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Header Tank Volume

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04 May 2023 07:25 #1 by Super User
Replied by Super User on topic Header Tank Volume
We do think of our systems as gravity fed, but that doesn't really take into account the amount of suction created by the cylinders during operation (even starting, when we pull the fuel/air mixture up into the engine).

First, you will know when the mains are dry by either (1) the indicator fpr them being at the bottom and/or the header tank indicator starting to drop. (Regulatory approval for our planes includes a gage for every tank (one for connected mains). It is, of course, incumbent upon the pilot to be aware of those things. If you do manage to miss that, the header will indeed provide close to 5-6 gallons of available fuel.

The rule of thumb is that if the header tank gage goes down, you should too.

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  • Robert James
  • Topic Author
04 May 2023 00:25 #2 by Robert James
Header Tank Volume was created by Robert James
Today I was doing owner maintenance and drained the Header Tank in my Alon into a gas can.
When the Header was empty the gas can was fully filled just past the full mark of  5.3 gal.
So now I know know my plane has about 50 min of reserve left when the mains are empty, but do I?
The first consideration is I will never know when the mains are really empty and I’ve only got fuel in the header tank left,
The second consideration is how much fuel might be left in the Header when the engine begins to fail due to fuel starvation? 
I say that because the flow rate started to slow down more and more as the Header got closer and closer to empty. Since the gas to the carburetor is gravity fed from the Header tank, the normal hydrostatic head decreases to a point where the carburetor might begin starving for fuel before the tank is completely empty. That being the case, we might have 10 or 15 minutes less flight time remaining then we estimated. Any thoughts,….?

 

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