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Garmin Magnetometer Placment (Again!)

Reflex

Well Known Member
Garmin Magnetometer Placement (Again!)

I know this has been covered and there are about as many answers as there are posts on this subject, but I have to ask. Given that Garmin has very specific recommendations on where not to place the magnetometer, where did you put it and why?

Based on the table below, it appears that there's really no place on an RV that truly meets all the requirements. My guess is that the best place may be on the right outside rib as far back from the strobes as possible (should be able to do 3+ feet).

I'm working on the -14 and the ADHARS shelf appears to be in violation of several of these recommendations; specifically, the landing gear and the heated pitot are too close.

In addition, a shelf behind the bulkheads is too close to the rudder cables, the stabilizer deck is too close to the tailwheel, etc.

See the table below from page 8-3 in the installation manual.

Thoughts?


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I put in in the tailcone

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We made a bracket and mounted it in the Tailcone on the top of the F-01407 bulkhead. I've had no issues with it mounted there.
 
I'm planning on Pitot in the left wing, Magnetometer right wing (don't want it in the bag because I'm going tailwheel and don't want unnecessary weight aft CG).

But even then.....My magnetometer will be relatively close to the right wing roll servo....

So you are right...numerous ways to skin the cat and they are not perfect per Garmin's letter of the law.
 
I used the kit mounting bracket and location for a GMU 22 in the left wing. No issues and passed all testing.
 
I put the GMU22 in the left wing on the shelf. I had a pitot heat controller that made the magnetometer crazy. When I went to a pitot heater that was just "on" and not with a controller, the magnetometer was good with it. My strobes and lights don't affect it at all, nor anything else inboard.

When I had the heat controlled pitot it didn't matter how I ran the power, or the ground, or anything; I tried quite a few cabling options. The only thing that mattered was if that controller was present. No controller no problem with simple twisted wire power to the pitot and ground at the wing root fuselage ground point.

The reason is that the dynon controller I had wasn't doing proportional control of current to keep the temp. It was On/Off and every on/off transition made a big flux change at the magnetometer. Having a simply switched heater has gotten rid of this big flux at every on/off of the controller transistor. Also, the controller was by design grounded at the base of the transistor to the case and thus to the airframe. I don't think this was the problem though because the flux effect at the magnetometer didn't go away with the controller hanging in space off the plane.

It should be possible to put a better control loop in the heat controller to get away from the simple on/off and make the control proportional (and more steady with less magnetic flux); but that is a manufacturer thing....
 
Mine is in the left wing location. I used the factory harness, G3X touch panel and everything that goes with it, unregulated pitot, LED lights, everything done pretty much per the plans. I ran the interference test several times because the results were so low I thought I might be doing it wrong.
 
I am just about to order the Garmin instruments. Why did you chose the GMU 22 over the GMU 11?

Available kit mounting bracket, standard left-wing location, and wiring harness compatibility. I'm not anticipating any issues whatsoever.

FWIW, I'm using the heated (but not regulated) Garmin GAP 26 pitot/AOA probe.
 
I too am doing exactly as what is in the plans, i.e. magnetometer mount in left wing, heated but unregulated pitot with twisted wiring, etc. The only difference is that I wrapped all cabling and conduit within about 18" of the center of the magnetometer with mu-metal. It's expensive, but it is supposed to shield against (at least to some degree) magnetic fields created by changing current such as wigwag lights and powering up the heated pitot. Might be overkill but I was trying to add some insurance that I wouldn't have any issues affecting the magnetometer.
 
Magnetometer Kit discontinuing from VAN?s

I just got off the phone with Vans?s. I was informed they no longer have the RV-14 GMU22 MOUNT KIT available. It seems the GMU11 is the new way.

Anyone have any insight or recommendations?
 
Gmu

While discussing this with my avionics guys, it was noted that the gmu11 uses the CAN bus. This can become an issue in the -10 due to the absolute length requirement of the CAN bus. The gmu22 apparently doesn?t use this wiring bus so it doesn?t add to the bus length.

This is what I was told...YMMV
 
I am not sure how much bigger a RV10 is compared to a RV14, but easily done in a RV14. The new maximum length of CAN is 66', based on my recent info unless it has changed again, and not too long ago it was 110'.

With a bit of planning, one can easily reach the wing tip which is one of the recommended places to install it under 66'. Of course if you put the GMU11 in the middle of the bus which the wire need to go to the wing tip and back to reach other devices, then you might run out. so it helps if you put the GMU11 at one end of the CAN bus.

Also worth noting that although Garmin recommends 10' away from any servo, many have done them in a RV with zero side effect.
 
And now I have found the "RV-14 GMU22 MOUNT KIT" on Vans page :D

Here is a picture of that mount kit and the GMU22.

It should be easy just to adapt this to hold a GMU11. The bottom plate slips right into the mount in the wing.

It provides a nice stable and flat platform.

picture-72.jpg
 
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