NACA Ducts and the GSA screen - aerodynamicist's opinion sought

Discussion in 'GS Boxers' started by viz, Oct 28, 2010.

  1. viz

    viz I Ride Ms Piggy

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    Surely there is an aerodynamicist on this forum - if so gotta question for him/her...

    (I am a simple bike rider, who in the past was a simple pilot, so I know enough about aerodynamics to make me somewhat dangerous)

    I am about to get my hot little hands on a very used GSA screen for the sole purpose of carving it up to experiment on reducing the problem of wind buffet at speed.

    It appears that the trick is to reduce the pressure differential formed between the front and rear side of the screen - the differential forming a "bubble of vacuum" that pops thus producing the buffet (probably not the best description - my ignorance showing).

    I saw this (note the scoop above the headlight and the slot in the screen)

    [​IMG]
    Photo credit to farcall

    And the thought occurred to me - how would a NACA duct http://en.wikipedia.org/wiki/NACA_duct go in the front in place of the scoop in that picture? On the sides?

    Pros:
    Properly inserted it would not detract from the screen strength. Cutting holes without reinforcing would weaken the screen

    Cons:
    Angle to the airflow might be too extreme to work effectively

    Any thoughts?

    viz
    #1
  2. walrond

    walrond Earth Wanderer

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    It's been done by one of inmates here. If I remember correctly the word NACA was in the thread title.
    #2
  3. viz

    viz I Ride Ms Piggy

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    Sorry folks - I did not even think of doing a search on this subject - I thought I have asked an original question! :doh

    Lotsa stuff, lotsa research. Thanks for the tip

    viz
    #3
  4. Reverse

    Reverse Armchair Tough

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    Not sure if the GSA screen is a good example for this; I ride with one and have never been bothered by buffeting. I'm 6'4" and the air hits me at face height, but it's a clean stream of air, no turbulence at all.
    #4
  5. Ricardo Kuhn

    Ricardo Kuhn a.k.a. Mr Rico Suave

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    #5
  6. crazyhawk99

    crazyhawk99 Been here awhile

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    Also being a former aviator (retired), my opinion is that as you suspect, the angle of airflow will be too direct to work as a NACA. As I recall, all NACA "vents" are normally somewhat parallel to the flow of air going over them.

    Just my 2 cents.
    #6
  7. Ricardo Kuhn

    Ricardo Kuhn a.k.a. Mr Rico Suave

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    A Experimenting on the 950 that works really well

    This is more of a "Air induction system" than Naca but it works really well too
    [​IMG]

    [​IMG]

    The view from the top
    [​IMG]

    Here you can see the two screens, the "Bouncing screen" in the stock location and the main screen a few degrees forward
    [​IMG]

    [​IMG]

    And Finally 1200GS ADVenture "Naca" windscreen

    [​IMG]

    [​IMG]

    view from the top with the space in between the screens
    [​IMG]

    The "Bounce" screen made out of a modified 1150 short screen, works really well with out much bending but some drastic cutting is require
    [​IMG]

    All this experiments work really well (reason I keep using the same shapes) with a dramatic decrease in wind buffeting and related noise
    [​IMG]
    #7
  8. ollka

    ollka Usually lost

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    Easier way is to buy Wunderlich Ergo Vario Screen, it works!
    #8
  9. Bill the Bong

    Bill the Bong Supern00ba

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    I did DIY NACA ducts on a 1150GS Powerbronze screen a couple of years ago. If memory serves, I stuffed up a good screen.
    #9
  10. Beezer

    Beezer Long timer Supporter

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  11. supershaft

    supershaft because I can

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    Most all the NACA research is public info. I suggest reading up on the vents in question. The "Y" shape of a NACA duct alone does NOT make a NACA duct. If I remember right, they need to be on a relatively flat and undisturbed surface to work efficiently and that is the tip of the iceberg. At any rate, all there findings and how they work and how to make one are easy to look up. They also describe what they found DIDN'T work. Thinking that some of the vents pictured in this thread are NACA vents is laughable!
    #11
  12. Ricardo Kuhn

    Ricardo Kuhn a.k.a. Mr Rico Suave

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    As usual is two kinds of people to be found, the ones that DO, (even is is not perfect and even horribly wrong) and the ones that seat on a office desk and criticize..

    Let see you work Super shaft so we can all laugh together
    #12
  13. SCFoster

    SCFoster It is what it is Supporter

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    Reducing wind buffet is not all that simple. I'm not an aerodynamics weenie (that's what we called them) but I do have an aeronautical engineering degree and spent plenty of hours in the wind tunnel. Back to the program.

    Most of the positive effect will take place, IMO, by how the lip is shaped at the point where the two bodies of air meet. One air-mass is at a relatively high speed from the front and the lower speed (or no speed) at the rear of the windshield. That's why a wing mounted at the top of the windscreen, or something like it, can introduce some airflow behind the upper lip and reduce the differential speeds (pressures) of the two bodies of air.

    Quite frankly, unless you have a wind tunnel handy, you're just guessing and wasting your time. Visualizing and modeling what an airflow will do is the stuff of super-computers. Especially at highway speeds, you start to have compressibility effects, which creates its own set of headaches. I've seen aerodynamics weenies scratching their heads for weeks, months and even years over problems, only to have some odd solution drop in by pure chance.

    But, grinding away at Plexiglas is fun, so don't let my ramblings deter you.
    #13