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04-17-2011, 05:42 AM
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Join Date: Sep 2006
Location: Locust Grove, GA
Posts: 97
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G3X OAT probe and shielding
I'm wiring up the OAT probe for my G3X, and it comes with a 3 conductor shielded cable. The manual calls for the shield to be connected to the backshell at the GSU73. I had planned for a circular connector (CPC) at each wing root. This would require that I cut the OAT cable to connect it through the CPC.
How important is it that the shield have connectivity all the way back to the AHARS (GSU73)? I figure I have 3 choices:
1. Connect the shield to a pin in the CPC
2. Ground the shield at the wing root
3. Don't connect the shield to anything.
Thoughts or suggestions?
Thanks,
Aaron
__________________
Aaron Sims
RV-10 (2015 Bronze Lindy)
RV-6A (sold)
Home Field: Mallards Landing (GA04)
Locust Grove, GA
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04-17-2011, 07:14 AM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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Hi Aaron,
My plan is the same as your's - a CPC connector at eh wing room. I am planning on carrying the shield through a pin - I am just guessing that the shield on the OAT is probably not THAT significant, and if I am wrong, it will not make the airplane fall out of the sky - I'll just have to go in and fix that detail. But I strongly suspect that the shielded OAT wiring is overkill....
Paul
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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04-17-2011, 08:22 AM
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Join Date: Feb 2005
Location: Northwestern USA
Posts: 1,209
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Since this same OAT probe is used on everything from LSAs to the Citation Ten, I believe the fact that they went overboard with shielding is due to lightning protection requirements for the big iron. On my airplane, I plan to carry the shield through the connector via a pair of pins, just as Paul described.
mcb
__________________
Matt Burch
RV-7 (last 90%)
http://www.rv7blog.com
VAF #836
Any opinions expressed in this message are my own and not those of my employer.
Last edited by mburch : 04-17-2011 at 11:37 AM.
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04-18-2011, 10:16 AM
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Join Date: Jun 2009
Location: Leesburg, Virginia
Posts: 50
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I can report from experience that we have several flying with the OAT shield carrying through connectors - both CPC and D Sub and like Matt said, there is not going to be a problem.
__________________
David Buckwalter
Avionics Systems, LLC.
Leesburg, VA
sales@avionikits.com 703-669-2669
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07-14-2016, 01:19 AM
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Join Date: Dec 2013
Location: Santa Clara, CA
Posts: 250
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Hi all.
An additional question on this - since the probes are resistive, do you see a wrong reading from the resistance added by the connectors? (I'd imagine not or just varying the wire lengths would also have some effect)
Thanks!
__________________
Rodrigo Damazio Bovendorp
San Jose, CA
RV-10 builder #41623
Build log at http://www.airplane.build/
VAF dues paid
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07-14-2016, 07:26 AM
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VAF Moderator / Line Boy
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,256
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With more than four years of experience, I can now say that the the CPC connector has been a pain - not for the shield, but becasue of some sort of corrosion that changes the resistance and biases the OAT readings high. I've had to go in and clean this up a couple of times now - and on an RV-3, that is a HUGE pain becasue there is just no room to easily get a hand in there to disconnect the CPC. It has taken me more than an hour of fiddling each time. Likewise, getting at it from the inside is hard becasue it is under the riveted seat pan.
Next time, I'd realize that the only way I am ever going to pull the wings off is if the airplane is in a field somewhere, so I woudl just run extra wires out the root and make the connections inside the fuse. Until you mount the wings, you just don't realize how little room is availabel between the root and the fusealge (on a -3).
Paul
__________________
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
http://Ironflight.com
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07-14-2016, 08:45 AM
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Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,070
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Maybe a thin coat of grease on the connections will help. If the connection is tight enough, the grease will be forced out from between the metal to metal contact point. The grease surrounding the contact point will help prevent corrosion.
__________________
Joe Gores
RV-12 Flying
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07-14-2016, 03:37 PM
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Join Date: Sep 2006
Location: Locust Grove, GA
Posts: 97
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Data point
So far, I'm just under 1.5 years and 130+ hours past my first flight. Thus far, I have not had any corrosion issues with connections in the CPC. However, the number of nights that the plane has had to live outside a hanger is small. On the other hand, I do live in one of the most humid areas of the country.
No problems either on temperature probes reading the correct values.
__________________
Aaron Sims
RV-10 (2015 Bronze Lindy)
RV-6A (sold)
Home Field: Mallards Landing (GA04)
Locust Grove, GA
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07-14-2016, 03:59 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Dielectric grease from the auto store should help!
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07-15-2016, 10:23 AM
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Join Date: Jul 2006
Location: Ione, California
Posts: 254
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I have used terminal strips in the fuselage just inside the side skin. Slip the wires through a grommet in the skin with a little service length. Eyelet terminals on each wire go to the strip that is glued to the floor. Label each connection by writing on the skin or label maker. When and if a wing has to come off just unscrew each wire. Could have as many as 12 connections that are relatively easy to get to with very solid connections.
Food for thought.
Rt
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