RE: Why can't we simply increase tank size for more flight time?
it's called head pressire and fuel draw.a large tank that os full has alot mire head pressure than a small tank.the fuel will want to gravity ffed to the engine so you atart with a needle that is closed more than normal.as the fuel depletes the head pressire decreases as does the fuel draw and the engine starts runnong lean and dies or overheats and gets damaged.