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Magnetometer / GMU 11 calibration

TShort

Well Known Member
I finally got the GMU 11 installed in an area with no interference; previously, it was lower in the tailcone, and the rudder cables were magnetized enough that the interference test failed.

It is now mounted on the Van's bracket in the top of the tailcone just aft of the baggage wall. Passed easily with no issues at all.

So I went to KMZZ to calibrate again using the compass rose.

Calibrated easily on the first try. Lined up on RWY22 for departure, heading reads correct.

Flying back, I lined up with east/west and N/S roads. My heading consistently reads 4-5 degrees right. Flying south, I read 185. Same for all directions. This is the same issue I had with the previous mounting location, and I assumed it was because of the interference failure.

I have not emailed g3expert yet, as I wanted to see if others had seen this, or if there is something I am missing. My understanding is that the EFIS / magnetometer accounts for declination automatically, so this shouldn't be it. I am pretty certain I was flying south / west, etc, as here in Indiana the roads are laid out pretty darn straight for the most part. This error is consistent, and repeatable.

This error causes other weird data; the displayed winds on the EFIS are way off of what weather is actually reporting.

Thanks in advance for any thoughts / assistance.
 
not sure you have a problem or not.
As we all know, the magnetic fields of the planet are varying constantly, one of the reason runway numbers can change over the years, i.e. when rounded up to the nearest 2 digits.
Not sure about Indiana and how the roads were laid out, but I doubt those are exactly on the actual major cardinal headings...
 
I agree - I am not sure I have a problem or not.

The roads here (most of them) are pretty square.

What more leads me to wonder if there is an issue is the reported winds (on the EFIS screen); the mismatch between my heading and ground track leads the system to believe there is more crosswind than there actually is.

The combination of the two things makes me think something is off...
 
Just something you can try:
Using the chart suplament (airport facilities directory) compare the painted runway numbers with the runway headings in the document. They are usually several degrees different.
Make a low pass down the runway and check heading.
Land and align the aircraft with the centerline and check the heading.

Another thing to consider is any rebar that may be in the concrete ramp area of the compass rose that you use. Could cause an error.
 
Thomas keep in mind the roads around us are oriented to true north and we have 5 deg. W variation, so it sounds like your calibration is correct. We took a Mooney over to MZZ a few weeks ago to do the mag calibration and noted a similar 'error'.
 
As bob mentions, tracking roads is not optimum for this. Find the winds aloft and fly two passes, back and forth on a reciprocal GPS track that is 90* from that wind. You are looking for hdg / trk offsets that are about the same, left vs right.

Larry
 
ok, just back from flying :)

Runway 26 in use today on my field, which is oriented 261? according to the plate. So I bugged 261 on the HDG (dual G5?s and GMU11).
Keeping the CL as good as I could during TO and later when landing and rolling out, heading shown was kinda between 259 and 260, so about 1.5? off which is far above my NAV skills ;)
 
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