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rv10(at)sinkrate.com
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 Posted: Tue Feb 26, 2008 9:49 am Post subject: voltage drop calulations |
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When computing the voltage drop for items grounded locally to the airframe on a metal airplane what length of wire do you use? Do you add any additional length to the wire for the ground wire? Does the chassis provide a measurable amount of resistance? Example… Let’s say I am grounding my wingtip nav lights locally to the airframe. The hot wire is 20ft in total with 1 ft wire grounding to the airframe. Do you use 21ft as your length value when calculating voltage drop? If you did have to account for the return through the chassis how would you decide on an ohm/ft value?
Sorry if this seems basic but I have never run across specifics of this in all my readings.
Ben Westfall
RV-10
[quote][b]
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nuckolls.bob(at)cox.net
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| Posted: Tue Feb 26, 2008 4:33 pm Post subject: voltage drop calulations |
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At 09:45 AM 2/26/2008 -0800, you wrote:
| Quote: | When computing the voltage drop for items grounded locally to the airframe
on a metal airplane what length of wire do you use?
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What ever that length is. The airframe adds a negligible
amount of resistance to the total.
| Quote: | Do you add any additional length to the wire for the ground wire? Does
the chassis provide a measurable amount of resistance?
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No.
| Quote: | Example& Let s say I am grounding my wingtip nav lights locally to the
airframe. The hot wire is 20ft in total with 1 ft wire grounding to the
airframe. Do you use 21ft as your length value when calculating voltage
drop? If you did have to account for the return through the chassis how
would you decide on an ohm/ft value?
|
If you really want a value, use .002 ohms as a
ballpark.
| Quote: |
Sorry if this seems basic but I have never run across specifics of this in
all my readings.
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This is because we generally don't have to worry about voltage
drop. Our airplanes are small. Even when figuring the round-trip
drop for feeder and ground in a composite airframe, the
suggested wire sizes in the tables are conservative enough
to accept at face value.
It's an interesting academic exercise but not very
fruitful in practice. If I were working on very long
runs of wire in a 767 or B52, I'd have to get out
the calculator and consider the need for up-sizing
a wire for voltage drop considerations.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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