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Drag on an airplane wing

  1. Aug 12, 2014 #1
    I am trying to measure the lift to drag ratio of a wing.
    I am measuring the lift by using a electronic scale.
    But how on Earth can I measure the drag force?
     
  2. jcsd
  3. Aug 12, 2014 #2

    Simon Bridge

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    Basically the same principle but do it sideways.

    Presumably you have the wing on a stand sitting on a scale?
    Put the scale on wheels, so the wind will blow it and the wing backwards.
    Use a newtonmeter to stop the motion.

    You can probably come up with something better - this is just to give you the idea.
     
  4. Aug 12, 2014 #3

    A.T.

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    Put a weight on the scale, and attach it with a string to your model (free to move horizontally), parallel to the airflow (via a pulley). The reduction of the measured weight is the drag force on the model.

    Or build a L-shaped lever, with the pivot at the corner. Attach model to top end, and put scale under bottom end. Take the lever arm ratio into account.
     
  5. Aug 12, 2014 #4

    AlephZero

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    The practical problem with both those ideas is that putting the measuring device in front of the wing will probably mess up the air flow before it reaches the wing. The L shaped lever idea could fix that problem, so long as you can still control the angle of attack of the wing in the experiment.
     
  6. Aug 12, 2014 #5
    Point the wing up and point the fan down.
    Then just use the same scale - after taring it with the fan off.
     
  7. Aug 12, 2014 #6

    AlephZero

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    Unless you measure the lift and drag forces with the same flow conditions, the results won't mean much.

    I assumed the OP was working in a wind tunnel, even if it is a simple home-built one. Just putting a fan in front of the wing won't tell you anything very useful about either lift or drag, since the airflow won't be uniform over the wing.
     
  8. Aug 12, 2014 #7
    He could be doing anything.
     
  9. Aug 12, 2014 #8

    rcgldr

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    Normally lift and drag are measured using two sensors, one for vertical force, one for horizontal force. There also needs to be some method to hold a constant angle of attack, while allowing the vertical and horizontal sensors to operate without being affected by the torque produced by the wing.
     
  10. Aug 13, 2014 #9

    CWatters

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    Amazing what you can do with some thread, a pulley and some small weights.
     
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