Today's Message Index:
----------------------
1. 05:58 AM - Re: Dual redundant electrical system (Robert L. Nuckolls, III)
2. 06:20 AM - Re: PMA-6000 Intercom - 28v install (Robert L. Nuckolls, III)
3. 07:20 AM - Avoiding strobe noise? (Dr. Andrew Elliott)
4. 12:40 PM - Re: Avoiding strobe noise? (Robert L. Nuckolls, III)
5. 01:59 PM - Re: PMA-6000 intercom 28V install (rampil)
Message 1
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| Subject: | Re: Dual redundant electrical system |
At 08:05 PM 5/14/2008 -0400, you wrote:
>X-MIME-Autoconverted: from 8bit to quoted-printable by matronics.com id
>m4F09XD3009485
>Content-Type: text/plain; x-avg-checked=avg-ok-7F1173FE; format=flowed
<snip>
>I've attached reduced size jpg files to respect the bandwidth guidelines,
>based on the original dxf files, but will verbally describe the unusual
>aspects as well. I can also make available the dxf files showing clearer
>detail if anyone wants them.
Can you .pdf the .dxf drawings from your CAD application?
The .jpg files are kind of "swiss-cheesy" difficult to
deduce the details of your design. I'll .pdf them and repost.
>The first component after the battery in most aircraft systems is the
>master relay, which isolates both the starter solenoid and the feed to the
>main and/or essential buses. It's usually a large heavy solenoid that must
>be rated to carry starter current but normally carries only a small
>fraction of that current, and it takes about an amp to keep it picked up.
>My design uses a 60A ANL fuse at the battery, feeding a heavy-duty
>automotive 70A relay in the cockpit next to the master switch and fuse
>bus. I expect the smaller lighter relay will be more reliable than a $17
>solenoid, especially because it is in a cooler lower vibration location,
>plus it will draw only one-tenth of the hold-in current which means more
>flying time in the event of battery only operation. In my specific system
>this is not insignificant, the 2 amp draw of two master relays would be
>~10% of the typical main bus load.
<snip>
Terry, you've obviously spent a great deal of time and thought
on this. At first blush, the system you propose is a relative
of Figure Z-14 as published at:
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z14L_1.pdf
http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z14L_2.pdf
This dual-alternator/dual-battery architecture was crafted over
a period of 15 or so years and embodies practices well demonstrated
in aircraft for over 60 years.
>Anyway, I'm completely open to suggestions and/or criticism. Ego should
>never get in the way of safety. I'd appreciate anything in the way of
>comment. I'm now at the point of being almost ready to start wiring things
>up, and need a reality check that what I intend to do makes sense.
What you've proposed will probably function as you envision it.
It's more complex than the Z-14 drawings in many respects
and may not meet design goals for aircraft systems design
where we strive for low parts count and failure tolerance.
This translates directly to reductions in weight, cost, and
pilot workload. This approach also increases reliability . . .
a part that isn't there cannot be a failure item in your finished
system.
You've cited rationale for features of your proposed
system that are not a concern for most folks in aviation. It
would be a much more direct path to "architectural nirvana"
to build on what's gone before than to stir a bunch of
parts into a totally new recipe.
At the risk of sounding like I'm suffering a "not invented
here" moment, could you take a bit of time and tell us where
you perceive that Z-14 does not meet personal design goals?
Bob . . .
Message 2
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| Subject: | Re: PMA-6000 Intercom - 28v install |
At 08:23 PM 5/7/2008 -0700, you wrote:
>PS Engineering s PMA-6000 intercom has the following note:
>
>
>To reduce the amount of heat dissipated in the audio selector panel, when
>used in a 28
>
>Volt aircraft, it is required that the 15-Ohm, 15-Watt dropping resistor
>(p/n 701-015-1501) be in-
>
>stalled in series with the power input.
>
>
>The install manual goes on to say failure to do so will generate
>unnecessary heat inside the unit and may void PS Engineering s warranty
>. Does anyone have experience installing one of these units in a 28V
>environment? Is the dropping resistor really required? The only reason I
>ask is the local radio shops don t seem to know much about it which makes
>me wonder if they ever used them. They all say they can order one but
>nobody has one in stock.
It is risky to disregard the words of the manufacturer's
installation manuals. It's also disappointing that the
manufacturers of this device did not craft a user-friendly
design.
The simplest thing to do is comply with the instructions.
The simplest way to do this is acquire a component like
this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=FVTS10-15-ND
Note that it can be mounted to some handy, out of the
way surface on a long screw. The data sheet at:
http://www.heiresistors.com/PDF/FVT_FST20%20spec.pdf
tells us the hole through the middle of this device is
0.19" in diameter . . .
The drill versus threaded sizes chart at:
http://www.phy.mtu.edu/~suits/tapsizes.html
says this is too small for a 10-32 screw but will
be just fine for an 8-32. The resistor data sheet suggests
we need one with 2" or so of over-all length. You'll
be cranking a hard force down against a ceramic tube.
Put a soft washer (some kind of rubber, plastic or even
two layers of paper from the box that comes with a tube
of toothpaste) between the end of the resistor and the
mounting surface. Tighten the screw down to finger
tight + 1 turn and spot the threads with some runny
super-glue to keep it from drifting off that pressure setting.
If your resistor comes with wires, clip them off.
Attach lead wires for intercom power to the resistor's
solder-tabs. Put double layer of heat-shrink over these
joints for vibration support.
This process has been used thousands of designs in
various vehicular products including airplanes. Simple,
lean, works as the manufacturer wishes and lasts a long
time.
BTW . . . the 15W rating is super conservative. The
intercom may draw 1A peak current but the AVERAGE
current will be much lower unless you're particularly
fond of playing Wagner at 100dB in the headphones.
Now, if you're REALLY wanting to make this more
complicated, you can purchase one of B&C's DIM3-28
dimmers at:
http://www.bandc.biz/cgi-bin/ez-catalog/cat_display.cgi?10X358218#dim3-28
and instead of installing the dimmer potentiometer,
you put the appropriate resistor between pins 1 and 3
to achieve a constant 14-volt output from the "dimmer".
Bob . . .
Message 3
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| Subject: | Avoiding strobe noise? |
I am building a 601XL (all aluminum), and have located the COMM antenna
on the bottom of the fuselage between the seats. (It's a taildragger,
so this is behind the gear.) I have the primary battery under the right
seat and am holding off locating the second battery until I see how the
W&B turns out.
It has turned out to be convenient, wiring-wise, to locate the strobe
power supply, an XPAK-604X-HR, under the left seat. In this location,
the coax to the COMM antenna and at least one of the wires to the strobe
heads will end up in close proximity.
My question is: Assuming the coax is properly terminated and the strobe
cables' shields are properly grounded at one end, is there going to be a
problem with strobe noise interfering with communications? (The strobe
cables have a foil shield with a drain wire. The drain wire is grounded
to the wing structure at the tip.)
If a problem is likely, are there any additional precautions I could
take to avoid one?
Thanks,
Andy Elliott, Mesa, AZ
N601GE (reserved)
601XL/TD, Corvair, building...
Message 4
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| Subject: | Re: Avoiding strobe noise? |
At 07:16 AM 5/15/2008 -0700, you wrote:
>I am building a 601XL (all aluminum), and have located the COMM antenna on
>the bottom of the fuselage between the seats. (It's a taildragger, so
>this is behind the gear.) I have the primary battery under the right seat
>and am holding off locating the second battery until I see how the W&B
>turns out.
>
>It has turned out to be convenient, wiring-wise, to locate the strobe
>power supply, an XPAK-604X-HR, under the left seat. In this location, the
>coax to the COMM antenna and at least one of the wires to the strobe heads
>will end up in close proximity.
>
>My question is: Assuming the coax is properly terminated and the strobe
>cables' shields are properly grounded at one end, is there going to be a
>problem with strobe noise interfering with communications? (The strobe
>cables have a foil shield with a drain wire. The drain wire is grounded to
>the wing structure at the tip.)
>
>If a problem is likely, are there any additional precautions I could take
>to avoid one?
>
Every time someone reports a "noise problem cured
by repositioning wiring" it was a demonstration of
some OTHER root cause.
When products are qualified to be used on airplanes,
they are qualified to both control emissions and
withstand certain stresses that are known to exist
in the aircraft environment.
The wiring you've cited are not particularly
communicative with respect to noise . . . assuming
that the installation of said wires is in accordance
with manufacturer's instructions.
In the heavy iron birds, we are seldom blessed with
enough room to run all the wires that are necessary
for operation much less comb them into potentially
antagonistic and/or victim systems.
The short answer is run them neatly together and
you'll be fine.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 5
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| Subject: | Re: PMA-6000 intercom 28V install |
To be clear, a switching power brick (aka DC-DC converter) turns DC
into AC then processes it and reconverts to DC. This process makes
audio and potentially RF noise. Noise injected into your intercom
will be a much worse problem than an old resistor hung on your firewall.
A resistor should also be about 1/10 the cost of a power brick. I
would guess available of amps to squander in a voltage dropping resistor
would not be an issue in your RV-10.
Cheers,
--------
Ira N224XS
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