G3X LRU Layout

I'm about to install mounts/mounting points for a list of G3X boxes behind the panel of an RV-7:

GAD 27
GAD 29
GDL 51R
GEA 24
GMC 507
GTR 20 (pair)

Should any particular LRU be located in a particular place, or near another, or at the physical end of a wiring harness? All tips welcome. Photos too. No point in re-inventing the wheel.
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Dan, I would consider the CAN bus daisy chain to be a starting point. For example if you have the GMU 11 in the back, that's usually a pretty good starting point for the CAN bus. I would sketch your daisy chain to be sure you can follow from LRU to LRU in a logical way and end up at a convenient LRU for termination. The GSA 28s can be problematic depending on where they are. I try to keep the CAN bus daisy chain as short as possible. The rest of the harness generally follows what I planned for the CAN bus.

I installed dual GTR 20s recently as shown in the attached photo. I found it convenient to make the tray and install it in the rear near where the antennas where going to be--in this case on the belly aft (obviously not an RV). Having both units side by side helps with the CAN bus and harness as you can go from one to the other quite easily. Keeps the antenna coax leads relatively short as well. And frees up a lot of space behind the panel.

As for LRU placement in general, an important consideration for me is to have plenty of room to access the connectors and to leave room for your hands to get in there to get them on and off. There is a tendency to underestimate the space each LRU needs. I always try to have nutplates on the other side of the LRUs for ease of removal/installation.

51R

The 51R needs to be aligned with the axis of the aircraft...

rocketman1988 said:

The 51R needs to be aligned with the axis of the aircraft...

Click to expand...

A G3X Touch installation with a real ADAHRS (GSU 25) shouldn't need to worry about this, as you'd never want to use the less-accurate attitude data from the GDL 5x with your tablet / portable GPS / etc.

Looking forward to seeing this thread develop - I've got a couple of screens to install myself in coming weeks. Rightly or wrongly I've gone for the remote mounted COM and XPONDER and need to give consideration to where I'm going to put them too.

Can bus not an issue

I wouldnt worry about the can bus routing when laying out the boxes. Once the boxes are placed, then route the can bus from box to box in the most efficent manner.

One thing is to consider is how one would remove boxes once the top skin is on and the only access will be from the bottom, under the panel..

Can bus not an issue

I wouldnt worry about the can bus routing when laying out the boxes. Once the boxes are placed, then route the can bus from box to box in the most efficent manner.

One thing is to consider is how one would remove boxes once the top skin is on and the only access will be from the bottom, under the panel.

Lastly, the GAD27 and GAE 24 gets lots of wires run from the various stuff. Those boxes may be best placed where those sensor wires are in direct line; no need to run all the EGT and CHT wires across the panel just to get to a poorly placed box.

Depending on where you have your radio stack it can get pretty busy pretty quickly.
I’ve always put the GEA forward of the sub panel. Straight run for the big bundle of sensor wires out thru the firewall. Perhaps consider the access panels in the top skin if you do this. I’ve done it with and without the access panels. The access is helpful if you need to fiddle in there. I have the Voltage regulators forward of the sub panel too but adjustable through the access panel.

You didn’t mention a GSU25 but I assume there’s one of those too.
It’s tight but doable to get the GAD27/GAD29/GSU25 onto the rear face of the sub panel and all accessible for replacement through the GDU hole in the panel.
A tray between the panel and sub panel under the GDU is another way of getting some extra mounting room.

mburch said:

A G3X Touch installation with a real ADAHRS (GSU 25) shouldn't need to worry about this, as you'd never want to use the less-accurate attitude data from the GDL 5x with your tablet / portable GPS / etc.

Click to expand...

It’s nice to have a backup…and for the OCD, the arrow on the 51R should be pointing forward…

You may find after a while that you want to add one more wire for whatever reason. Make sure that you have enough slack ("service loops") to do this -- but be mindful of vibration as well.

For example, I want to run an additional wire or two to the back of the GTN650 in the center stack, but to get access to the connector, I would need to remove at least several of the mounting trays in the center stack.

And folks who know more than I will give you details on separating power and ground from signal wires, and how to avoid ground loops -- the electrical kind.

Pat Hatch said:

For example if you have the GMU 11 in the back, that's usually a pretty good starting point for the CAN bus.

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Makes sense.

I installed dual GTR 20s recently as shown in the attached photo. I found it convenient to make the tray and install it in the rear near where the antennas where going to be...

Click to expand...

I had not considered rear mounting for the radios, but again, keeping the coax in the back makes a lot of sense.

I always try to have nutplates on the other side of the LRUs for ease of removal/installation.

Click to expand...

And torx screws, easier to R&R while upside down, one-handed, and blind.

Richard Connell said:

Perhaps consider the access panels in the top skin if you do this.

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There's a good point. Anyone have regrets about installing them?

You didn’t mention a GSU25 but I assume there’s one of those too.

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Yes, sorry. Has everyone found it acceptable to mount directly to the subpanel? The manual makes a big deal of structural stiffness. It can go on the back of a GDU4xx, but given the screen can be removed for easy access, I'd rather the pneumatic tubing run to a fixed location and just have a wire loop to the screens.

Ed_Wischmeyer said:

... details on separating power and ground from signal wires, and how to avoid ground loops..

Click to expand...

Thanks, got that covered.

Good stuff, keep it coming.

DanH said:

Has everyone found it acceptable to mount directly to the subpanel?

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Probably a good poll question.

In my installation the subpanel works well.

Dan,

I think Garmin advises against using the back of the screen to mount the GSU25 due to vibration effects on the accuracy of the strap down ADAHRS.

I flew my 7 with the GSU 25 mounted to the sub panel without issues. I did put doubler in with it to help stiffen things up.

LRU location

I put almost everything on the subpanel. Nutplates throughout. Wanted access to all components with a G3x removed while sitting in a seat. Also wanted to not open any static lines when removing PFD so hard mounted the GSU as far up and left as possible where the junction of the longeron/subpanel/deck skin makes the structure stiff and flex resistant. I’ll probably start flying with 1 Adhars, but when SteinAir built the harness I had a connector for the 2nd wired in. Nutplates are already there so easy addition. I installed the Vans acess panel kit, but put them outboard on the curved part of the deck skin. B&C regulator and ElectroAir control unit mount on rails on the right side. Added a fuse block here for some non critical circuits as I was running out of space for breakers on the panel. These components and the rails can be removed/installed through the access panel. Signal wires come through the left side of the firewall near the GEA and power wires on the right side for the GAD using stainless pass throughs with firesleeve.

Don Broussard
RV9 Rebuild in Progress (getting close)
57 Pacer

Kyle Boatright said:

Probably a good poll question.

In my installation the subpanel works well.

Click to expand...

I think this would be a good poll question.
My RV7 no issues at all on the sub panel.

My RV10 I went through 5 GSU25 units and 3 different mounting positions before achieving satisfactory performance. No joke. Very trying process to resolve.

They are extremely sensitive to vibration - the stiffest place possible still vibrates.
I had them bolted to the spar carry through. No good
Then the sub panel. No good.
Stiffened sub panel. One ok. One not ( right next to each other too!)
Finally they ended up on the back of the GDUs which was the last place I wanted to put them for all the reasons mentioned above.
To be fair some of the units fell into the Garmin SBs about “acoustic noise energy” (ask the RV12 people) so there was probably a hardware issue there somewhere too.
But anyway it’s a black art.
It took around 40 test flights and countless hours moving things (associated wiring changes etc) to diagnose and resolve.

No regrets with the access panels. I later on added wires into the back of the radio stack backshells through the access panels. That would been trying without them.

Something to think about.

My RV4 is limited for panel space. The 460 screen and switches are the only thing on the panel. The remote com and transponder are mounted in a vertical stack UNDER the tray for fuses ,ignition etc. to make them accessible without removing the boot cowl, the stack is on a slanted orientation so they will slide out UNDER the panel without removing 50 screws from the boot cowl. This leaves lots of room for the next owner to put G5 and other IFR stuff in the panel.

The Sling TSi guys build a rack which holds the remote LRU's (radios, xpdr, audio panel) vertically behind the LH GDU 460. You can access the rack through the hole in the panel after the 460 is removed, or you could make the rack so that it drops down by removing 4 screws. I never took any good photos of their install, but I did reverse-engineer it pretty well for a different project.

As to the GSU 25, they add a doubler to the inner (sub) panel which works well enough with their Rotax vibration anyway.



On my own RV-6, I installed the remote xpdr right behind the baggage bulkhead near the AP pitch servo, with the antenna on the belly just aft of that.

Brantel said:

Dan,

I think Garmin advises against using the back of the screen to mount the GSU25 due to vibration effects on the accuracy of the strap down ADAHRS.

I flew my 7 with the GSU 25 mounted to the sub panel without issues. I did put doubler in with it to help stiffen things up.

Click to expand...

On the contrary: I mounted my GSU 25 aft of the baggage bulkhead (using Vans AHRS mount), and have been struggling with likely vibration-related problems since Hour 0. Garmin suggested I try moving it to the rear of the GDU display on the panel. I wish I did this from the start, because if I really have to relocate this unit, I'll have to plumb AOA up front and a bunch of other wiring

Richard Connell said:

My RV10 I went through 5 GSU25 units and 3 different mounting positions before achieving satisfactory performance. No joke. Very trying process to resolve.

They are extremely sensitive to vibration - the stiffest place possible still vibrates.
I had them bolted to the spar carry through. No good
Then the sub panel. No good.
Stiffened sub panel. One ok. One not ( right next to each other too!)
Finally they ended up on the back of the GDUs which was the last place I wanted to put them for all the reasons mentioned above.

Click to expand...

Glad I'm not the only one going through this! I'm still in denial that I'm probably going to have to rewire this thing and pass more plumbing through the spar.

Draker said:

On the contrary: I mounted my GSU 25 aft of the baggage bulkhead (using Vans AHRS mount), and have been struggling with likely vibration-related problems since Hour 0. Garmin suggested I try moving it to the rear of the GDU display on the panel.

Click to expand...

Maybe the screen (and perhaps the whole panel) serves as an inertial mass?

Just for fun (and because it's an easy experiment), bolt a chunk of something dense to the opposite side of the baggage bulkhead. Mass changes frequency. Anyone know if a GSU 25 would care about proximity to a coupon of ordinary 1/4" mild steel plate?

BTW, in this thread I've read Garmin recommends both for and against mounting on the back of the display. Interesting.

My only after the fact thoughts are what will need access later or most often.
YMMV but I find myself upside down under the panel to remove the GTX23E while at Oshkosh to have Gamin do the update.
Also good access to the GDU so the pitot, static Alt check by someone else.
I got lucky in both cases and mine are accessible.

Draker said:

On the contrary: I mounted my GSU 25 aft of the baggage bulkhead (using Vans AHRS mount), and have been struggling with likely vibration-related problems since Hour 0. Garmin suggested I try moving it to the rear of the GDU display on the panel. I wish I did this from the start, because if I really have to relocate this unit, I'll have to plumb AOA up front and a bunch of other wiring

Click to expand...

DanH said:

BTW, in this thread I've read Garmin recommends both for and against mounting on the back of the display. Interesting.

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Maybe as a last resort or something to try but here is a clip straight out of the current installation manual.

While it appears Garmin intended on the screen being a good mounting option in the design phase, the real world threw them a curveball and as a result, they have generally not recommended the back of the screen as a first choice for mounting going all the way back to the initial release.

DanH said:

Maybe the screen (and perhaps the whole panel) serves as an inertial mass?

Just for fun (and because it's an easy experiment), bolt a chunk of something dense to the opposite side of the baggage bulkhead. Mass changes frequency. Anyone know if a GSU 25 would care about proximity to a coupon of ordinary 1/4" mild steel plate?

BTW, in this thread I've read Garmin recommends both for and against mounting on the back of the display. Interesting.

Click to expand...

Many of us here have mounted the GSU 25 to the display without incident for quite some time in some cases. I've always been curious why Garmin provisioned the mount if they didn't intend for it to be used. I think a lot depends on the mass of the panel as a whole and certainly if the panel is of the flimsy variety, you're likely going to have problems. It is a pain to remove the displays, but we've gotten used to it: just loosening 4 each AN3 bolts releases the GSU 25 and you can leave it hanging there while you remove the display. But you want to have a generous service loop (that includes the tubing) to facilitate this.

Struggled with vib also. My aft-of-the-baggage-bulkhead mount was very stiff, but I found (after a LOT of experimentation) that the mount had a torsional vibration mode. The "%deviation" parameter in the data logs is where you can quantify the magnitude of the issue.
I finally went from "engineered" mount to "beef" and used a 3/16" 6061-T6 plate. Resolved!
%deviation went from +300% to less than 20% with an occasional spike when I "change direction quickly"....

I will also go for the GDU mounting spot on the next 8. May need to add a diagonal brace to the bottom of the panel, but "should" be plenty stiff otherwise. I still like an analog ASI, so the plumbing will be there anyway.

fl-mike said:

Struggled with vib also. My aft-of-the-baggage-bulkhead mount was very stiff, but I found (after a LOT of experimentation) that the mount had a torsional vibration mode. The "%deviation" parameter in the data logs is where you can quantify the magnitude of the issue.
I finally went from "engineered" mount to "beef" and used a 3/16" 6061-T6 plate. Resolved!
%deviation went from +300% to less than 20% with an occasional spike when I "change direction quickly"....

Click to expand...

Interesting. I'll have to try this. One thing I did try without success was mounting the AHRS onto rubber bushings, the thought was it would dampen the vibrations. Didn't help at all. I didn't think to add a thick piece of metal to my mount. Would you mind sending me a PM with pictures of your beefy mount? Worth a try.

As a point of comparison, I regularly have flights where my AHRS Dev (%) as logged by the G3X is around 700%. I've never had a flight where it topped out at less than 415%. My average through all phases of flight (including on the ground) is 75%. I've run a number of analyses on the numbers and my AHRS deviation mosts positively correlates to %Pwr and RPM, which is why I'm blaming vibration.

Brantel said:

While it appears Garmin intended on the screen being a good mounting option in the design phase, the real world threw them a curveball...

Click to expand...

I saw that note in my reading. Based on the wording and what I've learned here (thanks guys!), my take is some panels are too shakey.

Keep it coming...

DanH said:

Has everyone found it acceptable to mount directly to the subpanel? The manual makes a big deal of structural stiffness. It can go on the back of a GDU4xx, but given the screen can be removed for easy access, I'd rather the pneumatic tubing run to a fixed location and just have a wire loop to the screens.

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RV-10. I originally mounted the GSU25 on the subpanel. Had AHRS issues on and off for months. Worked with Garmin to resolve. Got really good at recalibrating the compass . Eventually got help from an RV10 owner from Australia who helped identify the problem as vibration. Moved the GSU25 to the back of the center GDU460. Been rock solid for almost a year.

larrynew said:

RV-10. I originally mounted the GSU25 on the subpanel. Had AHRS issues on and off for months. Worked with Garmin to resolve. Got really good at recalibrating the compass . Eventually got help from an RV10 owner from Australia who helped identify the problem as vibration. Moved the GSU25 to the back of the center GDU460. Been rock solid for almost a year.

Click to expand...

Hi Larry
That was me

Ill try not to war and peace on this, but I think Garmin has been less than forthcoming with GSU issues and could save people A LOT of grief with some updated guidance.

Now that I see that more people coming out of the woodwork with same problem I should speak up.

Garmin repeatedly told me that it was a CanBus issue from the get go. I was skeptical as I have wired many and I think my work is of good quality. Each node was tested during construction in every install I've done. There were nil network errors, and swapping devices around on the bus made no difference.

I got 4 different support people cut and paste me the "troubleshooting guide" which was less than insightful.
Reluctantly, I rewired my entire RV10 CanBus - node by node - recalibrating each time - which made no difference. At this point I started getting cranky.
After expressing my displeasure with the support I effectively got left to my own devices. Maybe the timezone is an issue. I don't know. Im on good terms with the Australian people.

The penny dropped after I investgated the "acoustic noise vibration" SB some more.
Anecdotally, Garmin changed suppliers for some of the MEMS bits in the GSUs at some stage and they were "different". Maybe more sensitive in some modes. Carbon Cubs with them mounted on the wing spar were getting "rain" induced "acoustic vibration" as were RV12s with them on the floor down the back. There were various workarounds. The SB is worth a read. Eventually new GSUs was the solution I believe.

With this in mind, I went back and regressed the vibration data against RPM and power, and sure enough, as Ryan found, it was clearly correlated to various power/RPM combos.
It was from the very first flight! Then I set about moving them around, stiffening the subpanel etc until the only place it resolved was on the back of the GDU.

Larrys files exhibited similar RPM/Power v Vibration correlation.

DanH said:

Maybe the screen (and perhaps the whole panel) serves as an inertial mass?

Click to expand...

Yes, this definitely crossed my mind. I think the original "not on the back of the GDU" guidance could have been a result of aircraft that had shock mounted panels to isolate mechanical instruments.

In my mind, an aluminum airplane with a lycoming on the front is going to have plenty of vibration (acoustic or otherwise) no matter where you put the thing.

In short, having to move the thing around the airframe until it works is less than ideal. It seems clear now that in many aircraft, the only place current GSU25s dont suffer from vibration induced degraded performance, is the very same (and only) place Garmin tells you NOT to mount it.
This is worth addressing.

Richard Connell said:

It seems clear now that in many aircraft, the only place current GSU25s dont suffer from vibration induced degraded performance, is the very same (and only) place Garmin tells you NOT to mount it.

Click to expand...

I'm glad I potentially saved a lot of time by mounting it there in the first place.

The guidance against mounting it on the GDU has never made sense, in light of the fact that the GDU enclosure is machined with a nice flat mounting location with holes already tapped to receive the bolts Garmin ships with the GSU, and, if you use the facility they've clearly invested design effort to provide, you don't have to solve as many problems around space and cabling.

It also helps that if you're doing a retrofit panel conversion, the pitot and static lines you need are already routed to the back of the GDU, because that's where your six-pack used to be! Everything's easier.

For me, at least, it's worked there from day 1, and I've never regretted ignoring Garmin's installation advice regarding this one item.

There are a lot more G3X Touch systems in the field than there were when they wrote that advice. Perhaps they should update it. Or, at the very least, explain it.

- mark

Not to state the obvious, but when dealing with vibration issues, please tell me your prop has been balanced.

Webb said:

Not to state the obvious, but when dealing with vibration issues, please tell me your prop has been balanced.

Click to expand...

Yes. One of the very first things done.

This is a great thread! I have one more data point - an RV 14A with G3X/460 and GSU25 mounted on the back of the GDU460. I have had reversion failures (GSU25 fails, reverts to G5 until GDU25 reboots) on and off for several years. When it occurs, 1 per flight, sometimes twice - then no recurrence for a dozen flights. Troubleshooting with Garmin inevitably leads to recommendation to move the GSU25 to the subpanel. Because of the plumbing required, I’ve managed to put that change off. The problem will disappear for 6 months, and then rear it’s head again. I’ve always suspected there are software changes going on behind the scenes - especially when new data fields appear in the logs related to ADAHRS stability - software changes and problem disappears, then a few months later and it’s back.

I have another 14 in the works, and I was leaning to the subpanel - now … not so sure.

KeithB said:

This is a great thread! I have one more data point - an RV 14A with G3X/460 and GSU25 mounted on the back of the GDU460. I have had reversion failures (GSU25 fails, reverts to G5 until GDU25 reboots) on and off for several years. When it occurs, 1 per flight, sometimes twice - then no recurrence for a dozen flights. Troubleshooting with Garmin inevitably leads to recommendation to move the GSU25 to the subpanel. Because of the plumbing required, I’ve managed to put that change off. The problem will disappear for 6 months, and then rear it’s head again. I’ve always suspected there are software changes going on behind the scenes - especially when new data fields appear in the logs related to ADAHRS stability - software changes and problem disappears, then a few months later and it’s back.

I have another 14 in the works, and I was leaning to the subpanel - now … not so sure.

Click to expand...

Try temporarily clamping a diagonal piece of heavy angle from the bottom lip of the panel (under the GSU25) to a longeron or something. Or a "V" of braces. If you can move the panel by pulling on the bottom, you will probably have high "AHRS Dev (%)" values and get those issues.

fl-mike said:

Try temporarily clamping a diagonal piece of heavy angle from the bottom lip of the panel (under the GSU25) to a longeron or something. Or a "V" of braces. If you can move the panel by pulling on the bottom, you will probably have high "AHRS Dev (%)" values and get those issues.

Click to expand...

Id definitely try this. I agree in side by side RVs without any structure like this (remote coms/xpdrs etc) the unsupported panel span likely affects this negatively. Ive heard of a few like this in my research too.

My panel (RV10) has a centre console plus a radio stack frame and sub panel cutout reinforcement that would make a Boeing blush. Its a super stiff structure, with a fair bit of mass once you consider all the screens and radios bolted into it.
Subjectively, you can feel the difference in vibration with your hands across different parts of the cockpit. Little vibration in the panel, a little more on the glare shield for example.

Webb said:

Not to state the obvious, but when dealing with vibration issues, please tell me your prop has been balanced.

Click to expand...

Yes. Words added.

Richard Connell said:

Hi Larry
That was me
…
Larrys files exhibited similar RPM/Power v Vibration correlation.

Click to expand...

Hi Richard,
Yes, I definitely remember and I’m most grateful for the help. Zero problems since I moved the GSU25 from the subpanel to the back of the GDU460.

I was reluctant to put your name out there as an unpaid Garmin technical support volunteer .

Fuses

I put my fuses behind the MFD so i can access them by removing the 4 screws holding the MFD to the panel. YMMV

Rails and access panels

I used rails to mount my VPX and Transponder. I also have access panels on both sides of the foreskin for easy access. These are trial placement pictures but I basically kept it the same. I did mount my ADHRS in the tail area as suggested at the time (2016) and it has worked fine for me. I have not had to use the access panels but really glad they are there.

My goals for the avionics layout were to make LRU removal as easy as possible, and to provide some flexibility to change avionics in the future. My solution for that was to create a tray that's suspended from the tip-up panel support ribs; the center rib has an additional drop-down support. There were some gotchas but works reasonably well, and before someone calls me on it, yes, it adds a pound or so.

Two of the gotchas...regardless of the mounting approach, make sure the connector shell, coax connectors and cable loop are accounted for when you place your LRUs. My transponder (GTX-45R) mounting location left barely enough room for those connections. And as others have said, choose and locate your fasteners carefully. Some of my attach locations are close to being blind and I used hex-head #8 screws (NAS1801, IIRC) so I didn't have to get a screwdriver into some tight spots.

Link to the build site page that covers what I did - https://mightyrv.com/?p=3790.

HTH

Dave

Nice work Dave and great idea.

Thermos said:

My goals for the avionics layout were to make LRU removal as easy as possible ad also to provide some flexibility to change avionics in the future. My solution for that was to create a tray that's suspended from the tip-up panel support ribs; the center rib has an additional drop-down support. There were some gotchas but works reasonably well, and before someone calls me on it, yes, it adds a pound or so.

Some gotchas...regardless of the mounting approach, make sure the connector shell, coax connectors and cable loop are accounted for when you place your LRUs. My transponder (GTX-45R) mounting location left barely enough room for those connections. And as others have said, choose and locate your fasteners carefully. Some of my attach locations are close to being blind and I used hex-head #8 screws (NAS1801, IIRC) so I didn't have to get a screwdriver into some tight spots.

Link to the build site page that covers what I did - https://mightyrv.com/?p=3790.

HTH

Dave

Click to expand...

GSU Mounting Requirements

newt said:

I'm glad I potentially saved a lot of time by mounting it there in the first place.

The guidance against mounting it on the GDU has never made sense, in light of the fact that the GDU enclosure is machined with a nice flat mounting location with holes already tapped to receive the bolts Garmin ships with the GSU, and, if you use the facility they've clearly invested design effort to provide, you don't have to solve as many problems around space and cabling.

It also helps that if you're doing a retrofit panel conversion, the pitot and static lines you need are already routed to the back of the GDU, because that's where your six-pack used to be! Everything's easier.

For me, at least, it's worked there from day 1, and I've never regretted ignoring Garmin's installation advice regarding this one item.

There are a lot more G3X Touch systems in the field than there were when they wrote that advice. Perhaps they should update it. Or, at the very least, explain it.

- mark

Click to expand...

Hi Mark,

The responses in this thread illustrate the heart of the issue fairly well, there have been mixed results with mounting the GSU 25 to the rear of the GDU 46X Display. A significant variable in the success of a GDU mounted GSU 25 is the strength of the instrument panel, with less substantial panels providing too much flex to serve as a sufficient ADAHRS mounting location.

While we generally do not advise mounting the GSU 25 to the back of the display it is not disallowed and does work well in some installations. In my experience it is a rare occasion that a GDU mount works better than a subpanel mount, but I understand the frustration involved in reaching that conclusion, which typically requires coordination with our support group to reach.

The instructions provided in the installation materials provide a good general path for success in mounting these units, that work well for most aircraft. Two important pieces of guidance from that section, relating to choosing a good location, are:

• The GSU 25 must be mounted rigidly to the aircraft primary structure through strong structural members capable of supporting substantial loads
  
• Avoid placing the GSU 25 near sources of vibration or audible noise.

Of course there is an inherently high level of vibration in our aircraft, but different mounting locations transfer more or less of that vibration, to the housing of the ADAHRS unit. We have seen a lot of success with subpanel mounted ADAHRS unit, but of course there are exceptions, and sometimes a bit of trial and error is required.

It is important to meet compliance with the other guidance provided in that section as well.

Thanks,

Justin

Dan,
I work more in the certified world than experimental, but as stated often above I expect the panel thickness is just too thin on many experimentals.

Garmin recommends a .090” panel for many of the installs, and every full panel we build is that. Partial panels and sub panels can be less naturally.

I don’t believe our shop has every installed a “remote” GSU25 in a certified airframe - we simply mount it on the G3X. You’ll know of course instantly when doing the checks and calibrations, as the vibration check is one of the first to do, along with interference and swinging the gmu. I’ve never had a GSU fail vibration on a G3X. In contrast, I’ve had a lot of vibration failures on G5’s and GI-275’s in weak panels.

Airframes we have trouble with are often shock mounted panels. Remove the rubbers and hard mount the panel and it works fine.

While you got varying opinions on CAN bus use, I agree with those that preferred to lay out your LRU’s so you can start and stop on internally terminating units - it just seems to be a nicer/cleaner/smarter way to do it.
And with an autopilot installed, for example, don’t start at the panel, run to the tail, then back forward to run out the wing. Let the panel be midstream if it helps in your install, to keep the wiring and wire runs at a minimum.

Good luck.
Pb

If anyone's still interested in the AHRS vibration I reported, I've started a new thread with an update on my attempt to correct it: https://vansairforce.net/community/showthread.php?p=1686141