Matt's RV-7 Project » Electrical/Panel

Starter & alternator cables

Matt — Mon, 15 Aug 2011 01:00:52 +0000

I got the big cables run for the starter and primary alternator. Here's an overview shot, and I'll walk you through the details below:

I played around with several different variations of cable routing before I found a configuration I liked, which took several hours. Then I had to take it all apart, cut the cables to the proper length, and install the terminal ends with my crimping tool in the vise. This is 4 AWG wire in this photo.

Good thing I didn't forget to install the current sensor on the alternator cable before I crimped on the ends. Proper clocking of the terminals is important here too.

Young Ryan from work stopped by for a visit, and I put him right to work. An extra set of hands is… handy!

We made a spike catcher diode for the starter contactor out of a 1N5400 I had laying around. The anode connects to ground through one of the mounting bolts, and heatshrink insulates it all.

Here begins the tour. The starter cable leaves its contactor and heads towards the right side of the firewall (left in this picture). The alternator cable comes off the big current limiter, goes through the current sensor, and continues on in the same direction. You can also see the much smaller alternator field wire, which comes in from the top and parallels the whole works. Adel clamps are everywhere, holding the big cables securely.

This may be my crowning achievement in adel-clampery. Three clamps on the same bolt hold both the starter and alternator cables to the engine mount, and another adjacent pair holds the alternator current sensor. If you've ever dealt with adel clamps, you can imagine how fun it was to install all of this.

The two cables meet up at another set of clamps on the starboard gear socket:

Then they turn the corner and run in parallel through space up to the engine. I left a bit of slack to accommodate relative movement between the engine and the fixed components.

The wire bundle is clamped to the #3 cylinder induction tube and then runs forward from there.

The wiring runs along the top of the oil sump towards the front of the engine. It's hard to see, or even to photograph properly, but the exhaust pipes are nowhere near the wires – the pipes are at least three inches outboard, not visible in this photo.

Adel clamps attached to convenient sump bolts bring the wires around the corner and back around towards centerline. There's adequate clearance between the wires, oil sump, and prop governor line, and the wires are secure enough to avoid chafing.

The alternator cable then splits off and does a 180 back towards the alternator. A clamp on the bolt that holds the prop governor line in place keeps the cable from flopping around and rubbing against the nearby fuel hose.

This is a view of the same area, looking upward from below:

I put a knife splice joint and a service loop in the alternator field wire, and used plenty of heatshrink to support the wire where it goes into the (needlessly huge) plastic field connector. This seems like a prime location for a wire to fatigue and break, so I tried to secure things as well as I could.

Later on, I potted the connector with RTV to further secure the wires:

Meanwhile, the starter cable continues across to the port side of the engine, behind the starter itself (removed for this photo).

Note the clamping arrangement needed to bring the starter cable around the spine of the engine and then back up to clear the mixture bellcrank assembly. This is heavy 2 AWG wire, so you can't just bend it out of the way and hope it stays there, you have to bolt it down.

Around the back of the starter it goes, then bends forward to the starter terminal post:

From the front it looks like the starter cable must surely be rubbing on something back there, but from below you can see there's plenty of clearance between the wire and the starter housing:

No conflicts here:

I also had a rare burst of foresight, and brought out the air duct to check for interference with the starter cable. No problem here either:

It's good to have the two heaviest wires on the airplane installed for good. Just one of a million details left to do before this thing is finished…

Current sensor spacers

Matt — Sat, 23 Jul 2011 21:00:53 +0000

I'm using Amploc brand Hall effect sensors (most easily found as a GRT accessory) instead of shunts to measure alternator current in my airplane. You pass the bus wire through the middle of the sensor, which is a bit less than an inch in diameter:

The wire doesn't have to be centered inside the sensor, but I still wanted to come up with a way to secure it and make it look nicer. This just looks sloppy to me:

I went up to Airparts and bought some 1" diameter nylon rod, then turned it down on my lathe so it would exactly fit the inside diameter of the current sensors. Having a lathe is great, even if I am only barely competent at using it.

With a bit chucked in the tailstock, I center-drilled the nylon to fit the diameter of the wire. After I took this photo, I parted off what I needed and cleaned up the ends a bit.

Voila, now it's a perfect fit:

I made one spacer with a 3/8" hole to fit the #4 wire from the main alternator, and another one with a 5/16" hole to fit three turns of #10 wire for the secondary alternator. With a Hall effect sensor, running multiple turns of wire through the sensor gives you a current reading that's multiplied by the number of turns, which your engine monitor then divides back down to give you the true current value. This is a handy way to increase the accuracy of the measurement, as long as your EFIS supports it, which mine does. Since these are 100A sensors, three turns of wire from the 20+ amp standby alternator should be just about right.

I glued the spacers into the sensors with E6000. Nylon is resistant to most glues, but I'm hoping this stuff will grab hold of the roughed-up surface.

Next: Off to Oshkosh for a week…

Wiring and workshop cleanup

Matt — Sun, 16 May 2010 04:00:49 +0000

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.

Ignition power

Matt — Mon, 10 May 2010 02:00:02 +0000

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.

Wiring, cleanup

Matt — Mon, 12 Apr 2010 02:30:09 +0000

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…

More wiring

Matt — Mon, 05 Apr 2010 01:28:11 +0000

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.

Wiring

Matt — Sat, 20 Mar 2010 21:50:08 +0000

More splicing, crimping, soldering, et cetera. This photo shows the wiring for the tach sender and fuel flow transducer:

I also finally got around to uploading a new copy of my electrical system schematic:

GSU wiring

Matt — Mon, 08 Mar 2010 02:05:51 +0000

Finally, a warm weekend! After taking care of yard work and bills and house maintenance, I still had an entire afternoon to spend in the garage. I did a bunch of cleaning and straightening up, and then finished the last of the wires that runs to the lower connector on the GSU 73 ADC/AHRS/EIS unit. The upper connector is for all the various engine sensor inputs, which I'll begin hooking up soon enough.

Some of these connections need to be spliced six ways to sunday, and you have no choice but to do it right there on the airplane. A helping hand tool is indeed quite helpful for this. Note the heavy heatshrink on the jaws to protect the wires.

Antenna wiring

Matt — Sun, 13 Dec 2009 03:00:33 +0000

Good grief, has it been a month since I updated this thing? I've been trying to work on the airplane a little bit here and there, but between holiday travel, work projects, and cold weather, things have been pretty slow in the airplane factory.

I have, however, managed to get the previously installed antennas on top of the fuselage all wired up. Four lengths of RG-400 coax run down from the panel, through the spar, and back under the floorboards. They penetrate the F-706 baggage bulkhead via snap bushings, then run back and up the F-707 bulkhead protected inside plastic conduit.

I drilled small holes in the J-stringers so I could attach the conduit with tie wraps. On the left side of the fuselage, I used a piece of rubber tubing and some tie wraps to prevent the conduit from chafing on the static line.

The conduits run up either side of the F-707 bulkhead – more small holes and tie wraps – and then the coax emerges to connect to the antennas.

Two wires go forward to connect to the WAAS GPS antennas – one for each GNS 430W. I riveted little tabs of scrap aluminum to the lower flange of the F-787 stiffener, so I could secure the wires with adel clamps. Meanwhile, two more runs of coax go through grommets in the bulkhead and connect to the combo GPS/XM antenna that's just aft of F-707.

Here's another view, looking up from [my very uncomfortable position on] the floor. In this picture, the nose of the airplane is to the left.

Up at the forward end, the primary display unit gets a GPS connection, and the multi-function display gets an XM antenna hookup. Each 430W gets a GPS antenna connection too, although I forgot to take a picture of that.

Not surprisingly, the G3X GPS receiver can get a fix even inside my garage with the doors closed. With a good antenna and a strong receiver, you can't lose.

This doesn't look like much, but it took two days' worth of crawling in and out of the airplane to finish.

Map lights

Matt — Sun, 15 Nov 2009 03:00:46 +0000

I already mounted the dimmers for my cockpit map lights, but I didn't get around to wiring them until today. So here's what one of the LED map lights looks like:

I discovered that the inside diameter of the mounting base is exactly the same size as a cleco, which is really handy for drilling the mounting holes.

I dug the rollbar out of storage, clecoed it to the fuselage, marked and drilled pilot holes for map lights, and clecoed a light mounting base to each of the trangular gussets.

I match drilled the three mounting holes to the rollbar, then enlarged the center hole to 1/4" and drilled the mounting holes for miniature nutplates. I'll rivet these to the rollbar gusset once it's been re-powder-coated.

I like this location… it's out of the way and not likely to get broken off by passengers' feet, but still in a good location to be useful for reading a chart or for illuminating dark corners of the cockpit.

I used a very small grommet to pass the wires through the rollbar gusset:

The dimmer modules came with some miniature potentiometers. I soldered leads to the terminals:

…then used heatshrink over the joints:

…and finally put a piece of bigger heatshrink over the entire component, which should help prevent the wires from breaking off.

I drilled holes in the F-721 canopy decks to mount the dimmer pots:

I used some anodized aluminum knobs that match the ones I used for the panel light dimmer knobs. Eventually I'll make little placards to identify the function of the knobs, which will have the added side effect of covering up the holes for the anti-rotation tabs.

I finished up the wiring for the little dimmer modules and closed up the connectors. The power and ground wires that go to the lights themselves are not connected permanently yet, since I need to do a little further work to route them properly.

However, I did hook up each lamp with alligator clips just to make sure everything was wired correctly. Yup, seems to work:

I have something special in mind for making the connection between the lamps and dimmers, but it's not ready to show off just yet.

VOR antenna

Matt — Mon, 02 Nov 2009 01:00:55 +0000

A forum thread convinced me to buy and install a traditional cat whisker VOR/ILS antenna on the bottom of the fuselage, rather than the hidden wingtip type often seen on these aircraft. I'm happy to give up half a knot for reliable navigation performance.

I decided to mount the VOR antenna just aft of the F-710 bulkhead, which is just barely accessible when the empennage is attached. A doubler ties into the bulkhead and the F-779 bottom tail skin.

The doubler is made out of 0.063" alclad. Here it's drying after having alodine applied, although in retrospect I'm not exactly sure why I bothered to do this – the "puck" part of the antenna is plastic, and the mounting fasteners don't make electrical contact with anything in there. Oh well, at least it won't corrode.

Here it is riveted in place with the antenna attached via nutplates. The brown stain is alodine that ran downhill while it was drying.

It would be pretty easy to use driven rivets here during the initial build of the tailcone, but on a nearly finished fuselage with the empennage installed it's essentially impossible. Cherry Max rivets to the rescue.

Test-fitting the VOR antenna using some random bolts… when I go to install it for good I'll use AN525 screws instead:

When the rudder and elevators are installed, you won't be able to step on the VOR antenna, so no danger of tripping over it while walking around the back of the airplane.

Yeah, it's hanging out in the breeze, but the airflow down there will be pretty disturbed anyway, so it shouldn't cause too much drag (he said, despite having only a journeyman's understanding of aerodynamics). At least the nav radio reception should be pretty good!

Now that all seven of the antennas on the fuselage are mechanically installed, it's time to move on to wiring them… but that will have to wait for a future work session.

GPS antennas

Matt — Sun, 01 Nov 2009 01:00:52 +0000

My airplane needs a bunch of external antennas on top of the fuselage… one WAAS GPS antenna for each 430W, and a combined GPS/XM antenna for the G3X system. I cut up some 0.063" alclad and made a doubler for each antenna:

I chose to put the two WAAS GPS antennas on either side of the canopy track, about halfway between the F-706 and F-707 bulkheads. As long as they're not placed too far forward, the canopy will pass over the top of them as it lifts up and slides aft. I couldn't put them all the way at the aft end of the canopy track, since the upper fuselage stringers taper together and make it too narrow to for the antenna doublers to fit. I used a yardstick as a spacer to make sure I drilled the doublers parallel to the fuselage centerline, and to ensure adequate space for the canopy slider block to pass by.

Lots of big and small holes drilled in the top of the fuselage… no turning back now! The doublers will be riveted to the inside of the skin, of course, but it's way easier to drill them from the outside. I also had to shape them a bit with hand seamers, since a perfectly flat doubler won't quite lay down on the curved fuselage skin.

The third antenna doubler is located just aft of the F-707 bulkhead. There's plenty of room for the canopy slider block to fit between the antenna and the end of the track, so there should be no problem removing/reinstalling the canopy.

I alodined the doublers and fuselage skin for good electrical bonding, and riveted on floating nutplates.

John came over to help buck the rivets, while I crawled back into the tailcone to drive them from the inside.

The actual riveting went pretty quickly:

A shot of the finished rear antenna doubler:

Now the fuselage has sprouted a crop of antennas:

Victory! Thanks to John for the help.

Trim wiring

Matt — Mon, 19 Oct 2009 01:00:05 +0000

Not a lot of time to work on the airplane this weekend, but I did manage to finish wiring the aileron/elevator trim controller:

Need to order some more shielded wire in order to continue… not to mention find some time to work on the airplane for a change!

AOA wiring & indicator

Matt — Mon, 12 Oct 2009 01:00:11 +0000

The AFS angle of attack system comes with a wiring harness of sorts… actually it's just a a bundle of wire several feet long, with a d-sub connector on one end. Rather than try to splice their provided wiring into my electrical system, I just de-pinned all the wires except the ribbon cable that attaches the brain box to the display.

Then I ran all the various wires to the AOA brain box… power, ground, button inputs, flap detect switch, etc. Which looks a lot like a bunch of wires and a box:

I spent a couple days playing with scraps of sheet metal until I'd built a little cosmetic housing for the AOA system's glareshield display. The battery in my camera was dead, so sadly I don't have any photos of the process, but basically I just hammer-formed it out of thin alclad over wood blocks. The shape ended up being somewhat strange, since it has to sit level on the sloping glareshield.

Riveted together and painted… Sadly, I forgot to take a picture of the finished product mounted on the glareshield, but I'll put one up when I install it for good.

I did manage to get a photo of the grommet I put in the forward fuselage skin for the AOA display wires, which is much less interesting:

I plugged the display into the ribbon cable to give the AOA setup a basic functionality test. All the lights came on, so I guess it's working.

The ribbon cable connector is kind of a one-shot deal, so rather than risk breaking it trying to get it to release its grip on the ribbon cable, I just cut off the last foot or so and put it back in the box until I need to install it permanently.

The remaining length of ribbon cable will remain spooled up in the cockpit until I finally install the AOA display for good, at which point I'll cut it to length and splice the wires back together.

Fuel selector spotlight

Matt — Mon, 28 Sep 2009 02:00:14 +0000

When I was up refreshing my night currency in the rental 172 a few weeks ago, I noticed that Cessna put a little light bulb above the fuel selector valve so you can see it at night. I found this to be a nice touch, and thought it might be neat to put something like that in my airplane too.

I bought a blue LED from the local Radio Shack, and hooked it up to a bench power supply (along with a suitable dropping resistor) to see how bright it is. Yeah, that's probably plenty bright:

I soldered a 1k resistor to one of the leads, which will run the LED at about half brightness. Then I shrink-wrapped the resistor and leads:

I bought a couple different diameters of thin-wall aluminum tubing at the local hardware emporium, and made this little spotlight hood for the LED. The flange at the base of the LED is squared up against the end of the smaller tube, and it's all potted together with JB Weld.

I played with a lot of different mounting locations, and eventually settled on this spot at the forward end of the throttle quadrant. I made a little mounting plate out scrap alclad, painted everything black, and mounted the spotlight with an adel clamp. Although it's tight in there, the throttle cable has plenty of clearance from the lamp.

Here's a wider view. The end of the lamp is not visible to the pilot or passenger, so there won't be any glare.

Hey, how cool is this? I love doing these little custom touches.

Compass

Matt — Sun, 27 Sep 2009 01:00:56 +0000

Some time ago I bought an expensive SIRS whiskey compass, and preparing for its installation has been on my to-do list for quite some time. Since I'm still on flu recovery detail, I figured this would be an easy enough project. First I had to go find the rollbar, brace, and forward top skin:

I marked a location on the rollbar brace that puts the bottom of the compass about a half-inch above the glareshield, to allow room to install a nice-looking trim piece later on.

I marked a centerline on the rollbar brace using a handy piece of angle, and drilled two rivet holes using a V-block. I won't actually rivet the compass mount to the brace until I first send it off to be powder coated.

I tested the internal lighting with a bench power supply… yep, it works.

Then I ran wires from the panel light dimmer to a spot just below where the compass will mount, and put a plug on it. Didn't remember to take a picture of this, but you can imagine what it looks like. The compass is now back in its box, and will likely be one of the last pieces of instrumentation to be permanently installed.

Map light dimmers

Matt — Mon, 21 Sep 2009 01:00:18 +0000

I have this idea that I'll install a small map light on either side of the cockpit… I haven't figured out exactly where I'll put the dimmer knobs, or even the lights themselves, but that hasn't stopped me from buying a pair of LED lights and dimmer modules. One of the latter is shown here:

I mounted a dimmer to the F-721A canopy deck on either side of the cockpit, which seemed like an okay location.

I removed the included attachment feet and made some mounting brackets out of scrap alclad. The odd shape is required to clear the traces on the board, and the nutplates are there to allow me to remove the thing later on if it goes blooey.

Just to see if it would all work, I hooked up one of the dimmers to one of the map lights and a bench power supply…

Well, it all works. Eventually I'll find a place to put these.

Fixed radio stack reinforcement

Matt — Fri, 11 Sep 2009 02:00:34 +0000

You might recall I was displeased with the way the audio panel wiring was impinged upon by the crosswise brace at the top of the radio stack. This weekend, I fixed that particular glitch by drilling out the rivets in the piece of angle across the top of the cutout in the subpanel, and very carefully enlarging the cutout by another half-inch. At various times I was going after the subpanel with a unibit, a cutoff wheel in a dremel, various files, and a scotchbrite wheel in a die grinder… luckily I managed to avoid nicking any of the hundred or so wires back there.

New reinforcement pieces were cobbled together out of various pieces of scrap I had laying around. Since I was working around a bunch of existing structure that couldn't be moved, it was kind of a puzzle figuring out the best way to get everything attached securely together.

Here's what the finished product looks like from the aft side. Compared to the previous version, the new brace is substantially higher. There is a 0.032" spacer between the angle and the subpanel, which is bent around underneath to form a kind of cable guide.

A little piece of scrap angle ties the new horizontal brace to the existing vertical piece. It's kind of cheesy, but it's plenty strong. There's plenty of room now for cables and connectors to pass through. You can also see that I had to use another screw and nut in the inboard hole, since there was no way to get a squeezer in there and I didn't want to risk smashing something delicate with the rivet gun.

I also changed the desiccant material in the engine dehydrator plugs again… the dark blue one is filled with fresh silica, and the other one is old. Later on I baked the old silica until it was the same color and the new stuff, and dumped it back into the container.

Spar holes and wiring

Matt — Tue, 08 Sep 2009 02:21:35 +0000

How was your labor day weekend? I drilled two big holes through my airplane's wing spar:

Relax, I got approval from the factory first:

Matt,
Yes, you can provide additional holes within reason. Use the same diameter as we have, and also keep in mind the proper edge distance (2D). Also keep clear of other structure such as seat ribs, spar bars, flanges, brackets, etc.
Joe Blank Builder Support Vans Aircraft Inc.

Since doing this incorrectly would basically ruin the airplane (or at least be extremely time-consuming and painful to repair) I spent a lot of time measuring and contemplating various locations. I eventually picked a spot outboard of the F-716 seat ribs and inboard from the F-783 cover support ribs.

Vertically, the new holes are equidistant from the upper and lower spar reinforcing bars, and have more than enough distance from the existing holes I've been running wires through. I had to pull the wire bundles out of the way to drill the new holes, and I had to use an extension to keep the drill chuck from grinding up the ribs, but it all went just fine.

You can bet I deburred the heck out of these holes.

I wasted no time putting the new wiring holes to use… this is the coax for the transponder antenna, which runs down the right side of the forward cabin floor, goes up through one of the new holes, and then turns inboard before running down the right side of the center tunnel.

After passing through the rear spar, the transponder coax jogs outboard again and runs down the F-727 rib before passing through a bushing in the baggage bulkhead.

This is as far as I got before I had to go mow the lawn. Later on I'll figure out a way to secure the coax to the floor, and put on the BNC connector. By the way, this particular piece of coax is actually the same one I had previously cut and run to go to the nav antenna connection in the left wing root. Subsequently, this thread on VAF convinced me that it would be a better idea to instead use a V-shaped dipole antenna under the tail instead, so I ripped that cable back out. By happy coincidence, it was the perfect length to use for the transponder, so nothing is wasted.

I ran a few other wires this weekend too. The tail and each wing got power wires for the nav and strobe lights, plus a wire to synchronize all three strobes. I have decided to go with LED nav/strobe lights, although since I am an inveterate bet-hedger I made sure to size the wires for the strobe lights so they'd each be sufficient to run a single-output power supply for a more traditional certified light head, should I have a change of heart and decide to go that way instead. I also ran a spare wire to the right wing with an eye towards eventually using it to power an APRS tracker (someday).

Many feet of wire are ready to be run back to the tail too, although not everything is in place yet.

New game! Whenever you drill a hole in your spar, you have to take a drink. Tonight's beverage was a summer seasonal from Blue Moon, which was not half bad.

More wiring

Matt — Mon, 31 Aug 2009 02:00:45 +0000

I ran wires and installed connectors for the rudder trim switch (lower center) and its associated speed control (upper center).

I used some miniature connectors for the 26-gauge wire on the Ray Allen trim components. I used the size of pins and sockets that are rated for 22-26 gauge wires, and doubled the wire strands back on themselves before crimping… worked great. I also bundled all the small wires together with a piece of double-wall heatshrink to provide sort of a strain relief.

Same thing on the rudder trim switch side. Also: Dear Ray Allen company, what's up with you guys and 26-gauge wire? Would it kill you to use something slightly heavier than can be used with normal tools and connectors?

Since I have a habit of only posting extreme closeups, here's a few overview pictures to show how the wiring is progressing. First, a wide shot of the whole panel. The glare is due to the garage door being open to let the extremely nice weather in.

Big fat bundles of wires surround the main bus fuse blocks, but it's all relatively tidy.

Wire bundles running back through the spar and out to the wings. I'm starting to run out of room in the snap bushings that go through the F-704 center section. You only get a total of four half-inch diameter holes to pass all your wiring through, which may be enough for a simple VFR airplane but is totally inadequate for an intergalactic spaceship like I'm building. I know some people have drilled extra wiring holes here, but since the spar is so critical I think I will wait to get blessing from the factory before I go poking any more holes in it.

Looking aft towards the tail… I do have two extra snap bushings in the lower F-705 bulkhead web, which were approved by the factory. I had originally intended those to be used for running wires to the ELT and strobe power supply, but now I'm thinking of moving the ELT somewhere else (yes, again) and switching to LED strobes, which don't need a power supply. However, I have enough other wires and antenna cables that need to get back to the tailcone that I'll probably end up using these for other purposes. You can see in this photo I've already started running trim wires for the passenger stick through one of them.

Big coils of wire are starting to pile up aft of the baggage bulkhead, in preparation for some future date when I get around to crawling back into the aft fuselage to run wires to the empennage and aft-mounted antennas. Not to mention retrieving whatever else has fallen in there.