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<... jet pump connects to the outlet of the fuel pump, not the return from the pressure regulator ...>
That's where our problem lies. I had thought that the jet pump was in the return line picking up fuel from the transfer tank and delivering both return fuel and transfer fuel to the delivery tank.

If you did put the jet pump in the HP circuit wouldn't it pump all your fuel upstream into the transfer tank? And if it didn't (which I sort of doubt) what would happen when the supply tank went dry? Wouldn't you be drawing air from the tank into your HP circuit?

I'm pretty sure the jet pump is in the return circuit ... Jim S.

Mark R Steitle wrote:

Jim,

As I understand how this thing works, the jet pump connects to the outlet of the fuel pump, not the return from the pressure regulator. The pressure regulator return is free-flowing back to whichever tank you want. The flow through the jet pump could be controlled by a simple open/closed solenoid valve. Only problem I see is how to keep the fuel in the two tanks balanced. Maybe this could be done by switching the return fuel back & forth between the two tanks. Too much fuel in the left tank, return fuel to the right tank. Not enough fuel in the left tank, return fuel to the left tank. Not sure how to automate that function though. Perhaps a simple BASIC STAMP PC could compare readings from the two capacitive fuel probes and “decide” which tank has the least fuel and tell the return fuel to go to that tank. The whole system would be hands-off, except for the fuel pump ON/OFF switch on the panel.

Mark S.

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Jim Sower
Sent: Wednesday, February 16, 2005 9:48 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Fuel System Design - Jet Pump

Got no problem with that. It really sounded good at first blush. It just sounded to me that things kind of got out of hand when we looked a little deeper into the plumbing and mechanisms that we have to add to compensate for the fact that we can't turn the transfer pump off. Sounds to me like a really nice looking concept is going to get us INTO more trouble than it gets us OUT of.

Haven't heard much around the effect back pressure will have on regulator ... Jim S.

Mark R Steitle wrote:

Jim,

What I was envisioning is a simple electrical solenoid controlling fuel transfer. Forget all the lines from bottom of A to top of B, etc. Some sort of fuel level sensor could tell the solenoid when to open and close. (Some of you electronic whizzes will have to step in here.) This would free up the pilot to do other things, like watch for traffic.

Mark S.

<... 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 ... A full B empty... B full A empty ... A & B half full ... A & B full ... parked on a hill ... >
Sounds a lot like a ten-cent tail wagging a forty-dollar dog here. Didn't we set out to simplify something? How about just ONE line from B to A with a Facet pump. To get fancy, you could have a momentary ON for the pump that would cause it to pump for 2 or 3 min or something and then turn itself off.

Just trying to stay on message ... Jim S.

PS Has anyone actually seen the two-line-jet-pump and watched it actually WORK ??
(the devil made me say that )

Ernest Christley wrote:

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!!

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