REFLECTOR: Grounding Point

Ronnie Brown romott at adelphia.net
Fri Dec 3 07:00:04 CST 2004


For those of you who save your EAA Sport Aviation magazines, there is a good article on plastic airplanes and fuel systems in the March 2001 issue.  The author suggests grounding the fuel cap ring through a 1 megohm resistor to slowly discharge the difference in potential between the fuel cap and the fuel hose nozzle.  

The use of a cylindrical fine mesh screen would also help reduce chance of fire while the fuel is flowing.  

Ronnie


  ----- Original Message ----- 
  From: Alex Balic 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Friday, December 03, 2004 12:09 AM
  Subject: RE: REFLECTOR: Grounding Point


  Hey Al,
  I don't think that there is too much charge differential building up during actual fueling operations, I would think that when the fuel is flowing the charge could pass freely from the tank to the nozzle via the surface of the fuel and thereby keep the potential at or near zero- I will check up on this though..............I believe that the problem is that a spark occurs between the fuel nozzle and the aluminum cap, or between the nozzle and the skin in the vicinity of the cap when the two are brought into close contact just prior to fueling- assuming that the aircraft is not "grounded" to the fueling point.  There can be a lot of charge differential between the aircraft and the fuel truck due to many different reasons, and I am just trying to figure out the best way to make the differential zero before the fuel cap is opened, and/or placing the brass safety screen in the filler neck to prevent fire from entering the tank. 
   Like I said in a prior post I got severely jolted once re-fueling from a ground based pump station because I had the ground clip in one hand and touched the spam can I had just finished flying with the other- a mistake I will not repeat- and if I had fuel on my hand at the time I am pretty sure it would have ignited...
  About the chain- I was referring to the design that has the ball chain attached to the fuel drain line and it rolls around in the bottom of the tank- a chain that makes it into the fuel and attaches to the cap would certainly make more sense- and I think that touching the fuel ring with the nozzle before opening the cap would help as well.
  Alex








   -----Original Message-----
  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On Behalf Of Al Gietzen
  Sent: Monday, October 25, 2004 9:59 AM
  To: alex157 at direcway.com; 'Velocity Aircraft Owners and Builders list'
  Subject: RE: REFLECTOR: Grounding Point


    Subject: RE: REFLECTOR: Grounding Point



    the fuel itself is non conductive, it is the charge that is stripped from

    the surface of the flowing fuel that builds up on the surface of the skin

    and metal parts that causes the problem, the metal chain in the fuel trick

    is not effective, since there is not any way for the charge to pass to the

    chain.



    Alex;

    Knowing how to deal with this issue would be easier if there was a consistent understanding of what is happening.  Yes, the fuel in non-conducting, as is the fiberglass skin. But the static charge does travel on the surface of both.  If it didn't, there would be no possibility of a discharge, and no problem.



    My understanding (which I thought was consistent with the conclusions from the last go around on this) is that a potential (static charge) builds between the fuel surface and the nozzle because of the electrons being stripped from the fuel by the surface of the hose and nozzle; creating the possibility for a discharge from the fuel surface to the nozzle.  Metal contact at the fuel surface (the chain) provides a conducting path to the cap ring and, by contact, back to the nozzle/hose; thereby eliminating any spark.



    Or is my understanding flawed and oversimplified? Maybe there can be a pre-existing potential difference between fuel truck/fuel pump and the plane.  Maybe no one really knows what the problem is.  If they do, let me know.



    Al







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