The Twin Otter seems to be slower, though less fuel efficient than the
planes mentioned above. Probably the Air-Ships of the 30 were? Saw a
documentary about someone who went 1200km with a glider in the Andes.
Maybe Motor-gliders would be most efficient?

Yes- look at a Twin Otter.



Jonas Heisenberg wrote:

Thanks for your replies.

So as I understand it, these planes are constructed to operate most
economically at ca. 80-90% of their maximum speeds. Has it ever been
tried to build planes that are built specifically for lower speeds and
higher efficiencies (recent - no WWII)?

Jonas
At some point you'll reach a point of diminishing returns. As
speed decreases induced drag increases and you need to increase power
to maintain altitude/speed. Most jet aircraft have a maximum cruise
power, long range cruise power and intermediate cruise power setting.
Intermediate gives the best time to burn ratio, but if your prime
concern is fuel savings and extended range, then you could fly at the
LRC setting, which, in some aircraft, could yield up to a 15% increase
in range. The expense, though, is flight time.