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07-28-2014, 01:46 PM

#1171

Mark Vandervelden

Join Date: Jul 2012

Location: Bournmouth UNITED KINGDOM

Posts: 495

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Hi Fredo

The main tank once the system is filled draws only fuel from the two rear tanks and then air once there empty, It must remain a sealed unit and not draw any air until the rear tanks are empty or the rear tanks will not empty at all.
This is why the lines from the rear tanks and there vents must be equal so they empty symmetrically, If one rear tank empty's before the other it will continue to slowly draw from the remaining "fuller" tank but at a much slower rate.
This is because air will then be drawn through the empty tank easier than fuel can be from the part full one, in practice and in my experience both rear tanks are usually dry at the end of the flight, lets hope the main one is not

An other option and one "I don't recommend" is to plumb all the tanks in series IE empty one after the other, this creates quit a high draw for the pump when all the tanks are full and a comparatively low draw when only the front tank is full.
I have tried it and even on a well plumbed and as free flowing setup as feasible, first makes the poor little on-board pump work hard and then confuses it as the draw reduces which can lead to an uneven run, so for me its never a first option.

All the best Mark V

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