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.