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Principle of the Propeller

                                                                              
  

                     The Wedge                                                                                         The Screw   

The principle of the propeller originated from the simple mechanical Wedge.  If one were to lengthen the width (dimension into the page) of the wedge and wrap it around the axis of a cylinder in the shape of a coil or helix, it becomes the Screw.  If we now take just one or two threads of the screw, but increase its thread depth substantially, it will begin to take the shape of a fan, or propeller: 

Fan or Propeller

Aerodynamic propellers on airplanes have long blades, powered by piston or turbine engines, to push high volumes of air swiftly to generate thrust.  Hydrodymanic propellers for boats have much shorter blades and spin fast.  The resistance, or drag force, of water is about 1000 times
that of air. 

Airplane Propeller versus Boat Propeller