Today's Message Index:
----------------------
1. 06:34 AM - Re: Screw Terminals on B&C breakers... (Robert L. Nuckolls, III)
2. 06:49 AM - Re: Best way to connect SS screw to aluminium (Robert L. Nuckolls, III)
3. 07:02 AM - Re: Toggle Actuated Circuit Breakers (Robert L. Nuckolls, III)
4. 10:45 AM - New circuit board as strong as steel, because it is steel! (Robert L. Nuckolls, III)
5. 10:45 AM - Re: How to chose an EFIS (Robert L. Nuckolls, III)
6. 06:56 PM - Light Speed Ignition with OV (Joe)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Screw Terminals on B&C breakers... |
At 09:01 AM 2/6/2009, you wrote:
>
>Bob and the group,
>
>While rewiring my not-yet-flown-by-me Longeze I've been attempting
>to follow the interconnect philosophy (for power wiring) of:
>
>Fast-ons preferred for appropriate (lower) current connections,
>Studs w/ ring terminals (with either a self-locking nut or a 2nd
>(aka jam-nut) nut) for higher current,
>Screw-terminals, which aren't really lockable, to be avoided.
I'm not sure I can beat an enthusiastic drum
for "avoiding" screw terminals. After all, they've
been used in civil and military aircraft since day-one
and I'm aware of no considered movement to reduce
their numbers. The fasteners we really went after
were rivets when the molded/bonded composite structures
were conceived, crafted and qualified.
As we speak, there are hundreds of thousands of
airplanes in the word that use breakers like
and other devices with threaded fasteners not
unlike . . .
http://aeroelectric.com/Pictures/Wiring_Technique/A36_Firewall_A.jpg
http://aeroelectric.com/Pictures/Wiring_Technique/bus_bars_1.jpg
What I CAN suggest with enthusiasm is that
the non-professional assembler of components
has a higher probability of success (i.e. lower
risk of future failures) if the processes used
are "self calibrating". I.e. crimped as opposed to
soldered, fast-ons as opposed to torque sensitive
screws, etc. etc. A secondary consideration goes
to simple-reliability studies where all things
being equal, the lower parts-count assembly is
the more reliable.
>But I haven't been completely successful yet. What is recommended for:
>
>-The screw-terminal B&C breaker used for the alternator field winding?
>Blue locktite? Or use another breaker? Or don't worry about it?
It's not worthy of much worry. First because we're
building FAILURE TOLERANT aircraft . . . or at least
that's the goal. As you assemble EVERY bit and piece
of airplane, study the manner in which it might fail,
deduce whether or not the failure is pre-flight detectable,
deduce how you would become aware of the failure in
flight, deduce criticality of the failure and finally,
if loss of that component's functionality puts your
comfortable termination of flight at-risk, then
craft a Plan-B for dealing with it.
>Of my list, this one bothers me the most as the screws are small
>enough that it's not clear to me I can tighten them enough to get an
>appropriately gas-tight connection without stripping them. Not to
>mention the (imagined?) possibility of inadvertently loosening them
>by poking around behind the panel and moving the wire (and
>associated ring terminal) they are attempting to clamp.
At the current levels this breaker operates at, it's
not essential that the whole mating surface area under
the head of the screw be gas-tight. At the microscopic
level, you will find that when these 6-32 screws are
torqued "in the ball park", surface irregularities
(yeah it LOOKS and FEELS smooth . . . but the earth
is smoother than a billiard ball) will come together
with sufficient pressure to make the electrical joint.
That gas-tightness thing for the whole surface area
has more to do with keeping moisture/oxidants out
for longevity of the joint . . . that's when we get
the wrench out and crank that fat wire terminal down
good. Stuff behind the panel is not subject to much
splash.
>- The B+ connection on my alternator (ND external regulator type
>from a Toyota) which uses a metric nut and doesn't have room on the
>stud for a jam nut (I haven't looked for a high-temp self locking
>metric nut but that's probably the answer if I can find one),
Yeah, and as I recall those threads were pretty
coarse too. In fact, b-lead terminals are pretty
high on the list of reasons that alternators are
returned to B&C for repair. The nut works loose
and the terminal burns.
>- The brass screw terminals for the amp-meter leads at the shunt
>(from B&C) (blue locktite?)
>
>On a related note, can anyone point me to the appropriate torque
>standards for brass nuts onto brass studs (as on the B&C shunt and
>the B&C grounding blocks...)
If you have a torque wrench and your confidence
goes up by using it, then my all means. I can
tell you that none of the threaded fasteners
in the photos above were precision torqued. The
the band of satisfactory assembly between too
loose and too tight is really pretty big.
Most brasses have a tensile strength on the
order of 50K PSI, so look up the torque values
for any steel part of the same thread (AC43-13
has some tables) and adjust the value for brass
downward in proportion to their relative strengths.
Just for grins, take a 6-32 steel screw and a
brass nut (breaker combo) and see how hard it
is to fail the parts by twisting on them. If you
DO achieve failure, do it a couple of times. This
will give you some sense of limits for doing the
same task in your airplane. I think you'll find
that you're not inclined to put nearly so much
force on the parts to achieve satisfactory
"snugness".
>And, lastly, is there any (presumably metallurgical) reason it's a
>bad idea to use a non-brass nut (or jam-nut) on a brass stud?
Not sure I'd worry about it. The fat wires go onto
studs that are larger and fine threaded. Cranking
these puppies down without further "insurance"
is common practice.
Locktite on the automotive threaded b-lead
nut is about the only place I'd consider the
use of a magic elixir useful for fixture.
It's more important that fat wires on studs
not impart strong rotational moments under
vibration. Note the techniques used to
bundle wires in this photo.
http://aeroelectric.com/Pictures/Wiring_Technique/A36_Firewall_B.jpg
Bob . . .
>Thanks in advance,
>Steve.
>
>
>Checked by AVG - www.avg.com
>02/04/09 16:35:00
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Best way to connect SS screw to aluminium |
At 11:22 AM 2/6/2009, you wrote:
>I have a Bob Archer SA-006 antenna (BIG "E"). It is made out of
>2024-T4 .016".
>
>The shield of the cable is supposed to be connected to the aluminium
>"E" with a 4-40 stainless steel truss head screw. The only contact
>to the aluminium is the underside head of the screw. There is
>pheonelic on the other side.
>
>The antenna will be permanent bonded on the inside of the rudder
>with access only through major surgery, thus I want to try and make
>this connection a good as it can be.
>
>It happens antenna came assembled and the head is right over some
>painted markings.
>
>Should I just scotch bright and reassemble?
>
>Perhaps put a #4 phosphor bronze star washer under head?
Hmmmm . . . my mental image of your words suggests that
conduction from terminal passes is under a nut on a screw
through threads of a screw that passes through
an insulator and then to the head of a screw that's down
against the aluminum antenna structure? The general rule
for using threaded fasteners to make electrical connections
is NOT to depend on the screw or it's threads for anything
other than mechanical force to keep terminal and substrate
in good contact. Putting a phenolic (plastic) spacer in the
mate-up stack does not go toward the maintenance of pressure
over time.
Can you move the terminal over to the other side so that
it's down against the antenna? Can you counter bore the
phenolic so that the screw clamps up ONLY on terminal
and antenna. Can the screw be up-sized?
I'd like to see the phenolic out of the stack for
maintaining clamp up forces. If you can put in a
larger screw that would be good too. Clean the parts,
clamp up to torque recommended for the screw and
you're in good shape. If there's any chance the
joint can get wet in the future, coat the finished
joint with silicone grease before you close it all
up.
If the as-designed screw is also depended upon for
keeping the phenolic block in place, ADD a second
screw for that purpose so that you can dedicate
the terminal screw to it's singular task of maintaining
good conduction pressures over the lifetime of
the airplane.
Now, having conducted this little exercise, we'll
probably find that 20 years from now, nobody has
experienced any failures due to the concerns we've
studied. Nonetheless, there are rational reasons
for doing the exercise and implementing the practices
suggested. As you've implied, it's a lot easier
to do some simple things now than to fix some
really hard things later.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Toggle Actuated Circuit Breakers |
At 07:55 AM 2/5/2009, you wrote:
>
>With respect to life cycles how do the switch type circuit breakers
>hold up? I am looking at the Potter & Brumfield variety.
>
>
>Thanks
>
Go to the Matronics.com archives search and review
the 59 or so messages on AeroElectric-List that
mention "W31".
These are not the best breaker/switch in the world
nor are they the worst. Since we're building FAILURE
TOLERANT airplanes, use of these devices to meet
your design goals is not a decision fraught with
evil or risk.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | New circuit board as strong as steel, because it is |
steel!
At 07:51 PM 2/6/2009, you wrote:
>Hmm, just wondering why you would want to build the board onto
>alumninum and onto the inside of a D-sub aluminnum style
>shell. What benefit would that get you?
>
>Regarding glueing the board to aluminum, why can't the aluminum be
>anodined to accept the glue?
>
There are a host of packaging techniques and
materials designed to improve the transfer of
heat from surface mounted components to the outside
case or other heat dissipating features.
One of my clients builds a line of brushless dc
motor driven fans. The motors are in the .4 hp
class but only about 2" in diameter. They draw
10-12 amps at 28v in operation. Heat dissipating
components on the board must have a means by
which their waste energy is taken away with
enough efficiency to keep the parts of self-
destructing in a 70C environment. The boards
for these drivers are mounted under the 2" diameter
end bell. They are laminated onto aluminum
substrates that conduct heat from the components
to the motor housing.
Building devices inside some convenient, off-the-
shelf, INEXPENSIVE enclosure has a lot of attraction
for designers. I've designed perhaps a dozen devices
that were assembled on boards that would fit inside a
d-sub backshell. Here's a little two-day fix I did
for one of our super-sonic targets at Beech.
http://www.aeroelectric.com/temp/AEC9014B.pdf
Many others have exploited this
technique as well. Brother Vern Little's line of
audio system components are housed in D-sub friendly
shells. See:
http://www.vx-aviation.com/
My all-time winner of $cost$/performance ratio for
a data acquisition system (8 ch, 12-bit, 1000 samples/sec
on ALL 8 channels) was built into a double-ended
25-pin dsub shell, ran from a Windows 95 lap-top's
high performance parallel port and cost me $100.
You can just see this little critter peeking from behind
the laptop in . . .
http://www.aeroelectric.com/articles/AA_Bat_Test.pdf
It's been my experience that getting the electronics
to work is about 10% of the task. Getting the software
(if any) to work is 20% of the task. Getting it PACKAGED
with the minimum of labor, parts count, and procurement costs
is 30% of the task. Getting it holy-watered by the
boss, the ACO, and the customer is 50% of the task.
When you can assemble a device on a board that drops
into an off-the-shelf, 60 cent enclosure in 2 minutes
flat, you've made a SUBSTANTIAL improvement on the
cost of ownership for your product.
My best guess as to why the board mentioned in the
start of this thread was bonded to a steel substrate
is not because it need to be strong but because it
needed to be cool.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: How to chose an EFIS |
At 04:03 PM 2/5/2009, you wrote:
><peter@sportingaero.com>
>
>I have written an article about factors you might consider when buying an
>EFIS that has been published in the UK homebuilder magazine, Light Aviation.
>It might be of interest to some of you here.
>
>http://www.glosterairparts.co.uk/EFIS8pt1.htm
>
>Peter
Peter, if you'd be amenable to the idea of having this
work posted on aeroelectric.com, I'd be pleased to add
it. I'd be especially pleased to post the complete work
at such time as it becomes available.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Light Speed Ignition with OV |
There has been discussion recently about Light Speed Ignition with built
in OV protection based on a phone conversation with Light Speed. And
then someone posted an excerpt from the installation manual which reads
in part:
"Input voltages above 35 volts or reversed polarity will cause system
damage. For this reason it is mandatory that all aircraft using Plasma
CD Ignitions are equipped with over-voltage protection in their
alternator charging system(s)."
I interpret this to mean that there is no crowbar over-voltage
protection built into the Light Speed Ignition. Otherwise, how could it
be damaged if high voltage is shorted by internal OV protection? And
why would it be mandatory that the aircraft electrical system be
equipped with OV protection if it is already built into the ignition? I
suggest that there was a misunderstanding in the conversation and that
Light Speed Ignition systems do NOT have built-in crowbar over-voltage
protection. The company should issue a written statement to clarify
this issue. Otherwise prospective customers might not want to buy their
products if there is a perceived danger that a charging system failure
could stop the engine.
Joe
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|