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Question about wing tip design

Discussion in 'The Okie Corral' started by Roogalator, Sep 13, 2004.

  1. Roogalator

    Roogalator Senior Grackle

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    I know absolutely bugger all about airplane design and this is probably a really idiotic question but bear with me. Of late I've noticed that a lot of commercial airliners now have these weird flippy things on the ends of their wings. Most of them look like someone took the last section of the wing and bent it 90° up and some of them look like they just tacked on a small vertical section at the end of the wing.

    What the heck are these things and what are they for???
     
  2. hispeedlodrag

    hispeedlodrag needs vacation

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    These flippy things are winglets. At the wingtip, the higher pressure air below the wing attempts to equalize with the lower pressure air above the wing inducing a vortex or turbulent flow. The winglet controls this formation which increases the efficiency of the wing.
     

  3. Roogalator

    Roogalator Senior Grackle

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    Well that makes perfectly good sense. I wonder why they don't have winglets on all planes?
     
  4. Wulfenite

    Wulfenite The King

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    They're also sometimes refered to as tip sails.
     
  5. F14Scott

    F14Scott Luggage CLM

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    Some wing designs and expected operating environments preclude the costs associated with adding winglets. Generally, little, low-flying, slow wings wouldn't get enough of a boost from winglets to justify their weight, cost, and complexity.

    Sort of like why all cars don't have twin-turbos.
     
  6. JonnyB

    JonnyB Millennium Member

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    Or, "Why don't all cars have spoilers?"

    I don't think my Champ would benefit a great deal from winglets...

    JB
     
  7. F14Scott

    F14Scott Luggage CLM

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    Ya know, I thought of that analogy, but so many cars that don't need spoilers have them anyway, I decided against it. ;f
     
  8. Roogalator

    Roogalator Senior Grackle

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    Anyone know how fast a car has to be going before
    you get enough downward pressure from a spoiler
    to increase traction? I'm guessing by the fact that
    serious street-legal cars generally don't have them
    that it must be a higher speed than is practicable
    (let alone legal) on public roads.
     
  9. TheGrinch

    TheGrinch

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    A lot of controversy in engineering circles on whether the winglets are cost effective or not. I know we tried some winglets on 727's a few years ago and found that simply drooping the flaps a degree or two made more of a difference than the winglets.

    It could be the greatest thing since the angled deck, or simply marketing hype. Either way, it is a good place to paint a logo...

    Grinch
     
  10. Bushflyr

    Bushflyr ʇno uıƃuɐɥ ʇsnɾ Millennium Member

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    Rumor has it that Southwest is discontinuing their conversions. Boeing apparently pulled the 8% figure out of the proverbial tailpipe and it's not materializing.
     
  11. TheGrinch

    TheGrinch

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    I wouldn't be surprised at all. I would be surprised however, if SWA admitted that they were hornswaggled.

    For general informational purposes- even if the theory is correct, the effectiveness is greatest at high induced drag flight regimes- ie high altitiude at low IAS or slow speed during landing maneuvering. The second is a fraction of most airline flights, with low fuel flow decents and short level segments, often with the aircraft utilizing high drag configurations to fly at the proscribed ATC speeds. Hanging flaps and gear sort of negates the aerodynamic efficiency of high tech accoutrements.

    The first depends upon the aircraft payload and speed profile allowing for high altitude flight with a low induced drag. At highers indicated speeds, parasitic drag dominates any savings from induced.

    As everything aerodynamic, it is always a tradeoff.

    Grinch
     
  12. JCM298

    JCM298

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    Roogalator,

    A long time ago, I read someplace that "spoilers" on cars don't have any effect until the car reaches 105 MPH. the speed stuck in my mind but I have no idea where I saw it,

    John
     
  13. CaptainOveur

    CaptainOveur

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    Heck, think about the induced drag. Spoilers are needed when you are going 100+, but for one thing that kind of car is going to have GOBS of horsepower usually, enough to offset the induced drag.

    For most hondas and cars with less than 250hp, the spoiler is just more drag and they'll rarely, if ever, get up to the kind of speeds where it is needed.
     
  14. Tennessee Slim

    Tennessee Slim Señor Member CLM

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    Not exactly the same thing. Spoilers create lift, and lift , I'm sure you know, is directly proportional to drag. You can have drag without lift but you can't have lift without drag. Winglets cause drag, to be sure, but not because they generate lift (which, AFAIK, they don't).
     
  15. CaptainOveur

    CaptainOveur

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    Winglets do produce lift, they are and airfoil and are not at 90 degrees. That is one of the keys to their design. They stick out at an "angle" that is less than 90.
     
  16. Wulfenite

    Wulfenite The King

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    I always thought they produced thrust. The wing tip vortice curls up and impinges on the outter surface of the winglet to generate thrust in the same sense that a sail boat sail uses the wind (angle of attack) against the side of the sail to propell the boat.
     
  17. Tennessee Slim

    Tennessee Slim Señor Member CLM

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    So they're air foil shaped?
     
  18. CaptainOveur

    CaptainOveur

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    yep, better believe it. This is one of the reasons that there are more "benefits" than are initially obvious. You get more lift from the same sized wing by using the winglets, because they increase the lifting area a bit, that right there helps you carry a bit more load, and it doesn't make the wing much larger (which is important with transport-catagory aircraft that have to be packed next to each other in gates with equiment driving around)...

    They are like this; \____[]____/

    not like this |____[]____|
     
  19. Wulfenite

    Wulfenite The King

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    That makes very little sense though. Since lift is perpendicular to the chord line those angled tips would have very little verticle component of lift; most of it would be horizontal.

    Now a downward facing tip would contain the vortex, which would effectively increase the efficiency of the wing.
     
  20. Tennessee Slim

    Tennessee Slim Señor Member CLM

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    Ah! Now I stood under. I had assumed they were simply lenticular.