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p.mulwitz(at)worldnet.att
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 Posted: Sun Sep 10, 2006 8:26 am Post subject: Strobe wiring reality check. |
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With all the differing opinions on the conductivity of aluminum and
copper, I decided to do a little research and calculations to try to
come up with a fair analysis of this issue.
First, I found a nice web page that tells the actual story about
resistivity of aluminum and copper. It is:
http://www.schoolscience.co.uk/content/5/physics/copper/copelech2pg1.html
It shows copper is a better conductor than aluminum (which we all
knew already) but also tells how much better. It turns out the ratio
is only 3.2 /1.7 which means the cross section of an aluminum wire
needs to be 1.88 times larger in area to have the same resistance as
a copper wire. (This didn't surprise me a lot since I already knew
aluminum wire is commonly used for house wiring and for long distance
high voltage transmission lines.)
I went out to my shop and did a few measurements to see how large a
copper wire would have to be to have the same resistance as the
aluminum in my wing. The short answer is the aluminum wing is
roughly equivalent to a wire with a diameter of 59.5 mm. An
equivalent copper wire would have to be only 43.4 mm in diameter to
have the same resistance. (I will spare the list the math, anyone
wanting the details can send me an off-list email and I will send the
spreadsheet.)
Tying it all together, my calculations show it would take a copper
wire 43.4 mm in diameter to have the same electrical property
(resistance) as the wing does. This would be a really heavy ground
wire to string the length of the wing.
Caveats: For this to work, the power supply must be mounted in the
wing tip. Also, it assumes good contact between the skin and spar
which might not be the case if there is anti-corrosion paint used in
the joints. Also, I wouldn't use this method if the power supply for
the strobe was mounted in the fuselage since the voltage carried in
the wires is much higher than the 12V going to the power supply.
Paul
XL fuselage
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Sun Sep 10, 2006 4:48 pm Post subject: Strobe wiring reality check. |
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Aluminium cable is used on larger commercial liners for longer high voltage
runs something in the order of 400V(at) 100Hz. I don't think there is any Al
used for smaller apps. As for the wing tip strobes they are getting light
enough to be installed in the wingtips with no appreciable degradation of
the aircraft handling characteristics. Grounding of the lights themselves
is a non issue as they are regularly being installed in composite wings and
composite fairings on fling wings. Older heavier units can be safely
installed closer to the wing roots and wired with the appropriate wire. As
with all things RTFM ( Read the Funny Manual)
BTW the working voltage is close to 13.8V, rounded up that's 14V. The
battery will actually provide less than 12V
Noel
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