Not to beat a dead horse . . .but. .
I found the Fuel systems article. It was a CAFE foundation special report in
the March 2001 issue of Sport Aviation. (It was acting as a book mark in
Aircraft Spruce catlog). It's good reading.
The wet rag trick must have come after that report.
Cleve
On Fri, 20 Dec 2002, Fred Fillinger wrote:
>
> clevelee@cswebmail.com wrote:
> >
> > I was looking for my carefully misplaced article that was in Sport Aviation
> that
> > suggested the 1 meg resister, as part of an overall fuel system discussion.
.
> > .and you're right about the shopping time to locate the 1 meg resistor. Not
> > very common.
> >
> > Cleve
>
> I found it on my EAA CD-ROM - April, '87. The author correctly states
> that discharge time will extend to several microseconds (1 us per pf
> of capacitance), but "probably below ignition temperature of gas
> fumes" is unsupported anywhere else I can find. To the contrary,
> there's plenty of tech stuff at nasa.gov (as in Space Shuttle), and
> they're unhappy with > 10K ohms to control static discharge!
>
> In fact, the many-megohm resistance of the human body, plus 200pf of
> capacitance, doesn't suppress the static sparks we experience, where
> it does indeed jump the gap before we make contact. It is further the
> case that extending the discharge time can have little effect,
> provided the voltage is still sufficient to jump a gap and little is
> dissipated in the series resistor. What ignites fuel vapor is Joules
> - volts-amps-time - however in combination derived and above the
> threshhold (.25 milliJoules I think).
>
> I think practical considerations make it all moot. In connecting a
> bonding or grounding wire to the airframe, such as the exhaust pipe,
> any spark there is harmless. Or even before doing so, touching the
> filler cap to open it -- besides the resistor then not in the circuit
> -- any spark is also harmless since the cap is unvented.* Since any
> charge has then been removed from the A/C, the only remaining hazard
> is the flow of fuel, and for that, very low resistance in
> bonding/grounding is required, as the literature is consistent in
> implying that 1 meg of series resistance there is potentially
> hazardous, if the flow rate is high enough.
>
> *And -- on the older top-mount filler, ya didn't put the vents there,
> as I did not!
>
> Best,
> Fred F.
> The Europa Club website is at <<a
href="http://mail.cswebmail.com/jump/http://www.europaclub.org.uk>">http://www.europaclub.org.uk>;
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