8th January 2011 - Firewall and wiring

Having spent ages working out the order to install things in the fuselage I've made a start. I have decided to cover the fuselage on its wheels which means I can do most of the interior fit out and wiring before covering. The biggest puzzle has been the order in which to install the panel, fuel tank and combing in order to make both the install and future maintenance easy and minimise the amount of repeatedly installing and de-installing things during the build. So I'm now committed. The first job was to cover the interior of the firewall with some self adhesive felt material I found. This makes a nice finish and should damp vibration a bit. I tested the material for the impact of both heat and flame and it passed with flying colours - refusing to burn at all and just shrivelling a bit when a 400 degree C heat gun was played on it. The firewall was first screwed to the tabs on the frame and then the major firewall mounted components added. Then the panel with the power distribution unit was temporarily installed. The major power cables were then cut to length and terminated: switched power, unswitched power, earth, starter energise, main contractor energise, alternator field, starter warning, ammeter sense. The last picture shows the power distribution unit. This implements the Z11 schema for a generic light aircraft electrical system as documented in the Aeroelectric connection manual by Bob Nuckolls. The small fuseblock provides unswitched power for the power socket, clock and via a switch emergency power for the endurance bus. The large fuse block is the endurance bus and is powered either by the starter contactor via a diode or the emergency power switch. All essential services will be wired to this (radio, transponder, intercom, etc.) The bus bar connecting the fuses and switches is the main power bus. The two pullable fuses on this are for the alternator field and starter. The four switches are for the fuel pump, the nav lights, the strobes, and the autopilot (a separate switch for this is a mandatory requirement in the UK). The terminal strip along the bottom provides a ready supply of earth connections.

2nd January 2011 - High/Low Voltage warning system

A voltage low warning light is mandatory for all aircraft in the UK. Commercial versions are available but quite expensive so I constructed one. This flashes a warning light slowly when the system voltage drops below 12V and then after a period leaves the light on to avoid being too much of a distraction. It also flashes the light fast if the voltage rises above 15V. In addition the unit outputs the voltage on a opto isolated serial output so it can be read into the system monitor I've also built. The circuit and program is very simple and uses a Picaxe 08M microprocessor to do all the hard work. If you want to copy it and don't need the serial output just omit the optocoupler.

2nd January 2011 - Preparing the fuselage for covering

New years resolutions -
1: Keep the blog up-to-date
2: Do more on the build this year than last.

I haven't done much over the last few months but there is a little to report. I'm getting the fuselage ready for covering which means I want to make sure any internal structures that are going to be difficult to install post-covering are in place (e.g. the static system shown in the first picture) . I also want to avoid a mistake I made on my RV9A build when I painted the interior late in the build which made it tricky to get a reasonable result.

So I have final painted (in white polyurethane ) all tubing which will be exposed in the finished aircraft - door frames, front spar carry through, etc. I've also painted many of the aluminium pieces that will be installed. I'm now waiting on some decent weather to finish spray the fuel tank and to prime the control push rods. These all need installing before covering the fuselage.

I've also trial fit the panel and this has resulted in some mods. First, although I had put the radio at the top of the stack to clear the top of the tank I hadn't left enough clearance for the cross member that runs above the tank. Solving this meant moving the radio and GPS up 1/2" and fabricating a filler panel at the bottom of the stack.


I also realised that the way I had built the power distribution on a tray but with the switches and fuses screwed through the panel would make it very difficult to wire and maintain. So I cut out the panel round the holes for the switches with the router and made a front panel for the power distribution tray with holes cut in this for the fuses and switches. To keep it neat I then also cut out an insert for the hole in the panel so that everything is flush. I programmed the router to cut the insert with a clearance of 0.1mm all round to allow for painting (still to be done). As always I'm amazed at how accurate a MDF homebuilt system can work. The result of this work is that it will now be possible to remove five screws on the front of the panel and then drop the power distribution tray down to replace fuses and make any changes to the wiring.

Third, I had installed a 3-digit seven segment display at the bottom right of the panel. This will be connected to the digital compass I have built for the aircraft. The hole was cut on the CNC router and a red lens cut out to fit inside it. This looks very neat and tidy but unfortunately I had located it 3/16" too low and the display was fouling on the panel support cross member. I solved this by slicing the cross member in half horizontally where the display fits, removing about 2" of the top above the slice and then welding a flat plate cap over the missing section. Once filed and painted this looks fine but it all takes time. The other thing I've been building over the last months is various electronic bits and pieces for the aircraft - more of these in later blogs.