The dream of flight, first developed by the observation of nature, was inspired from birds and insects. However, the whirling fall and glide of seeds from trees like the sycamore, allowing a wide dissemination of the specie, is an alternative way of flight. That is probably the origin of conception of the Chinese top (reported by Ge Hong circa 400 BC), which is a small toy consisting in two blades attached to a stick, which rotation between the hands of an operator, generates lift and its vertical flight . The idea of using blade rotation, to fly a machine carrying a man, was developed by Leonardo da Vinci at the end of the XVth Century. His thinking was to adapt the Archimedes’ screw, which is a device for raising water from the ground level, to the vertical translation of a machine in the air (Figure 1). If no light and high-strength material existed at that time and no engine was available to provide enough power to fly that machine, its design was wrong in its mechanical concept. Contrary to the seeds falling from a tree, or the Chinese top, the shaft-driven rotor generates a torque which is transmitted to the nacelle making it swirl and leads to a loss of control. Thus, the lack of a proper counter-reacting torque system is the main drawback of that design. In addition, the rotor shape is far from an optimum use in the air.
Thierry M. FAURE
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