Another parametric fan (FreeCAD exercise)

This is an improved version of my [previous fan](https://www.thingiverse.com/thing:2996660). This one has a curve applied to the edge of the blades, which seems to be the standard with cooling fans for PCs and other electronics. I have also reduced the number of blades from 8 to 7. This new version should be quieter and perhaps even move more air.

Again I made this just as an exercise with FreeCAD.

I am just a beginner at CAD and FreeCAD but I am trying to learn it "the right way", that is, by applying principles of parametric design. You may want to try this:

- (If relevant) Set the FreeCAD language to English to make the instructions below easier to follow: in the menu "Edit" choose "Preferences" and on the "General" tab choose English.
- Open fan2.fcstd in the program.
- In the "Combo View" panel on the left, on the "Model" tab, double click the "Spreadsheet" object. The spreadsheet will open.
- In the menu "Windows" choose "Tile". The 3D view and the spreadsheet wil