Fred,
My DAR, Dennis Carley was fine with the penetrations I had on a Zenith
which were similar to yours but metal of course. The Subaru was so
dependent on the electrical, he asked that I consider using fire sleeve
over the critical fuel injection and ignition wiring especially near the
high heat areas and of course seal it all with RTV as you said, to deter
fumes and flame penetration. He did not make it mandatory, but asked me
to consider it because the harness was automotive wire and not mil spec
aviation wire... I looked at other aircraft builder techniques and
instead of running the wires through the fire sleeve, I noticed many RV
builders slit the fire sleeve and only use it near the firewall and in
high temp areas and not over the whole engine. Then they zip tie it...
That looks nasty. To seal the slit in the fire sleeve, I recommend F4
tape and RTV
F4 tape is a self adhering (non adhesive) silicone tape developed by
the military and when pulled is heat resistant and self adhering. I've
used it when you forget that piece of heat shrink, and it is awesome,
but somewhat expensive. See one of the vendors:
http://www.rescuetape.com<http://www.rescuetape.com/> or just Google
it.
My DAR feels like I do that if the fire is bad enough to burn up the
military spec wiring, you have more problems than worrying about the
insulation of the wires. If you just do, lets say, the 4-6 inches from
the firewall penetration with fire sleeve and F4 tape, at least that
will ensure the fire and fumes won't get through the firewall. If you
have automotive wire, change it or protect it unless it is of the new
high temp stuff....
As most of you know I build a large 6x12 D shaped access hole with a
flange and shear web reinforcing behind the firewall and fashion a
removable panel for access to more quick disconnect plugs at the rear of
the instrument panel. Attached to the removable panel, I secure one or
two plugs for quick disconnects. It takes me only a few minutes to pull
an engine or instrument panel as I try to make everything serviceable.
It takes longer to build, but if the engine or instrument panel is easy
to remove, you'll benefit from it in the long run. I prefer the metal
mil spec plugs as they are highly resistant to everything, but the AMP
brand plastic circular plugs are commonly used in my aircraft for
firewall penetrations also. They are not fire proof, but with an RTV
seal in the wire securing clamp on the rear of the plug to seal it, I
believe they hold up well. Like you Fred, I don't like to cut factory
bundles, but I will build a transition plug to go through the firewall
only because I can build a good and trustworthy plug. For instance, if
the EMS plug from the engine to computer has a D Sub, I will look at it
and determine if it is worth it for me to build a transition plug from
the engine through the firewall rather than drill a big hole. I would
like to pull the engine easily, and this means pulling the wire harness
with it. Another plug is used for the firewall mounted devices. A D
Sub is not fireproof nor is it strong, and so I don't use them as
firewall penetrations, especially since you have to cut out the firewall
and mount the D Sub to a metal panel anyway because the plug is too
short to be attached to the glass. If you decide to build a D Sub
firewall transition plug, the purist would glass up an insulated cover
or use a small metal cup with a flange for a fireproof cover. That is
overkill to me, so go with a hole and proper fire wall penetration cover
and put a transition plug behind the firewall for easy panel removal..
I leave the thermocouple wires as supplied by the probe manufacturer
(normally a spade), but then inside the airframe, I'll run the rest of
the way to the EIS with 20 gauge mil spec wire for CHT and EGT and have
had no problem. But one should continue to the EIS with the same wire
(thermocouple if the type is known) to the box. Not all manufacturers
supply the extra wire and I get away with using regular mil spec
aircraft wire without problems from the spades supplied by the factory
going to the Engine Management box. Works for me so far.
My DAR also does not like nyloc nuts anywhere on the engine. He prefers
to use loctite on studs, squeeze nuts or a cotter pins and castle nuts
on the engine.
Finally, the penetration hole is best sealed with a stainless firewall
penetration cover. The type that has a half a hole in each half, but
the two haves have a tab that actually overlaps and are secured with
screws and nutplates. A grommet cut to slip on the wires along with RTV
seals the hole well. Your setup looks like you have a slot which does
the same thing but in the fire wall material, so protect the wires and
rubber hose with a bit of fire sleeve, and seal it with RTV and go for
it.
Regards,
Bud
----- Original Message -----
From: Fred Klein<mailto:fklein@orcasonline.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Thursday, January 27, 2011 4:52 PM
Subject: Europa-List: firewall penetrations
On Jan 27, 2011, at 7:20 AM, JonSmith wrote:
> is it considered acceptable for the electric tacho wires to pass
> through the firewall via the multipin plug/ socket connector that I
> have all the other low current things going through (oil press/
> temp, starter solenoid control wire etc etc) or are the tacho wires
> subject to interference and should thus be routed separately?
All,
Every so often I read a post which gets my attention and prompts me to
reconsider aspects of my build...this is one of them.
As I've posted previously, my engine is a MPEFIed derivative ot the
Sube EA81which arrived w/ a fully complete and dyno-tested wiring
harness in a nice, neat, and tidy bundle with several rectangular 15
and 27 pin Dsub connectors intended to be plugged into the ECU (shock
mounted aft of the firewall) and a small control unit to be mounted on
the instrument panel.
In the process of mounting various sensors on the engine (EGT
thermocouples, oil temp. & pressure, coolant temp. & pressure, etc.),
I have a second bundle of wires...both bundles, of course, must
penetrate the firewall in some manner.
With a fair amount of ignorance and naivety, I have been loath to mess
with the ECU bundle; consequently, I've cut a slot in the firewall big
enough to slide the 27 pin Dsub connector thru and fabbed a cover
plate from firewall material which is secured w/ nutplates w/ a hole
sufficient for the bundle. A short length of split rubber hose
surrounding the bundle is intended to protect the wires from wear
against the raw edge of the firewall and cover plate.
With regard to the sensor bundle, having been advised to avoid
connectors in the thermocouple wires leading to my EMS unit which
degrade their accuracy to some degree, I have similarly drilled the
firewall and installed a rubber grommet as shown.
A couple of photos are attached.
Prior to flight test, it's my intention daub on a bit of RTV sealant
to stop any air leakage; all of the above appears to be consistent w/
techniques used for firewall penetrations on my 1946 Stinson.
Informed comment would be much appreciated.
Please be gentle,
Fred
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