First attempt at a shock cone
... will have to try different shapes to see what works best for the edf.
In particular the back end could be made longer to smooth out the airflow into the fan.
My intake diameter is now at around 94mm, but a sharp balsa intake ring still needs to be fitted.
The shock cone in the picture below is 64mm diameter, giving therefore an intake area of roughly 37.2 dm^2.
The 101mm fan I am using (inner rotor diam 42mm, outer rotor diam 96mm) has a FSA of ca. 58.5 dm^2,
so that would give a 64% intake - which is a bit on the small side
To get an 80% intake requires a smaller shock cone that's around 54mm in diameter, giving then an intake FSA of around 46.5 dm^2 ...
A 54mm diameter shock cone means making a second cone shaving off 5mm per side on the original (semi-scale) one which is not too bad.