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Erich_Weaver(at)URSCorp.c Guest
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Posted: Sat Apr 22, 2006 9:29 pm Post subject: firewall penetrations |
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Listers:
Lots of wire hanging around my RV-7A right now, waiting to be tamed. Im
following the Z-13/8 architecture and using a GRT EFIS/EIS. I labeled
items on the Z-13 figure as being either aft or forward of the firewall,
then sorted through the various EFIS/EIS wire call-outs to make a list of
all the wires needing to go through the firewall so I could plan wire paths
a little better:
1 battery bus to battery contactor
2 battery contactor to the S704-1 relay for the backup alternator
3 battery contactor to main bus
4 master switch to battery contactor
5 push to start switch to starter contactor
6 regulator for back-up alternator to backup alternator (two wires)
7 regulator for main alternator to main alternator
8 left ignition switch to p-mag (two wires)
9 right ignition switch to p-mag (two wires)
10 Groundpower switch to groundpower contactor
11 EIS to CHT(8 wires)
12 EIS to EGT wires (8 wires)
13 EIS to Hall effect current sensor (two wires)
14 Tach (EIS to P-mag)
15 EIS to OAT sensor (not sure where to put OAT sensor yet)
16 EIS to VDO oil pressure sensor
18 EIS to oil temp sensor
19 EIS to fuel pressure sensor (two wires)
I would like to minimize the number of firewall penetrations. Are any of
the above wires likely to cause problems with any others when bundeled
together? Did I overlook any wires?
For practical reasons only, Im considering two penetrations for the wires,
one for the various contactor wires near the left side of the firewall, and
the other for everything else, near the center or slightly to the left.
Any thoughts from those that have been there before would be appreciated
thanks guys
Erich Weaver
Erich Weaver
URS Corporation
130 Robin Hill Rd
Santa Barbara CA 93117
805-964-6010
FAX 805-9640259
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klehman(at)albedo.net Guest
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Posted: Sun Apr 23, 2006 6:36 am Post subject: firewall penetrations |
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Hi Eric
Except for not having magnetos, I have that and more all going through a
single firewall opening. More than a hundred wires for dual efi and
ignition etc. I preferred two openings but space was tight and one
opening turned out to be easier for me. Most low voltage efi sensors are
shielded. Power and ground wires such as fuel injector wires or
contactor coil feeds are twisted/braided pairs where convenient in
accordance with good aeroelectric book wiring practice. All ground wires
(except the two firewall to engine ground straps) go through that
opening which I think is a good thing. FWIW just this week I
investigated the signals with a scope and could find no evidence of
crosstalk or problems due to routing everything through the same
opening. I had expected to find some magnetic coupling but did not. I
even temporarilly rerouted the normally noisy ignition coil feeds (high
current pulses with 100 volt or so spikes) but it made no difference to
anything that I scoped.
Separate subject but the 1994 subaru DIS ignition coils (4 cylinder) are
physically one unit with a minor effort to isolate the iron cores a bit.
I believe I did see evidence of secondary coupling evidenced by short
duration high voltage spikes in the high voltage circuit when the
alternate coil fires. Could of been just crosstalk in the spark plug
wires but I suspect magnetic coupling at the coils.
Ken
Erich_Weaver(at)URSCorp.com wrote:
Quote: |
Listers:
Lots of wire hanging around my RV-7A right now, waiting to be tamed. Im
following the Z-13/8 architecture and using a GRT EFIS/EIS. I labeled
items on the Z-13 figure as being either aft or forward of the firewall,
then sorted through the various EFIS/EIS wire call-outs to make a list of
all the wires needing to go through the firewall so I could plan wire paths
a little better:
1 battery bus to battery contactor
2 battery contactor to the S704-1 relay for the backup alternator
3 battery contactor to main bus
4 master switch to battery contactor
5 push to start switch to starter contactor
6 regulator for back-up alternator to backup alternator (two wires)
7 regulator for main alternator to main alternator
8 left ignition switch to p-mag (two wires)
9 right ignition switch to p-mag (two wires)
10 Groundpower switch to groundpower contactor
11 EIS to CHT(8 wires)
12 EIS to EGT wires (8 wires)
13 EIS to Hall effect current sensor (two wires)
14 Tach (EIS to P-mag)
15 EIS to OAT sensor (not sure where to put OAT sensor yet)
16 EIS to VDO oil pressure sensor
18 EIS to oil temp sensor
19 EIS to fuel pressure sensor (two wires)
I would like to minimize the number of firewall penetrations. Are any of
the above wires likely to cause problems with any others when bundeled
together? Did I overlook any wires?
For practical reasons only, Im considering two penetrations for the wires,
one for the various contactor wires near the left side of the firewall, and
the other for everything else, near the center or slightly to the left.
Any thoughts from those that have been there before would be appreciated
thanks guys
Erich Weaver
Erich Weaver
URS Corporation
130 Robin Hill Rd
Santa Barbara CA 93117
805-964-6010
FAX 805-9640259
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Eric M. Jones
Joined: 10 Jan 2006 Posts: 565 Location: Massachusetts
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Posted: Sun Apr 23, 2006 8:06 am Post subject: Re: firewall penetrations |
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Many times we copy successful methods long after new and better ways of doing things are available. The idiom of firewall penetration devices using leather washers and two crescent-shaped stainless parts came from the days of metal-cowled airplanes and "A petrol-proof flexible tubing at last: an invention of the greatest importance to aviation NACA TM-48 October 1921". The FAA firewall-penetration flame test was designed for metal airplanes and engines where burning was a common hazard.
My hunch is that too much attention is paid to this relatively minor task. What might make more sense?--Armored fuel lines, fuel shutoffs, Purple-K; and a flame detector under the cowl.
My Glastar instructions include a stainless steel firewall--but it looks like extreme overkill to me. 3M Dot Paper will pass the FAA test and weighs a tiny fraction of stainless steel sheet.
Consider fire safety as a complete system. Those towel bar holders and firestop should not be depended upon as the whole solution.
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_________________ Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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