[freebeard]

The ventilators are fabricated from uniform strips that gather at the top and block air flow. Done for structural and fabrication reasons.

If you are looking for the experience, I'd start with a piece of timber bamboo somewhat longer than the height you want and split it into three staves. Find a tree trunk or water heater tank or something the right diameter to wrap them around. Wrap them side-by-side in a helical spiral. Clamp the ends and let them dry.

Then take them off and carve the inner face into an airfoil profile. Mount them on a vertical axle and you'd have a very high-performance rotor. Gang two alternators together on either side of the final drive gear or pulley. That arrangement can be structured as a harmonic dampener to prevent vibrations. I think an alternator would work backward, but [shrug].