REFLECTOR: Grounding Point for fuel tanks

[KeithHallsten]

I'm not really concerned about a spark deep within the tank, because the mixture there is so rich that combustion is impossible.  However, a spark right in the opening of the tank, where air and fuel vapor exist at every possible ratio, could be a big deal.  Since we have non-conductive tanks supported on non-conductive tires, there is the potential for a substantial static charge to exist on the tank and its filler ring when you taxi up to the fuel pump.  I don't want to dissipate that charge with a "SNAP" to the grounded fuel nozzle.

Therefore, I installed a wire from each fuel tank's filler ring to the aluminum tie-downs bolted to the ends of the CS spar during strake construction.  I plan to electrically connect the tie-downs to the central ground point at the firewall, which will bond them to each other as well as to the engine.  Simply connecting the ground clip from the fuel pump to either strake tie-down OR to an exhaust stack would assure that there could be no electrical voltage between the fuel nozzle and either fuel ring.  Problem solved, IMHO.

I ran the wire through the foam between the top and bottom skins of the strake top by "drilling" in from the edge with a sharpened threaded rod (#10-24, as I recall) then slipping the wire in through the resulting hole.  I made a gas-tight electrical connection to the fuel ring with a screw, nut and ring terminal.  I then backfilled the hole around the wire by injecting a wet micro slurry so that there was no void to make a weak spot or channel a fuel leak, and completed the strake construction.

Keith Hallsten
  
  ----- Original Message ----- 
  From: Al Gietzen 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Sunday, October 24, 2004 9:21 AM
  Subject: RE: REFLECTOR: Grounding Point


  I guess there are different views on this, but I see little relation (as in maybe "none") between grounding the exhaust pipe, and refueling safety.  The static charge buildup is between the nozzle and the fuel (surface); or the nozzle and the potential existing static charge on the surface of the strake due air friction.  So have a metal chain or cable from the cap ring hanging into the fuel, and keep the nozzle against the ring; and, if you have just landed, wipe the surface of the strake with a damp cloth before contacting the nozzle to the ring.



  Anyway, that's my take; but I've been wrong once before in my lifeJ.



  Al

  Subject: REFLECTOR: Grounding Point



  I didn't find a direct reference in the archives, so I was still wondering if the exhaust pipes is an adequate grounding point when refueling?  I always assumed it was but I'd hate this to be a FireBall Falacy.



  Chuck 



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