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Why could Leonardo da Vinci’s helical airscrew not function like a modern helicopter?

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Self-portrait of Leonardo da Vinci drawn in red chalk, showing an elderly man with long hair and a flowing beard, with a serious, contemplative expression. — Leonardo da Vinci Self-portrait, drawing by Leonardo da Vinci, c. 1517–18; in the Royal Library, Turin, Italy.

Leonardo da Vinci’s "helical airscrew," designed around 1487, is often viewed as a conceptual precursor to the modern helicopter. However, it could not function like a modern aircraft primarily because it lacked an adequate source of power to generate the necessary propulsion and lift.1

While modern helicopters rely on sophisticated engine-driven rotor systems to achieve vertical flight, Leonardo’s design was limited by the mechanical technology of his time. Beyond the fundamental issue of power, successful vertical flight requires complex control systems—such as cyclic and collective pitch control—to manage lift, torque, and stability, which were not present in his early sketches.1234