Avionics

From Matronics


Jim Ellis


Avionics Mounting Rails


Most builders use aluminum angle to mount a stack of radio racks to the back of the instrument panel. But there is a better way. Radiorax sells extruded aluminum shapes and fasteners designed for just this purpose.

The advantage is the ability to adjust the individual location of each component rack so that the face plates line up exactly where they belong. Plus the mounting itself is very strong and may not require additional strapping to support the back of the stack.

The disadvantage, at least for most homebuilders, is that the Radiorax hardware is very expensive...even in airplane terms.

You can, with a little work and not much money, fabricate your own rack support rails that work like the Radiorax mounts.

 Support rail layout on panel
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Support rail layout on panel
Eagle America, 1-800-872-2511, sells "heavy duty aluminum mini T-track" that makes for a great radio stack mounting rail. The gold anodized (now red anodized) aluminum extrusion is 3/4" wide x 3/8" deep and comes in lengths ranging from 18" to 48". For most installations one 36" long track is sufficient (item # 416-0361). The cost is $14.99 plus shipping. Measure the height of your stacked racks and cut two pieces of T-track equal to the measured height.


Now here's the hard part (and the work that was mentioned earlier). You will need to make your own square nuts that will slide in the track. You will need two to four nuts for each component in your stack. Short components like audio panels and transponders will require two nuts each while tall components like moving maps will require four. Each nut has a finished dimension of 7/16" x 7/16" x 3/16" thick and is drilled and tapped for a 6-32 screw. One way to make these is to cut a 7/16" wide strip of 3/16" thick aluminum about 10 to 12 inches long. Drill #36 holes about one half inch apart down the center of the strip. Thread each hole with a 6-32 tap and cut the strip half-way between each threaded hole. And there you are - twenty or so aluminum square nuts. Actually they don't have to be exactly square. As long as they are 7/16" wide, they can be slightly longer or shorter and still slide in the track.


 Assembled avionics stack with support rails
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Assembled avionics stack with support rails
To attach the racks to the rails you will need (depending on your installation) twenty or so 6-32x3/8" flat head machine screws. Phillips head screws work okay; however, if you can find socket head flat head screws, they are a little easier to install and adjust. To assemble slide the square nuts into the slots in the rails and align with the mounting holes in the sides of the racks. Insert the machine screws loosely into the nuts. You can now slide the entire rack up or down as needed. After final positioning, tighten the screws to lock the rack in place.


 Closeup of rack and panel support screws
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Closeup of rack and panel support screws
After the stack is assembled attach the rails to the back side of the panel. Drill and countersink the panel and drill through the T-track mounting rails for 8-32x1" flat head machine screws. Three or four per side should be sufficient.


 Rear view of avionics stack
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Rear view of avionics stack


 Finished front cutout with four recessed screws per side
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Finished front cutout with four recessed screws per side


Finished Panel installed in an RV9-A, tipup
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Finished Panel installed in an RV9-A, tipup
The finished result: An easily adjustable radio stack that is very strong and doesn't cost much.