Flying a Piper now and then with a friend. Have noticed that the plane must be connected to ground with a cable before filling petrol. This is of course to avoid sparks of static electricity, that could start a fire. But why is this not necessary with cars? They are also on insulating rubber tires.Roland

It might just be an extra safety precaution, or it may have something to do with the fact that your friend is getting his avgas from a truck rather than a pump in the ground (assuming that's how he gets it).

Hi all,I found an answer on another flying site:>>>>>>>>Here is an answer straight from Shell Belgium:For Dutch readers:"Geachte Heer,Er zijn twee redenen om dit te uitleggen.Het geleidbaarheid van Avgas (Vliegtuig benzine) en Jet A1 zijn lager dan auto benzine.Tijdens de� fuelling procedure (zeker met Jet A1 waar het debiet kan tot 7000 liter/minuut) veel statische elektriciteit is geproduceerd.Met zijn hoger snelheid en hoogte de vliegtuigen zijn ook vol van statische elektriciteit. Tijdens de fuelling procedure als een verschil van potentieel tussen het aard (pomp) en de vliegtuig is en vonk kan gebeuren.� �Met de hoger geleidbaarheid van auto benzine en hun lager snelheid zijn deze risico's niet aanwezig."TRANSLATED:Ok, first of all, dutch people: the question was answered by Shell in Belgium. And his name was very frensh, so never mind the spelling!Basically what he writes, is that Avgas and JetA1 are far worse conductors then Petrol gas (automobile).Especially pumping with high speeds means a lot of friction of the refueling itself (static buildup along the lines no decharges thru the fuel)!Other then that, he states that aircraft in general produce so much more static electricity (high dry altitudes and fast airflows), that it becomes unsave to refuel without grounding first.Since cars don't have that high an air friction and, as he states, use fuels that conduct better, the risk is minimized to neglectable.My personal experience is that a 747 plane came in from a flight and one of the mechanics wanted to work on one of the engines right away. The "grounder" wasn't ready yet. When the mechanic stood near (!) the engine a spark went from the engine, through his body to the ground.Moral: it's not just the refueling. Planes in general get a lot more static and are even dangerous for people in general working on the plane. >>>>>>>Hope this helps!!

Well sir, it DOES make sense. I never would have come up with the explanation on my own so I've learned something new for the day. Heh heh, guess that makes my day. I can go back to bed now. :D

Hi, First rule that goes back to the OLD prop days of when I was a flight line machanic is " GROUND THE AIRCRAFT FIRST " before doing ANYTHING to it !TONY USAF RET.

Thank you all of you for your explanations!Roland