Today's Message Index:
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1. 07:06 AM - Re: Fw: Aero Electric Post (Charlie England)
2. 08:19 AM - Re: Audio panel move - 10/18/21 (Ron Cox)
3. 08:51 AM - Re: Audio panel move (RV7ASask)
4. 03:09 PM - Re: Fw: Aero Electric Post (Robert L. Nuckolls, III)
5. 03:52 PM - Vacuum pad shear couplers (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Fwd: Aero Electric Post |
On Mon, Oct 18, 2021 at 9:42 PM Neal George <neal.george@gmail.com> wrote:
> Bob et al-
> One of my neighbors has experienced two sheared alternator couplings
> recently. Prior to the first event, his electrical system ran trouble-free
> for approximately 500 hours. More detail in his narrative below.
>
> Neal
> =====
>
> Within the last ~250 hours I've had two alternator shear couplings fail on
> my RV-6. The first failed after ~248 hours of flying, the second failed at
> less than two. The alternator is a Plane Power FS1-14B (30A, internally
> regulated, bolted to the accessory pad) and the airplane is wired using Bob
> Nuckoll's Z-11 diagram in the Aero Electric connection. This is the only
> alternator on the plane.
>
> The airplane is a full-up Dynon system (10" Skyview, ADS-B, transponder,
> wx rcvr), a Garmin GTR200 radio, landing light, strobes, nav light. None of
> the lights were turned on between repairing the first failure and the
> second one.
>
> The going failure theory is an intermittent connection in the field
> circuit that induces a heavy alternator load by turning it on and off but
> there isn't anything in the 1Hz data traces from the Dynon that indicates
> this is the case. Nor is there evidence of any loose connections or nicked
> wires in the field circuit.
>
> The image shows the volt and amp trace for the last 1.7 hour flight. The
> failure occurred around count #6184. The noise on the front end is startup
> and taxi. The blip around 2291 was plugging in an iPad.
>
> Any ideas on the failure mode?
>
>
> Keystone Aerospace LLC
> Gregg Costabile, President/Owner
> (850) 585-3149
> gcostabile@cox.net
>
Likely unrelated to failure, but,
What caused the current to drop from ~25A to zero, then jump back to ~25A
at the 230 point?
Again likely unrelated to failure, but,
5A continuous seems pretty low for a full Dynon system plus transponder
plus ADSB (if that means 'Out'), plus weather receiver, plus the idle
current for a comm radio. Have you verified that number using a separate
amp meter in-line with the bus?
To the shear coupling failures:
Is there any 'soft' element in their coupling to handle any torsional
resonance issues? Failing a shear coupling that quickly almost sounds like
either misalignment issues or torsional resonance related fatigue.
Charlie
Message 2
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| Subject: | Re: Audio panel move - 10/18/21 |
>
> ______________________________
> Time: 07:58:47 AM PST US
> From: "Robert L. Nuckolls, III" <nuckolls.bob@aeroelectric.com>
> Subject: RE: AeroElectric-List: Re: Audio panel move
>
> At 07:18 AM 10/18/2021, you wrote:
> >I think I would find it much easier to make a short extension on the
> >bench than to crawl up into the instrument panel with my soldering
> >iron and various other tools, but that's only me, a very old fart!
>
> From one ol' fart to another, agreed. MUCH reduced
> chance for errors that are EASY to make and very
> difficult to find/fix.
>
> 44 pin devices would be the sub-miniature D-Subs.
> Sorry. No inventory on that series of devices.
>
>
> Bob . . .
>
> I used a couple of these (cut to expose the needed conductors) when
installing my old Garmin in my Glasair panel. They screwed right into the
Garmin tray and make great contact.
I know the insulation isn't aviation-rated. But for this use in a protected
area, I just cant get too excited about it. (Especially in my
somewhat-flammable airplane.)
Amphenol CS-DSDHD44MF0-005 44-Pin HD44 Deluxe D-Sub Cable, Shielded,
Male/Female, 5', Gray https://www.amazon.com/dp/B00O072X3Q
The cable is plenty flexible, though a bit long. With a little looking, you
can likely find something closer to just the length you need.
Saves a lot of crimping and testing, or just cut it and do one end.
Probably costs about the same as 88 (plus re-dos) pins and a tool if you
don't have one.
Ron
Message 3
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| Subject: | Re: Audio panel move |
Thanks for the input. I was just surfing Amazon when the email came in from Ron
suggesting "Amphenol CS-DSDHD44MF0-005 44-Pin HD44 Deluxe D-Sub Cable, Shielded,
Male/Female, 5', Gray". I see they also have one in 2.5' "AMPHENOL CS-DSDHD44MF0-002.5"
which I think will be perfect.
Thanks Again.
David
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=503567#503567
Message 4
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| Subject: | Re: Fwd: Aero Electric Post |
>The going failure theory is an intermittent connection in the field
>circuit that induces a heavy alternator load by turning it on and
>off but there isn't anything in the 1Hz data traces from the Dynon
>that indicates this is the case. Nor is there evidence of any loose
>connections or nicked wires in the field circuit.
>
>The image shows the volt and amp trace for the last 1.7 hour flight.
>The failure occurred around count #6184. The noise on the front end
>is startup and taxi. The blip around 2291 was plugging in an iPad.
>
>Keystone Aerospace LLC
>Gregg Costabile, President/Owner
>(850) 585-3149
><mailto:gcostabile@cox.net>gcostabile@cox.net
>
There is no way to externally 'induce a heavy load' in the
alternator drive shaft by manipulating the field voltage.
Recall that alternator driving torque is proportional
to field flux which is proportional to field excitation
current. The field winding is an inductor . . . the reactive
opposite of a capacitor. Rapid changes in applied voltage to
a capacitor will indeed produce higher currents. Not so
with an inductor. A magnetic field building in response
to applied voltage changes in an inductor are OPPOSED
by that building field. This is called 'counter emf'.
This physical constraint tells us that an alternator's
shaft torque cannot be caused to 'spike' in response
to an application of normal voltage. Voltage available
to excite the field can only come from the bus which
in this case is battery driven. Further, the speed with
which shaft torque changes is moderated by the field's
natural tendency to RESIST variations in current due
to changes in applied voltage.
Example in point. Modern switching regulators in
TC aircraft operate at switching frequencies on
the order of 200 to 1000 cycles per second. An
oscilloscope on the field terminal will show a
variable pulse width, square wave peak to peak
amplitude equal to bus voltage.
Looking at the b-lead terminal, one cannot see
any artifacts that might correspond to those
large, rapid fluctuations in applied field
voltage.
So the idea that a plastic shear coupling can
be 'overstressed' by some anomaly in field
excitation simply has no foundation in physics.
It is far more likely that material or a process
used to fabricate the coupling is deficient.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 5
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| Subject: | Vacuum pad shear couplers |
So the idea that a plastic shear coupling can
be 'overstressed' by some anomaly in field
excitation simply has no foundation in physics.
It is far more likely that material or a process
used to fabricate the coupling is deficient.
I found some exemplar shear couplers from a
vacuum pump pad. The two disks at each end
are engaged by pins on hard, drive parts.
The cylinder of plastic between the disks
is the shear section.
Being plastic, it is not a trivial matter to
craft a well calibrated part for shear strength.
B&C went through some iterations of materials
before settling on a production configuration.
I'm pretty confident that Plane Power is having
difficulty with their present batch of parts.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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