by TheRyan
 P: 68 Windmill blade design i have not tried such design before, but just wanna share some thoughts, hope it helps... it seems to me the competition uses an electric fan to blow your windmill model, which generates electricity through a connected motor. Given the motor being the same, the main concern is how to convert effectively the fluid(air) flow energy to the kinetic energy of the windmill. In principle, the energy in fluid is related to Bernoulli term $$\rho$$$$U^{2}$$. The pressure buildup across the blade is minimal(atmospheric surrounding), so the major transfer machanism should be the change of momentum of the incoming fluid by the blades(i.e. accelerating the fluid into a different direction), and create a reaction force to push the blade. The major factor of the blade design is, therefore, to turn the flow by nearly 80$$^{o}$$~90$$^{o}$$ and to maintain the speed of the leaving fluid. The shape of the blade is the key, which have to prevent the loss of this Bernoulli term and to turn the fluid smoothly. How to do so? Often it is about streamlining the blades. A streamlined design with gradually changing curvature will turns the fluid direction by 90$$^{o}$$ without disrupting the flow. you can easily find turbine blade picture by some googling and get the idea. Your shape does not have to be very decent, a simple curvature in a card-board manner should capture most of the effects. Another key factor should be the frontal blade area. I think a windmill having comparable size as the fan is effective enough. The weight of the blade also constitute some friction loss.