【英语时差8,16】风力发电机2

（单词翻译）

 Turbines with one or two blades are actually even more efficient. But because they’re also lighter¹ and tend to spin faster, they’re also noisier. These designs also require a special tilting² hub that acts as a sort of shock absorber, which is expensive. On the other hand, having more than three blades raises other problems. For one thing, the extra material needed to build the blades raises the cost. And the more blades there are, the lighter and thinner they need to be. Relatively³ thin blades are more flexible, making them prone⁴ to bend and break. Three-bladed turbines aren’t perfect, but they avoid many of these problems. They’re powerful enough without being overly expensive. And they’re less noisy than their two bladed cousins.