After some testing of propellers that were already available, I decided (because I had the test tool anyway), to try it another way. 

Instead of setting up an aerodynamic model in the software, I decided to investigate whether the propeller could not be printed flat and then deformed with hot water (PLA) to deform the blades. The idea behind this was that the blades on the underside would have a smooth surface, which would improve the lift (airflow) of the propeller. 

The final result are these funny flying flowers. 

Print them flat, first layer 0.2 and other layers 0.16. You can provide the heart of the flower with a different color at a layer height of 1mm. 

Update 23-03:

I have added a bigger version (type A) and 2 other types (B & C) with more/bigger petals. 

For strength print these ones with 0.2 layer heights. Use infill 20%. Color change at 1.2mm. No mold, just bend with hot water. Experiment with bending, slight difference in bendings can make huge difference in flying properties. (which make it the more fun!) 

Files are in the folder [New Types (0.2 layer height)]

For the first model I made a bending template to give the different blades the same angle. I soon found that it was much easier and more fun to angle them by hand by dosing each one with a little bit of hot water and then giving it a light twist. I have attached the bending template anyway in case someone wants to try.

Due to the larger surface area of the blades (and smoother surface?), they stay in the air longer, have a different flight path and descend less quickly than the "technical" models.

The propeller is completely different in design than others, but because I used the square coupling I thought it was only fair to label this as a remix.