19-01: Wing Systems Wiring - Overview / Shop Practices

Before the bottom wing skins went on, i wanted to get as much wiring into the wing as i could, based on known equipment, as well as some assumptions. 

Known Equipment includes:

• Fuel Senders and ground in both wings
• Wiring for stall warning in left wing (however, i have not installed the stall warning vane or opened the hole in the leading edge)
• A VHF NAV antenna in the left wingtip
• A heated pitot tube in the right wing, with a sense wire in case i went with the version utilising a control box. 
• Ray Allen Trim Servo in the right wing

While, some assumptions include:

• Wiring for the FlyLeds Original Wing tip lights kit (nav and strobe lights)
• Wiring for the FlyLeds 4 spot combo light - 3/4 of the lights in each wing to be used as landing lights, and 1/4 as a taxi light (switched separately)
• Garmin GMU11 Magnetometer wiring in the left wing (at the ADAHRS mount location), including canbus wiring out and back to the unit
• Garmin GSA28 Roll Servo in the right wing including the canbus termination. This includes a wire for the additional RS232 backup data path used for certain AFCS controllers (but may not ended up being needed). 
• In addition, there is a hole in the left wing for a temperature probe (but no wiring installed for this). 

The AP Roll Servo RS232 data, the pitot sense wire and the stall warning wire are bundled in such a way they can be removed if not needed in the long run. 

PPPPP

To make sure i had everything sorted, i have 2 methods. Firstly, i am using the KiCAD software program to keep a proper schematic of the planned and installed system. Secondly, i am using an Excel based "Wire Book" which essentially tracks each wire or group of wires, and is used to work out how much of each type / color of wire to order, as well as maximum lengths (for voltage drop). I also plan out the circuit breakers and load / wire size which would be required for each device.

For clarity, i am using the term "cable" to mean a multi conductor cable, which may be shielded or just jacketed. A "wire" is either a single standalone wire, or one of the conductors in a "cable".  

As an example, lets look at a single cable - 'ATRIM PWR" - the power for the trim motor, which runs to the GSA28 Roll Servo:

In this case, this cable is a single 2 core shielded cable. It contains 2 wires, a white one and a white/blue stripe one. In this installation, the shield is left floating at the roll servo end (as indicated by the oval circle). The "WB" indicates that the wire has been logged into the Wire Book, and the "I" symbol indicates that the wire has been physically installed in the airframe.

Here you can see how the wire "ATRIM PWR" is routed through a CPC connector at the wing route. Again the shield is left floating in this case, and it would use pins 15 / 16 on the connector. The triangular symbols "ATRIM_PWR_1" etc allow the wire to be traced to another sheet in the schematic. In this case the "FR" - Fuse Right sheet. You can then trace them all the way to their source.

And so it went for all the installed equipment. Each device was wired in the software, then transferred to the Wire Book. I could then work out the approximate path of the wire, the correct gauge for the current load, it's proposed length and check the voltage drop was ok. I could then order the wire.

Here is the left wing schematic - as installed

Here is the right wing schematic - as installed

Planning like this also made me realise that i would have wires which were too large to fit in a standard dsub pin - i would need to have a series 2 CPC connector (for the smaller wires), and a series 1 CPC for the larger wires - the pins for these can carry up to 13 amps. The pins themselves are of 2 types - one for 14-18AWG and one for 20-24AWG. So you need the right pin for the connector, and the right pin for the gauge of the wire! 

This plethora of connector options was making my head hurt, so i did a little research and came up with a master connector reference document. This give all the correct part numbers for all the pins and connectors in a handy reference, including DSub, CPC and Deutsch, as well as a reference for the crimp terminals and BNC connectors. The part numbers listed are for digikey. Female connectors were used on the aircraft power source side - so when a device is disconnected, there are no live bare male pins. 

Installing the Wires

I used the KiCAD software to install the wires, going wire by wire. I also referred to my previous planning on Wing Systems wire routing. Each wire received labels as per the schematic - for instance one larger label would be "ATRIM PWR" on the jacket of the cable, then each wire inside the cable got an individual label "ATRIM PWR 1" etc. This worked tremendously well, and make easy work for pinning connectors later. I used a Rhino 5200 label printing device, with 6mm heat shrink tube (for single wires) and 9 or 12 mm tube for larger wires.

Here is an example of the CPC Series 1 (Type III) pins - which can handle up to 13 amps. There are actually 2 different pin types here! (purple stripe is 14-18 AWG, and yellow is 20-24 AWG)

Where a connector could be pinned now (such as the aileron trim servo motor) the wires were pinned and terminated in a connector. Where the device was not present (such as lights, magnetometer or roll servo) the wires were left with extra length. 

For the trim i used a 6 place Deutsch DTM connector.

Shield Terminations

Where a cable needed a shield termination, this was done as per the Garmin recommended "Quick Term" method. This method is used when a shield needs to be carried through a connector, or where a shield needs to be terminated to a connector backshell. These are shown in a couple of ways in the wiring schematics. 

 

The shield is terminated with a wire which loops backward from the solder sleeve, loops around and would have a ring terminal crimped on the end to be screwed onto the connector backshell. 

In this case, the wire from the shield termination normally goes out the front of the solder sleeve, and had a pin crimped on the end to carry through the connector, but in some cases where there isn't room it comes out the back of the solder sleeve and loops to the pin on the connector.

In this case, the shield is left "floating" - i.e. the braid is cut flush with the jacket and a piece of heat shrink is used to secure it. 

Before doing a real shield termination i had a couple of practices, including making up a test article. 

I used a couple of different sized solder sleeves - both are suitable, but the larger one is easier to slide on without disrupting the wire wraps. It also has a little more solder. 

I sued Raychem solder sleeves i purchased from Stein. 

The complete a termination, the first step is to trim off the jacket about 2" down from the end. It is better to do it longer, then trim the final wires to size. This exposes the inner braided shield. 

You then hold the shield around 1/2" from the end of the jacket and work it down to create a "mushroom". The mushroom is then trimmed off to leave about 1/2" of exposed shield braid. You then gently fold the shield braid back over the jacket. 

Here you can see the "mushroom"

Cutting off the mushroom. 

Here the shield braid has been gently folded back over the jacket.

Another image of how the shield is folder back over the jacket. 

You then need to connect a shield drain wire - so you can terminate the shield appropriately as per the schematic. To make this wire, i use the same gauge as the wires inside the cable, and strip it fairly long - about 3/4". I then untwist the wires, and fan then out into a flat pattern. This can then be bent 90 degrees to the wire, and wrapped around the shield/jacket to form a mechanical connection. 

Here the shield drain wire is fanned out..

And is wrapped tightly around the shield and the braid. 

Finally, the solder sleeve is installed so the ring of the solder is right over the wire wrap. Heat is them applied - the sleeve shrinks, the glue at each end melts out and you continue heating until you see the solder flow nicely into the joint. 

Solder sleeve prior to shrinking.

This is what a completed termination looks like. 

Here's a video showing how long it takes for the solder sleeve to melt - you really need to see the solder go shiny and flow into the wires.

BNC Coax Crimping

In the left wing i have run a RG400 coax line with a connector at the wing root, and a bulkhead connector at the tip route, so connect the DIY Archer VHF NAV Antenna

This was my first time making up a BNC - and with a bit of help from the Steinair BNC Video i was able to get it done with only one wasted connector! Why don't they give you more than one centre pin with each connector! The Stein COAX stripping guide was also invaluable.

First is to trim 3/8" down and remove the outer jacket and shield material.

Trimmed 3/8"

Next is to remove the jacket only (and leave the shield) down to 3/4" from the end (3/8" more than the last cut)

You then remove some of the centre insulation so the pin can fit on the end of the centre conductor.

A tiny gap should be seen at the end of the pin (like a DSub pin). You then crimp this pin in place.

Slide on the connector (don't forget the crimp sleeve first!). The shield goes on the outside of the body extension piece. 

You then crimp the body crimp to attach the shield to the connector. I also added a piece of heatshrink over the crimp which also served as the wire label.

I used these jaws in my ratchet crimper to do the job. 

At the end, it is good practice to get a multi-meter and check the connector. The centre pin should be totally isolated from the connector body. 

And i only lost one connector in the learning process!

Bundling / Routing Bundles

Once all the wires for each device were run, i then used wax wire lacing tape to lace the bundles together in a neat fashion. I tried to 'comb' the wires such that they were all running neatly and parallel to each other. I used the lacing tape to hold the bundles where there was an access panel - just in case i ever needed to cut the ties and remove a wire from the bundle i didn't have ties which were inaccessible. 

Where a bundle might have contacted a piece of the airframe, i used Nylon spiwrap around the bundle. I made sure each bundle was long enough to reach out of an access hole in order to attach the connectors at a later date - and this necessitated some 'service loops' in a couple of locations, such as the wingtip lighting bundle and the GSA28 roll servo bundle. 

In some cases i wanted to be able to secure the bundles to the structure, so i drilled a #30 hole, and attached a nylon cable tie mounting clip such as these. I then used genuine TyWrap branded cable ties to secure the bundle. Where the bundle was too thin to be held properly, i used a couple of wraps of self fusing silicone tape. In some places where i did not want to drill a hole (such as through the spar), i used a stick on cable tie mounting base such as the Hellerman Tyton 151-01557 MB3APT-I-PA66-BK.

Here as some general pictures of the bundling and lacing. The pink string is some builders string i have secured into the wings, in case i need to pull any wires through at a later date.

Landing light wire bundle (twisted 2 x power and 1 x ground)

The GSA28 servo wire bundle - ready for a connector. There was no room here for a service loop, so it is made at the next access hatch down the wing. 

Here is the service loop for the GSA28 rolls servo bundle - this was secured using a stick on mounting base.

A Deutsch DTM connector was used for the trim power / trim position bundle.

Here spiwrap was used to protect the bundle, and a Pclamp (ADEL clamp) used to secure the bundle away from the aileron controls.

The left wing fuel quantity and stall warning wires were routed so they came out of the last grommet with the other low power / data wires to be pinned through the CPC series 2 connector (dsub pins)

This is the magnetometer bundle in the left wing - i used a cable tie mount and some sprwrap to protect the bundle. It is of sufficient length that the cable tie can be cut and the bundle moved out of the access hatch for pinning to a Garmin connector later.

I used a P-Clamp (ADEL clamp) to make sure this bundle would never interfere with the aileron bellcrank.

The large service loop and cable tie mount for the wing tip lighting. 

For the pitot tube, there was some wiring and also the pneumatic tubing which needed to be secured. I decided to remove a bolt from one of the fuel tank attach zees and make up a small aluminium sheet bracket which i could then rivet a cable tie mount clip. I thought this was a lot more secure than a stick on one. The sheet used was the same thickness as the washer it replaced. I used 'handshake' connectors for the pitot heat power and ground and included a service loop. These wires should make it out of the pitot mast and i can connect the pitot tube from outside. Then it is just a case of using a single cable tie to secure it to the homemade clip through the adjacent access panel. The pneumatic tubes will be connected as per the diagrams from Stein below. 

 

Not wanting to use any teflon tape, i used this sealant on the NPT threads

The final install. The handshake connectors will be connected outside the airframe and then covered in heatshrink. I can then pull the bundle inside as i install the pitot tube, and reaching in from the access panels on either side, make up the service loop and secure it using the cable tie to the homemade clip.

Here you can see i used some 'caterpillar grommet' on the lightening hole, so there is no chafing of the pneumatic tubes or wires.

The homemade clip.

Making sure of edge distance for the holes.

Wing Root Connectors

As mentioned, i had planned 2 types of connectors at the wing roots. These are a low power (DSub pin) CPC Series 2 connector, and a higher power (13 amps, Type III pin) CPC Series 1 connector. I have used "reverse sex" connectors so i can use male pins on the wing side, and on the fuselage side i will used a female flange mounted connector screwed or perhaps riveted to the side of the fuselage. 

These connectors were checked and rechecked and pinned according to the schematic. Once a connector was pinned, the schematic was labelled with a "P" symbol. 

The "P" symbol means the connector was pinned for this wire.

Left wing connectors

Right Wing Connectors

A couple of items such as the landing lights and the pitot heat were grounded at the wing root. To do this, i installed a nutplate for a #8 screw, cleaned off the paint, and used some washers and a star washer to ensure a good ground. I will have to check later that the wing is grounded to the fuselage properly, or run a grounding strap. 

Here you can see a couple of the grounds leaving the bundle for the airframe. 

As depicted in the schematic

Now all the wiring is in place, i can move onto the trim system and bottom wing skins.