how about this...
create a blade (lying on construction plane for me) ...
move the pivot point to the correct location at the base of the blade
duplicate with smart transform 19 times...
(to make it look like a fan)
(mine were called pCube1, pCube2, ... pCube20)
then run this in the script editor:
for ($i=1;$i<20;$i++)
{
expression -s ("pCube" + $i + ".ry = pCube20.ry / 20 * " + $i + ";");
};
now rotate pCube20 around y (last blade) to animate the opening.
(each blade's rotation is set to correspondingly greater fractions of rotation of the top blade)
..
let me know if you need the file..