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If an aircraft had a single fuel tank, then getting fuel to the engine would
involve the following major pieces of equipment connected in series:  Fuel tank,
shut off valve, fuel pump, regulator valve, pipe to engine and a pipe back to
the fuel tank for the overflow. I'm forgetting about fuel filters and other
extraneous gear for redundancy.
 
Because we have multiple tanks, we end up manually selecting which tank feeds
fuel to the engine during any time period. We also end up having multiple fuel
pumps, one per tank, not for redundancy, but because we have to.
 
What is wrong with the following idea. I'm sure there must be something wrong
with it or it would have been implemented long ago.
 
The wings are mounted at an angle to the horizontal plane. Gravity would take
any fuel and attempt to empty the tanks if given an opportunity. If both tanks
emptied into a tiny 1 pint reservoir and that reservoir was considered the
"tank" in the first paragraph, wouldn't that get rid of the manual switching of
tanks, and reduce the amount of plumbing, connections and weight?  
 
I am assuming that non banked flight is 99.9% of all flight and therefore
gravity should act equally on both wing tanks. One way valves could prevent
reverse flow but that shouldn't even be a problem except in relatively rare
situations where centrifugal forces are present as in turns and other flight
where the wings aren't level. If one tank had more fuel in it than the other
tank, that tank would also exert more pressure into the tiny reservoir and
should empty at a faster rate till it is equal with the other tank. If there
were no reverse flow valves, the fuel would seek its level in both tanks.
 
What is wrong with this?
 
Bill Gradwohl
IV-P builder
N858B