Propeller airplanes exhibit diminishing speeds for energy expended starting in the 450mph range. I haven’t studied the science behind it, but it’s pretty obvious that it’s caused by radial air flow. These long air augers would increase radial air flow exponentially, and would substantially decrease power efficiency. Most of the length of these auger shafts would be plagued with extremely low air pressure ....little air to move, and suction from all directions.
“Propeller airplanes exhibit diminishing speeds for energy expended starting in the 450mph range.”
Propeller tips go supersonic.