I'm thinking of building a small vertical-axis wind turbine as a project over school vacation. By small I mean maybe three feet across and three or four feet high. I'm trying to come up with the best design. This type of turbine is good at generating torque, not RPM's, so I want to try to maximize torque. This type of vertical turbine works on drag, not aerodynamic lift. So the "scoops" facing into the wind on one side catch the wind, swinging the turbine, while the scoops on the opposite side are aerodynamically shaped (enough) to advance against the wind. If you google this subject for pictures you will see that there are many different approaches: wide short ones, narrow tall ones, ones with many scoops, ones with a few. I'm trying to understand how the size, shape, and mass (rotational inertia) of the turbine influences the torque output. Now imagine two turbines that are exactly the same shape and size. One is made of balsa wood, the other is steel. In a good constant breeze the balsa wood one will whizz around easily but you'll be able to stop it easily = low angular momentum. The steel one will have much more angular momentum. It won't accelerate as fast, but once its up to speed it can do more work. I've read that an ideal turbine of this type can at best move as fast as the wind. So does that mean that over a long enough period in a constant breeze, the heavy steel turbine will end up moving as fast as the balsa wood? Or under the same conditions, will it always move slower? If I imagine two paddle-wheels, one of balsa wood and one of steel, in a moving stream of water, it seems reasonable that they will spin at the same rate. But is that just because water isn't compressible? This suggests I build a heavier one to get that extra torque. Is that right? But obviously I can build one that's too heavy, too. Since rotational inertia for a cylindrical shell goes up with the square of the distance from the axis, I should try to maximize axis distance even at the expense of total area of the scoops. So that would mean a short, wide turbine rather than a narrow tall one. Am I thinking at all straight here? Thanks.