Matt --

Because you want to get rid of the charge quietly, without any sharp
transients that will cause RFI. You can come at the answer from an RC time
constant angle, from a total energy (power dissipation) angle, from a couple
of more exotic angles.

I myself like to think of it from the total energy point of view. That
charge starts out at some large potential. In travelling through the
resistor to get to the pin point, moving charge is the definition of
current, which by Ohm guarantees that there will be a power loss going
through the resistor, and hence a lower voltage to dissipate when it does
get to the pin point.

If you want to come at it from the RC time constant point of view (being
that the airplane is the conductor and the atmosphere is the capacitor) the
R of the RC is going to round the edges of those transients nicely.

YOu can't use too high a value resistor or the charge won't even see the pin
point. You can't use too low a value resistor or the charge won't lose any
power in gettint to the pin point.

How did I come up with a value of 100K to 1M? Simple. Back when I worked
for the airline, there was a spec on the static wicks on all the Boeings and
on all the McDonnells that said the static wicks should measure between 100K
and 1M from the attach point to the pin point(s). I figured if it was good
enough for McBoeing at 500 knots, it was good enough for Jim at 100 knots.

Jim


"Matt Whiting" wrote in message
...
RST Engineering wrote:
It is a hell of a lot easier to solder a 100K-1Meg resistor to a solder
lug with very short leads,


Jim,

Question: Why do you need the resistor? Since you want to get rid of
charge, why not just a sharp piece of wire?

Matt