Hey there Ian,
the electrical system is based on a so-called 'Z diagram' from Bob Nuckolls' Aeroelectric connection website (
http://www.aeroelectric.com/). Bob has been wiring aircraft for years and his approach to things is quite scientific. For example, he likes to use fast-on (male and female blade, crimped) terminals and connections as opposed to screwed ones. One classic argument against them is that g forces might pull them off. Bob did some tests and worked out that you would need to pull around 200 G to do that, in which case electrical issues would be the last of your problems...
As an electrical engineer Bob's arguements made a lot of sense to me so I have used them all over.
Anyway, I used a modified Z16 diagram for the Sling. The part that M&J were unsure of is that, right after the battery, there is a dirty great solenoid that connects the entire system to the battery. There is a short (5-7cm) thick bit of wire between the battery and this soleniod which is (almost) the only thing that will be live if you switch off the DC Master, or if the solenoid fails. This is what worried them- what if the soleniod fails? Well, firstly, its quite a special solenoid, oversized for the job and specially constructed by considering failures of other similar devices- as solenoids go this is a Rolls. Secondly, its position is important; if there is any electrical fault/ fire switching the DC MAster off immediately isolates the electrical system, except for that little piece of thick wire.
Inthe case that you do need to swtich the DC Master off there is a small wire that is directly connected to the battery that feeds a switch called the 'E-Bus Alt Feed'. This provides power to vital instruments only so that the flight can continue if that wire is still intact. It is in turn protected from fault by a device called a fusible link.
The whole system is carefully thought out with the idea that no single failure should make you land; you 'step back' to the E-Bus and the battery then should have enough life to get you down safely at an alternate. In this Slings case that would be impossible, so I was very careful with all the wiring, crimping and soldering. The harnass was protected from rubbing whereever I could figure out that it might rub and Tefzel insulated wire was used throughout (this insulation is a teflon derivative and is very tough and also fire/ heat resistant). 95% of the wires got a wire number on either side so that faults could be traced if required.
There are some other clever things as well, such as an overvoltage sensor; the dynamos/ alternators (its actually a dynamo) that are used in the Rotax engines can fail in a mode that increases the voltage rapidly- very unusual but should it occur you will fry all your electronics. The overvoltage will see this fault and immediately disconnect the dynamo, protecting your electronics and allowing you to continue on battery power alone.
I also used shielded wires for some circuits and in one case used a 'home made' shield for two potentially noisy wires - it was fantastic to hear that the system was noise free and in James' words the intercom "is crystal clear- best I've ever heard!" When we flew out with them to Pilanesberg I could hear how clear thier transmission was as well. A 'tab forrest' of fast on male blade connectors was soldered onto a copper plate that provided the negative connection for all the circuits so that there are no ground loops.
I was also most pleased to hear that the storm scope worked well- the antenna for that (very complex with a whole bunch of individually screened twisted pairs in an overall screened cable) was wired one bitterly cold evening at 3am in the Springs hanger as the guys bashed and moved the airframe around getting the wings installed!
The aircraft has an unusual fitting as well- a hooter; this was Mikes idea which he thought might help to scare birds away when flying low level near the coast. That was wired up that same evening a couple of hours earlier - Mike was under the aircraft on his back and the guys were trying to manoevre the wing into its slot (extra layers of paint was making this difficult and they had to keep removing it and sand paint away...). Without thinking I switched the DC Master on and pressed the hooter button. Mike must have been concentrating fiercly because he shot out and up from under the aircraft yelling 'yah, yah, yaaaah!' He had got one heck of a fright. It provided a laugh and a slight warm up for all of us.
Jay
A lone impulse of delight drove to this tumult in the skies...