This paper presents experimental results of 3-D flowfields in the fan tip region for two actual fans. It is shown that the fan performance can be significantly improved as proplets are attached to the blade tips. The improving mechanism have been studied and can be stated as follows: The proplets retain the tip vortex and thus the tip induced loss is reduced remarkably

and the additional propulsion moment is gained because the proplets partly balance the drag moment due to profile loss in the tip section. The conclusions presented in this paper may be applied to the tip section of propeller or helicopter rotor for performance improvement.