Matt's RV-7 Project

I used split plastic conduit from the auto parts store to cover the exposed wiring that runs up the firewall. I have the goal of not having any exposed wires visible to the pilot or passenger, and this is an easy way to hide them. I thought about continuing the plastic stuff all the way to the spar, but it's too fat to allow the fuel pump assembly and center cabin cover to be installed.

That pretty much does it for the wiring that I'm able to finish at the present time. There are still plenty of loose ends (literally! ha-ha!) but I need to work on some other areas first. My garage was becoming highly cluttered after a whole winter of electrical work, so I spent the evening cleaning and putting away stuff that didn't need to be out anymore.

Hmm, what to do with all these spools of aircraft wire?

A hardwood dowel and a piece of scrap lumber make a handy wire stand!

It's shocking how many little plastic containers of loose hardware I have floating around the garage:

It took me a couple hours, but I reclaimed about three quarters of it all, and put each item back in its little drawer. I still have a bunch of AN nuts and bolts, which I am not returning to the general population since I don't want an old beat-up fastener to accidentally be used for something important. Plus there's a bucket of miscellaneous parts that don't have a home right now.

Plenty of room for the next project now! Although I'm sure I'll have it looking like a pig sty in no time.

The wiring instructions for the Lightspeed ignition system are full of unusual requirements without explaining the reasons behind them. I decided to deviate from the suggested schematic in a few specific ways. Disclaimer: think carefully about how you wire your ignition system, and be careful when deviating from the manufacturer's recommendations.

To provide the ignition with a redundant source of power from my aux battery, I used a pair of Schottky diodes in a handy two-in-one package. Of course, the reason for using a Schottky here is to minimize the forward voltage drop. Power Schottkys are kind of hard to find in a convenient package – i.e. with mounting holes, insulated base, and non-solder terminals – but I got a tip about IXYS products and found this diode that is more than adequate for what I need.

The big red thing is a noise filter capacitor I installed to try and preemptively deal with the reported power supply ripple that the ignition has supposedly been known to generate. This is the same 26,000 uFd cap they install with MSD race-car ignitions, so hopefully it will do the trick. It's certainly big enough. It fits pretty well on the passenger-side subpanel, which is just a few inches aft of where the ignition will go.

The Lightspeed instructions tell you to use shielded wire for all the power connections, with the shield used as the ground return. This is impractical with my setup, although I did use shielded wire for the connections from the batteries to the diodes (with the shields used in the normal fashion, and grounded to a handy screw on the subpanel). A short length of wire connects all the ignition stuff to the single-point ground block on the firewall, and I deemed the wiring from the diodes to the capacitor to the ignition to be short enough as to not require me to fool around with shielding. Hopefully all this will be enough to avoid having ignition noise in my headphones.

Last wiring task of the day was to run a length of shielded wire from the ignition over to the corresponding switch on the pilot's side of the panel. The ignition always has power, even when the airplane is off, but it has a separate "enable" input that's wired just like a magneto P-lead. Closing the switch grounds the faux P-lead to its shield, disabling the ignition. I chose to use this approach rather than switching the power input (which you can also do) because the relative locations of all the various components would require that approach to use a whole lot more wire (and current-carrying, noise-radiating wire at that).

I would have spent more time working on the airplane this weekend, but I had to spend a whole afternoon fixing the mower. Grrr.

As best I can tell, I have finished running all the wires that pass through the cabin. Following a good vacuuming, I tidied up all the wiring runs under the floor and replaced the temporary twist-ties with plastic zip ties. I do love the look of an orderly wiring harness:

Everything is finished in the aux battery area. I used split corrugated wire loom where the wire bundles pass next to the battery tray, to prevent problems with chafing.

After closing out the center tunnel wiring runs, I reinstalled the aileron trim servo. The wires that will go to the control sticks don't actually connect to anything yet; that will happen later.

I used more plastic loom in the area where the wire bundle has to squeeze between the servo and the belly skin. Getting all the stuff installed in this tiny area was a (literal) pain.

Forward wiring runs all neatly bundled and secured to the floor:

Of course, up behind the panel it is a different story:

I temporarily reinstalled the fuel pump and selector valve to check the fit. The tubing runs I'd previously made, running from the bulkhead fittings in the F-783B cover support ribs to the fuel valve, won't fit anymore since the wire bundles are now in the way. I think I can work around this by using some different bulkhead fittings. Or at least I hope I can, since the airplane won't be going anywhere if I can't find a way to get fuel to the engine…

I've just been adding one wire after another, making a little progress with every work session. This is one of the two big connectors on the GSU 73, specifically the one that includes most of the engine/airframe analog and frequency inputs. Man, these high-density connectors can be tricky to deal with. The bundle of short wires pointing to the right is a collection of pigtails for all the shielded wires, which will eventually be affixed to the connector backshell. Just visible coming out of the D-sub connector is the harness for the config module, which is a little EEPROM device that backs up important calibration settings.

I keep checking little wiring jobs off my to-do list… here's the magneto P-lead. The magneto switch is upside-down, since closing the switch equals "no spark".

Here's the power and oil pressure connections to the Hobbs meter. I know I don't really need a mechanical hourmeter since I have all this fancy electronic stuff to keep track of the airframe time for me, but I feel better having something that absolutely cannot lose time; I had a bad experience with another vendor's EIS product once upon a time.

Forward of the firewall, the wiring for the engine sensors is just coiled up, since I have to finish the cowl and baffling before I can hook things up for good.