An acquaintance (my boss, actually, so please be nice) has suggested that, if a windmill could be made large enough, the tips of the blades could travel at the speed of light. Notwithstanding the impracticalities (there's no wind up there; the blades would surely strike the planets; where would the raw materials come from?), I'm intrigued by the prospect of travelling along one of the blades until I achieve the speed of light. Not me personally, although I could be pursuaded to go part-way. What are the theoretical limitations? The only rule is that the blades must remain ridgid and "straight." I added this rule because my next question is: Would the limitations on the tips of the blades travelling at the speed of light in turn limit the rate of rotation of the hub? We might also not place the windmill within a planetary system or anchor it to a massive object so as to avoid undue gravitational forces. As impressed as I may be with any formulae you may provide, lay responses would likely be of most interest to me. Also, if anyone has actually tried this, please post pictures. Oh yeah: I am not in the business of manufacturing or selling windmills, and this is not a Homework Question. Thanks in advance for any thought-provoking responses. The most concise yet informative response will win this contest.