Jeff,

 

To your first question on batteries/alternators I have several questions.

1. Are you using magnetos or electronic ignition? If you have dual electronic ignition I consider dual batteries/alternators essential. If you have a single electronic/single mag system then you need to seriously consider what happens if you lose the source to the electronic system?
2. Are you’re instruments all electric or do you have vacuum power backup? If all electric then I would again strongly consider dual batteries/alternators

 

Considering the avionics master I have to ask why you want one. The avionics today are very tough. I don’t consider them necessary. On the other hand, if you have dual power busses, and radios split between them for redundancy, then you need either no avionics master switches or two of them (one for each buss). A single switch is a single point failure.

 

Does your glass panel have an AHRS? If so you may wish to power it from both busses (thru diode isolators). Many of these cannot restart in flight and inadvertent hitting of an avionics master could render your primary flight display useless for the remainder of the flight.

 

These and many others have run through my head and been discussed here many times. I spent many years designing missile test range tracking and safety systems.  It’s not an easy question. First you need to understand how you intend to use your aircraft, and what could happen during failures. Try to write it out if you can to help clarify your expectations. The worst time to figure out how the system should work is in hard IFR when the lights starting to dim.

 

My two cents

 

Paul Bricker

N63PB