I've been spending gobs of time trying to figure out how in the world I will route all of the bulky coax up to the panel. For a bare bones plane, the existing holes would be enough for all of the wiring, but the original plans are decades old and avionics have changed! The issue is the spar carry through area. The stock setup has four 5/8" holes drilled through it for wiring. The center two holes are going to pretty much be filled up with data/power wire from the wings and rear of the plane. That leaves the two outboard holes for the antenna coax and the pitot tubing (the pitot tubing will split at a T after it enters the fuselage from the wing - one tube going back to the ADAHRS box behind the baggage bulkhead and the other tube going forward to the subpanel for the Garmin G5 I'll be using as a backup system). I think each hole can fit 2 coax cables. I need room for the coax coming from comm 1 & 2 (I only need one comm for VFR, but I'd like a second comm once I upgrade to IFR, and it would be far easier to just run the wire and install a second antenna now), ADSB, transponder, and IFR GPS for eventual IFR navigator. The GPS antenna that the AFS system uses is actually built differently, so it doesn't require a coax run, just data wires. So that means I need holes in the spar area for 5 runs of coax plus pitot tubing. At most I think I could manage 4 of the 6 with existing holes.
Van's realized this was becoming an issue over the years as systems got more complex, so they have a tech document that shows additional locations for drilling holes through the spar carry through. You can drill a shocking number of holes. Had I known I'd need more space, I would have drilled a few more holes way back when the parts were setting on the bench. Now it's a lot more difficult.
I printed out the templates Van's has that shows the allowed hole locations for the different bays. You can drill from a 5/8" hole up to a 1" hole. The allowable location of the hole just changes based on the size (the template basically shows a box for each size hole - the center of the hole has to land within the box). Access was easier said than done, but I did the gymnastics to get everything centered.
The horizontal center of the spar carry through is the least stressed, so it's best to drill the holes as close to that center line as possible. I moved the holes up from that line about a half inch so I could use the unibit without fear of hitting the fuel lines. The last thing I wanted to do was nick a line and have to redo it.
The aft side is pretty much the same story, but the hole is moved outboard a little because of the seat rib locations, creating a little jog from the aft to forward holes. I had much better access here, so the holes were far easier to do. I think the addition of those two holes should give me plenty of room for all of the wiring now.
I'm at the point where finishing wiring means I need to also start installing the actual devices. I grabbed the flap motor and reattached it to the housing and flap control arm. The housing structure doesn't really fit well without having the seat cross brace in place, but it's okay for the time being. I've been putting off riveting the top skin for a long time, but that day is coming. I can't put the cross brace in until the skin is riveted at the front sides. I think I just have to accept the fact that I'll need to crawl back into the tailcone to finish wiring no matter what, so I may as well put the top skin on so I can move forward with other things. I won't be able to rivet the skin completely until I have help, but I can rivet the front part that keeps me from installing the cross brace. Installing that cross brace has a trickle down effect. After that's in, I can finish the flap housing and the canopy latch system can be fine tuned and finalized.
Anyway, until then it's a piecemeal approach to tasks. I need to figure out a mounting system for the flap position sensor, but to do that I need to know what the throw of the flap arm is. This only runs on 12v, so I'll have to grab the car battery to run the motor in and out and determine the up and down limits. I didn't feel like pulling a battery out of the car today though.
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One of the other big chunks of wiring yet to do is for the heated seats. I need to locate where the switches will go, where to fit the relays (one for each seat), and how to route power to the seat cushions themselves. I saw that someone with similar seats actually put the relays in the spar gap, which I think is a great idea to save space. I'll make a bracket for each relay that will attach using one of the existing bolts in the spar carry through and hang the relay down in the spar gap below the seat pan. This means that the most convenient place for the switches is in the center of the seat pan, right over the spar gap. I hate that I'm having to drill in painted metal, so here's hoping nothing chips too bad. I laid out the location of the switch holes in the right seat pan (the right pan extends past center, whereas the left pan does not).
Thankfully the hole cut pretty cleanly and the paint will be fine. I still need to file a little square anti-rotation notch in each hole to keep the switches clocked in the right position. Another day.
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