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Avionics ground block

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Jekyll

Joined: 22 Feb 2006
Posts: 44

Posted: Sun Sep 24, 2006 8:31 pm Post subject: Avionics ground block

I'm planning a ground block for panel components using a fast-on tab ground (purchased from SteinAir) soldered to brass bar stock. I plan to  ground all avionics to this and then run a common ground wire to the main F/W mounted ground block. My question is thus: do I need to insulate the ground block from the aluminum frame or will the wires carry the ground better than the airframe, thus carrying the common ground to the main block?



Jekyll, RV-7A

nuckollsr(at)cox.net
Guest

Posted: Mon Sep 25, 2006 7:16 am Post subject: Avionics ground block

At 09:31 PM 9/24/2006 -0700, you wrote:



 	  Quote: 	
		  



I'm planning a ground block for panel components using a fast-on tab 

ground (purchased from SteinAir) soldered to brass bar stock. I plan 

to  ground all avionics to this and then run a common ground wire to the 

main F/W mounted ground block. My question is thus: do I need to insulate 

the ground block from the aluminum frame or will the wires carry the 

ground better than the airframe, thus carrying the common ground to the 

main block?


	




Check out Figure Z-15



http://aeroelectric.com/articles/Rev11/AppZ_R11J.pdf



and the "avionics/panel ground" concept described in.



http://aeroelectric.com/articles/Rev11/18Audio_R11.pdf



The latest updates to these documents suggest a means

for simplifying the ground system. The avionics ground

need not be as "hoggy" as the forest-of-fast-on-tabs

suggested for the firewall. Yes, the panel ground is

insulated from panel structure but it's something of

a moot point. Many of your panel mounted electro-whizzies

ground internally.



The important feature of the ground system that prevents

ground loop noise problems is that no single potential

victim system grounds in more than one place. I.e. you can

have a "string" of grounds that need to be "single point"

for the systems that use them.



Bob. . .

bob(at)flyboybob.com
Guest

Posted: Mon Sep 25, 2006 8:10 am Post subject: Avionics ground block

Hey 'lectric Bob,



You wrote:



<<

The important feature of the ground system that prevents

ground loop noise problems is that no single potential

victim system grounds in more than one place. I.e. you can

have a "string" of grounds that need to be "single point"

for the systems that use them.

 	  Quote: 	
		  >


	


When the teacher says "The Important feature ..." it is important to make

sure I understand.  Could you please say that again in a different way so

that I might understand?  I don't see a string of grounds evering being

'"single point" for the systems that use them.' Doesn't a string of grounds

connect a device to the previous and the next device in the string?  So by

definition, the string can't be single point.  I've just proved the teacher

wrong so I'm very leary of my logic.  Where's my bad ASSumption?



Regards,



confused Bob (Bob Lee)

N52BL  KR2

Suwanee, GA

91% done only 65% to go!

nuckollsr(at)cox.net
Guest

Posted: Mon Sep 25, 2006 11:46 am Post subject: Avionics ground block

At 12:08 PM 9/25/2006 -0400, you wrote:



 	  Quote: 	
		  



Hey 'lectric Bob,



You wrote:



<<

The important feature of the ground system that prevents

ground loop noise problems is that no single potential

victim system grounds in more than one place. I.e. you can

have a "string" of grounds that need to be "single point"

for the systems that use them.

 >>



When the teacher says "The Important feature ..." it is important to make

sure I understand.  Could you please say that again in a different way so

that I might understand?  I don't see a string of grounds evering being

'"single point" for the systems that use them.' Doesn't a string of grounds

connect a device to the previous and the next device in the string?  So by

definition, the string can't be single point.  I've just proved the teacher

wrong so I'm very leary of my logic.  Where's my bad ASSumption?


	


   I've added a third sheet to Z-15 which you can see at:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15-3.pdf



   Look this over and see if the words I used before make more

   sense . . .



   Bob . . .

Jekyll

Joined: 22 Feb 2006
Posts: 44

Posted: Mon Sep 25, 2006 1:07 pm Post subject: Re: Avionics ground block

Bob:



Thanks much. The 3rd page cleared it right up for me. We have both fulfilled our purpose - you have taught and I have learned!



Jekyll

bob(at)flyboybob.com
Guest

Posted: Mon Sep 25, 2006 3:18 pm Post subject: Avionics ground block

'lectric Bob wrote:



<<   I've added a third sheet to Z-15 which you can see at:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15-3.pdf



   Look this over and see if the words I used before make more

   sense . . .

 	  Quote: 	
		  >


	


Just as a point of reference, I'm talking about a conposite aircraft.  The

diagram makes sense but the words about stringing grounds from your origanal

post still don't.  What I get from the diagram in the link above is that the

stuff on the left side (viewed to read the lettering) is the wing ground.

The only stuff that you can string together is the stuff that don't matter

like strobes, landing/taxi lights

pitot heat and nav lights.  Everything else must go the the appropriate

(firewall, engine, or pannel) single point ground.



Did I get it right this time?



Regards,



confused Bob

nuckollsr(at)cox.net
Guest

Posted: Mon Sep 25, 2006 7:31 pm Post subject: Avionics ground block

At 07:17 PM 9/25/2006 -0400, you wrote:



 	  Quote: 	
		  



'lectric Bob wrote:



<<   I've added a third sheet to Z-15 which you can see at:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15-3.pdf



    Look this over and see if the words I used before make more

    sense . . .

 >>



Just as a point of reference, I'm talking about a conposite aircraft.  The

diagram makes sense but the words about stringing grounds from your origanal

post still don't.  What I get from the diagram in the link above is that the

stuff on the left side (viewed to read the lettering) is the wing ground.

The only stuff that you can string together is the stuff that don't matter

like strobes, landing/taxi lights

pitot heat and nav lights.  Everything else must go the the appropriate

(firewall, engine, or pannel) single point ground.


	


    Download the drawing again (I did it in a hurry this morning

    and was able to spiff it up a bit this evening). If your

    latest download doesn't come up in color, hit the 'refresh'

    icon on your browser.



    All of the stuff in blue is the ground system . . . the ground

    busses are "strung together" but in 3 separate locations in the a/c.

    "Local" grounds to airframe may be "scattered" about the airframe

    on a metal airplane when the item being grounded is not itself

    a potential victim. In your case for a composite airplane,

    local grounds are not possible and must, of course, be moved

    to the cockpit ground bus.



    Stuff in green have been properly grounded to a single point

    commensurate with system requirements. For example, CHT

    and many oil pressure senders ground to the engine . . . so

    for best accuracy (especially in canard pushers) the attending

    instrument should also be grounded to the crankcase . . . or

    at least the firewall ground bus.



    Stuff in red has been purposely "mis-grounded" to illustrate

    the potential for inserting errors/noise by tiny but significant

    voltage differences that may exist between grounds that are

    connected but not co-located on the airframe.

 	  Quote: 	
		  Did I get it right this time?


	


    Closer!



        Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

zk-vii(at)rvproject.gen.n
Guest

Posted: Mon Sep 25, 2006 8:45 pm Post subject: Avionics ground block

Hi Bob,



This leads to a question we have had,  we have a 'mid-ship ground forest of

tabs' aft of the spar with a dedicated AWG8 between it and the firewall

ground 'single point'.  Would you advocate insulating the mid ship forest

from the main fuselage or just bolting it up to the metal sub structure?



Thanks,



Carl



PS: Small typo in the text on the second page - leas cf least

--

ZK-VII - RV 7A QB - finishing? - New Zealand

http://www.rvproject.gen.nz/



[quote] --

bob(at)flyboybob.com
Guest

Posted: Tue Sep 26, 2006 1:56 am Post subject: Avionics ground block

'lectric Bob,



Thanks for taking the extra effort here.  It seems that the physics are

quite simple, it's the language that keeps getting in the way.  Your new

drawing makes it clear.



Regards,



not so "confused Bob"

nuckollsr(at)cox.net
Guest

Posted: Tue Sep 26, 2006 4:08 am Post subject: Avionics ground block

At 05:55 AM 9/26/2006 -0400, you wrote:



 	  Quote: 	
		  



'lectric Bob,



Thanks for taking the extra effort here.  It seems that the physics are

quite simple, it's the language that keeps getting in the way.  Your new

drawing makes it clear.


	


   Pictures DO help. The art of teaching is to figure out

   ways around communications barriers. I was in the video

   time base corrector business for a few years in the

   late seventies. For a time, we were re-branding our

   time base correctors for AKAI. I spent a week in California

   showing their technicians how the things worked and how to

   troubleshoot them.



   Their English was poor and my Japanese was non-existent

   but between our mutual understanding of television signals

   and the relatively universal language of schematics, we

   managed to share a lot of useful data.



   I need to re-format the drawing into something other

   than .pdf files generated directly from AutoCAD. The

   300K document is a bit of a hog to download!



   Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

nuckollsr(at)cox.net
Guest

Posted: Tue Sep 26, 2006 4:12 am Post subject: Avionics ground block

At 04:40 PM 9/26/2006 +1200, you wrote:



 	  Quote: 	
		  

<zk-vii(at)rvproject.gen.nz>



Hi Bob,



This leads to a question we have had,  we have a 'mid-ship ground forest of

tabs' aft of the spar with a dedicated AWG8 between it and the firewall

ground 'single point'.  Would you advocate insulating the mid ship forest

from the main fuselage or just bolting it up to the metal sub structure?



Thanks,



Carl


	


    No, in fact in your metal airplane, the mid-ship ground block

    is just a congregation of the otherwise scattered "local"

    grounds on the left side of the drawing. There's no value

    in adding any wires between the mid-ship ground block and

    the firewall mounted grounds. The resistance of the airframe

    will be a tiny fraction of that offered by the jumper wire.

    Hence the wire does not significantly alter/enhance the

    ground system.



    Bob . . .

chaztuna(at)adelphia.net
Guest

Posted: Tue Sep 26, 2006 4:19 am Post subject: Avionics ground block

At 03:45 PM 9/25/2006, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net>



 At 12:08 PM 9/25/2006 -0400, you wrote:



  	  Quote: 	
		  --> AeroElectric-List message posted by: "Bob Lee" <bob(at)flyboybob.com>



 Hey 'lectric Bob,



 You wrote:



 <<

 The important feature of the ground system that prevents

 ground loop noise problems is that no single potential

 victim system grounds in more than one place. I.e. you can

 have a "string" of grounds that need to be "single point"

 for the systems that use them.

 >>



 When the teacher says "The Important feature ..." it is important to make

 sure I understand.  Could you please say that again in a different way so

 that I might understand?  I don't see a string of grounds evering being

 '"single point" for the systems that use them.' Doesn't a string of grounds

 connect a device to the previous and the next device in the string?  So by

 definition, the string can't be single point.  I've just proved the teacher

 wrong so I'm very leary of my logic.  Where's my bad ASSumption? 	


   I've added a third sheet to Z-15 which you can see at:



  http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15-3.pdf

 

   Look this over and see if the words I used before make more

   sense . . .



   Bob . . . 	




 Bob,

  Am I missing something or simply misunderstanding your statement about the web link above having "3 sheets"? I only see two pages on the link above.

 Charlie Kuss

      [quote][b]

nuckollsr(at)cox.net
Guest

Posted: Tue Sep 26, 2006 5:37 am Post subject: Avionics ground block

 	  Quote: 	
		  >

>   I've added a third sheet to Z-15 which you can see at:

>

>http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z15-3.pdf

>

>   Look this over and see if the words I used before make more

>   sense . . .

>

>   Bob . . .

Bob,

  Am I missing something or simply misunderstanding your statement about 

 the web link above having "3 sheets"? I only see two pages on the link above.

Charlie Kuss


	


    Z-15 in the 'Conection is already a  two-sheet figure. The stuff I just 

published

    will be incorporated into Revision 12 as the third sheet.



    Bob . . .

nuckollsr(at)cox.net
Guest

Posted: Tue Sep 26, 2006 5:56 pm Post subject: Avionics ground block

At 02:07 PM 9/25/2006 -0700, you wrote:



 	  Quote: 	
		  



Bob:



Thanks much. The 3rd page cleared it right up for me. We have both 

fulfilled our purpose - you have taught and I have learned!


	


   . . . then today has been a good day.



   Bob . . .

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