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Friday, September 08, 2017

Ch 22 - Electrical/Avionics - Part 8

Panel #2 changes

Changes are inevitable and somewhat expected, the only question is how many times one has to remake something before it's ready for prime time.

Panel #1 had CAD mistakes of my own doing, and needed to be done over. Panel #2 tried to address those issues, plus a few other later concepts I wanted to implement.

An idea I needed to revisit was one I had early on about keeping harnesses separated until the junction box for ease of tracing. This planning decision caused a lot of real estate being wasted at the junction plate/box, the biggest offender being the GNS480 with four lightly used harnesses.

To save space I decided to combine all the wires I needed out of the GNS480 into a single 37 pin Dsub connector, update my wiring diagram, and just grow up. 

37 Dsub connector almost fully used now

4 into 1 harnesses

Top two Dsub are now gone

Latest wiring diagram

One other thing I didn’t want to give up was the current single axis autopilot. With the servo, the wiring, and the head unit already installed and working properly, it would be easy to just leave that in… if I could only find a new spot for it.

I thought I'd move the autopilot to where the airspeed indicator used to be

I went with the design above, and set out to machine this even more complicated part. It took me three days of challenging machining, and six setups using up to ten dowel pins at a time to try to maintain alignment and rigidity. The result wasn’t perfect by machining standards, but more than acceptable for the intended purpose, and 100 times better than doing it by hand.

Recycling the current autopilot would be great, at least until I can install the new servos.

The autopilot fit on the new panel was great.

One thing worth remembering is that the autopilot is actually square, not round, so it takes up more space behind the front face of the panel. 

Meanwhile, I acted on another good idea, riveting nut-plates behind the panel to be used when mounting the two EFIS.

These small nut-plates will be riveted onto the back of the panel

Cleco clamps hold them temporarily while I determine their exact location

I also use the clamps while drilling the first hole

To drill the second hole precisely, I insert a rivet in the first hole, then drill away.

This tool allows custom precision countersinks to be cut consistently

The rivets are squeezed and the panel is completed

Panel front side

I used the finished plate as a template to drill the holes into the junction box/plate.

This is way faster than setting it up on a CNC mill for drilling

Because of the increased thickness of the instrument panel, I had to counterbore its back side in order to allow the tiny PTT switch to protrude enough to secure it with a nut.

Counterbored the plate about half way down

PTT switch in the countersunk hole

PTT switch protruding just enough to the front of the panel

Here’s ow it turned out…

Panel, junction plate, and 5" (13 cm) standoffs

A view from the "nose cone"

Seems to fit quite well on the plywood panel

Added the goodies for a glamour shot

Of course, I still have to cut into the actual airplane, rip out everything no longer needed, then make sure my new panel fits.

On the software integration front, I am happy to say I have worked out most problems between the GNS480 and the GRT Mini-AP by discussing matters with GRT engineers, and I think I now have a system that should work well in flight.

I’ll attach here a video I made for the GRT engineers to highlight some of the issues I was having. Keep in mind most have been solved as I say in the description.

GNS480 and GRT Mini-AP integration issues

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