magnetometer installed on inspection panel cover? ok?

[alanbreck]

Question for A&Ps out there ...

I was looking at a plane the other day which had been recently upgraded to a pair or Garmin Gi275s (for AI and DG).
Heading for these displays was driven by a remote-mounted GMU11 magnetometer.

Here's what surprised me ...
The magnetometer was mounted to the backside of an inspection panel cover (way out on the wing).
Is that a kosher/approved install?
The nature of the mount was such that the round panel cover was "reinforced" a bit via extra rivets (6, I think?) attaching to the mount/bracket on the inside.

Ever seen this done before? (i.e. mounting hardware to an inspection panel cover)

 

[mtnquail]

Per Garmin’s guidance on installing these magnetometers, this would be incorrect installed as described.

The magnetometer is supposed to be rigidly mounted, which implies that it would not be on an easily removable part. It would be difficult to reinforce an inspection panel to the degree required fo provide an equivalent level of stiffness compared to a reinforced skin section.

Also, if it is installed with steel screws, or the panel has steel nutplates or tinnermans it would affect the accuracy of the magnetometer.

 

[Gary Ward]

I don't know if it is good idea to mount it on a inspection plate? Does it work there?

In 2018 this expert made a bracket that he showed me for my magnetometer. He pointed out that he bent it with or against the grain so it less likely to crack. Also showed me the custom shielded harness that was made for my plane.

So this past weekend I replaced the strobe power supply and took these pictures while I had the wing tip off. I have flown this plane 1300+hrs since and it has been flawless, the magnetometer and the 650 GPS, G5s.

I have to say the bracket is pretty slick and makes for a nice installation that won't be disturbed during annual inspections. I don't recall if the mounting screws were discussed or what there made of.

 

[MooneyDriver78]

I wonder if the wing tip installations will result in the headings being twitchy in turbulence resulting in the AP over controlling the plane and making the ride uncomfortable.
I prefer it mounted on the centerline back in the tail.

 

[Gary Ward]

I wonder if the wing tip installations will result in the headings being twitchy in turbulence resulting in the AP over controlling the plane and making the ride uncomfortable.
I prefer it mounted on the centerline back in the tail.

I have a GFC500 and it is very smooth. Only problems have been the servos. I now have all -21 servos and have kept my fingers crossed. The last -21 servo was installed early Feb 23 and it has been good ever since. The AP could not perform any better.
It's easier to access in the wing tip.
This is the same guy Scott replacing my last servo. I am so lucky to have him doing my avionics work. See the grease oozzing out of the old servo?

 

[TCABM]

I wonder if the wing tip installations will result in the headings being twitchy in turbulence resulting in the AP over controlling the plane and making the ride uncomfortable.
I prefer it mounted on the centerline back in the tail.

We haven’t experienced that issue in our G5s, but did have to have our GMU11 relocated to the aft empennage due to EMI interference. The installer admittedly shortcut the EMI survey and did the relocation gratis.

 

[Stewartb]

My magnetometer in the Cub is attached to a fabricated plate that bridges the wing spars. I have an inspection plate located to access the magnetometer, and I’ve needed to to chase down a poor connection, but it turned out to be in the wing root. If the plane in question passes the vibration tests and the magnetometer is functioning? I’d go with it. Providing there’s no ferrous metal interference and low vibration? It should work fine.

 

[bnt83]

Got three of them mounted in wingtips brackets allow fine tuning the leveling laterally, longitudinally and yaw.

 

[Dan Thomas]

Those screws might be non-magnetic stainless, and I hope those are stainless nylock nuts. But I don't think there are stainless Cherrymax mandrels.

I thought magnetometer hardware was supposed to be brass. Even many grades of stainless are magnetic.

 

[Bell206]

Ever seen this done before? (i.e. mounting hardware to an inspection panel cover)

Don't know about the 275 install but I believe in the G5 GMU11 manual it mentions no install on an access panel. That said, it can be done in some cases especially if available real-estate is limited or there are interference issues. However, the panel mount should be treated as a separate alteration outside the STC.

I thought magnetometer hardware was supposed to be brass.

Have seen stainless hardware in Garmin kits. However, there is some vendor tolerance to steel fasteners with some magnetometer installs especially with composite structures. The required interference checks will usually show if the mount hardware will be an issue.

 

[bnt83]

View attachment 121785

Those screws might be non-magnetic stainless, and I hope those are stainless nylock nuts. But I don't think there are stainless Cherrymax mandrels.

I thought magnetometer hardware was supposed to be brass. Even many grades of stainless are magnetic.

The thumb screws on these connectors are MAGNETIC.

 

[3393RP]

I don't know if it is good idea to mount it on a inspection plate? Does it work there?

In 2018 this expert made a bracket that he showed me for my magnetometer. He pointed out to me that he bent the metal the right way with or against the grain so it won't crack. I don't remember. Also showed me the custom shielded harness that was made for my plane.

So this past weekend I replaced the strobe power supply and took these pictures while I had the wing tip off. I have flown this plane 1300+hrs since and it has been flawless, the magnetometer and the 650 GPS, G5s.

I have to say the bracket is pretty slick and makes for a nice installation that won't be disturbed during annual inspections. I don't recall if the mounting screws were discussed or what there made of.

That's a nice bit of fabrication work.

 

[Gary Ward]

That's a nice bit of fabrication work.

That is what I was thinking when I took a second look at it 5 years later.

 

[Pinecone]

He pointed out that he bent it with or against the grain so it less likely to crack.

That would be an interesting trick, since the part has bends that are 90 degree to each other.

 

[Bell206]

That would be an interesting trick, since the part has bends that are 90 degree to each other.

You can layout the bend lines so all are at a 45 degree angle to the metal grain. Common practice in a number cases. But it doesn't work for all applications especially on the primary structure side.

 

[Ed Haywood]

 

[NavAir]

Not an A&P, but...

The magnetometer (KMT112) on my DA40 is mounted on an inspection cover on the right wing. The cover is attached with three brass screws, instead of the stainless steel ones used on all of the other access panels. This is a factory-installed system (Bendix/King).

 

[Pinecone]

You can layout the bend lines so all are at a 45 degree angle to the metal grain. Common practice in a number cases. But it doesn't work for all applications especially on the primary structure side.

That would make sense.,

But the original comment was he bent it with or against the grain.
45 degrees isn't really either.