Today's Message Index:
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1. 09:27 AM - Re: Starter Solenoid behavior with low Battery (Robert L. Nuckolls, III)
2. 09:32 AM - Re: Re: Starter Solenoid behavior with low Battery (Robert L. Nuckolls, III)
3. 12:14 PM - Re: Flexible Wire for Pull Out Fuse Tray? (Robert L. Nuckolls, III)
4. 01:17 PM - Re: Flexible Wire for Pull Out Fuse Tray? (Jeff Luckey)
5. 01:55 PM - Re: Flexible Wire for Pull Out Fuse Tray? (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: Starter Solenoid behavior with low Battery |
At 19:39 2015-04-28, you wrote:
Re-sending:
What about the proposal to eliminate the starter contactor? I am looking
at the Skytec dagram here:
http://www.skytecair.com/Wiring_diag.htm
The starter barely gets 10 volts after the master contactor and the
starter contactor in series. By eliminating the starter contactor, you
would have a hot wire to the starter whenever the master is on. Is this
a good idea or suicide
How do you arrive at that voltage level. What do you
believe voltage drop across the starter contactor
to be?
Actually, when you wire per the configuration recommended
by B&C since day-one of the light-weight starters, you
will have THREE contactors in series.
Battery, starter external, starter internal. SkyTec
was in favor of utilizing on the starter's
internal contactor hence the wiring diagram you
cited.
We elected not to recommend that as a general rule
based on a lot of history . . . some of which has
roots in the legacy Bendix-Style key switches
found on 100,000 single engine airplanes.
Here is a document I published almost 20 years
ago that explains the extra-ordinary stresses
placed on the crew-operated, starter switch
by modern, two-stage starter solenoid/contactor
www.aeroelectric.com/articles/strtctr.pdf
In this article I described the electrical
forces that are especially hard on slow-motion,
wiping contacts characteristic of the legacy
key switch. Forces that prompted an abortive
AD by the FAA issued first without understanding
the physics and corrected later when the 'fix'
didn't fix anything.
I'm not implying that there are not alternatives
based on other system constraints. For example,
this image . . .
Emacs!
. . . is found in figure Z-22 of the book. This
was a system driven 'fix' for the starter run-on
phenomenon observed when PM motors were becoming
popular. In this instance, one was required to
use the built-in contactor . . . so a buffer relay
was added to isolate the starter switch from
solenoid abuse.
This approach could be applied for ANY form
of starter motor thus eliminating the external
contactor. Given that the B&C starters were
going into both OBAM and TC aircraft (already
fitted with external contactors) we elected
to recommend external contactors as a matter of
common practice . . . B&C starters did not
have PM motors. The switch supplied with B&C
starter installation kits was pretty robust but
NOT suited to drive the starter's build in
solenoid-contactor.
So the short answer is, you can certainly eliminate
the external contactor . . . but it's a good idea
to know how that decision may create ripples
in the rest of the system.
Bob . . .
Message 2
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Subject: | Re: Starter Solenoid behavior with low Battery |
At 21:08 2015-04-28, you wrote:
Ok, I was worried there for a while thinking that either I burned up
my starter solenoid contacts and/or that it was mounted upside down.
Like I said in my original post, now that battery voltage is normal,
the starter solenoid is operating perfectly. However, I agree that I
probably abused it with the low battery situation, probably
shortening its expected service life, and I will be on the look out
for future problems with it. \
I don't think a one-of sticking event
is a predictor of future problems. The
welding material between contacts prone
to sticking consists of small mounds of
low-area metal that get displaced from
the contact mass during a low-battery
start attempt. Those features will be
flashed away during successive good-battery
start operations.
But we'll be interested in hearing if
you observe any contrary experience.
Bob . . .
Message 3
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Subject: | Re: Flexible Wire for Pull Out Fuse Tray? |
At 17:48 2015-04-28, you wrote:
Hello Bob,
Thanks again for all your help over the years of
our (wife and my) Lancair Legacy project.
In our electrical system design, weve gone with
a pull-out fuse tray that is on the right side of
the instrument panel. Its about 4 tall, 2
wide, 24 long and uses blade fuses that light up
when theyve blown. All the fuse blocks are
easily visible to the pilot when the tray is pulled out.
We chose this solution because of its simplicity
and minimum real estate on the Legacys small
instrument panel. In its implementation, though,
Im a bit concerned with the fatigue life of the
thick wires running to it with the tray being
pulled out and in for each flight with before
takeoff checks. The MIL-W-22759 wire in these
gauges is fairly stiff There are several since
the diodes between buses are on the avionics
shelf because of fuse tray space limitations.
Is there a very flexible 10 and 8 AWG wire that
we could use for the connections between our fuse
tray and avionics shelf, that can better handle
the fuse tray motion/flexing than the MIL-W-22759, and is air worthy?
Check out a big-box store's electrical
supplies. You can get a chunk of 10-3 drop
cord (SJ, SJO)and cut away the insulation to
acquire three, very flexible and robust
runs of 10AWG wire.
You won't find 8AWG drop cord but a welding
shop can sell you 6AWG welding cable that's
only a little larger than your 8AWG and probably
more flexible than the 8AWG Tefzel.
Bob . . .
Message 4
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Subject: | Re: Flexible Wire for Pull Out Fuse Tray? |
You can get a chunk of 10-3 drop
=C2- cord (SJ, SJO)and cut away the insulation to
=C2- acquire three, very flexible and robust
=C2- runs of 10AWG wire.
Bob, is that insulation "kosher" with respect to combustion by-products.
I thought that was the reason that Tefzel was the recommended wire/insulat
ion type.
-Jeff
On Wednesday, April 29, 2015 12:24 PM, "Robert L. Nuckolls, III" <nuck
olls.bob@aeroelectric.com> wrote:
ls.bob@aeroelectric.com>
At 17:48 2015-04-28, you wrote:
Hello Bob,
Thanks again for all your help over the years of
our (wife and my) Lancair Legacy project.
In our electrical system design, we=99ve gone with
a pull-out fuse tray that is on the right side of
the instrument panel.=C2- It=99s about 4 =9C tall, 2=9D
wide, 24=9D long and uses blade fuses that light up
when they=99ve blown.=C2- All the fuse blocks are
easily visible to the pilot when the tray is pulled out.
We chose this solution because of its simplicity
and minimum real estate on the Legacy=99s small
instrument panel.=C2- In its implementation, though,
I=99m a bit concerned with the fatigue life of the
thick wires running to it with the tray being
pulled out and in for each flight with before
takeoff checks.=C2- The MIL-W-22759 wire in these
gauges is fairly stiff=C2- There are several since
the diodes between buses are on the avionics
shelf because of fuse tray space limitations.
Is there a very flexible 10 and 8 AWG wire that
we could use for the connections between our fuse
tray and avionics shelf, that can better handle
the fuse tray motion/flexing than the MIL-W-22759, and is air worthy?
=C2- Check out a big-box store's electrical
=C2- supplies. You can get a chunk of 10-3 drop
=C2- cord (SJ, SJO)and cut away the insulation to
=C2- acquire three, very flexible and robust
=C2- runs of 10AWG wire.
=C2- You won't find 8AWG drop cord but a welding
=C2- shop can sell you 6AWG welding cable that's
=C2- only a little larger than your 8AWG and probably
=C2- more flexible than the 8AWG Tefzel.
=C2- Bob . . .
-
S -
-
=C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin.
Message 5
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Subject: | Re: Flexible Wire for Pull Out Fuse Tray? |
At 15:16 2015-04-29, you wrote:
You can get a chunk of 10-3 drop
cord (SJ, SJO)and cut away the insulation to
acquire three, very flexible and robust
runs of 10AWG wire.
Bob, is that insulation "kosher" with respect to combustion by-products.
I thought that was the reason that Tefzel was the recommended
wire/insulation type.
It depends on who you talk too. There's one well
meaning and vocal faction out there that thinks
Tefzel is spawn of the devil . . .
http://tinyurl.com/2f8uz
After you've spent some time in the test
lab letting the smoke out of things, you come
to realize that the flavor of smoke from any
combustible becomes a rather moot point.
Yeah, they do flame tests on insulation . . . by
plying it with a torch! After it appears sufficiently
antagonized that it should burn, you take away
the flame. If I recall the reasoning with any
accuracy, the flaming insulation should not propagate
along the wire, it should self extinguish in so
many seconds, it should not drip flaming
globs of insulation and . . . oh yeah . . .
should be minimally obnoxious to respiratory
system . . . the flavor of a fine pipe tobacco
being a design goal.
I've been present when wires were burned
either by accident or test. I've seen and smelled
lots of smoke . . . and there were no reminders
of grandpa's favorite pipe.
Most the flaming materials wienies seem to
think that there is increased risks for having
materials that will PROPAGATE or PROMOTE a fire
from any/un-named source . . . not many pilots I
know fly around with propane torches. Getting
a wire lit up by hard faulting to a battery is
exceedingly problematic unless the insulation is
VERY flammable . . . but wait, seems like those
fuses and circuit breakers are supposed to
keep things from going that far in the first
place. No . . .?
Airplanes have been wired with everything
from cotton covered rubber to super-exotic-
unobtanium for over a century. Yet in the annals
of aviation accidents, I'm aware of no incident
that was blamed on flammability of the insulation.
There may be some out there but they're a vanishingly
small proportion of totality of incidents.
INTEGRITY of insulation, yes. Swissair 111 wiring
sparked and set the airplane's cabin insulation
on fire. Look at the pictures of the 777 that
belly flopped in SFO. LOTS of stuff throughout
the cabin burned with some vigor . . . and I
doubt that anyone was reminded of their grandpa's
pipe in that incident either.
If the flaming materials wienies were really
taking their jobs seriously, then every new
requirement that strives for happy fires in the
cabin would have grounded the existing fleet
until sub-standard materials were replaced.
Hundreds of thousands of miles of 'sub-standard'
wire are airborne someplace over the planet
as we speak . . .
I suggest that the lowest risk path to personal
flight is grounded in good FMEA, craftsmanship,
and plan-b for highest risk failures. If
you've got serious smoke in the cockpit
that doesn't quit when you turn of the master
switch . . . well . . . the flavor of that
smoke is the least of your worries. I prefer to
design for no-fire as opposed to designing for
friendly fire.
Bob . . .
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