REFLECTOR: "Rube Goldberg" resistor for plastic airplanefuelsystems

Thu Jul 5 22:55:16 CDT 2007

I got curious about what CAFE was talking about, so I went to their website and read their paper titled "Fuel Handling Safety." It says,
In composite aircraft or aircraft equipped with fiberglass fuel tank(s), the fuel tank filler neck(s) may not be grounded. Homebuilders of such aircraft should make a special point of attaching an internal grounding wire from the tank filler neck to the aircraft's metal ground bus, and this, in turn, should be grounded to the landing gear. (Or to whatever piece of metal on the airframe we provide for the fuel truck's ground cable clamp.)

Doug Holub

  ----- Original Message ----- 
  From: Douglas Holub 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Thursday, July 05, 2007 10:15 PM
  Subject: Re: REFLECTOR: "Rube Goldberg" resistor for plastic airplanefuelsystems

  I think the author of that Sport Aviation article must have gotten something confused. 

  If there was a 100k resistor attached to the aluminum fuel tank filler ring, and if the fuel truck nozzle touched that resistor first instead of the filler ring, there wouldn't be a spark. 

  And if there was a place on the airframe designed for the fuel truck's grounding cable clamp, and if that place was connected to ship's ground, and if the ship's fuel tank filler ring was attached to ship's ground through a 100k resistor, then there wouldn't be a spark when the fuel truck's grounding cable clamped on to the airframe. But so what? That clamping location shouldn't be anywhere near any fuel vapors. 

  Someone on the AeroElectric list asked Bob Nuckols this question. He answered:

  When a fueler walks up to a Sundowner and puts the nozzle into
      the tank, the electrical connection between the fuel truck ground
      and the rim of the filler neck is pretty low resistance. I can't
      think of any good reason to make that something different for
      a plastic airplane.

        Bob . . .

    ----- Original Message ----- 
    From: Lawrence Epstein,MD 
    To: 'Velocity Aircraft Owners and Builders list' 
    Sent: Monday, July 02, 2007 2:07 PM
    Subject: Re: REFLECTOR: "Rube Goldberg" resistor for plastic airplanefuelsystems

    Good answer! Thanks for the explanation/reference. Just another example of something that seems logical, can be backwards if you don't know all the details.

    Larry E.

    -----Original Message-----
    From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Ron Brown
    Sent: Monday, July 02, 2007 12:03 PM
    To: Velocity Aircraft Owners and Builders list
    Subject: Re: REFLECTOR: "Rube Goldberg" reisitor for plastic airplane fuelsystems

    Brother Dave,

    This "rube goldberg" resistor is a development and suggestion by the Rube Goldberg aircraft division called the CAFE Foundation, documented in Sport Aviation, March 2001, excellent article on fuel systems for plastic airplanes starts on page 35, the specific recommendation is on page 40.

    I consider this a must read about plastic airplanes and their fuel systems.

    Quoting from the article "Using proper mounting techniques, route the (ground) wire into the cockpit and connect it to the ground bus through a resistor (approximately 1 meg ohm, 1 watt). The resistor limits the power of any static discharge by"spreading out" the discharge time, which turns the discharge arc to a corona-like discharge that is less likely to ignite the gas fumes. 

    "In any case, when fueling it is good practice to keep the nozzle in contact with the filler neck. If both the filler neck and the nozzle are grounded, there should be no problem. But you can't be too sure about some gas hoses and nozzles or ground connections to an airplane from the truck or pump." 

    However, if you touch the metal fuel nozzle to the fuel tank ring and there IS a static potential, there is a good chance of a spark and a small to very large poof as the fuel in the tank ignites.

    After hearing about a brand new Velocity, belonging to Melvin Ball in Montrose in Colorado that burned to the ground during a refueling accident (no details available - I have enquired - Mr. Ball didn't want to discuss).

    Not trying to be a smart A_ _, just trying to better educate the experimental aircraft building community.  

    Ronnie Brown

    EAA Technical Counselor

    EAA Flight Advisor 

    350 Educational Hours in a Velocity - and thousands of hours researching and learning while building! 

    ----- Original Message ----- 

    From: "David Staten" <Dastaten at earthlink.net>

    To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>

    Sent: Monday, July 02, 2007 2:10 AM

    Subject: Re: REFLECTOR: Fuel venting issue

    > If you connect the airframe ground to the truck, then there is no need 
    > for any kind of rube goldberg resistor. The airframe and the fuel truck 
    > are iso-electric at this point. Then.. for good measure, connect the two 
    > (truck and plane) to a grounding rod in the pavement or a tiedown.
    > 
    > Our velocity has grounded caps, with the ground wires connected to 
    > airframe ground. No resistors.
    > 
    > Dave
    > 
    >>"I also connected a ground wire from this vent line and it connects to the 
    >>filler cap. These vent lines are grounded through a 100 Kohm resistor to 
    >>ship ground. This reduces the amount of spark that would be generated if 
    >>there was a static charge difference between the fuel hose and the filler 
    >>caps."
    >>
    > 
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