I have my instrument rating so I intend to equip my RV with sufficient redundancy that a failure of any single instrument, avionic, or electrical component will not limit my ability to continue a safe flight, approach and landing. My plane will be 'All Electric', without any vacuum system, so redundant power sources are a necessity.
This electrical system is derived from Figure Z-13/8 as featured in revision 11N of the AeroElectric Connection. Modifications include the addition of an Avionics Master Switch, separate Avionics Bus, and a small Auxiliary Battery. Additionally, relays are used for switching the bus feed lines.
This airplane is being built for cross-country travel and will be used for occasional IFR. My essential electrical equipment list includes a Garmin GNS430 GPS/nav/comm, two EFIS screens and its associated AHRS, magnetometer and ARINC adaptor, a two-axis Trutrak autopilot, elevator trim, minimal cockpit lighting, and a Trutrak ADI flight instrument.
Non-essential avionics will include a second nav/comm radio, transponder and audio panel. Additionally, the fuel boost pump will be on the battery bus to allow it's use during landing in the event power to the main bus is off.
In addition to the above, the airplane also has one eMag and one pMag electronic ignition module. The eMag is dependent upon external power to function, but the pMag has the capability to generate its own power.
An essential and battery bus load analysis yields an approximate current draw of 10A, and up to 16A when the comm is transmitting. Because of this I will use a relay to energize the E-bus alternate feed path.
This load exceeds the output of the SD-8 auxiliary alternator, which should be around 6.2A at 2200 rpm, 6.8A at 2300 rpm and 7.2A at 2400 rpm. The deficit will be covered by the main battery capacity, which will be a 17 Ah battery. Assuming a 4A deficit, the battery reserve should comfortably allow a minimum of one hour to fly to a suitable airport, approach and land. If flying VFR there is also the option of turning off additional equipment to further reduce the load and continue to the original destination.
The EFIS displays and AHRS are all sensitive to reduced bus voltage that happens during engine cranking, so I have elected to equip the airplane with a small auxiliary battery to sustain these devices during engine start. During engine start the auxiliary battery powers the E-bus while remaining completely isolated from the plane's main DC power.
The non-essential avionics are on a separate avionics bus which is not powered during engine start nor during E-bus operations.
Under normal circumstances, all electrical loads will be carried by the main battery and alternators - the aux battery will be contributing nothing, remaining charged for when it's needed for the next engine start. The aux battery will be charged through a diode. This will let the aux battery charge whenever the main alternator is online, and will prevent the aux battery from backfeeding into the main bus with no active switching required. The diode will also do the job of dropping the 14.4V alternator voltage down to the ~13.8V float voltage recommended for VRLA batteries.
In the event of a main alternator, battery contactor or avionics master failure, the E-bus alternate feed will be turned on, providing power to the E-bus. The main and avionics buses are not powered during essential bus operations.
For reference, the main battery, battery contactor, and starter contactor will be located on the engine side of the firewall. All fuse blocks, relays, the aux battery and the essential bus diode will be mounted behind the firewall and forward of the sub-panel on the right side of the plane. A drop down panel will provide access to the fuse buses.
There's still a little more work to finalize on this design, including circuit protection, wire sizes, etc. Questions and comments are welcome. Feel free to e-mail me.
Total Construction Time: 100 hours and counting
January 13, 2008 (2 hours)
I've spent many hours planning my electrical system, but today was the first day I can say I actually started working on it. I partially constructed the hinged panel in the photo below for mounting my main three fuse blocks. This will make it much easier to access them later. I think I'll add a camlock that attaches to the bottom of the subpanel to hold it in position.
January 15, 2008 (2 hours)
Spend more time fabricating the support angles for the hinged fuse block panel, which is now mostly complete.
January 16, 2008 (2 hours)
Finished up the hinged fuse block panel. Credit for this idea goes to Bret Smith! I have to add a nutplate and hole to the bottom of the subpanel with a knurled knob to hold the fuse block panel in place. I also have some #10 screws on order to fasten the fuse blocks to the panel.
January 20, 2008 (4 hours)
It's been too cold to work too long in the garage this weekend. I've been experimenting around with making my own annunciator panel for a while. Today I started building it. I decided I wanted the total width of the display to be 7 1/2" wide, to match the width of the AFS EFIS screenm, with seven approx. 1" wide lighted panels.
I started with some 3/4" square aluminum tubing I picked up in the aviation department of Lowes. I cut a 1/2" wide x 7 1/4" slot in the front and drilled seven 1/4" holes in the back for the LED holders. I cut some small dividers using some scrap stiffener aluminum and glued them between each light area using some E6000 adhesive. I bought some 8000 mcd 45 degree white LEDs, which I wired up with a 330 ohm, 1/2 watt resistor.
Next I used Excel to size and print out my text strips in black and white on some clear sticker sheets I bought from Office Depot. The text colors come from clear plastic sheets behind the sticker paper that I picked up from a local craft store, which I doubled in thickness to get a bit deeper color. I didn't want to see the LEDs through the plastic, so I bought a translucent plastic report cover which sits behind the text strip and colors and diffuses the light. Finally I bought a piece of 0.080" lexan which I cut out to put in front of the text strip and which will sit roughly flush with the face of the panel when I'm all done. Once I light up the panel with a couple of test LEDs I noticed I could see some light shining through the black areas, so I applied some strips of black tape around all the text areas.
I still have to drill a couple of holes and add some nutplates at each end, plus make something to hold the lexan in place. I might also upsize the resistors used with the yellow text as they're a bit bright. Later I'll run all the wires to a 9-pin D-sub connector so it's easy to remove if I ever need to. The text in the picture below is simply what I used for my experimenting, so once I decide what I'm going to wire up to my annunciator panel I'll have to remake the whole text part as well. This turned out to be a lot of fun to build.
January 21, 2008 (1 hour)
Couldn't stand not working on the plane so I decided to brave the cold and drill my fuse blocks, relays and diodes to the drop down panel and one of the ribs.
January 22, 2008 (1 hour)
Spent a little time adding nutplates to the panel and ribs to hold the electrical components.
January 23, 2008 (1 hour)
Attached the electrical stuff to the panel and ribs, then marked and drilled the brake master cylinder to the firewall (okay - not really electrical but I don't have a firewall forward page yet) and started trying to drill the lightening holes in the battery box.
January 24, 2008 (1 hour)
Bought a better hole saw and drilled the lightening holes in the battery box then touched them up with some rustoleum paint.
January 26, 2008 (8 hours)
Spent a good part of today starting to run wires through the fuselage. I also mounted the Creativeair strobe power supply. Instead of running three wires from the panel to each nav light, I decided to add a little terminal strip to one of the ribs at the side of the tunnel. I'll probably add one on the opposite side of the tunnel as well for other wires including to the stick switches. I'll also add an adel clamp on each side of the tunnel to secure the large amount of wires that will be running through there. Finally I started drilling the brackets to the battery box and drilled lightening holes in the top bar that holds the battery in place.
January 27, 2008 (3 hours)
Finished up the main battery box and drilled it to the firewall. Also ran a couple more pair of wires, these ones for the wingtip taxi lights.
January 28, 2008 (2 hours)
Started fabricating a mounting bracket for the small auxiliary battery using a design cooked up by Bret Smith and me.
February 2, 2008 (3 hours)
Got my Molex crimper yesterday so today I added the connectors for the strobe lights and ran the wires through the fuselage. Decided I had to test them out and all three strobes worked just fine.
February 3, 2008 (5 hours)
First I added a 9-pin D-sub connector to the 26 ga wires from the flap position sensor. Next I tounted the sensor inside the flap motor housing and attached a rod with clevis ends to the flap actuator weldment. Then I ran the three wires forward through the tunnel. During the Superbowl I came inside and decided to work on my autopilot servo harnesses, including adding an extra wire for the pitch servo and attaching D-sub connectors to the servo ends.
February 4, 2008 (3 hours)
Pulled a whole lot more wires through the fuselage, including the autopilot servos, antennas and a few more power feeds. The snap bushings out the side of the fuselage to the wings are pretty much full, with just enough room for the OAT probe wires to the left wing. Got my stick grips today so I'll have a bunch of wiring to do for these, plus I think there's just a few other wires left I need to run.
February 10, 2008 (2 hours)
Temps were sub-zero all weekend again so I avoided the garage. I soldered the wires to the co-pilot stick, but held off on the pilot stick while I make sure I know what functions I want for these switches. I also started working on my LED position lights for the wingtips. I'm using some special lenses made for the Luxeon LEDs for the two forward facing ones. The specs show that I should have in excess of 60 candles of intensity forward. It's going to be really tight, but I'll be just able to get the two lenses and the wingtip taxi/wig-wag lights to fit.
February 13, 2008 (2 hours)
Fabricated a second mounting angle for the LED lenses and cutout a couple of face plates for the rear face of the wingtip cutouts. Scrapped the one I made using the aluminum as the cutting bit walked in the soft aluminum provided with the Creativeair kit and made a replacement with some spare 0.063" aluminum I have.
February 16, 2008 (2 hours)
Worked on getting the face plate holes just right for the lenses to stick out where I wanted them to. Then I drilled the mounting angle to the wingtip. Just for fun I hooked the LED's up to a 9 volt battery with a resistor in line and tested them out. I'll add two more LEDs, without lenses, to the other face of the wingtip cutout and this combination will meet all the FAA specs for coverage in all directions. The larger hole is for my wingtip lights and there will also be a strobe light mounted to the inside face of the cutout.
February 17, 2008 (6 hours)
Spent a bunch of time today trying to get my taxi lights fitted in around the LED lenses. Once I finally got it positioned where it was aimed through the center of the hole in the rear cutout face, I decided to test aim it. Once I fired the light up I found I was able to get it aimed close to straight ahead and level, but after a short bit I noticed that the outside of the wingtip fiberglass was getting pretty hot. Because I moved the light as outboard as I could, the clearance around it was pretty minimal, causing the heat to warm up the fiberglass more than I was comfortable with.
After spending some time seeing if I could find a solution, I think I'm going to skip the taxi lights in the wingtips and instead install the Duckworks leading edge landing light, upgrade it to HID, and call it good enough. So I decided I could go back to my original plan and face the wingtip cutouts with the mirrored plastic I bought long ago instead of using aluminum. I went ahead and cut and trimmed one face before calling it a night. Not a highly productive day, but at least now I've got a plan to keep moving forward.
February 18, 2008 (3 hours)
In the morning before work I went ahead and traced and cut out the three remaining mirrored faceplates for the wing cutouts. In the evening I didn't feel like messing around in the cold garage which was only around 20 degrees when I went out there. Instead I decided to solder up the switches in the pilot stick grip. With the seven switches, there sure are a lot of wires. I'm just barely going to be able to close the two halves together, although had I stuck with the 26 ga wire instead of 22 ga it might have been a little easier.
February 20, 2008 (1 hour)
Over the last two mornings before work I spent roughly an hour arranging the wires within the stick to get the two halves to close, then tied the wires up with some lacing cord and used clear shrink wrap to add laabels to each wire.
February 23, 2008 (2 hours)
Mounted my dual heater valve to the firewall. This was made up by another local builder and should help make winter flying much more bearable.
February 24, 2008 (1 hour)
With the heater valve in place, I decided on where to mount the battery and starter contactors. I went ahead and drilled the bolt holes and their associated nutplate rivet holes.
March 1, 2008 (1 hour)
Been very busy at work and got a nasty cold late in the week, so I barely got anything done. I managed to rivet the nutplates and doubler plate to the firewall and bolt the contactors in place before I finally had to crawl back inside and sleep half the day.
March 9, 2008 (4 hours)
After 10 days of fighting a flu bug I finally felt well enough to get back to work on the plane. I plan to concentrate on finishing the wings and aft fuselage over the next month or two, so once it warms up I can go full tilt on the canopy. In order to install the electrical stuff in the wingtips I decided to go ahead and drill and start riveting the nutplates that connect them to the wings. I plan to use #6 stainless screws and tinnerman washers so I can remove the wingtips whenever I need to. It felt good to be making progress again!
March 10, 2008 (4 hours)
Guess I'm still fighting this bug some, couldn't sleep most of the night. Finally I got up and around 3 a.m. I decided to solder together my APRS tracker. I take the amateur radio test this Thursday, so wanted to get it done soon. I'm not sure where I'm going to put it in my plane. With nav antennas in each wingtip, I don't want this transmitting near the same frequency range as our radios while only inches away.
Later in the evening I finished up riveting the nutplates to the wingtips, including positioning and drilling the nav antennas in place. I've decided to abandon my homegrown LED nav lights and use some Whelen or Aeroflash units instead. I've spent many, many hours trying to come up with a workable design that I feel meets all the requirements and also fits in the wingtip with my taxi lights and strobes. I've decided it's virtually impossible so enough wasting time already. So I cut new plates for mounting the taxi lights to the back of the wingtip cutout.
March 12, 2008 (1 hour)
Used my fly cutter to make the 2" holes in the plates for the wingtip lights plus drilled some holes for the mounting screws.
March 14, 2008 (1 hour)
Tonight I cut a large opening in the aft face of the wingtip cutouts, leaving just enough for three nutplates. Then I drilled, countersunk and riveted those nutplates in place.
March 15, 2008 (1 hour)
Had to drill and rivet three nutplates to each of the brackets that hold the taxi lights. Once that was done I installed the brackets in the wingtips and then screwed the wingtips to the wings. The trailing edge of one lines up nicely with the aileron, but the other is probably 3/16" off, so I'll need to eventually modify the wingtip to get better alignment.
March 16, 2008 (3 hours)
Decided I want to close up the aft top skins so I'm tring to finish up everything I can back there. I ran the five wires for the trim servo and also glued some zip tie bases to the fuselage to later secure some of the wires in the aft fuselage.
March 19, 2008 (1 hour)
Tied up some of the wires in the aft fuselage.
March 28, 2008 (2 hours)
Been doing both electrical and other miscellaneous stuff lately. I started making some little brackets to mount the little LED lights I bought from Van's for the baggage area. I also modified a cheap open end wrench I bought that I could use to tighten the nuts holding the flap sensor in place.
March 29, 2008 (1 hour)
Shot some paint on my baggage light brackets, added a nutplate to each and then tested them out. I really like how they came out. They light up the baggage area really nice.
May 7, 2008 (2 hours)
I'm waiting until this weekend to install the wings for the first time, so I jumped back to the electrical as long as I had some time to kill this evening. I remade one of the aux battery support angles, then primed the parts and riveted them together. I then bolted the support angle assembly to the support brackets. I also drilled an adel clamp to my fuse block tray in prep for starting the bus wiring.
May 10, 2008 (3 hours)
Got most of my power distribution wiring between my buses complete. It looks a little like a rats nest, and will only get worse, but it's really not that hard to wire. I found that I need a 1/4" ring terminal for the Schottky diode I'm using for my E-bus diode, which I don't have yet. I also need to order the wires and terminals that run from the battery contactor to the main and battery buses. My waterjet cut panel should arrive in the next week or two, then I'll be able to wire all the switches in place as well.
May 22, 2008 (1 hour)
Haven't gotten a lot done on the plane in the last couple of weeks because we've been busy with lots of other stuff around the house. Tonight I decided to start on the Duckworks landing light,so I marked and cut the initial hole out of the front of the wing.
May 24, 2008 (3 hours)
Worked on the plane off and on today, but managed to get my landing light pretty much done, including smoothing the wing cutout, cutting the plexiglass to fit, fitting the mounting bracket and nutplates to the ribs, and finally drilling and mounting the plexi cover in place.
June 5, 2008 (1 hour)
Received my panel today from fellow builder Jim Wright. He did a great job water-jet cutting my panel. I did a bit of deburring then I had to play a little. Here's my panel with the placards and switches in place including with the backlighting idea that Bret Smith came up with.
June 22, 2008 (1 hour)
Had a little time to kill this afternoon after gluing my canopy so I did a little more deburring of the panel edges.
June 26, 2008 (1 hour)
When I added about an inch of depth to the panel I extended the edges under the canopy decks to the fuselage sides where the vents will mount. I didn't consider that I wouldn't be able to get the panel in past the vertical bulkhead angles at the main spar. To fix this I took about 3/8" off the right side which let me put the panel in place. I also cut and bent the angles that will attach that part of the panel to the fuselage sides.
July 5, 2008 (3 hours)
This morning I decided to drill the angles that attach the lower part of the panel to the side skins. I took a fair amount of time trying to make sure the face of my panel was nice and flat. Once that was done I primed the angles and added nutplates for the screws from the panel. Then I decided it was a good time to enlarge the vent holes as they were undersized in my CAD file.
July 6, 2008 (8 hours)
I started working on mounting my avionics trays today. Instead of using the track I bought for this, I decided it was going to be easier to just use a couple of angles. I made a simple spreadsheet to help calculate exactly where each screw hole needed to be for each avionics, then laid them out on the angles. Once I drilled them they came out pretty much spot on. I had to file just a little off the opening in a couple of places to get the trays to fit. Finally I marked holes in the panel and match drilled them through the angles to #27 for #6 screws.
With that done, I decided to get to work on the AFS EFIS screen trays. Because I want mininal spacing between the screens and other stuff, I had to make a number of modifications to the tray flanges to get everything to fit. Once that was done, and the trays deburred, I laid out rivet holes, drilled them, then match drilled them to the panel.
For those following my progress, I'm jumping around a lot, including work on the Upper Fuselage & Cabin as well as the Canopy.