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Jeff, (and Scott)
I guess we'll just have to agree to disagree. You still misunderstand
my point. I am NOT saying to fly on without any alternators....as you
point out it is illegal if IFR. I was merely stating that this failure
mode should be used for this exercise in design. Remember, the original
question was a question of design, not of how your fly or FAR's.
I really feel you are stuck in the spam can area of thinking on this
electrical system issue, shown my your comment that a second alternator
should only be used to land. YES, with any spam can system (except
maybe the new Cirrus dual alt dual batt, or the Lancair Columbia 350 all
electric dual alt dual bat) I agree you are totally right, as they are
not designed up to our OBAM standards....an alternator fails, you better
find a place to land, and quick. However, with a system like Bobs
wonderfully designed Z14, losing an alternator still leaves you with a
system (one properly sized alternator for ESS operations and two
batteries with capacity to outlive your fuel) that is better than 90% of
the spam cans flying for the last 50 years. I see this as NO reason for
alarm, nor cancellation of any flight. If you do, please point out how,
as I'm learning a lot from this discussion, and would love to learn
more?
As far as the FAR's, what is required for IFR is listed in part
91.205(d) with item (7) saying: (7) Generator or alternator of adequate
capacity. I still hold that my second alternator meets this
requirement with a way to shed loads or essential buss (both of which I
have). AND I hold that if this happens, the system I am left with of
one alt and two batts is better than just about everything flying.
Hence, I have no reason for concern.
Your comment about "Boeing can't do it" has no bearing on this
discussion. We (fortunately) aren't held to the same silly standards
(or costs of proving our design) that Boeing is, and therefore, we can
develop new and better systems without the level of paperwork, COST, and
government bureaucracy that they have to go through. Last time I
looked, Boeing wasn't developing sytems for small GA aircraft anyway.
Per your hypothetical situation about pressing on after the alternator
failed. First, just so you are clear as you seem to be missed my point,
if BOTH alternators failed, I'm landing. However, I have the knowledge
and confidence in my system to know that if I need to go the full 30
minutes, or even 35 or 40 to get to a safe landing spot, that I have the
capacity to do that. Do you know what your capacity is? Now, if one
alternator failed, yes I would switch to essential buss (flip of two
switches, crossfeed on, alt off, and shed loads from CB's) and press on
with a system that is still better than 90% of those flying and I would
have little concern. All the "bells and whistles" would be off at this
point, so capacity (35A Supplenator) is not an issue. Can you point out
where my concern should be? If so, then 90% of the planes flying should
be concerned every time they take off. If I end up in the "rocks" it
won't be because of my electrical system. Talking to the FAA about my
electrical system would be a non-issue, as my electrical system would
still be better than 90% of whats out there.
You say the second or standby alternator is designed to get you to the
ground. Maybe in your system it is, but in mine and others with Z14, it
is designed to be a totally separate independent system and is NOT just
designed to be standby or a backup. It is always running (not a
standby) and is always prepared to take the loads of the other buss if
necessary. If it where an 8 amp alternator, then yes, you would be
right. However, it's a 35A self exciting alternator that is plenty
capable of running any simple IFR airplane.
Like I said before, my comment was about the DESIGN of the system. It
should be designed so it could go on, in essence, so it will be
overdesigned. As Scott mentioned this morning (and one of the main
reasons for my effort in over-design) usually, you don't know an
alternator has failed until your battery voltage has dropped below 12V
(that's where my light comes on to tell me). At this point, Scott is
correct that you are already at a reduced capacity. I plan to do
extensive testing on exactly what this capacity is (VFR day of coarse),
and I will post the results for everyone to benefit from. Scott is also
correct that most items will only operate down to around 9.5 volts or
so, some less, some more. The Ah ratings of batteries are givin from a
fully charged state down to like 10 volts I believe, so the capacities
are close, but still diminished, as you won't catch the immediate
alternator failure usually. All the better reason to have reserve
capacity.
Again, my comments were about DESIGN, not operation. Also, I asked, but
didn't get an answer about if you know what your reserve capacity is?
---
Shannon Knoepflein <---> kycshann@kyol.net
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