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Old 10-23-2009, 05:04 PM   #11 (permalink)
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..but, was the "final" Scientific Method criteria (ie: Repeatability) been done?

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Old 10-23-2009, 05:44 PM   #12 (permalink)
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Quote:
Originally Posted by botsapper View Post
Ecomodders want more performance...from dimples. The golf industry knows when you have a good thing & wants more distance & less drag... just add more dimples!!!
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Given the proper speed, a smooth sphere can go farther than a dimpled sphere. It all depends on the Reynolds number. The ball that would go farthest for an average lady does not have the same dimple design as the one that would go farthest for a pro long distance driver. The ball that goes farthest would be the one with dimples adapting themselves to the surface airspeed.

In theory dimples could work on some part of bluff bodies, but not to the extend they measured. Especially since they dimpled everything. It makes no sense whatsoever to dimple surfaces where the flow is laminar to start with.

I just don't like the way they tested it.
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Old 10-23-2009, 06:29 PM   #13 (permalink)
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Quote:
Originally Posted by tasdrouille View Post
I just don't like the way they tested it.
Well said. I agree 100%.

If dimples are to be used, they should be placed where the body shape drops away from the airstream too quickly, to energize the air in that location only.

You don't need to energize the air in places where it is still attached.

And any device that creates a small amount of turbulence would work. There's nothing special about dimples. Look at the numerous airplanes that have vortex generators on the wings to improve the stall characteristics.

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Old 10-23-2009, 06:55 PM   #14 (permalink)
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Looking at the results, they were doing something right.
I wrote in another thread how that Audi has dimpled plates on the undersides of some of their cars ( ironically, the dimples seem to be the same diameter as those use in the Mythbusters test ).
VW also had some of their cars with the dimples as well, and who can forget the well publicized dimpled underside of the Lexus LS-430 ?

I doubt any of us want to have huge dimples in the sides of our cars, but the undersides of our cars seem like a perfect place to have dimples.
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Old 10-23-2009, 07:18 PM   #15 (permalink)
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True, a smooth ball could have a lesser force barrier but that critical speed is attained @ 300+ mph, but a dimpled golf ball passes its critical Reynolds number and with a smaller drag tail @ 55 - 300mph. This is within the practical ranges of a stroked golf ball, struck by a 40"+/- golf club, & within a 4 degrees from tee level, initial launch speed of 160+ mph, consistent backspin and resultant Magnus force lift. A dimpled golf ball creates beneficial lift & stays aloft longer, thus travels longer. The configuration would take all of the advantage of the smaller drag resistance @ the most of its flight. Tests indicate greater lift on spinning dimpled golf balls but even non spinning dimpled golf balls still have lower drag tails compared to spinning/non spinning smooth balls.

Zipp dimpled bicycle wheel covers have shown very good Reynolds numbers compared to smooth ones. It only begs for ecomodders to now use & favor 'dimpled' wheel covers over smooth ones. Another one on the 'must' list.
http://www.zipp.com/_media/pdfs/tech..._the_edges.pdf
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Old 10-23-2009, 08:25 PM   #16 (permalink)
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...similar "smooth vs. rough/dimpled" analogies exist in the animal kingdom too, with the skins (actually cartlage-scales) of dolphins and sharks.

...smooth surfaces aren't always the "least" restrictive in the ocean either!
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Old 10-23-2009, 10:19 PM   #17 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...smooth surfaces aren't always the "least" restrictive in the ocean either!
Most water skis I've seen have a "pebbled" running surface. And most of the wake boards I've seen have dimples in the running surface.
FWIW.
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Old 10-23-2009, 11:12 PM   #18 (permalink)
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Quote:
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By the other thread, you mean the one about the perforated vinyl film?

Apples and oranges, Chris.

Adam and Jamie ran each test 5 times through for each variable, took measurements, using a reproducible method. They did take care to try and control other factors to isolate the effect they were looking for:

- Separate fueling systems for the measured interval
- Measuring/weighing the alternate fuel supply to determine consumption
- Only measuring the above at a constant, uniform speed each run
- Measuring across the same length of road for all runs

What was elided from the show, that may show any major or minor variations:
- Actual run data not published for all to see (sure looked like they recorded it, though)
- It's not known what the weather/wind speed and direction were, and if that fluctated, which could perturb testing runs

Atop that, they ran through models to see if there was an effect appreciable enough to bother testing full scale.

What are you actually trying to poke holes in, with what they presented?
No, I meant the other thread about this very topic.
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Old 10-23-2009, 11:14 PM   #19 (permalink)
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Quote:
Originally Posted by botsapper View Post
Zipp dimpled bicycle wheel covers have shown very good Reynolds numbers compared to smooth ones. It only begs for ecomodders to now use & favor 'dimpled' wheel covers over smooth ones.

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Old 10-23-2009, 11:21 PM   #20 (permalink)
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...ah, but the "aero"-hairdo dude definitely don't look very aerodynamic.

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