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Wire length in aluminum airframes

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ceengland7(at)gmail.com
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Posted: Thu Mar 03, 2016 7:39 am Post subject: Wire length in aluminum airframes

Bob, I'm in the midst of wiring my RV-7, & realized that I can't find an 

answer in 'the book' for this question. In the book and articles you've 

written, you mention total wire distance (out & back), referencing 

fiberglass airframes. But how do you compute wire length when you're 

using an aluminum airframe for ground return for things like landing 

lights, pitot heat, etc? Can the return path be essentially ignored, 

since the return 'conductor' is so massively oversized?



And just for the sake of discussion, would the answer change if it's a 

steel tube fuselage (significantly higher resistance for steel, but 

still massive)?



Thanks,



Charlie

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nuckolls.bob(at)aeroelect
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Posted: Sun Mar 06, 2016 4:15 pm Post subject: Wire length in aluminum airframes

At 09:40 AM 3/3/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Charlie England <ceengland7(at)gmail.com>



 Bob, I'm in the midst of wiring my RV-7, & realized that I can't find an answer in 'the book' for this question. In the book and articles you've written, you mention total wire distance (out & back), referencing fiberglass airframes. But how do you compute wire length when you're using an aluminum airframe for ground return for things like landing lights, pitot heat, etc? Can the return path be essentially ignored, since the return 'conductor' is so massively oversized? 	


   Yes . . . assume it to be . . . for all practical

   purposes . . . zero resistance ground.



 

  	  Quote: 	
		  And just for the sake of discussion, would the answer change if it's a steel tube fuselage (significantly higher resistance for steel, but still massive)? 	


   Not significantly higher . . . your aluminum airplane

   might measure a few milliohms stem to stern with

   steel being perhaps 50% higher. Neigher instance

   is significant in the grand scheme of things.



   Having said that, ground currents at engine cranking

   current levels should be brought to the most

   significant adjacent structure.



 

   Bob . . .

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