Today's Message Index:
----------------------
1. 01:29 AM - Re: Failure modes with Z12 (Robert L. Nuckolls, III)
2. 07:36 AM - Re: BMA Efis G4 Lite (LINDA WALKER)
3. 08:09 AM - Re: Failure modes with Z12 ()
4. 08:47 AM - Re: Failure modes with Z12 (user9253)
5. 10:17 AM - Re: Re: Failure modes with Z12 (Robert L. Nuckolls, III)
6. 10:40 AM - Re: Failure modes with Z12 (ignore earlier) (Robert L. Nuckolls, III)
7. 12:00 PM - FW: Re: S701 Contactor Failure Analysis (emrath)
8. 01:16 PM - fuel pressure sender ground (messydeer)
9. 01:56 PM - Re: fuel pressure sender ground (rampil)
10. 01:58 PM - Re: Failure modes with Z12 (user9253)
11. 02:26 PM - Re: Re: fuel pressure sender ground (Matt Prather)
12. 02:38 PM - Re: fuel pressure sender ground (messydeer)
13. 03:51 PM - Re: fuel pressure sender ground (Peter Pengilly)
14. 04:15 PM - Re: fuel pressure sender ground (rampil)
15. 04:55 PM - Re: fuel pressure sender ground (messydeer)
16. 07:38 PM - Re: fuel pressure sender ground (al38kit)
17. 08:36 PM - Re: fuel pressure sender ground (messydeer)
18. 08:57 PM - Re: B&C Regulators and water-falls (Robert L. Nuckolls, III)
19. 09:10 PM - Re: Re: Failure modes with Z12 (Robert L. Nuckolls, III)
20. 09:15 PM - Re: fuel pressure sender ground (rparigor@suffolk.lib.ny.us)
Message 1
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| Subject: | Re: Failure modes with Z12 |
At 01:34 PM 2/18/2010, you wrote:
>
>I am still vacillating between Z13/8 and Z12.
>
>I intend to use two electronic ignitions. The only thing that
>concerns me is an overvoltage event that burns out both ignitions.
>Probably very rare, considering the robust design
correct . . . not a useful point of concern . . .
>but perhaps a lightning strike,
No guarantees at all for lightning strike. I'm pretty sure
Klaus hasn't included lightning immunity in his design
goals . . . and in any case, system architecture wouldn't
offer any 'protection' except for a few of the possible
energy conduction pathways. One just generally needs to
stay away from
> or the failure of an overvoltage module?
Ov module failures don't cause ov conditions.
OV module failures would not catch and stop
an OV condition . . . AFTER a regulator failure.
That's dual failures on a single tank of fuel.
Exceedingly unlikely to the point
> Z12 would isolate the two and alleviate my concern.
Z12 is a single system with two alternators. Z13/8
is a variation on the same theme. Only Z-14 provides
near-total isolation between separate systems . . .
assuming your willing to let this concern drive
you decisions.
>Second, I frequently cruise at 2200rpm and the output of the SD-8
>would be only about 5A. For 0.8 pounds and $79 more, with an
>insignificant balance improvement, I can buy a 40A and 20A alternator
>instead, which is very tempting.
What are your design goals? Under conditions of
main alternator failure, could you NOT cruise as
fast as red line for the remainder of the flight?
>The concept of the essential bus diode is not used in Z12, so now we
>get to my question. It appears that after a failure of either battery
>contactor, there is no configuration to supply power to the
>corresponding battery bus. So duration of flight is limited by the
>battery capacity, rather than the capacity of the remaining alternator
>to supply all the ships loads with the cross feed contactor engaged.
>What change could be safely made to provide power to both battery
>buses without negatively impacting other features of Z12 ?
You must be talking about Z-14. Are you telling us that
both batteries are critical for sustained flight? What
loads are you running from each of the battery busses that
offers this condition?
Elegant system design eliminates all single points of
failure that put the mission at risk. You need to
make a list of the things you absolutely need to
continue flight to airport of intended destination.
For me, flying a spam can, that means shut down the
electrical system entirely and go to flight-bag
hand-helds. When I have the airport in sight, I've
got what ever the battery contains to finish the
flight.
The decision is not made by asking us for advice on
your concerns. The decision is driven by failure mode
effects analysis stacked against the equipment you
plan to carry on the panel and in the flight bag. Where
will those devices will get a couple hours of energy when
the alternator quits (which is increasingly rare).
Confidence only arises from a calculated Plan-B.
Bob . . .
Message 2
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| Subject: | Re: BMA Efis G4 Lite |
Thanks for all the comments, constructive and otherwise, to this request for
help.
Greg Richter is kindly going to make the repair and would like the community
to know that he is reachable by e-mail at: greg@bluemountainavionics.com.
I would think that this is the correct way to reach him despite his home
telephone number being out there.
Patrick Elliott
Message 3
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| Subject: | Failure modes with Z12 |
Jeff,
Bob's last 3 paragraphs put everything together. The risk adverse
individual (my wife) will question every level and only accept one final
outcome - total assumed security. That isn't going to happen. Look at
all the GA wrecks in the last few days - yikes. In a few year we'll be
lucky if we're allowed to fly.
So let's talk about failure modes as Bob mentions below. For your
example assume the worst case which is probably over water, right? Ok,
personally I have two Klaus jobs (wow, this guy is famous - just the
mention of the name Klaus, I'm so jealous), any-who I have the SD-8 and
a Dynon with HSI. So everything goes to hell, Don't tell Bob but I use
two batteries with Z-13 like Klaus recommends to run one module, so live
it up. This battery is 4.5 ah (very small), but the Klaus job will run
down to 5 volts (now, you're heading for the Bahamas and both
alternators die (hardly likely unless you've been pouring sand into
them) halfway between Palm Beach and Bimini - oh sh*%).
Ok, with my 1-2 amp Dynon (internal battery) and my sometimes 3 amp SL30
I can still do a non-precision landing at Bimini after running for an
hour (the 50 miles or so) on battery(s). Everything else is off and my
Dynon is running on internal battery (that sucker runs min 1.5 hours
just on the internal 16 volts it has saved up, and oh, since I have two
Dynons I can then turn on the other one and..) When I get near Bimini, I
turn on the radio because I've been monitoring my progress as Bob
mentioned with my handheld GPS and spare batteries. Hell, if I'm really
nuts I can even use my handheld radio to talk to the Bimini approach.
The Klaus jobs won't know the difference and if you're really cocky you
can turn one off and pull 5 volts for several hours before even the 17
ah battery dies. If that's used up, I kill it and move to my backup 4.5
ah battery and skip over Bimini and keep going to Nassau.
You get the point. Once you get setup, you simulate this on the ground.
If your system is 100%, you'll be sitting in your plane a long time
waiting for the battery to give up.
Moral of the story - Keep the batteries in your toys fresh and you'll
keep flying. Batteries and oil are cheap, don't skimp on either.
>From Bob N>
" Elegant system design eliminates all single points of
failure that put the mission at risk. You need to
make a list of the things you absolutely need to
continue flight to airport of intended destination.
For me, flying a spam can, that means shut down the
electrical system entirely and go to flight-bag
hand-helds. When I have the airport in sight, I've
got whatever the battery contains to finish the
flight.
The decision is not made by asking us for advice on
your concerns. The decision is driven by failure mode
effects analysis stacked against the equipment you
plan to carry on the panel and in the flight bag. Where
will those devices will get a couple hours of energy when
the alternator quits (which is increasingly rare)."
>
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of
Robert L. Nuckolls, III
Sent: Thursday, February 18, 2010 8:28 PM
Subject: Re: AeroElectric-List: Failure modes with Z12
<nuckolls.bob@aeroelectric.com>
At 01:34 PM 2/18/2010, you wrote:
>
>I am still vacillating between Z13/8 and Z12.
>
>I intend to use two electronic ignitions. The only thing that
>concerns me is an overvoltage event that burns out both ignitions.
>Probably very rare, considering the robust design
correct . . . not a useful point of concern . . .
>but perhaps a lightning strike,
No guarantees at all for lightning strike. I'm pretty sure
Klaus hasn't included lightning immunity in his design
goals . . . and in any case, system architecture wouldn't
offer any 'protection' except for a few of the possible
energy conduction pathways. One just generally needs to
stay away from
> or the failure of an overvoltage module?
Ov module failures don't cause ov conditions.
OV module failures would not catch and stop
an OV condition . . . AFTER a regulator failure.
That's dual failures on a single tank of fuel.
Exceedingly unlikely to the point
> Z12 would isolate the two and alleviate my concern.
Z12 is a single system with two alternators. Z13/8
is a variation on the same theme. Only Z-14 provides
near-total isolation between separate systems . . .
assuming your willing to let this concern drive
you decisions.
>Second, I frequently cruise at 2200rpm and the output of the SD-8
>would be only about 5A. For 0.8 pounds and $79 more, with an
>insignificant balance improvement, I can buy a 40A and 20A alternator
>instead, which is very tempting.
What are your design goals? Under conditions of
main alternator failure, could you NOT cruise as
fast as red line for the remainder of the flight?
>The concept of the essential bus diode is not used in Z12, so now we
>get to my question. It appears that after a failure of either battery
>contactor, there is no configuration to supply power to the
>corresponding battery bus. So duration of flight is limited by the
>battery capacity, rather than the capacity of the remaining alternator
>to supply all the ships loads with the cross feed contactor engaged.
>What change could be safely made to provide power to both battery
>buses without negatively impacting other features of Z12 ?
You must be talking about Z-14. Are you telling us that
both batteries are critical for sustained flight? What
loads are you running from each of the battery busses that
offers this condition?
Elegant system design eliminates all single points of
failure that put the mission at risk. You need to
make a list of the things you absolutely need to
continue flight to airport of intended destination.
For me, flying a spam can, that means shut down the
electrical system entirely and go to flight-bag
hand-helds. When I have the airport in sight, I've
got what ever the battery contains to finish the
flight.
The decision is not made by asking us for advice on
your concerns. The decision is driven by failure mode
effects analysis stacked against the equipment you
plan to carry on the panel and in the flight bag. Where
will those devices will get a couple hours of energy when
the alternator quits (which is increasingly rare).
Confidence only arises from a calculated Plan-B.
Bob . . .
Message 4
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| Subject: | Re: Failure modes with Z12 |
> "I am still vacillating between Z13/8 and Z12."
If you are undecided, go with Z-13/8. It is simpler, costs less, and weighs
less than Z-14 and is more reliable than most factory-built systems.
You are concerned about a battery contactor failure. How will you recognize
that a battery contactor failure has occurred? There might not be any symptoms
because the alternator would probably keep working. It would be necessary to
monitor the battery voltage to recognize a problem. Even with a failed battery
contactor, voltage on the main power distribution bus will be normal as long
as the alternator keeps working. The low voltage warning light on the regulator
does not warn of low battery voltage due to contactor failure.
If using Z-13/8, turning on the E-Bus Alternate Feed Switch will provide a parallel
path around the contactor from the main alternator to the battery. Although
voltage will be dropped across the diode and current is limited by the
15 amp fuse, it should be adequate for a fuel pump and ignition. In addition,
the aux alternator is connected to the battery side of the main contactor. Multiple
failures would have to occur before power is lost to critical engine ignition
and fuel systems that are connected to the battery. You might consider
connecting one ignition and fuel pump to the battery bus and the other set to
the E-Bus. Doing so insures that one set will keep working in the event of
a bad electrical connection.
What do you think Bob N.?
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=287195#287195
Message 5
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| Subject: | Re: Failure modes with Z12 |
At 10:44 AM 2/19/2010, you wrote:
>
>
> > "I am still vacillating between Z13/8 and Z12."
> If you are undecided, go with Z-13/8. It is simpler, costs less,
> and weighs less than Z-14 and is more reliable than most factory-built systems.
> You are concerned about a battery contactor failure. How will
> you recognize that a battery contactor failure has occurred? There
> might not be any symptoms because the alternator would probably
> keep working. It would be necessary to monitor the battery voltage
> to recognize a problem. Even with a failed battery contactor,
> voltage on the main power distribution bus will be normal as long
> as the alternator keeps working. The low voltage warning light on
> the regulator does not warn of low battery voltage due to contactor failure.
> If using Z-13/8, turning on the E-Bus Alternate Feed Switch will
> provide a parallel path around the contactor from the main
> alternator to the battery. Although voltage will be dropped across
> the diode and current is limited by the 15 amp fuse, it should be
> adequate for a fuel pump and ignition. In addition, the aux
> alternator is connected to the battery side of the main
> contactor. Multiple failures would have to occur before power is
> lost to critical engine ignition and fuel systems that are
> connected to the battery. You might consider connecting one
> ignition and fuel pump to the battery bus and the other set to the
> E-Bus. Doing so insures that one set will keep working in the
> event of a bad electrical connection.
> What do you think Bob N.?
>Joe
>
>--------
>Joe Gores
>
>
>Read this topic online here:
>
>http://forums.matronics.com/viewtopic.php?p=287195#287195
>
>
Bob . . .
////
(o o)
===========o00o=(_)=o00o========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
================================
Message 6
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| Subject: | Re: Failure modes with Z12 (ignore earlier) |
I'm eagerly awaiting system restore disks for my computer . . . seems
it's been invested with little gremlins that are not virii/malware
but instead associated with every software designer's desire to link
his/her application with everyone else. After 5-7 years of tug-a-war
between all those applications . . . their little squabbles are now
spilling out of the play-pen. Makes the computer do silly things like
"send now" before I've even edited the message!
. . . ain't this 'lectronix stuff wunderful . . .
At 10:44 AM 2/19/2010, you wrote:
> "I am still vacillating between Z13/8 and Z12."
If you are undecided, go with Z-13/8. It is simpler, costs less, and
weighs less
than Z-14 and is more reliable than most factory-built systems.
Agreed . . . keeping in mind that when airplanes come
down or even get into trouble with root causes in electrical
systems, somebody had to do something really . . . uh . . .
what's the PC term . . . inappropriate? Stacking
backup on top of backup without a carefully considered
FMEA (failure mode effects analysis) backed up with
equally well considered Plan-B is fraught with
risk.
An incident I'm working on right now involves seemingly
cool approaches to redundancy that set the stage for
single-points of failure for power to both ignition
systems in spite of TWO properly working alternators
and TWO charged batteries.
You are concerned about a battery contactor failure. How will you
recognize that a battery contactor failure has occurred?
Excellent question that drove the features of our 9011
multi-channel OV/LV monitoring device. A channel dedicated
to monitoring battery voltage will flag a battery contactor
that has opened after pre-flight . . .
There might not be any symptoms because the alternator would probably
keep working. It would be necessary to monitor the battery voltage
to recognize a problem. Even with a failed battery contactor,
voltage on the main power distribution bus will be normal as long as
the alternator keeps working. The low voltage warning light on the
regulator does not warn of low battery voltage due to contactor failure.
Correct.
If using Z-13/8, turning on the E-Bus Alternate Feed Switch will
provide a parallel path around the contactor from the main alternator
to the battery. Although voltage will be dropped across the diode
and current is limited by the 15 amp fuse, it should be adequate for
a fuel pump and ignition. In addition, the aux alternator is
connected to the battery side of the main contactor. Multiple
failures would have to occur before power is lost to critical engine
ignition and fuel systems that are connected to the battery. You
might consider connecting one ignition and fuel pump to the battery
bus and the other set to the E-Bus.
Yes!
Plans-B should also consider shutting down one of two ignition systems
during the endurance phase of flight at altitude. Keep in mind that
there are many, Many, MANY OBAM aircraft flying with one electronic
ignition and one mag. For all practical purposes the airplane flies
on a single ignition. 95% of all performance gains come when you
add the first electronic ignition . . . the mag is coasting. The second
electronic system is untaxed redundancy that consumes power from your
limited resources in the endurance mode of flight.
Doing so insures that one set will keep working in the event of a bad
electrical connection.
What do you think Bob N.?
Excellent example of the FMEA thought processes.
In the accident case I cited, simple direct feeds
to EACH ignition from SEPARATE batteries would have
offered a near bullet-proof hedge against risks.
In a Z-13 or Z-12 system, feeding one ignition from
the battery bus and the other from the e-bus is
a good move. Primary and secondary fuel delivery
systems should be spread around too.
There's no single-golden-righteous recipe for
success here. There are no two OBAM aircraft wired
the same way. This FMEA thingy is something as
necessary as learning how to buck a good rivet.
Bob . . .
Message 7
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| Subject: | S701 Contactor Failure Analysis |
Bob,
Thanks for taking time to do this. Very interesting. I hope my replacement,
provided by B&C "gratis" was not manufactured on the same day...... Marty
Time: 06:03:45 PM PST US
From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
Subject: AeroElectric-List: S701 Contactor Failure Analysis
Last year, Marty Emrath told us about the failure of a new contactor he had
purchased from B&C. B&C replaced the contactor but Marty was justifiably
curious as to root cause of the failure.
I offered to document a tear-down analysis and Marty sent
me the carcass. I was looking for something fun to do this afternoon so I
took the dead puppy apart.
The pictures at . . .
http://www.aeroelectric.com/Pictures/Contactors/S701_Failure_Teardown/
Are pretty much self explanatory. One thing is for certain. This product is
much more sophisticated than its ancestors that first took to the air in a
C-140.
The last picture tells the tale . . .
http://www.aeroelectric.com/Pictures/Contactors/S701_Failure_Teardown/TearDo
wn_10.jpg
Seems the assembler wasn't really awake yet when this
device went across their work station. One coil wire
was poorly soldered to its terminal . . . the other had
no solder at all.
Thanks for sharing your experience with us Martin!
Bob . . .
Message 8
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| Subject: | fuel pressure sender ground |
Hi!
I just got my Steward Warner fuel pressure sender and am wondering what a good
way to get a ground lead from it would be. The first pic shows its 1/8" npt stud
threaded into a T fitting in my mockup. Tech support said to use the npt stud.
But I can't imagine getting a tight fit with a ground ring that way, without
making the actual fitting looser.
He also said if I needed to, the top of the can near the edge could be tapped.
Any ideas?
Thanks,
Dan
--------
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=287245#287245
Attachments:
http://forums.matronics.com//files/fuel_regulator_and_pressure_sender_196.jpg
http://forums.matronics.com//files/sw_pressure_sender_139.jpg
Message 9
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| Subject: | Re: fuel pressure sender ground |
What close fit?
the size of the ring is not important as long as it slides over the
NPT. If the NPT Tee does not compress the ring, put a jam nut
over the ring.
--------
Ira N224XS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=287257#287257
Message 10
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| Subject: | Re: Failure modes with Z12 |
Bob,
I can not show you where you are wrong because you said nothing wrong and your
electrical drawings are very hard to improve upon. Comments in my previous post
were not meant to criticize or to suggest changes. I was only trying to explain
how the circuit worked and that there is no reason to be overly concerned
about a battery contactor failure in flight and that no changes to Z-13/8 are
required for dual electronic ignition (other than to tap power from two separate
points). When I asked for your opinion at the end of my previous post, I
was asking for your approval and to correct anything that I may have said that
was incorrect. I hope that you did not take it any other way. I have been
reading the AeroElectric List for a couple of years and have learned a lot and
respect your work and opinions. I commend you for offering free advice and taking
time to answer electrical questions from home-builders.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=287259#287259
Message 11
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| Subject: | Re: fuel pressure sender ground |
Most NPT is tapered. As such, my thinking is that the threaded joint must
become tight by the binding of the taper, not by contacting facing
surfaces.. If the installed lug (or jam nut) causes contacting of the
facing surfaces, I might be a bit concerned about long term sealing of the
joint.
http://en.wikipedia.org/wiki/National_pipe_thread
Regards,
Matt-
>
> What close fit?
> the size of the ring is not important as long as it slides over the
> NPT. If the NPT Tee does not compress the ring, put a jam nut
> over the ring.
>
> --------
> Ira N224XS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=287257#287257
>
>
Message 12
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| Subject: | Re: fuel pressure sender ground |
Bingo! That's exactly what I am concerned about, Matt :-)
Mr. Tech Dude mentioned tapping a 1/8" NPT washer...I suppose if there is room
enough (haven't gotten the aluminum T fitting to replace the brass one in the
pic) and if I tap it large enough so it doesn't prevent the stud from going in
all the way then it might work...hmm...
--------
Dan
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=287268#287268
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| Subject: | Re: fuel pressure sender ground |
Hose clamp around the sender to trap a ground wire? Solder a wire on to
the sender body? Bolt sender to a monifold bolted (and grounded) to the
firewall (or ground the mounting bolt)? Ground wire on the circular
metal thing?
BTW not sure I would use PVC pipe with push on fittings on a fuel line
under pressure! I use teflon braided pipe with integral firesleeve.
Peter
messydeer wrote:
>
> Hi!
>
> I just got my Steward Warner fuel pressure sender and am wondering what a good
way to get a ground lead from it would be. The first pic shows its 1/8" npt
stud threaded into a T fitting in my mockup. Tech support said to use the npt
stud. But I can't imagine getting a tight fit with a ground ring that way, without
making the actual fitting looser.
>
> He also said if I needed to, the top of the can near the edge could be tapped.
>
> Any ideas?
>
> Thanks,
> Dan
>
> --------
> Dan
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=287245#287245
>
>
> Attachments:
>
> http://forums.matronics.com//files/fuel_regulator_and_pressure_sender_196.jpg
> http://forums.matronics.com//files/sw_pressure_sender_139.jpg
>
>
>
Message 14
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| Subject: | Re: fuel pressure sender ground |
If worry about the sealing is your concern, use PTFE compound on the
joint.
If structural integrity is your issue, you should not be using the old
VDO automotive sensor in the first place as it has a huge moment arm
and NPT is not aerospace qualified. ANPT is better but is not compatible
with highest quality hose like Aeroquip 666.
If you are still wanting to use the VDO like Rotax used to for oil pressure,
strap it with a stainless hose clamp as suggested and safety wire it to
not rotate. Grounding at the clamp is optional but works if clean and the
sensor can is not corroded since under the clamp will not be as
anaerobic as under a jam nut to a ring terminal - i.e., more rust.
--------
Ira N224XS
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| Subject: | Re: fuel pressure sender ground |
Thanks, guys :-)
I could have mentioned this is mockup stuff, not the real McCoy. But $0.25/ft hose
would be a better budget fit! The tee shown is a brass one from the hardware
store. I'll replace it with an aluminum when it's delivered next week, along
with a bunch of other fittings.
Grounding to the adel clamp sounds reasonable. I could take off the pad on the
clamp holding the tee, then slip a ring over the bolt holding the two clamps together.
--------
Dan
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| Subject: | Re: fuel pressure sender ground |
First, to answer your question...If you check the resistance from the case of the
transducer to the engine case and find it to be minimal, forget about a separate
ground wire and ensure the case of the engine is common to your electrical
system.
Now for the biggie...
I would scrap this entire installation of the transducer and mount it on a braided
flexible line with a fitting having a flow restrictor.
It is a bad idea to mount any of these transducers in the manner you are attempting
and many instrument manufacturers do NOT recommend hard mounting them to
the engine...
I recall reading an accident report about a Questair Pilot who had mounted one
on some tubing...it failed in flight and he got to spend some time in the mountains
with a broken leg...alone.
Fittings are not good mounts in a vibration environment.
Just something to think about now...
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| Subject: | Re: fuel pressure sender ground |
Thanks A. :-)
I understand your comments about the electrical ground.
As far as the chance of this type of unit mounted in this manner failing, I'd like
some clarification. I take it you're saying this type of pressure sender
is okay, but not the way it is installed/supported, right?
And the Questair had one 'on some tubing'. Was this rigid tubing or hose? Seems
an installation that would fix the 1-lb sender to the engine mount would work,
as long as flexible hose goes in and out of it.
--------
Dan
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| Subject: | Re: B&C Regulators and water-falls |
Received at AeroElectric Connection today . . .
Bill Harrelson and I had a chance to review the
investigation and preliminary causes of an
in-flight fire in a Lancair IV-P that occurred
last spring (2009). The findings and conclusions
are not yet established, but the investigator
felt that some of the information discovered was
not in question, and would be useful to the
experimental community. We agreed to help spread the word=85as follows:
The accident aircraft experienced an in-flight
battery fire of the secondary electrical system
shortly after takeoff. The pilot was able to
return to the airport and extinguish the fire in
the tail section of the aircraft after landing.
The battery, case, and nearby components were
consumed/destroyed, and the aircraft fuselage
sustained significant heat damage from the aft
pressure bulkhead to the elevators/rudder. The
cause of the fire has not been absolutely
determined, but the lead/acid battery vents had
apparently been obstructed, resulting in a case
rupture and venting of hydrogen gas into the tail
section of the airplane. The exact cause of this
apparent over pressurization and rupture awaits
additional information and analysis. This finding
and the final NTSB report are expected within a
month and we will disseminate this report through the LML and LOBO
newsletter.
One initial result of the investigation was that
the B&C regulator for the secondary electrical
system was inoperative upon post-flight analysis.
The NTSB investigator conducted a detailed
examination and analysis of the defective unit
and determined that the electrical design was
robust and appropriate to the task. The unit was
mounted to the engine side of the firewall with
the spade terminal connectors projecting to the
side of the aircraft. This unit is not sealed,
and at some point liquid (probably water) entered
the metal box, most likely through the opening around the spade terminals,
Hmmm . . . They speak of "spade" terminals . . . I presume they're
referring to the screw-terminal strip.
and filled it to a depth of 1/4 to 1/2 inch. The
liquid allowed arcing among internal components
and to the case ground, leaving carbon tracks on
the circuit board and case, and destroying the electrical functionality.
It is certain that water and electronics don't
mix well. I'm not certain that mounting on the firewall
is an automatic no-no . . . we've been tying stuff
to firewalls since day-one but it IS a unique environment.
Shucks, look at all the firewall mounted electro-whizzies
on this airplane . . .
http://aeroelectric.com/Pictures/Wiring_Technique/Firewall_Ckt_Protection.jp
g
Way back when, Cessna modified the cowl attach fittings
to set on shock mounts instead of the firewall bulkhead.
It reduced cabin noise significantly. However, the gap
around the aft edge of the "floating cowl" allowed water
to run down the windshield of parked aircraft right down the
firewall. Believe it or not, there was a period of
time when Cessna was adding brushed on EPOXY seals to
the S701 style battery and starter contactors!
Seems that on a nice hot day, the contactor would exhale.
Then a nice cool shower came along and bathed the contactor
which inhaled liquid water thought the non-hermetic
cap seals. Now the water could only get out as a vapor
through repeated atmospheric transfers of gas from the
semi-tight enclosure.
Needless to day, even epoxy sealing was only marginally
successful in forestalling premature contactor death
due to rust. Those were the years I did my first alternator
regulator design for Cessna that featured an injection
molded case with o-ring sealed lid. It was a couple bux
more expensive than somebody else's design that was
manually doped with sealant at the enclosure gaps. A
risky, process sensitive design . . . but they liked
it.
A review of installation instructions provided
with B&C regulators recommends they be installed
inside the cockpit or in a similar
environmentally-protected area. This regulator
was mounted inside the engine compartment, as we
believe are the vast majority of Lancair
installations. When so installed, regulators are
subject to additional heat and cooling stresses,
as well as water/solvents from engine cleaning
and other maintenance when the cowling is
removed. If mounted in any position other than
with the spades down, liquid can enter in the
area of the spade terminals and will then be
trapped within the lower part of the enclosure,
immersing part of the main circuit board.
Right . . . so mount the terminal strips down and be cognizant
of the fact that you can't just spray everything down when
cleaning the engine. B&C suffered some bearing failures in
alternators way back when due to over-zealous use of high-
pressure, soapy-water.
If you are still building and have the option,
review the B&C recommendations on mounting
location and consider locating your B&C
regulator(s) inside the cockpit; preferably with
the spades down if there is any possibility of
liquid exposure. No matter the location, mount
them in such a way that they cannot ingest and retain water.
Excellent suggestion which applies to ALL accessories
not suitably protected from either nature or owner-generated
moisture issues. Shucks, we had many killobux of warranty
hassles on the C337 that featured a really nice radio
access hatch in the cowl deck forward of the windshield
but aft of the firewall. Seems the hatch seals liked to leak
a drip into the radios.
If you are not able to locate the regulator(s) as
recommended by B&C, consider shielding the
terminal strip area from liquids. We expect to
contact B&C about the feasibility of other
improvements that could be made, but will refrain
from making any recommendations until we receive their comments.
All good suggestions and plans for action . . . but I'll
suggest overly simplistic. These are increasingly
complex machines with features that do not fare well
when subjected to soapy water, snow, ice, rain-water,
ozone, hydraulic fluids, spilled 7-up, etc. etc.
By the way, when the B&C "regulators" were originally
conceived, we considered offering the regulator, LV-protection
and LV-warn as a trio of separate components. But it
was our design goal that EVERY user of B&C regulators
received the benefit of OV-protection and active notification
of low voltage. Hence the rather expensive "regulator" which
was really an "alternator control system".
The failure in the Lancair points out a weakness of
that design philosophy. Filling the box with water poses
a risk of killing both OV protection --AND-- regulator
functionality. I.e., SINGLE POINT OF FAILURE that produces
an uncontrolled runaway. Given what we know now, would
we have done it any different back then? Hard to tell.
We can learn from this failure instance and be cognizant
of as many risks as one can deduce individually and
collectively. This is what FMEA is all about. The
process benefits greatly from lessons learned . . . whether
on last months's battery fire or the last century=92s leaky
cowls.
Bob . . .
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| Subject: | Re: Failure modes with Z12 |
> When I asked for your opinion at the end of my previous post, I
> was asking for your approval and to correct anything that I may
> have said that was incorrect. I hope that you did not take it any
> other way. I have been reading the AeroElectric List for a couple
> of years and have learned a lot and respect your work and
> opinions. I commend you for offering free advice and taking time
> to answer electrical questions from home-builders.
Joe, I just re-read my posting. I'm sorry if
I sounded reproachful in any way. Please know that
it was unintentional. I abhor such behavior in
myself and discourage it in others. In fact, I think
I complimented your organization of the FEMA thought
process and attempted to amplify that stream of ideas.
To the best of my recollection, your postings have
always been helpful and technically accurate.
I value your participation on the List.
Bob . . .
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| Subject: | Re: fuel pressure sender ground |
Hi Dan
"I just got my Steward Warner fuel pressure sender
and am wondering what a good way to get a ground lead from it would
be."
I have a remote oil sender that is attached to a non
conductive line on my Rotax 914.
One option is to put some sort
of spacer that gets tightly squeezed between sender and fitting and attach
to that. I have heard of just washers used, thin NPT nuts or you could be
an idiot like I am going to be and turn a precision spacer and make it so
I get a tight fit. Like Ira said it dosen't have to be a real tight fit on
NPT, butI prefer that, but length is critical so you get enough
tension and allow NPT to seal. To be a further idiot I am also considering
installing a hose clamp on the OD of sender catching another ground to a
piece of brass or copper held by clamp.
I have other senders
with fairly small brass hex. I will install senders leaving first few
threads free of Loctite or sealant in hopes it gets a good ground to
block, but will also installMcMaster Carr small 3/8" wide
stainless steel mini hose calmps (like automobile fuel injection fuel line
clamps) grabbing a piece of copper or brass and use that as an aux.
ground. Stupid, simple and looks very nice as well.
Ron
Parigoris
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