Surface flow visualization has been carried out with tufts adhered to the surfaces of the rotating propeller blades.From the experimental results it is found that in part of four fifths of blade surface from hub to tip

the air flow runs from leading edge to trailing edge in the outward direction with some inclination to chord.In the region of one fifth near the blade tip

flow separation and reverse flow occur at the blade surface

circulation appears even in the serious case

in consequence negative thrust emerges

which cuts down the efficiency of the propeller obviously.