How Do Helicopters Fly?

For many people, helicopter flight is a mystery. Photo by Helen Krasner

Many people think it is a complete mystery that helicopters manage to fly at all.

They reckon that a helicopter is like a bumblebee – it shouldn’t be able to fly, but nobody told the bumblebee.

However, helicopters fly by the same aerodynamic principles as any other aircraft, and the basic principles are really not all that complicated.

Lift, Drag, Thrust and Weight

The force needed to keep an aircraft in the air is called ‘Lift.’  Lift is produced by air flowing over the wings.

The shape of the wings is designed so that the air flowing over the top surface has to travel further, and it therefore travels faster, than the air under the wing. This causes the pressure of the air on the top of the wing to be lower, and so effectively the wing – and therefore the aircraft – is sucked up by this lower pressure.

In fact, a certain amount of lift is produced by almost any object in a stream of air.  You can experience the process for yourself if you put you arm out of the window of a moving car.  You will feel your arm start to rise upwards, and this is due to lift.  But of course a correctly-shaped wing produces far more lift than this.

Lift is produced independently of power from the engine. However, the engine produces ‘Thrust,’ which gets the aircraft moving along the runway, so that air flows over the wings. Thrust also overcomes ‘Drag,’ which is the force which tries to oppose the motion of the aircraft through the air. The other force involved is ’Weight.’ and the weight of the aircraft determines how much lift is required to get it into the air.

As long as there is enough lift to overcome the aircraft’s weight, and enough thrust from the engine to overcome the drag, then the aircraft will fly.

What About Helicopters?

While a helicopter is a far more complex machine than an aeroplane, the fundamental principles of flight are the same.  The rotor blades of a helicopter are identical to the wings of an aeroplane –when air is blown over them, lift is produced.  The crucial difference is that the flow of air is produced by rotating the wings – or rotor blades – rather than by moving the whole aircraft.  When the rotor blades start to spin, the air flowing over them produces lift, and this can cause the helicopter to rise into the air.  So, the engine is used to turn the blades, and the turning blades produce the required lift. Very simple!

Controlling the Helicopter

However, there is rather more to it than that.  You need to be able to lift your helicopter into the air when you want to, rather than just have it rise up as soon as you start the engine.  In the case of an aeroplane, flight can start as soon as the aircraft is moving fast enough.  But in a helicopter, for all sorts of reasons, the blades need to turn at the same speed all the time.  So you need a different way to control the amount of lift produced.

Click to Read Page Two: Controlling Helicopter Lift

© Copyright 2012 Helen Krasner, All rights Reserved. Written For: Decoded Science
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  1. emm jai says

    i constructed a helicopter and i was successeul.. the helicopter lifts ud but cann’t move in the air. what can i do now?

  2. ogochukwu says

    i wish to build my own airplane nd am seeking enybody is going to sponsur me i hav the sence of doing it bt i did nt hav d money let do it in nigeria

  3. Amit srivastava says

    look,all u need a not only sharp blades but also……u know its size that can easily lift up your helicopters….and the length of the….blade should join its least distance….bczzzz…….whenvr its blades rotates faster your helicopters….will push more air down and its help to lift your helicopter up…………as u know ground effect…….

  4. idris adamu says

    for i have already create a helicopter but the only problem is how to control it when i lift it on the air that is my question please?

  5. chetan manorakar says

    if the weight of blade get more ,will it help for easy take off? because as weight increases the centrifugal force will be more and it will be help for take off.

    • Abhishek says

      It is not the centrifugal force which is responsible for the lift produced. It is the flow over the blades which produces the lift. Read how airfoils generate lift and you will understand. If the weight is more, it simply means that the downward pull is more due to gravity, and it will decrease the net upward force, resulting in more power consumption for lifting the helicopter upward.

  6. Cordell says

    I am a student at a charter school,and i am required to do a Genius project,and I chose the subject of how helicopters fly.if you have anything that can help me, can you send me some info? thank you for looking at my comment.

  7. raghu chouhan says

    Sir,how we calculate the ratio of weight,if by there will be more weight as it will not fly so how we get a better idea of its weight.

  8. David says

    Please how can i construct a small helicopter with slippers.what kind of electrical matterials will i use that will make it fly. Please answer me in time please.

  9. maxwell says

    Please. I need more elaborate information to help me construct a mini helicopter. And the kind of materials and electrical instrument I can make use of

    • rahul kumar says

      i know a another way of flying the airplane. in that we not need to more power and more extra electric motor.
      we not need any type of fule.
      in the basic principle of helicopter we need a rotor to rotate the air over the wings(blades) if we change the principle and rotate the air without using the wings(blades) then we xan also fly the cop. with a small distance travels just like a aeroplane. but after some time we can fly this just like a helicopter
      i have the basic project information in this project we not need the fule even in big hellicopter
      but i financial problem.
      if any one can finance me i can make the new generation of airplane that can operate with a small electrical energy.

  10. mike RAL says

    sorry to interrupt, “The rotor blades of a helicopter are NOT identical
    to the wings of an aeroplane”.. actually I have been told that they are somewhat
    symmetrical..If you calculate blade tip speed = blade circumference x r.p.m + forward flight….the answer is near the speed of sound.
    G-CHIS: the photo Robinson possibly could take you to CambridgeCollege over near Bedford…I visited there in 1985 as a friend was having the lads construct a water tunnel…for the study of helicopter main rotor blades.
    …carry on then ………….mikeR: AMT since 1981 (h500D, B206a/b)mostly

  11. Kunal says

    Ma’am is there a formula to calculate the lift for a helicopter. I am making a small Cancopter and want to know how can i judge the size of propellers. please help me out

    • 4k33m says

      A good guess is to make the blades approximately 1 and 2/3rds the total fuelsage length. Increase pitch or headspeed if nesscearry.

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