The
process of perfecting the windmill sail, making incremental improvements in efficiency,
took 500 years. By the time the process was completed, windmill sails had all the major
features recognized by modern designers as being crucial to the performance of modern wind
turbine blades, including 1) camber along the leading edge, 2) placement of the blade spar
at the quarter chord position (25% of the way back from the leading edge toward the
trailing edge), 3) center of gravity at the same 1/4 chord position, and 4) nonlinear
twist of the blade from root to tip (Drees, 1977). Some models also featured aerodynamic
brakes, spoilers, and flaps. The machine shown in Figure 4 (which was operating with two
of its buddies pumping water about one meter up from one irrigation pond to another in the
Netherlands in 1994) features leading edge airfoil sections.
Janet Ott on 04 Dec 11Check out this paragraph for more details of why things are placed where they are.
