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Date: Tue, 15 Feb 2005 16:12:56 -0500
From: Ernest Christley <echristl@cisco.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fuel System Design - Jet Pump
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> 
>
>Thoughts on the jet pump: 
>
> <>
>
>Fuel tank levels needs to be controlled in order to eliminate a 'heavy wing' which is very fatiguing on a long cross country.  Aileron trim can do it but that adds drag.  A valve can be used but that adds to the complexity again.
>
>Tracy
>

Looking over the diagram in the PDF that Ed sent.  The jet pump works 
all the time, constantly pumping fuel from the bottom of B into A, where 
the main pump can pick it up.  An important element to this is that 
there is a large return path for fuel to go from A to B.  If the tank is 
half full or more, all the fuel moved by the jet pump just flows back over.

In the airplane transfer, you'd want two lines.  One from the bottom of 
B to the jet pump.  Another from the mid level of A to the top of B.  
The lines need to stay below the tanks.  At no point will the the sides 
ever be more than 1/2 a tank different.  Consider:

A is full, B is empty
    Fuel will flow from A to B via the return line, until A is half empty.
B is full, A is empty
    Fuel will flow to A via the jet pump, until B is empty.
A and B are both half full
    Fuel will flow to A.  If A gets more than half full, fuel will flow 
back to B.
A and B are both full, and you park sideways on a hill.
    Fuel will flow to the ground until the high tank is empty. Doh!!