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The windmilling prop extracts energy from the mass flow through the propeller disk area. An 8-bladed prop can extract more energy from the mass flow, and does this at lower RPM than the 2-bladed prop. The extra energy it can harvest is due to lower tip losses. Pic above is from Principles of Helicopter Aerodynamics by J. Gordon Leishman, and shows results ...


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What is aerodynamic reason why turbine with 8 blades will rotate slower then with 2 blades? It won't, all else being equal. The speed of the turbine is governed by the aerodynamic forces on the blades and the resistance in the turbine. (By resistance I mean non-aerodynamic forces like drag in the bearings and the actual generator.) In a two-bladed turbine (...


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Imagine a propeller being turned by an engine suddenly losing power. How to make it a good generator as well as a good propeller? Probably a more symmetric airfoil. As seen here, a good airfoil shape will help create more lift/thrust from the relative wind. Interference will play a role in rotation speed. This is why more blades have a lower maximum ...


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