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The Helicopter Speed Limit - Helicopter Physics Series - #7 - Smarter Every Day 51

Helicopters have a speed limit that has nothing to do with laws.
当然 除非你应用的是物理定律
Well, unless you count the laws of physics.
嗨 我是Destin
Hey it’s me Destin.
欢迎回到《每天更聪明》 这是一个展示科学的舞台
Welcome back to Smarter Every Day. The show where we do science. So today
我今天 我事要向你们解释有关旋翼飞行不对称的趣事
I’m gonna explain to you something pretty interesting about the dissymmetry of rotor flight.
但在严肃起来之前 让我们先找点好玩的
But before we get too serious, let’s just have a little fun.
看这个 Carl将向我们展示夜间飞行
Check this out. Nighttime flying with Carl.
( rotor noise ) Sick!
( rotor noise )
( excited shouts )
( laughing )
Right there.
Here we’re going to do some light meeting with a helicopter at night.
( rotor noise )
( music )
( music )
看见没 仔细看 看回图片
Did you see that? Look real close. Go back to the image.
If you look on one side you see this really tight radius of curvature.
但是另外一边的曲率半径相对较大 这是为什么呢
But on the other side you see a much larger radius of curvature. What’s going on there?
好 为了解释旋翼的飞行不对称效应
OK so to explain the effects of this unsymmetric travel of the blades
我用木棍支起了一个旋翼 接下来我将转动它 看看有没有用
I’ve rigged one up on a stick here, and I’m gonna try, let’s see if this works.
好 当旋翼的前行桨叶转动起来的时候
There we go. So as the advancing blade comes around,
it’s moving faster relative to the air because the helicopter’s moving so you
add those two values together, but the retreating blade, you subtract
away the velocity of the blade from the forward air speed and that’s the total relative
velocity of the blade through the air. This causes some funny things.
让我们转动旋翼 证实一下我们的想法 当直升机启动时
OK Let’s start the blades and check things out. As the chopper flies forward, the air
空气流经直升机两侧 前行桨叶
flows over both sides of the helicopter. The advancing blade is also
travelling forward so this adds to the air velocity of the rotor on that side.
Now as long as the air speed of the rotor stays under the sound barrier you’re OK.
一旦直升机的转速超过这个速度 就会造成震波
But if the helicopter goes too fast you’ll create shock waves and start
会对事物造成毁坏 后行桨叶
to damage things. The retreating blade sees the same airflow of the vehicle movement
but because the blade is travelling in the opposite direction from that movement the
相对气流速度速度会变得更小 这叫做
actual air speed of that rotor is less. This creates something called
升力不对称性 为了抵消这种不对称 水平旋翼
Dissymmetry of Lift, and to counterract this the rotor on the retreating
side is given more pitch to produce more lift. This works up
旋翼会逐渐倾斜到一定角度 当直升机速度过快 后行桨叶迎角过大
to a point, but if the helicopter goes too fast, the pitch becomes too great and
导致失去升力 造成所谓的后行桨叶失速现象
you lose lift creating what’s called a retreating blade stall.
The cool thing about a retreating blade stall is that it is a self correcting problem. If you think
不要以为这是螺旋仪组件的作用 如果有左右升力不对称问题时
about it due to gyroscopic procession, if you have a dissymmetry of lift between a left
直升机不会因此翻转 因为有后行桨叶失速
and right side of the helicopter, it won’t roll the helicopter like you think it would, it
actually pitches it. That’s good news because as you’re flying along if you get too fast
后行桨叶失速会自动让直升机减速 帮你解决麻烦
and you get a retreating blade stall, it’ll just slow the helicopter down, automatically.
虽然还有很多相关现象我们没有在视频节目里涉及 但是
OK There’s a lot of things I did not cover in this video series, but for the most part you should be
相比开始 我们对直升机的了解已经有了很大程度的进步
way smarter than when we started on helicopters. Smart enough in fact where you can make an educated
guess as to which of these three helicopters is the fastest in the US Army inventory.
While you’re thinking about that please consider going to the Facebook page. I put all the photos from the
night flights on there.
Go download them, use them as your desktop background, stuff like that. While you’re there
记得要给我点个赞 如果对我们的节目有任何想法
please Like the Facebook page. Also if you have ideas for future Smarter Every Day episodes
请在推特上私信我们 我将感激不尽
please Tweet me, I’d appreciate that, at SmarterYoutube.
It’s been about a year since we started Smarter Every Day.
如果您对此期间的节目有任何的意见 我都将洗耳恭听
If you have ideas for a one year episode I’m all ears.
好了 话不多说 美军现役直升机里速度最快的是“切努克人”
OK. Enough babbling. The answer is the Chinook. It is the fastest in the US Army
我是Destin 希望我们的节目对您有所帮助 祝您一切顺利
inventory. I’m Destin. You’re getting Smarter Every Day. Have a good one.
( music )
(字幕:Andrew Jackson)
[ Captions by Andrew Jackson ]









审核员 LD