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1. 07:00 AM - Re: 2 alternators and 3 questions (Robert L. Nuckolls, III)
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| Subject: | Re: 2 alternators and 3 questions |
>
> Recommend you consider a Z-12 style installation. Leave
> the 17A alternator OFF unless needed during anticipated
> icing conditions . . . another condition that should
> be vanishingly rare -OR- failure of the SD-20.
> You're not going to experience dual alternator failure
> on ANY mission . . . energy rationing with
> an E-bus adds no value.
Have you conducted an electrical load analysis
by flight condition? There are forms that
assist in organizing the data available
at https://tinyurl.com/9rt6ymn
Included are some exemplar spread sheets
uploaded by various List members over
the years. I did notice that one of
the .xls spread sheets shows exterior
lighting as a running load coincident
with pitot heat.
My instructors taught that exterior
lights be turned off while in clouds. The
combination of variable reflection off passing
clouds combined with flashing of the
strobe is distracting and can induce
vertigo . . . I've experienced it
first hand.
Your RUNNING loads do not include
landing lights (unless you have a wig-wag
system or other recognition assist),
trims, landing gear or flap motors,
transmitter draws, etc. Just the steady
state running loads are used to evaluate
alternator adequacy and in some cases,
battery supported E-bus operations.
It may be that a well sorted
load analysis will mitigate concerns
for alternator adequacy. It also
helps you define what switches should
be ON and which ones OFF in the various
flight conditions. I suspect that your
suite of alternators will be shown
to be entirely adequate to all anticipated
missions . . . especially if your
exterior lights are all LED.
20 years ago the most energy hungry
system on the airplane was position
lights . . . 2A per bulb x 3 bulbs x
duration of flight. Xenon flash
strobes are way up there too. No longer the
case.
In your case, it seems likely that
a Z12 architecture with the PM alternator
as "standby" is possible . . . crunching
the numbers will confirm/deny that
assumption.
Bob . . .
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