Paul Visk wrote:
>> Mark L., I noticed on your wiring schematic on your website you
have a 7 Ahr backup battery. Would you still recommend that size? Is
it large enough to turn the engine over while airborne?I'm at a point
now to where I can pretty much put everything on and do a
weight-n-balance and find out if I need to move my corvair engine
forward to pinpoint my cg.<<
I never intended or expected that little 7Ah battery to start the
engine. It's there mainly as a backup power supply for fuel pump and
ignition system if the rest of the electrical system goes up in smoke.
It's isolated by a diode to keep it from being compromised by a main bus
melt-down. I do test it by starting the engine on it, which also takes
some electrical load off the main battery while it's spinning the engine
over using the main battery.
As a data point, my experience has been that a high compression Corvair
with a 54" prop will not restart in a glide if there is no power applied
to the starter, not even if you point it at the ground and run it up to
Vne. The starter circuit won't be the thing that makes your engine
quit, and it's so simple it's difficult to see how it could fail in
flight unless as a victim of collateral damage. Running out of battery
"juice" due to an alternator failure and not noticing the voltage drop
is probably when you'll find a backup battery the most useful. When you
do notice, you should have some idea of how far you can fly before you
kill the backup battery....to avoid unpleasant surprises. You'd
probably want to head for nearest airport with something like a 7Ah
battery. Your Corvair ignition system probably burns 3A at 3000 RPM,
with another amp going to the fuel pump, but that doesn't mean you can
fly almost 2 hours if you are running purely on the 7Ah battery.
For those who haven't seen it, the electrical system Paul is asking
about is at http://www.n56ml.com/electrical/index.html .
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