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Old 07-19-2009, 12:32 AM   #21 (permalink)
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Quote:
Originally Posted by anthonye81 View Post
Any claim for a 20% boost in MPG is always going to look dodgy!

For years aircraft have had micro-drilled holes in wing surfaces, which (if I remember correctly) create tiny pockets of low pressure when an airflow moves over the wing surface. The low pressure helps keep the airflow attached to the wing surface, albeit for the purposes of generating lift rather than reducing drag, but hey I guess it can work both ways. Fans of The Simpsons may remember Homer pickaxe'ing "speed holes" into his car, although they were slightly bigger than a fraction of a millimetre...

Any aero experts out there feel free to point out the bits I got wrong!
those holes iirc were fed by a compressor which caused them to ooze air
making the wings more productive during takeoff and landing effecively
lowering stall speed. bummer when they iced up though!

on the golfball skin... i remeber cycling helmets in the 90's that employed that thought. according to the tech which seemed to know his stuff, they worked.

on sharkskin it is not only the texture of the skin but also the loose, flabby
layers beneath the skin that allow oscilations by the sharks own movements
as well as the waters to be absorbed/disbursed, to make it such an efficent traveler.

longitudinal not transverse strips of silicone have been employed by both bicycle clothing manufatures as well as competitive swimwear companies - usually only to eventuallly get outlawed during competition.

i belive it was the last year that lance and his crew was sponsored by
discovery channel their speed suits as well as regular shorts/tops donned
tiny silicone dots throughout....

on surfboards and sailboards transverse 400 grit sandpaper scratches
are said to be the most effective surface treatment for speed.
that same grit is also supposed to simulate the surface texture
of extrude hone which is popularly used to smooth intake
manifolds for racing.

then of course during the 80's there was a 928 in competition
that sported reversed, raised (instead of sunken) NACA ducts
on parts of his vehicle. inspitation for airtabs???

lotsa surfaces can do lotsa good stuff if employed properly!


Last edited by max_frontal_area; 07-19-2009 at 12:39 AM..
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Old 07-30-2009, 10:28 PM   #22 (permalink)
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If this worked, the vinyl used on windows in vehicle wraps would work VERY well. It's mostly holes, perforated finely, so that it's almost fully transparent from the inside, but the image can be seen well from the outside. The small perforations should make it all work like a charm, if there's anything to it at all. Now it would be cool if you could get it perforated in the vortex generator / naca shape.
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Old 07-31-2009, 03:15 PM   #23 (permalink)
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I am active on a boat design forum and the golf ball surface topic resurrects every now and then. Yes it does work to certain extent - enough that dimpled/grooved surfaces are banned in many sailing classes. This is under water but same difference. Helps to keep the laminary flow following in areas where it would break loose otherwise.

Is it a significant difference in a car - I doubt.
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Old 07-31-2009, 04:00 PM   #24 (permalink)
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Sharkskin grooves are banned for their ability to maintain laminar flow at an impractical dollar cost. Dimples can help a boundary layer remain attached by starting or adding turbulence to make it thicker. If anybody wants to get around a dimple ban on boats, a few barnacles should do the trick.
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Old 08-01-2009, 02:45 AM   #25 (permalink)
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well sometimes it seems that in racing yachts there is no such thing as "impractical cost"

I know they got some good results in some boat in the past but the rule change probably means more that the authorities don't want to deal with it and keep reviewing the under bodies in speculation whether they are legal - easier to ban dimples altogether.
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Old 08-01-2009, 02:56 AM   #26 (permalink)
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Can you really quote a ban on dimples? They are used to ameliorate excreable shapes. Are there single-design classes with separation problems? The sharkskin ban I heard of was regarding the olympics*, where there is some attempt to make it a contest between athletes rather than well-financed technicians.

*Boycott Vancouver Winter Olympics, and their Sponsors, please.
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Old 08-01-2009, 10:13 AM   #27 (permalink)
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Ya'know, like a golf ball - Boat Design Forums

"Back in 12 meter days, I believe 3M had a surface treatment that did exactly what you are describing. It worked to some extent so was ruled illegal."

I have no better source now but remember reading about it before from more "reliable" source. In general the problem seems to be that its very hard to know in which area it would help and in which area it would only add skin friction (which is big deal on boats)

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