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Grounding to tube frame structures

 
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johnr470(at)aol.com
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PostPosted: Thu Feb 28, 2019 6:29 am    Post subject: Grounding to tube frame structures Reply with quote

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

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nuckolls.bob(at)aeroelect
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PostPosted: Thu Feb 28, 2019 7:18 am    Post subject: Grounding to tube frame structures Reply with quote

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 . . .


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jrevens



Joined: 21 Nov 2013
Posts: 33
Location: Arvada, CO

PostPosted: Mon Apr 15, 2019 9:09 am    Post subject: Re: Grounding to tube frame structures Reply with 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 -

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.


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John Evens
Thorp T-18 N71JE (sold)
Kitfox SS7 N27JE (built & flying)
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PostPosted: Mon Apr 15, 2019 9:34 am    Post subject: Grounding to tube frame structures Reply with quote

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.

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ceengland7(at)gmail.com
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PostPosted: Mon Apr 15, 2019 10:03 am    Post subject: Grounding to tube frame structures Reply with quote

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

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jrevens



Joined: 21 Nov 2013
Posts: 33
Location: Arvada, CO

PostPosted: Mon Apr 15, 2019 10:49 am    Post subject: Re: Grounding to tube frame structures Reply with quote

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.


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PostPosted: Mon Apr 15, 2019 11:38 am    Post subject: Grounding to tube frame structures Reply with quote

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
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PostPosted: Mon Apr 15, 2019 2:18 pm    Post subject: Grounding to tube frame structures Reply with quote

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 . . .


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PostPosted: Tue Apr 16, 2019 11:55 am    Post subject: Grounding to tube frame structures Reply with quote

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 . . .


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jim(at)PoogieBearRanch.co
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PostPosted: Tue Apr 16, 2019 2:56 pm    Post subject: Grounding to tube frame structures Reply with quote

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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