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Helicopters are impressive machines, but is there an upper limit to how big they can get?
直升飞机是种令人印象深刻的机器，但它们的体积有没有上限呢？
We spoke to this engineer at Boeing and here's what we learned:
通过与波音公司这位工程师的交谈，我们了解到：
One. Engineers are super into what they do, and that is awesome.
第一，工程师们对他们的日常工作非常投入，这真是太棒了。
Two. The bigger and heavier a helicopter gets, the more lift it needs.
直升机越大越重，所需要的升力也就越大。
The rotor blades are like spinning wings so they have to do the heavy lifting.
旋翼桨叶就像旋转的翅膀，所以他们必须做起沉重的提升工作。
Do we have an animation of that?
我们有关于那个的动画吗？
Helicopters can create more lift by adding more wing area, so a large helicopter would need as long a rotor blade as possible.
直升机可以通过增加更多的机翼面积来产生更多的升力，所以大型直升机需要尽可能长的旋翼桨叶。
But this creates all sorts of problems.
但这会产生各种各样的问题。
For example, the tips of the rotor blades can't go faster than the speed of sound or the turbulence will make the blades less efficient.
例如，旋翼桨叶的尖端不能超过音速，否则气流会使叶片效率降低。
The longer the blades get, the faster the tips travel.
叶片越长，尖端运动速度也就越快。
If the helicopter has an enormous and fast spinning rotor,
如果在直升机上安装的旋翼桨叶太大，速度太快，
it won't be able to fly very fast because the blade that's spinning in the same direction the helicopter is moving will be traveling through the air at its speed plus the helicopter's speed, bringing it closer to that speed limit.
那它就无法实现快速飞行了，因为在同一个方向上，旋转的直升机在空中将以自速加上旋翼桨叶的速度飞行，从而接近那个速度限制。
So, long blades would have to spin slowly, but that would require a lot of torque to move.
因此，长叶片必须缓慢旋转，但这将需要大量的扭矩。
That torque strains the transmission that connects the engines to the rotor, so to handle it the transmission would need to be big and heavy, and that's a no-no.
这种扭矩会拉紧发动机连接到转子上的变速器，所以为了处理它，又需要大而笨重的变速器，但这是不可能的。
Engineers could use shorter blades and add more of them, but then the hub in the middle of the rotor gets more complex.
工程师们可以使用较短的叶片，而增加叶片数量解决问题，但是转子中间的轮毂就会变得更加复杂。
Truly designing a giant helicopter is an engineering feat.
真正设计一架巨型直升机乃是一项工程壮举。
Helicopters could get even bigger if they used multiple rotors, and the V-12, did just that.
如果使用多个旋翼，直升机则可以变得更大，而V-12恰是这样。
At 67 meters wide from rotor tip to rotor tip, the prototype was wider than a Boeing 747.
两个转子尖端相距67米，样机比波音747还宽。
It remains the largest helicopter ever built, and proved that with imagination and engineering, the sky is the limit.
它仍是有史以来人类所建造的最大直升飞机，它证明利用想象力和工程技术，没有什么不可能。
For more epic stories of innovation that shaped our future, check out The Age Of Aerospace.com.
如果您还想获知更多塑造我们未来的壮举，请登录The Age Of Aerospace.com。
Thanks for watching, don't forget to subscribe!
感谢收看，欢迎订阅！
Amy's got the details on how helicopters fly in the first place here, and thanks for watching Seeker.
艾米那里有关于直升机从一开始是如何飞起来的细节，感谢观看Seeker。
Hey can we see that wing animation one more time?
嘿，我们能再看一下机翼的动画吗？
Aw, yeah. Uh huh. That was expensive.
哦，好的。嗯。那真价格不菲。
