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Garmin magnetometer location

Doug Rohrer

Well Known Member
Is anyone mounting their Garmin GMU11 magnetometer on the small deck aft of the last bulkhead under the VS on an RV-14/A? I did this successfully on an RV-9A, but I see many -14 builders are mounting the GMU11 in a wing or on a shelf in the fuse. Just wondering why???
 
The wing is where the manual says to put the GMU-22 it and there is a dedicated spot and bracket for it. There is some debate about this location for the GMU-22 but most of us haven't had any issues. Likely, folks are just defaulting to this since that's where the other unit goes.

The solid-state GMU-11 it's small enough to put anywhere. There aren't any restrictions beyond what Garmin says in their manual, just make sure it's protected (from the elements) and not near electronics that could interfere with its operation.

Also, note the can-bus cable length limitations pointed out in the Garmin manual.
 
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If you put the GMU11 in the wingtip, how do you mount it so that you know it is level in cruise flight? It seems wing mounting has to allow for dihedral and angle of attack. The rear deck is by definition level. Am I over-thinking this?
 
If you put the GMU11 in the wingtip, how do you mount it so that you know it is level in cruise flight? It seems wing mounting has to allow for dihedral and angle of attack. The rear deck is by definition level. Am I over-thinking this?

I think there are only 2-3* of dihedral. If the unit can't handle that and work well, it wouldn't be very accurate. Just my thoughts. This is an act of compromise and finding the least troublesome condition. I have to assume the magnetic interference is worse than 3* from level, but have no real idea.
 
If you put the GMU11 in the wingtip, how do you mount it so that you know it is level in cruise flight? It seems wing mounting has to allow for dihedral and angle of attack. The rear deck is by definition level. Am I over-thinking this?

Set it at the same angle as the aft deck then, or level the airplane and use that for your reference.
 
Left wing

I’m pretty sure the plans call for the 22 to be placed in the left wing. If you are using the Vans wiring harness (WH00125) that is the location where at least the wiring goes. (I’m traveling and going off memory which is always dangerous). The controversy is the pitot tube is in the same wing. I used twisted shielded 14 awg for the heat and ran the ground back to the panel. I heard Garmin will discontinue the 22 in favor of the 11 but not sure. So far the magnetometer in the left wing has worked fine and passes testing.
 
The GMU runs off the CAN bus so in the RT wing makes it easy to extend the CAN from the roll servo.
 
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It looks like I need to mount the GMU11 either in the right wing or on a shelf above and behind the pitch servo in the fuselage. These locations minimize the extra length of CAN BUS wiring needed in the system. Thanks for all the suggestions.
 
Did you still use the standard GSU-25C ADAHRS with GMU-22?

The wing is where the manual says to put the GMU-22 it and there is a dedicated spot and bracket for it. There is some debate about this location for the GMU-22 but most of us haven't had any issues. Likely, folks are just defaulting to this since that's where the other unit goes.

The solid-state GMU-11 it's small enough to put anywhere. There aren't any restrictions beyond what Garmin says in their manual, just make sure it's protected (from the elements) and not near electronics that could interfere with its operation.

Also, note the can-bus cable length limitations pointed out in the Garmin manual.

For those using the GMU-22, were you able to still use the standard GSU-25C ADAHRS or did you need to use the high performance (PMA'd) LRU kit?
 
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Just installed a GMU11 in a 9A this past weekend one bulkhead back from the baggage compartment bulkhead. Calibrated it and it's spot on with no issues.

YMMV
 
Mount orientation

For those of you mounting the GMU 11. What does “level” mean. Can I mount it upside down but level? Can I mount it on a vertical surface but screw holes “level”. Seems if you’re mounting in the wing- then it would best mount on the vertical wing rib. If I mount it in the fuse, then on. Shelf that is level but what if I put it on the underside of a shelf?

Garmin manual doesn’t give description.
 
Garmin does say.
 

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Thanks Webb. Didn’t read note 2. So if you mount in the wing, are you making an angle bracket attached to the rib? I’m building a 7 and don’t have any brackets included.
 
My GMU-22 is working perfectly in the wing bracket. I took some care to properly twist the pitot heat wiring and ground the pitot heat back at the fuselage. I originally had a pitot heat controller but switched to a plain on-off heater because the controllers are all on or all off and not proportional. The constant switching on and off of the controller caused a tic in the magnetometer reading. It remained accurate overall but the little swings every few seconds were annoying. Since then I’ve had no reason to miss the controller. My other planes didn’t have a controller for pitot heat anyway.

Part of the controller problem is that the box is also in the wing and it is grounded to the heater circuit so when it turns on, significant current goes right through the box into the wing and Not down the ground wire. Without a controller box for the pitot heat I can turn it on and off all day with nary a bump in the heading indicated.
 
Thanks Webb. Didn’t read note 2. So if you mount in the wing, are you making an angle bracket attached to the rib? I’m building a 7 and don’t have any brackets included.

Stein sells or you can make one.
 

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Mark, when using the GMU-22 you do not need the high performance version of the ADAHRS; the standard one works fine.
 
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