We had even more questions on fueling as a result of the article on explosive potentials in fueling your airplane from a fuel truck. One reader pointed out that he has a professional contractor’s tank in the bed of his pickup, and that he uses that tank to fuel his airplane. He wondered if using this rig could expose his plane to a potential static electrical charge, and in doing so, introduce the potential for an explosion while he was fueling his airplane.
FOR STARTERS, WE WELCOME THIS QUESTIONING ATTITUDE. By not assuming, and asking questions, we all learn. The owners question is a good one, but the answer depends on how his truck-mounted system is set up as much as anything else. Thus, we’ll look at the details of the situation, and provide some suggestions that you can use to make sure your portable fuel truck is safe for fueling.
Our owner in this case, had recently purchased a new hose and nozzle from an automotive fuel vendor. He wondered if this would cover his fueling issues, or whether he needed to take additional precautions. For starters, fuel equipment sold these days does have some internal protection – whether that protection works with your fuel system is the question. The only way to find out is with test equipment, such as an ohm meter. Check the resistance from the tip of the fuel nozzle to the fuel tank. You can hold the two components within a few feet of each other to perform this test — you don’t need test leads that are as long as the hose. The resistance between the two items should be very low, in the area of an ohm or less, to assure that the spark potential is reduced.
SOME TRUCK MOUNTED RIGS WERE DESIGNED FOR DIESEL. The explosion potential of diesel fuel is low, and some of these tanks may not be well protected from static discharge. Make sure your truck-mounted tank system is for the right fuel, and if it isn’t, that it has the correct bonding to the truck’s structure to keep the tank from becoming a static electricity nightmare.
WITH THAT SAID, you still need a ground strap (or bonding strap for purists) to keep static buildup from “lighting up” your life. Here is the problem: the hose is grounded (bonded) to the fuel tank on the truck. The truck and airplane each have a discreet electrical potential from where they have traveled / flown. Without a ground (bonding) strap connection between the two vehicles, when the fuel truck nozzle comes into contact with the airplane, those potentials will neutralize, and that usually means a spark.
NASTY OR NOT, sparks aren’t good around fuel. Thus, a grounding (bonding) connection between the two vehicles is needed. For the fuel truck, the fuel tank needs to be bonded to the truck, and the ground wire needs to be firmly connected to the truck, preferably to a major portion of the structure of the truck. At the connection point, the paint needs to have been cleaned away, to allow a minimum resistance connection between the lug and the truck.
For the airplane, the ground should be connected to a bare piece of metal, connected to the airframe and in contact with the fuel system. As an example, on Beech Bonanzas, you can hook up to the tiedown connections, since they are riveted to the airframe, and the airframe is connected to the fuel tanks by the fuel cap assemblies. In other planes, the solution may not be easy to find. Consult your POH for the best ground locations.
We’ve spent a good amount of time looking at how to fuel your airplane from different sources and methods, and it is for a good reason. The amount of energy in a gallon of avgas is impressive. By using the necessary precautions, you can assure that the energy in your avgas is put to good use, powering your aircraft, instead of burning it — and possibly you — to the ground.