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Attaching radio/GPS rack to panel

N546RV

Well Known Member
I'm currently in the process of cutting the panel for my -8. This question specifically pertains to mounting the Garmin GPS-175 in my panel - the only rack-mounted item I have to deal with. The -175 manual has diagrams for the panel cutout, but doesn't seem to have much in the way of guidance for actually securing the rack to the panel.

In fact, all I see is "Install the rack in the instrument panel with six #6-32 flat head screws and six self-locking nuts," referring to the screw holes in the sides of the rack. I assume it's my responsibility to create some sort of structure adjacent to the rack for this purpose.

Anyone got any photos/info on how they skinned this particular cat? I was originally thinking of a couple pieces of sheet, extending along the sides of the rack, and with a bent flang that would rivet to the panel - but I've got components on either side of the -175, and thus not a lot of material there to mount something like this, so I think I'll have to get a bit more creative.
 

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https://www.kitplanes.com/all-about-avionics-7/

Al angle riveted to the panel. Holes drilled at appropriate spacing.

That's one way to do it... the other way is a slight modification on this theme. The use of discrete nuts on those screws eventually will drive you insane should you ever decide to move or replace a radio. For that reason I strongly suggest using "clip nuts". They are self-retaining in that you can pull the screw out and the nut stays in place. They are self-locking in that the nut used in them is a high-temp thread deformation-style lock nut just like we use in the engine compartment. Plus they "float" slightly to take up some of the small "builder error" that sometimes happens when we are trying to get a whole bunch of holes to line up while working in awkward spaces.

No, they're not cheap. The first time you have to get behind the panel and get a wrench on one of those nyloc nuts shown in the photo you'll gladly spend a hundred bucks to avoid ever having to do it again. The good news is the clip nuts for an entire multi-radio stack won't cost ya a hundred bucks!

One example of a source for these clip nuts:
https://www.aircraftspruce.com/catalog/hapages/04-00151.php?clickkey=5665
 
With only one rack mounted radio this method may be overkill but it is definitely rigid.
 

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Rivet angle to the back of the panel.

I use 3/4”x3/4” 0.063” angle, but cut the side that gets riveted to the back of the panel down to 1/2”. This way you gain a little space on the panel (important for the RV-8 panel). I use standard hardware (screws and nuts) to secure the trays to the angles.

In the photo you can see the PS Engineering audio panel and the GTN-650 tray both have an single support angle connecting to the back of the tray. If you have a “radio stack” that creates more of a box this is not needed. For a single radios that you plan I recommend adding this support.

The hardest part of all this is drilling the holes in the angle for the trays. Look at the install manuals - many trays have either the top of bottom pane lip extending out a little. This lip is to be flush with the front the panel. Mark and then drill the holes after you get it all clamped in.

Note also this is a boatload easier if you design the panel to come out as a unit like I do.

Carl
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Yeah, angle pieces were my original thought, but I've now realized that my decision to flank the GPS-175 with the SV knob panel and intercom doesn't leave any space for this. If I'd thought about this before I started cutting, I could have just spaced those components off a bit to make room, but now it's too late for that.

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I do have the beginnings of an idea now, though. While I may not have room for unmodified angle, I can possibly modify some angle (or bend my own sheet) such that it ties into the inboard nutplates for the knob panel and intercom. I still think I'll want some more support for the rack, though - while the nutplate tie-ins should be good for holding the rack flush to the panel, I'm less sure about them being solely responsible for holding up the rack.

The slight good news is that the -175 only weighs 1.9#, and the CG is only about 2" off the panel, so the loads aren't nearly as bad as for, say, a GTN-650.

I guess the worst case is that I buy a replacement panel and redo stuff. Wouldn't be my favorite thing ever, but such is life.
 
Welp, moot point...turns out when I laid out the intercom cutout, I mixed up the margins and didn't notice until tonight. No material left for the nutplates. So time for a Van's parts order.

Just means I get the chance to do the rack right.
 
Whatever you do, do not use nylocs to secure the trays to the angle.
With the panel out of the airplane it seems like a great idea.
If you ever have to change a try your opinion will change rapidly, it can be almost impossible to get a wrench onto the nuts.
The best solution are Monadnock clip nuts https://www.aircraftspruce.com/catalog/hapages/04-00153.php, an alternative is to rivet in plate nuts.
The time/money spent replacing the nylocs will pay dividends in the future.
Pete
 
GPS 175 Installation

The Garmin installation manual in section 4.4.1 (pages 36-39) describes the installation of the unit in a panel without a radio rack.
 
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