Stupid Simple Downward Cooling fan duct

I find downward cooling to be VERY important in achieving high quality results.
After years of trying many different approaches to adding downward cooling to Rep1 style machines I decided it was time to do it in a way that meets all of my own requirements. These were:
1. Easy to install and remove VERY quickly to allow for fast access (i.e., no tear down) for clearing the filament path.
2. Use of a radial fan rather then a wimpy box fan.
3. Speed control
Basically I use a sturdy hook and l