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Actually, Tom, in that particular incident - a
second battery would have only enabled me to fly too far away from the only
safe airport to make a return and dead stick into. IF I
had realized the root cause (a switch accidently put in the wrong position) then
one battery would have worked just as well as two {:>).
Having said that, I certainly would not try to get anyone
to change their mind about using two batteries. . Some folks would not
feel comfortable even with two batteries - but, would add a second alternator,
etc. So, you have to think through your scenarios, the risk involved
and your personal risk tolerance. Yes, Bob now has several good electrical
designs - for just about any kind of power system you could come up with.
Back in 1992, I had never heard of Aeroelectric or Bob.
But, since my previous engine out almost 5 years previous
had been fuel related and the engine was sputtering in a similar manner - my
diagnostic side of the brain got locked in to searching for a fuel
problem (again) - but even switching tanks did no good - because, this time the
"fuel problem" was a decreasing electrical power. This incident clearly
pointed out the need for an emergency check list that involved checking both
fuel AND electrical systems. Coming up with one in your head with the
engine sputtering is not recommended {:>)
Contributing factors were two early design decisions that
on hindsight revealed shortcomings.
One was an electrical system design that permitted my
voltmeter to keep showing me the 13.8 volts being generated by the alternator
while the battery voltage was steadly decreasing. Yes, I had a low-voltage
light right in front of my eyes - but, it was wired into the alternator powered
circuit - so never showed low voltage because the alternator voltage was fine -
up to the point the relay released.
Now, had it occurred to me I
might have an electrical problem - and switched the volt meter to the battery
(instead of alternator) AND had thought to observe it, I would have seen the
battery voltage decreasing and that MIGHT have got me looking for an electrical
problem rather than a fuel problem. But, when you get your head locked
into one focus - and you truly have mental blinders on, NOT GOOD!
The second design deficiency was that the relay
holding the alternator On-Line was provided current solely by the battery
- so guess what happened when the battery juice got too low to hold the
alternator on-line? Right "CLACK!!!!!" followed immediately by all
lights, radios, LEDS, panel going dark. It gets even lonelier when the
lights go out. Had I two batteries - all of this would have happened
further from my emergency airport in Salem, Al.
No, I have not added the second battery back in after the
incident - because in my particular case, the incident had nothing to do
with one battery vs two battery - it was a case of a mis-positioned switch
which the pilot never recognized was the cause - until later on the ground,
cleaning off the seat cushion. The corrective action was to put a switch
guard over that particular switch so it could NOT be accidently toggled
incorrectly AND rewire my relay so that a dead battery would no longer
prevent my system from using the power of a perfectly good
alternator.
But, this is just my perspective - provided for anyone to
glean what they wish from it - if that is two batteries, two alternators or what
have you, then as always in this hobby, that is up to individual
choice.
Just don't make the same dumb mistakes I
made, we know how those turned out - advance the state of the art and make
NEW mistakes {:>)
Oh, yes, the switch I accidently activated (I think I
probably hit it with my foot getting out of the aircraft at the previous
refueling stop) was one that enabled me to detach my battery from the
alternator. The thought at design time was that if my alternator ran-away
with high voltage, I could isolate the battery from the alternator thereby
preventing the battery from overheating/boiling and get to an emergency landing
on battery power alone. Seemed like a good idea at the time.
Ed
Sent: Monday, August 22, 2011 12:35 PM
Subject: [FlyRotary] Re: Batteries
Joe,
Which Bob Knuckles system? Z19?
I realize Ed is happy with one battery, but I like two
batteries. The THUNK of relays all popping open and the
realization of "I turned off the alternator, and voltage dropped
way too low.... followed with LAND NOW!" would have convinced Ed to
have put the second battery back in! It sure got my attention on why two
batteries is a good thing!(Great Story, but I'll let Ed tell
it!)
So two batteries, and a BIG RED LIGHT with "low voltage" will go on
my panel.
I did the spread sheet with 17AH batteries and
flying time. Add in Night, and no place to easily land.... two
batties seem like a good trade off. My biggest shock was the
FORD style contactor needed 1Amp draw to remain closed. Shutting down
non essential, but leaving contactors, PDF, ECU and
coils.... System draw is around 15 Amps. 17AH implies
you'd have an hour, but at 15Amp draw... more like 30-40 minutes, hence two
batteries as 1 hour flying time makes finding a landing strip a
little easier.
Tom
From: Ed Anderson
<eanderson@carolina.rr.com>
To: Rotary motors in aircraft
<flyrotary@lancaironline.net>
Sent: Monday, August 22, 2011 11:20
AM
Subject: [FlyRotary] Re:
Batteries
Joe, I started out using two Concord 25AH RGB each
weighing 22 lbs for a total of over 44 lbs of battery (some joked I could get
home by using the start to crank the prop {:>)) ! I then transition to
two Odyssey PC-680 17AH batteries each weighing 14 lbs for a total of 28
lbs. Then after 6 years of flying with two batteries and never using the
second one - except to help crank on a cold morning, I removed one of
them. Have now been flying for over 4-5 years with one Odyssey
14lbs. I swap it out every two
years. Ed -------------------------------------------------- From:
< jskmberki@windstream.net> Sent:
Monday, August 22, 2011 11:59 AM To: "Rotary motors in aircraft" < flyrotary@lancaironline.net> Subject:
[FlyRotary] Batteries > What size an type of batteries are required
for the rotary? I am leaning toward using 2 batteries and use Bob Nuckols
system. Thanks for any help. > > Joe Berki > Limo
EZ > > -- > Homepage: http://www.flyrotary.com/> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
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