My avionics arrived – lots of big heavy boxes:
I extracted the radio trays and tried test fitting them to the panel. Immediately it was apparent that things were not going to be easy… the flange on the center subpanel rib (F-7108A) was totally in the way of the radio trays.
Here's a closeup of the problem, in which you can also see that the little ear by which the panel frame attaches the aft end of the rib is also in the way of mounting the avionics up high. I wish I'd had the Affordable Panels guy move my radio stack a half-inch to the right instead of lining up the left edge with the subpanel rib, because then I wouldn't have any fit problems. Anyway, I'll work with what I've got.
I thought about simply putting the avionics at the bottom of the radio stack cutout and filling the top few inches with switches or annunciators or something, but one look at the subpanel killed that idea. Since the subpanel is shorter than the panel itself, moving the radios down too far would mean that the entire bottom of the subpanel would be cut in two. That seems like it would weaken the structure unnecessarily, so I resolved to find a way to make the avionics fit at the top of the stack.
Here is the result… I cut off the aft flange and about a foot of the bottom flange, then riveted replacements made of 0.032" angle to the opposite side of the rib, out of the way of the radios. I also ground the little mounting ear off of the panel, and moved the screw hole to a new nutplate that's a half-inch to the left of the previous location.
Another view of the modification. You can see that the new bottom flange shares one rivet apiece with both the new aft flange and the remaining part of the old bottom flange, which makes it all pretty stiff. The whole thing is right next to a big piece of 1/8" angle (F-7108B) anyway, so I doubt it really matters whether or not this flange is even here, but it makes me feel better to have it. By the way, this is apparently a pretty common mod for two-place slider RV's, since the panel is so non-conducive to installing anything other than very basic avionics. Apparently they have improved this a lot in the RV-10, which is nice but doesn't help me any.
Now, the radio trays can go all the way to the top of the stack cutout.
I marked and then cut out a big chunk of the subpanel, since the nav/coms and transponder are too long to fit between the panel and subpanel. The subpanel is suddenly pretty floppy, but I will put enough reinforcement in this area that it should be no problem. One thing at a time.
With the subpanel cutout made, I was able to maneuver all the radio trays into more or less their correct positions. In this photo they're just clamped in place and not attached to anything, but the fit is pretty good. There will eventually be some aluminum angles to attach the trays to both panel and subpanel.
A view from above… it's obvious that in order to attach the top skin, I will have to either make the radio trays easily removable or use blind rivets. We'll see how it goes.
I unsheathed the precious radios from their protective packing in order to how the faceplates line up in relation to the trays. Also, this picture makes me feel kind of dizzy.
And finally, closeups of the serial number stickers for my records:
