Here is another reference point for an acceptable panel and
electrical configuration. It is the FAA-approved electrical system used
in Columbia (Cessna 350?). This is
certified for IFR and has been tested for failure modes including lightning
hits on the airframe which contains a metal mesh.
Key points:
1)
Dual
alternators and dual batteries on separate busses.
2)
Diode
fed essential buss with the primary flight display (PFD) on the essential buss
3)
Diode
fed avionics buss
4)
Manual
cross tie switch between busses.
5)
Not
shown: steam gage altimeter, airspeed indicator, and artificial horizon,
electrically driven spinning mass technology.
Note that the use of steam gages reflects Brent’s
recommendation. I put mine right up next to the Chelton’s –
two Chelton screens stacked one atop the other, and to their right, a column of
stream gages.
I am an engineer. I have analysed failures including
elusive computer system failures that took months to track down. I do not
trust computers with my life. Three computers (or five) with voting logic
and exhaustive testing as used in fly by wire airplanes works for me because
the system design assumes failure. The quantitative failure analysis
shows lower risk than getting out of bed. But for our homebuilt airplanes,
I do not trust computers with my life. Period.
I am not suggesting that the Columbia configuration is the BEST. I am suggesting
that more brainpower and failure analysis and experience contributed to this
design that we can come up in our group, and so one should take heed.
I used this as the basis for my electrical power
distribution except that lacking two 60 amp alternators I had to compromise
with a 25 amp alternator on B Bus which carries less of the load. In the
event of a primary alternator failure, it is load shedding time, a check list procedure.
Fortunately there is time to do this with deliberation, unlike the condition of
blank screens and no other data.
Fred, AKA
Captain Tuna, Chicken of the Skies