You could use:
- tiled clones (overkill, imho)
- the rotate copies LPE (wonderful! but not documented, watch youtube video and read release notes:
http://wiki.inkscape.org/wiki/index.php ... ate_copies)
- simple rotation of identical objects (so, create 1 fan blade, move its rotation center to the center of the circle, and rotate in 15° (times 4) steps).
For this, you need to click on an object a second time with the selection tool to enter rotation mode. Then you can grab the rotation center and move it to a different place (preferably snap it to that place). Then you can duplicate the blade (Ctrl+D), or clone it (Alt+D, if you might still change the original), and rotate it with the handles while holding Ctrl down to get 15° steps.