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The Coanda Effect

  1. Dec 24, 2013 #1
    The downwash from a helicopter rotor, if passed over a suitable surface below the rotor could produce a Coanda Effect. Will this influence lift?
     
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  3. Dec 24, 2013 #2

    berkeman

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    Beyond the ground effect? What are your thoughts?
     
  4. Dec 25, 2013 #3
    Thanks.I have insufficient knowledge of the aeronautical sciences to comment on ground effects or on the shape & size of the surface/s that will generate a Coanda.Just a thought experiment.
    ( formerly VU2BXD ).
     
  5. Dec 25, 2013 #4

    boneh3ad

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    The downwash is already pointing down. Using the Coandă effect to redirect the flow is only going to reduce the lift, though you could get some thrust out of it in return. This is already what the blades are designed to do, however, without any additional surface, so including a surface like that really gains you nothing and, due to the second law of thermodynamics, actually loses you some.
     
  6. Jan 6, 2014 #5

    Baluncore

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    The lift generated by a helicopter is created by the blade airfoil section, not by the down stream draft.
    Any down draft drag on the fuselage is wasteful, as it will drag the helicopter body downwards.

    A helicopter blade has very little, if any, twist along it's length, so only a short section of the blade is working at optimum efficiency. That enables a helicopter to get lift from both sides of the rotor when flying horizontally. But it also means that the maximum down draft is at a different distance away from the fuselage on each side and is airspeed dependent.
    It would be quite hard to predict where that down draft would be under operating conditions.
     
  7. Jan 6, 2014 #6

    cjl

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    Those aren't really independent - the airfoil produces a downdraft (it's how it works), and that is why lift is generated. Boneh3ad is correct - any redirection of this downwash is going to reduce the lift generated.
     
  8. Jan 6, 2014 #7

    Baluncore

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    Nothing is truly independent. The downwash is a reaction to the lift generated by the airfoil.

    Yes, Boneh3ad is correct, I never doubted it. Increasing lift by interfering with the downwash is the same as trying to lift yourself by your own boot laces, or a snake eating it's own tail.

    It becomes obvious when you consider the downwash as an historical artefact of the blade's lift, rather than implementing a postmodernist analysis/confusion of everything being inseparably connected.
     
  9. Jan 6, 2014 #8

    boneh3ad

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    It's really more of a chicken and egg kind of thing. One doesn't really "cause" the other (lift and downwash, that is). Rather, you simply can't have one without the other. They are simply the opposite ends of Newton's laws.
     
  10. Jan 6, 2014 #9

    AlephZero

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    That is not always true, for example, the increase in lift when hovering in ground effect.

    But I agree the OP's idea is very unlikely to work.

    You seem to be contradicting yourself there :confused:
     
  11. Jan 6, 2014 #10

    Baluncore

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    I agree that lift will be dependent on air density and that “ground effect” can therefore provide increased support to an aircraft when the downdraft flow downstream is impeded by something more fixed than clear air. Ground effect can save even more energy when an aircraft lands on the ground and stops it's engines.

    Science is the contradiction.
    Science employs a reductionist approach to analyse a complex universe.
    If things were truly independent there would be more than one universe.
    Only by modelling simplistic closed hypothetical universes, is science possible.

    P.S. The egg came first, then the chicken.
    The chicken is the best way eggs have of reproducing themselves.
     
  12. Jan 23, 2014 #11
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