Structure and motion analyses of the sails of Chinese Great Windmill

This study is to conduct analyses of the structure and operation of the sail of the Chinese Great Windmill based on the results of a reconstruction project of the vertical shaft type wind-power Chinese square-pallet chain-pumps during 2004–2006. According to the tests and analyses, the motion of the sail can be divided into three regions during a windmill cycle. Region I (the sail is positioned at the 1st limit position, ∅) and II (the sail is positioned at the 2nd limit position, λ) are both propelled but Region III is not. The hanging of the sail is an important aspect of installing (or starting) the Great Windmill. The length of the sheet and the point at which the end of the sheet is tied sets the sail at an optimal angle and are the deciding factors that generate greater work torque in the Great Windmill. If the sheet is tied on a crossing bar, when ∅ = 12.7°, and λ = 116.3°, it can obtain the maximum average torque (average torque factor = 2.263). If the sail is not constrained by the geometric relationship, the resulting maximum average torque (average torque factor = 2.271) can be derived using ∅ = 18.1°, λ = 120.8°.