I'd second Steve's questions. I've been worried about this, too, since I'm
worried
that a 914 with an Airmaster prop will
be rather nose-heavy, and thought that a RG battery of the minimum required for
cranking up front with a very
tiny battery in the back for backup might work and possibly save cabling weight.
Redundancy would also be desired
for a motorglider restart. Since I haven't got to this point, either, I thought
I'd throw out some of my findings for comment as well.
I started by asking Bob Ruckolls (Aeroelectric connection). He said:
1. Rotax 912/914 series crank with low power requirements - 0.6KW ( about 50A )
for a few seconds. 8AH RG
batteries will crank a Rotax.
2. 8AH is about all that's needed if you size your battery to allow comfortable
termination of flight (1HR after failure)
with essential electrical loads. And if you load-test your battery
regularly
to avoid suprises
3. A fore/aft dual small battery arrangement probably wouldn't save any weight
in cabling, and the small battery
shouldn't be used for cranking, but would provide desired redundancy for a
914 installation, which is totally
dependent upon electrical power for fuel delivery. An equal-sized dual
battery
arrangement would provide heavy
crank amps but would require heavy cabling, negating the advantage.
I note that in Tech Talk #25, the factory suggested wiring diagram states that
the battery must be 16AH minimum.
I don't see this anywhere in the installation manual. But if this is the case,
pretty much the front battery needs to
be 17AH.
Anyway, I looked at the catalog of batteries on B&C Specialties' Website. In
it,
there are some RG batteries with fairly
amazing AH/weight ratios that might moot the issue. Consider for example their
7.2AH/5 lb or their 20AH/15.3 lb
model. These batteries clock in at 1.44 and 1.31 AH/lb, far above the typical
1.0-1.15 AH/lb. Their 17AH/14 lb model
is not too shabby at 1.21 AH/lb. You could put two 7.2AH in parallel up front
and a third in the back and still probably
break even weight wise over a 17AH up front. If you could stand 15lbs up front,
the 20AH unit seems perfect except for
redundancy. In any case, it seems a bad thing to go with one honking >20AH
battery
since the AH/lb tends to go down
with capacity.
Whatever.
Tony, Bob J, any thoughts?
Shaun
----- Original Message -----
From: Steve Hagar
Subject: Looking down the road at batteries
I am not up to the point to needing any thing yet concerning batteries,
probably
over a year off for this. However I haven't seen much written here about
the dual setup required when runninng the 914 with its electric only fuel pumps.
Of those who have this setup what size battery is being used as the primary
unit
and what size unit is used for redundant or essential bus use? How does this
compare to the size of the single battery used on a 912 Europa. Were both
battery located around the same location?
Thanks for any input.
Steve Hagar
A143
Mesa AZ
--- Steve Hagar
--- hagargs@earthlink.net
|