This is a homemade steel propeller where the 'twists' have been carefully made to match the velocity of the wind along the propellers length. The bolt and nuts just out from the middle are for balancing, on the opposite side there is a magnet for the tacho sensor so the speed can be logged. I have no idea about the aerodynamics of this thing but it goes round a treat. Mounting is by a taper-lock which is solid and works well. The sprocket cogs are of no significance, it was just the cheapest way to get a taper-lock body made of mild steel. The sprocket was tricky to weld around the teeth, no doubt a better idea will emerge in time.
The diameter is 4 feet. I like this size because it is a good compromise between a reasonable amount of power and larger, stressy-prone props. (Click on picture to enlarge)