Some interesting opinions here! I like the 5 factors to assess the quality of any system. I am not smart enough to foresee all the practical implications of my design decisions at the design stage, and do not have sufficient time to do all the analysis I could - I need to go fly occasionally. Therefore I try to keep to design ideas published by others who have thought more about the fundamentals than me. But the over riding consideration is a single engine. No point in making the installed systems more than an order of magnitude more reliable than the engine (if we are able to assign numbers to electrical and electronic systems reliability, and also to engine reliability in amateur built aircraft).
To start with a broad purpose statement is helpful, such as
- mostly VFR local flying (1.5 hours flying from home) with one or two longer trips each year (> 5 hour's flying from home), occasional IFR/IMC.
What are the implications of this statement? Operating screw ups away from home will make a vacation a real chore, system design should avoid the need to think too much about system operation. In my experience screw ups often mean a flat battery. In my experience charging systems are the least reliable system on an aircraft, I would like two. (Lead-acid) Batteries are generally reliable if kept charged, or give plenty of warning of their up coming demise.
Having to remember to turn off several switches to prevent a flat battery seems to me to be asking for trouble. I like having a master relay, I also have a bypass switch connecting the bus bar directly to the battery if I want (need) to bypass the master relay. I also have an endurance bus that seemed like a great idea at design time, but actually the volt drop from the bus diode can be a problem for some of the electronics. I probably would not do that again. The ability to turn off all non-essential loads is important so they may be shed if needed. I like having a non-electrically dependent engine as I believe it gives me flexibility.
My conclusion is a twin generator, single battery system meets my needs. In general I am not a fan of back-up batteries due to maintenance overheads, but they add so much flexibility to modern EFISs that I am prepared to tolerate one (or perhaps two depending on equipment selection).
I want to start the engine with just one button. Should the engine quit while airborne (probably because of my mis-handling) I want to press one button to restore the noise. I don't like the idea of having to hold a mom switch while pressing the start button, its too complex, and requires too much dexterity, for my liking.
Currently LiPo batteries and all electric engines are just a little too immature to give me worry free trips away. I'm sure they will improve - or I will become more accepting of their qualities - but at the moment I am prepare to sacrifice some potential performance gains for what I perceive to be peace of mind.
Pete
