REFLECTOR: Oil lines and ground wire.

[Laurence Coen]

Scott,

As far as using the aluminum oil lines for a ground return, don't.  Their 
ability to conduct electricity is a function of cross sectional area and the 
material.  Aluminum has four times the resistance of copper for the same 
cross section.  1/2" aluminum tubing has a wall thickness of 0.035".  I 
calculated the cross sectional area and it is equivalent to a wire of about 
0.12" dia.  That's far too small even if it were copper.

The other question about up one side and down the other has been discussed 
before and as a result I chose to do it that way.  I believe that someone at 
the factory took measurements of temperature at both ends of both oil lines. 
The lines were in the same duct.  The oil flowing foreword lost 20 deg. F 
but the return oil was reheated 15 deg. F.  The two lines together were 
acting as a counter flow heat exchanger.  At least in theory, moving the 
return line to the other duct should make the oil entering the oil cooler 15 
deg. warmer thus increasing its' efficiency and getting perhaps another 5 
deg. drop in the return line.  I've never had my oil lines in the same duct 
so I am unable to test the theory.

Larry Coen
N136LC

----- Original Message ----- 
From: "Scott Derrick" <scott at tnstaafl.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Saturday, September 03, 2005 10:04 AM
Subject: REFLECTOR: Oil lines and ground wire.


> My plane came with high pressure hoses for oil lines. Both ran in the 
> pilot side duct.  I noticed that the manual calls for 1/2 " aluminum 
> lines.   I was considering replacing the high pressure rubber/steel flex 
> lines with aluminum.  Much lighter and smaller, those hydraulic lines are 
> huge and heavy.
>
> I was also considering running one up the pilot side and the other down 
> the copilot side to take advantage of the additional cooling benefits. 
> Has anybody done the comparison of running both in one duct and one in 
> each to see if there really is an advantage?
>
> Then I got to thinking about using the oil lines for my ground return path 
> from the battery to the engine?  Aluminum is a pretty good conductor, and 
> having two lines would seem to provide a substantial return path if I 
> bonded both tubes at both ends?
> Anybody do this?
>
> Scott
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