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PROPELLER WITH BLADES REVOLVING AT 90GRAD WHEN THE PROPELLER REVOLVES AT 180GRAD,AND RETURNING TO THEIR INICIAL POSITION WHEN IT REVOLVES AT 360GRAD
PROPELLER WITH BLADES REVOLVING AT 90GRAD WHEN THE PROPELLER REVOLVES AT 180GRAD,AND RETURNING TO THEIR INICIAL POSITION WHEN IT REVOLVES AT 360GRAD