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aviator921

Member
Draining fuel for weight and balance question?

Hello to all. I purchased an 8 last year and recently redid the panel. I need to do a new W & B and would like to know what the proper procedure to getting all the fuel out. Thank you.
 
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I leveled the plane at the canopy rail, disconnected the fuel line from the firewall to the mechanical pump, grounded the fuel "can" to the aircraft, put the disconnected fuel line into the tank and turned on the fuel pump.
 
Defuel Rig

Search for the above title and you will see my rig. I wanted to make sure everything was grounded. I had the luxury of empty tanks so I put a barbed fitting in the place of the sump drain fitting. You could set up a wide mouth fuel can like the one I used (Picked up from Cut Rate Auto Parts) and then just unscrew your drain plug and let if flow.

An alternative method which would leave any unusable fuel in the tank and make it part of your weight (a good thing), is to use your boost pump to pump the tank empty until it can't pick up more fuel. From the location of the pickup to the drain hole there is not very much unusable fuel, I have heard it is less than a cup but I have not determined this myself yet. You can undo the fuel hose at the firewall side and put it in a catch container and then turn on the boost pump to flow the fuel. The key is the steel rod in the fuel container. you want the fuel to have the same ground potential. As the fuel flows into the container the rod keeps the fuel in the container matched to the plane, also if you walk away touch the metal of the plane before you get near where there may be fuel vapors.

Cheers
 
Thanks for the quick reply guys. I will most likely go the fuel pump route. My right tank has a flop tube. Will I be able to get most the fuel out or am I better off draining that tank from below?
 
You don't want to get ALL of the fuel out. The objective is to get all of the usable fuel out.

I did the same. leveled the plane and pumped it out with the boost pump. When the pump lost suction, I was left with unusable fuel.
 
Do you want to do a weight and balance, or measure fuel tank capacity, or both?
If it is just W&B, why drain fuel at all? Instead fill the tanks, weigh it, calculate moment, then subtract out the weight and moment of the fuel. Not text book but it will give you the answer.
 
BobTurner said:
Not text book but it will give you the answer.
Click to expand...
If it gives you the right answer, it doesn't matter how you got it. There's nothing wrong with weighing it with full tanks, empty tanks, or anywhere in between. CG doesn't move much on the RV's with fuel burn anyway(*). The hard part is knowing accurately what your fuel level is when you're not completely full or completely empty.

(*) Note that I'm referring to just the CG of the fuel within the tank here, not overall CG of the aircraft. The "moment arm" for your fuel tank is officially the same at all fuel levels.
 
flyinga said:
I leveled the plane at the canopy rail, disconnected the fuel line from the firewall to the mechanical pump, grounded the fuel "can" to the aircraft, put the disconnected fuel line into the tank and turned on the fuel pump.
Click to expand...

This is correct, and I would like to add something else, sump the fuel tank drains until dry. Weigh the plane empty of fuel it's more accurate.
 
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