On Mon, 5 Sep 2005 19:46:37 -0000, "karel"
wrote:


"Robert Bonomi" wrote in message
...
In article ,
karel wrote:

"Robert Bonomi" wrote in message
...
In article ,
Scott Derrick wrote:
I have a pusher airplane with a nose oil cooler.

I am replacing the existing heavy hydraulic type(rubber/braided steel)
oil cooler lines with lighter metal lines. Either soft Aluminum or soft
copper 1/2 lines.

First question. I would like to use the lines as my ground return and
remove the 2 AWG wire I have now. Good idea?

*DAMN*STUPID* one!

Perhaps, yes.
Careful consideration is required, at least.
Which is exactly what O/P is doing.

Consider the cross-section area of #2 wire,
then compare with the cross-section area of the walls of the tubing.

Without considering what happens if/when a line _breaks_.

Agreed.
But is this any worse than a dedicated electrical ground cable breaking
loose?

HELL YES it is!!

The difference being the proximity of flammable materials to the point
where the sparks are being generated.

The point might be that oil lines are more prone to vibration
than a length of cable of whatever gauge.

"Instant" spark across the gap, With a ready supply of fuel being
delivered
to the scene.

The fuel being lubricating oil, I fancy a tremendous lot of sparks
would be required to actually make it fire.

You, sir, "don't know what you DON'T KNOW" about the size of the sparks
that get generated when a conductor carrying multiple tens of amps
is unexpectedly severed. (#2AWG copper is rated for in excess of 125
Amps.)

I'll gladly allow I've much to learn,
that's why I'm hanging around here.

Yet it seems clear to me that, in the average GA aircraft,
tens of amps will only be drawn during starting
(which admittedly is a strong moment for vibration)

Actually make that HUNDREDS of amps.

OR how easily 'lubricating oils' can be "convinced" to combust. No, they
are not very 'volatile' -- so they don't vaporize by themselves -- but
they 'atomize' fairly easily, which can, and often does, make for an
explosive
mixture.

On this point I'm grateful to learn from you.
KA