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Homework Help: How is lift generated?

  1. Nov 26, 2007 #1
    I've just finished the practical part of an investigation into lift and angle of attack. I also took airspeed readings over the top and bottom of the wing at the leading and trailing edges.

    What I'm having trouble with is grasping how lift is generated. I understand the underlying principles (both Newtonian and Bernoullian), but cannot quite understand why the airflow is turned by the aerofoil (apparently effects due to the Coanda Effect and the Continuity Equation are wrong).

    Further, I'm having slight problems with my results. I recorded the airspeed readings and noted that the airspeed over the top of the wing was generally faster than below, contrary to how lift should be generated, yet lift was acting anyway. Is this possible? Or have I made an error in measurements (you have to understand that my setup was unbelievably crude - I hadn't access to a real wind tunnel and was working with a fan, a box and a set of scales).

    Finally, I had also noticed that the high cambered aerofoil seemed to stall later than the symmetrical aerofoil. I put this down to the fact that the leading edge of the high-camber aerofoil stayed nearer the stagnation line, but I have no idea if this is right or not.

    Help with any of the above points would be very much appreciated!
  2. jcsd
  3. Nov 26, 2007 #2
    Essentially, lift is due to circulation. Circulation will occur in flow over an airfoil because of flow separation, which occurs due to a stagnation point near the back end of the airfoil.

    Try playing around with this website: http://www.grc.nasa.gov/WWW/K-12/airplane/foilsimu.html. You can learn a lot by fiddling around with it.
  4. Nov 27, 2007 #3
    Thanks a lot for your help. I needed a bit more of a layman's explanation, but I found http://web.mit.edu/2.972/www/reports/airfoil/airfoil.html" that cleared everything up (and what you said made suddenly so much more sense, because I hadn't fully understood circulation before).

    Finally! No more mucking around with this Coanda/Venturi Effect nonsense.

    For future reference of anyone looking for similar things, the above website was extremely useful, coupled with http://www.av8n.com/how/htm/airfoils.html" [Broken]
    Last edited by a moderator: May 3, 2017
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