A methodology for planning your wiring process by Amit Dagan
Home > Articles

After selecting the wiring schematic of your choice - which can be a very simple one or one with multi alternators and batteries (or anything in between) – you are ready for the next stage: planning the actual implementation of the wiring of your project.

To start with, you will have to plan where every component will be attached to the airframe. This includes not only switches, fuses / breakers, electrical instruments (e.g. the encoder, strobe power pack, radios) etc., but also other components that mount in the vicinity of the wires, and might cause constraints in the wire routing, such as flight instruments, vacuum lines, map box, etc.

Once you have everything mapped, and it is a good idea to have a drawing that shows this mapping, go ahead and measure some of the routing distances between the electrical components, taking into account any “obstacles” in the route the wires will follow, and “short cuts”, which are holes through bulkheads through which the wires can pass (via grommets or the likes).

Take these measurements and write them down. For example: Fuselage side skin to wingtip: 10 ft.; Nav antenna to panel: 25 ft.; Electronic ignition box to switch: …you get it. Measurements need not be exact, but round up rather than down.

Next, with your schematic as a reference, take one circuit at a time, and following it sequentially, describe the road it takes, as in the following example:

Fuse box 4 Landing light switch 4 Landing light fixture 4 local ground.

At the end of this line, write down the following data: The AWG# for the wire, the length of the run (this will be easy, now that you have all the separate measurements from the previous step), and finally – the fuse or breaker size, if applicable.

For practical reasons, do all of this in an excel sheet. You will later sort the sheet according to AWG# to determine what lengths you need to order from each size, and sort the sheet according to fuse rating, in order to determine how many fuses of each rating you need to buy.

If you want to be complete, as you “trace” the route of each circuit, you can also note which connectors you will need (butt-splice, ring terminal, female or male fast-on). Add all this information to your spread sheet, and you can make your shopping list even more complete.

A good idea is to add a certain percentage (50?) to every quantity before you order, to allow for mistakes and unforeseeables (I made up that word).

You may find that you already have some of the wires in your schematic, such as the shielded wire for the strobes. That’s OK – add them to your spread sheet too, for completion. This will aid you in the actual process of wiring.

Before you send in your order, take a good look at your tools. You will need good crimpers, for the various wires (stranded, coaxial) and connectors (ring terminals, D-sub pins), hardware, fuses, switches, shrink tube, zip ties – all this can go into your order. I recommend you take a look at www.steinair.com - I found this on-line store to have low prices for high quality products. [I am just a satisfied client passing along a builder’s tip; I have nothing to gain from this reference. A.D.]

Once you have everything you need, follow your list of circuits, and wire them one at a time. As you work your way down the list, mark everything you already wired. This will be a check list, a builders’ log entry, and - as you cross out the lines - a source for immediate satisfaction. If you want to skip a circuit, just make a mark next to it and continue down your list.

That’s basically it – along the way you will learn how to crimp connectors, test wires, heat shrink, solder, mark your wires, and more tricks of the trade.

Here’s a tip: Don’t go routing wires before the airframe part you are going through is permanently riveted. The wire spaghetti behind the instrument panel is going to make riveting very hard. Zip tying everything will help, but plan on doing the wiring after you completed riveting the structure behind the panel.

Here’s another tip: plan ahead and put zip tie mounting bases along the wire routes, for example in the tunnel where your elevator push rod runs, to support the wires that run to the tail.

Cable Tie Mounting Bases

 

 

 

 

 

An example of the excel sheet can be found in http://groups.yahoo.com/group/RV7and7A/files/

The name of the file is “wiringbooksample.xls”. You may need to be a member of this Yahoo group to see it. It is just an example; you will need to modify it to fit your own wiring needs.

Wires Spaghetti – Yummy?!