REFLECTOR: Good Friday Landing

[Scott Baker]

Hi Bruce,
True, the header fuel tank is probably lower than the engine's mechanical fuel pump - but remember, the main tanks (assuming they have fuel) are providing head pressure.  The bottom of the strake fuel tanks is roughly the same elevation (water line) a most engine driven fuel pumps.
Dave's situation is a little different.  His installation does not have an engine driven fuel pump.  The system in his aircraft was such that an electric fuel pump, mounted above the spar, sucked fuel uphill about (say about 20") and then pushed fuel under pressure to the engine.  Also, this fuel system is a constant displacement pump that has a recirculation (fuel return) design.  This means the electric pump is sucking a lot of fuel - guessing 30 gph or more - up hill through a 3/8" diameter line.  Add mogas into the equation - and the situation is ripe for fuel cavitation.
My thoughts.
SB
  ----- Original Message ----- 
  From: bdtopp at comcast.net 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Wednesday, April 06, 2005 10:40 AM
  Subject: RE: REFLECTOR: Good Friday Landing


  Al,
     I get what you are saying about the elec fuel pump, but, what about the mech fuel pump since this is the only pump running most of the time except for takeoff, landing or failed?  It will never be within a few inches below the level of fuel in the sump tank on a FG.  It's always sucking fuel upwards.
  Bruce  

    -------------- Original message -------------- 



    Randy,

        Thanks for the explanation.  I thought there must be a difference.  Doesn't this mean that all FG models could have the fuel starvation problem that Dave experienced?  Obviously nobody is since we haven't heard of this before (or have we?).  It doesn't make sense that moving the fuel pumps is going to solve Dave's problem since all FG models have the elec fuel pump equal to or higher than the sump tank and the mech fuel pump is always higher.  Has anybody besides Dave (and Sid on Starduster) experienced fuel starvation do to the location of fuel pumps?



    Bruce Topp



    Bruce;



    The pump doesn't need to be below the bottom of the sump tank; anywhere near the bottom is fine.  You just want it to be at least a few inches below the level of the fuel; which will always be at least at the top of the sump, unless you are about to run out of gas, or something else is wrong. It is not as much an issue with avgas as it is formulated with a higher minimum vapor pressure that auto fuel.



    Al



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