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unusable fuel

danny

Well Known Member
I drained the left tank with the fuel pump and came in just shy of 2oz of unusable fuel. So is it safe to assume that the right tank is pretty much the same? It's a taildragger so it's always in a climb pitch.
What's the general consensus on this?
Any and all comments appreciated.
danny
 
Yes, that's correct. For all practical purposes, the typical RV wing tank has "0" unusable fuel.
 
unusable fuel...

Thanks. The svc bulletin has been complied with. I'm curious now...I'll weigh with unusable fuel only but later I'll fill both tanks and see where the math gets me.
danny
 
Over 23-years ago, I put my taildragger RV-6 is level flying attitude to run the fuel tanks dry. I used the boost pump with the hose removed from the carb. When air started to be sucked from the tank, I stopped. Filling the tanks back up, I found that I had 1/2 gallon unusable fuel in each tank.

On one long cross country flight 20-years ago, I had more headwind that predicted. Flight was going to take longer than planned. Fuel burn would be such that I would be landing with just under 1-hour of fuel remaining. (Still FAA VFR legal in the USA.) Instead of having 1/2 of my total fuel in each tank, I decided to run the left tank dry so that all fuel remaining would be in the right tank. Watching fuel flow and fuel pressure, I saw both drop to zero and switched tanks. Engine never missed and never knew one tank was now empty. On the ground, the tank that was chosen to run dry (left tank) took 19 gallons of gas. As Mel said, there is 0 fuel unusable.

A repeat of this was done again to comply with one of Van's Service Bulletins about safety of the fuel pickup. The repeat was done circling my home airport till I saw fuel flow and fuel pressure drop on the selected tank. Switched to the tank with fuel then entered the traffic pattern, landed, taxied to my hangar and drained about 4 oz of fuel out of the tank before opening to comply with the service bulletin.
 
On one long cross country flight 20-years ago, I had more headwind that predicted. Flight was going to take longer than planned. Fuel burn would be such that I would be landing with just under 1-hour of fuel remaining. (Still FAA VFR legal in the USA.) Instead of having 1/2 of my total fuel in each tank, I decided to run the left tank dry so that all fuel remaining would be in the right tank. Watching fuel flow and fuel pressure, I saw both drop to zero and switched tanks. Engine never missed and never knew one tank was now empty. On the ground, the tank that was chosen to run dry (left tank) took 19 gallons of gas. As Mel said, there is 0 fuel unusable.

I did something similar during phase one testing (running a tank dry) to verify unusable fuel. I found the same thing - took 19 gallons to get it to the filler neck (RV-6/6A tanks hold 19 gallons each, for those unaware). I still assume ½ unusable for planning purposes but in practice it's not nearly that much. And, in practice, I'm not going to get anywhere near that intentionally anyway.

Mine are the standard aluminum tube pickups per plans.
 
Has anyone got any information about unusable fuel with flop tube as the pick up ?

Same advise applies - Test it.
In theory it should be very close to the same as a standard fuel pickup, depending on how it was installed...
I have pulled tanks apart with flop tubes that hung up on tank stiffeners, fuel vent lines, guide bracketry, even big globs of tank sealant. One flop tube was glued down, so not even functioning as a flop tube at all. One was hung up nearly 1.5" off the floor of the tank. So... Test It.
 
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