Hello folks, I tried googling this but found surprisingly little on it. Here is the problem: Assume that you have some constant wind speed. I want to run a windmill but I need to decide how big a windmill I want. The size is characterized by the length of the blades, r. There are no engineering constraints (I can build perfect, balanced windmills of any size). However, the mass of the windmill goes as r^2 and there is some constant friction coefficient on the axis. Given these conditions, is there an optimal r? The goal is to generate as much electricity as possible with the set windspeed. Okay, that was the physics part. If your answer was that the windmill should be built as large as possible, then what are the common engineering problems that occur as we scale up? In other words, why are real windmills not bigger than they currently are? And why are some smaller while others are bigger? Thanks!