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Construct a car which is propelled solely by wind energy

  1. Dec 12, 2004 #1
    I must construct a car which is propelled solely by wind energy. The car should be able to drive straight into the wind.
    Have you got any ideas?
     
  2. jcsd
  3. Dec 12, 2004 #2
    If you want to drive directly into the wind, rather than just tacking like a sailboat, a sail is no use to you.

    What you need is a car-mounted windmill facing into the wind, and have the windmill drive the wheels through gears or chains or pulleys etc.
     
  4. Dec 12, 2004 #3
    It's good idea but I want something more intersting. I want to surprise my teacher.
     
  5. Dec 12, 2004 #4

    brewnog

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    This thread came up recently in one of the engineering forums. As Ceptimus rightly points out, sails (as used on a yacht) are useless, and a windmill type configuration would be your best bet. Do some googling for a 'cup anemometer', that should be fruitful, and interesting enough for your teacher.
     
  6. Dec 13, 2004 #5

    Tide

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    I'm not entirely convinced that sails won't work. Clearly, a single sail will not work but how about a pair of them? They could tack in different directions with the lateral components of lift being equal and opposite but with the forward components adding. I'm not convinced it will work either but I can't dismiss it out of hand.
     
  7. Dec 13, 2004 #6
    A tacking sailing craft, whether it be a boat, sand yacht, or ice yacht has to react a force vector from the sails against one from the keel / wheels / skates to provide a component of force in the direction of travel.

    If the direction of travel is directly into wind, this is not possible. The force vector from the sail can't act at better than right angles to the wind. And even if it could act at right angles (which requires an infinite lift/drag ratio) it still wouldn't create any forward component when combined with the reaction force from the wheels (which again can't act at better than right angles to the direction of travel, even given perfect frictionless wheels and zero energy loss grippy tyres).

    For the same reason, you can't just use two or more sails reacting against each other. The sails each provide a sidways 'lift' component, and a backwards 'drag' component, and there is no way to combine these to end up with the required forward facing component.

    I suppose you could have one or more tacking small wheeled vehicles pulling the main vehicle. This would be the wind powered equivalent of a horse drawn waggon, except that the horses would be running zig-zag. :smile:

    Another method would be to fly controllable kites (two or more strings) from the vehicle, and use the varying line tension, and angles to power the wheels. This is really just the same as the windmill, except that you replace the windmill with kites. I don't think it would be anywhere near as practical as the windmill method.

    I like the idea of a vertical axis windmill (like a cup anemometer, or a Savonious rotor). This would provide forward drive irrespective of wind direction - with a horizontal axis mill, it would be necessary to point the rotor into the direction of the local airflow, requiring complex machinery - the vertical axis method eliminates this, though at the cost of efficiency.
     
    Last edited: Dec 13, 2004
  8. Dec 13, 2004 #7

    Tide

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    Ceptimus,

    Aha! I hadn't thought it through all the way but that makes sense. Scratch that idea.

    Thanks.
     
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