quote: I find the choice of engine configuration more unusual than the choice of fuel. A prop configuration demands high RPM, not torque, which is why inline and V-configuration engines were terrible in world war-era planes.
quote: I don't know of any hydrocarbon planes that can fly around for 4 days straight.
quote: That is a very special exception, with some extreme engineering feats (and extremely fragile). Not your common or mass produced plane.
quote: That one only lasted 2.8 days; so is actually not an exception.
quote: Diesel engines are higher torque than gasoline engines. So, for the same horsepower a gasoline engine will have higher RPMs, and would make a plane faster than if it used diesel. Hence why diesel engines are rarer for aircraft (though used more on airships, which are lumbering and slow, with a lot of mass that needs to be moved).
quote: Also, if you look just above in this thread you see our talk about Rutan; the only known plan to go over four days. But it was also very specially constructed and one of a kind (and very weak, it could not even weather storms). This UAV is far more standard in design despite its "bomb" shape, and to be mass produced. Can't really compare it to Rutan. Design has a critically important role as you point out, but the engines and fuel are -all part of the design-. Otherwise, why don't we design all our craft like Rutan to have 9 day longevity? Think about it a little more.
quote: Why would they choose hydrogen as fuel source over standard gas/diesel/avgas?