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Mounting the Magnetometer in the Wingtip

Pat Hatch

Well Known Member
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So we're talking about where to mount the two magnetometers in Bob Lund's RV-8. Jason Smith at Aerotronics suggested that a tail mount of a Garmin magnetometer is not passing the interference check during calibration (we're talking RV-8--tail location is fine in my RV-6). Steve at GarminX was also very encouraging. So we decided to try a wingtip mount in spite of the heavy iron pipe that is in the leading edge of the ailerons. That was a concern. Here are some pictures:



And the GRT Mini magnetometer installation in the opposite wint tip:



We did the Garmin Magnetometer Interference Test today for the first time and it passed! The highest interference level we got was 64% of the limit during full left aileron deflection, but apparently it was still well within the limits. We will report later on the GRT magnetometer results when we get to it.

We rolled the airplane out of the hangar today for the first time, ready for first engine start in the morning. More later.





 
I need to mount these two magnetometers as well and was going to put them both in the same wing. Did you consider mounting them both in the same wing? Is there a reason it should not be done?
 
Mark, I would say it would be fine but I'll defer to the experts. I have mounted magnetometers together in the past with no issues. Given the choice, however, I would want to eliminate any possibility for interference.
 
Do you see any effect on the magnetometer when the strobes discharge?

Almost none (2% was what I recall). If I had to do it over, I would have moved the magnetometers forward more because of this, especially since our strobes are LEDs. But I was concerned about the strobes, nav and landing lights in the wing tips.
 
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Do you see any effect on the magnetometer when the strobes discharge?

I have the GMU22 in my RV-8As wingtip, but mounted a little farther forward. My biggest source of interference is the landing light, but it's still well within limits. Both the landing lights and position/strobes are LED.
 
Just a data point

Guys, just another data point for your consideration.

I had my Dynon D10A magnetometer mounted in the right wingtip and it seemed to work fine. Of course, I didn't have much to compare it to.

When I changed to GRT MiniX's I put the magnetometer on the same mount in the right wing. During calebration it seemed to work fine and showed that it was a good place. However, it actual use I had large (10-15 degree) variations with my HXr. (HXr magnetometer mounted in fuse about 12" behind baggage real wall). My variations occurred only on 45 degree's off cardinal headings, and was worse to the SW. I moved the magnetometer forward in the right wingtip to get away from the aileron rod and that didn't change anything.

I finally just mounted it next to the one in the rear fuse and now they are both exactly the same on all headings. I've swung it a couple times and they match compass roses and runway mag headings exactly.

I'm just throwing this out. In my 8 I could not get the wing mount to give accurate headings.

Best
 
Us too.

We just did this one with the Garmin unit a couple of months ago. The wing tip works well if you mount the unit halfway between the spar and the back of the main wing body. The only thing we found was for the strobes and other lights in that wing tip we needed to run a ground wire into the main center section of the cabin, for all the lights and strobe. If you don't use the wing as your ground conductor from the outboard end of the wing, there will not be an electrostatic field in parted to the wing structure close to the magnetometer. The only thing that you have then, close to the unit is the steel in the hinge bolts, counter balance weight, and wing tip screws ( use stainless ). We got 30-40% or there about.
Hope this helps. Yours as always. R.E.A. III #80888
 
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How about the nut plates for the wing tip attach screws? I don't seem to be able to find any #6 size made of stainless. Is using steel Ok in this situation, or will it affect the magnetometer?
Regards,
Tom.
 
How about the nut plates for the wing tip attach screws? I don't seem to be able to find any #6 size made of stainless. Is using steel Ok in this situation, or will it affect the magnetometer?
Regards,
Tom.

We did find some in S.S., but left them standard for the first test and found the ones close to the unit did not amount to enough galvanic field to amount to changing them out. We just used the S.S. screws, ran the new ground wire and kept on going. Hope this helps. Yours, R.E.A. III #80888

P.S. Hope the devils are doing OK, down there.
 
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GRT and Dynon D10A magnetometer in same wing tip

When I purchased my RV7A from the original builder both magnetometers were mounted on the shelf just forward of the vertical stabilizer. As a result, every time I keyed the radio, magnetic interference was so great that both my GRT EFIS and my backup D10A headings would drift. The drift was so bad that I literally had no idea which was the most correct (neither were very close to actual magnetic heading). ForeFlight got me from Denver (where I bought the plane) to my home in OKC.

After talking to GRT and Aerotronics (who built my panel) I decided to move both magnetometers to a wing tip position. Originally I was going to put them in separate wing tips but D10A wire length limits forced me to place them in the same wing tip. I did my best to ensure appropriate separation from strobe and other electrical interference and paid very close attention to their alignment to within 2 degrees of level to the AHAR units.

I can report that heading differences between the dual GRT Horizon WS and my Dynon D10A have, since this move, (about a year and a half ago) at all times remained within one to two degrees of each other and actual magnetic heading. Strobes, landing light wires, and relatively close proximity of the two magnetometers (about a foot apart) to each other do not appear to impact headings. There is more than 18" distance from the landing and strobe lights from the magnetometers.

I also want to thank Pat Hatch publicly for his patience and support when I installed my Tosten multi-function grips last fall. Without his assistance that effort would have been a disaster. His "Ultimate Hub" is a truly great trim controller.
 
How about the nut plates for the wing tip attach screws? I don't seem to be able to find any #6 size made of stainless. Is using steel Ok in this situation, or will it affect the magnetometer?
Regards,
Tom.

Tom, I'd be more concerned about anything ferrous that moves. If it's stationary, not as much of a concern. We did use the stainless screws but the nutplates are just the regular ones. You should be fine. You'll discover any problems when you do your magnetometer interference check.
 
Pat, you just made my day (then again, I'm current working in the canopy, so any good news makes my day).
Other builders here have been telling me I should make a composite strip that the stainless screws bite into, however I was concerned about the longevity of such and would have rather just use nut plates, so thanks for confirming that it should work ok!
Tom.
 
above a wing access plate?

I plan on the wing tip but since the inspection plates have fewer screws to remove what would be wrong with above the second inspection plate behind the fuel tank on that rib?
 
Orientation settings

Pat

I mounted my grt magnetometer for the sport efis recently in the wing tip just like pat has pictured. Seems to be working well from an interference point of view.

However, I am a bit confused about the magnetometer orientation needing to be the same as the ahrs internal to grt sport.

Do I have to make a mount for the magnetometer and it needs be horizontally mounted? Or are there settings I can adjust ...? Curious to see what your ahrs and magnetometer orientation settings look like...


Tom, I'd be more concerned about anything ferrous that moves. If it's stationary, not as much of a concern. We did use the stainless screws but the nutplates are just the regular ones. You should be fine. You'll discover any problems when you do your magnetometer interference check.
 
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