any sense and I suspect it is only recording true track in the data log. Variation where I am is around 9 degrees.

Click to expand...

Hi Ed,

Can you share the airport/runway you were using, as well as some of the datalog deviations you are looking at? It may be easiest to send us an email to [email protected].

Thanks,

Justin

Z-EDD said:

Thanks for your thoughts Steve, I will admit that I have never seen that setup page, must get to know my system better! But I can only assume that it is in the default/ Auto setting. I have never been concerned with the displayed track on the PFD, I only have 13 hrs on her so far and have been focused outside the canopy mostly, but I'm pretty sure the Track displayed has always made sense. My query is mostly about the recorded data in the Data log which appears to be a true Track.

This came to light after a crosswind landing when I thought it would be fun to replay the data on flygarmin.com to watch the relationship between the Heading and Track. But it didn't make any sense and I suspect it is only recording true track in the data log. Variation where I am is around 9 degrees.

Click to expand...

Hi Ed,

Sorry, I missed the main aspect of your question. Yes, the GPS Track in the SD card flight data log is True versus Magnetic and is always True independent of what may have been selected for display units. The Magnetic Variation is also logged in that file each second, and if you add the two, you get Magnetic GPS Track.

I just looked at a video of an LPV approach I flew a couple of weeks ago and confirmed that the magnetic ground track that was shown on the PFD HSI each second (which agreed with the published final approach course) differed from the SD card logged ground track by an amount equal to the magnetic variation.

Steve