Name: 直升機是如何飛行的?（How does a Helicopter fly ?）
Uploaded: 2022-01-26T15:18:46.000Z
Duration: 8 min 29 s

They can take off and land without the need for our runway

They can hover in the air it can maneuver in any direction in a 360 degree space

This video will unveil the complexity in science behind flying a helicopter

After going through the physics behind the helicopter flying you will also understand why helicopter pilots are doing an incredibly complex job

本視頻將揭示直升機的複雜性和科學性

Helicopters use the Airfoil principle to generate lift

When the blades rotate relative to the air the special airfoil shape will generate lift force and make them fly

你會明白直升機駕駛員在做著極其複雜的工作

the blades derive rotation from an engine more specifically a turbo shaft engine

The compressor sucks the air in and pressurizes it fuel is burned in this pressurized and hot air

The hot exhaust leaves the combustion chamber passes through a series of turbine stages and make them turn

旋翼的特殊形狀使得空氣對旋翼產生升力，從而讓直升機飛起來

There are two Sets of turbines one turbine set turns the compressor and the other set turns the helicopters rotor shaft

Jet Engines of Airplanes are used to generate thrust force

However the primary function of the helicopters jet engine is to turn the rotor shaft

The most challenging part in helicopter operation is its controls that means how can it fly forward?

燃油在這高溫高壓的空氣劇烈燃燒

The answer is quite simple just rotate the helicopter towards the direction you want to move and just fly

When the helicopter is at an angle the Force produced by the blade is not vertical

The horizontal component of this Force will make the helicopter move in the desired Direction

飛機的噴氣式引擎通常用來產生推力

the vertical component of the Blade Force will Balance the gravitational force

而在直升機上的噴氣式引擎主要功能是用來扭動螺旋槳

Now the real challenge is how to turn the helicopter in the desired way?

直升機最具有挑戰性的地方，是動力控制

To learn the science behind helicopter turning we need to learn more about the airfoil principle

the lift produced by an airfoil varies with the angle of attack

Generally the greater the angle of attack the more the lift

Now think for a moment what happens if the one blade were at one angle of attack and others were at a different angle?

The lift forces acting on the blades will be different in this case

The variations in the lift forces will definitely result in a torque that can turn the helicopter

就是把旋翼朝著需要前進的方向扭動就好了

You can observe the beautiful blade motion required to achieve this non-uniform Lift Force distribution

It is clear that the blades must keep on changing angle of attack so that at one particular location the angle of attack is

Such complex Of the blades is easily achieved by a swash plate mechanism

Get an exploded view and understand the basic components first

The bottom Swash plate does not spin, but it can move and tilt as shown

A top swash plate is fitted on the bottom swash plate Via a bearing

So the top Swash plate kid inherit all the motion of Bottom Swash plate while at the same time it can rotate independently

要理解這背後的原理，我們首先得弄清楚旋翼原理

Top swash Plate is attached to the rotor Shaft with the help of a driver. So the top swash plate will always move with the blades

升力取決於旋翼與空氣流動方向的夾角

The blades are connected to the top swashplate with the help of control Rods

大體上來說，與流動方向夾角越大，升力越大

The interesting thing about this arrangement is that just by tilting the bottom swashplate

We will be able to achieve the varying Angle Criterion of the blades

如果其中一個旋翼的夾角與其他旋翼不同會怎樣？

We will always be able to maintain a positive

旋翼之間升力的不同就會對直升機產生一個扭矩

Angle of attack at the rear and a negative angle at the front portion of the rotor disk

由此你可用觀察到旋翼為了產生這種

in short Swashplate tilting backwards produces a torque as shown

不均勻的升力分佈形成的有趣現象

This kind of control is known as cyclic pitch

很顯然，旋翼的夾角必須不斷的變化

以這確定的一個位置產生的夾角是保持不變的

How will this torque affect the helicopters motion?

這麼複雜的旋翼運動其實就是簡單的

The most obvious answer is that the helicopter will turn forward and move as shown

Unfortunately this answer is completely wrong

What happens in reality is the helicopter will turn sideward as shown this is definitely a weird effect

By applying torque in One direction to a rotating object the object turns in Different direction

This effect is known as gyroscopic precession

Gyroscopic precession is not a new phenomenon of physics if you carefully apply Newton's second law of motion to rotary objects

上斜盤與下斜盤通過一個軸承進行連接

You will be able to predict this phenomenon according to Newton's second law Force is the rate of change of linear momentum?

這樣，上斜盤能夠獨立旋轉的同時

Similarly torque is rate of change of angular Momentum

Let's consider this rotating blade. It will have an angular momentum as shown now

上斜盤通過一根連杆與旋轉軸相連

assume that the helicopter has tilted as shown due to some torque action if

這樣上斜盤就和旋翼同步運動了

You victoria lee subtract the first angular momentum from the second you can figure out the torque required for this operation it

Is interesting to note that to turn the helicopter forward the torque applied should be towards sidewards that means to tilt the helicopter?

Forward the Swash plate should tilt sidewards as shown

You can again verify from Newton's second law of motion

我們就能同步控制每根旋翼的夾角大小

that if you keep the front portion at negative angle of attack and the back portion at positive Angle the

Gyroscopic precession is a truly intriguing phenomenon, but it conforms perfectly with Newton's second law of motion

我們能夠一直保持旋翼正後方時夾角為正，在前方為負

if you just lift the bottom swashplate without tilting it you can see how the angle of attack of all three blades will vary by

簡單來說，斜盤向後傾斜會產生這樣的扭力

This means that the helicopter lift Force will be the same in all three

Blades and the helicopter can move up or down without any tilt

這個扭力對直升機的運動產生什麼效果呢？

Such blade control is known as collective pitch

顯而易見的答案是直升機會向前飛

If you have ever seen a helicopter you are all sure to have seen a tail rotor

every single rotor helicopter needs this tail rotor for effective operation

實際情況是，直升機會這樣朝側方移動

Without the tail rotor the helicopter fuselage would have spun as shown

This is due to a consequence of Newton's third law of motion

To Understand it let's focus on the Force transmission part of the rotor

We know the rotor gets the force of rotation Via a bevel gear connected to the engine the engine?

Bevel gear Transmits Force to the rotor bevel gear as shown however according to Newton's third law of motion

陀螺進動在物理學中不是什麼新鮮事

the Rotor bevel gear should Transmit an equal and opposite Force to the engine bevel gear

如果你將牛頓第二定律應用於旋轉的物體

This reaction Force will make the whole helicopter turn opposite to the blade rotation along the helicopter center of gravity

The function of the tail rotor is to prevent such helicopter rotation by producing a force at the tail

By properly adjusting pitch angle of the tail rotor

Blades the Pilot can easily manipulate the tail rotor Force this way with the help of the tail rotor

同樣的，力矩是角動量的變化量

Yaw motion of the helicopter can also be achieved

All the physics behind helicopter operation means that flying a helicopter is a truly challenging task

minut variations in Blade Angles make huge variations in Helicopter Behavior

假設直升機要在某些力矩的作用下這樣轉動

Often the pilot has to do two or more operations together to achieve the desired motion

你得需要施加這樣的力矩來讓角動量從第一位置移到第二位置

moreover the helicopter does not respond instantaneously to your inputs so the pilot should possess a good sense of balance and

有趣的是，要讓直升機朝前方轉動

coordination to navigate the Helicopter properly

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這意味著，直升機要朝前方前進