Which aircraft had laminar flow wings?

Discussion in 'Aviation' started by spicmart, Sep 9, 2016.

  1. spicmart

    spicmart Member

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    There are many planes known to have laminar flow wings like the Mustang, Sea Fury, Hornet, Raiden etc.. Yet there are some I've never heard to have them but if you look at pictures one could think that they feature them.
    E.g. the Mosquito, the B-26 Marauder, some russian and japanese fighters.
    Their wing leading edge is sharper and not as round as those of planes like the 109, 190 Corsair etc.. Also the maximum wing thickness seems to be further aft. Might this be an indication if laminar flow wings?
     
  2. Shortround6

    Shortround6 Well-Known Member

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    Not really. Most "conventional" wing profiles had the max thickness at around 30% of the cord. it could vary a bit but that left an awful lot of "room" for variations in thickness of wing for the profiles. Like one wing could be very near max thickness at 20% cord and another with the same max thickness in actual numbers at 30% (the same location) but use more taper getting there so at 20% it is thinner. It could very well look different but it is not a laminar flow wing.
    Now before we get bogged down in what is laminar flow and what is not and NO wing outside a laboratory maintained laminar flow over the whole wing.
    In General a laminar flow wing kept the airflow over the wing from going turbulent for another 5-15% of the cord than the normal airfoils. perhaps even as high as 20%. Many airfoils could keep the airflow smooth (laminar) for the first 5-15% of the cord.

    a few extreme examples
    [​IMG]
    Please note that airfoil #3 was quite common on WW I biplanes. WHile it gave high lift at low speeds and was thin as measured in percent it was not only high drag but often had a bad stall.
     
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  3. Balljoint

    Balljoint Member

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    Agree with what’s been said. However, a wing is “more laminar” if the thickness portion is further back on the wing, i.e. so that the airstream has positive contact with the wing. Also, once the wing starts to fall away from the direction of the airstream, the Coanda effect can be enhanced by tripping the air flow to set up a turbulent boundary layer.

    As long as the airstream is “attached” to the wing, i.e. flying rather than stalling, it would seem that the flow is more or less laminar, i.e. organized and parallel. Perhaps someone with some actual knowledge can comment on this.


     
  4. pbehn

    pbehn Well-Known Member

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    Laminar Flow Airfoil

    Some interesting stuff on the above link.

    N.A. designed the mustang to be low drag the wings may have been designed to be laminar flow but from what I have read this was not achieved it requires surface cleanliness and smoothness not achievable on a combat aircraft in service. The whole aircraft was designed for low drag especially the close to zero cooling drag radiator, the whole plane was built to very fine tolerances to cut down drag at joints etc even the engine could be termed low drag as it had a lower profile than the early Merlins.

    from the above link (which surprised me)
    The Consolidated B-24 Liberator "Davis" airfoil was also a laminar flow airfoil, which predates the Mustang's. However, the designers of the B-24 only knew that their airfoil had very low drag in the wind tunnel. They did not realize that it was a laminar flow airfoil.

    Also the Tempest was supposed to have laminar flow wings to overcome problems of the Typhoons thick wings.
     
  5. tomo pauk

    tomo pauk Creator of Interesting Threads

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    Not just that Tempest have had a more modern wing profile, the wing itself was much thinner in and of somewhat greater area. A real improvement over the Typhoon's wings.
     
  6. Zipper730

    Zipper730 Member

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    Did David R. Davis realize that this low drag extended to high speed?
     
  7. Shortround6

    Shortround6 Well-Known Member

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    I could be wrong but in the case of the Davis airfoil it didn't.
    [​IMG]
    I would note that the extent of the laminar flow rarely (if ever) reached the figures shown in actual service aircraft.
    Some older airfoils
    [​IMG]
     
  8. pbehn

    pbehn Well-Known Member

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    SR the laminar flow discussion seems to be more like an abstract philosophical debate at time.

    "A favorable pressure gradient is required to maintain laminar flow. Laminar flow airfoils are designed to have long favorable pressure gradients. All airfoils must have adverse pressure gradients on their aft end. The usual definition of a laminar flow airfoil is that the favorable pressure gradient ends somewhere between 30% and 75% of chord."

    To my mind something that has only 30% of something is way short but that is what is said. Certainly 30% is better than nothing, the Davis profile as lower drag than others. it may or may not have 100% laminar flow but none did.
     
  9. Zipper730

    Zipper730 Member

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    Just to be clear a pressure gradient means the range of pressure along the foil? As for adverse pressure gradients, you mean something that produces a "suction" to basically hold the airflow onto the surface?
     
  10. KiwiBiggles

    KiwiBiggles Member

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    The "pressure gradient" refers to the change of pressure along the chord or the aerofoil. Intuitively, fluids flow readily from a higher pressure to a lower pressure. On the leading part of the aerofoil, the pressure is dropping along the chord, from ambient (or thereabouts) at the leading edge until the lowest pressure is reached; within this section of the chord we say that there is a favourable pressure gradient, and the flow stays largely attached to the surface. From the point of lowest pressure on, the pressure is increasing to once again reach ambient at the trailing edge; in this section the flow is 'fighting against' the unfavourable pressure gradient, and so has a tendency to detach from the surface and become turbulent.

    The design of early laminar flow aerofoils pushed the point of maximum thickness rearwards, to try to delay the onset of turbulence. Of course by moving the point of lower pressure further aft, the adverse pressure gradient becomes much steeper and more likely to become turbulent, so there is a delicate balance between keeping attached non-turbulent flow over as much as the chord as possible, and causing too much turbulence and detached flow towards the trailing edge.
     
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