Chapter 22 – Magnetometer wiring

Today was another lighter build day, not by design.

At this moment I was plagued by lack of specialized tooling: specifically drill bits.  After another 20 minute search I punted and ran down to Harbor Freight and bought a couple more sets of long drill bits, longer than our “standard” long aircraft grade #10 and 1/4″ bits.

After I got the correct sized long 1/4″ bit, I drilled a hole in the lower front corner of the CS spar left side interior bulkhead.  I don’t like punching a ton of holes all over the place, but I figured a 1/4″ through the bulkhead wasn’t going to put lives at risk.

I than routed my cheap 1/4″ plastic conduit from the CS spar interior bulkhead out through the top hole on the front side and end of the CS spar.  This is one the holes I made when drilling out the bolt holes to mount the wings to the CS spar.  I didn’t use Nylaflow here, again just a cheaper plastic tubing since it will never see the light of day and it really only serves the purpose as a conduit to run the wires from the outboard CS spar into the interior CS spar so I could grab ahold of them and run them the rest of the way.

Here’s the end result at the end of the spar near the mounted magnetometers.

After I terminated one set of 3 wires with D-Sub sockets, I then applied some heat shrink and inserted the sockets into their respective 9-pin D-Sub connectors.

I then attached the D-Sub backshells that came with the GRT magnetometers and connected the D-Sub connectors to the magnetometers.  If you look closely you can see that I also labeled the D-Sub backshells with the magnetometer component IDs.

Outboard electrical connections complete . . .

My next issue was once again drill bit related.  The narrow diameter hole just inside the large center oval CS spar hole, that goes from interior CS spar down into the hell hole for running all my wing light, etc. wiring outboard was just a bit too narrow to add in 6 x 22 AWG wires. I mean this wiring in there was SNUG.

I pulled all the wing light wires to widen the hole a bit, but the bigger required diameter hole naturally means a longer drill bit.  With the slight aft to forward angle inside the CS spar, albeit mostly vertical, I just didn’t have the clearance with any of my drills –including the smallest 12V and 90º right angle drills– to get in there and drill out the hole wider.  I need some stubby drill bits, which I have on the list to buy for my machining endeavors, but haven’t pulled the trigger yet.

So, with it being late I decided to punt and work on this tomorrow… at which point I’ll finish running these magnetometer wires forward, along the right side of the fuselage, in the bundle with all the other wires.

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