Abstract: A rotary, fluid-flow-to-mechanical/electrical power-conversion device including a generally cup-shaped, squirrel-cage rotor having a rotational axis, and including plural, circumferentially spaced, elongate, transverse-cross-sectionally arcuate airfoil (fluid-foil) blades sized and disposed about the rotational axis of the rotor with their respective long axes substantially paralleling the mentioned rotational axis. Blade-related dimensions and spacings are chosen whereby the ratio of blade-to-blade circumferential spacing a to blade transverse chord length b is characterized as one which: (a) resides in the general range of about 0.24 to about 0.4; or (b) resides, more preferably, within the somewhat narrower subrange of about 0.25 to about 0.35 within the mentioned general range; or (c) has, even more preferably (for use in many if not most circumstances), a value of about 0.33.