| Summary: | 碩士 === 逢甲大學 === 材料與製造工程所 === 95 === In order to investigate the phenomenon that liner motion will become rotational motion when subjects fall. We use rectangular blades with different aspect-ratios and vary the angles of the blades in the experiment. We observe the effect of air resistance and the efficiency of the energy transformation on the aspect-ratios and the angles of the wings when the blades fall. We let the vanes with the aspect-ratio of 1.5:1, 1.75:1, 2.0:1, 2.5:1 and 3.0:1 collocated with angles of 30˚, 60˚ and 90˚ fall from 2.5 meters and observe the changing phenomenon of the motion.
The result shows that, if we take the same blade and vary the angle gradually, the bigger the angle is, the slower the speed of rotation is. Besides, the resistance of the difference of the pressure to the blade goes greater, and the efficiency of the energy transformation increases. The blade with wider breadth of the wings takes much time to fall in a certain distance. Therefore, the falling speed slows down, the resistance increases, and the efficiency of the energy conversion goes down. Moreover, the rectangle blade with longer length of the wings takes much falling time. The falling speed goes slower, but the whirling speed is faster. So, the resistance causing the difference of the pressure increases and raises the efficiency of the energy transformation. It is found out the ninety angle between blades with aspect ratio of 2.5 has the highest energy conversion efficiency.
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