The feathered propellers of an RAF Hercules C.4
A propeller is essentially a type of fan which transmits power by converting rotational motion into thrust for propulsion of an aircraft through the air, by rotating two or more twisted blades about a central shaft, in a manner analogous to rotating a screw through a solid. The blades of a propeller act as rotating wings (the blades of a propeller are in fact wings or airfoils), and produce force through application of both Bernoulli's principle and Newton's third law, generating a difference in pressure between the forward and rear surfaces of the airfoil-shaped blades and by accelerating a mass of air rearward. (Full article...)