In a message dated 12/31/2007 1:39:57 P.M. Central
Standard Time,  randylsnarr@yahoo.com writes:

I am  looking for feedback from those who pull fuel
directly from their wings that  do not have slosh boxes installed. My fuel
pickups are in the typical place  (BL 50 about 2/3 of the way back between the
front and rear spar).
I am  contemplating changing the fuel system with a
3 way valve to pull from Left  Main and Right tanks.
I would be very interested to know if you ever
unport  the fuel and under which conditions it happens if  ever.



Randy,
 
I can only answer your question theoretically.  I
believe in the  simple system pretty much as designed for the wee Lancairs.
 As such, the  wings can be completely emptied into the header tank while in
level flight  (down to the last cupful), thus maximizing the available fuel onboard.   Drawing directly from a wing without a slosh chamber
means that at some  lesser fuel level, the wing feeding the engine can
unport via a slip, skid,  uncoordinated flight, high pitch angle (extended
climb or descent) or a  spin.  The fuel level may be different for each of the
conditions listed  and it is doubtful if any were tested whilst the wings were
off the airplane  when it is easy to check at certain pitch angles.  Let's see,
how about a  Vx, Vy or missed approach climb out with a standard rate  turn
(albeit slightly uncoordinated) away from the 1/4 filled  wing?  Does this mean the
checklists for takeoffs, landings and  approaches contains a check off  to
switch to the wing with a 1/2  or better fuel quantity?  So many bad possibilities
are extant.
 
Some planes that have 3-way selectors and pumps that
are  utilized to keep the header full, where the header is used for
takeoff and  landing or reserve only.  The selector valve is considered a backup in
case  a pump (or the complete electrical system) should fail.
 
Of course, others (like myself) keep the header tank
full (>8 gal) at  all times (engine sole fuel source) and have pre-made
the decision that  should they note a pump failure, the "nearest airport" GPS
function is  activated.  The safest way to reach your destination is with everything working - even if it takes a day or two longer.  We look at the  header
as the main fuel tank and the wings merely as aux tanks.
 
Scott Krueger  AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL  (KARR)

Darwinian culling phrase: Watch  This!



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