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Grounding to tube frame structures

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johnr470(at)aol.com
Guest

Posted: Thu Feb 28, 2019 6:29 am Post subject: Grounding to tube frame structures

What is the best method to ground a battery located behind the baggage compartment to a frame tube in a fabric covered aircraft?

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Feb 28, 2019 7:18 am Post subject: Grounding to tube frame structures

At 08:28 AM 2/28/2019, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: John Hulls <johnr470(at)aol.com>



 What is the best method to ground a battery located behind the baggage compartment to a frame tube in a fabric covered aircraft? 	


   You would like to have a gas-tight connection

   to structure . . . ideally a welded bolt-

   tab to accept the battery(-) lead.

   Is the airplane already covered?

   If not, adding the tab should be

   a relatively simple task.



 

 

   Bob . . .

jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Mon Apr 15, 2019 9:09 am Post subject: Re: Grounding to tube frame structures

This is not exactly on topic, but I would like to get Bob's take on it.  In a recent online forum, the writer posted the following in regards to the "forest of tabs" grounding structure -



 	  Quote: 	
		  Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path. 	




It seems a little silly to insulate the forest of tabs from the airframe and then connect it to the airframe with a wire to the pass through bolt.  I'm also wondering about bringing all other aircraft system grounds to the "Avionics" buss.  This was supposedly from an article in Kitplanes magazine.

Final Ground System.jpg

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_________________
John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

art(at)zemon.name
Guest

Posted: Mon Apr 15, 2019 9:34 am Post subject: Grounding to tube frame structures

I have two forests of tabs, one on each side of the firewall. There is a hefty bolt, 5/16 if I remember correctly but maybe 1/4, that physically supports the two electrically connects them to the firewall. It's a metal airplane.

One additional note: I had enough tabs in the forest inside the cabin that I did not bother with a seperate avionics ground bus. If I run out of tabs, I will add an avionics ground bus connected to one of the tabs.

    -- Art Z. 

On Mon, Apr 15, 2019 at 12:24 PM jrevens <jrevens(at)comcast.net (jrevens(at)comcast.net)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "jrevens" <jrevens(at)comcast.net (jrevens(at)comcast.net)>

 

 This is not exactly on topic, but I would like to get Bob's take on it.  In a recent online forum, the writer posted the following in regards to the "forest of tabs" grounding structure -

 

 

 > Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.

 	


-- 

https://CheerfulCurmudgeon.com/"Love wins. Love always wins." Morrie Schwartz

ceengland7(at)gmail.com
Guest

Posted: Mon Apr 15, 2019 10:03 am Post subject: Grounding to tube frame structures

On 4/15/2019 12:09 PM, jrevens wrote:

 	  Quote: 	
		   



 This is not exactly on topic, but I would like to get Bob's take on it.  In a recent online forum, the writer posted the following in regards to the "forest of tabs" grounding structure -

> Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.



 It seems a little silly to insulate the forest of tabs from the airframe and then connect it to the airframe with a wire to the pass through bolt.  I'm also wondering about bringing all other aircraft system grounds to the "Avionics" buss.  This was supposedly from an article in Kitplanes magazine.



 --------

 John Evens

 Thorp T-18 N71JE (sold)

 Kitfox SS7 N27JE (built &amp; flying)

I think the logic is that if the avionics ground bus is remote from the 
	


main ground bus at the firewall, keeping it isolated and running its own 

ground wire to the firewall serves the same purpose as the firewall 

mounted bus: to prevent ground 'loops' (noise in the ground path showing 

up in undesired locations).



Charlie



---

This email has been checked for viruses by Avast antivirus software.

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jrevens

Joined: 21 Nov 2013
Posts: 34
Location: Arvada, CO

Posted: Mon Apr 15, 2019 10:49 am Post subject: Re: Grounding to tube frame structures

 	  ceengland7(at)gmail.com wrote: 	
		  On 4/15/2019 12:09 PM, jrevens wrote:

 	  Quote: 	
		   



 This is not exactly on topic, but I would like to get Bob's take on it.  In a recent online forum, the writer posted the following in regards to the "forest of tabs" grounding structure -

> Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.



 It seems a little silly to insulate the forest of tabs from the airframe and then connect it to the airframe with a wire to the pass through bolt.  I'm also wondering about bringing all other aircraft system grounds to the "Avionics" buss.  This was supposedly from an article in Kitplanes magazine.



 --------

 John Evens

 Thorp T-18 N71JE (sold)

 Kitfox SS7 N27JE (built &amp; flying)

I think the logic is that if the avionics ground bus is remote from the 

	


main ground bus at the firewall, keeping it isolated and running its own 

ground wire to the firewall serves the same purpose as the firewall 

mounted bus: to prevent ground 'loops' (noise in the ground path showing 

up in undesired locations).



Charlie



---

This email has been checked for viruses by Avast antivirus software.

https://www.avast.com/antivirus 	




Agreed, Charlie.  I just couldn't see why you would want to insulate the forest of tabs from the firewall, as shown in the drawing.  The direct connection to the carry through bolt and the firewall seems simpler and smarter.  The author seems to imply that the forest of tabs must be insulated from the airframe, when the wire connecting it to the bolt connects it to the airframe anyway. I guess I just don't see the reasoning for "isolating" the bus when it is also connected with a conductor to the airframe.

_________________
John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)

ceengland7(at)gmail.com
Guest

Posted: Mon Apr 15, 2019 11:38 am Post subject: Grounding to tube frame structures

On Mon, Apr 15, 2019 at 1:55 PM jrevens <jrevens(at)comcast.net (jrevens(at)comcast.net)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "jrevens" <jrevens(at)comcast.net (jrevens(at)comcast.net)>

 

 

 ceengland7(at)gmail.com wrote:

 > On 4/15/2019 12:09 PM, jrevens wrote:

 > 

 > >  

 > > 

 > >  This is not exactly on topic, but I would like to get Bob's take on it.  In a recent online forum, the writer posted the following in regards to the "forest of tabs" grounding structure -

 > > 

 > > 

 > > > Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.

 > > 

 > >  It seems a little silly to insulate the forest of tabs from the airframe and then connect it to the airframe with a wire to the pass through bolt.  I'm also wondering about bringing all other aircraft system grounds to the "Avionics" buss.  This was supposedly from an article in Kitplanes magazine.

 > > 

 > >  --------

 > >  John Evens

 > >  Thorp T-18 N71JE (sold)

 > >  Kitfox SS7 N27JE (built &amp; flying)

 > > 

 > > 

 > > I think the logic is that if the avionics ground bus is remote from the 

 > > 

 > 

 > main ground bus at the firewall, keeping it isolated and running its own 

 > ground wire to the firewall serves the same purpose as the firewall 

 > mounted bus: to prevent ground 'loops' (noise in the ground path showing 

 > up in undesired locations).

 > 

 > Charlie

 > 

 > ---

 > This email has been checked for viruses by Avast antivirus software.

 > https://www.avast.com/antivirus

 

 

 Agreed, Charlie.  I just couldn't see why you would want to insulate the forest of tabs from the firewall, as shown in the drawing.  The direct connection to the carry through bolt and the firewall seems simpler and smarter.  The author seems to imply that the forest of tabs must be insulated from the airframe, when the wire connecting it to the bolt connects it to the airframe anyway. I guess I just don't see the reasoning for "isolating" the bus when it is also connected with a conductor to the airframe.

 

 --------

 John Evens

 Thorp T-18 N71JE (sold)

 Kitfox SS7 N27JE (built &amp; flying)



	




Ah; didn't even see his pic when I posted. You're right; absolutely no reason to isolate the firewall mounted FOT. 



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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 15, 2019 2:18 pm Post subject: Grounding to tube frame structures

 	  Quote: 	
		  

 > > > Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.  I think the logic is that if the avionics ground bus is remote from the 

 > main ground bus at the firewall, keeping it isolated and running its own 

 > ground wire to the firewall serves the same purpose as the firewall 

 > mounted bus: to prevent ground 'loops' (noise in the ground path showing 

 > up in undesired locations). 	


   Correct. See various examples in

   Figure Z-15   https://tinyurl.com/5wxzn7



   The 'avionics bus' is a CENTRAL grounding

   point located in closest practical proximity

   to potential noise VICTIMS(generally all

   panel mounted). This ground point may well

   be electrically common to the airframe . . .

   this would be true if your airplane is all

   metal and the panel structure gets 'hooked

   up electrically' to the rest of the airplane.



   The magic things about an avionics bus:



   (1) central location to potential VICTIMS



   (2) single point for grounding all components

       in constellation of potential VICTIMS.

       

   (3) this ground is NOT SHARED with any potential

       ANTAGONIST (all those other things scattered

       around the airplane).



   If the airplane is composite, then you'll need

   to extend the  avionics ground down to the firewall

   ground point with either a relatively robust

   bond wire (8awg is a bit overkill 12AWG is

   probably fine for modern suite of solid-state

   avionics).



   The avionics ground bus generally has lots

   of small wires none of which carries big

   currents. A product like this



  https://tinyurl.com/y44yngbm



   is much easier to mount in close proximity

   to the panel mounted electro-whizzies.



   For potential antagonists, grounding

   to the AIRFRAME can be managed with

   a product like this:



  https://tinyurl.com/y4gvepup



   But there's nothing magic about

   bringing all your airframe grounds

   to a single point. If you have an

   all-metal airplane, remote grounding

   of things like landing lights, strobe

   supplies, landing gear motors, batteries

   etc is quite practical.

  

   Insulating your ground system from the

   airframe is not recommended and has

   no demonstrable value. However, running

   all airframe grounds to the firewall thru-

   stud bus is not a 'bad' thing to do either.



 



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Apr 16, 2019 11:55 am Post subject: Grounding to tube frame structures

 	  Quote: 	
		  

   Insulating your ground system from the

   airframe is not recommended and has

   no demonstrable value. However, running

   all airframe grounds to the firewall thru-

   stud bus is not a 'bad' thing to do either.

 	


   I've had a couple private emails on this

   topic seeking amplification. If anyone

   needs more info or explanations in

   different words, don't hesitate to

   post here on the List.



   There's a lot of mis-understanding/

   mis-information about grounds 

   circulating in the OBAM aviation

   world . . . and if different 

   explanations are needed, I

   really need to know about it. 



 

 

   Bob . . .

jim(at)PoogieBearRanch.co
Guest

Posted: Tue Apr 16, 2019 2:56 pm Post subject: Grounding to tube frame structures

Bob,



I'll admit to being confused by this advice.  And since I'm building a

metal-winged, steel-tube fuselage airplane, I'd really like to

understand this better than I do now...  



I would appreciate a more thorough explanation, starting from the

assumption that I am NOT an electrical engineer, and my knowledge of

aircraft wiring is almost exclusively learned through this forum and

your book.



Jim Parker

------

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