Keeping object in air

  1. How much power (average) is required to keep a 1000 kg object still in air by putting a helicopter like rotating blades on it.(The entire weight of the motor to rotate the blades is included in 1000 kg).
  2. jcsd
  3. russ_watters

    Staff: Mentor

    There is no average; it is a function of rotor size: the larger the rotor, the lower the power. This is because lift comes from momentum change of the air (linear with velocity) while power comes from kinetic energy change of the air (a square function of velocity). But if you pick a rotor size we can walk you through the calc.
  4. Please tell with respect to any rotor size.
    I just want to know how much power i would be needing to keep it (1000 kg object) still in air at any height say 1 metre.
  5. russ_watters

    Staff: Mentor

    Sorry, I don't know any other way to say this: what you are asking is not possible. The answer you are looking for does not exist.
  6. As Russ says, the answer could be anything from zero to an enormous amount of power. There's no set amount of energy expenditure required to hold an object in place.
  7. maybe it's depend on the atmosphere pressure..
    As I know, helicopter when fly have maximum height, because higher than that, the atmosphere pressure too low
  8. PhysicoRaj

    PhysicoRaj 430
    Gold Member

    A lot of factors affect the power required to be produced by the rotor to keep masses afloat in the air, like rotor shape, rotor size, rotor speed, air viscosity, pitch of the blades, etc. But you can look into the thrust required to keep the object still, which can be calculated. Then you can decide the rotor design and then the power of the motor.
    A 1000 kg object can be kept afloat by a thrust of approx. 1000*g i.e., ~ 9806.65 N
    Then there are some thrust calculators on the internet which you can use. Input the correct parameters so as to get your answer. Hope this helps.
    Wiki - propeller thrust
  9. NascentOxygen

    Staff: Mentor

    Perhaps look at the human-powered helicopter quest to get a ballpark figure. The feat is borderline attainable, so find out the weight of the craft and pilot, and you know the power a superfit athlete can develop for a short time, so just scale this up by x5 or x10, whatever. Regard this as the lower bound for your goal. :smile:
  10. Baluncore

    Baluncore 3,305
    Science Advisor

    Helicopter and autogyro rotor blades are usually parallel, not twisted like a propeller blade.

    With the helicopter, air moves downwards, through the power driven, forward tilted rotor, as a reaction to the generated lift. At any point in time only a short section of a non-twisted blade is actively generating lift. That working section moves continuously throughout the rotation. The lift area of the rotor is much less than the full rotor disk. The part not generating lift generates drag.

    With an autogyro, air moves up through the free-wheeling rotor as the autogyro is pushed through the air by a separate propeller. Part of the blade is a turbine that drives the rotation, another part is an active lift generating section, the remainder is drag.

    In order to generate a maximum lift to drag ratio, a twisted blade could be used. The problem then is that when flying horizontally, the lift will move to one side due to the apparent airspeed over the rotor surface being the sum of the vehicle airspeed and the rotor rotation.

    Straight blades are inefficient but they are stable. The first human powered helicopter will have twisted blades and will hover only. Further advances will be a compromise between available excess energy and faster horizontal flight.

    The energy needed to stay in the air is less if you don't want to go anywhere.
  11. sophiecentaur

    sophiecentaur 14,690
    Science Advisor
    Gold Member

    Any heavier than air machine must stay up there as a result of air being directed downwards - one way or another. We have regular threads about the theory of wings and flight and there is a lot of shouting about Bernouili, as if he outranks Newton when it comes to aircraft (haha).
    When you look at an autogyro as a black box, you have a forward thrusting propellor which pushes the craft forward and, by a bit of clever aerodynamics, the passive rotor manages to defect air downwards, which provides the lift - just like any aircraft. There must be a difference between the speeds and volumes of the two air flows in the sections of the rotor to account for a net momentum change downwards - to give lift
  12. sophiecentaur

    sophiecentaur 14,690
    Science Advisor
    Gold Member

    This is interesting. What is the state of human powered helicopters? Human powered flight is one of those things that they have to go after but are doomed never to be doing it as well as birds and bats. It knackers me, just thinking of the effort involved to stay up there!
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