Bob and Karen Brown's Airplane Building Project


 
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WIRING

When I started this project, one of my main goals was to learn about the theory, design and fabrication of aircraft electrical systems.  Early on, I heard about Bob Nuckolls.  Bob has spent his lifetime in the trenches working for all the major aircraft manufacturers in Wichita.  He wrote a book to address the needs of the OBAM (Owner Built and Maintained) Experimental Aircraft community which has become the bible for that segment of aviation.  This aircraft is wired per Bob Nuckoll's philosophies as explained in that book, the "TheAeroelectric Connection".  As part of EAA Chapter 292, we organized a visit by Bob during 2005.

The electrical system on this aircraft is simple.  The plane has a 40 amp B&C Alternator and a voltage regulator from B&C which utilizes "crowbar" overvoltage protection.  There are 3 busses, a battery bus, which has just two fuses, one to the 12V Plug and the other to the E-Bus or Endurance Bus.  The Endurance bus has everything on it that I would "comfortably use to terminate a flight should there be an electrical malfunction".  The third bus is the "Main" bus and has everything else on it.  There is a switch on the panel that closes a "valve" called a Schottky diode, which allows power to flow directly from the battery to the E-Bus, but prevents power from going back into the Main bus.

Few breakers are used in this plane.  Circuit protection is achieved using fuseblocks like you might see on a car.

The basic design criteria for this craft: Failure of any electro whizzy installed in this aircraft will not affect the safe outcome of flight.  In other words should any circuit fail, should any switch fail, we can still fly safely to the nearest airport and land without concern.  That's the goal.  We will reset no breaker in flight, we will only use them for notification of device failure or (in the case of our electronic ignitions) as switches.

While we're on the subject of electronic ignitions, this airplane utilizes dual P-Mag ignitions.  Check 'em out at www.emagair.com.  P-Mag ignitions are a machined aluminum case that bolts to the engine where you'd normally bolt a magneto.  The similarity ends there.  Inside the P-Mag, and geared to the engine, is a permanent magnet alternator which generates it's own power to "send the sparks to the plugs" and control engine timing...like in your car.  The neat thing is that the P-Mag is also wired to the aircraft electrical system, but would only use power from your electrical system if it's internal alternator were to fail.  So basically, by installing two P-Mags, you have double redundancy (dual ignition systems each with dual operational modes).  As Howard Hughes said..."it's the wave of the future" for aircraft electrical systems in light aircraft.  That's my two cents...

 
 (Click any picture for a larger view with an explanation.)
Six Pin Plug Wire Tying Spool.  This is waxed dacron thread.  I learned to tie this stuff from Bob Nuckolls (check out Aeroelectric Connection) and now I love it.  It tensions well, gives the wire loom a nice feel.  I put these on every inch or two in the main wiring harness.  One roll will wire...a hundred airplanes.  Not really, but there's a LOT of this stuff on one spool. Wiring Kit from Vans.  If I had to do this over again, I'd just buy the stuff from Stein Air... Panduit Guns- If you've never used these, you'll wonder where they were all your life.  You set the tension by adjusting the 3 position lever at the bottome.  The tie-wrap slips into the side (from any position) and you simply pull the lever once or twice and SNIP!  The tie wrap is tensioned perfectly and cut off smoothly.  Yeah Baby! Wire Crimpers.  The yellow handled one uses a ratcheting action and crimps 12-22 ga wire and also crimps the portion of the terminal that grips the insulation.  The green handled crimpers are for antenna coax cable.  The red handled crimper is for machine pins...tiny wire stuff.  I bought these from B&C but lots of outfits sell them.  They are MUCH better than what you'll find in your local auto parts store...
Copper Bars I made from .063 copper that connect the battery contactor and the starter contactor. Battery Box constructed of steel, with lightening holes cut out using a holesaw.  Van's sells this kit. Main Bus and E-Bus.  The main bus is hinged and provides access to the (smaller) Endurance bus.  See AeroElectric Connection for the full story on this setup. Battery Bus.  My battery bus only has two circuits on it, the 12V accessory plug and the Endurance bus. Battery Contactor and Starter Solenoid.  They look pretty lonesome mounted here on the firewall...they'll have lots of company pretty soon.
Ground Block on the cockpit side of the firewall.  In later photos, you'll see this bus almost full!  I mapped it out and each wire is labeled in case I need to troubleshoot a circuit down the road. Forward Side of Ground Block.  This is the engine side.  There are just a few (like three...) grounds that connect here. Electrical Switches.  Because of poor planning on my part, I ended up mounting the switches in a horizontal position.  Some of you may say..."that's against convention".  I don't care, it works fine and looks fine.  I wouldn't do it over again this way, but I'm happy with the way it turned out.  Label label label.  This could have been prevented by better measurement during panel layout...I was guessing on the size and clearance requirements of the switches.  Don't do it that way. Test Wiring a 2—10 Switch Twelve Volt Power Plug installed on the right side of the panel to power the latest handheld electrowhizzy gadget.  There will be a RAM ball mount just to the left of this that will secure the handheld ...
Brackets for ACS 2002 Engine Monitor Box.  This photo was taken looking downward and shows the ground bus to the right, mounted with a through-bolt to the firewall. ACS 2002 Engine Monitor Mount.  This is a side view of the ACS 2000 engine monitor analog box.  The battery bus is visible to the left. Looking Up at the ACS 2002 Box.  This was a trial fit.  I took it out so I could run wires, etc and put it in just before I attached all the various sensor wires to it.  I left a long pigtail above it to allow it to be removed and lowered for service/maintenance. Strobe Power Mount sits under the floor of the baggage area. ELT Mounting Bracket I fab'd from some plate and some angles. It's riveted to the belly behind the baggage bulkhead.
E.L.T. Wire Routing.  The ELT antenna will mount on a bulkhead fitting to a small bracket which attaches to the upper longeron on the right side.  The antenna is an 8" rubber antenna. Installed ELT in area behind baggage bulkhead. Here I am running elevator trim wiring. The white wire is the cable with the wires that run the trim motor and send the signal back to the trim position indicator. Elevator Trim Plug Wiring.  The first time you work with these little suckers it will be a little frustrating.  I really to recommend cutting off a piece of the cable and practicing your connections...
Crimping Teeny Tiny Pins.  Yes, this sucks.  Buy a real crimper from B&C or elsewhere that crimps a 4-way crimp.  I used these little pins from Radio Shack before I discovered the machined pins from Stein Air...expensive and worth every penny. Pins on Elevator Trim Wires Plug for Elevator Trim Wiring.  This plug was assembled using ideas from the Aeroelectric Connection.  ShoeGoo provides strain relieve to these little wires.  After this set, I put heat shrink tubing over the back of this joing. Fuselage Side of Elevator Trim Plug.  This too was covered with heavy heat shrink tubing once the ShooGoo adhesive set. Elevator Trim Wire Route
Elevator Trim Wire Route Voltage Regulator Installed.  Yeah, this is the first position.  The FAA inspector gave me three good reasons to move it. Wiring for Rudder Strobe Finished Rudder Strobe Acorn Nuts on Tail Strobe
Soldering Battery Cable.  Yeah , it looks like crap...I redid it.  As I said, I wanted to do all this to learn something! View from above the right front inside fuselage area. This shot shows the voltage regulator in its original position. Wires wires everywhere...but they're all labeled. This is the new home for the B&C voltage regulator.  The little green thing below it is the amp transducer from the ACS engine monitor.  Read about the right hand rule in Aeroelectric Connection
This is a shot of the large piece of firesleeve over its metal flange, which is attached to the firewall.  This is the finished view of the wiring passing through the "fireproof" firewall penetration.  The wiring is sleeved in 1600F rated firesleeve (the black stuff) which is in turn sleeved in 2000F rated firesleeve.  The outer sleeve (the red sleeve) is then injected with Firestop2000 caulk and it's all held together with two stainless steel hose clamps. This is a diagram showing how to wire the sticks.  This 24 (or is it 26??) gauge wire is LITTLE.  Soldering it isn't for old geezers.  Just kidding, it's no big deal.  The instructions are very clear, just do a neat job, don't use too much solder at the joints, remember to put your heat shrink pieces on BEFORE you assemble the joint.  Bet you can guess why I give you that advice! This is another shot of some of the wiring diagrams for the sticks.  Ray Allen Company does a good job of simplifying some of the mystery of how all of this works... This is the finished job.  The pilot's side control stick.  There are buttons for push-to talk and up/down trim wired into this stick.  I drilled a hole at the bottom of the stick and inserted a tiny rubber grommet there to protect the wiring where it exits the steel tube.
This is the famous Schottky diode I bought from Eric at Perihelion Design.  I later mounted it in a heat sink and bolted it to a subpanel rib.  Eric has some good products and is a pleasure to do business with.  You may not agree with all his design philosophies...and that's OK.  He is still a reputable guy...I like him.  Subpanel area on right side.  The little black box is the Ray Allen relay that allows you to run the trim switch from either the trim buttons on the stick or using the rocker switch mounted on the panel.  All of this wiring is labeled, but has not yet been secured by lacing. This is a view behind the panel on the pilot's side.  The big black square box there is the Trutrak Attitude Indicator.  It is coupled to the GPS and derives heading information from that.  It also indicates vertical speed and has some warnings if you approach either bad end of the envelope...Also visible here is the back of the Trutrak Altrak altitude hold autopilot and some of the pitot/static tubes.  The cable in the foreground is the actuator for the parking brake. The head sink that the yellow wire loom runs to is the dimmer for the panel lighting and radios.  To the left, below the gray corner brace is the parking brake cable terminus.  The little black box there is the inverter which supplies AC power to the dimmable Lumilite light strip that will be under the glareshield and shining downward onto the panel.  I tested the whole thing in the hangar one night...it is way cool...literally.  The Lumilite strip draws next to no power, puts out no heat and lasts forever.  Perfect.
 
You can see one of the labels I made with the laser printer.  I just print whatever I want in 10pt bold Arius font and slip it into some clear heat shrink, shrink it on with the microtorch and voila!     This is one of the sensor wires to the ACS Analog box.  You have to solder a lead to the shield, then wire that into the "Shield" location for each sensor (EGT's, CHT's, Fuel Flow, Oil pressure, etc...there's lots of this to do and it's tedious, but not difficult.  Think about how you'd get back in there and work on it if you have to...that will either save your bacon or someone elses... Here is the EGT probe wire exiting the number one cylinder's exhaust.  These probes should all be pretty close to the same distance from the exhaust pipe flange.
 
  This shot just shows how I used adel clamps to secure wiring from the EGT/CHT sensors. These are switches in the top center of the panel.  The white labeled one is the wig-wag circuit on the landing lights.  Switch this puppy on while the landing lights are on and they alternate left to right, on an off...or wait, is that right to left??  Hmmm. This is a little teenyweeny diode you install in the trim circuit if you are using the trim rocker switch AND the stick grip switch.  No big deal, Ray Allen comes through with excellent directions on how to wire this thing.  Pay attention to which end the little rings are on...one way valves don't work well if they're not pointed in the right direction! I installed this aluminum with adhesive backing inside the wingtips to protect the fiberglass from heat put off by the 75W halogen lights in there.  I also mounted the landing light as well as the NAV/Strobe unit to a plate I fab'd from .040 aluminum.  I just thought it looked better...Yep, and it cost me about 5 hours more work.  Remember that every time you want to change something.
These are the wires that attach to the back of the Altrak altitude hold control switch. These are the wires that attach to the back of the Altrak altitude hold control switch after some dufus forgot to put the heat shrink on when he soldered them in place the first time.  I sure hope he learned something! Here the strobe cable makes the jump from the tail to the lower rudder fairing.  I'm not too thrilled with this.  We'll see what it does after awhile... I cut my own panel out...it was fun, it was rewarding, it made my heart rate increase every time I came near it with a drill or a saw or a file...but it turned out great.  The first time!  I started by laying out a grid pattern drawn on the panel and measured the location of items as roughed out by my cardboard panel mock up. This shot is looking down from above the forward fuselage area to the analog box for the ACS2002 engine monitor.  The service loop of wire will allow me to lower it should I need to change or adjust connections.  The service loop is secured with bad ass wire ties and is protected from chafing as it passes through the lightening hole in that rib.  The (almost full) ground block is visible to the right.
 
I built my own tray supports from a variety of aluminum angle and flat plate.  I had never done anything like this, so I looked at a few other airplanes and then built mine.  I'm really happy with the way it turned out. This is one way to look at $12,000 dollars worth of electrowhizzies.  Yep, it was sticker shock...   A granite slab makes a dandy spot to solder if you happen to have one laying around.  
         
Back of switch row in upper center of panel. Here are all the items needed to complete the automotive style ignition harness.  The crimpers at right were included in the kit from Emagair. These are the parts necessary to fab the end of each ignition cable.  The P-Mag includes the crimper to assemble this.  I chose the auto plug harness. This is the panel in progress. Another shot of the panel.
     
Right subpanel area showing E-Bus.  The main buss is folded down in this photo. Here is the left side of the panel showing the Angle of Attack display      
         
         
         
         
         

Last edited 13-Jan-2006