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Old 10-18-2008, 09:26 AM   #21
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You'd have to factor in the costs of making the molds, with dimples as opposed to flat or with ribs. As no one else has weighed in to my original question, I'm gonna take this as an answer, that the dimples on a larger surface can be bigger, and still function, and move forward.If I can figure out how to post pictures, I'll try to do so, when I get the ductwork complete. Might be a little while, as this is part of making the new floor, which the body will mount on. Some structural stuff, precise measuring, etc. involved.Should be challenging and fun!! Thanks again for the answer!! Jim
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Old 10-18-2008, 11:35 AM   #22
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Quote:
Originally Posted by dutchdivco View Post
I'm gonna take this as an answer, that the dimples on a larger surface can be bigger
It might not be about the size of the surface, but the speed or size of the object, or the airflow expected between the vehicle and the ground, or any of a million other variables...

I suspect that your conclusion is right anyway.
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Old 10-19-2008, 08:06 AM   #23
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Similar dimples can be seen on the bottom of some wake and knee boards. They are typically at the ends of the boards, presumeably to provide less drag when turned laterally.

Although it was hinted at earlier, I think it worth pointing out that dimples over the leading surfaces of an object are ineffective compared to a totally smooth surface. Where they impose their greatest benefit is at the rear surfaces, where laminar flow would tend to otherwise seperate from the surface. I.e., golf balls only have dimples all the way around because there is no way to guarantee which face will be fore/aft, but it assures that there will always be dimples at the critical zone of seperation. The extra dimples actually add to the drag, but it remains a net reduction overall.

For that reason, I think vortex generators or trip strips (turbulator etc.) are just as effective on a vehicle since we can generally deduce where they need to be on the body work. VW for examply already has that figured out with the turbo beetle extending spoiler. For design reasons however, it may not be in the optimal spot or as effective as it could be, but I doubt dimples would offer any improvement at least in the area where the spoiler exists.
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Old 10-19-2008, 11:50 AM   #24
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I was looking at the Festiva today and the back hatch isn't that dramatic, I thought it was almost vertical, but it looks like maybe a 60 deg slope. Granted this is more than on a round golf ball, but it still might help to have some dimples at the transition and halfway down the hatch. If only I could find some clear, stick, dimpled tape. I'm assuming larger dimples would be better, maybe 1/2" diameter, rather than tiny pinhole size on golf balls.

Any thoughts?

And yes, I was saying earlier that dimples will actually hurt compared to smoother or bubblier front sections. The point is that they create turbulence, but this turbulence helps keep the flow attached and seperate further down the shape of the object. Good turbulence. But only in the rear where it otherwise would be seperated and more turbulent, not in the front where it'd have been smooth anyway.
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Old 10-19-2008, 12:00 PM   #25
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Quote:
Originally Posted by itjstagame View Post
If only I could find some clear, stick, dimpled tape.
http://www.dimpletape.com/ http://www.lessgasmoremiles.com/

I've never used them, but do they still ship?
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Old 10-19-2008, 12:19 PM   #26
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Cool.

A search of dimple tape on google got me an old Gassavers thread on this exact subject: http://www.gassavers.org/showthread.php?t=1508

Also this place has the same tape for much cheaper: http://www.wingsandwheels.com/page29.htm The first link would be 10feet for $49, this is 10 meters for $38. They say the zigzag, turbulator is better though.
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Old 10-22-2008, 04:52 PM   #27
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I wanted to post some great links I found.

This one provides a great explaination of why the dimples work and how and also talks about vortex generators to improve flow over an already streamlined body: http://www.aerospaceweb.org/question...cs/q0215.shtml

This next one is an article talking about applying dimples to car and planes and lots of other things, stating that not a lot of testing has been done but improvements can be seen. The one guy owns Zipp which produces some AWESOME stuff for bicycle racing, check this out: http://www.zipp.com/wheels/detail.php?ID=33
And here's the article: http://www.racecar-engineering.com/a...-surfaces.html

That guy has a world patent on dimples on disk/rotors. I don't really understand the point on the disk/surface itself, but around the ellipsoidal wheel/tire makes tons of sense. They also have a patent on more ellipsoidal wheels with lips that transistion the flow better. They claim the wheel will actually pull you forward from lift!

Now, I really want to try this on the festiva, in lots of places too. I don't really like the dimple tape because there's very little information and it looks like one tiny line of dimples in the center, doesn't sound too helpful.

I saw other gassavers using bumps instead of dimples, do you think this would have the same effect? We need someone like trebuchet to chime in. A thought that just occurred to me, which I might actually try. Is velcro! Mostly because I have a bunch of super strong, 4" wide stuff laying around. They say a rough surface helps as much as dimples, I'm not sure whether I'd want to use the 'fuzz', which would make me like a tennis ball, or the 'hook' side, which even though they're tall and straight I think there's enough that it'd provide a rough surface. They're both kind of tall though...

Oh and both of those sources mentioned the same thing that wikipedia did, that hexagon dimples seem to show even more improvement and that lots of testing needs to be done to actually verify correct diameter, depth and proximity, etc. Any idea for creating hexagonal dimples? Maybe an 8mm hex driver and a hammer? :-)
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Old 11-04-2008, 08:42 PM   #28
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Not mentioned thus far is the fact golf balls spin in the air as they travel. The dimples delay the onset of drag and thus provide some measure of stability, which is a vital aspect of the golf ball.

That said I have yet to see any such dimples / hexagons or anything similar appearing on 747's etc which suggests to me a smoother panel may be a better option in this instance.

The panel from the Rabbit / Golf may be so shaped to return to it's initial shape after impact if it is in the area likely to be damaged from road debris.

Cheers , Pete.
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Old 11-05-2008, 04:32 AM   #29
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Old 11-05-2008, 06:26 AM   #30
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Actually when I started looking for dimple tape I found a lot of the DIY light-weight hangglider type planes using it and zigzag tape to try to get better results out of their smaller, tarp like wings. It seems it's first invention and use was for planes.

Here's another strange article using them http://www.dimpletape.com/article.htm
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