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firewall penetrations

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Erich_Weaver(at)URSCorp.c
Guest

Posted: Sat Apr 22, 2006 9:29 pm Post subject: firewall penetrations

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

Posted: Sun Apr 23, 2006 6:36 am Post subject: firewall penetrations

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

Posted: Sun Apr 23, 2006 8:06 am Post subject: Re: firewall penetrations

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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