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Z-19 questions

 
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jonlaury(at)impulse.net
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PostPosted: Fri Mar 17, 2006 11:39 am    Post subject: Z-19 questions Reply with quote

1. Why is there a 7A fuse between the main power distribution bus and the E-bus? The loads on the E bus are all fused.

2. The schematic shows alternate feeds for an ECU and fuel pump. I will have dual Light speed ignition, dual fuel pumps, and one EFI. To accomodate this, do I tap into the upstream legs supplying the dual diode feeds and add another dual diode feed, each, for the 2nd pump and ignition?

3. I want to have a dual feed, from Main & Engine batt. buses, w/circuit breaker to the EFI. Any elegant ideas to do this?

4. The E bus has an alternate feed path off the Main batt bus. Is it overkill to have a feed path from the Engine batt bus?

5. What is the "Auto" function of the Eng/Bat/Auto switch?

6. The fuse for the voltmeter is 1A at the Main Batt bus and 3A at the Eng Batt bus. Is this a typo or is there a reason for the difference?

Thanks,
John


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nuckollsr(at)cox.net
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PostPosted: Sat Mar 18, 2006 9:46 am    Post subject: Z-19 questions Reply with quote

At 11:34 AM 3/17/2006 -0800, you wrote:

Quote:


1. Why is there a 7A fuse between the main power distribution bus and the
E-bus? The loads on the E bus are all fused.

Fuses protect wires. FAA rule of thumb is any wire over 6" is
a candidate for protection. 7A fuse and 16AWG wire sizing
(as are all other fuses and wires) are subject to adjustment
in accordance with appliance choices and bus loadings unique
to your airplane.

Keep in mind that the z-figures are ARCHITECTURE drawings,
they are not instructions on how to wire your airplane.

Quote:
2. The schematic shows alternate feeds for an ECU and fuel pump. I will
have dual Light speed ignition, dual fuel pumps, and one EFI. To
accomodate this, do I tap into the upstream legs supplying the dual diode
feeds and add another dual diode feed, each, for the 2nd pump and ignition?

Stand-alone, dual accessories like ign and fuel pumps
get independent protected (fused) supplies through independent
switches. Only single, critical accessories like your
EFI will benefit from the diode isolated, multiple
feed path illustrated.
Quote:
3. I want to have a dual feed, from Main & Engine batt. buses, w/circuit
breaker to the EFI. Any elegant ideas to do this?

Just like Z-19 shows for engine primary switch. Why circuit breakers?
Quote:
4. The E bus has an alternate feed path off the Main batt bus. Is it
overkill to have a feed path from the Engine batt bus?

Depends on how much "killing" you want to do. We generally
draw the line at accommodating single failures for any given
flight. If you feel better about stacking lots of failures
up and devising a means for dealing with all of them, then
whatever additional alternate operating schemes you wish
to devise are in order.
Quote:
5. What is the "Auto" function of the Eng/Bat/Auto switch?


See http://aeroelectric.com/Catalog/AEC/9005/9005-701B.pdf

Quote:
6. The fuse for the voltmeter is 1A at the Main Batt bus and 3A at the Eng
Batt bus. Is this a typo or is there a reason for the difference?

No reason whatsoever. See item (1) above. Make the fuses/wires
match what YOUR airplane needs.

Bob . . .

< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >


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jonlaury(at)impulse.net
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PostPosted: Sat Mar 18, 2006 11:16 am    Post subject: Z-19 questions Reply with quote

Quote:
3. I want to have a dual feed, from Main & Engine batt. buses, w/circuit
breaker to the EFI. Any elegant ideas to do this?

Just like Z-19 shows for engine primary switch. Why circuit breakers?

Bob,

Thanks for your expanded reply on power feed.

I'm electing to CB the EFI because I only have one EFI. The manufacturer argues that the MTBF of the EFI unit is so many magnitudes greater than the MTBF of a recip engine, that I should consider a twin before dual EFI's. Also, he argues that the wiring/switching/sensing of dual units becomes the most likely point of failure in the system, ergo why have dual units. So because I will only have one EFI, I thought to myself that if it goes belly up, I would at least like to have the option of cycling a CB to see if it would re-light.

I still can't let go of the idea of dual EFI's controlled by an On-Off-On switch. I don't know why the units have to be integrated beyond sharing 4 sensors (throttle, temp, MP, RPM). But the manufacturer could sell me another unit and he's telling me, I don't want to do this. So the CB is buying me a tiny bit of feel-better.

John


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klehman(at)albedo.net
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PostPosted: Sat Mar 18, 2006 5:09 pm    Post subject: Z-19 questions Reply with quote

John

The advice to not make a primary system less reliable by adding backups
that could compromise it is good advice. However if you want a second
system, an independant second system can certainly be installed that
does not have any common failure points or share items with the primary
system. Ideally neither system should know that the other exists.

For example a backup efi might be a homemade megasquirt unit that shares
no sensors, wiring, injectors, etc. with the primary system. The
throttle sensor can be eliminated since airplane throttles are opened
slowly. The engine temperature sensor could be eliminated because the
engine will already be warm if the backup is needed. So a minimum system
needs a crank or cam sensor for rpm, a MAP sensor which is onboard the
$150. ish megasquirt, an inlet air temp sensor, one or more additional
injectors, an independant power source and a separate power switch. I'm
sure you already have a second fuel pump. A lot of reliability concerns
go away with the ability to just select another system.

Ken

John Burnaby wrote:

Quote:




>3. I want to have a dual feed, from Main & Engine batt. buses, w/circuit
>breaker to the EFI. Any elegant ideas to do this?
>
>

Just like Z-19 shows for engine primary switch. Why circuit breakers?

Bob,

Thanks for your expanded reply on power feed.

I'm electing to CB the EFI because I only have one EFI. The manufacturer argues that the MTBF of the EFI unit is so many magnitudes greater than the MTBF of a recip engine, that I should consider a twin before dual EFI's. Also, he argues that the wiring/switching/sensing of dual units becomes the most likely point of failure in the system, ergo why have dual units. So because I will only have one EFI, I thought to myself that if it goes belly up, I would at least like to have the option of cycling a CB to see if it would re-light.

I still can't let go of the idea of dual EFI's controlled by an On-Off-On switch. I don't know why the units have to be integrated beyond sharing 4 sensors (throttle, temp, MP, RPM). But the manufacturer could sell me another unit and he's telling me, I don't want to do this. So the CB is buying me a tiny bit of feel-better.

John











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nuckollsr(at)cox.net
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PostPosted: Sat Mar 18, 2006 9:17 pm    Post subject: Z-19 questions Reply with quote

At 10:45 AM 3/18/2006 -0800, you wrote:

Quote:


>3. I want to have a dual feed, from Main & Engine batt. buses, w/circuit
>breaker to the EFI. Any elegant ideas to do this?

Just like Z-19 shows for engine primary switch. Why circuit breakers?

Bob,

Thanks for your expanded reply on power feed.

I'm electing to CB the EFI because I only have one EFI. The manufacturer
argues that the MTBF of the EFI unit is so many magnitudes greater than
the MTBF of a recip engine, that I should consider a twin before dual
EFI's. Also, he argues that the wiring/switching/sensing of dual units
becomes the most likely point of failure in the system, ergo why have dual
units. So because I will only have one EFI, I thought to myself that if it
goes belly up, I would at least like to have the option of cycling a CB to
see if it would re-light.

I still can't let go of the idea of dual EFI's controlled by an On-Off-On
switch. I don't know why the units have to be integrated beyond sharing 4
sensors (throttle, temp, MP, RPM). But the manufacturer could sell me
another unit and he's telling me, I don't want to do this. So the CB is
buying me a tiny bit of feel-better.

Understand. Consider this:

You have no personal control over the EFI and no personal
knowledge of its reliability from the engineer's perspective.
There are tons of anecdotal evidence of the devices reliablity
given that millions are giving good service on road. On the
other hand, we know that the VAST majority of engine stoppage
leading to accidents is fuel starvation with the majority of
those cases falling at the feet of poor fuel management on
the part of the pilot.

So in considering two major data points that suggest the
(1) EFI is as close to golden as modern technology can make it
and (2) if the engine does quit, the most likely cause is
your screw-up. What are the things over which you do have
absolute control?

System architecture for starters. Okay, put a dual-feed path
isolation diode as close as practical to the EFI's power
input feeder. Supply two independent sources of power through
independent switching and feeder wires . . . like Z-19 suggests.
Now, is there value in having a circuit breaker versus a fuse?
The dual power and feeder paths are extremely unlikely to suffer
failures on any one flight. If some failure occurs that opens a
breaker, it is most likely to be someplace between the bus
and the input pin to the isolation diode. Anything downstream
of that point is in single-point of failure to the system
and we've already decided that those numbers (See 1 above)
are sufficiently comforting but will call for Plan-C should
the unthinkable happen.

What's the value of having breakers on the feeders? If the
breaker trips due to a fault between bus and diode
that feeder is down and out of service. Resetting the breaker
is useless and distracting when you should be shifting to
Plan-B where the alternate feed path steps in to save the day.

If the fault is downstream of the diode, then your faith
in the goodness of the EFI was over stretched and again,
the presence of a breaker is useless and distracting.
Plan-C is the order of the day - start picking your point
of arrival with the earth. Classical breaker installations
dictate bus bars at the panel which drives up your system's
parts count and increases the numbers of busses just
to satisfy a desire for breakers that have no demonstrable
value. If a breaker opens, likelihood of getting any system
back by resetting a breaker is exceedingly low. It's much
better to simply provide a second, independent path.

You also have absolute control over fuel management and
your earlier description called for dual, independently
powered and fed fuel pumps. So as long as you don't have
some fitting open up and spill all your fuel, the dual
pumps and ignition systems provide as much backup as
you're ever going to use. So, odds are still much greater
that your engine quits for lack of fuel than from any other
cause. Rather than breakers on the EFI lines, I'd vote for
active notification of low fuel will have more feel-better
value than circuit breakers.

Now the odds are stacked much more in your favor and
probability numbers for having a bad day are lower than
for the vast majority of certified single engine airplanes
flying today. Those are good odds indeed.

Bob . . .


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jonlaury(at)impulse.net
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PostPosted: Sat Mar 18, 2006 9:17 pm    Post subject: Z-19 questions Reply with quote

Ken,

I'm intrigued. Could one just put a single injector squirting into the intake plenum? What takes the sensor signals and fires it? Just remember, you're talking to an electro-phobe.

Thanks,
John


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jonlaury(at)impulse.net
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PostPosted: Sun Mar 19, 2006 1:34 pm    Post subject: Z-19 questions Reply with quote

How I love this list.

Thanks Bob, for once again clarifying the options and saving me time and money.

John

do not archive


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