Flexible fan device

Claim 1

A flexible fan device comprising: a power-driven rotating boss having an axis of rotation and a plurality of flexible blades extending radially outward therefrom, each of said blades having a root portion and a tip portion, the root portion gradually curving away in the downstream direction from a plane perpendicular to said axis of rotation to form an attachment angle of said root portion to said boss, wherein said tip portion is axially offset from said root portion toward the downstream side, the trailing edge of said tip portion is axially offset farther than the leading edge of the tip portion, and both the leading edge and the trailing edge of said tip portion lie on the downstream side of a plane through the center of said root portion and perpendicular to said axis of rotation, the cross-section of said blade thereby forming an S curve, whereby each blade is flexibly twisted under a centrifugal force so that the tip portion of each blade makes a variable angle with respect to the plane perpendicular to the axis of rotation of the boss means, said variable angle decreasing in response to an increase in speed of rotation of the boss means.