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Ground in an all wood airplane

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mrspudandcompany(at)veriz
Guest

Posted: Mon Jul 21, 2008 7:07 am Post subject: Ground in an all wood airplane

Bob,  

   

I am building an all wood plane and plan to use dual electronic ignition.  A small gnawing issue is grounding.  I will have a rear battery with only a single FAT wire ground coming up to the firewall.  Even though I will have my 2 ignition systems on separate battery busses this will leave me with a ground, single point of failure.  I have been kicking around some other ideas, but am concerned about generating ground loop noise.  I would be interested in your take on this.  

   

Thanks, as always for your advise,  

   

Roger  

       [quote][b]

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nuckolls.bob(at)cox.net
Guest

Posted: Mon Jul 21, 2008 8:31 am Post subject: Ground in an all wood airplane

At 11:02 AM 7/21/2008 -0400, you wrote:



 	  Quote: 	
		  Bob,



I am building an all wood plane and plan to use dual electronic 

ignition.  A small gnawing issue is grounding.  I will have a rear battery 

with only a single FAT wire ground coming up to the firewall.  Even though 

I will have my 2 ignition systems on separate battery busses this will 

leave me with a ground, single point of failure.  I have been kicking 

around some other ideas, but am concerned about generating ground loop 

noise.  I would be interested in your take on this.


	


    The large wires in your airplane are really

    robust. The thoughtfully installed ground wire

    is as reliable as prop bolts.



    The ground loop issue is addressed with the

    ground system architectures described in the

    'Connection. In the case of a non-conducting

    airplane, bringing everything to the single

    point ground location on the firewall will

    eliminate any concerns for "loops". In fact,

    you would have to go out of your way to

    create a ground loop in a non-conducting

    airplane.



    Bob . . .

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mrspudandcompany(at)veriz
Guest

Posted: Mon Jul 21, 2008 9:12 am Post subject: Ground in an all wood airplane

Bob,



Thanks!  This was basically my thoughts also, but I wanted to make sure I

wasn't overlooking something.



Roger

At 11:02 AM 7/21/2008 -0400, you wrote:



 	  Quote: 	
		  Bob,



I am building an all wood plane and plan to use dual electronic 

ignition.  A small gnawing issue is grounding.  I will have a rear battery 

with only a single FAT wire ground coming up to the firewall.  Even though 

I will have my 2 ignition systems on separate battery busses this will 

leave me with a ground, single point of failure.  I have been kicking 

around some other ideas, but am concerned about generating ground loop 

noise.  I would be interested in your take on this.


	


    The large wires in your airplane are really

    robust. The thoughtfully installed ground wire

    is as reliable as prop bolts.



    The ground loop issue is addressed with the

    ground system architectures described in the

    'Connection. In the case of a non-conducting

    airplane, bringing everything to the single

    point ground location on the firewall will

    eliminate any concerns for "loops". In fact,

    you would have to go out of your way to

    create a ground loop in a non-conducting

    airplane.



    Bob . . .

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klehman(at)albedo.net
Guest

Posted: Mon Jul 21, 2008 3:04 pm Post subject: Ground in an all wood airplane

Two separate ground straps from engine to firewall (or forest of tabs) 

may be a good idea on an electrically dependent engine though.  I like 

one of those to go to a starter bolt.

Ken



Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)cox.net>

 

 At 11:02 AM 7/21/2008 -0400, you wrote:

 

> Bob,

>

> I am building an all wood plane and plan to use dual electronic 

> ignition.  A small gnawing issue is grounding.  I will have a rear 

> battery with only a single FAT wire ground coming up to the firewall.  

> Even though I will have my 2 ignition systems on separate battery 

> busses this will leave me with a ground, single point of failure.  I 

> have been kicking around some other ideas, but am concerned about 

> generating ground loop noise.  I would be interested in your take on 

> this.

 

    The large wires in your airplane are really

    robust. The thoughtfully installed ground wire

    is as reliable as prop bolts.

 

    The ground loop issue is addressed with the

    ground system architectures described in the

    'Connection. In the case of a non-conducting

    airplane, bringing everything to the single

    point ground location on the firewall will

    eliminate any concerns for "loops". In fact,

    you would have to go out of your way to

    create a ground loop in a non-conducting

    airplane.

 

    Bob . . .

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Tue Jul 22, 2008 4:21 am Post subject: Re: Ground in an all wood airplane

Your problem is no different from those of all plastic airplanes. Seawinds have nose-mounted batteries and 32 feet of HUMONGOUS battery cable going to and from the tail mounted engine. (Note: SteinAir sells Seawind builders and others Perihelion Design Super-2-CCA. Perihelion still sells Super-4-CCA but that will go to SteinAir soon too.)



But this brings up the point that metal monocoque fuselage airplanes with rear-mounted batteries often use the fuselage for grounding. I suspect that this is a bad idea, and I suppose that in SOME cases this could cause starting problems and/or structural problems. Hundreds of amps through crappy corroded/primed/riveted joints in thin aluminum sheets scares me.



Has anyone seen, investigated or measured this???



"...faster horses, younger women, older whiskey, and more money..."

         --Cowboy Poet Tom T. Hall

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)cox.net
Guest

Posted: Thu Jul 24, 2008 6:59 am Post subject: Ground in an all wood airplane

At 05:21 AM 7/22/2008 -0700, you wrote:

 	  Quote: 	
		  



Your problem is no different from those of all plastic airplanes. Seawinds 

have nose-mounted batteries and 32 feet of HUMONGOUS battery cable going 

to and from the tail mounted engine. (Note: SteinAir sells Seawind 

builders and others Perihelion Design Super-2-CCA. Perihelion still sells 

Super-4-CCA but that will go to SteinAir soon too.)



But this brings up the point that metal monocoque fuselage airplanes with 

rear-mounted batteries often use the fuselage for grounding. I suspect 

that this is a bad idea, and I suppose that in SOME cases this could cause 

starting problems and/or structural problems. Hundreds of amps through 

crappy corroded/primed/riveted joints in thin aluminum sheets scares me.



Has anyone seen, investigated or measured this???


	


   I've heard a variety of horror stories about the effects

   of using an airframe as a ground return. Have no idea

   where these originated. My best guess is that someone

   observed and perhaps even measured the effects of increased

   corrosion of joints when subjected to additional stress

   of electron flow.



   Corrosion testing in the lab is a huge problem when it

   comes to relating the effects to a fielded installation.

   But let's consider the big picture. How many hours per

   year does an airframe take on the extra burden of electron

   flow in the sheet metal? 100, 200?  How strong are those

   currents compared to locally generated electrolytic

   currents? I.e., how much total voltage drop is realized

   at any locale on any joint as a result of that current flow . . .

   especially in light of the fact that point to point

   resistance of structure on most airplanes is a milliohm

   or less.



   It's obvious that the effects cannot be zero. But given

   that for every hour the airplane spends "powered up",

   it spends 40-100 hours powered down. I have to believe

   that the worst case effects of carrying that nav-light

   or pitot-heat ground to the airframe is insignificant

   in the overall scheme of things. I'll combine this idea

   with the fact that the industry still regularly uses

   local grounds on EVERY model of aluminum airplane.



   Bob . . .

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