Turbines with one or two blades are actually evenmore efficient. But because they’re also lighter andtend to spin faster, they’re also noisier. Thesedesigns also require a special tilting hub that acts asa sort of shock absorber, which is expensive. On theother hand, having more than three blades raisesother problems. For one thing, the extra materialneeded to build the blades raises the cost. And themore blades there are, the lighter and thinner theyneed to be. Relatively thin blades are moreflexible, making them prone to bend and break.Three-bladed turbines aren’t perfect, but they avoid many of these problems. They’re powerfulenough without being overly expensive. And they’re less noisy than their two bladed cousins.

　　带一个或两个叶片的涡轮机实际上更有效率。但是因为这样重量较轻，旋转速度更快，噪音也就更大。设计还需要一个特殊的作为一种减震器的倾斜轮轴，它很贵。另一方面，如果叶片超过三个也会引发其他问题。一方面，建造更多的叶片需要更多的材料，这提高了成本。而且叶片，叶片就要更轻，更薄。很薄的叶片也更灵活，但容易弯曲和断裂。三个叶片的涡轮机并不完美，但会避免这些问题。他们造价不高，但是功率足够了。而且两个叶片的涡轮机噪音小。