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Oswald efficiency

  1. Aug 17, 2007 #1
    i googled a lot, the best hit i got was
    " 'e' is a parameter which expresses the total variation of drag with lift. It is sometimes called the span efficiency factor or Oswald efficiency factor after Dr. W.B. Oswald who first used it. It would be 1.0 for an elliptically-loaded wing with no lift-dependent viscous drag, but for practical aircraft 'e' varies from about 0.75 to 0.90."

    i couldn't make much of it, can anyone elaborate a lil bit
     
  2. jcsd
  3. Aug 17, 2007 #2
    This "Proposal" refers to "Mises 1945".

    Link-1:
    http://www-scf.usc.edu/~tchklovs/Proposal.htm



    Some interesting stuff here but nothing on shape of wing tip.

    Link-2:
    --- Link Removed ----

    NOTE: Link-2 is somewhat a radical view and out of mainsteam but interesting.
     
    Last edited by a moderator: Aug 18, 2007
  4. Aug 17, 2007 #3
    --- LInk removed ----
    dont know about the first part, 2nd and 3rd part are complete crap.
    2.increasing angle of attack => increased Cl
    3.8ft span and 40 ft chord wing also ll produce same lift, but would be very unstable.
    right:confused::confused:
     
    Last edited by a moderator: Aug 18, 2007
  5. Aug 18, 2007 #4

    russ_watters

    User Avatar

    Staff: Mentor

    We don't give crackpots free advertising even if just via debunking here, kach. That link was utter crap. Rediculously absurd. It is breathtaking how much energy they have put into something so utterly devoid of any basis in reality. In fact, many of the key points were so far off that they don't even provide a starting place for debunking. Ie, the complaint about the Venturi effect described a process that bore little resemblence to the Venturi effect. So there was nothing to debunk. The line about Burt Rutan's Voyager having it's wing on upside-down was a real chuckler though. Yah, it produced negative lift while on it's takeoff roll. That's done on purpose so they don't spontaneously take off before the pilot rotates. They sit on their landing gear with a negative angle of attack. :rolleyes:
     
    Last edited: Aug 18, 2007
  6. Aug 18, 2007 #5
    ok now anyone for my question?????
     
  7. Aug 19, 2007 #6
    Oswald efficiency factor of the wing at a given lift coefficient is defined as ratio of the wing's induced drag coefficient and induced drag coefficient of the equal aspect ratio elliptic wing at that same lift coefficient. Since the elliptic planform will have the lowest induced drag among all planar forms of same aspect ratio at any given lift coefficient, then this ratio somehow reminds of an efficiency meassure, hence the name.

    Oswald efficiency factor in general depends on the lift coefficient (i.e. angle of attack). For example, a trapezoidal wing can be optimally twisted for some given angle of attack to produce induced drag near to that of an elliptic wing (near unity Oswald efficiency), but will become worse as the angle of attack shifts away from that optimized for.

    The importance of wing's Oswald efficiency depends on how large is the part of wing's induced drag in the total drag for designed for performance types. For example, in range-efficient cruise of an airliner I've read that the induced drag is like 20% of total, whereas it can be more than 50% for time-efficient high-altitude loiter of a surveillance UAV.

    But this is all textbook stuff, so sorry if I'm wasting your time by stating the obvious :)

    --
    Chusslove Illich (Часлав Илић)
     
  8. Aug 19, 2007 #7
    It seems one of my links hi-jacked your thread, I'm sorry about that.

    I can do a Google search as well as anyone else, but have little idea how to help you.

    This is what I found::

    Formulas and charts;
    http://www.desktopaero.com/appliedaero/potential3d/induceddrag.html
    Pictures and text:
    http://selair.selkirk.bc.ca/aerodynamics1/Drag/Page8.html
    I trust this will help to keep things on topic.
     
  9. Aug 19, 2007 #8
    well guess what!!!!! that didnt waste my time.
    that helps to understand it completely. i didnt knew what to compare it with first. making the elliptical lift distribution as the standard is a good definition
     
  10. Aug 19, 2007 #9
  11. Aug 19, 2007 #10
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