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-   -   Fuel flow question? (https://vansairforce.net/community/showthread.php?t=71685)

Dave12 05-03-2011 08:34 PM

Yes, the drain is out and what you describe is what I believe is happening.

JBPILOT 05-03-2011 09:05 PM

I just knew it - -
 
I'd be sorry for jumping in - - out of ideas ! ! ! !

When it is quiet, with no gas, does the pump sound like it will vibrate itself out of the plane ? ? ?

John Bender

Ausflyer 05-03-2011 11:07 PM

Gotcha!
 
Hi Dave,
You are not the first to have this problem. See this thread:
http://www.vansairforce.com/communit...eferrerid=8455
I put aside my fix until I had the aircraft finished. When I pull the top I want to put in a moeller gauge, Currently I manage the problem by using only the top half. But the new gauge and fresh proseal arrived this week, so its time to solve the problem.

I?m pretty unimpressed with the PAP test. It forces you to remove the tank and take the top off, at the end of the building process, if your tank fails. Why not a bench test before the lid goes on?

How are the pre-fabricated fuel tanks that Vans sells, tested?
http://www.vansairforce.com/communit...eferrerid=8455

I bet Vans does not just trust to luck when they sell a tank. So my first step will be to ask Vans for the details of their bench test.
Rod

BigJohn 05-04-2011 06:09 AM

For what it's worth...
 
Your situation is exactly how my fuel test went. During the last half gallon or so the pump sucks air and cavitates. That seems quite normal to me, since you are drawing fuel out of the tank at a faster than normal rate than you would in actual flight conditions. Approx 20gpm as opposed to 5 or 6.

In real life, in what circumstance would you be using the last half gallon of fuel anyway? Only in an extreme emergency, and by then you would be preparing for an emergency landing!

IMHO your tank is just fine, and I wouldn't spend any more time worrying about it. Build on!

Mich48041 05-04-2011 06:27 AM

Good idea, Rod
 
Quote:

Why not a bench test before the lid goes on?
That is a good idea. The tank could be filled with water to check for leaks and to wash out any debris. A test can be developed to measure flow rate at the tank outlet without using a pump, just gravity. Then if the flow rate is not adequate, the passageways can be cleaned out or enlarged easily before the tank lid is installed.
Joe

Ausflyer 05-05-2011 06:20 PM

I asked Vans tech staff about a bench test for fuel tanks, and what they did with their prefabricated tanks. Ken Scott replied:
?We don't have such a procedure. We know the tanks are built to
plan, so the flow from the tank will be adequate. There is no
procedure for the builder to test the tank before installation --
the PAP test is the real proof, because it tests the entire system,
rather than just the tank.?

Fair enough. My response was:
?I do admit to being surprised there is no bench test. I agree that the
definitive test is the one specified. In my case, I was certain that I
had double checked everything, before closing the tank. Some human
error has crept in there somewhere. I will let you knowq what I find
when I take the top off the tank?

So Dave, if I find the holes are clear when I take the top off the tank, I will have to work out my own bench test. I have a few ideas to base that test on. I would like to think that the engine would supply full power to the last drop of fuel at the most inconvenient moment. Such a moment might be a forced go-around. Food for thought.

Rod


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