The more I read on this subject, everyone doing it slightly different, the more ambivalent I get about selecting wing tanks.  On my Lyc powered Velocity I have both my wing tanks (highest place in the fuel system) gravity feeding my sump tank.  I have electric valves so I can DE-select one or the other wing tank in the case of assymmetric transfer to the sump.  The sump feeds the engine through pumps below the sump fuel level and the regulator vents back to the 5-gal sump.

What I will go to when I get my 13B installed, I'm going to have a "Supply" tank and a "Transfer" tank.  The Supply tank will gravity feed the 5-gal Sump which will feed the engine.  The regulator will return to the Supply (right wing) tank.  The Transfer (left wing) tank will have a line through a Facet pump to the Supply tank.  I periodically replenish the Supply tank with fuel from the Transfer tank.  That way, I will eventually run the Transfer tank plumb empty and operate late in the flight in the certain knowledge that every drop of fuel in the airplane is in the "selected" tank.

This scheme will assure maximum possible dilution / cooling of the warm return fuel.  The Supply and Transfer tanks will be vented to outside the airplane, and the sump will be vented to the Supply tank.  I can't think of a more foolproof (and vapor proof) scheme.  Could be improved upon if I were to run my Return fuel through a small air/fuel heat exchanger to cool it before it gets to the Supply tank.

Just a theory ... Jim S.




Paul wrote:

Hi, Rusty....My main tanks drain into the top of the surge tank. The fuel comes out of the bottom of the surge tank to the EFI pumps.  The returned fuel goes back into the top of the surge tanks.  No, it won't be difficult to add a vent line to the sump tank...Maybe you could stop over on one of your trips to fix an MRI somewhere and weld it into the aluminum surge tank for me, so I won't have to drain the fuel. (kidding).  It looks like adding a vent to the sump tank (into one of my mains)  is what I should do, and it won't be that difficult  Thanks.  Paul Conner

----- Original Message -----

From: Russell Duffy

To: Rotary motors in aircraft

Sent: Saturday, February 12, 2005 9:24 AM

Subject: [FlyRotary] Re: Vapor lock in sump/header tank.

A vent line from the top of your sump tank up to the top of both of your main tanks, but not tied into the main tank vent system.  

 

Paul, where are the lines physically located on your header tank now?  Are they all at, or near the bottom?  After reading all this info about vapor lock and header tanks, I have to agree that this is probably the prime suspect at the moment.  Vapor that builds up in the top of the tank has to have somewhere to go.  

 

I'm also assuming that you don't have return lines to your fuel tanks, which is probably why you're running the header tank in the first place.  I've been sketching this on a notepad, and so far haven't figured out a way to make this work without adding a vent somewhere.  

 

I fear the reply to this question, but how hard would it be to add a return line to at least one of your tanks?  

 

Rusty (already behind schedule for the day) 

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