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Ceengland
Joined: 11 Oct 2020
Posts: 379
Location: MS
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 Posted: Thu Jun 08, 2023 1:45 pm Post subject: Z101 switch state question: engine and main bus shutdown |
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On Thu, Jun 8, 2023 at 1:48 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
Looking at Z-101, The aux alternator control is not on the aux bus, but gets
powered by the battery bus as jcohen stated in a separate thread. However
the aux alternator and aux bus are both controlled by one switch (separate
halves of a double pole switch). Evidently the thinking is that if the primary
alternator fails, then the pilot will want both the aux bus and the aux
alternator turned on. Having one double pole switch control both functions
eliminates one switch on the panel. However, what if there is smoke in the
cockpit from a suspected electrical failure. Wouldn't the pilot want to shut off
both the battery contactor and the aux bus relay? But what if he wants the
aux alternator to keep running to power the engine bus? In an emergency,
the pilot's brain quits working. And so the simpler, the better. The pilot won't
remember if the switch needs to be in the middle or fully up. I suggest two
independent switches, one for aux alternator and one for aux bus.
--------
Joe Gores
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As drawn, it's a progressive switch, so you can't get aux alt without aux bus coming up first.
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Ceengland
Joined: 11 Oct 2020
Posts: 379
Location: MS
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| Posted: Fri Jun 09, 2023 9:35 am Post subject: Z101 switch state question: engine and main bus shutdown |
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On 6/9/2023 10:45 AM, Robert L. Nuckolls, III wrote:
| Quote: | | Quote: | I suggest two
independent switches, one for aux alternator and one for aux bus.
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Under what condition would one wish to have independent
control of battery and alternator that drives it? And
how would one recognize and respond to that condition
in flight?
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Bob,
For me, the critical factor here is not independent control of the battery; it's that the aux alternator is effectively playing the role of the internal generation system of a magneto; supplying electrical energy to the engine, even when the entirety of the airframe is made electrically 'cold'. As drawn in Z101:
[img]cid:part1.1lZm8pcj.XF0vCUg4(at)gmail.com[/img]
the aux alt cannot be working unless the aux bus is 'hot'. So, if we make the airframe 'cold', we're left with the battery running the high current-required engine control/injection system.
My choice on my project was to have both the output and the control source tied to the *engine* bus, so if muscle memory causes me to shut down the airframe in an emergency, I can react in the same way that I trained in old mag/carb aircraft. This leaves the aux alt supplying current to the engine bus.
Running an automotive style high pressure fuel injection system/computer/ignition places significantly higher demands on the electrical system, making battery-only operation a poor choice if there's any way to avoid it. Real world in-flight tests using a good-condition PC680 has demonstrated a max endurance of about 40 minutes of battery-only operation, even if the rest of the airframe loads are minimal. Reading the PC680 capacity specs aligns with real-world experience. Not acceptable, when it's so easy to work around it.
FWIW,
Charlie
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Ceengland
Joined: 11 Oct 2020
Posts: 379
Location: MS
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| Posted: Thu Jun 15, 2023 11:32 am Post subject: Z101 switch state question: engine and main bus shutdown |
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On Tue, Jun 13, 2023 at 3:28 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | | Quote: | Bob,
For me, the critical factor here is not independent control of the battery; it's that the aux alternator is effectively playing the role of the internal generation system of a magneto; supplying electrical energy to the engine, even when the entirety of the airframe is made electrically 'cold'. As drawn in Z101: |
What accessories will be fed from your
proposed aux bus loads that you would
not want to power in combination with
keeping the engine running?
Electrically induced smoke in cockpit is
an exceedingly tiny risk. So aside from
finding yourself on short-final-to-the-rocks,
when would you expect to want the electrical
system completely 'cold'? This condition
would call for the engine to be shut down
as well.
Muscle memory? When did this replace a
well conceived and practiced check
list? When faced with a need to reduce
energy consumption in a Z101 architecture,
I would think that line item 1 would be to
switch ENGINE BUS ALTERNATE source feeder ON.
Item 2 would be to switch AUX BUS ALT FEEDER
and AUX ALTERNATOR to ON. 3. Set master switch
to OFF to kill any potential main alternator field
drain and eliminate battery contactor drain.
snipped
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Muscle memory (or no memory at all) tends to replace just about everything if we're stressed. 
I don't necessarily disagree with any of the technical points, but most of us are going to revert to decades-old training & practices when we're not absolutely certain what we need to do. And beyond that, I know of a real-world case of someone running an alternative engine to electrical exhaustion when his alternator switch got bumped off. Obviously that should never happen, but moving to an alternative engine after decades of flying mags makes it easier to overlook stuff that wouldn't have mattered with a standard engine configuration.
Different strokes, I suppose.
Charlie
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