Hi Jon,
Here are my thoughts regarding standard power and ignition switches.
First, recognize that you are talking about four separate circuits here:
1) Master Buss Contactor power
2) Alternator Field power
3) Magneto Grounds
4) Starter Contactor
In commercial light aircraft, these are usually grouped into two physical switch
units. The standard keyed, rotary ignition (plus starter) switch is extremely
robust and rugged and very unlikely to fail as befits a life-safety control.
It is also quite compact in terms of panel space when compared with your
proposal
of replacing it with three separate switches, which if they are small will
have minute contact areas compared with the big rotary. Small contact areas
= short service life. The advantage to your proposal is possibly reduction in
price and a minute advantage in weight. Just because Rotax draws the ignition
circuit as two separate switches, does not imply that they do not favor standard
aviation practice, as opposite to standard snowmobile practice. As for
reliability,
consider the relative reliability of three hobbyist grade switches for
ignition/start vs a "bulletproof" AN spec'd part. In my Europa, I have a Bendix
rotary plus a separate push button starter switch. The duty cycle on the
start button is minute, but I have selected a part with can easily handle the
800 mA start Contactor load.
The two power contractors are usually controlled by single pole on-off switches
which can vary in form factor, i.e., bat / toggle, rocker, etc. In my PA-22,
there are no contactors (Mr Piper was cheap). In this case the Master Power
switch
is On-Off-On, in case one side of the switch fails. Back to the standard
arrangement: It is usually thought to be convenient to semi-gang them since
except for very trouble shooting they operate together.
For clarification, there is no such thing as a "standard pole" switch. The term
pole refers to the number of circuits controlled by the switch , eg, one pole,
double pole, 11-pole.
I hope this helps set out the design issues for this part of panel design.
--------
Ira N224XS
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