Today's Message Index:
----------------------
1. 05:32 AM - Re: Boeing switches (Eric M. Jones)
2. 06:20 AM - Re: Re: Master Switch/Contactor and Starter Questions (Robert L. Nuckolls, III)
3. 07:29 AM - Re: Re: Boeing switches (Robert L. Nuckolls, III)
4. 11:00 AM - Narco Transponder Tray Coax Connector ()
5. 11:05 AM - Re: Re: Boeing switches (Jay Hyde)
6. 12:17 PM - Master/Battery/Alt Field vs. Master/Battery and Alt Field... (Michael Burbidge)
7. 02:48 PM - Low voltage indicator with dual alternators (donjohnston)
8. 02:57 PM - Re: Narco Transponder Tray Coax Connector (Bill Putney)
9. 03:22 PM - Re: Re: Boeing switches (Robert L. Nuckolls, III)
10. 03:42 PM - Re: Narco Transponder Tray Coax Connector ()
Message 1
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Subject: | Re: Boeing switches |
My two cents:
Using two parallel switches to prevent trim runaway seems boneheaded, and wouldn't
stand a thorough engineering fault-tree review. Furthermore I'd bet that it
never prevented ANY problem from occurring.
Sure, I understand the intention, but I don't think it's good engineering.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=403912#403912
Message 2
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Subject: | Re: Master Switch/Contactor and Starter Questions |
At 07:13 PM 7/3/2013, you wrote:
><dgaldrich@embarqmail.com>
>
>I agree. It seems pointless to have 2 solenoids operating at the
>same time. The other issue is that I believe the Subaru solenoid
>moves the gear before the contactor part puts juice to the motor
>brushes. An aircraft type contactor would do both at the same time
>rather than sequentially. Have not dismantled one so I may be in error.
None of applications of an external contactor
proposed for modern starters "bypasses" functionality
of the built in solenoid/contactor. The
starter's built in solenoids do engage the pinion
gear before closing electrical connection for
the starter motor.
Variants to select from when using these modern
starters causes the builder to decide whether
the built in contactor is energized by the panel
mounted, START switch -OR- energized through a more
robust device.
There is a problem to be solved when the panel
mounted starter control is used to energize the
starter's built in contactor. Unlike legacy
'starter solenoids' controlling starters with
Bendix drives, the modern pinion engagement
solenoids have a very high coil current demand
during the first few milliseconds of being
energized. See: http://tinyurl.com/op5cs2g
Failure to recognize this difference in
solenoid/contator performance caused a
kerfuffle over burned start switch contacts
on the ACS-510 key swicch (clone of legacy
Bendix/Gerdes). ACS now sells a diode with two
terminals applied.
Emacs!
A critical need to install this diode across the
starter contactor engagement coil arose from the
alarming rate at which start contacts in the key
switch were destroyed by overstress when the legacy
starter/external contactor combo was replaced with
a light weight version with combination solenoid/
contactors. Many cars suffered similar failure modes
in their key-start switches.
SB92-01 from ACS originally place thier diode across
the switch contacts . . . wrong place. It was corrected
in a subsequent revision. See http://tinyurl.com/nva2xdy
B&C adopted the philosophy of jumpering the starter
solenoid coil right to the fat-wire terminal on
the starter . . . and controlling power to the
starter though a modern, starter contactor WITH
built in coil suppression diode. The external contactor's
inrush demands on the start switch are a small fraction
of that for direct control.
This philosophy posed a new problem when PM motor
starters began to show up on the airplane. PM motors
have a pronounced counter-emf during spin-down after
the power is removed. This would delay disengagement
of the pinion gear and was commonly called "starter
run on" . . . in fact it was better called "delayed
disengagement".
Starters with wound fields (B&C and some others)
do not suffer this indignity and function well with
the engagement solenoid jumpered directly to the
starter's fat-wire terminal.
In ANY case, the builder's design goals should
include providing a source of solenoid engagement
power that (1) is supplied through a low impedance
source (short and fatter than usual wires) and
(2) avoid running this power through the panel
mounted start switch.
If the starter is a PM version, the builder can
take advantage of the "I" terminal on many modern
starter cotactors and use it to SUPPLY current
to the engagement solenoid. This provides for
instant removal of coil power when the starter
switch is opened and prevents 'delayed disengagement'.
In this case, the builder would do well to have
diode coil suppression on BOTH the external contactor
coil AND the solenoid/contactor coil on the
starter.
Bob . . .
Message 3
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Subject: | Re: Boeing switches |
At 07:29 AM 7/4/2013, you wrote:
>
>My two cents:
>
>Using two parallel switches to prevent trim runaway seems
>boneheaded, and wouldn't stand a thorough engineering fault-tree
>review. Furthermore I'd bet that it never prevented ANY problem from occurring.
Whether or not a problem was demonstrably
prevented is irrelevant to the reliability
study. Good FMEA mitigation assumes that the
part WILL fail. Working out a logical means
by which single failures might go undetected
for no more than a single tank full of fuel
has been a time-honored legacy design goal.
>Sure, I understand the intention, but I don't think it's good engineering.
they are not used in PARALLEL. In the Boeing
case, they are in series with one side controlling
direction, the other side in SERIES controlling power.
Each side can be explored for functionality
in pre-flight, neither side capable of causing
a runaway-by-sticking.
Beech (and many others) uses the two spdt
switches to handle one half of a PM motor UP-OFF-
DN switching duty. Again, both sides easily
evaluated in pre-flight, neither side capable
of causing a runaway-by-sticking.
Lear (and many others) uses the 'coolie hat' to
drive relays that DID offer a possibility for runaway-by-
sticking. But their systems architecture included
a wheel-master-disconnect that removed power from
all trim systems along with the autopilot. I AM
aware of trim runaways in aircraft fitted with
wheel master disconnects that would not have happened
if the airplane had been fitted with the split
trim switch where the WMD switch provided the
mitigation.
Bob . . .
Message 4
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Subject: | Narco Transponder Tray Coax Connector |
Can someone point me to the part number/source for a replacement
90-degree,
bulkhead, slide-on, coax connector used on the Narco AT-150 transponder
tray? Any of the usual suspects (Mouser, Digi-Key, Allied, etc) carry
them?
Thanks,
James
Message 5
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Subject: | Re: Boeing switches |
Good argument Bob.... I use a switch on the panel to power the trim, but
that may be a bit far away for a quick reaction, before the trim lurks all
the way to the end.
Jay
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: 04 July 2013 04:29 PM
Subject: Re: AeroElectric-List: Re: Boeing switches
--> <nuckolls.bob@aeroelectric.com>
At 07:29 AM 7/4/2013, you wrote:
>--> <emjones@charter.net>
>
>My two cents:
>
>Using two parallel switches to prevent trim runaway seems boneheaded,
>and wouldn't stand a thorough engineering fault-tree review.
>Furthermore I'd bet that it never prevented ANY problem from occurring.
Whether or not a problem was demonstrably
prevented is irrelevant to the reliability
study. Good FMEA mitigation assumes that the
part WILL fail. Working out a logical means
by which single failures might go undetected
for no more than a single tank full of fuel
has been a time-honored legacy design goal.
>Sure, I understand the intention, but I don't think it's good engineering.
they are not used in PARALLEL. In the Boeing
case, they are in series with one side controlling
direction, the other side in SERIES controlling power.
Each side can be explored for functionality
in pre-flight, neither side capable of causing
a runaway-by-sticking.
Beech (and many others) uses the two spdt
switches to handle one half of a PM motor UP-OFF-
DN switching duty. Again, both sides easily
evaluated in pre-flight, neither side capable
of causing a runaway-by-sticking.
Lear (and many others) uses the 'coolie hat' to
drive relays that DID offer a possibility for runaway-by-
sticking. But their systems architecture included
a wheel-master-disconnect that removed power from
all trim systems along with the autopilot. I AM
aware of trim runaways in aircraft fitted with
wheel master disconnects that would not have happened
if the airplane had been fitted with the split
trim switch where the WMD switch provided the
mitigation.
Bob . . .
Message 6
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Subject: | Master/Battery/Alt Field vs. Master/Battery and Alt |
Field...
I'm sure I read a discussion of this question somewhere but can't find it.
I'm building an RV-9A, basic day/night VFR. I'm using the Basic Day/Night VFR system
diagram available from B&C website. It is almost identical to the Z-11 diagram
in Bob's book. One difference is that the Z-11 uses a 2 poll 3-throw switch
(2-10) for the master, so that the alternator can be switched on after start.
The Basic VFR diagram from B&C uses a 2 poll 2 throw switch (2-3) so that
the alternator field is on during start.
What are the advantages of isolating the alternator field during startup? My airplane
has a B&C 40 amp alternator. Which approach would you recommend?
Thanks,
Michael-
Message 7
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Subject: | Low voltage indicator with dual alternators |
I'm going to have a 60a primary and a 20a secondary alternator with B&C LR3C and
LS1A voltage regulators respectively.
If in the event of a primary alternator failure, and I switch to the secondary,
will the primary low voltage warning light (off of LR3C, pin 5) remain illuminated?
Or will switching off that alternator open the low voltage circuit?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=403960#403960
Message 8
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Subject: | Re: Narco Transponder Tray Coax Connector |
It's TED 9-30-10 connector. These are solder on connectors and have the
lowest profile (depth-wise).
http://hangar-10.com/products/Tray-Mount-Rf-Antenna-Connect.html
You should check with them to make sure a snap ring is included or you
may have to buy it separately.
There's also a DBA-600 that is a connector like you want with a female
BNC so you don't have a cable attached to your tray. You put a BNC on
the cable and connect it to this adapter. About the same price as the
9-30-10 but of course you have to do the BNC too.
http://hangar-10.com/products/Bnc-Tray-Adapter-W%7B47%7DSnap-Ring.html
Bill
On 7/4/13 10:59 AM, berkut13@berkut13.com wrote:
> Can someone point me to the part number/source for a replacement
> 90-degree,
> bulkhead, slide-on, coax connector used on the Narco AT-150 transponder
> tray? Any of the usual suspects (Mouser, Digi-Key, Allied, etc) carry
> them?
>
> Thanks,
> James
> *
>
>
> *
Message 9
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Subject: | Re: Boeing switches |
At 01:05 PM 7/4/2013, you wrote:
>
>Good argument Bob.... I use a switch on the panel to power the trim, but
>that may be a bit far away for a quick reaction, before the trim lurks all
>the way to the end.
You would do well to deduce the severity of a
trim runaway. Is the airplane controllable with
full trim either up or down? How fast does the
trim run with respect to pilot reaction times
needed to deal with a runaway? Are there stops
or limits to trim excursion necessary for the full
range of CG envelopes or will the system produce
more pitch authority than would ever be necessary
for normal operations?
In a Lear, at Mach cruise, the system is manually
failed and the pilot is obligated to keep hands in
the lap for 3 seconds. Only then can he move to
deal with the situation. After achieving a stable,
safe condition, recorded data is analyzed for
busting limits on attitude, altitude and airspeed
excursions.
The exercise is repeated and trim speeds then
adjusted until a sweat-free, runaway recovery
is assured.
The trim systems I've seen in some TC aircraft
are so slow that unexpected trims under worst
case conditions are no big deal. But what's the
story for YOUR airplane?
Yes, if trim speeds are brisk, trim authority high
and you have good reason for not reducing them, then some
form of inarguable override is indicated. Instructing
the pilot to pull a breaker for taming a trim runaway
is generally not acceptable . . . even panel mounted
switche situated amongst other switches will get
you frowns from the human factors guys.
At the same time, find out just how much risk is
associated with an uncontrolled trim event and
see if that can be engineered out as opposed to
stacking emergency ops hardware on top of the
design.
Bob . . .
Message 10
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Subject: | Re: Narco Transponder Tray Coax Connector |
Excellent! Exactly what I needed. Thanks.
From: Bill Putney
Sent: Thursday, July 04, 2013 4:57 PM
Subject: Re: AeroElectric-List: Narco Transponder Tray Coax Connector
It's TED 9-30-10 connector. These are solder on connectors and have the
lowest profile (depth-wise).
http://hangar-10.com/products/Tray-Mount-Rf-Antenna-Connect.html
You should check with them to make sure a snap ring is included or you
may have to buy it separately.
There's also a DBA-600 that is a connector like you want with a female
BNC so you don't have a cable attached to your tray. You put a BNC on
the cable and connect it to this adapter. About the same price as the
9-30-10 but of course you have to do the BNC too.
http://hangar-10.com/products/Bnc-Tray-Adapter-W%7B47%7DSnap-Ring.html
Bill
On 7/4/13 10:59 AM, berkut13@berkut13.com wrote:
Can someone point me to the part number/source for a replacement
90-degree,
bulkhead, slide-on, coax connector used on the Narco AT-150
transponder
tray? Any of the usual suspects (Mouser, Digi-Key, Allied, etc)
carry
them?
Thanks,
James
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