Abstract: A self-starting windmill of the vertical axis type. Upstanding helical in configuration, pivotally mounted outer blade members surround a central, rotatably mounted shaft are connected to the shaft by radially disposed strut members. Arcuate in planform, pivotally mounted inner blade members are mounted radially inwardly of the outer blade members in a collective triangular configuration and have their respective convex surfaces facing toward the shaft. A weight member and a spring member bias a preselected edge of each outer blade member against wind force.