This is in the ‘so simple it seems to have been overlooked’ category. Or maybe it was just too obvious to mention. In any case I haven’t seen it before. It is just an ordinary fan from a rectangle, with one edge glued to the other to make a full circle. Only, instead of the corrugations meeting the long edge at 90 degrees, they meet it at slightly less. That small change is enough to allow the whole thing to collapse, as a regular circular fan cannot. This is another instance of the guideline--I hesitate to call it a "law"--that in collapsible origami, skewed angles work better than perpendiculars. Perpendicularity is all about equilibrium, among multiple options and stresses; skewedness is all about disequilibrium--and decisiveness. If you make this, don’t forget that for a fan to form a circle, the long edge of the rectangle must be at least 2pi times the short one. A ratio of 6.5 to 1 is a reasonable approximation. How it came about: I’d been studying fan disk shapes made...
