Wind powered vehicle speeds much faster than wind; downwind! - Page 5 - SailNet Community
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post #41 of 42 Old 11-09-2010
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For those of you who have a working knowledge of trigonometry the explanation for this is 'astoundingly simple' and elegant .... you (the fan blades) are essentially dividing by the sine of 'close to zero' which by mathematical solution approaches 'infinite force'.

In common laymans terms you can do the same thing with a slippery 'pumpkin seed' between two fingers: you press your thumb and forefinger together onto the slippery pumpkin seed, and the pumpkin seed 'rockets' out between your fingers as a result. In the case of the fan blades, the pitch angle of the blades is soooooo close to zero that any input/energy from the moving wheels gets 'magnified' by literally hundreds of times as an effect onto the 'blades' (less the friction of the transmission system), and the greatly magnified speed of the blades coupled with precise aerodynamics .... moves the vehicle MUCH faster than the speed of the wind .... all because the blades pitch angle is 'dividing the energy input by the sine of the pitch angle of the blades'.

Its all due to the BRILLIANT 'application of elemental trigonometry' (aka: *pumpkin seed effect*). If you would have actually understood your high school trigonometry teacher, the valid explanation of why this vehicle is covered in the early session of a simple HS trigonometry class.

The folks who did this are profound MATHEMATICIANS. Sadly, understandable mathematics isnt taught anymore in the USA; hence, the misperceptions and doubts that are being stated about this brilliant and yet simple accomplishment simply by the application of very basic engineering and mathematical fundamentals. Elegantly profound, extremely simple !!!!!
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post #42 of 42 Old 07-19-2011
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Actually, our blade pitch is not terribly small. We use variable pitch, but run about an 18 foot pitch at our design point (prop advances 18 feet in one rotation). That puts the prop tips about 20 degrees out of plane - giving them an angle of attack around 5 degrees at speed.
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