Garmin GMU 11 Magnetometer placement

[John]

Looking to have a GI 275 HSI installed in my 1966 Mooney M20C. Where is the GMU 11 Magnetometer being installed in other installations. 

[ArtVandelay]

In the tail, on a shelf.

[EricJ]

Usually in the tail or in a wing.   Mine is in the tail on a shelf.

 

[Andy95W]

I put my GMU-11 in the right wing.  Came out nice, but making sure it was level was a pain and running the wires to the fuselage was not easy.  Tail cone would probably be a better method.

[BDPetersen]

Tail shelf worked for me but had to deal with electrical interference from belly strobe. (Needed ground to be run to battery)

[Ragsf15e]

Mine is in the tail too which makes wiring easier but possibly could have more interference due to all the electrical stuff there.  Wing may be more difficult but easier to calibrate.  Mine works perfectly in the tail.

[carusoam]

For comparison…

Mooney installed the BK magnetometer in the right wing, half way out…

The nearest access panel looks like they used brass rivets to hold it in place, instead of SS screws…

 

So… keep an eye out for odd types of magnetic interference…

PP thoughts only,

-a-

[Aerodon]

I have made several of these for Mooney / Piper.  Wide enough straddle the hole in the wing rib, tilted 7 degrees, predrilled for GMU11.

Send me an email, supercub180@gmail.com if you need one.

 

Aerodon

 

[PT20J]

The KAP 150 magnetometer for my J was installed in the left wing. It was removed when the previous owner installed an Aspen PFD which had the magentometer in the RSM located on the tailcone where it worked fine. When I had the GMU 11 installed, I had it put where the King unit was because I figures that had already been tested. Installer tells me the biggest issue is unshielded wiring for strobes.

Skip

[John]

Thanks everyone 

john

[DCarlton]

A few questions if folks have time... 

What documentation is required for the brackets or shelves?  Do you need a drawing?  

For the wing option, does anyone have a pic handy of the wires running through the root into the cabin?  Which rib is it installed on?  

I like the tail option, but a young avionics guy tried to talk me out of it yesterday.  Said he's had too much interference and error messages when installing in the tail.  I like to mount mine where the Brittain mag sensor used to dangle in the tail but it's hard to reach.  

Thanks.  

 

[EricJ]

1 hour ago, DCarlton said:

A few questions if folks have time... 

What documentation is required for the brackets or shelves?  Do you need a drawing?  

I'd think citing AC 43.13 would be sufficient for that.

[Aerodon]

1 hour ago, DCarlton said:

A few questions if folks have time... 

What documentation is required for the brackets or shelves?  Do you need a drawing?  

For the wing option, does anyone have a pic handy of the wires running through the root into the cabin?  Which rib is it installed on?  

I like the tail option, but a young avionics guy tried to talk me out of it yesterday.  Said he's had too much interference and error messages when installing in the tail.  I like to mount mine where the Brittain mag sensor used to dangle in the tail but it's hard to reach.  

Thanks.  

 

On an M20K, the wires run through holes in front of the tank.  I did not manage to fish the wires through without drilling out a couple of inspection panels.  I made the mount out of 0.032, I think that was based on a drawing or instruction I found in one of the Garmin manuals (G3x, G5 etc).  The manual recommend installing in a wing, but plan on redoing your nav and strobe lights so that the ground is run past the magnetometer to the fuselage.

The bracket I made straddles a wing rib lightening hole and has the correct tilt.  I can measure how far from the fuselage Mooney mounted the magnetometer on the left wing.

I did a tail mount in a C172 a few years back, no interference issues (but i did run new grounds), but it would occasionally lose the heading signal.  

Don

 

 

 

[WaynePierce]

In my 1985 J it's in the wing just outboard of the fuel tank.

[PT20J]

Mooney is pretty good about running ground wires to most loads rather than just using the airframe. My installer didn’t have any issues. He told me Cessnas are the worst and he’s had to rewire the strobes on every one he’s done to get the GMU to calibrate. I had mine placed in the left wing above the same access panel where the factory mounted the original KCS 55 magnetometer. I figured they had already decided that was a good spot 

[DCarlton]

On 2/7/2023 at 12:41 PM, Aerodon said:

On an M20K, the wires run through holes in front of the tank.  I did not manage to fish the wires through without drilling out a couple of inspection panels.  I made the mount out of 0.032, I think that was based on a drawing or instruction I found in one of the Garmin manuals (G3x, G5 etc).  The manual recommend installing in a wing, but plan on redoing your nav and strobe lights so that the ground is run past the magnetometer to the fuselage.

The bracket I made straddles a wing rib lightening hole and has the correct tilt.  I can measure how far from the fuselage Mooney mounted the magnetometer on the left wing.

I did a tail mount in a C172 a few years back, no interference issues (but i did run new grounds), but it would occasionally lose the heading signal.  

Don

 

 

 

Considering adding an external mag to an AV30.  Any reason to not run the wires through the same holes and grommets as the pitot tube if mounted in the left wing?  Guessing these were the holes you used in front of the tank?  Thanks.  

[N201MKTurbo]

I guess I’m a right wing kind of guy. I put mine in the right wing to get away from the pitot heater. It draws a lot of current. It has worked great there for 7 years and passed the interference test with no issues.

[DCarlton]

3 hours ago, N201MKTurbo said:

I guess I’m a right wing kind of guy. I put mine in the right wing to get away from the pitot heater. It draws a lot of current. It has worked great there for 7 years and passed the interference test with no issues.

Good point.  I'll likely have my carpet out later this year during a tank reseal; it may be a good time to snake the wires.  Just planning ahead.  

[EricJ]

Just survey it carefully.   If the left wing winds up being the best spot, tested with pitot heat on and off, just shield the wires.   The pitot heat is DC, which is not usually a big problem for interference to the wiring.   I think most pitots use resistive heat, which should minimize any issues with the magnetometer itself.    All of this stuff is why sometimes the magnetometer winds up in the tail, though. 

[N201MKTurbo]

15 minutes ago, EricJ said:

Just survey it carefully.   If the left wing winds up being the best spot, tested with pitot heat on and off, just shield the wires.   The pitot heat is DC, which is not usually a big problem for interference to the wiring.   I think most pitots use resistive heat, which should minimize any issues with the magnetometer itself.    All of this stuff is why sometimes the magnetometer winds up in the tail, though. 

So, a DC current won't emit any electrical fields, but it will produce a static magnetic field. And the magnetic field is proportional to the current. And the pitot heater is one of the biggest current draws in the plane. So the magnetometer itself will only be susceptible to magnetic fields. Granted, the support circuitry in the GMU11 may be susceptible to electrical interference and may look to the system as a magnetic anomaly. 

[EricJ]

17 minutes ago, N201MKTurbo said:

So, a DC current won't emit any electrical fields, but it will produce a static magnetic field. And the magnetic field is proportional to the current. And the pitot heater is one of the biggest current draws in the plane. So the magnetometer itself will only be susceptible to magnetic fields. Granted, the support circuitry in the GMU11 may be susceptible to electrical interference and may look to the system as a magnetic anomaly. 

Yes, if the question is whether the wiring is susceptible to interference in the signals if it is routed near the pitot wiring, it's unlikely to be an issue, and can be mitigated against transients by using shielded wire.   The magnetometer itself may be susceptible to the field, so surveying with the heater on and off is worthwhile.   Since the heater is resistive it's less likely to be a problem than if it was a coil, but, as you say, it's pretty high current, so worth checking.   I think this is why a lot of them wind up in the tail.   That and roll servos in the wings. 

[N201MKTurbo]

20 minutes ago, EricJ said:

  That and roll servos in the wings. 

Another good reason to put it in the right wing. 

[ArtVandelay]

Another good reason to put it in the right wing. 

My roll servo is in the right wind, my GMU is in the tail, high up on its own shelf.