What fundamental limitation prevented the Aerial Screw from functioning as designed?

Required immense, sustained power that human muscle could not provide

The Aerial Screw, which serves as a conceptual forerunner to the modern helicopter, demonstrated sound mechanical principles regarding generating lift by rotating a device to compress air. Despite the conceptual soundness of the design, its execution was fatally limited by the available power source. The drawings illustrate a mechanism intended to produce substantial lift, but this action demanded an immense and sustained level of power input. Given the technological limitations of the Renaissance, this power could only be supplied by human muscle, which, even through mechanical advantage like a crank mechanism, was insufficient to generate the necessary rotational force required for sustained flight or lift. This dependence on power beyond human capability is what kept the Aerial Screw conceptual rather than functional.