Wind Tunnel

I'm now on the mk2 wind tunnel :-)
The mk1 proved the principle and gave some useful figure for drag. It needed some baffles to help achieve linear air flow as the rotating fan created a vortex, which ironically held the arrow steady in the centre but made it spin V rapidly.
Mk1 arrow wind tunnel

I've reverted to the 65mm drainpipe for the mk 2. I've made a grid of thin sheet metal (from the back of a old scrapped oven) to smooth the airflow, this is pushed up into a cardboard tube. The plastic drainpipe fits down inside the cardboard tube with the slight gap between two blocked off with draught excluder. This arrangement gives a nice clean interface between the grid and allows me to try longer pipes or other arrangements.

I've made a flared wooden inlet for the top end of the pipe, as a further possible improvement, mostly just for the fun of doing it... dunno if it will make any difference.

As a test I made up some 9.5" lengths of 3/8" Ash arrows shaft with different nock styles the other end of the shaft was tapered and had a thread glued to it to allow the shaft to dangle into the pipe.
The results were nicely measurable as were as you might expect with the tapered nock having less drag and the one cut square having most.