surface of blade 12 are greater than the wind forces f 2 applied to the convex portion since the concave portion tends to collect the forces and the convex portion tends to deflect the forces the resulting differential results in an imbalance of forces on blade 12 and rotation of rotor 14 savonius wind turbines are well known for their compactness and relative efficiencies during a wide range of wind speeds from various directions savonius turbines are one of the simplest turbines and are considered u201c drag u201d type devices they typically consist of two or more u201c c u201d shaped blades having an u201c s u201d cross sectional shape when viewed along its vertical axis of rotation the backs of the blades do not help with rotation and are typically designed to shed air so as not to increase drag on the turbine since the u201c c u201d shaped blades collect wind forces directed against their surfaces and the forces are greater on those surfaces than the backs of the blades the differential in applied forces causes the blades to turn while the savonius type vwat shown in fig1 is typically used because of its omni directional properties u2014 the ability to be driven by wind forces from any direction u2014 it is somewhat inefficient because.